ASSEMBLY OF NANOELECTROMECHANICAL SYSTEMS (NEMS) WITH A SCANNING PROBE MICROSCOPE

Ari Requicha
Laboratory for Molecular Robotics, University of Southern California

Microelectromechanical systems (MEMS) have reached the marketplace, with annual sales of several million pressure sensors and accelerometers, primarily to the automotive industries. Research and development in MEMS is under way at many institutions. It is now time to begin studying nanoelectromechanical systems (NEMS), which are the new frontier in miniaturization. Nanometer-scale devices have dimensions comparable to the atoms and molecules that make up all matter, living or inanimate. Control over the structure of matter at the atomic or molecular scale will undoubtedly trigger a major revolution in man-made artifacts.

NEMS will decrease systems space and energy requirements and increase speed of operation simply because they are smaller than any other electromechanical systems previously built. But these are not their most important characteristics. More interestingly, they open two new areas of potential applications that cannot be tackled with current technology. First, they can be used in applications that require very small sizes. For example, typical cells have dimensions in the order of a few micrometers. To penetrate into a damaged cell and repair it requires devices with dimensions on the nanometer scale. Second, macroscopic materials and devices that are molecularly perfect can be built by assembling successively larger components, beginning with nanometer-scale primitives constructed through precise control at the molecular level. These materials and devices would be orders of magnitude stronger than those produced in today's technology, which have minute imperfections that cause them to fail under stress.

Research in nanoelectronics is taking place at many laboratories worldwide, but little attention is being paid to nanoelectromechanical devices and systems. A few researchers are designing NEMS through molecular simulation techniques. However, none have been built, and fabrication processes for them are unavailable. There is a major need to produce physical prototypes for NEMS to demonstrate feasibility, and to guide design efforts so as to ensure manufacturability.

MEMS are built today through extensions to semiconductor fabrication technology, which is well established but has known size limitations. New techniques are needed to reach characteristic lengths of a few nanometers. Several laboratories are exploring self-assembly approaches, which use chemical processes to build nanostructures. Self-assembly is a promising technique to build highly-repetitive or symmetrical structures, but is unlikely to produce, by itself, the asymmetric structures needed in nanomachinery. This talk focuses on a different approach that seeks to construct NEMS by precisely positioning and assembling molecular-sized components, and is being pursued in an interdisciplinary effort at USC's Laboratory for Molecular Robotics, and a few other laboratories.

We are developing techniques for constructing NEMS by manipulating nanosized structures with a Scanning Probe Microscope (SPM). The initial nanostructures produced are simple planar patterns built by assembling colloidal gold balls. Our approach blends knowledge from macrorobotic manipulation and assembly with the physics and chemistry of nanoscale phenomena.

The talk will review basic concepts of SPM-based manipulation, survey past work, and discuss the current status of our project and its research directions.