Grazing Incidence Reflection Research Articles

极紫外Mg/SiC、Mg/Co多层膜的稳定性

To research the stability of Mg-based multilayers,two groups of multilayers,20 and [Mg/SiC]20 were coated on a Si(100) substrate by magnetron sputtering method.The two samples were tested by a microscopy,a surface roughness experiment and an X-ray grazing incidence reflectivity test at room temperature and a relative humidity of 80%.The contract experiments on multilayer damage for Mg/Co和Mg/SiC were performed in the same condition.The results show that after being exposed in the atmospheric environment for 4 days,the damaged area and surface roughness of the Mg/SiC multilayer sample are up to 26.34% and 10 nm,respectively,while those of the Mg/Co multilayer sample are 2.78% and 5 nm,respectively.After 6 days,the 1st reflection peak of Mg/SiC sample is completely disappeared,and Mg/Co sample still has a peak of 47.63% reflectivity.The experimental results show that the Mg/Co multilayer sample has a better environmental stability as compared with the Mg/SiC multilayer.The X Photoelectron Spectroscopy(XPS) shows that the productions of the damaged Mg-based multilayers are mainly MgCO3,Mg(OH)2 and modest MgO.Moreover,the content ratio of Mg(OH)2 and MgCO3 in the inner layer is significantly higher than that in the surface layer.Experimental results suggest that the reason for Mg-based multilayer damage is the erosion of H2O(g),so the capping layer of Mg-based multilayer should prevent the H2O(g) penetrating into the mulilayer.

Conversion of basal plane dislocations to threading edge dislocations in 4H-SiC epilayers by high temperature annealing

Conversion of basal plane dislocations (BPDs) to threading edge dislocations (TEDs) is found in 4H-SiC epilayers after being annealed simply at high temperatures. Grazing incidence reflection synchrotron x-ray topography for the dislocations in the epilayers before and after annealing confirmed that some of the BPDs in the epilayers had converted to TEDs from the epilayer surface by the annealing. Observations on the dislocation behavior during annealing are explained in detail, and the mechanism of BPD conversion is discussed. It is argued that the conversion proceeds through the cross slip of constricted BPD segments towards the surface on the prismatic plane driven by the image force as well as TED glide driven by the line tension. Certain kinetic processes during annealing may facilitate the formation of constriction.

Spectral research on an AlGaAs epitaxial material for a terahertz quantum-cascade laser

The spectral properties of a series of AlGaAs epitaxial films were studied by using a Fourier transform infrared spectrometer with an 80-degree grazing incidence reflection unit. The AlAs-like transversal optical phonon was obviously observed in the spectra, but the longitudinal optical phonon was obscured in the transmission spectra. The variation curves for the transversal optical phonon energy were acquired from the two kinds of spectra and were compared with each other and with the early results. A comparison of the results show that the grazing incidence reflection spectrum is better in reflecting the AlAs-like phonon energy of an AlGaAs epitaxial film and could be a supplementary means in the characterization of the material for a terahertz quantum-cascade laser.

Conversion of Basal Plane Dislocations to Threading Edge Dislocations by High Temperature Annealing of 4H-SiC Epilayers

ABSTRACTConversion of basal plane dislocations (BPDs) to threading edge dislocations (TEDs) has been observed in 4H-SiC epilayers by simple high temperature annealing. Grazing incidence reflection synchrotron X-ray topography was used to image the dislocations in the epilayers. By comparing the X-ray topographs before and after annealing, some of the BPDs were confirmed to convert to TEDs from the epilayer surface. The dislocation behaviors during annealing are explained and the mechanism of BPD conversion is discussed. It is argued that the conversion process is realized by constricted BPD segments cross-slipping to the prismatic plane driven by the image force and TED glide on its slip plane driven by the line tension. Certain kinetic processes may assist the formation of constrictions on the BPDs.

