Optical and electronic characterization of organic monolayers on silicon(001)

Surface-tethered organic molecules are of increasing interest in a number of potential applications, including electronic and optical devices and chemical sensors. Aromatic molecules are of particular interest because of the unique optical and electronic properties exhibited within monolayer thin films. In this dissertation, optical and electronic characterizations of organic molecules have been coupled to address important issues such as electron transfer within the covalent bond, aromatic influences at the interface, bonding-induced band bending, and valence band dispersion of the π electrons within the adsorbed organic layer.; Systematically varying the atomic tether of small molecules showed the optical response of the silicon interface was determined largely by electron transfer through the covalent tether, confirming the intimate connection between optical and electronic properties at the interface. Electronic and optical properties of conjugated π-systems tethered to silicon identified anisotropic valence band structure as well as anisotropic π-π* transitions within the adsorbed monolayer. Optical transitions attributed to bonding-induced localization of bulk silicon were also observed. These experiments confirm that it is possible to create a macroscopic optical anisotropy in organic films of a monolayer thickness on silicon surfaces using the Si(001) dimers to control the molecular orientation.; The effect of aromaticity on the interfacial properties was further probed by the attachment of different aromatic species that form a similar interfacial bond. The band-bending and valence band dispersion were found to vary for the differing aromatic structures as well as differing substrate dopant identity signifying the role of the aromatic structure and substrate, in addition to that of the covalent tether, in determining the electrical and optical properties at the interface.; Further insight into the optical response of aromatic molecules was achieved through careful studies varying the aromatic structure and atomic tether. Major contributions to the optical response from the conductivity of the covalent bond at the interface and the aromatic structure within the monolayer film were identified.