Multicrystal X-ray Diffractometer Research Articles

VGF bulk growth, crystalline perfection and mechanical studies of CdZnTe single crystal: A detector grade materials

Bulk size (∼80 mm long and 20 mm dia.) with high quality single crystal of Cadmium Zinc Telluride (CZT) has been successfully grown by Vertical Gradient Freeze (VGF) method using five zone furnace. The powder X-ray diffraction analysis confirms the phase of CZT crystal and growth direction was found to be (111). The grown crystal was cut and polished into different pieces and crystalline perfection was studied by high-resolution X-ray diffraction (HRXRD) by employing a multicrystal X-ray diffractometer. The HRXRD study shows that the crystalline perfection of the grown crystals is quite good. The mechanical properties were carried out on the (111) face of different portions (2–1, 2-2-, 6–2, 6–4) of CZT single crystal at room temperature in the load ranging from 0.1 to 5.0 N. The load independent hardness values for 2–1, 2-2, 6–2 and 6–4 are found to be 0.62, 0.65, 0.61 and 0.55 GPa, respectively. In addition, the observed crack profile of indentation mark has been recorded and various other parameters such as dependence of crack length, fracture toughness, brittle index number, yield strength were also calculated and discussed.

Growth and characterization of novel organic 3-Hydroxy Benzaldehyde-N-methyl 4 Stilbazolium Tosylate crystals for NLO applications

The 3-Hydroxy Benzaldehyde-N-methyl 4-Stilbazolium Tosylate (3- HBST) is a new organic NLO crystal and it is a new derivative in stilbazolium tosylate family. In this work we have synthesized 3-HBST and the single crystal was grown by conventional slow cooling method. The structure and lattice parameters of the grown crystal were determined by the single crystal X-ray diffraction (XRD) technique and it is exhibiting good crystalline nature which is observed from the powder XRD. In order to check the crystalline quality the rocking curve was recorded using multi crystal X-ray diffractometer. The functional groups were identified from both FTIR and NMR spectral analyses. The π–π* and n–π* optical transition energy levels were estimated from the absorption peaks. The NLO property was confirmed by measuring relative SHG efficiency by Kurtz powder test; it shows 24 times higher SHG efficiency than that of urea. In order to test the mechanical stability the Vickers and Knoop micro hardness measurement were carried out and found that the micro hardness number decreases with increasing load. The melting point was determined from Differential Scanning Colorimetry (DSC).

Investigation on structural, spectral, and thermal properties of l-histidinium glutarate monohydrate (LHG)

l-histidinium glutarate monohydrate, an organic nonlinear optical crystal has been successfully grown from deionized water by slow solvent evaporation method at room temperature. Crystal structure and its lattice parameters were identified by single-crystal X-ray diffraction technique. Crystalline perfection of the grown crystal was studied by high-resolution X-ray diffraction rocking curve measurements by employing a multicrystal X-ray diffractometer. FT-IR and FT-Raman spectral studies were employed to identify the presence of various functional groups and mode of vibrations in the crystal. Thermal behavior of the crystal was studied by TG–DTA, TG–DTG, and DSC analyses. Optical absorption of the crystal in the wavelength region 200–1,000 nm was studied by UV–Vis–NIR spectral analysis. Kurtz and Perry powder technique was employed to find the second harmonic generation efficiency of the crystal.

A study of as-grown, poled and reduced Rh-doped KNbO3 single crystals by high-resolution X-ray diffraction, Raman scattering, photoluminescence and dielectric measurements

