Sunil Verma

In situ measurement of pH and supersaturation-dependent growth kinetics of the prismatic and pyramidal facets of KDP crystals

The effect of pH and supersaturation on the growth kinetics of the pyramidal (1 0 1) and prismatic (1 0 0) faces of KDP crystals is reported. Growth rates of these faces at the microscopic level are measured usingthe laser-polarisation– interference technique, and a comparative analysis is carried out. In the light of these results, an attempt has been made to clear the ambiguity surrounding the effect of pH on the growth rates of KDP crystals along the a- and the c-axis. We have found that the growth rate of (1 0 1) as well as (1 0 0) face is maximum at stoichiometric pH of 4.2 (at all supercoolings considered), and it decreases on either side of this value. This is in agreement with the results of Efremova et al. (Crystallogr. Rep. 38(5) (1993) 674), and contradictory to those of Wang et al. (J. Crystal Growth 83 (1987) 471), Marecek et al. (Kristall Technik 4(1) (1969) 39) and Rashkovich et al. (J. Crystal Growth 151 (1995) 145) where it is reported that growth rate of (1 0 0) face increases if we go above the stoichiometric pH. For performing these on-line and in situ studies, a novel crystal-growth cell, a special seed-orienting mechanism for mounting the desired crystal face in the laser beam path, and a data acquisition system were developed. The shadowgraphy technique was employed for makingan accurate measurement of the saturation temperature. r 2002 Elsevier Science B.V. All rights reserved.

Nucleation kinetics, growth, mechanical, thermal and optical characterization of sulphamic acid single crystal

Sulphamic acid (HSO3NH2) is a potential material that exhibits excellent piezoelectric and non-linear optical properties. Nucleation and growth kinetics give valuable information about the crystal growth process, which can be employed in the growth of large size crystals. Thus we have studied its nucleation parameters such as solubility, metastable zone width, induction period, interfacial tension, critical free energy, volume free energy change, critical nucleus and found that good quality sulphamic acid crystal can be grown at low temperature. Growth of good quality crystal was done by adopting slow evaporation solution growth technique at room temperature and as a result, good quality single crystal was grown. The grown bulk single crystal of the title compound was subjected to various characterization analyses. Its unit cell dimensions were confirmed using powder X-ray diffraction. Further its crystalline perfection was assessed using high resolution X-ray diffraction and X-ray topography techniques and it was found that it is reasonably good. Its various functional groups were identified from the Fourier transform-Raman method. Nanoindentation was performed to identify the load dependence and independence of hardness (H) and Youngs modulus (E) using the Oliver–Pharr method and it was found that both H and E exhibit peak load dependence. Photopyroelectric study was performed to identify its thermal properties such as thermal diffusivity (α), thermal conductivity (k), thermal effusivity (e), and heat capacity (cp). These studies reveal that it has high thermal stability compared to other single crystals. The optical homogeneity of the grown crystal was assessed using a birefringence interferometer and it was found to be reasonably good.

Synthesis and single crystal growth of L-proline cadmium chloride monohydrate and its characterization for higher order harmonic generation applications

The semi-organic non linear optical single crystal of L-proline cadmium chloride monohydrate was successfully synthesized and the single crystal was grown by a slow evaporation solution growth technique, using double distilled water as the solvent. The lattice dimensions of the grown crystal were examined by powder X-ray diffraction and it was found to belong to the orthorhombic crystal system with a noncentrosymmetric space group. Its crystallinity was assessed by a high resolution X-ray diffraction method and its structural imperfections were recorded using X-ray topography. The presence of functional groups was identified from heteronuclear correlation methods. Its optical behavior was examined by birefringence and photoluminescence and its optical constants were determined from UV-Vis. analysis. Its thermal and third order nonlinear optical properties were characterised by photopyroelectric and Z-scan methods, respectively. The mechanical and ferroelectric behavior was also assessed on the grown single crystal of L-proline cadmium chloride monohydrate.

