Scanning Probe Investigations of Multidentate Thiol and Spatially Confined Porphyrin Nanoassemblies using Nanoscale Lithography

Abstract

Approaches to prepare spatially selective surfaces were developed in this dissertation for constructing nanopatterns of organic thin film materials. Nanoscale surface patterns were prepared using immersion particle lithography and scanning probe lithography combined with organothiol chemistry. Organic thin films and nanomaterials can be patterned with tunable periodicities and designed shapes by selecting the diameter of mesospheres used as surface masks or scanning probe lithography, respectively. The surface platforms of well-defined nanopatterns are ideal for high resolution investigations using scanning probe microscopy (SPM). Local measurements of surface properties and conductive properties combined with nanolithography were accomplished at the molecular level. Sample characterizations were accomplished with selected modes of SPM. Scanning probe studies can be used to probe the morphological and physical properties of samples, when spatially confined nanomaterials are prepared. Atomic force microscopy (AFM) can be used to analyze many types of samples in ambient and liquid environments. Arrays of nanostructures formed with newly designed molecules and porphyrins were fabricated using the spatial selectivity of chemical patterns prepared with nanolithography. The designed nanopatterns were evaluated for morphological details and physical properties. A newly designed bidentate organosulfur compound, i.e. 16-[3,5-bis(mercaptomethyl)phenoxy] hexadecanoic acid (BMPHA), was selected for study. The solution phase self-assembly onto Au(111) was investigated with scanning probe-based nanolithography and particle lithography. The two thiol groups of BMPHA were specially designed as surface linkers for improved stability. The orientation of BMPHA on Au(111) was investigated by referencing the heights of n-alkanethiols as an in situ molecular ruler. Protocols for patterning porphyrin nanostructures i.e. nanodots and nanorods on Au(111) were developed based on protocols with immersion particle lithography. Porphyrins with and without a central metal ion, 5,10,15,20-tetraphenyl-21H,23H-porphine (TPP) and 5,10,15,20-tetraphenyl-21H,23H-porphine cobalt(II) (TPC) were patterned using immersion particle lithography. Individual nanorods and nanodots of porphyrins were spatially isolated into well-defined, nanoscale arrangements directed by a template film of a nanopatterned thiol monolayer. The conductivity of the nanostructures of the porphyrins was evaluated using conductive probe-atomic force microscopy (CP-AFM). The studies evaluate the applicability of nanolithography for preparing surface platforms for the measurements of morphological and physical properties at the nanoscale.