As-grown and chemically reduced Rh-doped (1500 p.p.m.) KnbO3 single crystals grown by the Czochralski method have been characterized. Reduction of the grown crystals at different levels was carried out under a mixture of CO and CO2 gases as the crystals were grown with excess oxygen. The effect of reduction and poling on crystalline perfection was studied by high-resolution X-ray diffraction (HRXRD) using a multi-crystal X-ray diffractometer developed in-house. The diffraction curves of the as-grown, electrically poled, moderately reduced and heavily reduced single-crystal specimens show remarkable differences. The studies by HRXRD reveal that poling has some influence on the improvement of crystalline perfection, while chemical reduction has a great influence on crystalline perfection; at moderate reduction the crystal becomes nearly perfect, but when the reduction is very heavy the crystal quality decreases slightly, although it is still better than for unreduced samples. Asymmetry of the diffraction curves with respect to the peak position reveals that the as-grown specimens contain a high concentration of both vacancies and self-interstitials. After poling, the concentration of self-interstitial defects is lowered to some extent. When the specimen is moderately chemically reduced, the scattered intensity on both sides of the peak is greatly reduced, showing that the concentrations of both vacancies and interstitials are reduced to a great extent owing to chemical reduction. This clearly indicates that, as a result of the chemical reduction of oxygen in the crystal, crystalline perfection is enhanced significantly. However, under heavy chemical reduction, the number of vacancy defects is increased to a significant extent. Raman scattering, dielectric and photoluminescence studies also show interesting features, with excellent correlation with the degree of crystalline perfection influenced by the processes of reduction and poling.

Crystal growth, structural, thermal and mechanical behavior of l-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals

Single crystals of l-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) have been grown successfully from the solution of l-arginine and 4-nitrophenol. Slow evaporation of solvent technique was adopted to grow the bulk single crystals. Single crystal X-ray diffraction analysis confirms the grown crystal has monoclinic crystal system with space group of P21. Powder X-ray diffraction analysis shows the good crystalline nature. The crystalline perfection of the grown single crystals was analyzed by HRXRD by employing a multicrystal X-ray diffractometer. The functional groups were identified from proton NMR spectroscopic analysis. Linear and nonlinear optical properties were determined by UV–Vis spectrophotometer and Kurtz powder technique respectively. It is found that the grown crystal has no absorption in the green wavelength region and the SHG efficiency was found to be 2.66 times that of the standard KDP. The Thermal stability of the crystal was found by obtaining TG/DTA curve. The mechanical behavior of the grown crystal has been studied by Vicker’s microhardness method.

Effect of Mg doping on the growth aspects, crystalline perfection, and optical and thermal properties of congruent LiNbO3single crystals

Mg-doped congruent lithium niobate single crystals were grown by the Czochralski technique. High-quality single crystals were grown using a novel seeding technique in a resistive heating furnace. Analysis of crystalline perfection carried out by a multi-crystal X-ray diffractometer revealed that the grown crystals do not contain any structural grain boundaries but do contain point defects. The transmission characteristics showed an enhancement of band gap with an increase in Mg concentration. Conoscopy patterns revealed that the grown crystals are homogeneous and the incorporation of Mg into the lattice does not affect the optical sign (negative uniaxial) of the crystal. The refractive index measurements carried out using a prism coupler showed an increase in the optical birefringence (Δn), while the refractive index was found to decrease with the increase in doping concentration. Further, thermal conductivity was found to decrease with Mg incorporation in the lattice owing to phonon scattering from the Mg ions and, as a consequence, at high concentrations (>4 mol%) crack formation occurred. However, optimization of growth conditions reveals that a slower pulling rate leads to crack-free lithium niobate crystals even at 6 mol% Mg doping.

Synthesis, crystalline perfection, optical and dielectric studies on metal–organic tri-allylthiourea cadmium chloride (ATCC) nonlinear optical single crystal by solution growth technique

A family of optically negative organometallic, allylthiourea complex single crystals such as ATCC, ATCB, ATMC and ATMB are extensively studied for their application in nonlinear optical (NLO) devices. In this category of materials, allylthiourea serves as double ligand to form co-ordination complexes with metals. Allylthiourea cadmium chloride single crystals were grown by solvent evaporation and temperature lowering techniques in an optimized pH value. X-ray rocking curve of the grown crystal was recorded with high resolution multicrystal X-ray diffractometer. The obtained single sharp peak reveals that the grown crystal specimen is free from structural grain boundaries. The grown crystal has wider transparency window with the lower cut-off wavelength at 285nm. The refractive index measurements at three different laser wavelengths (633nm; 1.72503, 825nm; 1.71053 and at 1061nm; 1.70085) indicate decrease in index value with increasing laser wavelength. The Kurtz and Perry powder technique was used to confirm the NLO property of the as grown crystals. The dielectric constant of the as grown crystal is measured for various frequencies and temperatures and chemical etching analysis is also carried out and the obtained results are presented.

