David Kirkpatrick

July 6, 2010

Nano-scale light mills now a reality

I’ll just say, wow! The NEMS applications are particularly interesting.

From the link:

While those wonderful light sabers in the Star Wars films remain the figment of George Lucas’ fertile imagination, light mills – rotary motors driven by light – that can power objects thousands of times greater in size are now fact. Researchers with the Lawrence Berkeley National Laboratory and the University of California Berkeley have created the first nano-sized light mill motor whose rotational speed and direction can be controlled by tuning the frequency of the incident light waves. It may not help conquer the Dark Side, but this new light mill does open the door to a broad range of valuable applications, including a new generation of nanoelectromechanical systems (NEMS), nanoscale solar light harvesters, and bots that can perform in vivo manipulations of DNA and other biological molecules.

Nano-sized light mill drives micro-sized disk (w/ Video)

This STM image shows a gammadion gold light mill nanomotor embedded in a silica microdisk. Inset is a magnified top view of the light mill.

April 8, 2010

Direct chemical vapor deposition used to create graphene

This development from the Lawrence Berkeley National Laboratory is a major breakthrough toward commercializing graphene. The link goes to a news release on this development, but it also serves as a very nice quick-hit primer on graphene as a material.

The release:

Graphene Films Clear Major Fabrication Hurdle

APRIL 08, 2010

Lynn Yarris

Graphene, the two-dimensional crystalline form of carbon, is a potential superstar for the electronics industry. With freakishly mobile electrons that can blaze through the material at nearly the speed of light – 100 times faster than electrons can move through silicon – graphene could be used to make superfast transistors or computer memory chips. Graphene’s unique “chicken wire” atomic structure exhibits incredible flexibility and mechanical strength, as well as unusual optical properties that could open a number of promising doors in both the electronics and the photonics industries. However, among the hurdles preventing graphite from joining the pantheon of star high-tech materials, perhaps none looms larger than just learning to make the stuff in high quality and usable quantities.

“Before we can fully utilize the superior electronic properties of graphene in devices, we must first develop a method of forming uniform single-layer graphene films on nonconducting substrates on a large scale,” says Yuegang Zhang, a materials scientist with the Lawrence Berkeley National Laboratory (Berkeley Lab). Current fabrication methods based on mechanical cleavage or ultrahigh vacuum annealing, he says, are ill-suited for commercial-scale production. Graphene films made via solution-based deposition and chemical reduction have suffered from poor or uneven quality.

Zhang and colleagues at Berkeley Lab’s Molecular Foundry, a U.S. Department of Energy (DOE) center for nanoscience, have taken a significant step at clearing this major hurdle. They have successfully used direct chemical vapor deposition (CVD) to synthesize single-layer films of graphene on a dielectric substrate. Zhang and his colleagues made their graphene films by catalytically decomposing hydrocarbon precursors over thin films of copper that had been pre-deposited on the dielectric substrate. The copper films subsequently dewetted (separated into puddles or droplets) and were evaporated. The final product was a single-layer graphene film on a bare dielectric.

“This is exciting news for electronic applications because chemical vapor deposition is a technique already widely used in the semiconductor industry,” Zhang says.

“Also, we can learn more about the growth of graphene on metal catalyst surfaces by observing the evolution of the films after the evaporation of the copper. This should lay an important foundation for further control of the process and enable us to tailor the properties of these films or produce desired morphologies, such as graphene nanoribbons.”

Zhang and his colleagues have reported their findings in the journal Nano Letters in a paper titled, “Direct Chemical Vapor Deposition of Graphene on Dielectric Surfaces.” Other co-authors of this paper were Ariel Ismach, Clara Druzgalski, Samuel Penwell, Maxwell Zheng, Ali Javey and Jeffrey Bokor, all with Berkeley Lab.

In their study, Zhang and his colleagues used electron-beam evaporation to deposit copper films ranging in thickness from 100 to 450 nanometers. Copper was chosen because as a low carbon solubility metal catalyst it was expected to allow better control over the number of graphene layers produced. Several different dielectric substrates were evaluated including single-crystal quartz, sapphire, fused silica and silicon oxide wafers. CVD of the graphene was carried out at 1,000 degrees Celsius in durations that ranged from 15 minutes up to seven hours.

“This was done to allow us to study the effect of film thickness, substrate type and CVD growth time on the graphene formation,” Zhang says.

