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Molybdenum disulfide (MoS2) is a semiconducting transition metal dichalcogenide that is known to be a catalyst for both the hydrogen evolution reaction (HER) as well as for hydro-desulfurization (HDS) of sulfur-rich hydrocarbon fuels. Specifically, the edges of MoS2 nanostructures are known to be far more catalytically active as compared to unmodified basal planes. However, in the absence of the precise details of the geometric and electronic structure of the active catalytic sites, a rational means of modulating edge reactivity remain to be developed. Here we demonstrate using first-principles calculations, X-ray absorption spectroscopy, as well as scanning transmission X-ray microscopy (STXM) imaging that edge corrugations yield distinctive spectroscopic signatures corresponding to increased localization of hybrid Mo 4d states. Independent spectroscopic signatures of such edge states are identified at both the S L2,3 and S K-edges with distinctive spatial localization of such states observed in S L2,3-edge STXM imaging. The presence of such low-energy hybrid states at the edge of the conduction band is seen to correlate with substantially enhanced electrocatalytic activity in terms of a lower Tafel slope and higher exchange current density. These results elucidate the nature of the edge electronic structure and provide a clear framework for its rational manipulation to enhance catalytic activity.

Here, we present a simple platform for the use of the enhanced emission of 16-mercaptohexadecanoic acid (16-MHA) capped CdSe quantum dots (QDs) as a probe for ultrasensifive copper(II) detection. In this study, the photoluminescence (PL) of the QDs was first enhanced by Ag nanoprisms which were self-assembled on Si surfaces and then further increased by photobrightening. Using this approach, the control and different analytes could be readily probed all on a single platform using fluorescence microscopy. The enhanced PL intensity of CdSe QDs was selectively quenched in the presence of [Cu.sup.2+], accompanied by the emergence of a new red-shifted luminescence 'band. The quenching mechanism was found to be due to a cation exchange mechanism as confirmed by X-ray photoelectron spectroscopy (XPS) measurements. Herein, we have demonstrated that this simple methodology can offer a rapid and reliable detection of [Cu.sup.2+] with a detection limit as low as 5 nM and a dynamic range up to 100 [micro]M in a fixed fast reaction time of 5 min. The potential applications of this technique were tested in two ways, for mixed-ion solutions and in physiological fluids, and both experiments exhibited good selectivity toward [Cu.sup.2+]. 10.1021/ac902985p

Poly(methyl methacrylate) (PMMA) thin films (~150 nm) on silicon were bombarded with [SF.sub.5.sup.+] polyatomic primary ion projectiles at -75 [degrees]C, 25 [degrees]C, and 125 [degrees]C. The crater bottoms were then characterized using a combination of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS). AFM results indicated increased sputter-induced topography formation in the order of -75 [degrees]C < 125 [degrees]C < 25 [degrees]C, consistent with earlier SIMS depth profile results which illustrated optimum depth profile characteristics at low temperatures and less favorable characteristics at room temperature. (1) XPS results indicated that there was a significant amount of C remaining at the crater bottom at 25 [degrees]C, suggesting that there is a large amount of organic material remaining despite the loss in characteristic PMMA secondary ion signal in the SIMS depth profile. Specifically, C/Si ratios increased in the following order: -75 [degrees]C < 125 [degrees]C < 25 [degrees]C, consistent with the trend in topography observed in the AFM results. High-resolution C(ls) spectra of the PMMA film indicated a decrease in the O C=O component with sputtering at both -75 [degrees]C and 25 [degrees]C. However, there was very little change in the C(ls) spectra in samples sputtered at 125 [degrees]C. This was determined to be a result of ion-induced depolymerization which is expected to occur at higher temperatures in PMMA. Residual gas analysis (RGA) gave results that were consistent with this hypothesis, showing increased amounts of PMMA monomer at higher temperatures. Principle components analysis (PCA) of SIMS spectra showed increased PMMA secondary ion intensifies coupled with increased O signal in PMMA sputtered at 125 [degrees]C. Conversely, SIMS spectra acquired in the sputtered PMMA at -75 [degrees]C, and to a smaller degree at 25 [degrees]C, showed increased C signals, decreased O intensifies, and the appearance of peaks indicative of polycyclic aromatic hydrocarbons, all consistent with increased chemical damage. Overall, these results indicate that while there is increased damage occurring at -75 [degrees]C, there is still a significant improvement in the depth profile characteristics. It is concluded that the enhancement in low-temperature depth profiles in PMMA results mainly from the changes in the physical properties of the PMMA at low temperatures, yielding a significant reduction in sputter-induced topgraphy.

A benchtop method for the synthesis and transfer of materials to and from polymers (STOMP), which finds applications in constructing sensors electronic devices and optical material and layered photonic gap structures is presented. The features fabricated by STOMP are found to be strongly dependent on the structure of the polymer stamp and its mechanical properties, the compression of the metal films and the respective interfacial forces between the stamp films and substrate.

Photolithographically generated patterns are created on immobilized CdSe QD thin films by fine-tuning their optical properties postsynthetically. The optically modified QDs have shown enhanced selectivity for binding of different ligand, which has helped in preparing optically reconfigurable surfaces for display and sensing applications.

Solution chemistry methods are used for preparing bimetallic CuPt alloy nanoparticle catalysts with controllable sized and shapes. The mixed-metal nanoparticles have displayed excellent catalytic properties for CO oxidation, with light-off temperatures that are nearly 200 K below those of conventional supported Pt catalysts.