Study of the influence of dopants on the crystalline perfection of ferroelectric glycine phosphite single crystals using high-resolution X-ray diffraction analysis

Good quality and optically transparent single crystals of pure and doped glycine phosphite (GPI) were grown by both solvent-evaporation and temperature-cooling techniques. Dopants were chosen in different categories, namely transition metals (Cr, Mn, Co, Ni, Zn, Mg, Cd), rare-earth metals (Ce, Nd, La), dyes (rhodamine B, malachite green, fluorescein) and an amino acid (L-proline). The concentration of dopants was chosen depending on the category of dopants and the quality of crystallization during the growth process. The crystalline perfection of the as-grown pure and doped GPI crystals was investigated by high-resolution X-ray diffraction at room temperature. A multicrystal X-ray diffractometer employing a well collimated and highly monochromated Mo Kα1beam and set in the (+, −, −, +) configuration was employed. Most of the crystal specimens show excellent crystalline perfection. However, grain boundaries, low-angle tilt boundaries, and vacancy and interstitial point defects were observed in some crystal specimens.

Influence of defects on the quality and optical studies of sodium p-nitrophenolate dihydrate, a nonlinear optical material

Nonlinear optical material of sodium p-nitrophenolate dihydrate was synthesized by employing the technique of controlled evaporation and the effect of temperature on growth morphology was investigated. Single crystal XRD analysis confirms that the crystals with different morphologies have the same lattice parameters. The high-resolution X-ray diffraction curves recorded by a multicrystal X-ray diffractometer revealed the presence of very low angle tilt boundaries. The green emission band at 524 nm is due to the existence of defects on the crystal which corroborated with HRXRD studies. The wide band gap of the SPND crystals confirms the large transmittance in the visible region.

Growth and characterization of glycine picrate—Remarkable second-harmonic generation in centrosymmetric crystal

Remarkable second-harmonic generation (SHG) efficiency has been observed in the glycine picrate (GP) though it crystallizes in centrosymmetric structure. Bulk single crystals of GP with a good size of ~20×10×3 mm 3 have been successfully grown by the slow cooling method in aqueous medium. Powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) and FT-Raman studies have confirmed, respectively, the crystal structure and functional groups of the grown crystal. Crystalline perfection of single crystals has been evaluated by high-resolution X-ray diffractometry (HRXRD) using a multicrystal X-ray diffractometer and found that the grown crystals are nearly perfect. Nonlinear optical (NLO) behavior of glycine picrate crystals has been studied for the first time by Kurtz powder technique and its second-harmonic generation efficiency is found to be 2.34 times higher than that of KDP. Transparency of crystals in UV–vis–NIR region has also been studied. Dielectric measurements have been carried out using an impedance analyzer over a wide range of frequency (100 Hz–3 MHz) at room temperature. The slight decrease in dielectric constant has been observed as the frequency is increased and the dielectric loss is very low for the entire frequency range. The ac conductivity is almost constant up to 1 MHz and sudden increase has been observed above this frequency.

Growth and characterization of organic non-linear optical crystal 4-hydoroxy benzaldehyde- N-methyl 4-stilbazolium tosylate (HBST)

The 4-hydroxy benzaldehyde- N-methyl 4-stilbazolium tosylate (HBST), a good non-linear optical (NLO) crystal has been synthesized and the single crystal has been grown by slow evaporation method. In this work we have used ethyl acetate mixed methanol (1:1 ratio) as solvent. The lattice parameters were calculated from the powder X-ray diffraction patterns and compared with previous reports. The crystalline perfection has been verified with multicrystal X-ray diffractometer. The functional groups were identified from FTIR and NMR spectral studies. In order to know the optical quality of the grown crystal, the UV–Vis–NIR absorption spectrum was recorded and optical transition energy levels were also calculated. The thermal properties were analyzed from TG/DTA data. The relative SHG efficiency was compared with urea by Kurtz powder method.

