Biomedical subjects

S Alex Kandel

Publications and source records attributed to S Alex Kandel.

6 recordsLinked to original sources

PubMed2006

Structural rearrangement of c(70) monolayers induced by octanethiol adsorption.

Mixed monolayers of C70 and octanethiol are prepared on Au(111) by a sequential adsorption method. A partial C70 monolayer is first formed and characterized, followed by the vapor deposition of octanethiol. This results in a well-ordered alkanethiol film where single C70 molecules and small molecular clusters are located at domain boundaries and in disordered regions. Substrate step defects have a large influence on the spatial distribution of C70; adjacent to a substrate defect, C70 binds preferentially on the upper terrace and is depleted on the lower terrace. We explain these observations as resulting from the kinetics of alkanethiol monolayer formation, and we present a simple model for the evolution of surface structure in the C70/octanethiol system.

Adsorption↗

PubMed2006

Collision-induced annealing of octanethiol self-assembled monolayers by high-kinetic-energy xenon atoms.

Collisions with high-energy xenon atoms (1.3 eV) induce structural changes in octanethiol self-assembled monolayers on Au(111). These changes are characterized at the molecular scale using an in situ scanning tunneling microscope. Gas-surface collisions induce three types of structural transformations: domain boundary annealing, vacancy island diffusion, and phase changes. Collision-induced changes that occur tend to increase order and create more stable structures on the surface. We propose a mechanism where monolayer transformations are driven by large amounts of vibrational energy localized in the alkanethiol molecules. Because we monitor incremental changes over small regions of the surface, we can obtain structural information about octanethiol monolayers that cannot be observed directly in scanning tunneling microscopy images.

Journal Article↗

PubMed2006

Observation of single dinuclear metal-complex molecules using scanning tunneling microscopy.

We report a scanning tunneling microscopy (STM) investigation of a dinuclear organometallic molecule, trans-[Cl(dppe)2Ru(C[triple bond]C)6Ru(dppe)2Cl] (Ru2), absorbed on a Au(111) surface; this molecule is a potential candidate for use in molecular quantum-dot cellular automata (QCA) devices. Isolated Ru2 molecules were observed under ultra-high-vacuum conditions. Submolecular structure was clearly discernible in the STM images, with a bright feature corresponding to each of the two Ru-ligand complexes within the Ru2 molecule. Rotation and translation of the Ru2 molecules were observed to be induced by the STM tip under some tunneling conditions.

Journal Article↗

PubMed2006

Structural changes of an octanethiol monolayer via hyperthermal rare-gas collisions.

In situ scanning tunneling microscopy is used to measure the effect of hyperthermal rare-gas bombardment on octanethiol self-assembled monolayers. Close-packed monolayers remain largely unchanged, even after repeated collisions with 0.4 eV argon and 1.3 eV xenon atoms. In contrast, gas-surface collisions do induce structural changes in the octanethiol film near defects, domain boundaries, and disordered regions, with relatively larger changes observed for xenon-atom bombardment.

Journal Article↗

PubMed2005

Ambient-pressure vapor deposition of octanethiol self-assembled monolayers.

Scanning tunneling microscopy was used to characterize self-assembled monolayers (SAMs) of octanethiol on Au(111), created using vapor deposition at elevated temperatures and ambient pressure. Monolayers contained large, close-packed ( radical3 x radical3)R30 degrees domains with sizes considerably larger than those typically formed from conventional solution-phase preparation and with crystallographically straight domain boundaries. New striped surface phases were also observed, including a 13 x radical3 phase with a density that was 69% of the close-packed density; these striped phases appeared topographically higher in STM images than close-packed monolayers.

Letter↗

PubMed2003

Substrate-mediated interactions and intermolecular forces between molecules adsorbed on surfaces.

Adsorbate interactions and reactions on metal surfaces have been investigated using scanning tunneling microscopy. The manners in which adsorbates perturb the surface electronic structure in their vicinity are discussed. The effects these perturbations have on other molecules are shown to be important in overlayer growth. Interactions of molecules with surface steps are addressed, and each molecule's electron affinity is shown to dictate its adsorption sites at step edges. Standing waves emanating from steps are demonstrated to effect transient molecular adsorption up to 40 A away from the step edge. Halobenzene derivatives are used to demonstrate how the surface is important in aligning reactive intermediates.

Adsorption↗