Grazing Incidence Conditions Research Articles

Acoustic properties of multiple cavity resonance liner for absorbing higher-order duct modes.

This paper describes analytical and experimental studies conducted to investigate the acoustic properties of axially non-uniform multiple cavity resonance liner for absorbing higher-order duct modes. A three-dimensional analytical model is proposed based upon transfer element method. The model is assessed by making a comparison with results of a liner performance experiment concerning higher-order modes propagation, and the agreement is good. According to the present results, it is found that the performance of multiple cavity resonance liner is related to the incident sound waves. Moreover, an analysis of the corresponding response of liner perforated panel-cavity system is performed, in which the features of resonance frequency and dissipation of the system under grazing or oblique incidence condition are revealed. The conclusions can be extended to typical non-locally reacting liners with single large back-cavity, and it would be beneficial for future non-locally reacting liner design to some extent.

Asymmetric skew X-ray diffraction at fixed incidence angle: application to semiconductor nano-objects

A procedure for obtaining three-dimensionally resolved reciprocal-space maps in a skew X-ray diffraction geometry is described. The geometry allows tuning of the information depth in the range from tens of micrometres for symmetric skew diffraction down to tens of nanometres for strongly asymmetric skew geometries, where the angle of incidence is below the critical angle of total external reflection. The diffraction data are processed using a rotation matrix formalism. The whole three-dimensional reciprocal-space map can be measured by performing a single azimuthal rotation of the sample and using a two-dimensional detector, while keeping the angle of incidence and the X-ray information depth fixed (FIXD method). Having a high surface sensitivity under grazing-incidence conditions, the FIXD method can be applied to a large variety of Bragg reflections, particularly polar ones, which provide information on strain and chemical composition separately. In contrast with conventional grazing-incidence diffraction, the FIXD approach reveals, in addition to the lateral (in-plane) components, the vertical (out-of-plane) component of the strain field, and therefore allows the separation of the scattering contributions of strained epitaxial nanostructures by their vertical misfit. The potential of FIXD is demonstrated by resolving the diffraction signal from a single layer of InGaN quantum dots grown on a GaN buffer layer. The FIXD approach is suited to the study of free-standing and covered near-surface nano-objects, as well as vertically extended multilayer structures.

Linear chirped slope profile for spatial calibration in slope measuring deflectometry.

Slope measuring deflectometry is commonly used by the X-ray optics community to measure the long-spatial-wavelength surface figure error of optical components dedicated to guide and focus X-rays under grazing incidence condition at synchrotron and free electron laser beamlines. The best performing instruments of this kind are capable of absolute accuracy on the level of 30-50 nrad. However, the exact bandwidth of the measurements, determined at the higher spatial frequencies by the instrument's spatial resolution, or more generally by the instrument's modulation transfer function (MTF) is hard to determine. An MTF calibration method based on application of a test surface with a one-dimensional (1D) chirped height profile of constant amplitude was suggested in the past. In this work, we propose a new approach to designing the test surfaces with a 2D-chirped topography, specially optimized for MTF characterization of slope measuring instruments. The design of the developed MTF test samples based on the proposed linear chirped slope profiles (LCSPs) is free of the major drawback of the 1D chirped height profiles, where in the slope domain, the amplitude strongly increases with the local spatial frequency of the profile. We provide the details of fabrication of the LCSP samples. The results of first application of the developed test samples to measure the spatial resolution of the BESSY-NOM at different experimental arrangements are also presented and discussed.

Damage threshold of coating materials on x-ray mirror for x-ray free electron laser.

We evaluated the damage threshold of coating materials such as Mo, Ru, Rh, W, and Pt on Si substrates, and that of uncoated Si substrate, for mirror optics of X-ray free electron lasers (XFELs). Focused 1 μm (full width at half maximum) XFEL pulses with the energies of 5.5 and 10 keV, generated by the SPring-8 angstrom compact free electron laser (SACLA), were irradiated under the grazing incidence condition. The damage thresholds were evaluated by in situ measurements of X-ray reflectivity degradation during irradiation by multiple pulses. The measured damage fluences below the critical angles were sufficiently high compared with the unfocused SACLA beam fluence. Rh coating was adopted for two mirror systems of SACLA. One system was a beamline transport mirror system that was partially coated with Rh for optional utilization of a pink beam in the photon energy range of more than 20 keV. The other was an improved version of the 1 μm focusing mirror system, and no damage was observed after one year of operation.

