Johansson Geometry Research Articles

Chemical sensitivity of the Kα X-ray emission of Ti and Cr compounds induced by 2 MeV protons

Kα x-ray emission induced by 2 MeV protons in thick Ti metal, TiO, Ti2O3, TiO2, MgTiO3, FeTiO3, TiC, TiN, TiB2, Cr metal, Cr2O3, CrO2, CrO3, K2Cr2O7 targets was measured using a wavelength dispersive spectrometer employing Johansson geometry to study chemical sensitivity of X-ray spectra. In the spectra the main Kα1 and Kα2 components as well as the KαL1 multiple ionization satellites were clearly resolved. The Kα1 and Kα2 peak positions and widths were extracted directly from the measured spectra in a consistent way. The results were compared with the existing data obtained by proton and photon induced ionization mechanisms, with the results of multiplet calculations, and with the observed chemical effects found in the related experimental Kβ spectra measured on the same Ti and Cr compounds at earlier times. The results obtained confirm linear correlations of the Kα1 first moments (M1) and the Kα center of gravity energy shifts with the central metal formal oxidation state, as well as between the Kα1 line widths and the Kα1 - Kβ1 M1 and/or centre of gravity energy shifts. The Kα energy shifts calculated by multiplet structure method for Cr compounds agreed with the experimentally obtained trends. Keywords: X-ray emission spectroscopy, High resolution X-ray spectra, Ti and Cr compounds, PIXE, Multiple ionization satellites.

M shell ionization of Ar induced in near-central collisions with MeV protons

High energy resolution x-ray emission spectra of Ar induced in collisions with 0.75–3.0 MeV protons were measured using a complete in-vacuum curved-crystal x-ray emission spectrometer in Johansson geometry. The satellite lines were clearly resolved in the measured spectra and their intensity relative to the parent diagram line was used to extract the M shell single ionization probability for near-central collisions. The experimental values are compared to the theoretical predictions calculated within the semiclassical approximation (SCA) and also the binary encounter based geometrical model. Very good agreement with experimental data was achieved for the SCA values employing concise Dirac–Hartree–Fock wave functions for the description of valence M shell electrons.

Resonant inelastic X-ray scattering on atoms and simple molecules in the tender X-ray region

We present the main characteristics of the experimental set-up used to perform gas-phase RIXS studies in the tender X-ray range. A complete in-vacuum curved-crystal X-ray emission spectrometer in Johansson geometry has been built for a 2–6keV energy range with sub natural line-width energy resolution. The spectrometer operates in a dispersive geometry, employing a relatively large X-ray source placed inside the Rowland circle and a position sensitive detection of diffracted X-rays. A short review of the most recent experimental applications is given focusing on RIXS studies on isolated atoms and molecules.

Control of the chemical state change of sulfur in solid compound targets during high-resolution PIXE measurements

A high-energy-resolution wavelength-dispersive (WD) X-ray spectrometer in the Johansson geometry, which allowed energy resolution below the natural linewidth of the Kα lines was employed in measurements of the proton-induced Kα X-ray emission spectra for six typical sulfur compounds (CdS, Na2SO3, Na2 S2O5, NaHSO3, (NH4)2SO4, and Na2SO4) to investigate the chemical state change during 2.4-MeV proton irradiation with a current density of 7.5 nA/mm2. We found that the chemical state change of each compound depended on the various factors affecting the surface temperature increase, such as target thickness, mounting method, and existence of active cooling during the measurement. The chemical state of sulfur on the target surface of S4+ compounds was gradually changed into S6+ without exception through irradiation under poor cooling conditions. Sulfur compounds of the S0 and S6+ states with closed shell structures were proven to be chemically stable against proton bombardment, as expected. However, (NH4)2SO4 was found to be most sensitive to proton irradiation among the sulfur compounds, and S0, one of the reaction products, became a major element at doses higher than 3 × 108 Gy. If thick targets were mounted by using a carbon adhesive tape, chemical state change could be observed in some cases even with lowtemperature cooling down to −80 °C, however, the chemical state change seemed to be remarkably suppressed by using very thin targets mounted with a silver paste even without active cooling. In conclusion, the chemical states of sulfur compounds could be preserved without significant change for an accumulated dose of about 3 × 107 Gy, equivalent to a typical high-resolution PIXE scanning period, by adopting a proper target preparation scheme to discharge proton-induced thermal energy effectively from the irradiated target surface.