A combination of scanning Raman mapping and spectroscopy, plus scanning electron and atomic force microscopy confirmed the presence of continuous single-layer graphene films coating metal-free areas of dielectric substrate measuring tens of square micrometers.

“Further improvement on the control of the dewetting and evaporation process could lead  to the direct deposition of patterned graphene for large-scale electronic device fabrication, Zhang says. “This method could also be generalized and used to deposit other two-dimensional materials, such as boron-nitride.”

Even the appearance of wrinkles in the graphene films that followed along the lines of the dewetting shape of the copper could prove to be beneficial in the long-run. Although previous studies have indicated that wrinkles in a graphene film have a negative impact on electronic properties by introducing strains that reduce electron mobility, Zhang believes the wrinkles can be turned to an advantage.

“If we can learn to control the formation of wrinkles in our films, we should be able to modulate the resulting strain and thereby tailor electronic properties,” he says.

“Further study of the wrinkle formation could also give us important new clues for the formation of graphene nanoribbons.”

This work was primarily supported by the DOE Office of Science.

The Molecular Foundry is one of the five DOE Nanoscale Science Research Centers (NSRCs), premier national user facilities for interdisciplinary research at the nanoscale.  Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative.  The NSRCs are located at DOE’s Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge and Sandia and Los Alamos National Laboratories.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California. Visit our website at www.lbl.gov.

Additional Information

A copy of the Nano Letters paper “Direct Chemical Vapor Deposition of Graphene on Dielectric Surfaces” can be viewed here: http://pubs.acs.org/doi/abs/10.1021/nl9037714

For more about Berkeley Lab’s Molecular Foundry visit http://foundry.lbl.gov/

For more about the DOE NSRCs visit http://nano.energy.gov

Left panel (a) an optical image of a CVD graphene film on a 450 nanometer copper shows the finger morphology of the metal; panel (b) is Raman 2D band map of the graphene film between the metal fingers, over the area marked by the red square in (a). (image from says Yuegang Zhang)

(a) Optical image of a CVD graphene film on a copper layer showing the finger morphology of the metal; (b) Raman 2D band map of the graphene film between the copper fingers over the area marked by the red square on left. (image from Yuegang Zhang)

To make a graphene thin film, Berkeley researchers (a) evaporated a thin layer of copper on a dielectric surface; (b) then used CVD to lay down a graphene film over the copper. (c) The copper dewets and evaporates leaving (d) a graphene film directly on a dielectric substrate.

To make a graphene thin film, Berkeley researchers (a) evaporated a thin layer of copper on a dielectric surface; (b) then used CVD to lay down a graphene film over the copper. (c) The copper dewets and evaporates leaving (d) the graphene film directly on the dielectric substrate.

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 16, 2009

CO2 capture and geothermal energy

More green tech backed with Department of Energy money. Sounds interesting if nothing else.

From the link:

Backers of this as-yet-unproven concept secured a big endorsement and much-needed cash with the U.S. Department of Energy’s recent award of $338 million in federal stimulus funds for geothermal energy research. Some $16 million of the funds will be shared by nine carbon dioxide-related projects led by Lawrence Berkeley National Laboratory and other national labs, Sunnyvale, CA-based combinatorial chemistry firm Symyx Technologies, and several U.S. universities.

The idea: Carbon dioxide that’s cycled through hot regions kilometers underground can efficiently bring heat to the surface, where it can be used to generate electricity. The likelihood is that the process would leave lots of carbon dioxide underground, and thus out of the atmosphere, according to Symyx project leader and materials scientist Miroslav Petro. “You’re sequestering CO₂ and at the same time generating power from it.”

October 26, 2009

Nanoparticle self-assembly news

Via KurzweilAI.net — here’s the latest in nanotech news.

New Route To Nano Self-assembly Found

ScienceDaily, Oct. 25, 2009

Researchers at Lawrence Berkeley National Laboratory have found a way to induce nanoparticles to assemble themselves into complex arrays, using block copolymers with surfactants as mediator molecules.

Read Original Article>>

October 22, 2009

Solar costs are dropping

Interesting news from the Lawrence Berkeley National Laboratory.

The release:

Installed cost of solar photovoltaic systems in the US fell in 2008

Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) released a new study on the installed costs of solar photovoltaic (PV) power systems in the U.S., showing that the average cost of these systems declined by more than 30 percent from 1998 to 2008. Within the last year of this period, costs fell by more than 4 percent.