Directional growth of organic NLO crystal by different growth methods: A comparative study by means of XRD, HRXRD and laser damage threshold

Unidirectional benzophenone single crystals grown by vertical Bridgman (VB), microtube-Czochralski (μT-CZ), uniaxially solution crystallization method of Sankaranarayanan–Ramasamy (SR) were characterized using X-ray diffraction (XRD), high-resolution XRD (HRXRD), laser damage threshold (LDT) studies and the results were compared. The XRD study exhibits the growth direction of the benzophenone crystal ingots. The HRXRD curves recorded by multicrystal X-ray diffractometer (MCD) revealed that the crystals grown by all the three methods contain internal structural grain boundaries. The SR grown sample shows relatively good crystalline nature with the full-width half-maximum (FWHM) of the main peak of 39 arcsec. While, the VB grown crystal contain multiple low-angle ( α⩾1 arcmin) grain boundaries, probably due to thermal stress during post-growth annealing caused by the difference in the lattice expansion coefficients of the crystal and the ampoule, whereas such thermal stress are absent in μT-CZ grown sample due to the free standing nature of the grown crystal. Hence, the μT-CZ grown crystals contain only one very low-angle ( α<1 arcmin) grain boundary. LDT study shows that the SR grown benzophenone crystal has higher LDT than the samples grown by other methods, probably due to relatively high-crystalline perfection of the SR grown crystals.

Growth and characterization of a new potential NLO material from the amino acid family— l-prolinium picrate

l-prolinium picrate (C 5H 10NO 2) +. (C 6H 2N 3O 7) −, an organic nonlinear optical (NLO) material possessing a large second harmonic generation (SHG) efficiency (74 times higher than that of the standard KDP) was grown by slow evaporation method. The identity of the crystals was confirmed by using single-crystal X-ray diffraction. The crystalline perfection was studied by multicrystal X-ray diffractometer. Fourier transform infrared (FTIR) spectroscopic studies, optical behavior such as UV–visible–NIR absorption and SHG conversion efficiency were investigated to explore the NLO characteristics of the above material. The structural features of the material leading to the large SHG efficiency are discussed. Microhardness measurements and dielectric studies of the compound were also carried out.

Study of point defects in as-grown and annealed bismuth germanate single crystals

Point defects and their clusters in bismuth germanate single crystals free from grain boundaries and having low density of dislocations were studied by high-resolution diffuse X-ray scattering measurements. Differences in defects in the colourless crystals (type A) and the crystals having yellow tinge (type B), which were grown with different raw materials, were investigated. In addition, interesting differences in defect structures in specimens from different regions of the same boule were investigated. Specimens with diffracting surfaces along (111), (112) and (100) planes were studied. A multicrystal X-ray diffractometer employing a well collimated and highly monochromated Mo Kα1 beam and set in (+,−,−,+) configuration was employed. The diffraction curves of all the samples were quite narrow with half-widths in the range 7–11 arcsec, which are close to the theoretically expected values, if instrumental broadenings are taken into account. The observed distribution of diffuse X-ray scattering (DXS) intensity showed that not all the point defects are isolated but a significant fraction are agglomerated into clusters. Experimental data of DXS intensity were analysed by using a phenomenological model for a small concentration of dislocation loops wherein the point defects are loosely clustered with weak interactions among them. From this analysis, the cluster radius R cl, cluster volume A cl, the number of point defects within a cluster N cl and the relative concentration of the point-defect clusters among the samples were estimated. It was observed that cluster sizes do not vary from sample to sample. However, it was found that the concentration of clusters is approximately twice in the coloured sample compared with that of the colourless sample from the same boule. Annealing of the crystals at 1273 K produced an increase in point-defect clusters by a factor of ∼200. It was accompanied by a reduction in volume of clusters by a factor of ∼0.14.

