Characterization of redox-active monolayers for use in molecular memory devices. Part I: Self-assembled molecular monolayers on gold. Part II: Covalently linked molecular monolayers on semiconductors

The work described herein, includes an evolutionary progression beginning with the initial realization that redox active molecules may be used to bridge novel synthesis of molecular materials to microelectronic memory storage devices. This realization has set forth motivation to develop and characterize a molecule-based high-density electronic storage media that is scalable in design and complexity for use in real world electronic devices.; Focused on this objective, early studies of (+230) thiol-anchored porphyrin monolayers on micron-sized Au architectures afford the unique redox characteristics that make porphyrins amendable to information storage. Initial studies set forth the first objective, to demonstrate a molecule-based approach with high-density storage operating at low power using the process of self-assembly and a well-characterized S-Au binding scheme. The second objective was to demonstrate scalability of the medium to hybrid semiconductor platforms such as Si(100) and Ge(100).; A number of important advances were made in the process of constructing and characterizing hybrid platforms for electronic information storage. First, a complete fabrication protocol was developed which is universal to all Group VI elements, anchoring the redox monolayers covalently to device-grade Si(100). The molecules exhibit robust characteristics, which include high level of stability under real world conditions over large number of cycles, operation at elevated temperatures, and processing at high temperatures in the gas or solution phase. Collectively, the new fabrication methodology meets the operational and processing challenges required for fabricating computational devices. Second, the electrical behavior of the surface bound layers was fully characterized through established voltammetric, and amperometric techniques to examine the kinetics of the redox process at the molecule/electrode interface. Success in this step affords the means to electronically measure the extent of the monolayers surface concentration, charge storage, and kinetics of electron transfer, three properties that must be understood and controlled in a prototype device. In conjunction with these studies, the structural information of the monolayers was also examined through X-ray spectroscopic, and FTIR methods that selectively probed the binding mode, surface packing density, and monolayer orientation. More importantly, the findings demonstrate a strong correlation between monolayer structure and the electron transfer properties through Group VI/Si interfaces. In general, the rate of electron exchange in the read sequence is several orders of magnitude faster than their charge dissipation rates of tens of seconds. This is a desirable property from the standpoint of molecular memory device development, in particular where a state of the art traditional trench capacitor in DRAM leaks its charge on the order of ∼10 ms.; Collectively these findings show the significance and feasibility of introducing chemical tuning and scalability onto metal and silicon based microelectronic device materials. The ability to demonstrate the rational derivitization of surface bound species, stable under low potentials over numerous cycles, has enabled us to take a step closer to constructing a prototype device. Production of the first successful hybrid molecular based device for electronic memory applications will undoubtedly pave an evolutionary path toward technological progress in new materials for the semiconductor industry.