David Kirkpatrick

November 2, 2010

Cool nanotech image — growing nanowires

Cool image and interesting process

nanotechnology image
In the growth of sapphire nanowires using the vapor-liquid-solid method, scientists have observed that a facet at the liquid-solid interface alternately grows and shrinks, which promotes nanowire growth. These images are from the video below. Image credit: Sang Ho Oh, et al.

From the link:

Nanowires can be grown in many ways, but one of the lesser-understood growth processes is vapor-liquid-solid (VLS) growth. In VLS, a vapor adsorbs onto a liquid droplet, and the droplet transports the vapor and deposits it as a crystal at a liquid-solid interface. As the process repeats, a nanowire is built one crystal at a time. One advantage of the VLS process is that it allows scientists to control the nanowire’s growth in terms of size, shape, orientation, and composition, although this requires understanding the growth mechanisms on the atomic scale. In a new study, scientists have investigated the steps involved in VLS growth, and have observed a new oscillatory behavior that could lead to better controlled nanowire growth.

Hit the link for a video of the process.

June 2, 2010

Copper nanowires may improve solar cells and displays

This is an interesting use of nanotech because it looks like it might be market-ready much sooner than later, and as team member Benjamin Wiley puts it, “If we are going to have these ubiquitous electronics and solar cells we need to use materials that are abundant in the earth’s crust and don’t take much energy to extract.”

Also from the link:

A team of Duke University chemists has perfected a simple way to make tiny copper nanowires in quantity. The cheap conductors are small enough to be transparent, making them ideal for thin-film solar cells, flat-screen TVs and computers, and flexible displays.

“Imagine a foldable iPad,” said Benjamin Wiley, an assistant professor of chemistry at Duke. His team reports its findings online this week in .

Nanowires made of  perform better than carbon nanotubes, and are much cheaper than silver nanowires, Wiley said

March 5, 2010

Silicon nanowires may improve solar costs

Silicon photovoltaics offer incredible solar cell efficiency and now it looks like nanotechnology may offer a way to add low production cost to that mix. This type of headway and improvement is what will make solar a market-viable power option.

The release:

Trapping Sunlight with Silicon Nanowires

MARCH 03, 2010

Lynn Yarris

This photovoltaic cell is comprised of 36 individual arrays of silicon nanowires featuring radial p-n junctions. The color dispersion demonstrates the excellent periodicity present over the entire substrate. (Photo courtesy of Peidong Yang)

This photovoltaic cell is comprised of 36 individual arrays of silicon nanowires featuring radial p-n junctions. The color dispersion demonstrates the excellent periodicity over the entire substrate. (Photo from Peidong Yang)

Solar cells made from silicon are projected to be a prominent factor in future renewable green energy equations, but so far the promise has far exceeded the reality. While there are now silicon photovoltaics that can convert sunlight into electricity at impressive 20 percent efficiencies, the cost of this solar power is prohibitive for large-scale use. Researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab), however, are developing a new approach that could substantially reduce these costs. The key to their success is a better way of trapping sunlight.

“Through the fabrication of thin films from ordered arrays of vertical silicon nanowires we’ve been able to increase the light-trapping in our solar cells by a factor of 73,” says chemist Peidong Yang, who led this research. “Since the fabrication technique behind this extraordinary light-trapping enhancement is a relatively simple and scalable aqueous chemistry process, we believe our approach represents an economically viable path toward high-efficiency, low-cost thin-film solar cells.”

Yang holds joint appointments with Berkeley Lab’s Materials Sciences Division, and the University of California  Berkeley’s Chemistry Department. He is a leading authority on semiconductor nanowires – one-dimensional strips of materials whose width measures only one-thousandth that of a human hair but whose length may stretch several microns.

“Typical solar cells are made from very expensive ultrapure single crystal silicon wafers that require about 100 micrometers of thickness to absorb most of the solar light, whereas our radial geometry enables us to effectively trap light with nanowire arrays fabricated from silicon films that are only about eight micrometers thick,” he says. “Furthermore, our approach should in principle allow us to use metallurgical grade or “dirty” silicon rather than the ultrapure silicon crystals now required, which should cut costs even further.”

Yang has described this research in a paper published in the journal NANO Letters, which he co-authored with Erik Garnett, a chemist who was then a member of Yang’s research group. The paper is titled “Light Trapping in Silicon Nanowire Solar Cells.”

A radial p-n junction consists of a layer of n-type silicon forming a shell around a p-type silicon nanowire core. This geometry turns each individual nanowire into a photovoltaic cell.

A radial p-n junction consists of a layer of n-type silicon forming a shell around a p-type silicon nanowire core. This geometry turns each individual nanowire into a photovoltaic cell.

Generating Electricity from Sunlight

At the heart of all solar cells are two separate layers of material, one with an abundance of electrons that functions as a negative pole, and one with an abundance of electron holes (positively-charged energy spaces) that functions as a positive pole. When photons from the sun are absorbed, their energy is used to create electron-hole pairs, which are then separated at the interface between the two layers and collected as electricity.

Because of its superior photo-electronic properties, silicon remains the photovoltaic semiconductor of choice but rising demand has inflated the price of the raw material. Furthermore, because of the high-level of crystal purification required, even the fabrication of the simplest silicon-based solar cell is a complex, energy-intensive and costly process.

Yang and his group are able to reduce both the quantity and the quality requirements for silicon by using vertical arrays of nanostructured radial p-n junctions rather than conventional planar p-n junctions. In a radial p-n junction, a layer of n-type silicon forms a shell around a p-type silicon nanowire core. As a result, photo-excited electrons and holes travel much shorter distances to electrodes, eliminating a charge-carrier bottleneck that often arises in a typical silicon solar cell. The radial geometry array also, as photocurrent and optical transmission measurements by Yang and Garrett revealed, greatly improves light trapping.

“Since each individual nanowire in the array has a p-n junction, each acts as an individual solar cell,” Yang says. “By adjusting the length of the nanowires in our arrays, we can increase their light-trapping path length.”

While the conversion efficiency of these solar nanowires was only about five to six percent, Yang says this efficiency was achieved with little effort put into surface passivation, antireflection, and other efficiency-increasing modifications.

“With further improvements, most importantly in surface passivation, we think it is possible to push the efficiency to above 10 percent,” Yang says.

Combining a 10 percent or better conversion efficiency with the greatly reduced quantities of starting silicon material  and the ability to use metallurgical grade silicon, should make the use of silicon nanowires an attractive candidate for large-scale development.

As an added plus Yang says, “Our technique can be used in existing solar panel manufacturing processes.”

This research was funded by the National Science Foundation’s Center of Integrated Nanomechanical Systems.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research for DOE’s Office of Science and is managed by the University of California. Visit our website at http://www.lbl.gov.


Peidong Yang (Photo by Roy Kaltschmidt, Berkeley Lab Public Affairs)

Peidong Yang (Photo by Roy Kaltschmidt, Berkeley Lab Public Affairs)

Additional Information

For more about the research of Peidong Yang and his group, visit the Website at http://www.cchem.berkeley.edu/pdygrp/main.html

For more about the Center of Integrated Nanomechanical Systems (COINS) visit the Website at http://mint.physics.berkeley.edu/coins/

November 27, 2009

Semiconducting nanowires are coming

With all the news about nanotechnology and wiring that’s been coming out over the last year or so, this release is no surprise.

The release:

November 26, 2009

Nanowires key to future transistors, electronics

WEST LAFAYETTE, Ind. -

Nanowire formation
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A new generation of ultrasmall transistors and more powerful computer chips using tiny structures called semiconducting nanowires are closer to reality after a key discovery by researchers at IBM, Purdue University and the University of California at Los Angeles.The researchers have learned how to create nanowires with layers of different materials that are sharply defined at the atomic level, which is a critical requirement for making efficient transistors out of the structures.

 

“Having sharply defined layers of materials enables you to improve and control the flow of electrons and to switch this flow on and off,” said Eric Stach, an associate professor of materials engineering at Purdue.

Electronic devices are often made of “heterostructures,” meaning they contain sharply defined layers of different semiconducting materials, such as silicon and germanium. Until now, however, researchers have been unable to produce nanowires with sharply defined silicon and germanium layers. Instead, this transition from one layer to the next has been too gradual for the devices to perform optimally as transistors.

The new findings point to a method for creating nanowire transistors.

The findings are detailed in a research paper appearing Friday (Nov. 27) in the journal Science. The paper was written by Purdue postdoctoral researcher Cheng-Yen Wen, Stach, IBM materials scientists Frances Ross, Jerry Tersoff and Mark Reuter at the Thomas J. Watson Research Center in Yorktown Heights, N.Y, and Suneel Kodambaka, an assistant professor at UCLA’s Department of Materials Science and Engineering.

Whereas conventional transistors are made on flat, horizontal pieces of silicon, the silicon nanowires are “grown” vertically. Because of this vertical structure, they have a smaller footprint, which could make it possible to fit more transistors on an integrated circuit, or chip, Stach said.

“But first we need to learn how to manufacture nanowires to exacting standards before industry can start using them to produce transistors,” he said.

Nanowires might enable engineers to solve a problem threatening to derail the electronics industry. New technologies will be needed for industry to maintain Moore’s law, an unofficial rule stating that the number of transistors on a computer chip doubles about every 18 months, resulting in rapid progress in computers and telecommunications. Doubling the number of devices that can fit on a computer chip translates into a similar increase in performance. However, it is becoming increasingly difficult to continue shrinking electronic devices made of conventional silicon-based semiconductors.

“In something like five to, at most, 10 years, silicon transistor dimensions will have been scaled to their limit,” Stach said.

Transistors made of nanowires represent one potential way to continue the tradition of Moore’s law.

The researchers used an instrument called a transmission electron microscope to observe the nanowire formation. Tiny particles of a gold-aluminum alloy were first heated and melted inside a vacuum chamber, and then silicon gas was introduced into the chamber. As the melted gold-aluminum bead absorbed the silicon, it became “supersaturated” with silicon, causing the silicon to precipitate and form wires. Each growing wire was topped with a liquid bead of gold-aluminum so that the structure resembled a mushroom.

Then, the researchers reduced the temperature inside the chamber enough to cause the gold-aluminum cap to solidify, allowing germanium to be deposited onto the silicon precisely and making it possible to create a heterostructure of silicon and germanium.

The cycle could be repeated, switching the gases from germanium to silicon as desired to make specific types of heterostructures, Stach said.