Diffraction of H from LiF(001): From slow normal incidence to fast grazing incidence

Describing diffraction of atomic and molecular projectiles at fast grazing incidence presents a real challenge for quantum theoretical simulations due to the high incidence energy (100eV–1keV) used in experiments. This is one of the main reasons why most theoretical simulations performed to date are based on reduced dimensional models. Here we analyze two alternatives to reduce the computational effort, while preserving the real dimensionality of the system. First, we show that grazing incidence conditions are already fulfilled for incidence angles ⩽5°, i.e., incidence angles higher than those typically used in experiments. Thus, accurate comparisons with experiment can be performed considering diffraction at grazing incidence, but with smaller total incidence energies, whilst keeping the same experimental normal energy in the calculations. Second, we show that diffraction probabilities obtained at fast grazing incidence are fairly well reproduced by simulations performed at slow normal incidence. This latter approach would allow one to simulate several experimental spectra, measured at the same normal incidence energy for several incidence crystallographic directions, with only one calculation. This approach requires to keep the full dimensionality of the system.

Atomic layer deposition of copper sulfide thin films

Atomic Layer Deposition (ALD) of copper sulfide (CuxS) thin films from Cu(acac)2 (acac=acetylacetonate=2,4-pentanedionate) and H2S as Cu and S precursors is reported. Typical self-saturated reactions (“ALD window”) are obtained in the temperature range Tdep=130–200°C for an average growth per cycle (GR)=0.25Å/cycle. The morphology, crystallographic structure, chemical composition, electrical properties and optical band gap of thin films were investigated using scanning electronic microscopy (SEM), X-ray diffraction under Grazing Incidence conditions (GI-XRD), X-ray reflectivity (XRR), energy dispersive spectrometry (EDS), Hall effect measurements, and UV–vis spectroscopy. The obtained copper sulfide films are heavily p-doped (charge carrier concentration~1021–1022cm−3) with optical band gaps in the range of 2.2–2.5eV for direct and 1.6–1.8eV for indirect band gaps. Depending on the number of ALD cycles, multiphase compounds (made of digenite Cu1.8S, chalcocite Cu2S, djurleite Cu31S16 and covellite CuS) or single-phase digenite Cu1.8S films are obtained via a growth mechanism that involves in-situ copper reduction and loss of sulfur by evaporation.

Surface diagnostics by ion scattering spectroscopy in gaseous environment

Nowadays, it is important to perform in-situ analysis of composition and thickness of ultra-thin (∼5-50 Å) surface layers in the course of the surface exposure to plasma or its components. For this aim, a new experimental facility based on the MEPhI Mass Monochromator is being developed, where low and medium energy ion spectroscopy of samples is used just after or during plasma exposure/ion treatment. A differentially pumped energy analyzer is used for recoil ion spectroscopy under grazing incidence conditions in the automated ion mass monochromator. A built-in Penning plasma source is used for plasma/ion treatment of samples. In this paper, the influence of the working gas (during the plasma source operation) on the energy spectra of reflected and recoil ions is studied. It is shown that the peak shape of the energy spectrum of scattered H+ ions increases during gas injection, and, at the same time, the signal intensity of the ionized recoils from the sample decreases. Nevertheless, analysis of the surface composition and thickness of the outer layer could be done at pressures ranging up to 10-4 Torr.

Six-dimensional theoretical study of H2 scattering from LiF(001): From thermal to high incidence energies

SynopsisWe have computed an accurate potential energy surface (PES) describing the electronic structure of the system H2/LiF(001). Based on this PES, we have performed an analysis of the dynamics of the system trying to understand recent experimental results obtained at fast grazing incidence conditions.

Deposition of ultra thin CuInS2 absorber layers by ALD for thin film solar cells at low temperature (down to 150 °C)

Two new processes for the atomic layer deposition of copper indium sulfide (CuInS2) based on the use of two different sets of precursors are reported. Metal chloride precursors (CuCl, InCl3) in combination with H2S imply relatively high deposition temperature (Tdep = 380 °C), and due to exchange reactions, CuInS2 stoechiometry was only achieved by depositing In2S3 layers on a CuxS film. However, the use of acac- metal precursors (Cu(acac)2, In(acac)3) allows the direct deposition of CuInS2 at temperature as low as 150 °C, involving in situ copper-reduction, exchange reaction and diffusion processes. The morphology, crystallographic structure, chemical composition and optical band gap of thin films were investigated using scanning electronic microscope, x-ray diffraction under grazing incidence conditions, x-ray fluorescence, energy dispersive spectrometry, secondary ion mass spectrometry, x-ray photoelectron spectroscopy and UV–vis spectroscopy. Films were implemented as ultra-thin absorbers in a typical CIS-solar cell architecture and allowed conversion efficiencies up to 2.8%.

