Desi Americans Jumpstart Nanoelectronics   
by: Francis C. Assisi

05 February 2005 --If available in bulk quantities, nanowires could enable the bottom-up assembly of next generation devices, sensors, thin films, composites and systems. However, the ability to synthesize nanostructures with desired characteristics still remains a challenge towards realizing several of the promising applications.

In order to overcome the limitations associated with the current state-of the art processes, Desi scientists have developed new concepts for synthesizing nanowires. The two Desi scientists at HP Labs have devised a method of growing and connecting semiconductor nanowires in place, which could eventually lead the way to molecular electronics as well as more effective sensors for detecting toxic gases and other chemical or biological substances.

The scientists Saif Islam and Shashank Sharma, along with Ted Kamins and Stan Williams, describe how they formed silicon nanowires between vertical silicon "walls." The wires start growing from one wall, extend across the space between walls, then attach firmly to the other wall to form strong mechanical connections.

The scientists say that by using large numbers of these "nanobridges" in parallel, they were able to obtain the high surface-to-volume ratio needed for sensors. Other potential applications include interconnecting "leads" in nanometer-scale electronic circuits and devices within nanowires (transistors, for example). This technology also provides a platform for molecular electronic devices.

"Computing efficiency has increased by a factor of about 100 million in the past 40 years, but there appear to be no physical reasons why it can´t be improved by a factor of a billion," says Stan Williams, director of the Quantum Science Research (QSR) group, who initiated and leads molecular electronics research at HP.

In their paper, which is scheduled for publication March 2005 in Applied Physics A, Special Issue on Nanotechnology, the researchers argue that HP Labs’ approach has several advantages over competing ones that have relied on carbon rather than silicon. Nanowires formed from silicon are more versatile and controllable than carbon nanotubes, and they are more easily integrated into conventional integrated-circuit processes.

The paper’s authors are all members of HP Labs’ widely recognized Quantum Science Research (QSR) group. In related work, QSR has achieved important results and been granted key patents in techniques that could make practical the fabrication of molecular-scale electronic devices.

Sharma, who is a postdoctoral fellow with the Quantum Science Research Group at HP, Palo Alto, says: "My work at HP Labs focuses primarily on using chemical vapor deposition to form nanostructures by ‘self-assembly’ approach. In this approach, the chemical reactions providing the precursors for nanowire growth (silicon and germanium) are locally enhanced by a metal catalyst. I focus my efforts on controlling both the catalyzing nanoparticles and also the chemical reactions providing the silicon or germanium."

Earlier, while on his doctoral project at the University of Louisville, Sharma and his mentor Prof. Mahendra Sunkara obtained a patent for providing a synthesis technique to grow bulk quantities of semiconductor nanowires at temperatures less than C. Their method of synthesizing semiconductor fibers was by placement of gallium or indium metal on a desired substrate, placing the combination in a low pressure chamber, and raising the temperature of the metal to a few degrees above its melting point by microwave excitation, whereby the reactants form fibers of the desired length.

M. Saif Islam was born in Bangladesh and received his B.S. degree in Physics from Middle East Technical University (METU), Ankara in 1994 and M.Sc. degree in physics from Bilkent University, Ankara, Turkey in 1996. He received his M.S. and a Ph.D. in Electrical Eengineering from the University of California-Los Angeles (UCLA) in 1999 and 2001, respectively. Before joining UC Davis in 2004, Dr. Islam worked at Hewlett-Packard Laboratories, Gazillion Bits Inc. and SDL Inc./JDS Uniphase Corporation as a Staff Scientist, Senior Scientist and Post Doctoral Research Fellow. He also served as an adjunct faculty member with the ECE department of San Jose State University, San Jose, CA.

Dr. Islam is the principal investigator of the Integrated Nanodevices and Systems Research (i-nano) of UC Davis. He has developed two novel nano-device integration and mass-production techniques termed ´nano-bridges´ and ´nano-colonnades´ that are entirely compatible with existing microelectronics fabrication processes. His current research objectives include the development of massively parallel synthesis and integration processes for nano-structures for potential applications in single cell transport measurements, bio-chemical sensing, nanoelectronics, nanophotonics, memory and logic devices for future computing.

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