Having a heterostructure makes it possible to create a germanium “gate” in each transistor, which enables devices to switch on and off.

The work is based at IBM’s Thomas J. Watson Research Center and Purdue’s Birck Nanotechnology Center in the university’s Discovery Park and is funded by the National Science Foundation through the NSF’s Electronic and Photonic Materials Program in the Division of Materials Research.

PHOTO CAPTION:
Researchers are closer to using tiny devices called semiconducting nanowires to create a new generation of ultrasmall transistors and more powerful computer chips. The researchers have grown the nanowires with sharply defined layers of silicon and germanium, offering better transistor performance. As depicted in this illustration, tiny particles of a gold-aluminum alloy were alternately heated and cooled inside a vacuum chamber, and then silicon and germanium gases were alternately introduced. As the gold-aluminum bead absorbed the gases, it became “supersaturated” with silicon and germanium, causing them to precipitate and form wires. (Purdue University, Birck Nanotechnology Center/Seyet LLC)

November 12, 2009

Silicon nanowires

Carbon gets most of the nanotech ink, but here’s some news on silicon nanowires.

The release:

Understanding mechanical properties of silicon nanowires paves way for nanodevices

IMAGE: These are silicon nanowires used in the in-situ scanning electron microscopy mechanical testing by Dr. Yong Zhu and his team.

Click here for more information.

 

Silicon nanowires are attracting significant attention from the electronics industry due to the drive for ever-smaller electronic devices, from cell phones to computers. The operation of these future devices, and a wide array of additional applications, will depend on the mechanical properties of these nanowires. New research from North Carolina State University shows that silicon nanowires are far more resilient than their larger counterparts, a finding that could pave the way for smaller, sturdier nanoelectronics, nanosensors, light-emitting diodes and other applications.

It is no surprise that the mechanical properties of silicon nanowires are different from “bulk” – or regular size – silicon materials, because as the diameter of the wires decrease, there is an increasing surface-to-volume ratio. Unfortunately, experimental results reported in the literature on the properties of silicon nanowires have reported conflicting results. So the NC State researchers set out to quantify the elastic and fracture properties of the material.

“The mainstream semiconductor industry is built on silicon,” says Dr. Yong Zhu, assistant professor of mechanical engineering at NC State and lead researcher on this project. “These wires are the building blocks for future nanoelectronics.” For this study, researchers set out to determine how much abuse these silicon nanowires can take. How do they deform – meaning how much can you stretch or warp the material before it breaks? And how much force can they withstand before they fracture or crack? The researchers focused on nanowires made using the vapor-liquid-solid synthesis process, which is a common way of producing silicon nanowires.

IMAGE: Dr. Yong Zhu and his research team stand front of a scanning electron microscope. From left to right, they are Feng Xu, Qingquan Qin and Yong Zhu.

Click here for more information.

 

Zhu and his team measured the nanowire properties using in-situ tensile testing inside scanning electron microscopy. A nanomanipulator was used as the actuator and a micro cantilever used as the load sensor. “Our experimental method is direct but simple,” says Qingquan Qin, a Ph.D. student at NC State and co-author of the paper. “This method offers real-time observation of nanowire deformation and fracture, while simultaneously providing quantitative stress and strain data. The method is very efficient, so a large number of specimens can be tested within a reasonable period of time.”

As it turns out, silicon nanowires deform in a very different way from bulk silicon. “Bulk silicon is very brittle and has limited deformability, meaning that it cannot be stretched or warped very much without breaking.” says Feng Xu, a Ph.D. student at NC state and co-author of the paper, “But the silicon nanowires are more resilient, and can sustain much larger deformation. Other properties of silicon nanowires include increasing fracture strength and decreasing elastic modulus as the nanowire gets smaller and smaller.”

The fact that silicon nanowires have more deformability and strength is a big deal. “These properties are essential to the design and reliability of novel silicon nanodevices,” Zhu says. “The insights gained from this study not only advance fundamental understanding about size effects on mechanical properties of nanostructures, but also give designers more options in designing nanodevices ranging from nanosensors to nanoelectronics to nanostructured solar cells.”

###

The study, “Mechanical Properties of Vapor-Liquid-Solid Synthesized Silicon Nanowires,” was co-authored by Zhu, Xu, Qin, University of Michigan (UM) researcher Wei Lu and UM Ph.D. student Wayne Fung. The study is published in the Nov. 11 issue o fNano Letters, and was funded by grants from the National Science Foundation and NC State.

August 13, 2008

All-nanowire loaded chip

Just after blogging on UC Berkeley’s recent research gift from Applied Materials, this story appears in the inbox. The university has created the first integrated circuit using nanowires as both sensors and electronic components.

This technology has a lot of possibities, even beyond silicon chips.

From the second link:

Nanowires make good sensors because their small dimensions enhance their sensitivity. Nanowire-based light sensors, for example, can detect just a few photons. But to be useful in practical devices, the sensors have to be integrated with electronics that can amplify and process such small signals. This has been a problem, because the materials used for sensing and electronics cannot easily be assembled on the same surface. What’s more, a reliable way of aligning the tiny nanowires that could be practical on a large scale has been hard to come by.

A printing method developed by the Berkeley group could solve both problems. First, the researchers deposit a polymer on a silicon substrate and use lithography to etch out patterns where the optical sensing nanowires should be. They then print a single layer of cadmium selenide nanowires over the pattern; removing the polymer leaves only the nanowires in the desired location for the circuit. They repeat the process with the second type of nanowires, which have germanium cores and silicon shells and form the basis of the transistors. Finally, they deposit electrodes to complete the circuits.

University of California, Berkeley, researchers were able to create an orderly circuit array from two types of tiny nanowires, which can function as optical sensors and transistors. Each of the circuits on the 13-by-20 array serves as a single pixel in an all-nanowire image sensor.

Squared away: University of California, Berkeley, researchers were able to create an orderly circuit array from two types of tiny nanowires, which can function as optical sensors and transistors. Each of the circuits on the 13-by-20 array serves as a single pixel in an all-nanowire image sensor.

July 29, 2008

Nanowire lawns sense images

Filed under: Science, Technology — Tags: , , , — David Kirkpatrick @ 1:00 pm

From KurzweilAI.net — another nanotech breakthrough from researchers at the University of California at Berkeley.

Nanowire lawns make for sheets of image sensors
New Scientist news service, July 28, 2008

University of California, Berkeley researchers are growing a mixed “lawn” of two kinds of nanowires to make a new kind of cheap, high-quality image sensor array that could be made in meter-scale sheets.

The arrays are reliable, flexible and easy to scale up. They could be grown to form rolls of tape several meters in diameter with all the needed components to do active sensing, translate the data, and transmit it wirelessly.

 
Read Original Article>>

July 3, 2008

Solar moratorium news, nanowire memory and tiny, tiny computer chips

From KurzweilAI.net — the US government comes to its senses on the solar moratorium, breakthroughs in nanowire memory, and computer chips heading toward smaller than 10 nanometers.

U.S. Lifts Moratorium on New Solar Projects
New York Times, July 3, 2008

Under increasing public pressure over its decision to temporarily halt all new solar development on public land, the Bureau of Land Management said Wednesday that it was lifting the freeze, barely a month after it was put into effect.

See also: Citing Need for Assessments, U.S. Freezes Solar Energy Projects

 
Read Original Article>>

 

New Nanowire-Based Memory Could Beef Up Information Storage
PhysOrg.com, July 2, 2008

University of Pennsylvania researchers have created a type of nanowire-based information storage device that is capable of storing three bit values rather than the usual two.

This ability could lead to a new generation of high-capacity information storage for electronic devices.

The phase changes are achieved by subjecting the nanowires to pulsed electric fields. This process heats the nanowires, altering the core and shell structure from crystalline (ordered) to amorphous (disordered). These two states correspond to two different electrical resistances.

The third value corresponds to the case where the core is amorphous while the shell is crystalline (or visa versa), resulting in an intermediate resistance.

Creating information storage from nanowires can be done via “bottom-up” approaches, using the natural tendency of tiny structures to self-assemble into larger structures, so they may be able to break free of the limitations faced by traditional “top-down” methods, such as patterning a circuit onto a silicon wafer by depositing a nanowire thin film.

 
Read Original Article>>

 

Intel’s Gelsinger Sees Clear Path To 10nm Chips
ChannelWeb, June 30, 2008

Intel sees a “clear way” to manufacturing chips under 10 nanometers, according to Pat Gelsinger, VP of Intel’s Digital Enterprise Group.

The next die shrink milestone will be the 32nm process, set to kick off next year, followed by 14nm a few years after that and then sub-10nm, he said.

 
Read Original Article>>

June 27, 2008

Nanowire circuits and tracking asteroids

From KurzweilAI.net, the House passed a bill to begin tracking potential Earth-strike asteroids, and a new low-cost, high-volume method of integrating nanowires onto silicon has been developed.

House passes bill mandating a plan for asteroid warning and deflection
KurzweilAI.net, June 27, 2008

In recently passed H.R.6063, The U.S. House of Representatives would direct the NASA Administrator to develop plans for a low-cost spacemission to rendezvous with the Apophis asteroid and attach a tracking device (subject to Senate approval).

The Apophis is expected to pass at a distance from Earth that is closer than geostationary satellites in 2029.

The bill would also require the Director of the White House’s Office of Science and TechnologyPolicy (OSTP) to develop a policy within two years for notifying Federal agencies and relevant emergency response institutions of an impending near-Earth objectthreat. And the OSTP would be required to recommend a Federal agency (or agencies) to be responsible for protecting the Nation from any near-Earth object anticipated to collide with Earth, and for implementing a deflection campaign.

 

Researchers develop new technique for fabricating nanowire circuits
Nanowerk News, June 26, 2008

Scientists at Harvard University and German universities of Jena, Gottingen, and Bremen have developed a reproducible, high-volume, low-cost fabrication methodfor integrating nanowire devices directly onto silicon.

The method incorporates spin-on glass technology, used in silicon integrated circuits manufacturing, and photolithography, transferring a circuit pattern onto a substrate with light. These devices can then function as light-emitting diodes, with the color of light determined by the type of semiconductor nanowire used.

Because nanowires can be made of materials commonly used in electronics and photonics, they hold great promise for integrating efficient light emitters, and could lead to the development of a completely new class of integrated circuits, such as large arrays of ultra-small nanoscale lasers that could be designed as high-density optical interconnects or used for on-chip chemical sensing.

