atomic-force-microscopy-red-light-photoreceptors-using-peakforce

Atomic Force Microscopy of Red-Light Photoreceptors Using PeakForce Quantitative Nanomechanical Property Mapping

Atomic force microscopy (AFM) uses a pyramidal tip attached to a cantilever to probe the force response of a surface. The deflections of the tip can be ...

Northeastern Illinois University

The formation of monolayers of alkylsilanes on a gold surface is characterized by X-ray photoelectron and reflection-absorption infrared spectroscopies. The reaction occurs through the activation of multiple Si-H bonds. Reactivity of the newly synthesized systems to oxygen and water is reported.

Formation of alkylsilane-based monolayers on gold.

Scanning tunneling microscopy (STM), in conjunction with X-ray photoemission (XPS) and reflection-absorption infrared (RAIRS) spectroscopy, has been used to investigate the reaction of octahydridosilsesquioxane clusters (H(8)Si(8)O(12)) on the Si(100)-2x1 and Si(111)-7x7 surfaces. The clusters exhibit a markedly different reactivity upon exposure to the two clean silicon surfaces. STM data is presented that, in conjunction with XPS and RAIRS data, provides numerous constraints upon possible geometries for the chemisorbed clusters. The sum of the data is consistent with a dissociative reaction mechanism on Si(100)-2x1, resulting in cluster attachment to the surface via a single vertex. Conversely, data of Si(111)-7x7 subject to a saturation exposure of H(8)Si(8)O(12) is presented that is highly suggestive of cluster decomposition on the surface.

The differential reactivity of octahydridosilsesquioxane on Si(100)-2x1 and Si(111)-7x7: a comparative experimental study.

Scanning tunneling microscopy data of a mixed monolayer comprised of a 40:60 ratio of H8Si8O12 and C6H13-H7Si8O12 clusters on gold are presented. The images display a composite monolayer surface with well-defined domain regions of the individual components. Holes present at face-centered cubic (fcc) sites of the starting Au/H7Si8O12 adsorbate layer indicate the location of active sites for impinging C6H13-H7Si8O12 clusters. Adsorption of a C6H13-H7Si8O12 cluster likely yields a mobile hydrogen atom available to recombine with and desorb an adjacent H8Si8O12 cluster. Hydrogen atom diffusion along substrate [121] directions is the proposed pattern formation mechanism of the mixed monolayer. Imaging of the spherosiloxane cluster domains identifies a novel terrace-based active site located in the fcc regions of the Au(111) 23 x square root3 surface reconstruction.

Chemical imaging of terrace-based active sites on gold.

The spatially anisotropic kinetics involved in the chemical reaction between highly ordered pyrolytic graphite (HOPG) and a beam containing hyperthermal (approximately 8 km s(-1)) O((3)P) atomic oxygen and molecular oxygen yields unique surface morphologies. Upon exposure at moderate sample temperatures (298-423 K), numerous multilayer circular pits embedded in the reacted areas have been observed with the use of atomic force microscopy and scanning tunneling microscopy. These pits have diameters spanning nanometers to micrometers and depths from a few to tens of nanometers. The most striking characteristic of these pits is the convex curvature of the pit bottoms, where the highest point on the pit bottom is at the center and the lowest point occurs around the peripheral edge. Such structure arises by the interplay between kinetics of pit nucleation, the spatially anisotropic kinetics involved in the lateral and downward reactivity of HOPG, and the fluence of atomic oxygen. These kinetics, which are also influenced by the high reactivity of the translationally hot impinging oxygen atoms, govern the overall morphological evolution of the surface.

Spatially anisotropic etching of graphite by hyperthermal atomic oxygen.

The formation of mixed monolayers of hydridospherosilsesquioxane clusters (H(8)Si(8)O(12)) and alkylsilanes (H(2n+1)C(n)SiH(3)) on Au has been investigated using X-ray photoelectron and reflection-absorption infrared spectroscopies and scanning tunneling microscopy. All of the techniques indicate the displacement of the majority of the siloxane clusters from the surface in favor of the alkylsilane.

Article	Year
Formation of alkylsilane-based monolayers on gold. Journal of the American Chemical Society\| PubMed ID: 12059181	2002
The differential reactivity of octahydridosilsesquioxane on Si(100)-2x1 and Si(111)-7x7: a comparative experimental study. Ultramicroscopy\| PubMed ID: 12801655	2003
Chemical imaging of terrace-based active sites on gold. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 15835678	2004
Spatially anisotropic etching of graphite by hyperthermal atomic oxygen. The journal of physical chemistry. B\| PubMed ID: 16851995	2005
Formation of mixed monolayers of silsesquioxanes and alkylsilanes on gold. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 17073488	2006

Kenneth T. Nicholson

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