Fabrication of nanoelectronic devices using self-assembled two-dimensional arrays of monolayer protected clusters

The successful endeavor of the semiconductor industry to double the density of devices every 18 months (i.e. Moore\u27s law) has relied on the ability to continually reduce feature sizes. The ability to design devices with features smaller than a few nm (10−9 m) will require fabrication techniques and interconnect architectures that are unfeasible using lithography. This necessitates a paradigm shift, from a top-down to a bottom-up approach, in the way electronic devices and sensors will be fabricated in the future. Entities that have been proposed as building blocks for future devices include organic molecules that exhibit rectifying properties and Monolayer Protected Clusters (MPC\u27s) of gold. This research focuses on the development of techniques that will be part of a toolbox to form nanoelectronic devices using MPC\u27s, particularly alkanethiol coated gold nanoclusters. A specific goal of the research is the fabrication of a chemresistive sensor (Nanonose) involving a bilayer of gold clusters with a porphyrin molecule interconnecting the two layers. The molecule acts as the sensing element by changing its conductance, due to a shift in its electronic energy levels, caused by absorption of different chemical species. Several novel processes were developed to facilitate the fabrication of a ‘Nanonose’ structure including the preparation of monolayer arrays of alkanethiolate protected gold clusters at the air-water interface having ordered domains centimeters in diameter, a stamping technique for transferring such an array onto a flat substrate, and a method for patterning such arrays on the micron scale. The MPC arrays were characterized by Transmission Electron Microscopy (TEM), UV-Vis spectroscopy, and Conductive Probe Atomic Force Microscopy (CP-AFM). Electrical characterization of lateral conduction through the arrays was carried out on an interdigitated pattern of gold electrodes that were modified with different molecular layers. The salient features of the results are the reduction in the lateral conductance of the arrays from ca. 1011 Ω/□ to 108 Ω/□ on displacing the alkanethiol coating with conjugated dithiol molecules and the absence of a significant contact resistance between the array and the gold electrode. These results provide a basis for the manufacture of robust nanoelectronic device structures using MPC\u27s