Comparison of dynamical theory and phase-object approximation for neutron scattering from periodic structures

Dynamical theory (DT) calculations have been successfully developed to explain neutron spin-echo resolved grazing-incidence scattering from diffraction gratings. The theory, without any adjustable parameters, has been shown in previous publications to accurately reproduce the sensitivity of the spin-echo polarization signal to sample specifications and scattering geometry. The phase-object approximation (POA), which is computationally less demanding than the DT, has also been used to analyze neutron spin-echo polarization data obtained from diffraction gratings. In this paper, POA and DT calculations are compared for neutron scattering from various diffraction gratings in different geometrical settings. POA gives a good description of the data for transmission cases, where the neutron beam is incident at large angles to the average grating surface. However, for the grazing-incidence reflection cases that were studied, the POA does not fit the data using the independently determined dimensions of the measured gratings. On the other hand, the good agreement between dynamical theory and the data from gratings with known profiles paves the way for its use to extract profile information from periodic samples with unknown structures.

Development of microperiodic mirrors for hard x-ray phase-contrast imaging

Differential phase-contrast imaging with hard x rays can have important applications in medicine, material sciences, and energy research. Phase-contrast methods based on microperiodic optics, such as shearing interferometry, are particularly attractive because they allow the use of conventional x-ray tubes. To enable shearing interferometry with x rays up to 100?keV, we propose using grazing-incidence microperiodic mirrors. In addition, a simple lithographic method is proposed for the production of the microperiodic x-ray mirrors, based on the difference in grazing-incidence reflectivity between a low-Z substrate and a high-Z film. Using this method, we produced prototype mirrors with 5-100?mum periods and 90?mm active length. Experimental tests with x rays up to 60?keV indicate good microperiodic mirror reflectivity and high-contrast fringe patterns, encouraging further development of the proposed imaging concept.

Active Microstructured Optical Arrays of Grazing Incidence Reflectors

The UK Smart X-Ray Optics (SXO) programme is developing active/adaptive optics for terrestrial applications. One of the technologies proposed is microstructured optical arrays (MOAs), which focus X-rays using grazing incidence reflection through consecutive aligned arrays of microscopic channels. Although such arrays are similar in concept to polycapillary and microchannel plate optics, they can be bent and adjusted using piezoelectric actuators providing control over the focusing and inherent aberrations. Custom configurations can be designed, using ray tracing and finite element analysis, for applications from sub-keV to several-keV X-rays, and the channels of appropriate aspect ratios can be made using deep silicon etching. An exemplar application will be in the microprobing of biological cells and tissue samples using Ti Kα radiation (4.5 keV) in studies related to radiation-induced cancers. This paper discusses the optical design, modelling, and manufacture of such optics.

Surfactant induced orientation of non-centrosymmetric polyoxometalate clusters in Langmuir–Blodgett films

The trivacant Keggin-type polyoxometalate Na 10- α-SiW 9O 34 (SiW 9) was encapsulated by the cationic surfactant dimethyl dioctadecylammonium (DODA) and forms an organic–inorganic complex. Stable Langmuir monolayers of this surfactant-encapsulated cluster complex form at the air–water interface and can be transferred onto solid substrates with a transfer ratio of 1.0 ± 0.02. Fourier transform infrared spectroscopy at grazing incidence reflection condition reveals that the non-centrosymmetric SiW 9 clusters are highly oriented in the films with their symmetry axis aligned preferably perpendicular to the layer plane. We propose a model in which the orientation state of SiW 9 is induced by the different electrostatic interactions between DODA molecules and different positions at the SiW 9 surface.

Wolter optics for neutron focusing

Focusing optics based on Wolter optical geometries developed for X-ray grazing incidence beams can be designed for neutron beams. Wolter optics are formed by grazing incidence reflections from two concentric conic sections (for example, a paraboloid and a hyperboloid). This has transformed observational X-ray astronomy by increasing the sensitivity by many orders of magnitude for research in astrophysics and cosmology. To increase the collection area, many reflecting mirrors of different diameters are nested with a common focal plane. These mirrors are fabricated using nickel-electroformed replication techniques. We apply these ideas to neutron focusing using nickel mirrors. We show an initial test of a conical mirror using a beam of cold neutrons.