Study of point defect clusters in high purity single crystals of silicon grown by Czochralski and float-zone methods by diffuse X-ray scattering technique

Results of study of point defect clusters in high purity ( ∼ 10 kΩ · cm ) dislocation-free Czochralski (Cz) and float-zone (FZ) grown crystals (∼ 50 mm diameter, 11 mm thick, p-type) are reported. A multicrystal X-ray diffractometer set in (+, −, −, +) geometry and employing a well-collimated Mo K α 1 beam was used. High resolution X-ray diffractometry, absolute integrated intensity measurements and diffuse X-ray scattering (DXS) measurements were carried out. The specimens gave sharp diffraction curves and the integrated intensities were found to be close to the theoretical value for an ideally perfect silicon crystal. DXS measurements were made around 111 reciprocal lattice point (RLP) along four directions of K ∗ : [111], [1̄1̄1̄], [01̄1] and [011̄]. K ∗ is the vector which connects the elemental reciprocal volume under investigation with the nearest RLP. From the analysis of the DXS intensity versus K ∗ plots, it was found that the source of DXS is interstitial defect clusters in Cz-grown crystals and vacancy defect clusters in FZ-grown crystals. By using a phenomenological model, the values of cluster size R cl, cluster volume A cl and number of defects per cluster N cl, respectively, were found to be: 0.8 μm, 2.02 × 10 −16 cm 3, 1.26 × 10 6 for Cz specimen and 0.6 μm, 1.32 × 10 −16 cm 3, 8.3 × 10 5 for the FZ specimen.

Schottky barrier heights of Ir/p-Si and Ir/strained p-Si1-xGex junctions

Low barrier height Schottky diodes, Ir/p-Si and Ir/p-Si1-xGex with x=14%, have been investigated using current-voltage (I-V) analysis. The crystalline quality, the Ge fraction and the strain state of the Si1-xGex alloy were investigated using a high-resolution multicrystal X-ray diffractometer. The Schottky barrier height of the Ir/strained p-Si0.86Ge0.14 junction was found to be 70 meV smaller than that of the Ir/p-Si junction. The relationship between this barrier height difference and the energy band structure of Si/strained Si1-xGex is discussed.

Study of point defect clusters produced by BF+2 implantation in silicon single crystals

High-resolution diffuse x-ray scattering (DXS) measurements made with a multicrystal x-ray diffractometer have been used to characterize point defect clusters produced by 90-keV and 135-keV BF+2 implantations (fluence=1×1015 cm−2). The specimens were 50-mm-diam (100) silicon single crystals (n type; 4–6 Ω cm resistivity). A highly monochromated and collimated Kα1 is obtained by three-plane (111) silicon single crystals oriented in (+,−,−) setting. The DXS intensity around 400 reciprocal lattice point was measured along [&amp;lt;sx&amp;gt;100&amp;lt;be&amp;gt;±] directions. Implantation produced a slight broadening of diffraction curves from ∼6 to ∼7 arcsec. From unimplanted regions diffuse scattering was primarily due to isolated interstitial point defects in the investigated volume of reciprocal space. Implantation was found to produce interstitial point defect clusters. Experimental data has been analyzed by using a phenomenological model for dislocation loops by using a curve fitting method. The values of loop size Rcl, volume of the loops Acl, and number of defects per loop Ncl have been determined. For implantation energies of 90 and 135 keV, these are, respectively, Rcl=1.47×10−4 and 1.29×10−4 cm, Acl=2.92×10−16 and 2.27×10−16 cm3, and Ncl=1.46×107 and 1.37×107.

The intensity distribution observed with a multi-crystal X-ray diffractometer

Expressions are obtained for the intensity distributions which are observed when Bragg reflections are studied using an X-ray multi-crystal diffractometer. The expressions are obtained for both Bragg and Laue geometry at the sample, and assuming that the monochromator, sample and analyser elements are all perfect crystals. Detailed calculations are made of several configurations with both laboratory-based and synchrotron sources, and the results are compared with experimental measurements. The comparison shows that the theory gives reliable results not only for the half-widths of the distributions, but also for the tails of the distributions resulting from the dynamical effects in one or more of the crystals.

New and accurate technique for determination of orientation of the straight edges of single-crystal wafers

An x-ray traverse topograph of the specimen wafer is recorded with diffracting planes nearly parallel to the straight edge. The scan is adjusted to have the image of the straight edge on one side. A projected image of the diffracting planes is also recorded on the same photographic film in the form of a stationary topograph (a sharp line) at a short distance from the traverse topograph. The angle between the image of the straight edge and the stationary topograph is measured directly. Accuracy of ±3 arcmin is achieved. A multicrystal x-ray diffractometer or a standard x-ray diffraction topography camera can be used. A few illustrative results obtained with silicon wafers are described.