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An atomic-scale depiction of the SketchSET shows three wires (green bars) converging on the central island (center green area), which can house up to two electrons. Electrons tunnel from one wire to another through the island. Conditions on the third wire can result in distinct conductive properties. Credit: Jeremy Levy, Univ. of Pittsburgh.

Good news, Moore’s Law: You are still not extinct. A group of researchers recently announced the development of a single-electron transistor that is said to be the first of its type made entirely of oxide-based materials. Named SketchSET, the transistor device demonstrates an approach to making erasable electronics that require about one-thousandth the area used in Intel Pentium processors (i.e., at the 45 nanometer production node). Moreover, one of the researchers says it could lead to self-contained devices that can create, as needed, their own transistors as well as other electronic components and circuitry.

A news release from University of Pittsburgh describes the transistor as consisting of an island formation that can house up to two electrons. According to the release, “the number of electrons on the island, which can be only zero, one or two, results in distinct conductive properties. Wires extending from the transistor carry additional electrons across the island.”

This research, published in Nature Nanotechnology (doi:10.1038/nnano.2011.56), reports that the transistor’s central component, an “island” only 1.5 nanometers in diameter, operates with the addition of only one or two electrons. That capability would make the transistor important to a range of computational applications, from “ultradense nonvolatile memories, nanoscale hybrid piezoelectric and charge sensors as well as building blocks in quantum information processing and simulation platforms.”

According to the Pitt release, the tiny central island also could be used as an “artificial atom” for developing new classes of artificial electronic materials, such as exotic superconductors with properties not found in natural materials.

The lead researcher, Jeremy Levy, is a professor of physics and astronomy at the University of Pittsburgh and a member of The American Ceramic Society. Other institutions involved in the research include Laboratório Nacional de Luz Síncrotron, Brazil; Instituto de Física ‘Gleb Wataghin’, Universidade Estadual de Campinas-UNICAMP, Brazil; University of Wisconsin–Madison’s Department of Materials Science and Engineering; and Hewlett Packard Laboratories.

Short for “sketch-based single-electron transistor,” SketchSET’s name was reportedly coined by Levy because the technique works like a microscopic Etch A Sketch, the drawing toy of Levy’s youth that inspired his idea. The technique was originally developed in 2008.

Levy’s group leverages the properties they find at the interface between a crystal of strontium titanate and a 1.2 nanometer layer of lanthanum aluminate. Using the conducting probe of an atomic force microscope, they can precisely and reversibly toggle the metal–conductor transition in desired regions at the SrTiO₃–LaAlO₃ interface. They then use these techniques to create wires and transistors of nanometer dimensions. Explicit in this is another important characteristic: These electronic devices can then be “erased,” and the interface can be used over again.

This work could represent a disruptive technology, in terms of how electronic devices are fabricated. Levy says in a brief video on this topic (see below) that this work technology could create a stark alternative to the current chip fabrication systems. He says instead of enormous chip fab plants, “In principle, what we are doing can be scaled down to the size of the object in which that system we create — the transistor system — would reside. So, in fact, you might imagine putting all the capabilities required to create these structures within the object, itself, something on the size of an (Apple) iPod Nano.”

The group’s research is supported in part by grants from DARPA, the Army Research Office, NSF and the Fine Foundation.

In addition to this research, Levy is also leading a $7.5 million, multi-institutional project to construct a semiconductor with properties similar to SketchSET. This five-year project is intended to overcome some of the most significant challenges related to the development of quantum information technology. Levy is working on this project with researchers from Cornell University, Stanford University, University of Michigan, University of Wisconsin–Madison and University of California, Santa Barbara. This project began in August 2010 and is funded by the Air Force Office of Scientific Research’s Multi-University Research Initiative.

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Back in November, I wrote about the work of Di Gao, an assistant professor in the University of Pittsburgh’s Swanson School of Engineering, regarding mimicking the action of lotus leaves to create self-cleaning coatings that could be applied to anything from windows to warehouses. One of Gao’s applications is a superhydrophobic silica nanoparticle–polymer coating that could be used to prevent ice build up on critical surfaces such as roofs, wings, etc. (FYI, the anti-icing material is an acrylic polymer with organosilane-modified silica particles of diameters ranging from 20 nm to 50 nm.)

Yesterday, we received an intriguing release from Pitt reporting that, in response to the oil spill in the Gulf of Mexico, Gao and his researchers have demonstrated a reusable superhydrophilic filter system for separating oil from water and that the filter has already been successfully tested in the Gulf near Louisiana.

Gao hasn’t published directly on this topic yet, so most of the details are still unknown. However, it appears that the filter has a simple cotton substrate that is coated in a hydrophilic–oleophobic polymer that blocks oil while allowing water to pass through. Gao has yet to say exactly what’s in the polymer, but the preparation only requires that the cotton material be dipped in the polymer and allowed to dry.

