Electron irradiation induced reduction of the permittivity in chalcogenide glass (As2S3) thin film

We investigate the effect of electron beam irradiation on the dielectric properties of As2S3 Chalcogenide glass. By means of low-loss Electron Energy Loss Spectroscopy, we derive the permittivity function, its dispersive relation, and calculate the refractive index and absorption coefficients under the constant permeability approximation. The measured and calculated results show, to the best of our knowledge, a heretofore unseen phenomenon: the reduction in the permittivity of <40%, and consequently a modification of the refractive index follows, reducing it by 20%, hence suggesting a significant change on the optical properties of the material. The plausible physical phenomena leading to these observations are discussed in terms of the homopolar and heteropolar bond dynamics under high energy absorption.Comment: 22 pages, 7 figures, manuscript in preparation to send to Physical Review

Unusual activity of rationally designed cobalt phosphide/oxide heterostructure composite for hydrogen production in alkaline medium.

Design and development of an efficient, nonprecious catalyst with structural features and functionality necessary for driving the hydrogen evolution reaction (HER) in an alkaline medium remain a formidable challenge. At the root of the functional limitation is the inability to tune the active catalytic sites while overcoming the poor reaction kinetics observed under basic conditions. Herein, we report a facile approach to enable the selective design of an electrochemically efficient cobalt phosphide oxide composite catalyst on carbon cloth (CoP-CoxOy/CC), with good activity and durability toward HER in alkaline medium (η10= -43 mV). Theoretical studies revealed that the redistribution of electrons at laterally dispersed Co phosphide/oxide interfaces gives rise to a synergistic effect in the heterostructured composite, by which various Co oxide phases initiate the dissociation of the alkaline water molecule. Meanwhile, the highly active CoP further facilitates the adsorption-desorption process of water electrolysis, leading to extremely high HER activity

Oxidant-Dependent Thermoelectric Properties of Undoped ZnO Films by Atomic Layer Deposition

Extraordinary oxidant-dependent changes in the thermoelectric properties of undoped ZnO thin films deposited by atomic layer deposition (ALD) have been observed. Specifically, deionized water and ozone oxidants are used in the growth of ZnO by ALD using diethylzinc as a zinc precursor. No substitutional atoms have been added to the ZnO films. By using ozone as an oxidant instead of water, a thermoelectric power factor (σS²) of 5.76 × 10^–4 W m^–1 K^–2 is obtained at 705 K for undoped ZnO films. In contrast, the maximum power factor for the water-based ZnO film is only 2.89 × 10^–4 W m^–1 K^–2 at 746 K. Materials analysis results indicate that the oxygen vacancy levels in the water- and ozone-grown ZnO films are essentially the same, but the difference comes from Zn-related defects present in the ZnO films. The data suggest that the strong oxidant effect on thermoelectric performance can be explained by a mechanism involving point defect-induced differences in carrier concentration between these two oxides and a self-compensation effect in water-based ZnO due to the competitive formations of both oxygen and zinc vacancies. This strong oxidant effect on the thermoelectric properties of undoped ZnO films provides a pathway to improve the thermoelectric performance of this important material

Design of a core\u2013shell Pt\u2013SiO2 catalyst in a reverse microemulsion system: Distinctive kinetics on CO oxidation at low temperature

The mechanism of formation of Pt@SiO2 as a model of core\u2013shell nanoparticles via water-in-oil reverse microemulsions was studied in detail. By controlling the time of growth of Pt precursors, Pt(OH)x, after hydrolysis in NH3 aq. before adding SiO2 precursor (TEOS), Pt nanoparticles with a narrow size distribution were produced, from ultrafine metal nanoparticles (<1 nm) to 6 nm nanocrystals. Separately, the thickness of SiO2 was controllably synthesized from 1 to 15 nm to yield different Pt@SiO2 materials. The Pt@SiO2 core\u2013shell catalysts exhibited a higher rate of CO oxidation by one order of magnitude with a positive order regarding CO pressure. The SiO2 shell did not perturb the Pt chemical nature, but it provided different coverage of CO in steady-state CO oxidation

A process to enhance the specific surface area and capacitance of hydrothermally reduced graphene oxide

The impact of post-synthesis processing in reduced graphene oxide materials for supercapacitor electrodes has been analyzed. A comparative study of vacuum, freeze and critical point drying was carried out for hydrothermally reduced graphene oxide demonstrating that the optimization of the specific surface area and preservation of the porous network are critical to maximize its supercapacitance performance. As described below, using a supercritical fluid as the drying medium, unprecedented values of the specific surface area (364 m2 g-1) and supercapacitance (441 F g-1) for this class of materials have been achieved

CO \u3c inf\u3e 2 conversion: The potential of porous-organic polymers (POPs) for catalytic CO \u3c inf\u3e 2 -epoxide insertion

© The Royal Society of Chemistry. Novel porous organic polymers (POPs) have been synthesized using functionalized Cr and Co-salen complexes as molecular building blocks. The integration of metalosalen catalysts into the porous polymer backbone permits the successful utilization of the resultant functionalized material as a solid-state catalyst for CO2-epoxide cycloaddition reactions with excellent catalytic performance under mild conditions of temperature and pressure. The catalysts proved to be fully recyclable and robust, thus showing the potential of POPs as smart functional materials for the heterogenization of key catalytic elements

Surface Passivation of MoO₃ Nanorods by Atomic Layer Deposition toward High Rate Durable Li Ion Battery Anodes

We demonstrate an effective strategy to overcome the degradation of MoO₃ nanorod anodes in lithium (Li) ion batteries at high-rate cycling. This is achieved by conformal nanoscale surface passivation of the MoO₃ nanorods by HfO₂ using atomic layer deposition (ALD). At high current density such as 1500 mA/g, the specific capacity of HfO₂-coated MoO₃ electrodes is 68% higher than that of bare MoO₃ electrodes after 50 charge/discharge cycles. After 50 charge/discharge cycles, HfO₂-coated MoO₃ electrodes exhibited specific capacity of 657 mAh/g; on the other hand, bare MoO₃ showed only 460 mAh/g. Furthermore, we observed that HfO₂-coated MoO₃ electrodes tend to stabilize faster than bare MoO₃ electrodes because nanoscale HfO₂ layer prevents structural degradation of MoO₃ nanorods. Additionally, the growth temperature of MoO₃ nanorods and the effect of HfO₂ layer thickness was studied and found to be important parameters for optimum battery performance. The growth temperature defines the microstructural features and HfO₂ layer thickness defines the diffusion coefficient of Li-ions through the passivation layer to the active material. Furthermore, ex situ high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction were carried out to explain the capacity retention mechanism after HfO₂ coating

Visualizing Bulk-to-Surface Carrier Diffusion via Band-bending of Solar Cell Materials by 4D Electron Microscopy at Low Applied Potential

Utilizing four-dimensional scanning ultrafast electron microscopy (4D-SUEM) is a powerful tool to monitor charge dynamics at material surfaces and interfaces especially for the application in renewable energy field. Herein, we uncover unique physical features for 4D-SUEM upon reducing the acceleration of probed primary electrons to 1 keV, for wide range of materials including various single crystals, thin films and quantum dots upon the presence of oxidized and neat surfaces. Working at 1 keV helps to uncover the migration of photogenerated carriers originating from both sub-surface and bulk layers, under the influence of the carriers scattering and the band-bending phenomena. This approach provides a new avenue for the spatial and temporal access to the surface exclusive dynamics in renewable energy materials to unlock their interfacial behaviors at the nanoscale level