Chao-Cheng Kaun

MoSe2 nanosheets and their graphene hybrids: synthesis, characterization and hydrogen evolution reaction studies

MoSe2 nanosheets and MoSe2/graphene hybrids have been prepared by a facile hydrothermal method. The number of layers of the MoSe2 nanosheets is typically <10 as confirmed directly by transmission electron microscopy and indirectly by a red shift of the characteristic A1g Raman peak. The hydrogen evolution reaction (HER) studies show that the onset potentials of MoSe2 and MoSe2/RGO hybrids are only ∼0.15 V vs. RHE and ∼0.05 V vs. RHE, respectively, about 20–30 mV lower than those of MoS2 and its graphene hybrids reported previously. Density functional theory calculations reveal that the Gibbs free energy for atomic hydrogen adsorption (ΔG0H) on MoSe2 edges is closer to thermoneutral than that on MoS2, with an H coverage of about 75% on the edge under operating conditions, which is also higher than that of MoS2 reported in the literature. The consistency between the experimental and computational results indicates that MoSe2 nanosheets have potential to be a better HER catalyst than their MoS2 counterpart.

Effect of electrode orientations on charge transport in alkanedithiol single-molecule junctions.

Using first-principles calculations based on the density functional theory and the nonequilibrium Greens functions approach, we study the charge transport in Au-alkanedithiol-Au single-molecule junctions with different electrode orientations and molecular lengths. We attribute the recently measured high-/low-conductance in these heterostructures to two distinct electrode orientations, [100] and [111], which can control the electrode-molecule coupling as well as the tunneling strength by way of diverse band structures. Our detailed analysis on the transmission spectra suggests that even a single alkanedithiol junction can serve as a double quantum-dot system to yield tunable quantum interference.

Digitized Charge Transfer Magnitude Determined by Metal–Organic Coordination Number

Well-ordered metal-organic nanostructures of Fe-PTCDA (perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride) chains and networks are grown on a Au(111) surface. These structures are investigated by high-resolution scanning tunneling microscopy. Digitized frontier orbital shifts are followed in scanning tunneling spectroscopy. By comparing the frontier energies with the molecular coordination environments, we conclude that the specific coordination affects the magnitude of charge transfer onto each PTCDA in the Fe-PTCDA hybridization system. A basic model is derived, which captures the essential underlying physics and correlates the observed energetic shift of the frontier orbital with the charge transfer.

Metallic nanograins: spatially nonuniform pairing induced by quantum confinement

It is well known that the formation of discrete electron levels strongly influences the pairing in metallic nanograins. Here, we focus on another effect of quantum confinement in superconducting grains that was not studied previously, i.e., spatially nonuniform pairing. This effect is very significant when single-electron levels form bunches and/or a kind of shell structure. We find that, in highly symmetric grains, the order parameter can exhibit variations with position by an order of magnitude. Nonuniform pairing is closely related to a quantum-confinement-induced modification of the pairing-interaction matrix elements and size-dependent pinning of the chemical potential to groups of degenerate or nearly degenerate levels. For illustrative purposes, we consider spherical metallic nanograins and also rectangular shapes. We show that the relevant matrix elements are, as a rule, enhanced in the presence of quantum confinement, which favors spatial variations of the order parameter, compensating the corresponding energy cost. The size-dependent pinning of the chemical potential further increases the spatial variation of the pair condensate. The role of nonuniform pairing is smaller in less symmetric confining geometries and/or in the presence of disorder. However, it always remains of importance when the energy spacing between discrete electron levels

Spin-Dependent Molecule Symmetry at a Pentacene–Co Spinterface

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Mapping polarization induced surface band bending on the Rashba semiconductor BiTeI

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Ultra-small metallic grains: effect of statistical fluctuations of the chemical potential on superconducting correlations and vice versa.

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Engineering the interlayer exchange coupling in magnetic trilayers.

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Spin filtering of a termination-controlled LSMO/Alq3 heterojunction for an organic spin valve

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Conductance Switching in Single-Peptide Molecules through Interferer Binding

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