David Kirkpatrick

October 2, 2010

Quantum dots may lead to ultraefficient solar cells

This sounds promising.

From the link (emphasis mine):

Although researchers have steadily increased the amount of electricity that solar cells can produce, they face fundamental limits because of the physics involved in converting photons to electrons in semiconductor materials. Now researchers at the University of Wyoming have demonstrated that by using novel nanomaterials called quantum dots, it might be possible to exceed those limits and produce ultraefficient solar cells.

The theoretical limitation of solar cells has to do with the widely varying amounts of energy from photons in sunlight. The amount varies depending on the color of the light. No matter how energetic the incoming photons are, however, solar cells can only convert one photon into one electron with a given amount of energy. Any extra energy is lost as heat. Scientists have hypothesized that quantum dots, because of their unusual electronic properties, could convert some of this extra energy into electrons. They’ve calculated that this approach could increase the theoretical maximum efficiency of solar cells by about 50 percent.

Solar dots: A micrograph shows lead-sulfide quantum dots, each about five nanometers across, coating an electrode of titanium dioxide.
Credit: Science

August 26, 2010

Cool nanotech image — microneedles

Cool to look, even more cool when put into practice. Microneedles can deliver quantum dots into skin and should lead to new diagnosis and treatment of medical conditions such as skin cancer.

And now, the image:

Hollow microneedles open the door to new techniques for diagnosing and treating a variety of medical conditions, including skin cancer. Image reproduced by permission of the Royal Society of Chemistry.

For more on microneedles, here’s the full release.

August 17, 2010

Nanotech and solar efficiency

Nanotechnology and solar energy get a lot of virtual ink around here, and I always enjoy getting the chance to blog about both topics in the same post. This study finds that incorporating quantum dots in photovoltaic solar cells through nanoscience should both increase the efficiency of the cells and reduce their cost. A win-win all the way around.

From the link:

As the fastest growing energy technology in the world, solar energy continues to account for more and more of the world’s energy supply. Currently, most commercial photovoltaic power comes from bulk semiconductor materials. But in the past few years, scientists have been investigating how semiconductor nanostructures can increase the efficiency of solar cells and the newer field of solar fuels.

Although there has been some controversy about just how much nanoscience can improve solar cells, a recent overview of this research by Arthur Nozik, a researcher at the National Renewable Energy Laboratory (NREL) and professor at the University of Colorado, shows that semiconductor nanostructures have significant potential for converting solar energy into electricity


June 17, 2010

Quantum dot research may lead to dramatic solar efficiency increase

Filed under: Science — Tags: , , , , — David Kirkpatrick @ 11:47 pm

This seems like a week full of a lot of good solar efficiency news. As I’ve written many, many times (hit the solar link in the sidebar), solar power needs continued breakthroughs in two areas to become market-viable — costs must continue to come down and efficiency needs to continue to increase. This news out of UT Austin points toward potential very dramatic efficiency increases.

From the link:

Conventional solar cell efficiency could be increased from the current limit of 30 percent to more than 60 percent, suggests new research on semiconductor nanocrystals, or quantum dots, led by chemist Xiaoyang Zhu at The University of Texas at Austin.

Zhu and his colleagues report their results in this week’s Science.

The scientists have discovered a method to capture the higher energy sunlight that is lost as heat in conventional .

The maximum efficiency of the silicon solar cell in use today is about 31 percent. That’s because much of the energy from sunlight hitting a solar cell is too high to be turned into usable electricity. That energy, in the form of so-called “hot ,” is lost as heat.

If the higher energy sunlight, or more specifically the hot electrons, could be captured, solar-to-electric power conversion efficiency could be increased theoretically to as high as 66 percent.

If you prefer the raw feed, here’s the release the linked story is based on.

May 26, 2010

Graphene as quantum dots

Nanoelectronics is a major — and important — field right now, and graphene and its cousin graphane are very important materials research components. Both of the nanomaterials are getting a lot of  hype, particularly graphene, but there’s far too much smoke for there not to be at least a little fire. It’s exciting to keep watch on the news to see the breakthroughs as they happen, and eventually cover real-world, market-ready uses for graphene and graphane.

The release:

Graphane yields new potential

Rice physicists dig theoretical wells to mine quantum dots

Graphane is the material of choice for physicists on the cutting edge of materials science, and Rice University researchers are right there with the pack – and perhaps a little ahead.

