A. B. P. Vogels

Bio: A. B. P. Vogels is an academic researcher. The author has contributed to research in topics: Diffraction & Voigt profile. The author has an hindex of 1, co-authored 1 publications receiving 1034 citations.

Use of the Voigt function in a single-line method for the analysis of X-ray diffraction line broadening

Abstract: The use of the Voigt function for the analysis of the integral breadths of broadened X-ray diffraction line profiles forms the basis of a rapid and powerful single-line method of crystallite-size and strain determination which is easy to apply. To avoid graphical methods or interpolation from tables, empirical formulae of high accuracy are used and an estimation of errors is presented, including the influence of line-profile asymmetry. The method is applied to four practical cases of size-strain broadening: (i) cold-worked nickel, (ii) a nitrided steel, (iii) an electrodeposited nickel layer and (iv) a liquid-quenched AlSi alloy.

X-ray diffraction of III-nitrides

Abstract: The III-nitrides include the semiconductors AlN, GaN and InN, which have band gaps spanning the entire UV and visible ranges. Thin films of III-nitrides are used to make UV, violet, blue and green light-emitting diodes and lasers, as well as solar cells, high-electron mobility transistors (HEMTs) and other devices. However, the film growth process gives rise to unusually high strain and high defect densities, which can affect the device performance. X-ray diffraction is a popular, non-destructive technique used to characterize films and device structures, allowing improvements in device efficiencies to be made. It provides information on crystalline lattice parameters (from which strain and composition are determined), misorientation (from which defect types and densities may be deduced), crystallite size and microstrain, wafer bowing, residual stress, alloy ordering, phase separation (if present) along with film thicknesses and superlattice (quantum well) thicknesses, compositions and non-uniformities. These topics are reviewed, along with the basic principles of x-ray diffraction of thin films and areas of special current interest, such as analysis of non-polar, semipolar and cubic III-nitrides. A summary of useful values needed in calculations, including elastic constants and lattice parameters, is also given. Such topics are also likely to be relevant to other highly lattice-mismatched wurtzite-structure materials such as heteroepitaxial ZnO and ZnSe.

Shape and Crystal-Plane Effects of Nanoscale Ceria on the Activity of Au-CeO2 Catalysts for the Water–Gas Shift Reaction†

Abstract: The water–gas shift (WGS) reaction (CO+H2OQCO2+H2) plays an important role in fuel processing for polymer electrolyte membrane (PEM) fuel-cell applications. The hydrogen in the reformate gas is upgraded by removal of the carbon monoxide, which is a strong poison of the anode catalysts in current PEM fuel cells. Active shift catalysts that are also stable under the operating conditions of practical fuel-cell systems are under intense study, and nanostructured Au-CeO2, first reported by Fu et al. as a promising lowtemperature shift catalyst, holds a prominent position. This catalyst exploits the strong interaction of ceria with finely dispersed and stabilized gold atoms and clusters on the surface of ceria. Gold nanoparticles and clusters that interact strongly with oxide supports were first described by Haruta et al. to be extremely active CO oxidation catalysts. Numerous studies since then have reaffirmed the activity of well-dispersed gold for CO oxidation and many other reactions. While a full mechanism of this catalytic process still needs to be established, even for the simplest of these reactions (CO oxidation), a careful investigation of the reported strong metal–support interaction through structural studies may provide further mechanistic insights as well as rationalize the design of practical catalysts. For the WGS reaction on Au-CeO2, the importance of nanoscale ceria as a support that stabilizes active gold species has been demonstrated recently. Hydrolysis methods for the synthesis of ceria nanocrystals have proven to be powerful for controlling particle size and crystal shape. For example, Yan et al. have obtained single-crystalline CeO2 nanopolyhedra ({111} and {100}), nanorods ({110} and {100}), and nanocubes ({100}) by hydrolysis of cerium(III) salts, combined with a hydrothermal treatment, and have further found that oxygen storage takes place both at the surface and in the bulk for nanorods and nanocubes but is restricted to the surface for nanopolyhedra, just like its bulk ceria counterpart. Trovarelli et al. have studied the rearrangement of CeO2 crystallites under airaging and the exposure of more reactive {100} surfaces for CO oxidation. Very little is known for Au-CeO2 composite polycrystalline nanomaterials with respect to the shape/crystal plane effect of CeO2 on the gold species< activity/stabilization as highly active catalysts for the WGS reaction. Herein, we present activity correlations with the shape (rod, cube, polyhedron) and crystal plane of nanoscale ceria as a support for gold catalysts for this reaction. The interaction between deposited gold and different crystal orientations is investigated at ambient pressure andmonitored by several analytical techniques, including transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction by hydrogen (H2-TPR). Figure 1 depicts our two-step preparation process, which includes hydrothermal synthesis of ceria nanorods, nano-

Light-induced lattice expansion leads to high-efficiency perovskite solar cells

Abstract: Light-induced structural dynamics plays a vital role in the physical properties, device performance, and stability of hybrid perovskite–based optoelectronic devices. We report that continuous light illumination leads to a uniform lattice expansion in hybrid perovskite thin films, which is critical for obtaining high-efficiency photovoltaic devices. Correlated, in situ structural and device characterizations reveal that light-induced lattice expansion benefits the performances of a mixed-cation pure-halide planar device, boosting the power conversion efficiency from 18.5 to 20.5%. The lattice expansion leads to the relaxation of local lattice strain, which lowers the energetic barriers at the perovskite-contact interfaces, thus improving the open circuit voltage and fill factor. The light-induced lattice expansion did not compromise the stability of these high-efficiency photovoltaic devices under continuous operation at full-spectrum 1-sun (100 milliwatts per square centimeter) illumination for more than 1500 hours.