Nanofabrication of Tetraphenyl Porphyrin Surface Assemblies Linked With Tin Tetrachloride: a Scanning Probe Microscopy Investigation

Scanning probe microscopy (SPM) and colloidal lithography methods were used to study the covalent coupling of porphyrins to surfaces. In this dissertation, experimental methods for SPM operation, techniques, and applications are described. Measurement of tip-sample interactions between a sharp tip and surface is translated into digital image data maps with x-, y-, and z-data. Colloidal lithography can be used to fabricate test platforms for AFM studies. The periodicity and arrangement of the designed nanostructures is determined by the size of the colloidal particles used for surface masks. Data processing is required to obtain images and topography information from raw AFM data. Background removal and plane leveling of the image are commonly used processing steps, and color mapping offers advantages for discriminating differences in surface composition.\nThe use of coated tips for SPM studies was reviewed to examine the breadth of functionalities afforded by tip modification. Electrical, magnetic, and optical SPM modes use a coated tip for measurements. Molecular coatings can increase image resolution and can be used for chemical mapping of functional groups at the interface. Metal and molecular coatings have been used for scanning probe nanolithography to prepare nanometer-size features on surfaces. Physical vapor deposition, Au-S chemisorption, silane chemistry, amine coupling, and physisorption are approaches used for coating SPM probes. Coating include materials such as metals, biomolecules, carbon nanotubes, and catalysts.\nInvestigations into the self-assembly of porphyrins with metal chlorides was accomplished with tapping-mode atomic force microscopy (AFM). Porphyrins are a class of macrocyclic compounds with optical and electrical properties suitable for use in molecular electronics and photovoltaics. Adsorbing porphyrins onto a surface in a controlled manner can impart useful characteristics for tailoring surface properties. Tetraphenyl porphyrin (TPP) was coupled to Si(111) by tin(IV) tetrachloride pentahydrate to form Sn-TPP. Porphyrin molecules were covalently bound to the surface in a coplanar configuration, skewered by a O-Sn-O bridge. Colloidal lithography was used to direct the assembly of Sn-TPP for form nanoring assemblies. Experimental protocols were adjusted to evaluate the growth of the nanostructures as a function of concentration and immersion time, to provide useful information of optical, magnetic, and electric properties.