Jinlong Yin

Enhancement of the Hydrogen Evolution Reaction from Ni-MoS2 Hybrid Nanoclusters

This report focuses on a novel strategy for the preparation of transition metal–MoS2 hybrid nanoclusters based on a one-step, dual-target magnetron sputtering, and gas condensation process demonstrated for Ni-MoS2. Aberration-corrected STEM images coupled with EDX analysis confirms the presence of Ni and MoS2 in the hybrid nanoclusters (average diameter = 5.0 nm, Mo:S ratio = 1:1.8 ± 0.1). The Ni-MoS2 nanoclusters display a 100 mV shift in the hydrogen evolution reaction (HER) onset potential and an almost 3-fold increase in exchange current density compared with the undoped MoS2 nanoclusters, the latter effect in agreement with reported DFT calculations. This activity is only reached after air exposure of the Ni-MoS2 hybrid nanoclusters, suggested by XPS measurements to originate from a Ni dopant atoms oxidation state conversion from metallic to 2+ characteristic of the NiO species active to the HER. Anodic stripping voltammetry (ASV) experiments on the Ni-MoS2 hybrid nanoclusters confirm the presence of Ni-doped edge sites and reveal distinctive electrochemical features associated with both doped Mo-edge and doped S-edge sites which correlate with both their thermodynamic stability and relative abundance.

Layer by layer removal of Au atoms from passivated Au(111) surfaces using the scanning tunneling microscope: Nanoscale “paint stripping”

Layer by layer removal of gold atoms from the (111) surface of gold has been performed using the scanning tunneling microscope. The process is made possible by a chemisorbed self-assembled monolayer (SAM) of dodecanethiol molecules on the surface, which gives rise to a reduced bonding strength between the top two layers of gold atoms. The gold atoms and associated adsorbed molecules are peeled off and displaced laterally by the STM tip, and the size of the modified area (down to ∼10×10 nm) is more or less determined by the scan size.

Liquid phase deposition of supramolecular monolayers of zinc porphyrin molecules on graphite

Molecular monolayers of zinc porphyrins deposited from liquid sources on graphite substrates have been characterized using atomic force microscopy. The morphology of the molecular layers shows a strong dependence on both the structure of the individual molecules and the properties of the solvent used for the deposition. By controlling the concentration of the starting solution and the amount of liquid applied to the graphite surface, single layer high molecular weight films have been successfully grown with a variety of zinc porphyrin molecules. The nucleation and growth, similar to those commonly observed in vapour deposition, have been found to depend on the strength of the intermolecular interaction as well as the level of interaction between the solvent molecules and the substrate.

Performance of Preformed Au/Cu Nanoclusters Deposited on MgO Powders in the Catalytic Reduction of 4‐Nitrophenol in Solution

The deposition of preformed nanocluster beams onto suitable supports represents a new paradigm for the precise preparation of heterogeneous catalysts. The performance of the new materials must be validated in model catalytic reactions. It is shown that gold/copper (Au/Cu) nanoalloy clusters (nanoparticles) of variable composition, created by sputtering and gas phase condensation before deposition onto magnesium oxide powders, are highly active for the catalytic reduction of 4-nitrophenol in solution at room temperature. Au/Cu bimetallic clusters offer decreased catalyst cost compared with pure Au and the prospect of beneficial synergistic effects. Energy-dispersive X-ray spectroscopy coupled with aberration-corrected scanning transmission electron microscopy imaging confirms that the Au/Cu bimetallic clusters have an alloy structure with Au and Cu atoms randomly located. Reaction rate analysis shows that catalysts with approximately equal amounts of Au and Cu are much more active than Au-rich or Cu-rich clusters. Thus, the interplay between the Au and Cu atoms at the cluster surface appears to enhance the catalytic activity substantially, consistent with model density functional theory calculations of molecular binding energies. Moreover, the physically deposited clusters with Au/Cu ratio close to 1 show a 25-fold higher activity than an Au/Cu reference sample made by chemical impregnation.

Excited states of surfaces and nanostructures in the VUV (Invited Paper)

This paper reports on progress in the VUV spectroscopy of surfaces and nanostructures, as facilitated by two experimental innovations. In Scanning Probe Energy Loss Spectroscopy (SPELS) electrons backscattered from the tipsurface junction are detected when an STM tip is operated in field emission mode. Energy loss features in the range 1300 eV have been observed, corresponding to optical absorption spectra from the IR through to the VUV and X-ray regions. Recent data suggests in addition that SPELS can record local secondary electron emission spectra. SPELS offers spatial resolution on the 10 nm scale. High Harmonic Generation (HHG) of VUV light provides a complementary probe of the excited states of surfaces and nanostructures, offering a temporal resolution of order 100 fs or below. The utility of the High Harmonic source is demonstrated by an investigation of the visible fluorescence from thin films of passivated CdSe nanocrystals, as a function of excitation energy, decay time and temperature, which thus emerge as new scintillators for VUV applications.