Biomedical subjects
Publications and source records attributed to Daniel R Fosnacht.
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.
Chemisorbed monolayers of octylgermane (C8H17GeH3) on gold have been formed by vapor deposition in ultrahigh vacuum. The monolayer has been characterized by X-ray photoelectron and reflection absorption infrared spectroscopies (XPS and RAIRS) and scanning tunneling microscopy (STM). XPS data indicate the monolayer can be oxidized by exposure to ozone. STM images exhibit a complex pattern which can be modeled as strain-mediated spinodal decomposition.
The oxidation of alkylsilane monolayers on Au has been studied by X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, contact-angle measurements, and scanning tunneling microscopy. Exposure of the monolayers at 298 K to pure O(2) or H(2)O (>5 x 10(-5) Torr and >150 000 L) does not cause oxidation. Ambient atmosphere only causes oxidation if direct sight lines are maintained to the sample. Ozone exposure results in rapid monolayer oxidation. Oxidation initially occurs only at the Si atom, resulting in formation of a cross-linked siloxane monolayer that retains alkyl surface termination. Prolonged ozone exposures result in the oxidation and subsequent loss of the alkyl chain.
Investigations of octylsilane (C8H17SiH3) monolayer pattern formation on Au(111) are reported. Scanning tunneling microscopy data display the evolution of a approximately 6 nm scale pattern of interwoven features concomitant with ejection of surface Au atoms and relaxation of the Au(111) 23xsqrt[3] surface reconstruction. Numerical simulations suggest the surface dynamics are governed by a substrate strain-mediated spinodal decomposition mechanism, novel to organic monolayer formation. Collectively, the experimental and theoretical data indicate strain-inducing Si-Au bond interactions drive the pattern formation and the alkyl chains play a negligible role.
Ultrahigh vacuum scanning tunneling microscopy data investigating octylsilane (C8H17SiH3) monolayer pattern formation on Au(111) are presented. The irregular monolayer pattern exhibits a 60 A length scale. Formation of the octylsilane monolayer relaxes the Au(111) 23 x square root3 surface reconstruction and ejects surface Au atoms. Au adatom diffusion epitaxially extends the Au(111) crystal lattice via step edge growth and island formation. The chemisorbed monolayer covers the entire Au surface at saturation exposure. Theoretical and experimental data suggest the presence of two octylsilane molecular adsorption phases: an atop site yielding a pentacoordinate Si atom and a surface vacancy site yielding a tetracoordinate Si atom. Theoretical simulations investigating two-phase monolayer self-assembly dynamics on a solid surface suggest pattern formation results from strain-induced spinodal decomposition of the two adsorption phases. Collectively, the theoretical and experimental data indicate octylsilane monolayer pattern formation is a result of interfacial Au-Si interactions and the alkyl chains play a negligible role in the monolayer pattern formation mechanism.
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