M.Sc Thesis

M.Sc StudentGozlan Nira
SubjectCoverage Effect of Self-Assembled Polar Molecules on the
Surface Energetics of Gold and Silicon
DepartmentDepartment of Chemical Engineering
Supervisor PROF. Hossam Haick
Full Thesis textFull thesis text - English Version


This thesis examines the coverage effect of adsorbed polar molecules on the surface energetics of Si and Au. Alkylthiols or alkylsilanes having a common backbone and binding groups but differ in their exposed functional groups, were formed by self-assembly on Au or (native-) SiOx/Si substrates with varied surface coverage (~10-98%). The electrical characteristics of the resulted surfaces were studied and correlated with the microscopic (dis-)order, density of defect sites, and adsorption patterns within the monolayer, as revealed by Scanning Tunneling Microscopy (STM), Fourier transform infrared (FTIR) spectroscopy, and X-ray Photoelectron Spectroscopy (XPS).

The results show that systematic control of the work function of conductors or semiconductors can be achieved not only by controlling the properties of the molecular dipoles, but also by their coverage on the surface. For the Si case, optimal control over the work function of SiOx/Si was achieved even with half (~50%) coverage of molecular dipoles. For the Au case, complete order within the SAM film even at 86% coverage, where small pinholes existed, led to depolarization, and the surface coverage stopped playing any role in controlling the metal’s work function. The results indicate that the requirements on the molecule on electronic surfaces are significantly and nearly completely relaxed. Therefore, the ability of the molecules to form pinhole-free coverage will not be important. In addition, formation of laterally inhomogeneous molecular layers, is in the direction of, and may lay the foundation for, the implementation of multiple functions on hard or flexible substrates, with lateral resolution down to tens of nanometers.