NIST team proves bridge from conventional to molecular electronics possible

Caption: Side and top views of the NIST molecular resistor. Above are schematics showing a cross-section of the full device and a close-up view of the molecular monolayer attached to the CMOS-compatible silicon substrate. Below is a photomicrograph looking down on an assembled resistor indicating the location of the well. Credit: NIST. Usage Restrictions: None.

Researchers at the National Institute of Standards and Technology (NIST) have set the stage for building the “evolutionary link” between the microelectronics of today built from semiconductor compounds and future generations of devices made largely from complex organic molecules. In an upcoming paper in the Journal of the American Chemical Society,* a NIST team demonstrates that a single layer of organic molecules can be assembled on the same sort of substrate used in conventional microchips.

The ability to use a silicon crystal substrate that is compatible with the industry-standard CMOS (complementary metal oxide semiconductor) manufacturing technology paves the way for hybrid CMOS-molecular device circuitry—the necessary precursor to a “beyond CMOS” totally molecular technology—to be fabricated in the near future.

Scientists classify crystal structures by the particular plane or “face” cutting through the crystal that is exposed. Most research to date on silicon substrates for molecular electronic devices has been done with a crystal orientation that is convenient for organic molecules but incompatible with CMOS technologies. For their electronic device, the NIST team first demonstrated that a good quality monolayer of organic molecules could be assembled on the silicon orientation common to industrial CMOS fabrication, verifying this with extensive spectroscopic analysis.

They then went on to build a simple but working molecular electronic device—a resistor—using the same techniques. A single layer of simple chains of carbon atoms tethered on their ends with sulfur atoms were deposited in tiny 100-nanometer deep wells on the silicon substrate and capped with a layer of silver to form the top electrical contact. The use of silver is a departure from other molecular electronic studies where gold or aluminum has been used. Unlike the latter two elements, silver does not displace the monolayer or impede its ability to function.

The NIST team fabricated two molecular electronic devices, each with a different length of carbon chain populating the monolayer. Both devices successfully resisted electrical flow with the one possessing longer chains having the greater resistance as expected. A control device lacking the monolayer showed less resistance, proving that the other two units did function as nonlinear resistors.

The next step, the team reports, is to fabricate a CMOS-molecular hybrid circuit to show that molecular electronic components can work in harmony with current microelectronics technologies. ###

This work was funded in part by the NIST Office of Microelectronics Programs and the Defense Advanced Research Projects Agency (DARPA) MoleApps Program.

* N. Gergel-Hackett, C.D. Zangmeister, C.A. Hacker, L.J. Richter and C.A. Richter. Demonstration of molecular assembly on Si (100) for CMOS-compatible molecular-based electronic devices. Journal of the American Chemical Society, Vol. 130, No. 13 (April 2, 2008), pp 4259-4261. Published online March 7, 2008.

Contact: Michael E. Newman michael.newman@nist.gov 301-975-3025 National Institute of Standards and Technology (NIST)

Tags: Nano or Nanotechnology and Nanotech or National Institute of Standards and Technology and molecular electronics or complementary metal oxide semiconductor

Professor Toh-Ming Lu named fellow of the Materials Research Society

Toh-Ming Lu, the R.P. Baker Distinguished Professor of Physics, has been named a lifetime fellow of the Materials Research Society (MRS). The MRS has recognized Lu for his contributions to the advancement of materials research, specifically his “seminal contributions to the fundamental understanding of thin film morphological evolution.”

This is the first year that MRS has named a class of fellows. Lu joins a distinguished group that includes 34 researchers selected for their outstanding contributions to the field. He will be formally honored during the 2008 MRS Spring Meeting on March 26, 2008, in San Francisco.

A nanomaterials expert, Lu strives to develop new, high-performing nanostructures that can be used in integrated electronics, semiconductors, and energy storage devices. His lab uses new approaches to develop unique nanostructures and analyze those structures as they grow. His imaging and analysis techniques allow researchers to fully understand how and why different growth techniques grow nanomaterials in very specific ways. His lab is also developing techniques that deposit ultra-thin layers of conductive metals and dielectrics on to surfaces to develop new, super-fast and efficient electronics and nanodevices.

Lu joined Rensselaer in 1982. He formerly served as director of the Center for Advanced Interconnect Science and Technology and chairman of the physics department at Rensselaer. Lu is a fellow of the American Association for the Advancement of Science, the American Physical Society, and the American Vacuum Society. He is author of more than 400 technical papers and holds nine patents related to his research. He has earned numerous other honors, including Rensselaer’s Early Career Award in 1986, the SRC Invention Award in 1988, the Rensselaer Center for Integrated Electronics Faculty Award in 1993, the William Wiley Distinguished Faculty Award in 2002, the Materials Research Society Medal Award in 2004, and the SRC Faculty Leadership Award in 2005.

Lu earned a bachelor’s in physics from Cheng Kung University in Taiwan, a master’s in physics from Worcester Polytechnic Institute, and a doctorate from the University of Wisconsin, Madison.

The Materials Research Society was established in 1973. It strives to create links between researchers working in the ever-expanding field of materials science. Currently, more than 14,000 researchers are members of MRS.

Contact: Gabrielle DeMarco demarg@rpi.edu 518-276-6542 Rensselaer Polytechnic Institute

Tags: Nano or Nanotechnology and Nanotech or Rensselaer Polytechnic Institute and nanomaterials or nanostructures