 
Read Original Article>>

May 15, 2008

Nanowire solar cells and black holes

From KurzweilAI.net, nanotech that may boost solar efficiency and black holes may have an escape hatch of sorts

Nanowires may boost solar cell efficiency, engineers say
PhysOrg.com, May 14, 2008

University of California, San Diego electrical engineers have created experimental solar cells spiked with nanowires that could lead to highly efficient thin-film solar cells of the future.

 
Read Original Article>>

Physicists Demonstrate How Information Can Escape From Black Holes
PhysOrg.com, May 14, 2008

Physicists at Penn State and the Raman Research Institute in India have discovered such a mechanism by which information can be recovered from black holes.

They suggest that singularities do not exist in the real world. “Information only appears to be lost because we have been looking at a restricted part of the true quantum-mechanical space-time,” said Madhavan Varadarajan, a professor at the Raman Research Institute. “Once you consider quantum gravity, then space-time becomes much larger and there is room for information to reappear in the distant future on the other side of what was first thought to be the end of space-time.”

 
Read Original Article>>

May 7, 2008

Display nanowires, ultramicroelectrodes, more affordable solar news

From KurzweilAI.net — Upright copper nanowires may be key to better flat panel displays, single-walled carbon nanotubes form ultramicroelectrodes, more news on solar electricity that rivals fossil fuels in cost.

Nanowires for Displays
Technology Review, May 6, 2008

Researchers at the University of Illinois in Urbana Champaign have developed a simple process to grow upright copper nanowires on different surfaces.

The nanowire arrays could find use in field-emission displays, a new type of display technology that promises to provide brighter, more vivid pictures than existing flat-panel displays.

 
Read Original Article>>

Nanotube production leaps from sooty mess in test tube to ready formed chemical microsensors
PhysOrg.com, May 6, 2008

University of Warwick chemists have produced single-walled carbon nanotubes that instantly form ultramicroelecrodes that could be used to create biocompatible, ultrasensitive sensors with high signal-to-noise ratios and fast response times.

The research team is exploring how these ultramicroelecrodes could be used to measure levels of neurotransmitters and catalysis in fuel cells.

 
Read Original Article>>

Focusing on Solar’s Cost
Technology Review, May 7, 2008

Solar startup Sunrgi says that it will soon be able to produce electricity from the sun at costs that are competitive with fossil-fuel generation.

The company has created a concentrated photovoltaic system that uses a lens to focus sunlight up to 2,000 times sun concentration onto tiny solar cells that can convert 37.5 percent of the sun’s energy into electricity. Stronger concentrations of sunlight allow engineers to use much smaller solar cells, making it more economical to use higher-efficiency–but higher-cost–cells.

 
Read Original Article>>

October 16, 2010

Cool nanotech image — graphene

Filed under: et.al., Science, Technology — Tags: , , , , , — David Kirkpatrick @ 9:12 am

Actually the accompanying article is pretty cool, too, so do take the time to check it out.

But now, the image …

This image of a single suspended sheet of graphene taken with the TEAM 0.5, at Berkeley Lab’s National Center for Electron Microscopy shows individual carbon atoms (yellow) on the honeycomb lattice.

Also from the link:

In the current study, the team made graphene nanoribbons using a nanowire mask-based fabrication technique. By measuring the conductance fluctuation, or ‘noise’ of electrons in graphene nanoribbons, the researchers directly probed the effect of quantum confinement in these structures. Their findings map the electronic band structure of these graphene nanoribbons using a robust electrical probing method. This method can be further applied to a wide array of nanoscale materials, including graphene-based electronic devices.

“It amazes us to observe such a clear correlation between the noise and the band structure of these graphene nanomaterials,” says lead author Guangyu Xu, a physicist at University of California, Los Angeles. “This work adds strong support to the quasi-one-dimensional subband formation in graphene nanoribbons, in which our method turns out to be much more robust than conductance measurement.”

One more bit from the link, from the intro actually:

In last week’s announcement of the Nobel Prize in Physics, the Royal Swedish Academy of Sciences lauded graphene’s “exceptional properties that originate from the remarkable world of quantum physics.” If it weren’t hot enough before, this atomically thin sheet of carbon is now officially in the global spotlight.

So expect to hear a lot more about graphene in the coming months. Of course if you’re a regular reader of this blog, you’ve been getting a pretty steady (aside from the last month of light blogging) diet of graphene since almost day one (since February 2008 to be exact).

September 3, 2010

Graphene transistors hit 300 GHz

Via KurzweilAI.net — Great news, but as always I’d love to see a market-ready application come out of this research in the near future. Blogging about nanotech breakthroughs is all well and good, but it is excellent when I get the chance to blog about a real-world application of said breakthroughs.

From the link:

High-speed graphene transistors achieve world-record 300 GHz

September 3, 2010 by Editor

UCLA researchers have fabricated the fastest  graphene transistor to date, using a new fabrication process with a  nanowire as a self-aligned gate.

Self-aligned gates are a key element in modern transistors, which are semiconductor devices used to amplify and switch electronic signals.  Gates are used to switch the transistor between various states, and self-aligned gates were developed to deal with problems of misalignment encountered because of the shrinking scale of electronics.

“This new strategy overcomes two limitations previously encountered in graphene transistors,” professor of chemistry and biochemistry Xiangfeng Duan said. “First, it doesn’t produce any appreciable defects in the graphene during fabrication, so the high carrier mobility is retained. Second, by using a self-aligned approach with a nanowire as the gate, the group was able to overcome alignment difficulties previously encountered and fabricate very short-channel devices with unprecedented performance.”

These advances allowed the team to demonstrate the highest speed graphene transistors to date, with a cutoff frequency up to 300 GHz — comparable to the very best transistors from high-electron mobility materials such gallium arsenide or indium phosphide.

Graphene, a one-atom-thick layer of graphitic carbon, has great potential to make electronic devices such as radios, computers and phones faster and smaller. With the highest known carrier mobility — the speed at which electronic information is transmitted by a material — graphene is a good candidate for high-speed radio-frequency electronics. High-speed radio-frequency electronics may also find wide applications in microwave communication, imaging and radar technologies.

Funding for this research came from the National Science Foundation and the National Institutes of Health.

More info: UCLA news

September 1, 2010

More memory news …

… to join this earlier post from today on memristor storage, this one on silicon nanocrystals and 3D storage.

From the second link, the release:

Silicon oxide circuits break barrier

Nanocrystal conductors could lead to massive, robust 3-D storage

Rice University scientists have created the first two-terminal memory chips that use only silicon, one of the most common substances on the planet, in a way that should be easily adaptable to nanoelectronic manufacturing techniques and promises to extend the limits of miniaturization subject to Moore’s Law.

Last year, researchers in the lab of Rice Professor James Tour showed how electrical current could repeatedly break and reconnect 10-nanometer strips of graphite, a form of carbon, to create a robust, reliable memory “bit.” At the time, they didn’t fully understand why it worked so well.

Now, they do. A new collaboration by the Rice labs of professors Tour, Douglas Natelson and Lin Zhong proved the circuit doesn’t need the carbon at all.

Jun Yao, a graduate student in Tour’s lab and primary author of the paper to appear in the online edition of Nano Letters, confirmed his breakthrough idea when he sandwiched a layer of silicon oxide, an insulator, between semiconducting sheets of polycrystalline silicon that served as the top and bottom electrodes.

Applying a charge to the electrodes created a conductive pathway by stripping oxygen atoms from the silicon oxide and forming a chain of nano-sized silicon crystals. Once formed, the chain can be repeatedly broken and reconnected by applying a pulse of varying voltage.

The nanocrystal wires are as small as 5 nanometers (billionths of a meter) wide, far smaller than circuitry in even the most advanced computers and electronic devices.

“The beauty of it is its simplicity,” said Tour, Rice’s T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science. That, he said, will be key to the technology’s scalability. Silicon oxide switches or memory locations require only two terminals, not three (as in flash memory), because the physical process doesn’t require the device to hold a charge.

It also means layers of silicon-oxide memory can be stacked in tiny but capacious three-dimensional arrays. “I’ve been told by industry that if you’re not in the 3-D memory business in four years, you’re not going to be in the memory business. This is perfectly suited for that,” Tour said.

Silicon-oxide memories are compatible with conventional transistor manufacturing technology, said Tour, who recently attended a workshop by the National Science Foundation and IBM on breaking the barriers to Moore’s Law, which states the number of devices on a circuit doubles every 18 to 24 months.

“Manufacturers feel they can get pathways down to 10 nanometers. Flash memory is going to hit a brick wall at about 20 nanometers. But how do we get beyond that? Well, our technique is perfectly suited for sub-10-nanometer circuits,” he said.

Austin tech design company PrivaTran is already bench testing a silicon-oxide chip with 1,000 memory elements built in collaboration with the Tour lab. “We’re real excited about where the data is going here,” said PrivaTran CEO Glenn Mortland, who is using the technology in several projects supported by the Army Research Office, National Science Foundation, Air Force Office of Scientific Research, and the Navy Space and Naval Warfare Systems Command Small Business Innovation Research (SBIR) and Small Business Technology Transfer programs.

“Our original customer funding was geared toward more high-density memories,” Mortland said. “That’s where most of the paying customers see this going. I think, along the way, there will be side applications in various nonvolatile configurations.”

Yao had a hard time convincing his colleagues that silicon oxide alone could make a circuit. “Other group members didn’t believe him,” said Tour, who added that nobody recognized silicon oxide’s potential, even though it’s “the most-studied material in human history.”

“Most people, when they saw this effect, would say, ‘Oh, we had silicon-oxide breakdown,’ and they throw it out,” he said. “It was just sitting there waiting to be exploited.”

In other words, what used to be a bug turned out to be a feature.

Yao went to the mat for his idea. He first substituted a variety of materials for graphite and found none of them changed the circuit’s performance. Then he dropped the carbon and metal entirely and sandwiched silicon oxide between silicon terminals. It worked.

“It was a really difficult time for me, because people didn’t believe it,” Yao said. Finally, as a proof of concept, he cut a carbon nanotube to localize the switching site, sliced out a very thin piece of silicon oxide by focused ion beam and identified a nanoscale silicon pathway under a transmission electron microscope.

“This is research,” Yao said. “If you do something and everyone nods their heads, then it’s probably not that big. But if you do something and everyone shakes their heads, then you prove it, it could be big.