Oxide Nanolayers in Stratified Samples Studied by X-Ray Resonant Raman Scattering at Grazing Incidence

X-ray resonant Raman scattering is applied at grazing incidence conditions with the aim of discriminating and identifying chemical environment of iron in different layers of stratified materials using a low resolution energy dispersive system. The methodology allows for depth studies with nanometric resolution. Nanostratified samples of Fe oxides were studied at the Brazilian synchrotron facility (LNLS) using monochromatic radiation and an EDS setup. The measurements were carried out in grazing incident regime with incident photon energy lower than and close to the Fe-K absorption edge. The result allowed for characterizing oxide nanolayers, not observable with conventional geometries, identifying the oxidation state present in a particular depth of a sample surface with nanometric, or even subnanometric, resolution using a low-resolution system.

Scattering of H(D) from LiF(1 0 0) under fast grazing incidence conditions: To what extent is classical dynamics a useful tool?

Diffraction experiments of atoms and molecules under fast grazing incidence conditions have opened a new field in surface science. This experimental effort calls for complementary theoretical studies, which would allow a detailed analysis of experimental data. Here, we have analyzed the ability of classical dynamics simulations to reproduce experimental results. To perform this study, a DFT (density functional theory) based potential energy surface, describing the interaction between a H atom and a LiF(100) surface, has been computed. Diffraction probabilities have been simulated by means of a classical binning method. Our results have been found to be in qualitative good agreement with recent experimental measurements.

Depth Profiling Nano-Analysis of Chemical Environments using Resonant Raman Spectroscopy at Grazing Incidence Conditions

Both X-ray total reflection and X-ray Raman scattering techniques were combined to discriminate chemical environments in depth-profiling studies using an energy dispersive system. This allowed, for the first time, to resolve oxidation state on surface nanolayers with a low-resolution system. Samples of pure Cu and Fe oxidized in tap water and salty water, respectively, were studied in the Brazilian synchrotron facility using monochromatic radiation and an EDS setup. The measurements were carried out in total reflection geometry with incident energy lower and close to the K absorption edge of both elements. The results allowed observing the presence of very thin oxide layers, usually not observable with conventional geometries of irradiation. They also permit the identification of the compound present in a particular depth of the sample with nanometric, or even subnanometric, resolution using a low-resolution system.

X-ray characterization techniques for the assessment of surface damage in crystalline wafers: A model study in AlN

A high-resolution X-ray diffraction method with enhanced surface sensitivity has been used to investigate the effects of various polishing steps on the near-surface region of single crystal substrates. The method involves the study of a highly asymmetric reflection, observable under grazing incidence conditions. Analysis of rocking curve measurements and reciprocal space maps (RSMs) revealed subtle structural differences between the polished substrates. For aluminum nitride wafers, damage induced from diamond sawing and mechanical polishing was readily identifiable by on-axis rocking curves, but this method was unable to distinguish between sample surfaces subjected to various degrees of chemical mechanical polishing (CMP). To characterize sufficiently these surfaces, (10.3) RSMs were measured to provide both qualitative and quantitative information about the near-surface region. Two features present in the RSMs were utilized to quantitatively assess the polished wafers: the magnitude of the diffuse scatter in the omega-scans and the elongation of the crystal truncation rod. The method is able to distinguish between different degrees of CMP surface preparation and provides metrics to quantify subsurface damage after this polishing step.

High angular resolution slope measuring deflectometry for the characterization of ultra-precise reflective x-ray optics

Slope measuring deflectometry has become a standard technique for inspection of ultra-precise reflective optical elements of synchrotron applications. We will report on the inspection of ultra-precise adaptive synchrotron mirrors (bimorph mirrors) to be used under grazing incidence condition. The measurements were performed at the BESSY-II Optics Laboratory of the Helmholtz Zentrum Berlin using the nanometer optical component measuring machine (NOM). Based on the data obtained by the optical measurements, we in this paper simulate the characteristics of the achievable x-ray focus by ray tracing calculations, demonstrated in the case of bimorph mirrors of the EMBL MX1 beamline for macromolecular crystallography at DESY's synchrotron radiation source PETRA III in Hamburg.