Determination of layer-thickness variation in periodic multilayer by x-ray reflectivity

A method basically determining individual layer thicknesses in actual periodic multilayers has been developed, that solves simultaneous equations of positions of peaks appearing in wavelet transform curve of x-ray grazing incidence reflectivity. The determination was demonstrated on a Ni/C periodic multilayer fabricated by magnetron sputtering. Using the layer thicknesses obtained by the method, further accurate of thickness, roughness, and density of each layer was performed by Parratt’s model. The special feature that the topmost and bottom-most layers were thicker than other layers was clearly observed. The former is attributed to oxidation and the latter is attributed to the effect of deposition on thick substrate. The mean fluctuations of other layers are 2.6% in C layers and 4.2% in Ni layers attributed to random fluctuations at deposition. Numerical analysis and statistical hypothesis tests have been carried out to discuss noncumulative and cumulative layer-thickness fluctuations in fabrication process.

Nanoscale piezoresponse of 70 nm poly(vinylidene fluoride‐trifluoro‐ethylene) films annealed at different temperatures

AbstractIn order to characterize the piezoelectric properties of 70 nm thick poly(vinylidene fluoride‐trifluoroethylene), P(VDF‐TrFE), films grown by a spin‐coating technique, both nanoscale manipulation and polarization switching were studied using piezoresponse force microscopy (PFM). We varied the annealing temperature from 75 °C to 145 °C and achieved a high‐quality 70 nm P(VDF‐TrFE) film annealed at the temperature of 95 °C. Ferroelectric domains and their properties were confirmed using X‐ray diffraction, grazing incidence reflection absorption Fourier Transform Infrared (GIRA‐FTIR) and PFM analysis. The ferroelectric domains in the film were homogeneously switchable below 5 V with a remnant d33 of 14.9 pm/V. This offers our rationale for a promise in energy harvesting and switchability would be good for plastic electronics. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A grazing incidence x-ray streak camera for ultrafast, single-shot measurements

An ultrafast x-ray streak camera has been realized using a grazing incidence reflection photocathode. X-rays are incident on a gold photocathode at a grazing angle of 20° and photoemitted electrons are focused by a large aperture magnetic solenoid lens. The streak camera has high quantum efficiency, 600 fs temporal resolution, and 6 mm imaging length in the spectral direction. Its single shot capability eliminates temporal smearing due to sweep jitter, and allows recording of the ultrafast dynamics of samples that undergo nonreversible changes.

A new dual-purpose ultrahigh vacuum infrared spectroscopy apparatus optimized for grazing-incidence reflection as well as for transmission geometries

A newly designed ultrahigh vacuum (UHV) infrared spectroscopy apparatus dedicated to the spectroscopic characterization of oxides, singles crystals as well as powders, is described. It combines a state-of-the-art vacuum Fourier transform infrared (FTIR) spectrometer (Bruker, VERTEX 80v) with a novel UHV system (PREVAC) consisting of load-lock, distribution, measurement, and magazine chambers. The innovative design allows carrying out both reflection-absorption IR spectroscopy experiments at grazing incidence on well-defined oxide single crystal surfaces and FTIR transmission measurements for powder particles. A further unique feature of the apparatus is the entirely evacuated optical path to avoid background signals from gas phase H(2)O, CO(2), and other species, thus creating the possibility to record high-quality IR data with high sensitivity and stability, an essential prerequisite for monitoring molecular species adsorbed on oxide single-crystal surfaces. The unique performance of this new apparatus with regard to the spectroscopic characterization of adsorbates on oxide single crystals as well as on powder particles is demonstrated by case studies for two different materials, TiO(2) and ZnO.