“It doesn’t matter how many people don’t believe it. What matters is whether it’s true or not.”

Silicon-oxide circuits carry all the benefits of the previously reported graphite device. They feature high on-off ratios, excellent endurance and fast switching (below 100 nanoseconds).

They will also be resistant to radiation, which should make them suitable for military and NASA applications. “It’s clear there are lots of radiation-hardened uses for this technology,” Mortland said.

Silicon oxide also works in reprogrammable gate arrays being built by NuPGA, a company formed last year through collaborative patents with Rice University. NuPGA’s devices will assist in the design of computer circuitry based on vertical arrays of silicon oxide embedded in “vias,” the holes in integrated circuits that connect layers of circuitry. Such rewritable gate arrays could drastically cut the cost of designing complex electronic devices.

###

Zhengzong Sun, a graduate student in Tour’s lab, was co-author of the paper with Yao; Tour; Natelson, a Rice professor of physics and astronomy; and Zhong, assistant professor of electrical and computer engineering.

The David and Lucille Packard Foundation, the Texas Instruments Leadership University Fund, the National Science Foundation, PrivaTran and the Army Research Office SBIR supported the research.

Read the abstract here: http://pubs.acs.org/journal/nalefd

High-resolution images are available for download here:
https://stage.media.rice.edu/images/media/NewsRels/0830_F2.jpg
https://stage.media.rice.edu/images/media/NewsRels/0830_F2a.jpg
https://stage.media.rice.edu/images/media/NewsRels/0830_F2b.jpg
https://stage.media.rice.edu/images/media/NewsRels/0830_F2c.jpg
https://stage.media.rice.edu/images/media/NewsRels/0830_F2d.jpg

NOTE: The first image (F2) is a key to the other four.

CAPTION: A 1k silicon oxide memory has been assembled by Rice and a commercial partner as a proof-of-concept. Silicon nanowire forms when charge is pumped through the silicon oxide, creating a two-terminal resistive switch. (Images courtesy Jun Yao/Rice University)

(Note: I recommend hitting the link for the first image — 0830_F2.jpg. It’s too big to run in this blog full-size, but it’s a great illustration of the chip.)

Memristor storage coming in 2013

Filed under: Business, Science, Technology — Tags: , , , , , — David Kirkpatrick @ 9:48 am

Of course, we’ll have to see if this tech is still state-of-the-art three years down the road.

From the link:

An electronic component that offers a new way to squeeze more data into computers and portable gadgets is set to go into production in just a couple of years. Hewlett-Packard announced today that it has entered an agreement with the Korean electronics manufacturer Hynix Semiconductor to make the components, called “memristors,” starting in 2013. Storage devices made of memristors will allow PCs, cellphones, and servers to store more and switch on instantly.

Making memories: This colorized atomic-force microscopy image shows 17 memristors. The circuit elements, shown in green, are formed at the crossroads of metal nanowires.
Credit: StanWilliams, HP Labs

Memristors are nanoscale electronic switches that have a variable resistance, and can retain their resistance even when the power is switched off. This makes them similar to the transistors used to store data in flash memory. But memristors are considerably smaller–as small as three nanometers. In contrast, manufacturers are experimenting with flash memory components that are 20 nanometers in size.

“The goal is to be at least double whatever flash memory is in three years–we know we’ll beat flash in speed, power, and endurance, and we want to beat it in density, too,” says Stanley Williams, a senior fellow at HP who has been developing memristors in his lab for about five years.

Nanotech making water more safe

This development can make a real quality of life difference in developing countries without running water and disaster areas, and it can make “roughing it” just a little bit less rough.

The release:

High-speed filter uses electrified nanostructures to purify water at low cost

IMAGE: This scanning electron microscope image shows the silver nanowires in which the cotton is dipped during the process of constructing a filter. The large fibers are cotton.

Click here for more information.

By dipping plain cotton cloth in a high-tech broth full of silver nanowires and carbon nanotubes, Stanford researchers have developed a new high-speed, low-cost filter that could easily be implemented to purify water in the developing world.

Instead of physically trapping bacteria as most existing filters do, the new filter lets them flow on through with the water. But by the time the pathogens have passed through, they have also passed on, because the device kills them with an electrical field that runs through the highly conductive “nano-coated” cotton.

In lab tests, over 98 percent of Escherichia coli bacteria that were exposed to 20 volts of electricity in the filter for several seconds were killed. Multiple layers of fabric were used to make the filter 2.5 inches thick.

“This really provides a new water treatment method to kill pathogens,” said Yi Cui, an associate professor of materials science and engineering. “It can easily be used in remote areas where people don’t have access to chemical treatments such as chlorine.”

Cholera, typhoid and hepatitis are among the waterborne diseases that are a continuing problem in the developing world. Cui said the new filter could be used in water purification systems from cities to small villages.

Faster filtering by letting bacteria through

Filters that physically trap bacteria must have pore spaces small enough to keep the pathogens from slipping through, but that restricts the filters’ flow rate.

IMAGE: This is professor of materials science and engineering Yi Cui.

Click here for more information.

Since the new filter doesn’t trap bacteria, it can have much larger pores, allowing water to speed through at a more rapid rate.

“Our filter is about 80,000 times faster than filters that trap bacteria,” Cui said. He is the senior author of a paper describing the research that will be published in an upcoming issue of Nano Letters. The paper is available online now.

The larger pore spaces in Cui’s filter also keep it from getting clogged, which is a problem with filters that physically pull bacteria out of the water.

Cui’s research group teamed with that of Sarah Heilshorn, an assistant professor of materials science and engineering, whose group brought its bioengineering expertise to bear on designing the filters.

Silver has long been known to have chemical properties that kill bacteria. “In the days before pasteurization and refrigeration, people would sometimes drop silver dollars into milk bottles to combat bacteria, or even swallow it,” Heilshorn said.

Cui’s group knew from previous projects that carbon nanotubes were good electrical conductors, so the researchers reasoned the two materials in concert would be effective against bacteria. “This approach really takes silver out of the folk remedy realm and into a high-tech setting, where it is much more effective,” Heilshorn said.

Using the commonplace keeps costs down

But the scientists also wanted to design the filters to be as inexpensive as possible. The amount of silver used for the nanowires was so small the cost was negligible, Cui said. Still, they needed a foundation material that was “cheap, widely available and chemically and mechanically robust.” So they went with ordinary woven cotton fabric.

“We got it at Wal-mart,” Cui said.

To turn their discount store cotton into a filter, they dipped it into a solution of carbon nanotubes, let it dry, then dipped it into the silver nanowire solution. They also tried mixing both nanomaterials together and doing a single dunk, which also worked. They let the cotton soak for at least a few minutes, sometimes up to 20, but that was all it took.

The big advantage of the nanomaterials is that their small size makes it easier for them to stick to the cotton, Cui said. The nanowires range from 40 to 100 billionths of a meter in diameter and up to 10 millionths of a meter in length. The nanotubes were only a few millionths of a meter long and as narrow as a single billionth of a meter. Because the nanomaterials stick so well, the nanotubes create a smooth, continuous surface on the cotton fibers. The longer nanowires generally have one end attached with the nanotubes and the other end branching off, poking into the void space between cotton fibers.

“With a continuous structure along the length, you can move the electrons very efficiently and really make the filter very conducting,” he said. “That means the filter requires less voltage.”

Minimal electricity required

The electrical current that helps do the killing is only a few milliamperes strong – barely enough to cause a tingling sensation in a person and easily supplied by a small solar panel or a couple 12-volt car batteries. The electrical current can also be generated from a stationary bicycle or by a hand-cranked device.

The low electricity requirement of the new filter is another advantage over those that physically filter bacteria, which use electric pumps to force water through their tiny pores. Those pumps take a lot of electricity to operate, Cui said.

In some of the lab tests of the nano-filter, the electricity needed to run current through the filter was only a fifth of what a filtration pump would have needed to filter a comparable amount of water.

The pores in the nano-filter are large enough that no pumping is needed – the force of gravity is enough to send the water speeding through.

Although the new filter is designed to let bacteria pass through, an added advantage of using the silver nanowire is that if any bacteria were to linger, the silver would likely kill it. This avoids biofouling, in which bacteria form a film on a filter. Biofouling is a common problem in filters that use small pores to filter out bacteria.

Cui said the electricity passing through the conducting filter may also be altering the pH of the water near the filter surface, which could add to its lethality toward the bacteria.

Cui said the next steps in the research are to try the filter on different types of bacteria and to run tests using several successive filters.

“With one filter, we can kill 98 percent of the bacteria,” Cui said. “For drinking water, you don’t want any live bacteria in the water, so we will have to use multiple filter stages.”

Cui’s research group has gained attention recently for using nanomaterials to build batteries from paper and cloth.

###

David Schoen and Alia Schoen were both graduate students in Materials Science and Engineering when the water-filter research was conducted and are co–lead authors of the paper in Nano Letters. David Schoen is now a postdoctoral researcher at Stanford.

Liangbing Hu, a postdoctoral researcher in Materials Science and Engineering, and Han Sun Kim, a graduate student in Materials Science and Engineering at the time the research was conducted, also contributed to the research and are co-authors of the paper.

August 27, 2010

Oil spill news

Filed under: Science, Technology — Tags: , , , , , , , — David Kirkpatrick @ 12:18 pm

Came across two interesting news items on oil spills. One is on a technology developed by MIT researchers on cleaning up surface oil after a spill and the second involves the BP Deepwater Horizon spill and how microbes may be cleaning at least the oil in deep water plumes.

From the second link:

Microbes may become the heroes of the Gulf of Mexico oil spill by gobbling up oil more rapidly than anyone expected. Now some experts suggest we ought to artificially stimulate such microbes in stricken marshland areas to aid their cleanup.

Evidence published this week shows that deep-water microbes in the Gulf may be rapidly chewing up BP’s spilled crude. This could sway federal authorities to use petroleum-digesting microbes or fertilizer additives that can stimulate naturally occurring bacteria for future spills. Such measures were originally rejected for the BP spill.

From the first link, the story on MIT’s oil spill clean-up tech comes from KurzweilAI.net:

MIT researchers unveil autonomous oil-absorbing robot

August 27, 2010 by Editor

Researchers at MIT have created a robotic prototype that could autonomously navigate the surface of the ocean to collect surface oil and process it on site.