X-ray study of surface layers of air-annealed Be12Ti and Be12V samples using synchrotron radiation

Titanium beryllide Be12Ti and vanadium beryllide Be12V are considered to be promising materials for advanced neutron multipliers in the helium-cooled breeding blanket of DEMO reactor. A study of the surface layers of oxidized beryllide specimens by means of powder X-ray diffraction technique is presented in this work. The phase composition of the near-to-surface layers of Be12Ti and Be12V specimens was investigated at the Single Crystal Diffraction (SCD) beamline at ANKA synchrotron facility after air-annealing at 800°C. A high surface sensitivity of measurements was achieved at grazing incidence conditions by varying the incidence angle. Since beryllium has low values of X-ray absorption, the near-surface regions having depths from 2 up to 20μm were investigated. The main objective of the work is the evaluation of composition of the reactant products which can influence the parameters of retention and release of radiogenic gases.

GISAXS/GIXRD View of ZnO Films with Hierarchical Structural Elements

ZnO films constituted of porous sheet-like structures, formed by calcination of precursor, were examined using scanning electron microscopy and simultaneous small-angle scattering and diffraction of the synchrotron-sourced X-rays, under the grazing-incidence conditions. The presented analysis enabled insight into the complexity of the film morphology, which revealed substrate sensitivity on the microscopic and nanoscopic length scales. The average size and spatial arrangement of nanoparticles, single-crystal domains, and the average size and features of nanopores in sheet-like structures were determined for films deposited on glass, polycrystalline ZnO layer, and silicon.

Complementary Characterization of Buried Nanolayers by Quantitative X-ray Fluorescence Spectrometry under Conventional and Grazing Incidence Conditions

The determination of the thickness and elemental composition is an important part of the characterization of nanolayered structures. For buried nanolayers, X-ray fluorescence spectrometry is a qualified method for the thickness determination whereas conventional electron emission based methods may reach their limits due to rather restricted information depths. The aim of the presented investigation was the comparison of reference-free X-ray fluorescence spectrometry under conventional and grazing incidence conditions offering complementary information with respect to quantification reliability, elemental sensitivity, and layer sequences. For this purpose, buried boron-carbon layers with nominal thicknesses of 1, 3, and 5 nm have been studied using monochromatized undulator radiation in the laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the synchrotron radiation facility BESSY II. The results for the two beam geometries are compared and show particulate good agreements, thus encouraging the complementary use of both methodologies.

Fast computation of scattering maps of nanostructures using graphical processing units

Scattering maps from strained or disordered nanostructures around a Bragg reflection can be either computed quickly using approximations and a (fast) Fourier transform or obtained using individual atomic positions. In this article, it is shown that it is possible to compute up to 4 × 1010 reflections atoms s−1using a single graphics card, and the manner in which this speed depends on the number of atoms and points in reciprocal space is evaluated. An open-source software library (PyNX) allowing easy scattering computations (including grazing-incidence conditions) in the Python language is described, with examples of scattering from non-ideal nanostructures.

X-ray diffracted intensity for double-reflection channel-cut Ge monochromators at extremely asymmetric diffraction conditions

The width and integrated intensity of the 220 X-ray double-diffraction profile and the shift of the Bragg condition due to refraction have been measured in a channel-cut Ge crystal in an angular range near the critical angle of total external reflection. The Bragg angle and incidence condition were varied by changing the X-ray energy. In agreement with the extended dynamical theory of X-ray diffraction, the integrated intensity of the double diffraction remained almost constant, even for the grazing-incidence condition very close to the critical angle for total external reflection. A broadening of the diffraction profile not predicted by the extended theory of X-ray diffraction was observed when the Bragg condition was at angles of incidence lower than 0.6°. Plane wave topographs revealed a contrast that could be explained by a slight residual crystal surface undulation of 0.3° due to etching to remove the cutting damage and the increasing effect of refraction at glancing angles close to the critical angle. These findings confirm that highly asymmetric channel-cut Ge crystals can also work as efficient monochromators or image magnifiers at glancing angles close to the critical angle, the main limitation being the crystal surface preparation.

Coherent Reflection of He Atom Beams from Rough Surfaces at Grazing Incidence

We report coherent reflection of thermal He atom beams from various microscopically rough surfaces at grazing incidence. For a sufficiently small normal component k(z) of the incident wave vector of the atom the reflection probability is found to be a function of k(z) only. This behavior is explained by quantum reflection at the attractive branch of the Casimir-van der Waals interaction potential. For larger values of k(z) the overall reflection probability decreases rapidly and is found to also depend on the parallel component k(x) of the wave vector. The material specific k(x) dependence for this classic reflection at the repulsive branch of the potential is discussed in terms of an averaging out of the surface roughness under grazing incidence conditions.