Scientific Publications 2004
2004. "Synthesis and Electrochemical Properties of Single-Crystal V₂O Nanorod Arrays by Template-Based Electrodeposition." Journal of Physical Chemistry B 108(28):9795-9800. Abstract This paper reports a study on template-growth and electrochemical properties of single-crystal vanadium pentoxide (V₂O₅) nanorod arrays from VOSO₄ aqueous solution using electrochemical deposition. Uniformly sized vanadium oxide nanorods with a length of about 10 ím with diameters ranging from 100 to 200 nm were grown over a large area with near unidirectional alignment. These nanorods have single-crystalline structure with a growth direction of . Electrochemical property analysis indicates that nanorod array electrodes have significantly higher current density and energy storage density than sol-gel-derived V₂O₅ films.
2004. "Probing Nanosecond Protein Motions of Calmodulin by Single-Molecule Fluorescence Anisotropy." Applied Physics Letters 85(12):2420-2422. Abstract Proteins operate as part of molecular networks that perform specific cellular functions. To understand the complex molecular network, it is important to study individual processes within the network such as protein motions and protein-protein interactions.
2004. "Probing Nanosecond Protein Motions of Calmodulin by Single-Molecule Fluorescence Anisotropy." Applied Physics Letters 85(12):2420-2422. Abstract Proteins operate as part of molecular networks that perform specific cellular functions. To understand the complex moleucular network, it is important to study individual processes within the network such as protein motions and protein-protein interactions.
2004. "Single-Molecule Study of Protein-Protein Interaction Dynamics in a Cell Signaling System." Journal of Physical Chemistry B 108(2):737-744. Abstract We report a combined single-molecule fluorescence and molecular dynamics (MD) simulation study of protein-protein interactions in a GTP-binding intracellular signaling protein Cdc42 in complex with a downstream effector protein WASP. A 13- kDa WASP fragment which binds only the activated GTP-loaded Cdc42 was labeled with a novel solvatochromic dye and used to probe hydrophobic interactions significant to Cdc42/WASP recognition. Our single-molecule fluorescence measurements have shown conformational fluctuations of the protein complex and suggested multiple conformational states at a wide range of time scales might be involved in protein interaction dynamics. Single-molecule experiments have revealed the dynamic disorder or protein-protein interactions within the Cdc42/WASP complex, which may be important for regulating downstream signaling events.
2004. "Temperature-Dependent Yield of Frenkel Pairs Generated by Valence Excitation in NaCl." Physical Review. B, Condensed Matter 69:155102. Abstract The dynamics of the formation of self-trapped excitons (STEs) and Frenkel pairs upon band-gap excitation have been studied in NaC1 by femtosecond time-resolved spectroscopy at temperatures ranging from 6 to 330K. We found that the primary yield of Frenkel pairs was governed by the process of exciton relaxation that terminated within 10 ps of excitation for all temperatures studied. The yield increases with temperature, and is anticorrelated with the yield of triplet STEs, showing a strong effect of temperature on branching during exciton relaxation. We discuss the mechanism of the temperature-dependent branching of excitons based on the present results and knowledge accumulated from studies of other crystals.
2004. "Ion-Beam Synthesis of Epitaxial Au Nanocrystals in MgO." Journal of Materials Research 19(5):1311-1314. Abstract The formation of Au nanoclusters in MgO using ion implantation and subsequent annealing has been investigated. Approximately 1200 and 1400 Au₂⁺ ions/nm₂ were implanted in MgO(100) substrates at 300 and 975 K, respectively. Subsequent annealing in air for 10 hours at 1275 K promoted the formation of Au nanostructures in MgO. The sample implanted at 300 K showed severe radiation damage. In addition, two-dimensional platelet-like structures with possible composition of Au and MgO were formed during implantation in the sample that was implanted at 300 K. In contrast, Au implantation at 975 K promoted the nucleation of Au nanostructures during implantation. Subsequent annealing of both samples show three-dimensional clusters in MgO. However, the 975 K implanted sample shows clean high quality single crystal Au clusters that have an epitaxial relationship to MgO(100).
2004. "Ab initio study of AmCl+: f–f spectroscopy and chemical binding." Journal of Chemical Physics 121(12):5661-5675. Abstract A valence full configuration interaction study with a polarized double-ζ quality basis set has been carried out for the lowest 49 electronic states of AmCl+. The calculations use a pseudopotential treatment for the core electrons and incorporate a one-electron spin–orbit interaction operator. Electrons in the valence s, p, d, and f subshells were included in the active space. The resulting electronic potential energy curves are largely repulsive. The chemical bonding is ionic in character with negligible participation of 5f electrons. The molecular f – f spectroscopy of AmCl+ arises essentially from an in situ Am2+ core with states slightly redshifted by the presence of chloride ion. Am+ + Cl asymptotes which give rise to the few attractive potential energy curves can be predicted by analysis of the f – f spectroscopy of isolated Am+ and Am2+. The attractive curves have substantial binding energies, on the order of 75–80 kcal/mol, and are noticeably lower than recent indirect measurements on the isovalent EuCl+. An independent empirical correlation supports the predicted reduction in AmCl+ binding energy. The energies of the repulsive curves are strongly dependent on the selection of the underlying atomic orbitals while the energies of the attractive curves do not display this sensitivity. The calculations were carried out using our recently developed parallel spin–orbit configuration interaction software.
2004. "Epitaxial Growth and Properties of Cobalt-doped ZnO on α-Al₂O₃ Single-Crystal Substrates." Physical Review. B, Condensed Matter 70(5):054424. Abstract Co-doped ZnO (CoxZn₁-xO) is of potential interest for spintronics due to the prediction of room-temperature ferromagnetism. We have grown epitaxial CoxZn₁-xO films on Al₂O₃(012) substrates by metalorganic chemical vapor deposition using a liquid precursor delivery system. High concentrations of Co (x < 0.35) can be uniformly incorporated into the film without phase segregation. Co is found to be in the ⁺² oxidation state, independent of x. This material can be grown n type by the deliberate incorporation of oxygen vacancies, but not by inclusion of ~1 at. % Al. Semiconducting films remain ferromagnetic up to 350 K. In contrast films without oxygen vacancies are insulating and nonmagnetic, suggesting that exchange interaction is mediated by itinerant carriers. The saturation and remanent magnetization on a per Co basis was very small (< 0.1 B/Co), even in the best films. The dependence of saturation magnetization, as measured by optical magnetic circular dichroism, on magnetic field and temperature, agrees with the theoretical Brillouin function, demonstrating that the majority of the Co(II) ions behave as magnetically isolated S = 3/2 spins.