Grazing Incidence Angle Research Articles

The state of zinc in methanol synthesis over a Zn/ZnO/Cu(211) model catalyst.

The active chemical state of zinc (Zn) in a zinc-copper (Zn-Cu) catalyst during carbon dioxide/carbon monoxide (CO2/CO) hydrogenation has been debated to be Zn oxide (ZnO) nanoparticles, metallic Zn, or a Zn-Cu surface alloy. We used x-ray photoelectron spectroscopy at 180 to 500 millibar to probe the nature of Zn and reaction intermediates during CO2/CO hydrogenation over Zn/ZnO/Cu(211), where the temperature is sufficiently high for the reaction to rapidly turn over, thus creating an almost adsorbate-free surface. Tuning of the grazing incidence angle makes it possible to achieve either surface or bulk sensitivity. Hydrogenation of CO2 gives preference to ZnO in the form of clusters or nanoparticles, whereas in pure CO a surface Zn-Cu alloy becomes more prominent. The results reveal a specific role of CO in the formation of the Zn-Cu surface alloy as an active phase that facilitates efficient CO2 methanol synthesis.

The concept of a stigmatic flat-field X-ray spectrograph based on conical diffraction

The optical scheme of a flat-field stigmatic X-ray spectrograph, which includes a grazing-incidence focusing mirror and a concave fan-type diffraction grating crossed with respect to the mirror and mounted in a conical diffraction scheme, is calculated analytically. Spectral images of a point monochromatic source are obtained by numerical ray tracing, confirming the high quality of spectral images at a level of 1 × 4 μm. It is assumed that the use of small grazing incidence angles in combination with the application of multilayer reflective coatings, including aperiodic ones, will make it possible to extend the working spectral range of the stigmatic spectrograph to the region of the ‘tender’ (ℏω ≈ 1.5 – 6 keV) X-ray range.

Latent image characterization by spectroscopic reflectometry in the extreme ultraviolet

Background: In the extreme ultaviolet (EUV) lithography process the performance of the photoresist is a crucial factor regarding the quality and critical dimensions of the fabricated structures. Aim: The characterization of the latent image structures in photoresists during the process steps before the development of the resist is key to understand the relation between the material of the resists, the selection of process parameters, and the resulting quality of fabricated structures. Approach: Spectroscopic EUV reflectometry is a nondestructive metrology technique that measures the broadband reflectance of samples in the EUV spectral range and under grazing incidence angles. The technique offers a combination of high sensitivity to nanoscale structural parameters of periodic structures as well as a high sensitivity to the material composition samples, enabling the characterization of latent images of periodic structures. Results: Measurements of the reflectance of an EUV-exposed and unexposed photoresist reveal the contrast in optical constants after the resists are treated with a post-exposure bake as well as shrinkage of the resist layer thickness. Based on this data, simulative studies on latent images of periodic grating structures are conducted showing the possibility to extract information on the structure parameters including the latent image profile and surface topography. Conclusion: Spectroscopic EUV reflectometry shows to be sensitive to the contrast of exposed and unexposed photoresist which commends the technique to be adequate for the characterization of latent images in photoresists.

Measurement of bistatic sea surface scattering with a parametric acoustic source.

This work presents the results from a series of bistatic sea surface scattering experiments conducted in shallow water using a parametric acoustic array as a source and a receiver comprising a horizontal linear array. The experiments measured scattering at three frequencies (4, 8, and 15 kHz) and at three incident grazing angles (13º, 20º, and 30º). The measurements were made over a 5 day period during which a variety of environmental conditions were encountered. This paper provides an outline of the experiments and presents some results for the forward scattering strength. The results show that the wave direction has a significant effect on the surface forward scattering. At each incident grazing angle, the fluctuations of scattering strength due to environmental conditions decreases as the frequency increases.

Identification of BRDF parameters with spectral measurements in the visible light spectrum towards solar irradiation evaluation in urban environment for photovoltaïc technologies

In order to incorporate real construction material reflectance properties in a Monte-Carlo ray tracing algorithm, a representative cladding material is characterised with a spectrophotometer to obtain reflectance angular distribution. These measurements are used to design a BRDF model with a reduced number of parameters that are further identified, along with their confidence intervals. Obtained results are compared to reflectance coefficients measured with an integrating sphere. The prospects of such a model is to allow for a more accurate modelling of the optical properties of materials in reflection. This knowledge can then allow a better integration of photovoltaic technologies, both in terms of energy and visual acceptance. For the particular HPL cladding material tested and despite a highly specular behavior at grazing incidence angles, we found that the specular term only amounts to 4% of reflection.