The system, called Seaswarm, is a fleet of vehicles that may make cleaning up future oil spills both less expensive and more efficient than current skimming methods.

The Seaswarm robot uses a conveyor belt covered with a thin nanowire mesh to absorb oil. The fabric, previously featured in a paper published in the journal Nature Nanotechnology, can absorb up to twenty times its own weight in oil while repelling water. By heating up the material, the oil can be removed and burnt locally and the nanofabric can be reused.

The Seaswarm robot, which is 16 feet long and seven feet wide, uses two square meters of solar panels for self-propulsion. With just 100 watts, the equivalent of one household light bulb, it could potentially clean continuously for weeks.

Using swarm behavior, the units will use wireless communication and GPS and manage their coordinates and ensure an even distribution over a spill site. By detecting the edge of a spill and moving inward, a single vehicle could clean an entire site autonomously or engage other vehicles for faster cleaning.

MIT researchers estimate that a fleet of 5,000 Seaswarm robots would be able to clean a spill the size of the gulf in one month. The team has future plans to enter their design into the X-Prize’s $1 million oil-cleanup competition. The award is given to the team that can most efficiently collect surface oil with the highest recovery rate.

By autonomously navigating the water’s surface, Seaswarm proposes a new system for ocean-skimming and oil removal. Video: Senseable City Lab

More info: MIT news

July 15, 2010

Acid bath may lead to armchair quantum wires

More nanotech news.

The release:

Nanotubes pass acid test

Rice researchers’ method untangles long tubes, clears hurdle toward armchair quantum wire

HOUSTON – (July 14, 2010) – Rice University scientists have found the “ultimate” solvent for all kinds of carbon nanotubes (CNTs), a breakthrough that brings the creation of a highly conductive quantum nanowire ever closer.

Nanotubes have the frustrating habit of bundling, making them less useful than when they’re separated in a solution. Rice scientists led by Matteo Pasquali, a professor in chemical and biomolecular engineering and in chemistry, have been trying to untangle them for years as they look for scalable methods to make exceptionally strong, ultralight, highly conductive materials that could revolutionize power distribution, such as the armchair quantum wire.

The armchair quantum wire — a macroscopic cable of well-aligned metallic nanotubes — was envisioned by the late Richard Smalley, a Rice chemist who shared the Nobel Prize for his part in discovering the the family of molecules that includes the carbon nanotube. Rice is celebrating the 25th anniversary of that discovery this year.

Pasquali, primary author Nicholas Parra-Vasquez and their colleagues reported this month in the online journal ACS Nano that chlorosulfonic acid can dissolve half-millimeter-long nanotubes in solution, a critical step in spinning fibers from ultralong nanotubes.

Current methods to dissolve carbon nanotubes, which include surrounding the tubes with soap-like surfactants, doping them with alkali metals or attaching small chemical groups to the sidewalls, disperse nanotubes at relatively low concentrations. These techniques are not ideal for fiber spinning because they damage the properties of the nanotubes, either by attaching small molecules to their surfaces or by shortening them.

A few years ago, the Rice researchers discovered that chlorosulfonic acid, a “superacid,” adds positive charges to the surface of the nanotubes without damaging them. This causes the nanotubes to spontaneously separate from each other in their natural bundled form.

This method is ideal for making nanotube solutions for fiber spinning because it produces fluid dopes that closely resemble those used in industrial spinning of high-performance fibers. Until recently, the researchers thought this dissolution method would be effective only for short single-walled nanotubes.

In the new paper, the Rice team reported that the acid dissolution method also works with any type of carbon nanotube, irrespective of length and type, as long as the nanotubes are relatively free of defects.

Parra-Vasquez described the process as “very easy.”

“Just adding the nanotubes to chlorosulfonic acid results in dissolution, without even mixing,” he said.

While earlier research had focused on single-walled carbon nanotubes, the team discovered chlorosulfonic acid is also adept at dissolving multiwalled nanotubes (MWNTs). “There are many processes that make multiwalled nanotubes at a cheaper cost, and there’s a lot of research with them,” said Parra-Vasquez, who earned his Rice doctorate last year. “We hope this will open up new areas of research.”

They also observed for the first time that long SWNTs dispersed by superacid form liquid crystals. “We already knew that with shorter nanotubes, the liquid-crystalline phase is very different from traditional liquid crystals, so liquid crystals formed from ultralong nanotubes should be interesting to study,” he said.

Parra-Vasquez, now a postdoctoral researcher at Centre de Physique Moleculaire Optique et Hertzienne, Universite’ de Bordeaux, Talence, France, came to Rice in 2002 for graduate studies with Pasquali and Smalley.

Study co-author Micah Green, assistant professor of chemical engineering at Texas Tech and a former postdoctoral fellow in Pasquali’s research group, said working with long nanotubes is key to attaining exceptional properties in fibers because both the mechanical and electrical properties depend on the length of the constituent nanotubes. Pasquali said that using long nanotubes in the fibers should improve their properties on the order of one to two magnitudes, and that similar enhanced properties are also expected in thin films of carbon nanotubes being investigated for flexible electronics applications.

An immediate goal for researchers, Parra-Vasquez said, will be to find “large quantities of ultralong single-walled nanotubes with low defects — and then making that fiber we have been dreaming of making since I arrived at Rice, a dream that Rick Smalley had and that we have all shared since.”

###

Co-authors of the paper are graduate students Natnael Behabtu, Colin Young, Anubha Goyal and Cary Pint; Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry, and Robert Hauge, a distinguished faculty fellow in chemistry, all at Rice; and Judith Schmidt, Ellina Kesselman, Yachin Cohen and Yeshayahu Talmon of the Department of Chemical Engineering, Technion-Israel Institute of Technology, Haifa, Israel.

The Air Force Office of Scientific Research, the Air Force Research Laboratory, the National Science Foundation Division of Materials Research, the Robert A. Welch Foundation, the United States-Israel Binational Science Foundation and the Evans-Attwell Welch Postdoctoral Fellowship funded the research.

Read the abstract at: http://pubs.acs.org/doi/abs/10.1021/nn100864v

For more about Rice’s 25th anniversary Year of Nano celebrations, visit: http://buckyball.smalley.rice.edu/year_of_nano/

June 15, 2010

The thick or thin solar question …

… has been solved by nanotech based on coaxial cable.

From the link:

“Many groups around the world are working on nanowire-type solar cells, most using crystalline semiconductors,” said co-author Michael Naughton, a professor of physics at Boston College. “This nanocoax cell architecture, on the other hand, does not require crystalline materials, and therefore offers promise for lower-cost solar power with ultrathin absorbers. With continued optimization, efficiencies beyond anything achieved in conventional planar architectures may be possible, while using smaller quantities of less costly material.”

Optically, the so-called nanocoax stands thick enough to capture light, yet its architecture makes it thin enough to allow a more efficient extraction of current, the researchers report in PSS’s Rapid Research Letters. This makes the nanocoax, invented at Boston College in 2005 and patented last year, a new platform for low cost, high efficiency solar power.

Boston College researchers report developing a “nanocoax” technology that can support a highly efficient thin film solar cell. This image shows a cross section of an array of nanocoax structures, which prove to be thick enough to absorb a sufficient amount of light, yet thin enough to extract current with increased efficiency, the researchers report in the journal Physica Status Solidi. Credit: Boston College

June 11, 2010

Nanoscale circuits on graphene

Via KurzweilAI.net — For all those fresh graduates out there, one word — graphene.

Simple way to create nanocircuitry on graphene developed
KurzweilAI.net, June 11, 2010

method of drawing nanoscale circuits onto atom-thick sheets of graphene has been developed by researchers at the U.S. Naval Research Laboratory, Georgia Institute ofTechnology, and the University of Illinois at Urbana-Champaign.


(University of Illinois at Urbana-Champaign)

The simple, quick one-step process for creating nanowires, based on thermochemical nanolithography (TCNL), tunes the electronic properties of reduced graphene oxide, allowing it to switch from being an insulating material to a conducting material.

Scientists who work with nanocircuits are enthusiastic about graphene because electrons meet with less resistance when they travel along graphene compared to silicon and because today’s silicon transistors are nearly as small as allowed by the laws of physics. Graphene also has the edge due to its thickness – it’s a carbon sheet that is a single atom thick.

However, no one knew how to produce graphene nanostructures with such a reproducible or scalable method until now.

More info: Georgia Institute of Technology

February 26, 2010

Quantum physics improving electronics and autos

Or so this news from Princeton purports.

The release:

SCIENTISTS FIND AN EQUATION FOR MATERIALS INNOVATION

Posted Feb 25, 2010By Chris Emery

Professor Emily Carter and graduate student Chen Huang developed a new way of predicting important properties of substances. The advance could speed the development of new materials and technologies. (Photo: Frank Wojciechowski)

Princeton engineers have made a breakthrough in an 80-year-old quandary in quantum physics, paving the way for the development of new materials that could make electronic devices smaller and cars more energy efficient.

By reworking a theory first proposed by physicists in the 1920s, the researchers discovered a new way to predict important characteristics of a new material before it’s been created. The new formula allows computers to model the properties of a material up to 100,000 times faster than previously possible and vastly expands the range of properties scientists can study.

“The equation scientists were using before was inefficient and consumed huge amounts of computing power, so we were limited to modeling only a few hundred atoms of a perfect material,” said Emily Carter, the engineering professor who led the project.

“But most materials aren’t perfect,” said Carter, the Arthur W. Marks ’19 Professor of Mechanical and Aerospace Engineering and Applied and Computational Mathematics. “Important properties are actually determined by the flaws, but to understand those you need to look at thousands or tens of thousands of atoms so the defects are included. Using this new equation, we’ve been able to model up to a million atoms, so we get closer to the real properties of a substance.”

By offering a panoramic view of how substances behave in the real world, the theory gives scientists a tool for developing materials that can be used for designing new technologies. Car frames made from lighter, strong metal alloys, for instance, might make vehicles more energy efficient, and smaller, faster electronic devices might be produced using nanowires with diameters tens of thousands of times smaller than that of a human hair.

Paul Madden, a chemistry professor and provost of The Queen’s College at Oxford University, who originally introduced Carter to this field of research, described the work as a “significant breakthrough” that could allow researchers to substantially expand the range of materials that can be studied in this manner. “This opens up a new class of material physics problems to realistic simulation,” he said.

