Indus-2 Synchrotron Source Research Articles

Development of high aspect ratio X-ray parabolic compound refractive lens at Indus-2 using X-ray lithography

A synchrotron beamline dedicated to soft and deep X-ray lithography is operational on Indus-2 synchrotron source and is being used for high aspect ratio microfabrication. This X-ray lithography facility provides the access to X-ray mask fabrication, X-ray exposures and development of micro-nano structures. We report the development of planar parabolic refractive X-ray lenses in SU-8 for energy range 8---20 keV using this facility. The focussing properties of X-ray lenses were studied with synchrotron radiation in the X-ray energy range 8---20 keV on the moderate emittance machine Indus-2. A focal spot of 11 μm at 15.9 keV is obtained with a gain of 18.

M sub shell X-ray emission cross section measurements for Pt, Au, Hg, Pb, Th and U at 8 and 10 keV synchrotron photons

M sub shell X-ray emission cross sections of Pt, Au, Hg, Pb, Th and U at 8 and 10keV photon energies have been determined with linearly polarized photon beam from Indus-2 synchrotron source. The measured cross sections have been reported for the first time and were used to check the available theoretical Dirac–Hartree–Slater (DHS) and Dirac–Fock (DF) values reported in literature and also the presently derived Non Relativistic Hartree–Slater (NRHS), DF and DHS values for Mξ, Mδ, Mα, Mβ, Mγ, Mm1 and Mm2 group of X-rays.

EXAFS study of mixed ligand copper complexes having nicotinic acid as one of the ligands

Copper K-edge EXAFS spectra of the copper (II) complexes [Cu3(NA)4(dca)2(H2O)8].2H2O (1) and [Cu2(2,2'-bipy)(NA)2](ClO4)2.H2O (2) (where NA = Nicotinic acid; dca = dicyanamide anion; 2,2'-bipy = 2-2' bipyridine) having different coordination environments and geometries have been investigated. The complex 1 is supposed to have six coordinated geometry and complex 2 five coordinated geometry. EXAFS has been recorded at the K-edge of copper in the complex at the dispersive EXAFS beamline at 2 GeV Indus-2 synchrotron source at RRCAT, Indore, India. Theoretical models have been generated for both the complexes separately using their reported crystal structures. These theoretical models have been fitted to the respective experimental EXAFS data and the structural parameters, which include bond lengths, coordination numbers and thermal disorders, have been determined. The results obtained have been found to be comparable with those reported using crystallography. The coordination geometry about the copper (II) ion has been depicted for both the complexes. Further, copper has been found to be in +2 oxidation state in both the complexes. The study shows that the dispersive EXAFS beamline can be used to obtain information about the coordination geometry of a sample, though the beamline provides limited range of EXAFS data.

EXAFS study of tetramethylethylenediamine copper(II) complexes with Cl and Br as secondary ligands

Extended X-ray absorption fine structure (EXAFS) have been recorded at the K-edge of copper in binuclear copper(II) complex [Cu(tmen)Cl2] (1) and its analogous complex [Cu(tmen)Br2] (2) (where tmen = tetramethylethylenediamine), using the dispersive EXAFS beamline at 2 GeV Indus-2 synchrotron source at RRCAT, Indore, India. Theoretical model has been generated for 1 using its available crystallographic data [1] and then fitted to the experimental EXAFS data of 1 to obtain its structural parameters, which include bond-lengths, coordination numbers and thermal disorders. The results obtained have been found to be comparable with the crystallographic results. As complex 2 is analogous to complex 1, the same theoretical model, which was generated for 1, has been fitted to the experimental EXAFS data of 2. The structural parameters, thus determined for 2 have been reported. The coordination geometry around the copper center in both the complexes has been depicted showing the bond-lengths obtained in the present study. It has been demonstrated that if crystal structure is available for a complex from X-ray crystallographic studies, the structural parameters can be determined for an analogous complex from EXAFS studies. Further, the values of the chemical shifts suggest that copper is in +2 oxidation state in these complexes.