The number of solar PV systems in the U.S. has been growing at a rapid rate in recent years, as governments at the national, state, and local levels have offered various incentives to expand the solar market. With this growth comes a greater need to track and understand trends in the installed cost of PV.

“A goal of government incentive programs is to help drive the cost of PV systems lower. One purpose of this study is to provide reliable information about the costs of installed systems over time,” says report co-author Ryan Wiser.

According to the report, the most recent decline in costs is primarily the result of a decrease in PV module costs. “The reduction in installed costs from 2007 to 2008 marks an important departure from the trend of the preceding three years, during which costs remained flat as rapidly expanding U.S. and global PV markets put upward pressure on both module prices and non-module costs. This dynamic began to shift in 2008, as expanded manufacturing capacity in the solar industry, in combination with the global financial crisis, led to a decline in wholesale module prices,” states the report, which was written by Wiser, Galen Barbose, Carla Peterman, and Naim Darghouth of Berkeley Lab’s Environmental Energy Technologies Division.

In contrast, cost reductions from 1998 through 2007 were largely due to a decline in non-module costs, such as the cost of labor, marketing, overhead, inverters, and the balance of systems.

The study—the second in an ongoing series that tracks the installed cost of PV—examined 52,000 grid-connected PV systems installed between 1998 and 2008 in 16 states. It found that average installed costs, in terms of real 2008 dollars, declined from $10.80 per watt (W) in 1998 to $7.50/W in 2008, equivalent to an average annual reduction of $0.30/W, or 3.6 percent per year in real dollars.

Costs Differ by Region and Type of System

Other information about differences in costs by region and by installation type emerged from the study. The cost reduction over time was largest for smaller PV systems, such as those used to power individual households. Also, installed costs show significant economies of scale—small residential PV systems completed in 2008 that were less than 2 kilowatts (kW) in size averaged $9.20/W, while large commercial systems in the range of 500 to 750 kW averaged $6.50/W.

Installed costs were also found to vary widely across states. Among systems completed in 2008 and less than 10 kW in size, average costs range from a low of $7.30/W in Arizona, followed by California, which had average installed costs of $8.20/W, to a high of $9.90/W in Pennsylvania and Ohio. Based on these data, and on installed cost data from the sizable German and Japanese PV markets, the authors suggest that PV costs can be driven lower through large-scale deployment programs.

The study also found that the new construction market offers cost advantages for residential PV systems. Among small residential PV systems in California completed in 2008, those systems installed in residential new construction cost $0.80/W less than comparably-sized systems installed in rooftop retrofit applications.

Cash Incentives Declined

The study also found that the average size of direct cash incentives provided by state and local PV incentive programs declined over the 1998-2008 study period. Other sources of incentives, however, such as federal investment tax credits (ITCs), have become more significant. For commercial PV systems, the average combined after-tax value of federal and state ITCs, plus direct cash incentives provided by state and local incentive programs, was $4.00/W in 2008, down slightly from its peak in 2006 but still a near-record-high. Total after-tax incentives for residential systems, on the other hand, were at an historic low in 2008, averaging $2.90/W, their lowest level within the 11-year study period.

The drop in total after-tax incentives for both commercial and residential PV from 2007 to 2008 more than offset the cost reduction over this period, leading to a slight rise in the net installed cost, or the installed cost facing a customer after receipt of financial incentives. For residential PV, net installed costs in 2008 averaged $5.40/W, up 1% from the previous year. Net installed costs for commercial PV averaged $4.20/W, a 5% rise from 2007.

###

The report “Tracking the Sun II: The Installed Cost of Photovoltaics in the U.S. from 1998�,” by Ryan Wiser, Galen Barbose, Carla Peterman, and Naim Darghouth may be downloaded from http://eetd.lbl.gov/ea/emp/re-pubs.html. The research was supported by funding from the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (Solar Energy Technologies Program) and by the Clean Energy States Alliance.

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

August 14, 2009

Lawrence Berkeley National Laboratory building 100Gbps Ethernet

Man, that’s fast!

From the link:

Looking to build a blazing Ethernet network that will exclusively support science research, Lawrence Berkeley National Laboratory, is receiving $62 million to develop what it calls the world’s fastest computer network.