The new theory traces its lineage to the Thomas-Fermi equation, a concept proposed by Llewellyn Hilleth Thomas and Nobel laureate Enrico Fermi in 1927. The equation was a simple means of relating two fundamental characteristics of atoms and molecules. They theorized that the energy electrons possess as a result of their motion — electron kinetic energy — could be calculated based how the electrons are distributed in the material. Electrons that are confined to a small region have higher kinetic energy, for instance, while those spread over a large volume have lower energy.

Understanding this relationship is important because the distribution of electrons is easier to measure, while the energy of electrons is more useful in designing materials. Knowing the electron kinetic energy helps researchers determine the structure and other properties of a material, such as how it changes shape in response to physical stress. The catch was that Thomas and Fermi’s concept was based on a theoretical gas, in which the electrons are spread evenly throughout. It could not be used to predict properties of real materials, in which electron density is less uniform.

The next major advance came in 1964, when another pair of scientists, Pierre Hohenberg and Walter Kohn, another Nobel laureate, proved that the concepts proposed by Thomas and Fermi could be applied to real materials. While they didn’t derive a final, working equation for directly relating electron kinetic energy to the distribution of electrons, Hohenberg and Kohn laid the formal groundwork that proved such an equation exists. Scientists have been searching for a working theory ever since.

Carter began working on the problem in 1996 and produced a significant advance with two postdoctoral researchers in 1999, building on Hohenberg and Kohn’s work. She has continued to whittle away at the problem since. “It would be wonderful if a perfect equation that explains all of this would just fall from the sky,” she said. “But that isn’t going to happen, so we’ve kept searching for a practical solution that helps us study materials.”

In the absence of a solution, researchers have been calculating the energy of each atom from scratch to determine the properties of a substance. The laborious method bogs down the most powerful computers if more than a few hundred atoms are being considered, severely limiting the amount of a material and type of phenomena that can be studied.

Carter knew that using the concepts introduced by Thomas and Fermi would be far more efficient, because it would avoid having to process information on the state of each and every electron.

As they worked on the problem, Carter and Chen Huang, a doctoral student in physics, concluded that the key to the puzzle was addressing a disparity observed in Carter’s earlier work. Carter and her group had developed an accurate working model for predicting the kinetic energy of electrons in simple metals. But when they tried to apply the same model to semiconductors — the conductive materials used in modern electronic devices — their predictions were no longer accurate.

“We needed to find out what we were missing that made the results so different between the semiconductors and metals,” Huang said. “Then we realized that metals and semiconductors respond differently to electrical fields. Our model was missing this.”

In the end, Huang said, the solution was a compromise. “By finding an equation that worked for these two types of materials, we found a model that works for a wide range of materials.”

Their new model, published online Jan. 26 in Physical Review B, a journal of the American Physical Society, provides a practical method for predicting the kinetic energy of electrons in semiconductors from only the electron density. The research was funded by the National Science Foundation.

Coupled with advances published last year by Carter and Linda Hung, a graduate student in applied and computational mathematics, the new model extends the range of elements and quantities of material that can be accurately simulated.

The researchers hope that by moving beyond the concepts introduced by Thomas and Fermi more than 80 years ago, their work will speed future innovations. “Before people could only look at small bits of materials and perfect crystals,” Carter said. “Now we can accurately apply quantum mechanics at scales of matter never possible before.”

February 20, 2010

Paper batteries and eTextiles

The 2010 AAAS (American Association for the Advancement of Science) annual meeting is going on as I type, so there is a lot of news coming out fast and furious from the conference. I’m going to try and restrain myself and only post what really strikes my fancy, or what sounds like a game-changing advancement in any particular field.

Like I regularly do, this news will presented in the form of the raw press release. Yeah, it’s a bit lazy to drop the release on you with minimal, if any, commentary from me, but I don’t want to be a gatekeeper of the information being put out and I don’t want to spin the news by selectively writing from a release. With a raw release you get all the information the organization/scientist/whoever put the release out wanted to make public and you can use that information as you see fit. Do keep in mind any release is going to have some manner of bias, even science releases, so read them with that in mind, but do enjoy this exciting news as it comes out.

This release is on nanotechnology and how it is allowing for paper batteries and supercapacitors and is creating a new fabric technology called “eTextiles.”

The release:

Nanotechnology sparks energy storage on paper and cloth

Stanford researcher Yi Cui and his team are re-conceptualizing batteries using nanotechnology

IMAGE: Bing Hu, a post-doctoral fellow in Yi Cui’s research group at Stanford, prepares a small square of ordinary paper with an ink that will deposit nanotubes on the surface that…

Click here for more information.

By dipping ordinary paper or fabric in a special ink infused with nanoparticles, Stanford engineer Yi Cui has found a way to cheaply and efficiently manufacture lightweight paper batteries and supercapacitors (which, like batteries, store energy, but by electrostatic rather than chemical means), as well as stretchable, conductive textiles known as “eTextiles” – capable of storing energy while retaining the mechanical properties of ordinary paper or fabric.

While the technology is still new, Cui’s team has envisioned numerous functional uses for their inventions. Homes of the future could one day be lined with energy-storing wallpaper. Gadget lovers would be able to charge their portable appliances on the go, simply plugging them into an outlet woven into their T-shirts. Energy textiles might also be used to create moving-display apparel, reactive high-performance sportswear and wearable power for a soldier’s battle gear.

The key ingredients in developing these high-tech products are not visible to the human eye. Nanostructures, which can be assembled in patterns that allow them to transport electricity, may provide the solutions to a number of problems encountered with electrical storage devices currently available on the market.

The type of nanoparticle used in the Cui group’s experimental devices varies according to the intended function of the product – lithium cobalt oxide is a common compound used for batteries, while single-walled carbon nanotubes, or SWNTs, are used for supercapacitors.

Cui, an assistant professor of materials science and engineering at Stanford, leads a research group that investigates new applications of nanoscale materials. The objective, said Cui, is not only to supply answers to theoretical inquiries but also to pursue projects with practical value. Recently, his team has focused on ways to integrate nanotechnology into the realm of energy development.

“Energy storage is a pretty old research field,” said Cui. “Supercapacitors, batteries – those things are old. How do you really make a revolutionary impact in this field? It requires quite a dramatic difference of thinking.”

While electrical energy storage devices have come a long way since Alessandro Volta debuted the world’s first electrical cell in 1800, the technology is facing yet another revolution. Current methods of manufacturing energy storage devices can be capital intensive and environmentally hazardous, and the end products have noticeable performance constraints – conventional lithium ion batteries have a limited storage capacity and are costly to manufacture, while traditional capacitors provide high power but at the expense of energy storage capacity.

With a little help from new science, the batteries of the future may not look anything like the bulky metal units we’ve grown accustomed to. Nanotechnology is favored as a remedy both for its economic appeal and its capability to improve energy performance in devices that integrate it. Replacing the carbon (graphite) anodes found in lithium ion batteries with anodes of silicon nanowires, for example, has the potential to increase their storage capacity by 10 times, according to experiments conducted by Cui’s team.

Silicon had previously been recognized as a favorable anode material because it can hold a larger amount of lithium than carbon. But applications of silicon were limited by its inability to sustain physical stress – namely, the fourfold volume increase that silicon undergoes when lithium ions attach themselves to a silicon anode in the process of charging a battery, as well as the shrinkage that occurs when lithium ions are drawn out as it discharges. The result was that silicon structures would disintegrate, causing anodes of this material to lose much if not all of their storage capacity.

Cui and collaborators demonstrated in previous publications in Nature, Nanotechnology and Nano Letters that the use of silicon nanowire battery electrodes, mechanically capable of withstanding the absorption and discharge of lithium ions, was one way to sidestep the problem.

The findings hold promise for the development of rechargeable lithium batteries offering a longer life cycle and higher energy capacity than their contemporaries. Silicon nanowire technology may one day find a home in electric cars, portable electronic devices and implantable medical appliances.

Cui now hopes to direct his research toward studying both the “hard science” behind the electrical properties of nanomaterials and designing real-world applications.

“This is the right time to really see what we learn from nanoscience and do practical applications that are extremely promising,” said Cui. “The beauty of this is, it combines the lowest cost technology that you can find to the highest tech nanotechnology to produce something great. I think this is a very exciting idea … a huge impact for society.”

###

The Cui group’s latest research on energy storage devices was detailed in papers published in the online editions of the Proceedings of the National Academy of Sciences in December 2009 (“Highly Conductive Paper for Energy-Storage Devices”) and Nano Letters in January 2010 (“Stretchable, Porous and Conductive Energy Textiles”).

Cui’s talk at the symposium “Nanotechnology: Will Nanomaterials Revolutionize Energy Applications?” is scheduled for 9:50 a.m. Feb. 20 in Room 1B of the San Diego Convention Center.

Video/photos:
Conductive eTextiles: Stanford finds a new use for cloth
http://news.stanford.edu/news/2010/february1/batteries-from-cloth-020510.html

At Stanford, nanotubes + ink + paper = instant battery
http://news.stanford.edu/news/2009/december7/nanotubes-ink-paper-120709.html

February 15, 2010

A little nano bling …

… may lead to some serious nanotech applications in medicine, data protection and supercomputing.

The release:

Digging deep into diamonds, applied physicists advance quantum science and technology

Diamond nanowire device could lead to new class of diamond nanomaterials suitable for quantum cryptography, quantum computing, and magnetic field imaging

IMAGE: A diamond-based nanowire device. Researchers used a top-down nanofabrication technique to embed color centers into a variety of machined structures. By creating large device arrays rather than just “one-of-a-kind ” designs,…

Click here for more information.

CAMBRIDGE, Mass., By creating diamond-based nanowire devices, a team at Harvard has taken another step towards making applications based on quantum science and technology possible.

The new device offers a bright, stable source of single photons at room temperature, an essential element in making fast and secure computing with light practical.

The finding could lead to a new class of nanostructured diamond devices suitable for quantum communication and computing, as well as advance areas ranging from biological and chemical sensing to scientific imaging.

Published in the February 14th issue of Nature Nanotechnology, researchers led by Marko Loncar, Assistant Professor of Electrical Engineering at the Harvard School of Engineering and Applied Sciences (SEAS), found that the performance of a single photon source based on a light emitting defect (color center) in diamond could be improved by nanostructuring the diamond and embedding the defect within a diamond nanowire.

Scientists, in fact, first began exploiting the properties of natural diamonds after learning how to manipulate the electron spin, or intrinsic angular momentum, associated with the nitrogen vacancy (NV) color center of the gem. The quantum (qubit) state can be initialized and measured using light.