Research on a Simulation Model of a Skywave Over-the-Horizon Radar Sea Echo Spectrum

The capability of a skywave over-the-horizon radar (SWR) to achieve the continuous observation of a wide range of ocean dynamics parameters via a single ionospheric reflection has been demonstrated by many scholars. In order to expand the method of SWR detection of ocean dynamics parameters, a simulation model of an SWR sea echo spectrum based on the Barrick sea surface scattering cross-section model (Barrick model) and 3D ray-tracing method, suitable for a narrow-beam, frequency-modulated continuous-wave radar system (FMCW), was established. Based on this model, we simulated ideal and contaminated SWR sea echo spectra, respectively with the 3D electron density data output by the International Reference Ionosphere (IRI) model. Then, we further analyzed the effects of the grazing incidence angle, scattering angle, scattering azimuth angle and fetch length on the sea surface scattering cross-sections, the retrieval precision of the sea surface wind direction, and the root-mean-square (RMS) wave height, using the simulation data calculated by the Barrick model. The results show that these angles and fetch length cause a small expansion and contraction of the scattering cross-section, and have no influence on the retrieval precision of the sea surface wind direction, but will affect the retrieval precision of the RMS wave height; the influence of the grazing incidence angle and scattering angle is ~2.5 times that of the scattering azimuth angle. The ideal SWR sea echo spectrum has small broadening, but the ionosphere phase contamination will cause serious broadening and shifting of the SWR sea echo spectrum, and the higher order nonlinear term has greater contamination.

Raman Spectroscopy as a Key Method to Distinguish the Ferroelectric Orthorhombic Phase in Thin ZrO2‐Based Films

Inducing and detecting the polar orthorhombic phase are crucial for the establishment of ferroelectricity in HfO2‐ and ZrO2‐based thin films. Unfortunately, commonly used structural characterization techniques such as grazing incidence angle X‐ray diffraction (GIXRD) only partially allow an accurate detection of this crystalline phase, whose characteristic pattern almost coincides with the one of the tetragonal phase. As a consequence, phase determination is commonly based on peak deconvolution tracing the position of the main peak at 2θ values of around 30°, which can be assigned both to the t(101) and the o(111) plane directions and additionally be influenced by mechanical stress in the layers. Alternatively, epitaxial layers are required to differentiate the phase. Herein, using an integrated experimental–computational approach, it is shown how Raman spectroscopy can distinguish between the monoclinic, the tetragonal, and the orthorhombic phase of ZrO2. The Raman spectra calculated from first principles match the experimentally measured data and thus enable an unambiguous phase assignment. Therefore, Raman spectroscopy proves to be a powerful technique for discerning the three main crystalline phases in these materials. As demonstrated by the good agreement between structural and electrical data, it can therefore be used to predict ferroelectricity in the addressed layers.

Enabling large ferroelectricity and excellent reliability for ultra-thin hafnia-based ferroelectrics with a W bottom electrode by inserting a metal-nitride diffusion barrier

Metal-nitride layers were used as tungsten (W)-diffusion barriers for ultra-thin (<5 nm) Hf0.5Zr0.5O2 (HZO)-based ferroelectric capacitors with W as the bottom electrode. The influence of various metal nitrides (e.g., TiN, HfN, and ZrN) on the leakage properties, ferroelectricity, and reliability of the HZO capacitors was systematically investigated to identify appropriate materials for use as diffusion barriers in TiN/HZO/W stack capacitors. All the metal-nitrides were observed to significantly suppress W diffusion, resulting in a reduced leakage current. A comparative study between diffusion barriers revealed that the TiN/HZO/W stack capacitor with a ZrN layer exhibited the largest remanent polarization (2Pr) of 23 μC/cm2, as well as the highest reliability. This was attributed to the ZrN forming a ZrO2 interfacial layer, which could contribute to polarization switching and improve reliability. We quantitatively calculated the interfacial capacitance by performing the pulse switching measurement. In addition, crystal structures and diffusion properties with various metal nitrides are evaluated by analyzing grazing-angle incidence x-ray diffraction and x-ray photoelectron spectroscopy. These results provide a guideline for the fabrication of ultrathin HZO-based capacitors with stable ferroelectricity, reduced leakage, and excellent reliability.