Energy-dispersive X-ray diffraction beamline at Indus-2 synchrotron source

An energy-dispersive X-ray diffraction beamline has been designed, developed and commissioned at BL-11 bending magnet port of the Indian synchrotron source, Indus-2. The performance of this beamline has been benchmarked by measuring diffraction patterns from various elemental metals and standard inorganic powdered samples. A few recent high-pressure investigations are presented to demonstrate the capabilities of the beamline.

A comparative study of the spectra recorded at RRCAT synchrotron BL-8 dispersive EXAFS beamline with other beamlines

The aim of the present work is to make a comparative study of the EXAFS spectra recorded at the BL-8 dispersive EXAFS beamline at 2 GeV Indus-2 synchrotron source at RRCAT, Indore (India) with those recorded at other synchrotron EXAFS beamlines, viz., X-19A at NSLS, BNL (USA), EXAFS wiggler beamline 4-1 at the SSRL (USA) and beamline 11.1 at ELETTRA (Italy). For this purpose, EXAFS spectra at Cu K-edge in copper metal have been recorded at these four beamlines. Further, EXAFS spectra at Cu K-edge in a copper complex have also been recorded at BL-8 beamline and beamline 11.1 at ELETTRA (Italy). The obtained experimental μ(E) data have been background-subtracted and then normalized. The normalized data have been then converted to χ(k) data, which have been Fourier-transformed and then fitted with the theoretical model, thereby yielding different structural parameters. It has been shown that the results obtained from the EXAFS spectra recorded at the BL-8 beamline are comparable with those obtained from other synchrotron EXAFS beamlines and also with the crystallographic results reported by earlier workers. The reliability, usefulness and data quality of the BL-8 beamline have been discussed.

Coordination geometry around copper in a Schiff-base trinuclear copper complex using EXAFS spectroscopy

In the present investigation, we have studied extended X-ray absorption fine structure (EXAFS) spectra of a trinuclear Schiff-base copper complex tetraaqua-di-μ3-(N-salicylidene-DL-glutamato)-tricopper(II)heptahydrate, [Cu3(C12H10NO5)2 (H2O)4]. 7H2O, in which three metal sites are present. One metal site is square-pyramidal (4+1) and other two similar metal sites are tetragonally distorted octahedral (4+2). EXAFS has been recorded at the K-edge of copper in the complex at the dispersive EXAFS beamline at 2 GeV Indus-2 synchrotron source at RRCAT, Indore, India. The analysis of EXAFS spectra of multinuclear metal complexes pose some problems due to the presence of many absorbing atoms, even when the absorbing atoms may be of the same element. Hence, using the available crystal structure of the complex, theoretical models have been generated for the different copper sites separately, which are then fitted to the experimental EXAFS data. The two coordination geometries around the copper sites have been determined. The contributions of the different copper sites to the experimental spectrum have been estimated. The structural parameters, which include bond-lengths, coordination numbers and thermal disorders, for the two types of copper sites have been reported. Further, copper has been found to be in +2 oxidation state at these metal sites.

EXAFS study of tetrakis(imidazole) dinitratocopper (II) complex

The extended X-ray absorption fine structure (EXAFS) spectra at the K-edge of copper in tetrakis(imidazole)dinitratocopper(II) complex [Cu(im)4(NO3)2] (im= imidazole), has been recorded using the dispersive EXAFS beamline at the 2 GeV Indus-2 synchrotron source at RRCAT, Indore, India. The EXAFS data analysis has been done using the computer programs Athena and Artemis. Theoretical model has been generated using the available crystal structure of the complex and fitted to its experimental EXAFS data. The structural parameters thus obtained, which include bond-lengths, coordination numbers and thermal disorders, have been reported. The results obtained have been found to be in good agreement with crystallographic results. The coordination geometry around the copper site has been determined and depicted. Further, copper has been found to be in +2 oxidation state in this complex.

