Black phosphorus (BP) has recently attracted intense research interest due to its unique thickness-dependent and anisotropic electronic and photonic properties, and has shown promising potential in nanophotonic, nanoelectronics and energy storage applications. However, the application of BP in practical devices is hindered by its high commercial cost. To further reduce the cost and accelerate the development of BP, a highly efficient preparation strategy for low-cost BP must be found. Herein, we report such a method via a modified chemical vapor transport (CVT) method by replacing high-purity red phosphorus (RP) with a low-purity precursor counterpart. We show that this method can drastically reduce the cost of manufacturing by several orders of magnitude. Furthermore, the BP produced using low-cost RP shows nearly the same crystal quality, high purity, local chemical structure, and electronic properties, compared with those of the high-cost BP prepared by the traditional CVT method. Most importantly, exfoliated phosphorene nanosheets prepared from the low-cost BP exhibit promising hydrogen evolution reaction (HER) activity. Owing to the high quality and high conversion efficiency, the low-cost BP holds promising potential in future scientific research and industrial applications.

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Phosphorene, single- or few-layered black phosphorus, has been rediscovered as a promising two-dimensional material owing to its unique optical, thermal, and electrical properties with potential applications in optoelectronics, nanoelectronics, and energy storage. However, rapid degradation under ambient condition highly limits the practical applications of phosphorene. Solving the degradation problem demands an understanding of the oxidization process. We, for the first time, apply synchrotron-based X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure (XANES), and scanning transmission X-ray microscopy (STXM) for the nanoscale chemical imaging of phosphorene degradation. Through these methods, we have identified chemical details of the morphological effect and clarified thickness and proximity effects, which control the oxidization process. Furthermore, the entire oxidization process of phosphorene has also been studied by in situ XPS and XANES, showing the step-by-step oxidization process under the ambient condition. Theoretical calculations at the density functional theory level support experimental findings. This detailed study provides a better understanding of phosphorene degradation and is valuable for the development of phosphorene-based materials.

Vanadium dioxide (VO2) thin films were deposited on silicon (100), quartz, and r-cut sapphire substrates by DC magnetron sputtering at 650 degrees C. The thin films were characterized by Raman spectroscopy and imaging, scanning electron microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDS), and Transmission Electron Microscopy (TEM). The optical transmittance and hence the insulator-to-metal transition (IMT) and metal-to-insulator transition (MIT) were characterized as a function of temperature. The effects of substrate material on VO2 thin film's growth, microstructure, stoichiometry and optical properties were investigated. The results show that the as-deposited VO2 thin films on Si, quartz, and sapphire all show a near-zero IR transmission in switched metallic state; especially VO2 thin film grown on sapphire shows superior IMT characteristics compared with previously published works on thin VO2 films, and very close to its bulk single crystal form, which is probably due to the significantly reduced imperfections in the film and the interface, and especially the highly preferred growth with similar paralleled grain orientation of VO2 on sapphire arising from both the high deposition temperature and epitaxial growth. The spectral transmittance of the films on quartz and sapphire substrates was analyzed to extract the optical constants n and k as a function of wavelength. No significant difference between optical properties could be observed for films deposited on quartz and sapphire substrates indicating that the differences in microstructure of these films play a minor role in their optical properties. n and k spectra are, in general, in agreement with previously reported works. The absorption coefficient versus photon energy characteristics indicate that VO2 in the insulating phase possesses a direct bandgap at 2.6 eV and an indirect bandgap of 0.52 eV. Raman imaging was used to map the phase mixture of various regions of the film at micron scale (1.2 mu m x 1.2 mu m) during heating and cooling scans through the IMT and MIT. The dependence of the integrated Raman intensities at 220 cm(-1) and 600 cm(-1) on the temperature shows an excellent correlation with the optical transmittance through the IMT and MIT, both during heating and cooling scans. It is shown that the transformation occurs by the growth of one phase at the expense of the other and, in the IMT/MIT region, both phases coexist. (C) 2020 Elsevier B.V. All rights reserved.