Angular Distribution of Polarized X-Ray Cherenkov Radiation at Grazing Incidence Angles

Angular Distribution of Polarized X-Ray Cherenkov Radiation at Grazing Incidence Angles

Table-top interferometry on extreme time and wavelength scales.

Short-pulse metrology and dynamic studies in the extreme ultraviolet (XUV) spectral range greatly benefit from interferometric measurements. In this contribution a Michelson-type all-reflective split-and-delay autocorrelator operating in a quasi amplitude splitting mode is presented. The autocorrelator works under a grazing incidence angle in a broad spectral range (10 nm - 1 μm) providing collinear propagation of both pulse replicas and thus a constant phase difference across the beam profile. The compact instrument allows for XUV pulse autocorrelation measurements in the time domain with a single-digit attosecond precision and a useful scan length of about 1 ps enabling a decent resolution of E/ΔE = 2000 at 26.6 eV. Its performance for selected spectroscopic applications requiring moderate resolution at short wavelengths is demonstrated by characterizing a sharp electronic transition at 26.6 eV in Ar gas. The absorption of the 11th harmonic of a frequency-doubled Yb-fiber laser leads to the well-known 3s3p64p1P1 Fano resonance of Ar atoms. We benchmark our time-domain interferometry results with a high-resolution XUV grating spectrometer and find an excellent agreement. The common-path interferometer opens up new opportunities for short-wavelength femtosecond and attosecond pulse metrology and dynamic studies on extreme time scales in various research fields.

Plasma-assisted template removal and consolidation of silica coatings on polycarbonate

This paper presents a fast and efficient method of removing the template from silica thin films on polycarbonate. Radiofrequency-generated oxygen plasma induced the decomposition of the non-ionic surfactant. The reference samples were silica coatings on silicon, which had different pore sizes. We removed the surfactant by solvent extraction and calcination from these samples. Grazing incidence angle X-ray diffraction analysis shows a highly ordered arrangement of mesopores. The formation of the face-centred cubic structure of mesopores is independent of the substrate and the template removal method. Atomic force microscopy analysis showed open-pore channels after oxygen plasma etching. It also proved that the ammonia treatment increases the hardness of the layer. A short air-plasma treatment is effective for the consolidation of the silica layer and improves the abrasion resistance of the layer on polycarbonate. Air plasma treatment is an alternative to the long heat treatment process. We performed environmental tests according to the relevant ISO standards for optical coatings. Air plasma treated silica coatings have passed all the weathering tests. Therefore, it can be used in outdoor applications, such as a protective layer for the plastic cover of LED street lights. These thin films on polycarbonate have at least one year of service life and are weather-resistant. Plasma treatment can consolidate the silica network and the thin films on polycarbonate have high light transmission (T = 98.8 %).

A sliced-3D approach to finite-difference time-domain modeling by optimizing perfectly matched layers

Finite-difference time-domain forward modeling is often used to gain a more quantitative understanding of the interactions between electromagnetic fields and targets. To undertake full 3D simulations, the computational demands are challenging, so simulations are often undertaken in two dimensions, in which assumptions in the propagation of electromagnetic fields and source type can result in errors. We have developed the concept of a sliced-3D simulation, wherein a thin slice of a 3D domain with strictly 2D geometry is used to minimize computational demands while obtaining synthetic waveforms that contain full 3D propagation effects. This approach requires optimization of perfectly matched layer (PML) boundary condition parameters so as to minimize the errors associated with the source being located close to the boundary, and as a result of grazing-incident angle wave conversion to evanescent energy. We explore the frequency dependence of PML parameters, and we establish a relationship between complex frequency stretching parameters and effective wavelength. The resultant parameter choice is shown to minimize propagation errors in the context of a simple radioglaciological model, in which 3D domains may be prohibitively large, and for a near-surface cross-borehole survey configuration, a case in which full-waveform inversion may typically be used.

An Accurate Integral Equation Formulation to Scattering of Periodic Grating Structures

Broadband wave transmission grating structures have potentials in many engineering applications. Theoretical predictions of the transmission spectra and near field characteristics of such structures are crucial for the understanding and design of wave functional gratings. However, accurate theoretical modeling of the wave interactions with such periodic grating structures turns out to be difficult, especially at near grazing incidence angles. In this paper, an efficient and accurate method to solve the scattering of periodic grating structures is proposed based upon integral equation formulations utilizing periodic lattice Green's functions. The method of moments is used to discretize the integral equation with the pulse basis function and the point matching scheme. The imaginary wavenumber extraction technique and the integral transformation approach are combined to efficiently and accurately evaluate the period Green's function. Meanwhile, an over-determined testing scheme on the integral equation is devised to overcome the intrinsic internal resonance of surface integral equations. Such strategy has significantly improved the numerical accuracy of the proposed approach. Calculation results are compared with Comsol simulations for various scenarios, and the proposed approach is found to be predicting physically sound results when Comsol fails at certain frequencies and incident angles. The proposed method is applicable to grating periodic structures of various shapes and it provides a useful reference and tool for researchers and designers.