Some hints to Gao’s approach might be found in a 2007 Langmuir paper that discusses creating a superoleophilic layer on a Si surface:

“We demonstrate that porous Si films fabricated by a convenient gold-assisted electroless etching process, which possess a hierarchical porous structure consisting of micrometer-sized asperities superimposed onto a network of nanometer-sized pores, are able to induce a superhydrophobic phenomenon on an intrinsically hydrophilic hydrogen-terminated Si surface and a superoleophobic phenomenon on an intrinsically oleophilic self-assembled monolayer-coated Si surface. Through comparison with porous Si films consisting of vertically aligned straight pores, which are hydrophilic and oleophilic, we show that an overhang structure resulting from the hierarchical porous structure is essential to preventing water and oil from penetrating the texture of the films and inducing the observed macroscopic superhydrophobic and superoleophobic phenomena.”

Gao’s system works well enough that the oil can still be preserved, and one idea he has for an approach to large oil spills is to use what he describes as trough-shaped versions of his filter, which would be dragged presumably across the surface of the water.

Because of the stresses that are involved with dragging anything through water, I am fairly certain that this means that the cotton substrate would have to be heavily reinforced, for example, by laminating it to strong netting.

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Computer-generated illustration of Lotus effect. (Credit: William Thielicke.)

A group of researchers from the University of Pittsburgh, University of California Riverside and the Ross Technology Corporation joined a growing list of researchers studying the superhydrophobic property of lotus leaves and now say the insights they gained showed them a way to develop a particle–polymer coating that prevents ice formation in both lab and real–world testing.

Lotus leaves have fascinated researchers for several years because moisture that hits the leaves rolls off and takes with it accumulated dirt and debris. Once this superhydrophobic “Lotus effect” was revealed, many research groups launched efforts to develop nanomaterials with the goal of developing self-cleaning coatings for glass, mirrors, hospital equipment and even whole buildings.

This new group, however, took a slightly different tack and used the lotus leaves to understand the relationship between water-repellency and snow–ice accumulation on superhydrophobic surfaces. In a paper recently published in Langmuir, they report on the successful use of silica nanoparticle–polymer composites to deter icing, especially in situations involving supercooled water, such as freezing rain and “impact ice,” that fouls highways, creates havoc with airplane lift surfaces and drags down electric power lines.

In their paper, the group reports on making a superhydrophobic surface material by combining an acrylic polymer with organosilane-modified silica particles of diameters ranging from 20 nm to 20 μm. They then coated parts of an aluminum plate with the particle-polymer composites and exposed the plate under laboratory conditions to supercooled water. They repeated the experiment 20 times for each particle size. The pay off is that they found excellent anti-icing capabilities when the silica particles were in the 20-50 nm range, but the anti-icing strength decreased significantly when the particles were larger than 50 nm.

An aluminum plate glazed with superhydrophobic coating (left) repelling the supercooled water. For the uncoated plate (right), the water freezes on contact and ice accumulates. (Credit: University of Pittsburgh.)

The group coated half of another aluminum plate and half of a satellite-TV dish antenna with a layer of the 50 nm composite, and placed both of these outdoors near Pittsburgh where they were exposed to a freezing rain last January. The uncoated sides of the plate and dish were covered with ice, but the treated halves were ice-free.

Because of the particle-size dependency, they group cautions against assuming that all superhydrophobic surfaces have anti-icing properties. Likewise, they say further research is needed on understanding ice adhesion, hydrodynamic conditions and the structure of water film on superhydrophobic surfaces where icing still occurs.

The lead author of the paper is grad student Liangliang Cao, and much of the work was done by in Pitt professor Di Gao’s lab.

Update: Di Gao has kindly provided us with additional images of the coating at work:

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Conventional thinking says that a block of salt can’t stretch, but researchers from Sandia National Laboratories and the University of Pittsburgh are saying they aren’t so sure anymore.

In an article published in Nanoletters, members of the group describe how they were poking around a small piece of salt with an interfacial force microscope when they noticed that salt stuck to the tip of the IFM and clung with it even as the tip was moved away from the main piece of salt. They learned they could stretch the salt nanowire-like tendrils to lengths from 580 nm to 2,191 nm.

“It’s not supposed to do that,” said Sandia principal investigator Jack Houston in a SNL news release. “Unlike, say, gold, which is ductile and deforms under pressure, salt is brittle. Hit it with a hammer, it shatters like glass.”

Houston and the others believe that at the interface between the IFM tip and the salt surface, salt molecules formed a ductile meniscus. Houston said he thinks the reason this is occurring is that because surface molecules don’t have an atomic lattice above them, they are free to be more mobile than interior salt molecules.

The discovery may have application in desalination systems. It may also provide insight on sea salt aerosols. These aerosols are linked to cloud nucleation and lead to environmental problems, such as smog, ozone destruction and asthma.

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