Specifically, the lab will utilize the Energy Sciences Network (ESnet) to build a prototype 100Gbps Ethernet network to connect Department of Energy supercomputer centers at speeds 10 times faster than current ESnet. ESnet serves an estimated 50,000 to100,000 DOE users, as well as more than 18,000 non-DOE researchers from universities, government agencies, and private industry.

January 23, 2009

Nanoscale lasers and whispering galleries

Big breakthrough in tiny lasers — the apps here include lightening quick communications and data handling (photonics) and optical microchips.

The release:

Plasmonic whispering gallery microcavity paves the way to future nanolasers

The principle behind whispering galleries – where words spoken softly beneath a domed ceiling or in a vault can be clearly heard on the opposite side of the chamber – has been used to achieve what could prove to be a significant breakthrough in the miniaturization of lasers. Ultrasmall lasers, i.e., nanoscale, promise a wide variety of intriguing applications, including superfast communications and data handling (photonics), and optical microchips for instant and detailed chemical analyses.

 

Researchers with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the California Institute of Technology have developed a “whispering gallery microcavity” based on plasmons – electromagnetic waves that race across the surfaces of metals. Such a plasmon wave has very small wavelength compared with the light, enabling the scaling down optical devices beyond diffraction limit of the light. Cavities are the confined spaces in lasers where light amplification takes place and this new micro-sized metallic cavity for plasmons improves on the quality of current plasmonic cavities by better than an order of magnitude.

“We have shown for the first time that metallic microcavities based on surface plasmons can have a large quality factor and can thereby enable ultra-small device fabrication and strong enhancement of the light,” said Xiang Zhang, a mechanical engineer who holds a joint appointment with Berkeley Lab’s Materials Sciences Division and the University of California (UC) Berkeley where he directs the NSF Nano-scale Science and Engineering Center.

“Plasmonic microcavities have uniquely different physical properties when compared to dielectric cavities and can extend microcavity research in entirely new ways, particularly at nanoscale dimensions,” said Kerry Vahala, a physics professor at Cal Tech and authority on photonic devices. “Our work shows that the full potential of this new class of device can be realized with careful design and material control.”

Zhang and Vahala led this collaborative research which is reported in the January 22, 2009 edition of the journal Nature. The paper is entitled: “High-Q surface-plasmon-polariton whispering-gallery microcavity.” In addition to Zhang and Vahala, other authors of the paper were Bumki Min, Eric Ostby, Volker Sorger, Erick Ulin-Avila and Lan Yang.

 

Surface Plasmons and Whispering Galleries

Just as the energy in waves of light is carried through space in discrete or quantized particle-like units called photons, so, too, is the energy in waves of charged gas (plasma) carried in quantized particle-like packets called plasmons, as they travel along metallic surfaces. When photons excite the collective electron oscillations at the interfaces between metal and dielectric (insulator) materials, they can form yet another quasi-particle called a surface plasmon polariton(SPP). Such polaritons play an important role in the optical properties of metals and can be used to manipulate light on a nanoscale.

“Metal-dielectric materials, also known as plasmonics, can be used to confine an optical field to a very small scale, much smaller than conventional insulators,” said Min, lead author on the Nature paper and former postdoctoral researcher in Zhang’s Lab, now an assistant professor at the Korea Advanced Institute of Science and Technology (KAIST). “This capability, often termed as breaking the light diffraction, is unobtainable with dielectric materials alone.”

The main obstacle to working with plasmonic materials for creating nanoscale lasers has been a low quality or “Q” factor, which is a measure of power loss in the lasing cavity – a laser cavity with a high-Q factor has a low power loss. Enter the whispering gallery phenomenon, which Cal Tech’s Vahala has used to boost the Q factor of dielectric microcavities. Whispering galleries are found in circular or elliptically shaped buildings, such as St. Paul’s Cathedral in London, where the phenomenon was first made famous, or Statuary Hall in the U.S. Capitol building.

The prevailing theory behind why whispering galleries work (first proposed in 1871 by British astronomer George Airy to explain St. Paul’s cathedral) is that sound originating at one point along the circumference of an enclosed sphere is reflected to another point along the circumference opposite the source. Vahala and his group applied this idea to dielectric microcavities, and Zhang and Min along with Ostby, Sorger and Ulin-Avila applied the idea to plasmonic microcavities.

 

“In these sphere-shaped microcavities, optical waves propagate in a similar way that sound waves propagate in a whispering gallery,” said Zhang. “They continue to circle around the edge of the cavity sphere and smoothness of the edge enhances or boosts the cavity’s Q factor.”

