Grazing Incidence Conditions Research Articles

Grazing incidence scattering of vibrationally excited H 2 molecules from metal surfaces

We have studied the scattering of vibrationally excited H 2 molecules from metal surfaces under fast grazing incidence conditions, by means of quasi-classical calculations based on six-dimensional potential energy surfaces. We show that, in spite of the fast parallel motion, the reorientation of the molecule along the trajectory plays a fundamental role on the scattering, being responsible for the nonmonotonic behavior observed as a function of the normal incidence energy, similar to that observed under slow normal incidence conditions. The present study has allowed us to further prove that the interaction between a H 2 molecule and an ordered metal surface under fast grazing incidence conditions is, in general, governed by the normal momentum of the molecule.

Surface channelling and energy losses of 4 keV hydrogen and fluorine ions in grazingscattering on Au(111) and missing row reconstructed Au(110) surfaces

We present the results of an experimental and theoretical study of surface channelling andenergy loss of 4 keV hydrogen and fluorine ions in grazing scattering on a missing rowreconstructed Au(110) surface and a Au(111) surface. We performed measurements ofenergy losses for grazing angle scattering in surface channelling conditions forvarious azimuthal orientations of the crystal. Experimental results are discussedin the light of trajectory calculations of hydrogen and fluorine ions scatteredunder grazing incidence conditions on the surface. A nonlinear model is usedin order to calculate the ion energy loss in these crystalline systems. Ab initioelectronic crystal structure calculations and semi-classical simulations are performedand allow us to delineate various trajectory classes that correspond to differentcontributions in the energy loss spectra for various azimuthal orientations of the surface.

F-62 Characterization of Nanoparticles with X-ray Spectrometry Under Grazing Incidence Conditions

F-62 Characterization of Nanoparticles with X-ray Spectrometry Under Grazing Incidence Conditions

Contribution of Ni KLL Auger Electrons to the Probing Depth of the Conversion Electron Yield Measurements

The averaged attenuation length of emitted electrons with the conversion electron yield (CEY) method was evaluated for Ni films with the x-rays below and above the Ni K absorption edge. The evaluated attenuation length was 13.1 nm with the x-rays below the Ni K absorption edge, and it became 24.0 nm with the contribution of Ni KLL Auger electrons that had the attenuation length of 78.1 nm. The probing depth of the CEY measurements are determined both the penetration depth of x-rays and the attenuation length of emitted electrons, and the modification of the probing depth was investigated with the grazing incidence condition. The glancing angle dependence of the CEY was compared with the model calculation, and the probing depth of around 1.6 nm was realized under the total reflection condition. The probing depth was controlled from 1.6 nm to the attenuation length by changing the glancing angle.

Molecular effects in grazing incidence collisions of H2 with metal surfaces

We have studied the reactive scattering of H2 under grazing incidence conditions and fast collision energies (0.2–2.0 keV), by means of classical dynamics calculations performed with first-principle six-dimensional potential energy surfaces for H2/NiAl(110) and H2/Pd(111). We show that fast light molecules can be used to determine dissociative adsorption probabilities at thermal energies and beyond, from the dissociation threshold up to the saturation limit. The later suggests that this approach is an ideal complement to traditional sticking experiments at thermal energies to determine dissociative adsorption curves up to the saturation limit.

Elemental depth profiling of Cu(In,Ga)Se 2 thin films by reference-free grazing incidence X-ray fluorescence analysis

The semiconductor band gap of the Cu(In,Ga)Se 2 (CIGSe) compound can be varied by the In to Ga ratio. This composition variation determines the photovoltaic properties of CIGSe thin films. Their composition depth profile has to be optimized in order to obtain maximum efficiencies in solar cell applications. Synchrotron-radiation-based X-ray fluorescence (XRF) analysis under grazing incidence conditions provides non-destructive access to the compositional depth profile of the CIGSe thin films and, hence, represents a new non-destructive method, which does not require well-characterized standards for calibration purposes. Based on an analytical description of the physical processes, fluorescence line intensities of the specimen can be calculated by using fundamental atomic parameters. The general suitability of the method for determining depth gradients in CIGSe thin films is first shown by calculations. Reference-free XRF test measurements were carried out at the FCM beamline in the PTB laboratory at BESSY II. X-ray fluorescence was induced by photon excitation at energies of 4.0 keV and 10.5 keV, respectively, using various shallow incident angles. The calculations and the experimental measurements show that even small differences in the Ga/In profile may be distinguished, indicating that grazing incidence XRF is a promising tool for a non-destructive characterization of compositional depth profiles. Further refinement of the operational parameters may contribute to the sensitivity of the method.