Researchers mentored by Boris Yakobson, a Rice professor of mechanical engineering and materials science and of chemistry, have discovered the strategic extraction of hydrogen atoms from a two-dimensional sheet of graphane naturally opens up spaces of pure graphene that look – and act – like quantum dots.

That opens up a new world of possibilities for an ever-shrinking class of nanoelectronics that depend on the highly controllable semiconducting properties of quantum dots, particularly in the realm of advanced optics.

The theoretical work by Abhishek Singh and Evgeni Penev, both postdoctoral researchers in co-author Yakobson’s group, was published online last week in the journal ACS Nano and will be on the cover of the print version in June. Rice was recently named the world’s No. 1 institution for materials science research by a United Kingdom publication.

Graphene has become the Flat Stanley of materials. The one-atom-thick, honeycomb-like form of carbon may be two-dimensional, but it seems to be everywhere, touted as a solution to stepping beyond the limits of Moore’s Law.

Graphane is simply graphene modified by hydrogen atoms added to both sides of the matrix, which makes it an insulator. While it’s still technically only a single atom thick, graphane offers great possibilities for the manipulation of the material’s semiconducting properties.

Quantum dots are crystalline molecules from a few to many atoms in size that interact with light and magnetic fields in unique ways. The size of a dot determines its band gap – the amount of energy needed to close the circuit – and makes it tunable to a precise degree. The frequencies of light and energy released by activated dots make them particularly useful for chemical sensors, solar cells, medical imaging and nanoscale circuitry.

Singh and Penev calculated that removing islands of hydrogen from both sides of a graphane matrix leaves a well with all the properties of quantum dots, which may also be useful in creating arrays of dots for many applications.

“We arrived at these ideas from an entirely different study of energy storage in a form of hydrogen adsorption on graphene,” Yakobson said. “Abhishek and Evgeni realized that this phase transformation (from graphene to graphane), accompanied by the change from metal to insulator, offers a novel palette for nanoengineering.”

Their work revealed several interesting characteristics. They found that when chunks of the hydrogen sublattice are removed, the area left behind is always hexagonal, with a sharp interface between the graphene and graphane. This is important, they said, because it means each dot is highly contained; calculations show very little leakage of charge into the graphane host material. (How, precisely, to remove hydrogen atoms from the lattice remains a question for materials scientists, who are working on it, they said.)

“You have an atom-like spectra embedded within a media, and then you can play with the band gap by changing the size of the dot,” Singh said. “You can essentially tune the optical properties.”

Along with optical applications, the dots may be useful in single-molecule sensing and could lead to very tiny transistors or semiconductor lasers, he said.

Challenges remain in figuring out how to make arrays of quantum dots in a sheet of graphane, but neither Singh nor Penev sees the obstacles as insurmountable.

“We think the major conclusions in the paper are enough to excite experimentalists,” said Singh, who will soon leave Rice to become an assistant professor at the Indian Institute of Science in Bangalore. “Some are already working in the directions we explored.”

“Their work is actually supporting what we’re suggesting, that you can do this patterning in a controlled way,” Penev said.

When might their calculations bear commercial fruit? “That’s a tough question,” Singh said. “It won’t be that far, probably — but there are challenges. I don’t know that we can give it a time frame, but it could happen soon.”

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Funding from the Office of Naval Research supported the work. Computations were performed at the Department of Defense Supercomputing Resource Center at the Air Force Research Laboratory.

May 25, 2010

A seven atom transistor

Via KurzweilAI.net — We are heading toward the terminus of physical computing components. Can’t get a whole lot smaller than seven atoms.

Quantum leap: World’s smallest transistor built with just 7 atoms
PhysOrg.com, May 24, 2010

The world’s smallest precision-built transistor — aquantum dot of just seven phosphorus atoms in a single silicon crystal — has been created by scientists from the UNSW Centre for Quantum Computer Technology and the University of Wisconsin-Madison.

At present, the length of a commercial transistor gate is about 40 nanometers (billionths of a metet). The new device has features about 10 times smaller at 4 nanometers.


Template of the quantum dot device showing a central hole where seven phosphorus atoms are incorporated
Read Original Article>>

May 12, 2010

Semi-conductor nanocrystals and quantum computing

Another step toward quantum computing.

The release:

Quantum move toward next generation computing

McGill researchers make important contribution to the development of quantum computing

This release is available in French.

