Biomedical subjects

Ivan Stich

Publications and source records attributed to Ivan Stich.

4 recordsLinked to original sources

PubMed2005

Nanomanipulation using only mechanical energy.

We present the first computational study targeting the nanomanipulation capability of dynamic surface force microscopy. Using a very simple but challenging model, an antisite defect on a III-V(110) surface, we show how the defect can be manipulated in both the attractive and the repulsive modes and identify the role of the tip-sample interaction: either lowering the barriers or pushing the system over a high stress state using exclusively the mechanical energy stored in the oscillating cantilever. Our study also sheds light on other key issues, such as chemical resolution, explaining why vacancies are the only defects imaged in topography, and dissipation contrast formation, identifying a physical mechanism to explain the intriguing small shift between topographical and damping images.

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PubMed2005

Electronic origin of disorder and diffusion at a molecule-metal interface: self-assembled monolayers of CH3S on Cu111.

The relationship between structure, interfacial electrostatics, bonding, and dynamics of organic molecules on metals is studied using a self-assembled monolayer of methylthiolate, CH3S, on Cu(111). The flat adsorption energy landscape of CH(3)S/Cu(111) results from metal-to-molecule charge redistribution which allows for a high mobility of CH3S. This contributes a nonuniform diffuse background to Bragg scattering, which needs to be considered in diffraction analyses. Ramifications on the interpretation of experimental data and the potential impact on the design of metal-organic interfaces are discussed.

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PubMed2004

Detaching thiolates from copper and gold clusters: which bonds to break?

The interaction of alkanethiolates with small coinage metal clusters of copper and gold was studied based on density functional theory with a focus on the metal-thiolate junction. Calculation of fragmentation energies indicate that for Cu(n)-thiolate (n = 1,3,5,7, and 9) there is a progressive lowering in energy for the fragmentation of the S-C bond in the thiolate from a value of 2.9 eV for n = 1 to 1.4 eV for n = 9. The detailed electronic origins of this specific weakening are attributed to a polarization of electron density in the S-C bond as induced by bonding with the Cu(n) cluster. For the gold analogues, this effect is not observed and fragmentation at the S-C bond experiences only a slight 10% destabilization as n increases from 3 to 9. The relativistic origin of this difference between Cu and Au is discussed, and an analysis of bonding considerations is presented.

Journal Article↗

PubMed2003

Covalent and reversible short-range electrostatic imaging in noncontact atomic force microscopy.

We present a computational study of atomic-scale image formation in noncontact atomic force microscopy on metallic surfaces. We find two imaging scenarios: (1). atomic resolution arising due to very strong covalent tip-sample interaction exhibiting striking similarity with the imaging mechanism found on semiconductor surfaces, and (2). a completely new mechanism, reversible short-range electrostatic imaging, arising due to subtle charge-transfer interactions. Contrary to the strong covalent-bond imaging, the newly identified mechanism causes only negligible surface perturbation and can account for results recently observed experimentally.

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