The color center “communicates” by emitting and absorbing photons. The flow of photons emitted from the color center provides a means to carry the resulting information, making the control, capture, and storage of photons essential for any kind of practical communication or computation. Gathering photons efficiently, however, is difficult since color-centers are embedded deep inside the diamond.

“This presents a major problem if you want to interface a color center and integrate it into real-world applications,” explains Loncar. “What was missing was an interface that connects the nano-world of a color center with macro-world of optical fibers and lenses.”

The diamond nanowire device offers a solution, providing a natural and efficient interface to probe an individual color center, making it brighter and increasing its sensitivity. The resulting enhanced optical properties increases photon collection by nearly a factor of ten relative to natural diamond devices.

“Our nanowire device can channel the photons that are emitted and direct them in a convenient way,” says lead-author Tom Babinec, a graduate student at SEAS.

Further, the diamond nanowire is designed to overcome hurdles that have challenged other state-of-the-art systems—such as those based on fluorescent dye molecules, quantum dots, and carbon nanotubes—as the device can be readily replicated and integrated with a variety of nano-machined structures.

The researchers used a top-down nanofabrication technique to embed color centers into a variety of machined structures. By creating large device arrays rather than just “one-of-a-kind” designs, the realization of quantum networks and systems, which require the integration and manipulation of many devices in parallel, is more likely.

“We consider this an important step and enabling technology towards more practical optical systems based on this exciting material platform,” says Loncar. “Starting with these synthetic, nanostructured diamond samples, we can start dreaming about the diamond-based devices and systems that could one day lead to applications in quantum science and technology as well as in sensing and imaging.”

###

Loncar and Babinec’s co-authors included research scholar Birgit Hausmann, graduate student Yinan Zhang, and postdoctoral student Mughees Khan, all at SEAS; graduate student Jero Maze in the Department of Physics at Harvard; and faculty member Phil R. Hemmer at Texas A&M University.

The researchers acknowledge the following support: Nanoscale Interdisciplinary Research Team (NIRT) grant from National Science Foundation (NSF), the NSF-funded Nanoscale Science and Engineering Center at Harvard (NSEC); the Defense Advanced Research Projects Agency (DARPA); and a National Defense Science and Engineering Graduate Fellowship and National Science Foundation Graduate Fellowship. All devices have been fabricated at the Center for Nanoscale Systems (CNS) at Harvard.

February 3, 2010

The latest in display tech — multitouch skin

Filed under: Business, Media, Science, Technology — Tags: , , , , — David Kirkpatrick @ 2:25 pm

Via KurzweilAI.net — Like almost all announcements of this type of product, I’ll  be much more interested when this is available on the open market with practical applications. Of course, it’s still pretty cool to contemplate.

Multitouch ‘Skin’ Transforms Surfaces Into Interactive Screens
Physorg.com, Feb. 2, 2010

A new large-format multi-touch technology launched today by DISPLAX will transform any non-conductive flat or curved surface, such as glass, plastic or wood, into a multitouch screen.

DISPLAX Multitouch Technology uses a controller that works by processing multiple input signals it receives from a grid of nanowires embedded in the film attached to the enabled surface. Each time a finger is placed on the screen or a user blows on the surface, a small electrical disturbance is caused. The microprocessor controller analyzes this data and decodes the location of each input on that grid to track the finger and air-flow movements.
Read Original Article>>

December 12, 2009

“Hot electrons” and solar cells

Filed under: Science — Tags: , , , , — David Kirkpatrick @ 4:29 pm

The latest solar breakthrough news.

The release:

Elusive ‘hot’ electrons captured in ultra-thin solar cells

Shrinking cells snares charges in less than one-trillionth of a second

CHESTNUT HILL, MA (12/11/2009) – Boston College researchers have observed the “hot electron” effect in a solar cell for the first time and successfully harvested the elusive charges using ultra-thin solar cells, opening a potential avenue to improved solar power efficiency, the authors report in the current online edition of Applied Physics Letters.

When light is captured in solar cells, it generates free electrons in a range of energy states. But in order to snare these charges, the electrons must reach the bottom of the conduction band. The problem has been that these highly energized “hot” electrons lose much of their energy to heat along the way.

Hot electrons have been observed in other devices, such as semiconductors. But their high kinetic energy can cause these electrons, also known as “hot carriers,” to degrade a device. Researchers have long theorized about the benefits of harnessing hot electrons for solar power through so-called “3rd generation” devices.

By using ultrathin solar cells – a film fewer than 30 nanometers thick – the team developed a mechanism able to extract hot electrons in the moments before they cool – effectively opening a new “escape hatch” through which they typically don’t travel, said co-author Michael J. Naughton, the Evelyn J. and Robert A. Ferris Professor of Physics at Boston College.

The team’s success centered on minimizing the environment within which the electrons are able to escape, said Professor of Physics Krzysztof Kempa, lead author of the paper.

Kempa compared the challenge to trying to heat a swimming pool with a pot of boiling water. Drop the pot into the center of the pool and there would be no change in temperature at the edge because the heat would dissipate en route. But drop the pot into a sink filled with cold water and the heat would likely raise the temperature in the smaller area.

“We have shrunk the size of the solar cell by making it thin,” Kempa said. “In doing so, we are bringing these hot electrons closer to the surface, so they can be collected more readily. These electrons have to be captured in less than a picosecond, which is less than one trillionth of a second.”

The ultrathin cells demonstrated overall power conversion efficiency of approximately 3 percent using absorbers one fiftieth as thick as conventional cells. The team attributed the gains to the capture of hot electrons and an accompanying reduction in voltage-sapping heat. The researchers acknowledged the film’s efficiency is limited by the negligible light collection of ultra-thin junctions. However, combining the film with better light-trapping technology – such as nanowire structures – could significantly increase efficiency in an ultra-thin hot electron solar cell technology.

###

In addition to Naughton and Kempa, the research team included Professor of Physics Zhifeng Ren, Research Associate Professor and Laboratory Director Andrzej A. Herczynski, Research Scientist Yantao Gao, doctoral student Timothy Kirkpatrick, and Jakub Rybczynski of Solasta Corp., of Newton MA, which supported the research. Naughton, Kempa and Ren are principals in the clean energy firm as well.

October 30, 2009

Improving dye-sensitized solar cells

Efficiencies are going up and costs and holding steady or falling. All this bodes well for the future of solar power.

From the link:

Dye-sensitized solar cells are flexible and cheap to make, but they tend to be inefficient at converting light into electricity. One way to boost the performance of any solar cell is to increase the surface area available to incoming light. So a group of researchers at Georgia Tech has made dye-sensitized solar cells with a much higher effective surface area by wrapping the cells around optical fibers. These fiber solar cells are six times more efficient than a zinc oxide solar cell with the same surface area, and if they can be built using cheap polymer fibers, they shouldn’t be significantly more expensive to make.

The advantage of a fiber-optic solar-cell system over a planar one is that light bounces around inside an optical fiber as it travels along its length, providing more opportunities to interact with the solar cell on its inner surface and producing more current. “For a given real estate, the total area of the cell is higher, and increased surface area means improved light harvesting and more energy,” says Max Shtein, an assistant professor of materials science and engineering at the University of Michigan who was not involved with the research.

Solar on fiber: An optical fiber (left) is covered in dye-coated zinc-oxide nanowires (closeup, right). Both images were made using a scanning electron microscope.
Credit: Angewandte Chemie

September 18, 2009

The future of technology looks pretty bright

Filed under: Business, Science, Technology — Tags: , , , , — David Kirkpatrick @ 6:23 pm

I’ve blogged on all three of the technologies — OLEDs and nanowires pretty extensively — but this is a very nice thumbnail sketch of what’s at the edge of the real-world horizon, if not already here.

From the last link:

Have a look at just three technologies that have the ability to completely revolutionize IT from the ground up: memristors, nanowires and OLEDS.

Memristors are transistor-like devices made out of titanium dioxide that can remember voltage state information. They hold the potential for completely revolutionizing storage and processing technologies because they erase the distinction between processing and storage (you can do both/and on the same chip). More prosaically, they make it possible to create storage devices that require no power. How will that affect your data center?

Then there are nanowires: tiny wires no more than a single nanometer in width that can be conductors, insulators or semiconductors (albeit with weird quantum properties). These can form the basis for embedded intelligent networks — sensor and control networks that are actually built into the materials and devices they control. (Take that, smart grids!)

Finally, there are organic LEDs, which have the interesting property that they can be printed onto things such as wallpaper at relatively low cost. Sony has developed OLED monitors, and GE is looking into OLED wallpaper. So in a couple of years, your new office (or home office) may come equipped with wallpaper that, at the touch of a button, can turn into a floor-to-ceiling high-resolution display. (Think of the bandwidth requirements).

Each of these technologies holds the possibility of completely reshaping IT within the next few years. And the conjunction of all three could make the conjunction of the transistor and fiber optics look like a warm-up act.

August 16, 2009

DNA scaffolding and circuit boards

A release red hot from the inbox:

IBM Scientists Use DNA Scaffolding To Build Tiny Circuit Boards

Nanotechnology advancement could lead to smaller, faster, more energy efficient computer chips

SAN JOSE, Calif., Aug. 17 /PRNewswire-FirstCall/ — Today, scientists at IBM Research (NYSE:IBM) and the California Institute of Technology announced a scientific advancement that could be a major breakthrough in enabling the semiconductor industry to pack more power and speed into tiny computer chips, while making them more energy efficient and less expensive to manufacture.

  (Photo:  http://www.newscom.com/cgi-bin/prnh/20090817/NY62155-a )
  (Photo:  http://www.newscom.com/cgi-bin/prnh/20090817/NY62155-b )
  (Logo:  http://www.newscom.com/cgi-bin/prnh/20090416/IBMLOGO )

IBM Researchers and collaborator Paul W.K. Rothemund, of the California Institute of Technology, have made an advancement in combining lithographic patterning with self assembly – a method to arrange DNA origami structures on surfaces compatible with today’s semiconductor manufacturing equipment.

Today, the semiconductor industry is faced with the challenges of developing lithographic technology for feature sizes smaller than 22 nm and exploring new classes of transistors that employ carbon nanotubes or silicon nanowires. IBM’s approach of using DNA molecules as scaffolding — where millions of carbon nanotubes could be deposited and self-assembled into precise patterns by sticking to the DNA molecules – may provide a way to reach sub-22 nm lithography.