Bulk growth of ninhydrin single crystals by solvent evaporation method and its characterization for SHG and THG applications

Ninhydrin is a well-known compound generally used in amino acid synthesis and also for detecting the latent fingerprints on porous surfaces. Single crystals can be grown by dissolving the compound in double distilled water at ambient temperature, and can be used as a potential material for second and third harmonic generation applications. The grown specimen was subjected to different characterization techniques in order to find out its suitability for device fabrication. Its lattice dimensions have been confirmed by X-ray powder diffraction and its crystalline quality has been assessed by high resolution X-ray diffraction and X-ray topography methods. The presence of functional groups was identified from HETCOR analysis and confirmed the absence of impurities during crystallization. Its optical properties have been examined by photoluminescence and birefringence analyses. Its thermal parameters such as thermal diffusivity, thermal conductivity and specific capacity have been carried out by following photopyroelectric method. Third order nonlinear optical measurements have been carried out using Z-scan technique and its nonlinear optical absorption coefficient has been determined.

Crystalline perfection, optical and third harmonic generation analyses of non-linear optical single crystal of L-lysine acetate

The potential organic non-linear optical single crystal of L-lysine acetate has been grown by slow evaporation solution growth technique (SEST) at room temperature. It crystallizes in the monoclinic system with space group of P2(1). The crystalline perfection of the grown single crystal has been examined by high resolution X-ray diffraction analysis (HRXRD). The functional groups of the synthesized compound have been identified by (13)C NMR, (1)H NMR and FTIR analyses. The optical absorption studies show that the crystal is transparent in the entire visible region with a cut-off wavelength of 236 nm. The optical band gap is found to be 5.29 eV. The steady-state PL spectra was recorded for pure L-lysine acetate crystal at room temperature. The third harmonic generation efficiency of the crystal has been evaluated by Z-scan technique and its non-linear optical coefficient has been calculated. Birefringence measurement has been carried out in order to see the optical homogeneity of the grown specimen. Its electrical properties has been assessed by dielectric measurement at different temperatures. The calculated optical band gap is 5.29 eV. Its thermal parameters like thermal diffusivity (α), thermal effusivity (e), thermal conductivity (k) and heat capacity (C(p)) have been determined by photopyroelectric technique. Vickers micro hardness studies were carried out using a Vickers hardness tester equipped with a diamond square indenter. The piezoelectric measurement for L-lysine acetate has been also been carried at ambient condition.

Growth technique to increase the device purpose yield of a KDP crystal and assessment of its quality using X-ray and optical techniques

A methodology to increase the device purpose yield of a KDP crystal is reported in this paper. The method is based on increasing the cross-section of the prismatic sector {100} of the growing KDP crystal at the expense of the unusable pyramidal cap portion by restricting the growth of the crystal up to a particular height, decided by the solution–air interface in the crystallizer. Due to the lack of solution above the interface, the crystal ceases to grow in the upward direction whereas it continues to grow laterally. This leads to an increase in the usable volume of the grown crystal for the fabrication of crystal elements required for electro-optic switching and frequency conversion applications. An empirical relationship has been introduced as a condition to grow flat-top shaped KDP crystals. It relates the growth parameters with the apparatus design parameters. Several flat-top shaped crystals have been grown as a validation of the growth methodology and the empirical relationship. The influence of the growth methodology on the crystalline quality of the grown crystal was assessed by measuring the defect structure of different sectors of the grown crystal by X-ray topography (XRT). The crystalline perfection was estimated by recording the rocking curve widths using high resolution X-ray diffraction (HRXRD). The optical quality was assessed by measuring the UV-vis-NIR transmission of the different sectors of the crystal and the refractive index homogeneity using interferometric techniques of conoscopy. It is found that restricting the growth of the crystal in the [001] direction by the solution–air interface does not have any detrimental effect on the crystalline and optical qualities of the grown crystal.