Design and performance of a versatile curved-crystal spectrometer for high-resolution spectroscopy in the tender x-ray range

A complete in-vacuum curved-crystal x-ray emission spectrometer in Johansson geometry has been constructed for a 2-6 keV energy range with sub natural line-width energy resolution. The spectrometer is designed to measure x-ray emission induced by photon and charged particle impact on solid and gaseous targets. It works with a relatively large x-ray source placed inside the Rowland circle and employs position sensitive detection of diffracted x-rays. Its compact modular design enables fast and easy installation at a synchrotron or particle accelerator beamline. The paper presents main characteristics of the spectrometer and illustrates its capabilities by showing few selected experimental examples.

Crossover and valence band Kβ X-rays of chromium oxides

Kβ X-ray spectra of chromium metal and selected chromium oxides were measured twice using medium resolution flat crystal spectrometer and high resolution spectrometer employing Johansson geometry after excitation with 2 MeV proton beams. The positions and intensities of crossover ( Kβ″) and valence ( Kβ 2,5) band X-rays relative to the primary Kβ X-ray components were extracted in a consistent way. The results were compared with the existing data obtained by proton and photon induced ionization mechanisms and theoretical predictions. The obtained results in peak relative positions and intensities were analyzed in order to study dependence on the chromium oxidation states and chromium–oxygen bond lengths in selected chromium oxides. Our results obtained by both spectrometers confirm that the linear trend observed for the valence peak relative energy shift as a function of chromium oxidation number does not depend on the experimental resolution. Experimental results for normalized intensities (i.e. relative intensities divided with the number of chromium–oxygen pairs) of crossover and valence band X-rays obtained by both spectrometers are in very good agreement, and follow exponential relationship with the average Cr―O bond lengths in corresponding chromium oxides. The observed trends in crossover and valence X-rays normalized intensities could be used to measure the average chromium–oxygen bond length in various chromium oxides, with the sum of both crossover and valence X-ray normalized intensities being the most sensitive measure.

A high resolution X-ray crystal spectrometer to study electron and heavy-ion impact atomic collisions

We have studied fast ion-atom and electron-atom collision processes using a reconditioned high resolution X-ray spectrometer. The X-rays, generated by the collisions, are dispersed by a curved ADP crystal (Johansson geometry) and detected by a gas proportional counter. A self-written LabVIEW based program has been used to give precise and controlled movement to the crystal and for data acquisition. The performance was tested by detecting the Kα diagram and satellite lines of several elements. The Kα satellite lines of Al have been studied in collision with 3–12 keV electrons and 40 MeV C4+ ions. In ion collisions as large as four L-vacancies are created simultaneously with the K-vacancy, compared to two satellites in case of the e-impact. In addition, we have measured the X-rays from H-, He- and Li-like Si ions which arise due to the electron loss/capture process in highly charged 80 MeV Si7+ ions in collision with thin carbon foil. Approximate charge state distribution has been obtained using this new technique.

Chemical state analysis employing sub‐natural linewidth resolution PIXE measurements of Kα diagram lines

AbstractA high‐energy resolution crystal spectrometer in Johansson geometry, which allows energy resolution below the natural linewidth of the Kα diagram lines, was employed in the measurements of proton‐induced Kα x‐ray emission spectra of titanium and sulfur pure and compound targets. The results demonstrate a clear dependence of the Kα energy shifts on the chemical state of the element in the sample. This dependence permits the chemical state speciation of low‐Z elements in an unknown sample by employing high‐resolution PIXE measurements of the Kα line. The potential of the technique in speciation studies is demonstrated in the case of an aerosol sample. The analysis of the Kα line obtained from the high‐energy resolution proton‐induced S Kα x‐ray spectrum allowed the identification of sulfur in the aerosol sample as sulfate ([SO4]2−). Copyright © 2005 John Wiley & Sons, Ltd.

Performance and application of a high energy monochromated Cu Kα 1 X-ray source for the electron spectroscopy of materials

A Cu Kα 1 sealed tube X-ray source ( hν = 8047.8 eV) and LiF(2 2 0) Johansson geometry monochromator crystal have been interfaced to a Scienta ESCA300 spectrometer for high energy XPS studies of materials, in particular for the measurement of Auger parameters associated with deep core levels in metallic alloys. The detailed arrangement of the source, monochromator and spectrometer combination is described, and factors affecting the overall intensity and resolution are discussed. The optimisation and characterisation of the system are also described. Several examples of Cu Kα 1 excited survey spectra (Cr, Fe, stainless steel), deep core level spectra (Cr 1s, Fe 1s) and Auger spectra (Cr KLL, Cr LMM, Fe KLL) are presented, which illustrate the capability of the system. Auger vacancy satellites are identified in the Cr LMM spectrum. For a series of Cr–Si alloys measurements are reported of the change in the Cr Auger parameter on going from metal to alloy.

