Formation, characterization and sub-50 nm patterning of self-assembled monolayers with embedded disulfide bonds

In this dissertation, the insertion of disulfide bonds into SAMs and selective cleavage of the embedded disulfide bonds to form sub-50 nm chemical patterns are described. The ultimate goal is to use the sub-50 nm chemical patterns as templates to confine the attachment of molecular quantum-dot cellular automata (QCA) cells or DNA tiles for molecular electronic application.; First, formation and characterization of self-assembled monolayers (SAMs) with embedded disulfide bonds is studied. Two different strategies are tried to obtain smooth and uniform SAMs with embedded disulfide bonds for lithography processing. The first is to introduce embedded disulfide bonds into SAMs through zirconium-phosphonate chemistry, and the second is to form organosilane monolayers by using an organosilane precursor with an embedded disulfide bond. Zirconium-phosphonate monolayers with embedded disulfide bonds were quite rough, whereas organosilane monolayers with embedded disulfide bonds were smooth and continuous. The embedded disulfide bonds were intact and react normally after monolayer formation according to chemical cleavage study. In particular, maleimide molecules can selectively attach on the fresh cleaved thiol-terminated surface but not on SAMs with embedded disulfide bonds surface.; Second, both Zr-P monolayers with embedded disulfide bonds and organosilane monolayers with embedded disulfide bonds were tried as organic resists for atomic force microscopy (AFM) anodization and electron beam lithography (EBL) to form sub-50 nm patterns. However, only organosilane monolayers with embedded disulfide bonds are suitable for high-resolution patterning, which requires smooth monolayers for visualization. AFM anodization on phenyl (3-trimethoxysilypropyl)disulfide achieved 20-nm resolution lines. In the patterned region, both topographic and chemical alternations have happened, as based on AFM topographic and phase contrast images. EBL with an accelerating voltage of 30 kV generated 30 nm resolution chemical patterns on this monolayer. According to AFM topographic and friction images, XPS damage simulation, Auger gun irradiation, and chemical rebinding tests, the chemical changes are consistent with cleavage of the disulfide bonds to form sulfhydryl groups.