An EUV Stokes polarimeter designed for operation up to 150 eV photon energy has been fabricated and commissioned (with red, green and violet light). The polarimeter consists of two identical 4-mirror optical groups acting as a phase retarder and analyser respectively. Each group is capable of independent azimuthal rotation about the beam without deviating the beam. The mirrors are gold coated and operating at 80 degrees angle of incidence. Such an instrument can determine both the full Stokes vector of the incoming light and the optical constants (polarizance and phase delay) of the optical elements of the polarimeter, which are then translated into the optical constants (n and k) for gold and compared to the literature values. The effects of various misalignment and mis-setting errors are considered.

Ratio of two peaks in X-ray induced vanadium L3M23M45 Auger electron spectra has been used to monitor oxidation state of V2O3 thin film surface followed by vacuum annealing. The V2O3 film was grown with sol-gel method on the Al2O3 (0001) substrate. The O 1s, V 2p core-level X-ray photoelectron spectra and V L3M23M45 Auger electron spectra were measured from the film as function of annealing temperature. Brief exposure of the film to the air turned surface vanadium to 4+ oxidation state. Annealing in UHV at 455 K completely converted vanadium to 3+. The binding energy (BE) difference between O 1s and V 2p(3/2) core-level changed from 14.0 eV to 14.9 eV as annealing temperature increased from room temperature to 455 K. Intensity ratio of the two peaks in V L3M23M45 Auger electron spectra, peak originated from O 2p region to that from V 3d region, changes from 0.91 to 0.63. In combination with measurement from VO2 film, relation between intensity ratio of V L3M23M45 doublet and the oxidation state of vanadium was established by comparison with BE difference between O 1s and V 2p(3/2) core-level. V L3M23M45 Auger electron spectra can be useful tool for scanning Auger microscope (SAM) to get high spatial resolution vanadium ion distribution. A few points to consider for application toward SAM mapping have been discussed.

In this work, VO2 thin films were deposited on Si wafers (onto (100) surface) by DC magnetron sputtering under different cathode bias voltages. The effects of substrate biasing on the structural and optical properties were investigated. The results show that the metal-insulator transition (MIT) temperature of VO2 thin films can be increased up to 14 K by applying a cathode bias voltage, compared to deposition conditions without any bias. The decrease in the transition efficiency and increase in the transition temperature are attributed to the enlarged grain size, increased defects, and the residual stress in the VO2 thin films induced by biasing. The optical transmittance measurements for different thickness films indicate an attenuation coefficient of 3.1 × 107 m-1 at 2000 nm or an extinction coefficient of 4.9 in the metal phase. The optical transmittance vs wavelength characteristics point to an indirect bandgap of 0.6 ± 0.5 eV and significant scattering in the bulk and/or at the interface.

Vanadium dioxide (VO2) thin films of different thickness have been deposited on Si substrates by using DC magnetron sputtering. The effects of substrate pre-treatment by means of seeding (spin coating and ultrasonic bathing) and biasing on the structure and optical properties were investigated. Seeding results in a smaller grain size in the oxide film, whereas biasing results in square-textured crystals. VO2 thin films of 150 nm thick show a near-zero IR transmission in switched state. Especially, the 150 nm thick VO2 thin film with seeding treatment shows an enhanced switching efficiency. (C) 2018 Elsevier B.V. All rights reserved.