In this study, Zhang and his collaborators created a high-Q SPP whispering gallery microcavity by coating the surface of a high-Q silica microcavity with a thin layer of silver.

 

Explained Zhang, “Whenever light propagates in a metal it experiences some loss of power and this obviously reduces the performance of a device. Silver is the metal with the lowest loss, that is available.”

 

Whereas previous plasmonic microcavities achieved a best Q factor below 100, the whispering gallery plasmonic microcavity allows Q factors of 1,376 in the near infrared for SPP modes at room temperature.

 

“This nearly ideal value, which is close to the theoretical metal-loss-limited Q factor, is attributed to the suppression and minimization of radiation and scattering losses that are made possible by the geometrical structure and the fabrication method,” said Min, who believes that there is still room for plasmonic Q-factor improvement by geometrical and material optimizations.

Min said one of the first applications of the whispering gallery plasmonic microcavity is likely to be the development of a plasmonic nanolaser.

“To build a working laser, it is essential to have both the laser cavity (or resonator) and the gain media,” Min said.  “Therefore, we need a good, high-Q plasmonic microcavity to make a plasmonic nanolaser. Our work paves the way to accomplish the demonstration of a real plasmonic nanolaser.  In addition, fundamental research can also be pursued with this plasmonic cavity, such as the interaction of a single light emitter with plasmons.”

This work was supported by the U.S. Air Force Office of Scientific Research MURI program, and by the NSF Nanoscale Science and Engineering Center.

 

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

December 6, 2008

Super ceramic

Lots of great applications for this material.

The release:

December 05, 2008

Scientists Create Tough Ceramic That Mimics Mother of Pearl

Biomimicry – technological innovation inspired by nature – is one of the hottest ideas in science but has yet to yield many practical advances. Time for a change. Scientists with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have mimicked the structure of mother of pearl to create what may well be the toughest ceramic ever produced.

The roughness of the alumina/PMMA hybrid ceramic controls the strength of the interfaces, which is critical in determining the material’s overall toughness as it affects the sliding process in the polymeric "mortar" layers.

The roughness of the alumina/PMMA hybrid ceramic controls the strength of the interfaces, which is critical in determining the material’s overall toughness as it affects the sliding process in the polymeric “mortar” layers.

Through the controlled freezing of suspensions in water of an aluminum oxide (alumina) and the addition of a well known polymer, polymethylmethacrylate (PMMA), a team of researchers has produced ceramics that are 300 times tougher than their constituent components. The team was led by Robert Ritchie, who holds joint appointments with Berkeley Lab’s Materials Sciences Division and the Materials Science and Engineering Department at the University of California, Berkeley.

“We have emulated nature’s toughening mechanisms to make ice-templated alumina hybrids that are comparable in specific strength and toughness to aluminum alloys,” says Ritchie. “We believe these model materials can be used to identify key microstructural features that should guide the future synthesis of bio-inspired, yet non-biological, light-weight structural materials with unique strength and toughness.”

The results of this research were reported in the December 5, 2008 issue of the journal Science, in a paper entitled:“Tough, bio-inspired hybrid materials.” Co-authoring the paper with Ritchie were Etienne Munch, Max Launey, Daan Hein Alsem, Eduardo Saiz and Antoni Tomsia.

 

Naturally Tough

Mother of pearl, or nacre, the inner lining of the shells of abalone, mussels and certain other mollusks, is renowned for both its iridescent beauty and its amazing toughness. Nacre is 95-percent aragonite, a hard but brittle calcium carbonate mineral, with the rest of it made up of soft organic molecules. Yet nacre can be 3,000 times (in energy terms) more resistant to fracture than aragonite. No human-synthesized composite outperforms its constituent materials by such a wide margin. The problem has been that nacre’s remarkable strength is derived from a structural architecture that varies over lengths of scale ranging from nanometers to micrometers. Human engineering has not been able to replicate these length scale variances.

brick and mortar structure of alumina/PMMA hybrid

In the “brick-and-mortar” phase of the alumina/PMMA hybrid, aragonite “bricks” slide past each other to dissipate strain energy while the polymer “mortar” acts as a lubricant.

