Electrochemical characteristics of redox active monolayers for use in molecular memory devices

Basic functions of a computer include information processing and storage. In typical computer systems these operations are performed by devices that are capable of switching states often referred to as “1” and “0”. In most cases such switching devices are fabricated from semiconducting devices such as transistors and capacitors. Because of the huge data storage requirements of modern computers a need for new, compact, low-cost, high capacitance, high speed memory devices continues to exist. This thesis introduces a novel method for storing information on the surface of a conducting substrate that is amenable for integration into a molecular memory device. Information is stored in the discrete redox states of redox active molecules attached to Au and Si(100) surfaces. The molecules are electrically read and written at potentials of 1.6 V and below and posses up to 4 distinct redox states.; The electrochemical properties critical to device performance were investigated by two new techniques one of which will measure the standard electron transfer rate and is dubbed swept waveform AC voltammetry (SWAV) and the other will quantify the monolayer charge storage capabilities and is dubbed open circuit potential amperometry (OCPA). The new techniques have been validated and provide essential data to explore the relationship between molecular structure and electrochemical properties. Using SWAV and OCPA it was observed that long charge retention times are only possible if a monolayer exhibits a slow standard electron transfer rate. Furthermore charge retention and electron transfer are affected by the nominal surface concentration (Γ) of the redox species forming the SAM. It is proposed that at high Γ the monolayer is shielded from solvation thereby sterically hindering the monolayers access to counter ion. The steric hindrance at high Γ is manifested in more positive peak potentials, heterogeneous cyclic voltammetric behavior, slow electron transfer rates, and long charge retention times. The effects of linker composition, linker length, molecular architecture and surface concentration on charge retention and electron transfer rates will be discussed.