Solubility, crystal growth, morphology, crystalline perfection and optical homogeneity of lithium p-nitrophenolate trihydrate, a semiorganic NLO crystal

A good optical quality bulk single crystal of a semiorganic non-linear optical material, lithium p-nitrophenolate trihydrate has been grown by a slow cooling solution growth method. The solubility of the material was measured in water before attempting the growth by cooling. The grown crystal was subjected to X-ray diffraction for phase identification and high resolution X-ray diffraction study for assessing its crystalline quality. A rocking curve with full width half maximum of 18 arc s exhibits the good crystalline quality of the crystal. Transmission study shows that the crystal has ∼75–80% transmission in the visible and near infra red spectrum making it a potential material for non-linear optical applications in this spectral range. The refractive index homogeneity, which is an index of the optical quality of the crystal was investigated using birefringence and Mach–Zehnder interferometry. The uniformity of the fringe pattern in both the interferograms show that the crystal has good refractive index homogeneity and is free from any defects. The experimental morphology of the crystal has been found to match with the morphology simulated on the basis of the Bravias–Friedel–Donnay–Harker law.

Unidirectional growth of large size urea doped L-cysteine hydrochloride monohydrate NLO organic crystal and investigations of its crystalline and optical properties.

Organic crystals of urea doped L-cysteine hydrochloride monohydrate have been grown by unidirectional solution growth technique. The crystal grown by this technique has high growth rate as compared to the crystals grown using conventional slow cooling method. This method is ideally suited to grow crystals along a specific direction. The growth process was monitored at regular intervals of time in a time-lapsed manner to estimate the growth rate and also monitor its quality visually. The grown crystal was subjected to different characterizations in order to confirm the phase of the grown crystal, its crystalline perfection and optical properties. The X-ray diffraction confirmed the phase of the crystal. The rocking curve recorded using high resolution X-ray diffraction (HRXRD) technique reveals that the crystal grown using conventional slow cooling method has internal gain boundaries whereas that grown by unidirectional technique has high degree of crystalline perfection. The bonding environment present in the crystal was characterized by FTIR spectroscopy where vibrational frequencies of the different functional groups present were identified. The optical quality of the crystal was characterized using UV-vis-NIR spectrophotometer and Mach-Zehnder interferometer. The nonlinear optical response of the crystal was measured using Kurtz-Perry method and found to be 1.4 times that of a KDP crystal.

Flow Visualization and Modeling of Convection During Growth of KDP Crystals

Buoyancy-driven convection is an important limiting factor during the growth of KDP crystals from their aqueous solution. Convection patterns have been visualised using a shadowgraph technique, and numerically analyzed. A numerical model is developed to obtain two-dimensional refractive index distribution averaged along the length of the growth chamber, followed by the tracing of light rays through the region of interest. The refractive index gradients around the crystal become sharper as the growth progresses, and manifest itself as high contrast plumes in the shadowgraph image. Estimates of the physical displacement of the light rays as they pass through the KDP solution have been found to be insignificant in comparison to the extent of disturbance, indicating that the higher order effects such as interference and scattering are negligible during shadowgraphic imaging of convection around a growing crystal. The experimental and numerical results show the utility of optical imaging of the convective field for monitoring crystal growth.

Crystalline perfection, thermal, mechanical and optical investigations on solution grown l-arginine monohydrochloride single crystal

In the present work we report crystallization and detailed analyses on l-arginine monohydrochloride single crystal an efficient material for nonlinear optical applications. The crystal of titled material was grown using slow evaporation solution growth technique using double distilled water as solvent. Single crystal X-ray diffraction technique revealed that lattice dimensions of grown crystal are in good agreement with the reported literature and it crystallised in monoclinic crystal system. High resolution X-ray diffraction study revealed that crystalline perfection is fairly good. Optical homogeneity and variation of birefringence across the sample cross-section was studied using birefringence interferometer. Specific heat and thermal conductivity of grown crystal was measured using photopyroelectric technique and was found to be higher than many organic and inorganic crystals. Its various mechanical properties and resistance toward deformation was examined using nano-indentation technique. Further laser damage threshold value and phase matching angle was also measured.