IMAGE: These images show the electrostatic energy given off when electrons are added to a quantum dot. They were made with an atomic-force microscope.

Click here for more information.

Physicists at McGill University have developed a system for measuring the energy involved in adding electrons to semi-conductor nanocrystals, also known as quantum dots – a technology that may revolutionize computing and other areas of science. Dr. Peter Grütter, McGill’s Associate Dean of Research and Graduate Education, Faculty of Science, explains that his research team has developed a cantilever force sensor that enables individual electrons to be removed and added to a quantum dot and the energy involved in the operation to be measured.

Being able to measure the energy at such infinitesimal levels is an important step in being able to develop an eventual replacement for the silicon chip in computers – the next generation of computing. Computers currently work with processors that contain transistors that are either in an on or off position – conductors and semi-conductors – while quantum computing would allow processors to work with multiple states, vastly increasing their speed while reducing their size even more.

Although popularly used to connote something very large, the word “quantum” itself actually means the smallest amount by which certain physical quantities can change. Knowledge of these energy levels enables scientists to understand and predict the electronic properties of the nanoscale systems they are developing.

“We are determining optical and electronic transport properties,” Grütter said. “This is essential for the development of components that might replace silicon chips in current computers.”

IMAGE: These images show the electrostatic energy given off when electrons are added to a quantum dot. They were made with an atomic-force microscope.

Click here for more information.

The electronic principles of nanosystems also determine their chemical properties, so the team’s research is relevant to making chemical processes “greener” and more energy efficient. For example, this technology could be applied to lighting systems, by using nanoparticles to improving their energy efficiency. “We expect this method to have many important applications in fundamental as well as applied research,” said Lynda Cockins of McGill’s Department of Physics.

The principle of the cantilever sensors sounds relatively simple. “The cantilever is about 0.5 mm in size (about the thickness of a thumbnail) and is essentially a simple driven, damped harmonic oscillator, mathematically equivalent to a child’s swing being pushed,” Grütter explained. “The signal we measure is the damping of the cantilever, the equivalent to how hard I have to push the kid on the swing so that she maintains a constant height, or what I would call the ‘oscillation amplitude.’ ”

Dr. Aashish Clerk, Yoichi Miyahara, and Steven D. Bennett of McGill’s Dept. of Physics, and scientists at the Institute for Microstructural Sciences of the National Research Council of Canada contributed to this research, which was published online late yesterday afternoon in the Proceedings of the National Academy of Sciences. The research received funding from the Natural Sciences and Engineering Research Council of Canada, le Fonds Québécois de le Recherche sur la Nature et les Technologies, the Carl Reinhardt Fellowship, and the Canadian Institute for Advanced Research.

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July 31, 2009

Quantum computing — a breakthrough and a warning

The potential power of quantum computing is astonishing, and a lot of research is going into creating quantum computers. Of course there’s always a dark side to anything — a quantum computer that realizes the full potential of the technology will also render current security and encryption obsolete overnight.

This post is a about a breakthrough involving the building blocks of matter and how that adds to quantum computing research, and also a cautionary tale from a researcher who is preparing for the security needs when the first quantum computer arises.

First the warning:

So far, so good, despite an occasional breach. But our security and our data could be compromised overnight when the first quantum computer is built, says Dr. Julia Kempe of Tel Aviv University‘s Blavatnik School of Computer Science. These new computers, still in the theoretical stage, will be many times more powerful than the computers that protect our data now.

Laying the groundwork to keep governments, companies and individuals safe, Dr. Kempe is working to understand the power of quantum computers by designing algorithms that fit them. At the same time, she is figuring out the limits of quantum computers, something especially important so we can build safety systems against quantum hackers.

“If a very rich person worked secretly to fund the building of a quantum computer, there is no reason in principle that it couldn’t be used for malevolent power within the next decade,” she says. “Governments, large corporations, entrepreneurs and common everyday people will have no ability to protect themselves. So we have to plan ahead.”

And now the breakthrough:

Discovery about behavior of building block of nature could lead to computer revolution

A team of physicists from the Universities of Cambridge and Birmingham have shown that electrons in narrow wires can divide into two new particles called spinons and a holons.

The electron is a fundamental building block of nature and is indivisible in isolation, yet a new experiment has shown that electrons, if crowded into narrow wires, are seen to split apart.