Optimization of x‐ray monochromating systems: application to LiF(220) crystal with Johansson geometry for Cu K (8047.78 eV)

AbstractThe design of monochromated x‐ray sources for high‐energy XPS is of particular importance. Prediction of the final result and the effect of the experimental parameters is very important if optimum performance is to be obtained in practice. A computer program has been written to calculate crystal reflectivity, collection solid angle and integrated beam intensity for any singly and doubly bent crystal diffractor. The intensity profile, size and shape of the image‐spot produced by the diffracted x‐rays on any arbitrary plane are then predicted by ray tracing. The application of the program to optimize a LiF(220) crystal with Johansson geometry for Cu K (8047.78 eV) will be demonstrated. Copyright © 2004 John Wiley & Sons, Ltd.

Chemical state analysis of sulfur in samples of environmental interest using high resolution measurement of Kα diagram line

The proton induced Kα X-ray emission spectra of pure and some compound targets of sulfur were measured with a crystal spectrometer in Johansson geometry, which enables energy resolution below the natural linewidth of the measured Kα line. From these measurements the absolute energies of the S-Kα 1,2 lines were experimentally determined. In addition, the energies of the KαL 1 X-ray satellite lines, appearing in these spectra as a result of the radiative decay of atomic states with one hole in the K shell and one in the L subshells, were also measured. The measured Kα diagram and satellite line energies depend crucially on the S chemical state. The measured diagram line energies, as well as their relative intensity ratios obtained from the X-ray spectra of different S compounds, allow the deconvolution of X-ray spectra of mixed targets containing two different S compounds and the accurate determination of their mass ratio. Finally, the proton induced S-Kα X-ray spectrum from an aerosol sample was collected and the measured energies of the Kα 1,2 lines were used to specify the chemical state of S in the aerosol as a sulfate ([SO 4] 2−). In conclusion, the results of the present paper demonstrate that the S-Kα 1,2 emission energies depend on the S chemical state and, therefore, their determination allows the chemical state speciation of S in a given sample.

Chemical state analysis of sulfur in samples of environmental interest using high resolution measurement of K$alpha; diagram line

The proton induced Kα X-ray emission spectra of pure and some compound targets of sulfur were measured with a crystal spectrometer in Johansson geometry, which enables energy resolution below the natural linewidth of the measured Kα line. From these measurements the absolute energies of the S-Kα 1,2 lines were experimentally determined. In addition, the energies of the KαL 1 X-ray satellite lines, appearing in these spectra as a result of the radiative decay of atomic states with one hole in the K shell and one in the L subshells, were also measured. The measured Kα diagram and satellite line energies depend crucially on the S chemical state. The measured diagram line energies, as well as their relative intensity ratios obtained from the X-ray spectra of different S compounds, allow the deconvolution of X-ray spectra of mixed targets containing two different S compounds and the accurate determination of their mass ratio. Finally, the proton induced S-Kα X-ray spectrum from an aerosol sample was collected and the measured energies of the Kα 1,2 lines were used to specify the chemical state of S in the aerosol as a sulfate ([SO 4 ] 2− ). In conclusion, the results of the present paper demonstrate that the S-Kα 1,2 emission energies depend on the S chemical state and, therefore, their determination allows the chemical state speciation of S in a given sample.

Kαx-ray satellite lines of Si induced in collisions with 1–3-MeV protons

The Ka x-ray emission spectra of Si bombarded by 1-3-MeV protons were measured with a crystal spectrometer in Johansson geometry, enabling energy resolution below the natural linewidth of the measured Kα line. The KαL 1 and KαL 2 (KαL 1 , 2 ) x-ray satellite lines appearing in these spectra as a result of the radiative decay of atomic states with one hole in the K shell and one or two in the L subshells were precisely measured. The energies and intensities of the main components that could be resolved within the satellite lines are given. It has been demonstrated that the latter do not depend on proton energy and are essentially the same as in photon-induced spectra. The overall KaL 1 satellite intensity relative to the Ka diagram line has been used to deduce the L-shell ionization probabilities induced in near-central proton collisions. The experimental values were compared to the theoretical values calculated with the semiclassical approximation, with the three-body classical trajectory Monte Carlo model, and the classical binary-encounter-based geometrical model.

