Probing nanoparticle assemblies and substrate effects on self-assembled monolayers

Scanning tunneling microscopy (STM) has been used to probe alkanethiolate self-assembled monolayers (SAMs), and structures relevant to electronics at the nanometer scale. A molecular insertion procedure was utilized to isolate dithiol molecules within an alkanethiolate SAM on Au{lcub}111{rcub}. This process positions dithiol molecules in close proximity to defect sites and directs molecular orientation. Molecular insertion forced the dithiol molecules to adopt an orientation with a single surface-thiolate bond, while the other thiol terminus protrudes from the SAM. The behavior of these inserted dithiol molecules was investigated, and it was determined that the inserted dithiol molecules are mobile on the surface. Apparent tunneling barrier height images acquired simultaneously with topographic images have been used to differentiate the components with binary component SAMs.; In a related series of experiments, nanoparticles were attachment covalently to the Au{lcub}111{rcub} surface by depositing alkanethiolate-stabilized gold nanoparticles onto alkanethiolate SAMs inserted with dithiol molecules. It was determined that the identities of the host SAM as well as the ligand shell of the nanoparticle both play significant roles in the immobilization process. Through a combination of shorter stabilizing ligands on the nanoparticles and the use of a thinner SAM, these nanoparticles are immobilized through a covalent interaction with the inserted dithiol molecules. The electronic characteristics of immobilized nanoparticles using current-voltage measurements were examined, and evidence for single-electron tunneling was observed due to the presence of Coulomb blockade.; Different thermal annealing procedures have been investigated to vary the defect density, defect type, and domain structure of SAMs. These experiments studied the role of solvent permeation and molecular mobility within alkanethiolate SAMs. It has been determined that solvent molecules permeate the SAM at defect sites, and alkanethiolate molecules move to sites to maximize their intermolecular interactions.; The investigation of alkanethiolate SAMs was extended to palladium surfaces. Both palladium thin films and Pd{lcub}111{rcub} single crystals were investigated as potential surfaces for self-assembly of ordered alkanethiolate films. These experiments provided evidence that suggest alkanethiolate SAMs do not form ordered structures on these surfaces, even after thermal annealing to promote molecular mobility and form ordered structures.