Synthesis And Monomolecular Electrical Properties Of Cyclic Silane

Bulk silicon, the bedrock of information technology, consists of the deceptively simple electronic structure of just Si-Si σ bonds. Diamond has the same lattice structure as silicon, yet the two materials have dramatically different electronic properties. Molecular forms are the essential components of the bulk semiconductor. Moreover, as silicon electronics continues to scale to smaller length scales the connection between molecular silicon and silicon from bulk single crystals will become more explicit. In silicon electronics, conformation and strain of the molecular has been found to an important parameter to insert and control to maximize performance.This thesis focuses on cyclosilanes. There are many of these types of structures that have been prepared. For example cyclotetrasilane, cyclopentasilane, cyclohexasilane. The important point in context of this thesis is that they will be functionalized allowing them to be incorporated in molecular electronic devices for transport measurements. The scanning tunneling microscope based break-junction technique(STM-BJ) is one of the most widely used experimental set-ups to provide a basic understanding of transport mechanisms across junctions with single molecules bonded to metal electrodes. For example, STM-BJ measurements can be used to determine the mechanism for charge transfer(tunneling, resonant transport or sequential hopping) or to understand the nature of charge carriers(electrons or holes) in single molecule junctions. However, these types of single molecule measurements are not limited to advancing the field of molecular electronics – indeed, as we propose here – it can be used to understand fundamentals of charge transfer across cyclosilanes as building blocks for organic electronic devices. Some pretty interesting findings include:(1) cyclopentasilane: for the cis- isomer we see two peaks, less than an order of magnitude apart; for the trans- isomer we see one peak, around the same value as the low peak of the cis- isomer. The result is in agreement with the DFT calculations.(2) multiple conformers, both cis- isomer and trans- isomer, form these conductance states.(3) extended cyclopentasilanes: We found that the molecular conductance decreases exponentially with increasing chain length with a decay constant β = 0.61 ± 0.07, which is similar to the linear Si chains with a decay constant β = 0.7.