Molecular Effects inH2Scattering from Metal Surfaces at Grazing Incidence

Collisions of fast atoms with surfaces at grazing incidence have been recently proposed as a promising new tool to determine surface parameters with unprecedented accuracy. Here we show, by means of classical dynamics calculations performed with first-principles six-dimensional potential energy surfaces for H2/NiAl(110) and H2/Pd(111) that, under grazing incidence conditions, fast light molecular projectiles are also useful to determine sticking probabilities at thermal energies, from the threshold up to the saturation limit. Thus they are the ideal complement to traditional experiments at thermal energies to determine sticking curves up to the saturation limit.

Slurry and cavitation erosion resistance of thermal spray coatings

The slurry and cavitation erosion resistance of six thermal spray coatings were studied in laboratory and compared to that of an uncoated martensitic stainless steel. Nickel, chromium oxide and tungsten carbide coatings were applied by oxy fuel powder (OFP) process and chromium and tungsten carbide coatings were obtained by high velocity oxy fuel (HVOF) process. The microstructure of the coatings was analyzed by light optical microscopy (LOM) and scanning electron microscopy (SEM), as well as by X-ray diffraction (XRD). The cavitation erosion resistance of the coatings was measured in a vibratory apparatus according to ASTM G32 standard and the slurry erosion tests were carried out in a modified centrifugal pump in which the samples were conveniently placed to guarantee grazing incidence conditions, as well as in a high velocity jet erosion testing machine. The results showed that the slurry erosion resistance of the steel can be improved up to 16 times by the application of the thermally sprayed coatings. On the other hand, none of the coated specimens showed better cavitation resistance than the uncoated steel in the experiments. The main mass removal mechanisms observed in all the coatings submitted to slurry erosion were micro-cutting and micro-ploughing as well as detachment of hard particles. In cavitation erosion, OFP coatings showed brittle fracture and microcracking, and in nickel-based coatings some ductile deformation was also observed. In HVOF coatings, detachment of small particles led to coalescence of pores in WC/Co coatings while in CrC coatings the main wear mechanism was brittle fracture of particles.

Electronic density corrugation and crystal azimuthal orientation effects on energy losses of hydrogen ions in grazing scattering on a Ag(110) surface

We present a detailed study of the energy losses of hydrogen ions that are scattered off an Ag(110) single-crystal surface for primary energies between 1 and 4 keV. We performed measurements for grazing angles as a function of crystal azimuthal orientation, which show large differences in energy losses. Experimental results are discussed by means of trajectory calculations of protons scattered under grazing-incidence conditions on the surface. Using nonlinear models for the stopping power, ab initio crystal structure calculations of the electronic density, and semiclassical simulations, we obtain data that are in very good agreement with experimental results. These simulations allow us to properly take into account the variations of the surface electronic density and hence obtain an accurate description of the energy loss processes for ion scattering along various azimuthal orientations of the target.

Fluorescence analysis of a multilayer (Zr(10 nm)/[Fe(1.6 nm)/Cr(1.7 nm)]26/Cr(50 nm)/glass) structure under grazing incidence conditions

Element-specific measurements of the fluorescent radiation combined with measurements of the reflectivity curves have been performed for a Zr(10 nm)/[Fe(1.6 nm)/Cr(1.7 nm)]26/Cr(50 nm)/glass sample with the use of a new experimental setup created at the Institute for Analytical Instrumentation. The experimental data have been processed using a FLUO simulation program package implemented in the Visual C++ environment. The Zr, Fe, Cr, and Sn depth profiles have been reconstructed via coprocessing of reflectivity and fluorescence yield curves that were measured for each of these elements.

Parameter study of self-absorption effects in Total Reflection X-ray Fluorescence–X-ray Absorption Near Edge Structure analysis of arsenic