Design of monochromatic X-ray imager with a pinhole and a logarithmic spiral Bragg mirror for Z-pinch diagnose

Monochromatic self-emission X-ray imaging is a powerful way to diagnose the imploding Z-pinch plasmas. Several approaches have been successfully developed to image the 0.1–1keV continuous emission of a time evolving Z-pinch plasma, including the using of a filtered pinhole camera and a filtered pinhole camera combined with a grazing incidence reflection mirror or a planar multilayer mirror, but these techniques might be unfeasible when the instrument is keyed to image the 1–10keV K-shell emission due to the inherent constraints such as limited mirror-filter match and/or large energy dispersion. In this paper, we proposed a novel monochromatic X-ray imaging approach that employs a pinhole camera and a logarithmic spiral Bragg mirror. The logarithmic spiral Bragg mirror is a non-dispersive monochromator that break the constraints meted in the planar mirror and thus can be used to image the K-shell emission. The geometrical imaging theory of this new instrument and the instrument design and evaluation are discussed.

Development of piezoelectric actuators for active X-ray optics

Piezoelectric actuators are widely utilised in adaptive optics to enable mirrors having an actively controlled reflective surface for the purpose of the wavefront correction by reducing the effects of rapidly changing optical distortion. Two new prototype adaptive X-ray optical systems are under development with the aim of approaching the fundamental diffraction limit. One proposed technology is microstructured optical arrays (MOAs) involving two or four piezoelectric strips bonded to a silicon wafer to produce a micro-focused X-ray source for biological applications, and which uses grazing incidence reflection through consecutive aligned arrays of channels obtained using deep silicon etching. Another technology is large scale optics which uses a thin shell mirror bonded with 20–40 piezoelectric actuators for the next generation of X-ray telescopes with an aim to achieve a resolution greater than that currently available by Chandra (0.5"). PZT-based piezoelectric actuators are being developed in this programme according to the design and implementation of the proposed mirror and array structures. Viscous plastic processing is chosen for the preparation of the materials system, which is subsequently formed and shaped into the suitable configurations. Precise controls on the thickness, surface finish and the curvature are the key factors to delivering satisfactory actuators. Unimorph type piezoelectric actuators have been proposed for the applications and results are presented regarding the fabrication and characterisation of such piezo-actuators, as well as the related design concepts and comparison to modelling work.

Study on the layer structure of W/C multilayers deposited by magnetron sputtering using x‐ray reflectivity

AbstractA study on the layer structure of W/C multilayers deposited by magnetron sputtering is reported. In the study, soft x‐ray resonant reflectivity and hard x‐ray grazing incidence reflectivity of the W/C multilayers were measured. The imperfections at the interface such as interdiffusion and formation of compounds were dealt with by two methods. On analyzing the experimental results, we found that the incorporation of an interlayer was a more suitable method than the traditional statistical method to describe the layer structure of a W/C system we fabricated. The optical constants of each layer at a wavelength of 4.48 nm were also obtained from the analysis. Copyright © 2008 John Wiley & Sons, Ltd.

Thickness-dependent crystal orientation in poly(trimethylene 2,6-naphthalate) films studied with GIWAXD and RA-FTIR methods

The thickness dependence of the crystal orientation of poly(trimethylene 2,6-naphthalate) (PTN) films was clearly demonstrated using the methods of two-dimensional grazing incidence wide angle X-ray diffraction (2D GIWAXD) and grazing incidence reflection absorption FTIR (RA-FTIR) spectroscopy. The 2D GIWAXD results showed that for films thicker than 200nm, the “c” axis (main chain direction) and “b” axis of crystal unit cell are almost parallel to the sample surface, whereas for thin films the “c” axis is preferentially perpendicular to the film plane in the crystalline phase of isothermally crystallized PTN films. The anisotropic orientation of the naphthalene rings in the isothermally crystallized PTN film was also confirmed. By analyzing the relative absorbance of the parallel band (1602cm−1) to the one of perpendicular band (917cm−1), the thickness dependence of the crystal orientation suggested by the GIWAXD results was also confirmed. Furthermore, the naphthalene rings in the isothermally crystallized thick films were found to lie flat on the film plane. The chain orientations derived from the GIWAXD and RA-FTIR results in this work were found to be consistent with the “flat-on” and “edge-on” lamellar orientation for the thin and thick films, respectively, which has previously been reported in many polymer systems.