On the method of calibration of the energy dispersive EXAFS beamline at Indus-2 and fitting theoretical model to the EXAFS spectrum

A procedure for calibration of the recently developed energy dispersive EXAFS beamline at the Indus-2 synchrotron source at RRCAT, Indore, India has been described. The procedure involves recording of absorption spectra of two standard samples, whose absorption edge energies are well-established. Two methods have been considered for calibration. In the first method, the position of the first maximum of the derivative of absorption curve is taken as the position of the edge energy. In the second method, the position of the point at half edge step in the absorption curve is taken as the position of the edge energy. It has been shown that only the first method gives same values of dispersion even when the beam current is varied and should be used for calibrating the experimental spectra. Further, it is recommended that the performance of the beamline for a particular setting should be checked by recording and analysing EXAFS of a standard. Hence, the procedure for analysis and extracting information about the various parameters that can be determined by fitting the EXAFS data with a theoretical model has also been described, by taking the example of K-absorption spectra of copper metal foil recorded on this beamline.

First commissioning results from high resolution vacuum ultraviolet beamline at Indus-1 synchrotron source

A high resolution vacuum ultraviolet beamline has been developed and installed at the 450 MeV synchrotron source Indus-1 operating at the Raja Ramanna Centre for Advance Technology, Indore, India. This beamline is useful for photoabsorption studies of atoms and molecules in the VUV region of 1050–3000 Å. The beamline consists of three major components: a pre-focusing optical system, a gas phase absorption setup and a 6.65 m vacuum ultraviolet spectrometer in off-plane Eagle mount. The performance of the beamline has been evaluated by recording VUV absorption spectra of xenon, oxygen and sulphur dioxide using synchrotron radiation from Indus-1. The resolution achieved is 0.1 Å with a 1200 ln/mm grating. Spectra obtained agree well with the ones published earlier. Details of the design, development and performance testing of the beamline are discussed.

Optical properties of indium phosphide in the 50–200Å wavelength region using a reflectivity technique

The optical constants of indium phosphide (InP) in the soft x-ray region of 50-200 Å are determined from angle-dependent reflectivity measurements. The measurements are carried out using the reflectivity beam line at the Indus-1 synchrotron source. The derived optical constants are compared with tabulated values of Henke et al. [At. Data Nucl. Data Tables 54, 181 (1993)]. Experimental values of δ and β are in close agreement with the tabulated values in the lower wavelength region of 50-120 Å. The experimental value indicates an edge shift of 0.4 Å toward the lower wavelength side from the phosphorous L-edge value of 92 Å. However, above the 120 Å region, where the indium N(2) edge falls at 160.7 Å, there is a huge difference between experimental and tabulated values. Both delta and beta values are significantly higher. In contrast to tabulated values of the β/δ ratio, which is more than 1 above the 140 Å region, the experimental measured ratio is found to be less than 1. This study presents the first reported experimental values of optical constants for InP in this wavelength range, to the best of our knowledge.

Resonant soft X-ray reflectivity as a sensitive probe to investigate polished zinc sulphide surface

Resonant soft X-ray reflectivity measurements at and near the L 3 absorption edge of sulphur have been performed on mechanically polished zinc sulphide using Indus-1 synchrotron source. A sulphur rich surface (∼15 nm thick) consisting of two layers with gradient electron density distribution was uniquely determined. As compared to bulk ZnS, the top layer has ∼30–50% less electron density whereas, the intermediate layer has ∼10–18% less electron density. Conventional hard X-ray reflectivity measurement at Cu Kα wavelength also indicates low electron density (sulphur rich) surface of ZnS but the technique was found insensitive for unique determination of electron density distribution. Optical constants of ZnS in the soft X-ray region (100–250 eV) have been reported for the first time and were in good agreement with the theoretically reported values.

