NANOMETER-SCALE ELECTRONICS AND STORAGE K. F. KELLY, * Z. J. DONHAUSER, P. A. LEWIS, R. K. SMITH, and P. S. WEISS Departments of Chemistry and Physics, The Pennsylvania State University 152 Davey Laboratory, University Park, PA 16802-6300, USA Abstract. The ability to control the placement of molecules is essential for the patterning and fabrication of nanoscale electronic devices. We apply selective chemistry and self-assembly in combination with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in the nanostructures that we create. We illustrate three successful approaches: (1) phase separation of self-assembled monolayers (SAMs) by terminal and internal functionalization, (2) phase separation of SAMs induced by post-adsorption processing and (3) control of molecular placement by insertion into a self-assembled monolayer. These methods demonstrate the possibilities of patterning films by exploiting the intrinsic properties of the molecules. We then employ these self-assembled monolayers as a means to isolate molecules with electronic function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. Using self-assembly techniques in combination with scanning tunneling microscopy (STM) we are able to study candidate molecular switches individually and in small bundles. Alkanethiolate SAMs on gold are used as a host two-dimensional matrix to isolate and to insulate electrically the molecular switches. We then individually address and electronically probe each molecule using STM. The conjugated molecules exhibit reversible conductance switching, manifested as a change in the topographic height in the STM images. The origins of switching and the relevant aspects of the molecular structure and environment required will be discussed. 1. Introduction Control and stabilization of molecular assemblies at the nanometer scale are crucial steps in the fabrication of molecular-scale devices. Current techniques such as photolithography or electron beam lithography [1] and ‘soft lithography’ [2,3] are limited in their resolution and cannot reproducibly achieve patterns with dimensions at the nanometer scale. At the other end of the spectrum, single molecule manipulation has been successfully demonstrated using scanning probe microscopy, but is unable to produce devices in parallel and is still too time consuming to be practical as a fabrication technique [4-8]. We anticipate the need to combine the speed and versatility * Present Address: Department of Electrical Engineering, Rice University, Houston, TX 77251, USA