Enhancing the surface sensitivity of in-situ/operando characterization of palladium membranes through polarization modulation and synthesis of optically smooth palladium thin films

Operando infrared reflection absorption spectroscopy (IRAS) is a powerful technique for elucidating the fundamental mechanisms by which reactive gases such as CO, C3H6 and H2S poison (inhibit) H2 permeation across palladium (Pd) and Pd-alloy H2 separation membranes, by integrating in-situ IRAS detection of chemical species adsorbed on the membrane surface with simultaneous measurement of H2 permeation rates on the same sample. Achieving high sensitivity to detection of surface-adsorbed species under realistic operating conditions is a significant challenge, however, because infrared absorption from gas-phase species can obscure the relatively weak absorption bands associated with surface-adsorbed species, and IRAS requires optically smooth Pd membrane surfaces to specularly reflect the infrared light at grazing angle incidence. This work addresses both of these challenges by (1) installing a photoelastic modulator in the infrared beam path to modulate the polarization of the infrared light between s- and p-polarization (PM-IRAS), and (2) by developing a new electroless plating method for synthesis of optically smooth Pd thin film membranes. The net result is a ~10× enhancement in the sensitivity to detection of surface-adsorbed CO in the presence of gas-phase CO, relative to IRAS characterization with commercial Pd foil. This work represents a significant advancement in the development and application of surface-sensitive operando membrane characterization, which is a relatively new research methodology that is expected to have a significant impact on membrane science in the coming years because of its unique ability to directly correlate membrane atomic/molecular structure to its performance under realistic operating conditions.

The microstructure and tribological properties of M50 steel surface after titanium ion implantation

Titanium ions with different energies and doses were implanted into the M50 steel surface. In addition, titanium and nitrogen ion co-implantation was applied for comparison. The tribological properties and wear resistance of the implanted samples were characterized using a sliding friction tester, grazing incidence angle X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, surface profiler, Raman spectrometer, and nanoindentation tests. The results indicated that the compounds of the titanium ion–implanted samples mainly consisted of titanium and TiO2, CrN interstitial compounds formed after titanium and nitrogen ion co-implantation, thus generating an implantation layer that exhibited high nano-hardness and low wear rates. The linear contact sliding friction coefficient curves for the implantation samples were composed of an initial stage, ascent stage, and stable stage. The tribological properties effectively improved with increasing titanium ion implantation energies and doses. In addition, this beneficial effect became much more significant at a higher titanium ion dose. The titanium and nitrogen ion–co-implanted samples formed Fe2O3 and Fe3O4 tribo-oxide layers after the wear test, which were partially responsible for reducing the wear. The dominant wear mechanisms of the implanted samples were abrasive wear and oxidative wear.

Effects of Weakly Nonlinear Waves on Acoustic Scattering from the Ocean Surface

The elevation of ocean waves is always modeled in linear theory as a superposition of the sinusoidal components with crests and troughs of identical heights. However, under some circumstances, the wave amplitude is outside the linear range and presents as a weakly nonlinear asymmetrical waveform with sharper crests and shallower troughs. We studied the impact of the weakly nonlinear effect of ocean waves in deep and intermediate waters on acoustic scattering from the surface of the ocean using two rough surface models with fractal geometry and power law spectral behavior in the equilibrium range. The classic Weierstrass–Mandelbrot function was used to model the linear waves and a new fractal function, the fractional Weierstrass function developed in studies of electromagnetism, was used to model the weakly nonlinear waves. We evaluated these two models using the Pierson–Moskowitz spectrum and the incident wavelength. The bistatic scattering strength was obtained via a numerical method based on the “exact” solution of the integral equation. The weakly nonlinear phenomenon led to a very small reduction in the narrow area around the specular reflection angle and a small increase in the remaining wide area, including the backpropagation area with a scattering angle [Formula: see text]. The differences in backscattering strength between the two models were similar to the bistatic scattering strength in the backpropagation area and did not depend on the incident grazing angle.