Two years ago, however, Berkeley Lab researchers Tomsia and Saiz found a way to improve the strength of bone substitutes through a processing technique that involved the freezing of seawater. This process yielded a ceramic that was four times stronger than artificial bone. When seawater freezes, ice crystals form a scaffolding of thin layers. These layers are pure ice because during their formation impurities, such as salt and microorganisms, are expelled and entrapped in the space between the layers. The resulting architecture roughly resembles that of nacre.

“Since seawater can freeze like a layered material, we allowed nature to guide the process by which we were able to freeze-cast ceramics that mimicked nacre,” said Tomsia when this research was reported.

Engineered to be Tough

In this latest research, Ritchie, working with Tomsia and Saiz, refined the freeze-casting technique and applied it to alumina/PMMA hybrid materials to create large porous ceramic scaffolds that much more closely mirrored the complex hierarchical microstructure of nacre. To do this, they first employed directional freezing to promote the formation of thin layers (lamellae) of ice that served as templates for the creation of the layered alumina scaffolds. After the ice was removed, spaces between the alumina lamellae were filled with polymer.

Robert Ritchie (seated) led a research effort in which the microstructure of mother of pearl was mimicked to create what may well be the toughest ceramic ever produced. Collaborating with Ritchie were (from left) Maximilien Launey, Daan Hein Alsem, Eduardo Saiz and Antoni Tomsia.

Robert Ritchie (seated) led a research effort in which the microstructure of mother of pearl was mimicked to create what may well be the toughest ceramic ever produced. Collaborating with Ritchie were (from left) Maximilien Launey, Daan Hein Alsem, Eduardo Saiz and Antoni Tomsia.

“The key to material toughness is the ability to dissipate strain energy,” says Ritchie. “Infiltrating the spaces between the alumina layers with polymer allows the hard alumina layers to slide (by a small amount) over one another when load is applied, thereby dissipating strain energy. The polymer acts as a lubricant, like the oil in an automobile engine.”

In addition to making the lamellar scaffolds, the team was also able to fabricate nacre-like “brick-and-mortar” structures with very high alumina content. They did this by collapsing the scaffolds in a perpendicular direction to the layers then sintering the resulting alumina “bricks” to promote brick densification and the formation of ceramic bridges between individual bricks.

Says Saiz, “Using such techniques, we have made complex hierarchical architectures where we can refine the lamellae thickness, control their macroscopic orientation, manipulate the chemistry and roughness of the inter-lamellae interfaces, and generate a given density of inorganic bridges, all over a range of size-scales.”

Next Step

For ceramic materials that are even tougher in the future, Ritchie says he and his colleagues need to improve the proportion of ceramic to polymer in their composites. The alumina/PMMA hybrid was only 85-percent alumina. They want to boost ceramic content and thin the layers even further. They also want to replace the PMMA with a better polymer and eventually replace the polymer content altogether with metal.

Says Ritchie, “The polymer is only capable of allowing things to slide past one another, not bear any load. Infiltrating the ceramic layers with metals would give us a lubricant that can also bear some of the load. This would improve strength as well as toughness of the composite.”

Such future composite materials would be lightweight and strong as well as tough, he says, and could find important applications in energy and transportation.

This research was supported by DOE’s Office of Science, through the Division of Materials Sciences and Engineering in the Basic Energy Sciences office.

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

October 22, 2008

Moving toward quantum computing

Making headway, it seems. This is amazing — storing information inside the nucleus of an atom!

From the link:

The problem: How do you isolate a quantum bit from a noisy environment to protect the deli-cate quantum information, while at the same time allowing it to interact with the outside world so that it can be manipulated and measured?

The team, with scientists and engineers from Oxford and Princeton universities and Lawrence Berkeley National Laboratory, reported a solution to this problem in the Oct. 23 issue of the journal Nature.

The team’s plan was to devise a hybrid system using both the electron and nucleus of an atom of phosphorous embedded in a silicon crystal. Each behaves as a tiny quantum magnet capa-ble of storing quantum information, but inside the crystal the electron is more than a million times bigger than the nucleus, with a magnetic field that is a thousand times stronger. This makes the electron well-suited for manipulation and measurement, but not so good for storing information, which can become rapidly corrupted. This is where the nucleus comes in: when the information in the electron is ready for storage, it is moved into the nucleus where it can survive for much longer times.

Go below the fold for a release from October 23 on this story.

(more…)

August 2, 2008

Looking inside aerogels

Aerogels are pretty amazing substances with many uses. This press release covers using X-ray diffraction to get a 3D nanoscale look inside aerogels.