The electronic structure and charge redistribution of 6s conduction charge and 5d charge in Au and Pt alloys, Au9Pt and AuPt9 have been investigated using a charge compensation model. It is found that, both the Au and Pt 4f binding energy (BE) exhibits a negative shift in the alloys relatively to the pure metal in apparent disagreement with electroneutrality considerations (Au is the most electronegative metallic element); more interestingly, the negative Au 4f BE shift in Au-Pt alloy is in contrast to previous observations for a large number of Au bimetallic systems with more electropositive hosts in which the more electropositive the host„ the more positive the Au 4f BE shift. This anomaly is counter intuitive to electronegativity considerations. This dilemma was resolved by the charge compensation model in which both electronegativity and charge neutrality can be satisfied and the overall charge flow δ, onto Au is small and positive and δ arises from charge flow of 6s conduction charge, Δnc onto Au site, which is partially compensated by the depletion of 6d charge Δnd at the Au site (δ = Δnc+ Δnd ∼0.1 >0). The much larger Coulomb interaction between 4f and 5d than that between 4f and 6s results in positive 4f BE shifts. The Au 4f BE shift in Au-Pt alloys together with 193Au Mössbauer data were used in the charge compensation model analysis which shows that the model is still valid in that the Au 4f shift in Au-Pt alloy arises from mainly conduction charge gain with little depletion of d charge at the Au site. The model also works for Pt. The Au and Pt 5d character in the alloys have been examined with valence band spectra which show both maintain their d characteristic in dilute alloys with Pt d piling up at the Fermi level, and the top of the Au valence band being pushed toward the Fermi level; this is confirmed with DFT densities of state calculations. When Pt is diluted in Au, it gains d charge as evident from the reduction in whiteline intensity at the Pt L3-edge XANES. What emerges from this work is a picture in which the s-d charge compensation in Au bimetallic alloys is triggered by electronegativity difference between Au and the host. For Au-Pt and Au-Pd systems, the difference in electronegativity is very small, conduction charge transfer dominates, and the Au 4f shift is negative whereas in most Au bimetallics, the larger the electronegativity difference, the larger the compensation and the larger the Au 4f shifts.

V2O5 thin films are well-known "smart" materials due to their reversible wettability under UV irradiation and dark storage. Their surfaces are usually hydrophobic and turn into hydrophilic under UV irradiation. However, the V2O5 thin films deposited by magnetron sputtering in present work are superhydrophilic and turned into hydrophobic after days' of storage in air. This change can be recovered by heating. The effects of many factors including surface roughness, irradiation from visible light, UV, & X-ray, and storage in air & vacuum on the reversible switching of wettability were investigated. The results show that air absorption is the main factor causing the film surface change from superhydrophilicity to hydrophobicity. (C) 2017 Elsevier B.V. All rights reserved.

In this study Pt nanoparticles supported on NiO, MnO2, and on carbon black were prepared and tested for the ammonia electrooxidation reaction (AmER) in alkaline media. The morphology and structure of the catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), nitrogen physisorption, and their surface properties were studied using synchrotron radiation photoelectron spectroscopy (SRPES). Cyclic voltammetry, chronoamperometry and Tafel plots were used to study the electrochemical behavior of ammonia on Pt/metal oxide catalysts. Pt/NiO showed the highest current density and the lowest onset potential for AmER (-0.48 V vs. Hg/HgO) which increased in the order E-onset(Pt/NiO) < E-onset(Pt/MnO2) < E-onset(Pt/C). The reaction kinetic order with respect to the concentration of ammonia is close to zero, indicating fast surface adsorption of ammonia in agreement with previous studies on polycrystalline Pt electrodes, whereas the apparent Tafel slopes were found higher (56 69 mV dec(-1)) than previously reported values for Pt (39 mV dec(-1)). Our results show that the nature of the support strongly influences the size and electronic properties of the Pt nanoparticles, and as a result their electrocatalytic activity for AmER. Crown Copyright (C) 2016 Published by Elsevier Ltd. All rights reserved.

Ammonia electro-oxidation reaction (AmER) was investigated by using conventional electrochemical experiments, direct ammonia fuel cell (DAFC) and galvanostatic electrolysis experiments. The working electrode/anodes were composed of carbon supported PtRu/C nanoparticles (NPs) with atomic Pt:Ru ratios of 100:0, 90:10, 70:30 and 50:50. The resulting nanoparticles ranged between 5.1 and 7.3 nm in size depending on the Ru content and were analyzed by XRD, TEM and synchrotron radiation photoelectron Spectroscopy (SRPES). Alloying Pt with Ru shifted AmER to the lower onset potentials compared to Pt/C. Among nanostructured PtRu/C electrocatalysts, the Pt90Ru10 composition showed the best activity and stability in the conventional electrochemical (cyclic voltammetry and chronoamperometry) experiments, DAFC and 8 h galvanostatic electrolysis. The concentration of nitrite and nitrate was doubled using PtRu/C 90:10 compared to Pt/C, because of excess of OHads species formed on Ru. The results show that the addition of small amount of Ru to Pt NPs improves the AmER due to additional formation of OHads that promote the reaction on alloyed PtRu nanoparticles. Crown Copyright (C) 2016 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. All rights reserved.