Total reflection X-ray Fluorescence (TXRF) analysis in combination with X-ray Absorption Near Edge Structure (XANES) analysis is a powerful method to perform chemical speciation studies at trace element levels. However, when measuring samples with higher concentrations and in particular standards, damping of the oscillations is observed. In this study the influence of self-absorption effects on TXRF–XANES measurements was investigated by comparing measurements with theoretical calculations. As(V) standard solutions were prepared at various concentrations and dried on flat substrates. The measurements showed a correlation between the damping of the oscillations and the As mass deposited. A Monte-Carlo simulation was developed using data of the samples shapes obtained from confocal white light microscopy. The results showed good agreement with the measurements; they confirmed that the key parameters are the density of the investigated atom in the dried residues and the shape of the residue, parameters that combined define the total mass crossed by a certain portion of the incident beam. The study presents a simple approach for an a priori evaluation of the self-absorption in TXRF X-ray absorption studies. The consequences for Extended X-ray Absorption Fine Structure (EXAFS) and XANES measurements under grazing incidence conditions are discussed, leading to the conclusion that the damping of the oscillations seems to make EXAFS of concentrated samples non feasible. For XANES “fingerprint” analysis samples should be prepared with a deposited mass and sample shape leading to an acceptable absorption for the actual investigation.

Near-edge x-ray absorption fine structure measurements using a laboratory-scale XUV source

We present a compact setup for near-edge x-ray absorption spectroscopy at the carbon K-edge based on a laser-driven plasma source. To generate the required broad-band emission in the spectral range of the ‘water window’ (λ = 2.2–4.4 nm) a krypton gas puff target was used. The table-top setup consisting basically of the laser-plasma source and a flat-field spectrometer can be used for near-edge x-ray absorption fine structure experiments in transmission as well as reflection under grazing incidence conditions (ReflEXAFS). The latter method offers the advantage that thin film preparation is not necessary and that the surface sensitivity is strongly enhanced. The results obtained for thin polymer films show good agreement with synchrotron data. Furthermore, we use the ReflEXAFS method to investigate changes in the chemical composition of PMMA induced by extreme ultraviolet (EUV) radiation. The spectra indicate a loss of the carbonyl functional group upon irradiation as well as crosslinking effects at high EUV radiation doses.

Observation of reflected X-rays from end face of organic thin film

During the irradiation of white X-rays of synchrotron radiation on copper phthalocyanine thin film on a Si wafer (CuPc/Si) under the grazing incidence condition, X-rays from the end face of the CuPc layer were observed by solid state detector. These were understood to be refractions through the CuPc layer and reflections from the CuPc/Si, because their energy variation as a function of the X-ray exit angle followed Snell's law. We also discussed the similarities and differences between the observed phenomenon and X-ray waveguide phenomenon.

High-k Gate Dielectric Films Studied by Extremely Asymmetric X-ray Diffraction and X-ray Photoelectron Spectroscopy

We studied HfAlOx(N)/SiO2/Si films which were fabricated by the layer-by-layer deposition and annealing (LL-D&A) method with different annealing conditions. In this time, in-situ annealing was performed at various temperatures in an NH3 ambient. In addition, post-deposition annealing (PDA) was performed for some samples. For each sample, the interfacial lattice strain was evaluated using extremely asymmetric X-ray diffraction and the local dielectric constant near the Al atoms was measured by X-ray photoelectron spectroscopy (XPS). Observation of the strain field was done by measuring the X-ray rocking curve of the Si 113 reflection of the Si (001) substrate under grazing incidence conditions. It was found that in the case of the samples without PDA, for higher in-situ annealing temperatures compressive strain is introduced and the local dielectric constant becomes lower. For the samples with PDA, the differences of the lattice strain and the local dielectric constant are small for different in-situ annealing temperatures.

Effect of oxygen adsorption on the energy losses in grazing scattering of hydrogen ions on Ag(1 1 0)

In this work we present a study of the effect of oxygen adsorption on the energy loss of 4keV hydrogen ions, which are scattered off an Ag (110) single-crystal surface with varying coverages of oxygen. In this case oxygen adsorption leads to an added row reconstruction of the surface. We performed measurements for grazing angles as a function of crystal azimuthal orientation, which show large differences in energy losses. Experimental results are discussed in the light of trajectory calculations of protons scattered under grazing incidence conditions on the surface. Using non-linear models for stopping power, ab initio crystal structure calculations of the electronic density and semi-classical simulations, we obtain data that is in very good agreement with experimental results. These simulations in particular allow us to properly take into account the variations of the surface electronic density and hence obtain an accurate description of the energy loss processes for ion scattering along various azimuthal orientations of the target.

Energy and charge distributions of fast nitrogen ions reflected from metal surface at grazing incidence

Energy and charge distributions of ions scattered under grazing incidence conditions from metallic surfaces are studied theoretically. The energy distribution of scattered ions with fixed charge is calculated by the energy distribution of reflected ions with equilibrium charge and charge fraction of these ions. The charge fractions of scattered ions are estimated by charge exchange cross sections. We calculated the energy and charge distributions of 1MeV nitrogen ion scattered from platinum surface. The calculation results are in qualitative agreement with experimental data.