Enhanced heteroepitaxial growth of CoCrPt–SiO2 perpendicular magnetic recording media on optimized Ru intermediate layers

The crystallographic growth, interfacial roughness, and magnetic properties of CoCrPt–SiO2 perpendicular magnetic recording media prepared on various types of Ru intermediate growth layers were systematically investigated based on high angle and omega offset x-ray diffraction scans, rocking curve scans, synchrotron radiation based grazing incidence reflectivity scans, and magneto-optical Kerr hysteresis loops. For samples that make use of one Ru growth layer, voltage bias applied on the Ru layer was seen to have two observable effects: (1) the dispersion in the Ru(00⋅2) perpendicular texture increased, but that of the Co(00⋅2) remained unchanged, leading to identical layered growth and (2) the in-plane a-lattice parameter of the Ru decreased leading to enhanced heteroepitaxy with the Co. There was no significant change in the Ru–Co interfacial roughness with changing the bias on the Ru layer. The bias effect can be used to optimize the design of the Ru intermediate layers. A scheme that makes use of two Ru growth layers consisting of a bottom Ru layer prepared under zero bias, which is inserted below a second Ru layer prepared under biased conditions, is shown to lead to significant benefits such as improved texture without affecting the magnetic properties. This is due to the different functional roles ascribed to each of the Ru growth layers.

The small-angle and wide-angle X-ray scattering set-up at beamline BL9 of DELTA

The multi-purpose experimental endstation of beamline BL9 at the Dortmund Electron Accelerator (DELTA) is dedicated to diffraction experiments in grazing-incidence geometry, reflectivity and powder diffraction measurements. Moreover, fluorescence analysis and inelastic X-ray scattering experiments can be performed. Recently, a new set-up for small-angle and wide-angle X-ray scattering utilizing detection by means of an image-plate scanner was installed and is described in detail here. First small-angle X-ray scattering experiments on aqueous solutions of lysozyme with different cosolvents and of staphylococcal nuclease are discussed. The application of the set-up for texture analysis is emphasized and a study of the crystallographic texture of natural bio-nanocomposites, using lobster and crab cuticles as model materials, is presented.

Whispering-gallery modes in photonic tubes

Microcavity structures are designed to enhance the interaction of light with matter. Wavelength-scale structures that confine light can be used to make highly efficient micro-lasers and sensors. Planar, spherical, and cylindrical geometries have all been developed to make efficient micro-resonators. Among these devices, the microcylindrical or microcapillary dielectric resonators have generated significant interest due to their small size and material compatibility with telecommunication optical fibers.1 The cylindrical cavity format is also compatible with a large variety of sensing modalities such as immunoassaying and molecular diagnostic assaying. Recent efforts to develop efficient micro-tube emitters focused on optical modes that are concentrated at the surface of dielectric materials. The main physical phenomenon exploited for this development is grazing-incidence total internal reflection of light resulting in ‘whispering-gallery’ modes (WGMs). In thesemodes, light propagates in planes near the surface, with integer numbers of wavelengths along closed circumferential trajectories. The high degree of confinement of light in WGM results in a high resonance quality factor (Q). Experimentally, the most widely-studied configuration of thin-wall microtube cavities is the microcapillary filled with a highly luminescent dye solution. Both diameter (typically 50-200μm) and wall thickness can be controlled by the etching of commercially-available glass samples in an HF-water solution.2 However, the short-distance evanescent field in these microcavities and the limited photostability of dye molecules are retarding factors for potential applications. In the small-size regime (with diameters less than 10μm), semiconductor microdisks of finite height—micropillars—have been widely used as a tool to control spontaneous emission and confine photons in three dimensions. The evanescent field in Figure 1. Room-temperature photoluminescence spectra of a single free-standing microtube recorded with polarizer orientation parallel to the microtube axis (red trace) and with polarizer rotated by 90 (black trace).