Characterization of surface and subsurface defects induced by abrasive machining of optical crystals using grazing incidence X-ray diffraction and molecular dynamics

IntroductionSurface and subsurface defects were easily induced during abrasive machining process of optical crystals due to their high brittleness. Accurate characterization of these defects is the prerequisite for obtaining optical components with high surface integrity. ObjectivesThis work aims to evaluate subsurface defects of CaF2 single crystals induced by abrasive machining, the mappings between micro cracks and diffraction pattern curves, and the influence of micro cracks on lattice structures. MethodsMolecular dynamics simulation, grazing incidence X-ray diffraction experiments and cross-sectional TEM detection were used in this work. ResultsIn grazing incidence X-ray diffraction (GIXD) detection experiments on lapping and polished specimens, shifts phenomenon of the peak position under the non-theoretical grazing incidence angle indicated that the subsurface was damaged to a certain extent. The micro cracks of the subsurface were evaluated by the consistent characteristic of “peak drift” of the diffraction pattern curve in both experiments and simulations. In addition, cross-sectional TEM results showed that regular micro cracks were found on the subsurface, which agreed well with the simulation results. ConclusionThe subsurface defects of CaF2 single crystals induced by abrasive machining, and the influence of micro cracks on lattice structures can be evaluated by molecular dynamics simulation. The simulation results revealed the mappings between the micro cracks and diffraction pattern curve, which demonstrated that a phenomenon of “peak drift” occurred near the diffraction angle of a specific crystal plane. This work provided a novel technology for the nondestructive testing of defects of single crystal materials at nano- and micro- scales.

Heavy ion irradiation induced defects in Zircaloy-4

Radiation damage induced in Zircaloy-4 by 20 MeV Au ions was investigated using Grazing x-ray diffraction (GIXRD), positron annihilation techniques, micro-and nano-hardness techniques. The irradiations were performed at room temperature in the fluence range 1 × 1013–5 × 1014 ions cm−2 corresponding to 0.07–3.63 displacements per atom (dpa). The grazing incidence angle x-ray diffraction (GIXRD) revealed the presence of the hydride precipitates in the analyzed zircaloy-4. According to our experimental data it is found that the amount of these precipitates decreases after irradiation as emphasized by GIXRD and Positron Annihilation Lifetime Spectroscopy (PALS) results. The same data revealed also a zircaloy-4 swelling above a certain dose. From the combination of domain size/microstrain with the micro- and nano-hardness results, we conclude that the Zircaloy hardening is mainly due to the dislocation formation indicating the effect of the microstructure on the mechanical properties. Moreover, from the dose dependence of irradiation hardening we conclude that the transition point from low-dose to high-dose regime is observed around 0.07 dpa.

Vpliv časa nanašanja nanostebričastih TiZrN filmov z OAD-tehniko in hkratnim reaktivnim magnetronskim naprševanjem

Well-separated inclined nanocolumnar TiZrN films were grown on silicon-wafer substrates by reactive magnetron co-sputtering with the oblique-angle-deposition (OAD) technique. The crystal structure, thickness, morphology and chemical composition of the prepared TiZrN films were investigated with the X-ray diffraction technique at the grazing-incidence angle (GIXRD), field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). The length, diameter and tilt angle of the nanocolumnar TiZrN films were evaluated. The microstructure and chemical composition were analyzed with transmission electron microscopy (TEM). The results indicated that the film crystallinity and physical morphology were influenced by the deposition time due to the self-annealing effect, which occurred during the nanocolumnar growth. Moreover, the hardness and surface wettability of the TiZrN films were studied using a nanoindentater and the water-contact-angle method, respectively. It was found that the hardness and hydrophobic surface of the TiZrN films decreased with the increasing deposition time.

Enhancement of mesoscopic fluctuations in transmission of light through a disordered medium at grazing angles

We study how intensity fluctuations in transmission through a disordered slab change depending on the regime of wave transport. A system with large (compared to the wavelength of light) inhomogeneities is considered. Within a diagrammatic approach, the variance of the total transmission coefficient is calculated numerically beyond the diffusion approximation. A great enhancement of fluctuations is found in the crossover from the ballistic to the diffusive transport at the grazing angles of incidence on the sample surface. The effect originates from the reflection of waves that propagate nearly parallel to the sample boundaries and experience scattering through small angles, and reveals itself both in transmission and reflection and in correlations between the transmitted and reflected fluxes.