We have designed a Ni-graphene composite for hydrogen storage with Ni nanoparticles of 10 nm in size, uniformly dispersed over a graphene substrate. This system exhibits attractive features like high gravimetric density, ambient conditions, and low activation temperature for hydrogen release. When charged at room temperature and an atmospheric hydrogen pressure of 1 bar, it could yield a hydrogen capacity of 0.14 wt %. When hydrogen pressure increased to 60 bar, the sorbent had a hydrogen gravimetric density of 1.18 wt %. The hydrogen release could occur at an operating temperature below 150 °C and completes at 250 °C.

Ultrathin amorphous FePO4 coating derived by atomic layer deposition (ALD) is used to coat the 5 V LiNi0.5Mn1.5O4 cathode material powders, which dramatically increases the capacity retention of LiNi0.5Mn1.5O4. It is believed that the amorphous FePO4 layer could act as a lithium-ions reservoir and electrochemically active buffer layer during the charge/discharge cycling, helping achieve high capacities in LiNi0.5Mn1.5O4, especially at high current densities.

CuInS2 (CIS) nanocrystals (NCs) prepared optimally via a one-pot solvothermal method exhibit a high absorption coefficient and an ideal band gap for solar cell light-absorbing materials. We find that the initial Cu/In ratio in the synthesis determines the final composition of CIS, and this further dictates the photoelectrochemical performance of the CIS NC films. X-ray absorption near-edge spectroscopy excludes the presence of a secondary phase and suggests a difference in surface band bending and in ligand-CIS interaction. These findings will aid in optimizing the design of CIS NC films to achieve the highest possible photovoltaic efficiency.

Photoemission spectroscopy (PES) has been used widely to study the electronic structure of valence and core levels. However, conventional PES is surface-sensitive. To probe the interface and bulk properties of materials, hard X-ray photoemission spectroscopy (HXPES) has received increasing interest in the last decade, because of the deep probing ability of photoelectrons with higher kinetic energies (2–10 keV). Recently, a HXPES system was developed at the Canadian Light Source, using the high-energy version of a R4000 electron analyzer-based spectrometer connected to a medium-energy beamline, the soft X-ray microcharacterization beamline (SXRMB). Excellent performance of the beamline and the spectrometer is demonstrated herein using Au Fermi and 4f core lines; and the controlled probing depth of HXPES at SXRMB is demonstrated by tuning the photon energy (2–9 keV) in the study of a series of SiO2/SiC multilayer samples. Combined with the high-resolution X-ray absorption spectroscopy available at the SXRMB, the HXPES offers a powerful nondestructive technique for studying bulk properties of various materials.

Valence band energy shifts for pure zirconium and a model zirconium alloy (Zircaloy-4) in oxidized and hydrided states have been investigated with X-ray photoelectron spectroscopy (XPS) and X-ray Absorption Near-Edge Structure (XANES) technique. With XANES, we show that O/H interactions in oxidized Zr can be detected in the near-edge region of O K. Using density functional theory (DFT) simulations, we have determined where H atoms bond in the monoclinic ZrO2 lattice. The preferred stoichiometry is ZrO2:H, but the O-H bond is weak; increasing H causes the H atoms to form H-2 molecules rather than O-H bonds. These interactions cause energy shifts in the Zr 3d XPS spectra. The results illustrate the complex processes of hydrogen and oxygen interactions at the Zr surface. (C) 2014 Elsevier B.V. All rights reserved.

The absorbing layer in state-of-the-art colloidal quantum-dot solar cells is fabricated using a tedious layer-by-layer process repeated ten times. It is now shown that methanol, a common exchange solvent, is the main culprit, as extended exposure leaches off the surface halide passivant, creating carrier trap states. Use of a high-dipole-moment aprotic solvent eliminates this problem and is shown to produce state-of-the-art devices in far fewer steps.

Chemical composition of the discharge products as well as charging overpotential of the Na–air cell is correlated with the kinetic parameters.