The full release and two of the provided images:

X-Ray Diffraction Looks Inside Aerogels in 3-D

A multi-institutional team of scientists has used beamline 9.0.1 at the Advanced Light Source to perform high-resolution x‑ray diffraction imaging of an aerogel for the first time, revealing its nanoscale three-dimensional bulk lattice structure down to features measured in nanometers, billionths of a meter.

Aerogels, sometimes called “frozen smoke” or “San Francisco fog,” are nanoscale foams: solid materials whose sponge-like structure is riddled by pores as small as nanometers across and whose strength is surprising, given their low density. Many porous materials are extraordinary for their properties as insulators, filters, and catalysts; they are used to produce clean fuels, to insulate windows and even clothing, to study the percolation of oil through rock, as drug-delivery systems, and even to cushion the capture of high-velocity comet fragments in outer space.

“The smallest pore size is the key to the strength of porous materials and what they can do,” says Stefano Marchesini, an ALS scientist at Berkeley Lab, who led the research. “Seeing inside bulk porous materials has never been done before at this resolution, making this one of the first applications of x-ray diffractive microscopy to a real problem.” 

Team members from Lawrence Livermore National Laboratory, the University of California at Davis, Arizona State University, Argonne National Laboratory, and Berkeley Lab performed the x‑ray diffraction imaging and have published their results online in Physical Review Letters, available to subscribers at http://link.aps.org/abstract/PRL/v101/e055501.

Seeing inside foam

One way to study aerogels and other nanofoams is with electron microscopy, which can image only thin, two-dimensional slices through the porous structure of the material. Another method is straightforward x-ray microscopy, using zone plates as “lenses”; microscopy can penetrate a sample but has difficulty maintaining resolution at different depths in the material. Small-angle x‑ray scattering (SAXS) can also gather limited structural information from finely powdered aerogels, but SAXS cannot provide full three-dimensional information. None of these techniques can capture the 3-D internal structure of nanofoam samples measured in micrometers, a few millionths of a meter across.

X-ray diffraction approaches the problem differently. A laser-like x-ray beam passes all the way through the sample and is diffracted onto a CCD detector screen; diffraction patterns are repeatedly stored while the sample is moved and rotated. A typical series requires approximately 150 views in all.

The individual diffraction patterns are then processed by a computer. The way the photons in the beam are redirected from each component of the structure is different for each orientation, and comparing their intensities serves to position that component precisely in three-dimensional space. Thousands of iterations are required – in the present study, team member Anton Barty of Livermore led the solution of almost 100 million measured intensities, as opposed to the 100 thousand or so typical of, say, protein crystallography – but the end result is a 3‑D image of the tiny sample at nanometer-scale resolution.

Foam-like structures are described in terms of interconnecting lattice beams and the nodes where they intersect. These elements became vividly apparent in the reconstructed 3-D images of the aerogel used in the imaging at the ALS, which was made of tantalum ethoxide (Ta2O5), a ceramic material proposed for cladding capsules of hydrogen isotopes for inertial-confinement fusion experiments being pursued at Livermore.

“The strength and stiffness of foam-like structures are expected to scale with their density, relating the density of individual elements like beams and nodes to the overall density,” Marchesini says. “But below about 10 percent density, the strength of aerogels like the ones we tested – on the order of 1 percent density – is orders of magnitude less than expected.”

Of the theories that seek to explain this phenomenon, one is the “percolation” model, in which fragments become detached from the load-bearing structure and add mass without contributing to strength. The alternate “heterogeneities” model proposes that the structure is increasingly riddled with defects like micron-sized holes and buckles more easily.

A third theory is the “diffusion-limited cluster aggregation” model: blobs of material accumulate that are connected by thin links, instead of sturdy beams between nodes.

“The high resolution we achieved allowed us to see which of these models more accurately described the actual observed structure,” Marchesini says. By seeing the foam from the inside, the team was able to see exactly how it was structured, and the shape and dimensions of each component. “The structure was far more complex than anything we’d seen in earlier images obtained using this technique.”

What the team observed in their 3-D images of the tantalum ethoxide aerogel was a “blob-and-beam” structure consistent with the third model, that of diffusion-limited cluster aggregation. The observed structure explained the relative weakness of the low-density material and also suggested that changes in methods of preparing aerogels might improve their strength.