Use of oriented polycrystalline films in x-ray optics

X-ray diffractors having doubly curved crystal planes can have a high collection efficiency for radiation from a point source and can provide point-to-point focusing of monochromatic x rays as shown by some of the authors. These kinds of diffractors can be used to form x-ray microprobes that can give lower detection limits than electron microprobes or to make wavelength dispersive spectrometers with better signal and signal/background ratio than conventional ones employing the Johann or Johansson geometry. However, fabrication of diffractors of the desired geometry by the use of bent crystals has been difficult. In this paper, we explore the use of oriented polycrystalline films to fabricate doubly curved diffractors for x rays of short wavelength.Oriented polycrystalline films (OPF) have been of interest for many applications, e.g., magnetic recording media, non-linear optical device components, inexpensive large-area substrates for semiconductor device fabrication, etc. These films consist of small monocrystalline grains that have a high degree of preferential orientation of one crystallographic axis relative to the substrate surface.

Asymmetrically cut crystals for synchrotron radiation monochromators

Asymmetrically cut crystals are interesting for use in synchrotron radiation monochromators because of their good energy resolution characteristics and their focusing properties. Ray tracing codes, such as SHADOW, are very efficient in the design and development of new optical devices. In order to determine the convenience of using asymmetrically cut crystals for x-ray monochromators, SHADOW has been extended to include these kinds of crystals. The physical approach to ray tracing asymmetrically cut crystals is based on the coexistence of two periodic structures. One of these is the bulk periodic structure of the Bragg planes. Such a structure determines the existence of a rocking curve near the Bragg condition, and is implemented in SHADOW following the Darwin–Prins formalism of the dynamical theory of diffraction. The second periodic structure is a one-dimensional grating on the crystal surface, formed by the truncation of the lattice planes with the surface. This grating is responsible for the focusing properties of these crystals and plays an essential role in determining the trajectory of the rays. The combination of an asymmetric crystal and a nonplanar surface can be easily achieved by bending (Johann case) to provide improved properties. More complex cases such as the ground-bent crystals (i.e., Johansson geometry) can be considered as a particular case of asymmetrical crystals in which the angle between the Bragg planes and the surface change along the crystal surface. All these cases have been implemented in SHADOW.

Stepped Diffractor for Point Focusing of Monochromatic X RAYS

Point focusing x-ray diffractors can be obtained by a geometry that corresponds to rotating the Johansson geometry about a line joining the source and image points. Methods by which such a diffractor can be made from bulk single crystal materials have been previously described. In the present paper, we consider the design of a diffractor with a stepped surface that could utilize layered diffracting materials such as multiple monomolecular films or layered synthetic microstructure (LSM). First we consider the effect of the diffractor material's rocking curve on the performance in focusing diffractors. Then we consider limitations on the focusing that arise from the width of the rocking curve and the finite size of the steps, and we give an example of the design parameters of a point focusing diffractor with stepped surface.Effect of The Rocking Curve. Width For diffractors used in focusing applications, it is important to know the physical basis for the rocking curve in order to determine whether the width of the rocking curve will affect the angle of diffraction.

Focusing properties of curved x-ray diffractors

Calculations are described and results are given for the focusing properties of six curved x-ray diffractors for Bragg angles ranging from 15° to 75°. The geometries considered include cylindrical, spherical, and toroidal cases. The type of slit necessary to eliminate stray radiation in applications of doubly curved diffractors to scanning monochromators is discussed. Three of the most efficient diffractors are compared with respect to the solid angle for collection of x rays and the possible spectral resolution. A diffractor with spherically curved planes and toroidally curved surface is shown to be superior to the Johansson geometry and the spherically curved plate.

X-ray optics of doubly curved diffractors

Calculations of the x-ray optics of four types of doubly curved diffractors are described and the results are compared with similar results for singly curved diffractors (Johann and Johansson geometry). In these calculations the locus of points on a curved diffractor’s surface is determined for a given deviation from the Bragg angle when the diffractor is used at Bragg angles ranging from 15 to 75 degrees. The six cases discussed include cylindrical, spherical, and toroidal geometries. The calculations are used as a basis for comparing the collection efficiency and the spectral resolution when these diffractors are used in scanning monochromators. It is shown that doubly curved diffractors are superior to singly curved ones and that a diffractor with spherical planes and toroidal surface provides the best performance of all of the diffractors considered if a wide range of Bragg angles must be covered.

Large aperture point-focusing diffractor for x rays

A doubly bent germanium single crystal with toroidally curved crystal planes was used to obtain three-dimensional focusing of monochromatic x rays from a microfocus source. The Johansson geometry in radial planes was obtained by cutting a cylindrically curved lamella, polishing, etching, and bending over a spherical mold of ∼50 mm radius at 740 °C. The bent crystal was aligned to obtain the Cu Kα (333) reflection in the spot which had a principal focus of ∼100 μm. Allowing for anode pitting and extraneous reflections, the observed x-ray intensity was ∼10 times lower than expected theoretically. The discrepancy was attributed to imperfect bending and crystal defects.