The utility of this approach lies in the fact that the positioned DNA nanostructures can serve as scaffolds, or miniature circuit boards, for the precise assembly of components – such as carbon nanotubes, nanowires and nanoparticles – at dimensions significantly smaller than possible with conventional semiconductor fabrication techniques. This opens up the possibility of creating functional devices that can be integrated into larger structures, as well as enabling studies of arrays of nanostructures with known coordinates.

“The cost involved in shrinking features to improve performance is a limiting factor in keeping pace with Moore’s Law and a concern across the semiconductor industry,” said Spike Narayan, manager, Science & Technology, IBM Research – Almaden. “The combination of this directed self-assembly with today’s fabrication technology eventually could lead to substantial savings in the most expensive and challenging part of the chip-making process.”

The techniques for preparing DNA origami, developed at Caltech, cause single DNA molecules to self assemble in solution via a reaction between a long single strand of viral DNA and a mixture of different short synthetic oligonucleotide strands. These short segments act as staples – effectively folding the viral DNA into the desired 2D shape through complementary base pair binding. The short staples can be modified to provide attachment sites for nanoscale components at resolutions (separation between sites) as small as 6 nanometers (nm). In this way, DNA nanostructures such as squares, triangles and stars can be prepared with dimensions of 100 – 150 nm on an edge and a thickness of the width of the DNA double helix.

IBM uses traditional semiconductor techniques, the same used to make the chips found in today’s computers, to etch out patterns, creating the lithographic templates for this new approach. Either electron beam or optical lithography are used to create arrays of binding sites of the proper size and shape to match those of individual origami structures. The template materials are chosen to have high selectivity so that origami binds only to the patterns of “sticky patches” and nowhere else.

The paper on this work, “Placement and orientation of DNA nanostructures on lithographically patterned surfaces,” by scientists at IBM Research and the California Institute of Technology will be published in the September issue of Nature Nanotechnology and is currently available at: http://www.nature.com/nnano/journal/vaop/ncurrent/abs/nnano.2009.220.html.

For more information about IBM Research, please visit http://www.research.ibm.com/.

To view and download DNA scaffolding images, in high or low resolution, please go to: http://www.thenewsmarket.com/ibm.

Photo:  http://www.newscom.com/cgi-bin/prnh/20090416/IBMLOGO
http://www.newscom.com/cgi-bin/prnh/20090817/NY62155-b
http://www.newscom.com/cgi-bin/prnh/20090817/NY62155-a
PRN Photo Desk, photodesk@prnewswire.com
Source: IBM
  

Web Site:  http://www.research.ibm.com/

June 17, 2009

Shape of cobalt nanoparticles affects behavior

Interesting nanotech news from the NIST.

The release:

Shape matters in the case of cobalt nanoparticles

IMAGE: These cubes of cobalt (left/top), measuring about 50 nanometers wide, are showing scientists that, on the nanoscale, a change in shape is a change in property. Unlike smaller spherical cobalt…

Click here for more information. 

Shape is turning out to be a particularly important feature of some commercially important nanoparticles—but in subtle ways. New studies* by scientists at the National Institute for Standards and Technology (NIST) show that changing the shape of cobalt nanoparticles from spherical to cubic can fundamentally change their behavior.

Building on a previous paper** that examined the properties of cobalt formed into spheres just a few nanometers in diameter, the new work explores what happens when the cobalt is synthesized instead as nanocubes. Nanoparticles of cobalt possess large magnetic moments—a measure of magnetic strength—and unique catalytic properties, and have potential applications in information storage, energy and medicine.

One striking difference is the behavior of the two different particle types when external magnetic fields are applied and then removed. In the absence of a magnetic field, both the spherical and cubic nanoparticles spontaneously form chains—lining up as a string of microscopic magnets. Then, when placed in an external magnetic field, the individual chains bundle together in parallel lines to form thick columns aligned with the field. These induced columns, says NIST physicist Angela Hight Walker, imply that the external magnetic fields have a strong impact on the magnetic behavior of both nanoparticle shapes.

But their group interactions are somewhat different. As the strength of the external field is gradually reduced to zero, the magnetization of the spherical nanoparticles in the columns also decreases gradually. On the other hand, the magnetization of the cubic particles in the columns decreases in a much slower fashion until the particles rearrange their magnetic moments from linear chains into small circular groups, resulting in a sudden drop in their magnetization.

The team also showed that the cubes can be altered merely by observing with one of nanotechnology’s microscopes of choice. After a few minutes’ exposure to the illuminating beam of a transmission electron microscope, the nanocubes melt together, forming “nanowires” that are no longer separable as individual nanoparticles. The effect, not observed with the spheres, is surprising because the cubes average 50 nm across, much larger than the spheres’ 10 nm diameters. “You might expect the smaller objects to have a lower melting point,” Hight Walker says. “However, the sharp edges and corners in the nanocubes could be the locations to initiate melting.”

While Walker says that the melting effect could be a potential method for fabricating nanostructures, it also demands further attention. “This newfound effect demonstrates the need to characterize the physico-chemical properties of nanoparticles extremely well in order to pursue their applications in biology and medicine,” she says.

 ###

 * G. Cheng, R.D. Shull and A.R. Hight Walker. Dipolar chains formed by chemically synthesized cobalt nanocubes. Journal of Magnetism and Magnetic Materials, May 11, 2009, Vol. 321, issue 10, pp. 1351—1355.

** G. Cheng, D. Romero, G.T. Fraser and A.R. Hight Walker. Magnetic-field-induced assemblies of cobalt nanoparticles. Langmuir, December 2005. See Oct. 20, 2007, Tech Beat article, “Magnetic Nanoparticles Assembled into Long Chains”.

June 5, 2009

Graphene beats copper in IC connections

It’s been a while since I’ve had the chance to blog about graphene, but here is the latest on the carbon nanomaterial.  (Be sure to hit the second link for images.)

The release:

Graphene May Have Advantages Over Copper for Future IC Interconnects

New Material May Replace Traditional Metal at Nanoscale Widths

Atlanta (June 4, 2009) —The unique properties of thin layers of graphite—known as graphene—make the material attractive for a wide range of potential electronic devices. Researchers have now experimentally demonstrated the potential for another graphene application: replacing copper for interconnects in future generations of integrated circuits.

In a paper published in the June 2009 issue of the IEEE journal Electron Device Letters, researchers at the Georgia Institute of Technology report detailed analysis of resistivity in graphene nanoribbon interconnects as narrow as 18 nanometers.

The results suggest that graphene could out-perform copper for use as on-chip interconnects—tiny wires that are used to connect transistors and other devices on integrated circuits. Use of graphene for these interconnects could help extend the long run of performance improvements for silicon-based integrated circuit technology.

“As you make copper interconnects narrower and narrower, the resistivity increases as the true nanoscale properties of the material become apparent,” said Raghunath Murali, a research engineer in Georgia Tech’s Microelectronics Research Center and the School of Electrical and Computer Engineering. “Our experimental demonstration of graphene nanowire interconnects on the scale of 20 nanometers shows that their performance is comparable to even the most optimistic projections for copper interconnects at that scale. Under real-world conditions, our graphene interconnects probably already out-perform copper at this size scale.”

Beyond resistivity improvement, graphene interconnects would offer higher electron mobility, better thermal conductivity, higher mechanical strength and reduced capacitance coupling between adjacent wires.

“Resistivity is normally independent of the dimension—a property inherent to the material,” Murali noted. “But as you get into the nanometer-scale domain, the grain sizes of the copper become important and conductance is affected by scattering at the grain boundaries and at the side walls. These add up to increased resistivity, which nearly doubles as the interconnect sizes shrink to 30 nanometers.”

The research was supported by the Interconnect Focus Center, which is one of the Semiconductor Research Corporation/DARPA Focus Centers, and the Nanoelectronics Research Initiative through the INDEX Center.

Murali and collaborators Kevin Brenner, Yinxiao Yang, Thomas Beck and James Meindl studied the electrical properties of graphene layers that had been taken from a block of pure graphite. They believe the attractive properties will ultimately also be measured in graphene fabricated using other techniques, such as growth on silicon carbide, which now produces graphene of lower quality but has the potential for achieving higher quality.

Because graphene can be patterned using conventional microelectronics processes, the transition from copper could be made without integrating a new manufacturing technique into circuit fabrication.

“We are optimistic about being able to use graphene in manufactured systems because researchers can already grow layers of it in the lab,” Murali noted. “There will be challenges in integrating graphene with silicon, but those will be overcome. Except for using a different material, everything we would need to produce graphene interconnects is already well known and established.”

Experimentally, the researchers began with flakes of multi-layered graphene removed from a graphite block and placed onto an oxidized silicon substrate. They used electron beam lithography to construct four electrode contacts on the graphene, then used lithography to fabricate devices consisting of parallel nanoribbons of widths ranging between 18 and 52 nanometers. The three-dimensional resistivity of the nanoribbons on 18 different devices was then measured using standard analytical techniques at room temperature.

The best of the graphene nanoribbons showed conductivity equal to that predicted for copper interconnects of the same size. Because the comparisons were between non-optimized graphene and optimistic estimates for copper, they suggest that performance of the new material will ultimately surpass that of the traditional interconnect material, Murali said.

“Even graphene samples of moderate quality show excellent properties,” he explained. “We are not using very high levels of optimization or especially clean processes. With our straightforward processing, we are getting graphene interconnects that are essentially comparable to copper. If we do this more optimally, the performance should surpass copper.”

Though one of graphene’s key properties is reported to be ballistic transport—meaning electrons can flow through it without resistance—the material’s actual conductance is limited by factors that include scattering from impurities, line-edge roughness and from substrate phonons—vibrations in the substrate lattice.

Use of graphene interconnects could help facilitate continuing increases in integrated circuit performance once features sizes drop to approximately 20 nanometers, which could happen in the next five years, Murali said. At that scale, the increased resistance of copper interconnects could offset performance increases, meaning that without other improvements, higher density wouldn’t produce faster integrated circuits.

“This is not a roadblock to achieving scaling from one generation to the next, but it is a roadblock to achieving increased performance,” he said. “Dimensional scaling could continue, but because we would be giving up so much in terms of resistivity, we wouldn’t get a performance advantage from that. That’s the problem we hope to solve by switching to a different materials system for interconnects.”

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