Into the future

“We’d like to use x-ray diffraction to study a range of porous materials and nanostructures in general, for example porous polymers developed at the Molecular Foundry for storing hydrogen as fuel – and at even higher resolutions,” Marchesini says. “To do so, David Shapiro, who built the end station we used for this work, is working with us to overcome some obstacles.”

One is time. At present, each sample takes months of work. After preparation, the experiment first requires one or two days of mounting, rotating, and exposing the sample to the x-ray beam, about a minute per view – because of a slow detector – for 150 views. There follow weeks of computation time. “And after all this, you can find out the sample was no good, so you have to start over,” Marchesini says.

Improved sample handling, faster detectors, and a beamline dedicated to x-ray diffraction are principal goals. The Coherent Scattering and Diffraction Microscopy (COSMIC) facility, a top priority in the ALS strategic plan, will provide intense coherent x-rays with full polarization control.

“We are also collaborating with Berkeley Lab’s Computational Research Division to develop efficient and robust algorithms to speed up the time needed to construct the 3-D image from the individual rotated views,” Marchesini says. “This will open an entire spectrum of possibilities for new ways of seeing the very small – not just aerogels but virtually any unknown object, from nanostructures to biological cells.”

This work was principally supported by the Department of Energy through a variety of grants, by Laboratory Directed Research and Development programs at Livermore, and additionally by the National Science Foundation.

Additional information

  • “Three-dimensional coherent X-ray diffraction imaging of a ceramic nanofoam: determination of structural deformation mechanisms,” by A. Barty, S. Marchesini, H. N. Chapman, C. Cui, M. R. Howells, D. A. Shapiro, A. M. Minor, J. C. H. Spence, U. Weierstall, J. Havsky, A. Noy, S. P. Hau-Riege, A. B. Artyukhin, T. Baumann, T. Willey, J. Stolken, T. van Buuren, and J. H. Kinney, appears in Physical Review Letters online publication and is available to subscribers at http://link.aps.org/abstract/PRL/v101/e055501.
  • More about beamline 9.0.1 at the Advanced Light Source
Silicon aerogel acting as an insulator

Silicon aerogel acting as an insulator

 

A 500-nanometer cube of aerogel from the interior of the 3-D volume, reconstructed by x-ray diffraction. The foam structure shows globular nodes that are interconnected by thin beam- like struts. Approximately 85 percent of the total mass is associated with the nodes; relatively little of the mass is in the load-bearing links.
A 500-nanometer cube of aerogel from the interior of the 3-D volume, reconstructed by x-ray diffraction. The foam structure shows globular nodes that are interconnected by thin beam- like struts. Approximately 85 percent of the total mass is associated with the nodes; relatively little of the mass is in the load-bearing links.

July 29, 2008

Nanoscale sensor weighs single atom of gold

This is pretty amazing. Researchers with Berkeley Lab and the University of California at Berkeley have created a “scale” that can weigh a single atom of gold.

From the link (it’s an article/press release mix):

There’s a new “gold standard” in the sensitivity of weighing scales. Using the same technology with which they created the world’s first fully functional nanotube radio, researchers with Berkeley Lab and the University of California (UC) at Berkeley have fashioned a nanoelectromechanical system (NEMS) that can function as a scale sensitive enough to measure the mass of a single atom of gold.

Alex Zettl, a physicist who holds joint appointments with Berkeley Lab’s Materials Sciences Division (MSD) and UC Berkeley’s Physics Department, where he is the director of the Center of Integrated Nanomechanical Systems, led this research. Working with him were members of his research group, Kenneth Jensen and Kwanpyo Kim.

“For the past 15 years or so, the holy grail of NEMS has been to push them to a small enough size with high enough sensitivity so that they might resolve the mass of a single molecule or even single atom,” Zettl said. “This has been a challenge even at cryogenic temperatures where reduced thermal noise improves the sensitivity. We have achieved sub-single-atom resolution at room temperature!”

The new NEMS mass sensor consists of a single carbon nanotube that is double-walled to provide uniform electrical properties and increased rigidity. One tip of the carbon nanotube is free and the other tip is anchored to an electrode in close proximity to a counter-electrode. A DC voltage source, such as from a battery or a solar cell array, is connected to the electrodes. Applying a DC bias creates a negative electrical charge on the free tip of the nanotube.  An additional radio frequency wave “tickles” the nanotube, causing it to vibrate at a characteristic “flexural” resonance frequency.

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