Oct 30 2009
The AVS 56th International Symposium & Exhibition next month in San Jose, CA will showcase advances in alternative energy, materials research, nanotechnology, and medicine. Highlights of papers from among the 1,250 talks and posters at the meeting are described below.
The symposium takes place November 8-13, 2009 at the San Jose Convention Center. Reporters are invited to attend the conference free of charge. Registration information can be found at the end of this release.
1) SEMICONDUCTOR TRANSISTORS -- MOVING BEYOND SILICON
Since its invention 60 years ago at Bell Labs, the transistor has driven an exponential increase in computing power. Keeping up with Moore's law -- which says the number of transistors on integrated circuits should reliably double every two years -- has led to the development of progressively smaller and faster versions of these tiny electronic switches.
But modern computers, which cram nearly a billion silicon dioxide transistors onto their chips, will soon need a new kind of transistor to keep the trend going. "Silicon has reached a fundamental limit," says Christopher Hinkle, a material scientist at the University of Texas, Dallas. "To increase the transistor performance, we have to move to higher-mobility materials."
Hinkle is building transistors out of a material that engineers have been testing for thirty years: gallium arsenide. He and his colleagues believe that semiconductors containing gallium arsenide may offer the next step in computing speed. At the AVS meeting, they will present data showing how to overcome one of the limitations of the material to take a step towards fast semiconductor transistors that function reliably.
"The transistors that we've produced are faster than silicon transistors right now," says Hinkle. Transistors made of an indium, gallium, and arsenic semiconductor offer a potential ten-fold boost in switching speed. But these transistors are not reliable right now because transistors fabricated out of semiconductors have tricky surface chemistry -- dangling chemical bonds at the surface create traps that affect how charge moves.
Hinkle's group thinks they have solved the problem --- a layer of gallium oxide (Ga2O3) that forms at the surface when gallium reacts with oxygen and creates lots of these traps. They will discuss the improvements that they have achieved by coating semiconductors either with silicon or with another gallium compound that has better electrical properties.
The talk "III-V MOS Device Performance Enhancement by Detection and Control of Individual Surface Oxidation States" is at 4:00 p.m. on Wednesday, November 11, 2009. Abstract: http://www.avssymposium.org/Open/SearchPapers.aspx?PaperNumber=SS1+EM-MoA-1
2) NANO-PLATINUM FOR MICRO FUEL CELLS
When people dream of a "hydrogen economy," they dream of a state that relies heavily on hydrogen fuel -- which, in simple terms, burns hydrogen and oxygen and produces electricity and water. Such an economy is still a long way from being realized, but the use of hydrogen in fuel cells for a variety of purposes in industry is considerable today. Better designs and reduced fabrication costs are crucial here, as they are for any other high-tech product.
A hydrogen-based fuel cell, basically an engine for mixing hydrogen with oxygen in the presence of a catalyst, usually employs two electrodes separated by a membrane. At one electrode (the anode), hydrogen molecules are split into positively charged protons and negatively charged electrons. The electrons proceed out into an external circuit as electricity while the protons migrate into one-way membranes that only allow protons through. At the other electrode (the cathode) oxygen is mixed with the returning electrons and the protons to form water.
One of the major expenses in making fuel cells is the platinum catalyst. Antonella Milella and her colleagues at the University of Bari in Italy have been working to reduce the amount of platinum needed by resorting to ever-smaller platinum particles, ensconced in a polymer matrix. Presently their platinum nanoparticles are as small as 3 nanometers in size and reside in a catalytic electrode only 500 nanometers wide. This reduction in the size of the components, Milella says, allows for decreasing the overall amount of platinum used while keeping output power high enough, and helps to promote the further miniaturization of fuel cells. This might lead to micro-fuel-cells powering microelectronic components.
The talk "Plasma Deposition of Platinum-Based Nanocomposite Films as Fuel Cell Electrocatalysts" is at 9:40 a.m. on Wednesday, November 11, 2009. Abstract: http://www.avssymposium.org/Open/SearchPapers.aspx?PaperNumber=PS2+TF-WeM-6
3) MOVIES OF A NANOTUBE BENDING AND TWISTING
Nanotubes are tiny molecular cylinders with a variety of properties and potential applications in future medical, electronic, and other devices. As with any material, engineers would like to be able to characterize the strength and physical properties of these materials by stretching them, twisting them, heating them, or loading weight on top of them until they crumble or bend.
These measurements are easy to make on new composite materials that contain nanotubes, but scientists have found it difficult to characteristics the strength and physical properties of a single nanotube.
Ifat Kaplan-Ashiri and her colleagues at Weizmann Institute of Science in Israel have now made the first such measurements on nanotubes made of tungsten disulfide. By attaching two ends of a nanotube on opposite tips of a device called an atomic force microscope, they can tease the ends in one or more directions and measure the force needed to push, pull, or twist the tubes. They have movies showing the bending and stretching of nanotubes under an applied force, and they can correlate these measurements with the number of defects in the nanotube (atoms that are not tungsten or sulfur).
One thing that this direct testing has revealed is that a tungsten disulfide nanotube can be stretched to a unexpected degree. Their measurements show that pulling both ends of a tungsten disulfide nanotube will stretch it out to a length about 14 percent longer than its original before it breaks -- surprising for a material that is considered completely brittle, says Kaplan-Ashiri. In addition, the results of the experiments agree very well with theoretical calculations, which demonstrates the crystalline perfection of the nanotubes.
The talk "Excitonics" is at 5:00 p.m. on Tuesday, November 10, 2009. Abstract: http://www.avssymposium.org/Open/SearchPapers.aspx?PaperNumber=TR+SS-TuA-10