Behavior of mesospheric ozone under nearly polar night conditions

The spatio-temporal behavior of the ozone mixing ratio in the upper mesosphere/mesopause region under nearly polar night conditions is one phenomenon not completely understood and reproduced by models thus far. On the basis of a sophisticated 3D-model of the dynamics and chemistry of the middle atmosphere (0–150 km) particularly designed to investigate the extended mesopause region, we examine the spatio-temporal structure of this phenomenon and discuss it in terms of chemistry. The most marked feature is a pronounced ozone maximum around 72 km, also called the tertiary ozone maximum, and a large decrease of the mixing ratios around 80 km. This feature was also found by means of ground-based microwave measurements in middle latitude at Lindau (51.66 °N) and high latitude at ALOMAR (69.29 °N) during the night in the winter season. It was, however, absent during the daytime hours. The calculations brought evidence that the enhanced ozone values occur in a latitudinal band close to the polar night terminator. It is confined both to a height range approximately between 66 and 77 km and to a certain latitudinal range which alters with the season according to the change of the polar night terminator. For a constant latitude there are two annual maxima of the ozone mixing ratio that occur nearly symmetrically about the winter solstice. These maxima are more widely separated at higher latitudes. The theoretical analysis of this phenomenon showed that while ozone is formed under nearly grazing incidence conditions the radiation that dissociates water vapor is almost completely absorbed. This means that the formation of hydrogen radicals that destroy odd oxygen is significantly reduced but there is still some atomic oxygen production that permits ozone formation during the short twilight periods close to the polar night terminator. The loss of the accumulated ozone takes place partly through the Chapman reactions of a pure oxygen system and partly through catalytic reactions, including HO x radicals that result from O( 1D) oxidation of the even hydrogens H 2 and H 2O and a residual photolysis of H 2O. The O( 1D) oxidation is important because the ozone dissociation rate is only slightly reduced for grazing incidence conditions in that region. Within the region of the large ozone decrease near 80 km the chemistry is marked by a steady increase of atomic hydrogen entailing a decrease of ozone and HO 2. The poleward directed meridional wind also transports ozone into the polar night.

Phonon Modes at the2H−NbSe2Surface Observed by Grazing Incidence Inelastic X-Ray Scattering

We have determined the dispersion of acoustic and optical surface phonon modes 2H-NbSe2 at the by inelastic x-ray scattering under grazing incidence conditions. Already, at room temperature, an anomaly is observed close to the charge density wave -vector position located at about one-third along the Gamma-M direction of the Brillouin zone. Our results indicate that the anomaly for the surface mode occurs at a lower energy than that measured in bulk sensitive geometry in the same experiment, showing evidence of a modified behavior in the uppermost layers. We demonstrate that inelastic x-ray scattering in grazing incidence conditions provides a unique tool to selectively study either surface or bulk lattice dynamics in a single experiment.

Role of projectile charge state in convoy electron emission by fast protons colliding with LiF(0 0 1)

Target ionization and projectile ionization differential cross sections are used to calculate the electron emission spectra by fast proton impact on ionic crystal surfaces under grazing incidence conditions. Both bare protons and neutral hydrogen species are considered. We use a planar potential approach to determine the projectile trajectory that later on allows us to calculate the charge state fractions. We show that, although the fraction of protons is significantly higher, the contribution from neutral hydrogen ionization has to be considered. The energy and angular dependence of the spectra is analyzed.

Effects of grazing incidence conditions on the x-ray diffuse scattering from self-assembled nanoscale islands

Grazing incidence small-angle x-ray scattering and grazing incidence x-ray diffraction from SiGe nanoscale islands grown on Si(001) substrate were investigated. Experiments and corresponding theoretical simulations based on the distorted-wave Born approximation were carried out. The strain field inside and in the vicinity of the SiGe islands was calculated in the framework of linear elasticity theory using the numerical finite element method. The diffuse intensity pattern in reciprocal space reveals a well-resolved fine structure with prominent maxima and a complicated fringe pattern. The distribution of diffuse intensity in reciprocal space strongly depends on the angle of incidence with respect to the sample surface. The results obtained substantiate the important role of basically five (grazing incidence small-angle x-ray) and nine (grazing incidence diffraction) scattering channels that have to be considered for a complete understanding of the scattering scenario. A refined island model concerning shape, size, and Ge composition was elaborated.