The electron is responsible for carrying electricity in wires and for making magnets. These two properties of magnetism and electric charge are carried by electrons which seem to have no size or shape and are impossible to break apart.

However, what is true about the properties of a single electron does not seem to be the case when electrons are brought together. Instead the like-charged electrons repel each other and need to modify the way they move to avoid getting too close to each other. In ordinary metals this does not usually make much difference to their behaviour. However, if the electrons are put in a very narrow wire the effects are exacerbated as they find it much harder to move past each other.

In 1981, physicist Duncan Haldane conjectured theoretically that under these circumstances and at the lowest temperatures the electrons would always modify the way they behaved so that their magnetism and their charge would separate into two new types of particle called spinons and holons.

The challenge was to confine electrons tightly in a ‘quantum wire’ and bring this wire close enough to an ordinary metal so that the electrons in that metal could ‘jump’ by quantum tunneling into the wire. By observing how the rate of jumping varies with an applied magnetic field the experiment reveals how the electron, on entering the quantum wire, has to fall apart into spinons and holons. The conditions to make this work comprised a comb of wires above a flat metal cloud of electrons. The Cambridge physicists, Yodchay Jompol and Chris Ford, clearly saw the distinct signatures of the two new particles as the Birmingham theorists, Tim Silk and Andy Schofield, had predicted.

Dr Chris Ford from the University of Cambridge’s Cavendish Laboratory says, ‘We had to develop the technology to pass a current between a wire and a sheet only 30 atomic widths apart.

‘The measurements have to be made at extremely low temperatures, about a tenth of a degree above absolute zero.

‘Quantum wires are widely used to connect up quantum “dots”, which may in the future form the basis of a new type of computer, called a quantum computer. Thus understanding their properties may be important for such quantum technologies, as well as helping to develop more complete theories of superconductivity and conduction in solids in general. This could lead to a new computer revolution.’

Professor Andy Schofield from the University of Birmingham’s School of Physics and Astronomy says, ‘The experiment to test this is based on an idea I had together with three colleagues almost 10 years ago. At that time the technology required to implement the experiment was still a long way off.

‘What is remarkable about this new experiment is not just the clarity of the observation of the spinon and holon, which confirms some earlier studies, but that the spinon and holon are seen well beyond the region that Duncan Haldane originally conjectured.

‘Our ability to control the behaviour of a single electron is responsible for the semiconductor revolution which has led to cheaper computers, iPods and more. Whether we will be able to control these new particles as successfully as we have the single electron remains to be seen. What it does reveal is that bringing electrons together can lead to new properties and even new particles.’

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 Notes to Editors

1. The paper is published in Science 10.1126/science.1171769 at http://dx.doi.org/10.1126/science.1171769

2. The experiment was performed in Cambridge’s Cavendish Laboratory with theoretical support from scientists at the University of Birmingham’s School of Physics and Astronomy.

February 4, 2009

Quantum dots and better computers

From KurzweilAI.net— Very cool Single-atom quantum dots made of silicon. This nanotech breakthrough has very real implications in improving computer performance by reducing both size and power consumption.

Single Atom Quantum Dots Bring Real Devices Closer
PhysOrg.com, Jan. 27, 2009

Scientists at Edmonton’s National Institute for Nanotechnology have invented quantum dots less than a nanometer in diameter and containing only one atom of silicon.

By controlling electrons at a smaller scale than transistors, the quantum dots could allow for silicon-based computers 1,000 times smaller in size and with a 1,000-times reduction in power consumption.

 
Read Original Article>>

April 18, 2008

Single atom thick graphene transistors

Filed under: Science, Technology — Tags: , , , , , — David Kirkpatrick @ 2:48 pm

From KurzweilAI.net:

Atom-thick material runs rings around silicon
NewScientist.com news service, April 17, 2008

University of Manchester researchers have used graphene to make some of the smallest transistors ever, at one atom thick and ten atoms wide.


credit: MU Mesoscopic Physics Group

They found that cutting small quantum dots of graphene gave the material switchable conductivity. Dots just a few nanometers across trap electrons due to quantum effects, and applying a magnetic field to the smallest dots lets current flow again, making a switchable transistor. The smallest dots that worked as transistors contained as few as five carbon rings–around 10 atoms or 1 nm wide.

Previous graphene transistors were significantly bigger–ribbons 10 nm across and many times longer.

 
Read Original Article>>