Estimation of higher order modes of INDUS-2 RF cavity using combined electromagnetic–thermal–structural simulations

Higher order modes (HOMs) are one of the reasons for beam current limitations and beam lifetime in synchrotron light sources such as INDUS-2. At higher beam current, the HOMs of the RF cavity may resonate with the beam frequencies (in the beam spectrum) leading to beam instability. Therefore, knowledge of the HOMs of an RF cavity is a necessary part of operations for any synchrotron source. INDUS-2 synchrotron source has 4 elliptically shaped RF cavities, which are operated at a fundamental frequency of 505.812 MHz. The RF cavity HOM spectrum is very sensitive to its conducting surface, which is affected mainly by the thermal loading and tuner movement. An accurate estimation of the cavity frequency spectrum with realistic boundary conditions is possible by a combined (coupled) electromagnetic–thermal–structural analysis. The methodology adopted for this coupled simulation is explained in this paper. The HOM spectrum and electromagnetic parameters of INDUS-2 cavity are simulated using 3D electromagnetic high frequency finite element method in ANSYS. The simulated data sets are compared with the cold model test data of the RF cavities for validation of the numerical simulations. Further, the observed spectra of the INDUS-2 electron beam at various stored beam currents and energies are also studied to find parasitic HOMs. Indicative HOM observations and the simulation data results can be used for shifting the harmful modes.

First results from a dispersive EXAFS beamline developed at INDUS-2 synchrotron source at RRCAT, Indore, India

A dispersive extended X-ray absorption fine structure (EXAFS) beamline employing an elliptically bent crystal and a position-sensitive CCD detector has been developed at the BL-8 bending magnet port of INDUS-2 synchrotron source at RRCAT, Indore, India. The beamline enables simultaneous measurement of X-ray absorption spectra over the range of 5–20 keV in a short span of time. The beamline performance has been investigated by measuring the absorption spectra of metal foils and oxide powders. The EXAFS measurements on crystalline Pb 5Ge 3O 11 samples were performed for the first time in literature. The average Pb–O bond length obtained from these measurements is found to agree well with the theoretically estimated value.

Network compaction and surface deformation in the hydrogenated silicon nitride film upon soft x-ray/VUV illumination

In the present study, modifications in a hydrogenated silicon nitride film by soft x-ray/VUV (vacuum ultra violet) radiations are investigated using in situ soft x-ray reflectivity measurements at Indus-1 synchrotron source. The illumination experiments are performed at $10\ifmmode^\circ\else\textdegree\fi{}$ grazing incidence angle at which the majority of incident radiation (belonging to $10\phantom{\rule{0.3em}{0ex}}\mathrm{eV}\text{--}250\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$) are restricted to $\ensuremath{\sim}8.0\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ depth, except near the $\mathrm{Si}\text{\ensuremath{-}}\mathrm{L}$ absorption edge $(100\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ where photons penetrate much deeper into the film and initiate photochemical changes. Resultantly, the film density has increased along with a change in surface morphology. Due to illuminations, hydrogen bonds responsible for voids and network deformation are more likely to break and pave the path for the formation of more compact ${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ network. Evolution of hydrogen changes the surface morphology significantly. Atomic force microscopy confirms the formation of nano clusters at the surface. The out diffusion of hydrogen near the surface is responsible for surface deformation. Probable mechanism of surface modification and network compaction is discussed.

Development of Angle Resolved Photoelectron Spectroscopy Beamline at Indus-1 Synchrotron Radiation Source

A beamline for angle resolved photoelectron spectroscopy (ARPES) using Indus-1 synchrotron source has been recently commissioned at the Centre for Advanced Technology, Indore India. The optical system for the beamline consists of a prefocussing toroidal mirror, 1.4 meter toroidal grating monochromator (TGM-1400) and a post-focussing toroidal mirror to cover the spectral region of 40A to 1000A. The beamline is coupled with an ARPES experimental station which houses the indigenously built electron analyser, sample manipulator, LEED/Auger probes, sputter etch Ar ion gun, sample load and lock facility. In this paper we are presenting the photoemission spectra of some solid samples which have been recorded through this beam line.

X-ray multilayer optics: growth and characterization

Growth of X-ray multilayer optics is done using an ultra high-vacuum electron beam deposition. High-vacuum reflectometer station on Indus-1 synchrotron source is described. Representative studies on Mo/C X-ray multilayers are presented.