Narrow Results

Natural FeTiO₃ (illuminate) and synthesized FeTiO₃, single crystals were characterized by Rutherford backscattering spectroscopy combined with channeling technique and particle-induced x-ray emission (RBS-C and PIXE). The results obtained by the ion beam analysis were supplemented by the x-ray diffraction analysis to identify the crystallographic phase. Oriented single crystals of synthesized FeTiO₃ were grown under the pressure control of CO₂ and H₂ mixture gas using a single-crystal floating zone technique. The crystal quality of synthesized FeTiO₃ single crystals could be improved by the thermal treatment but the exact pressure control is needed to avoid the precipitation of Fe₂O₃ even during the annealing procedure. Natural FeTiO₃ contains several kinds of impurities such as Mn, Mg, Na and Si. The synthesized samples contain Al, Si and Na which are around 100 ppm level as impurities. The PBS-C results of the natural sample imply that Mn impurities occupy the Fe sublattice in FeTiO₃ or in mixed phase between ilmenite and hematite.

The essential steps required to create thick GaN films and seed crystals for bulk crystal growth are described. These include the growth of low dislocation density GaN films by hydride vapor phase epitaxy and the separation of films from their growth substrates. Also addressed are issues of processing thin and thick films to create compliant layer substrates for thick film HVPE growth and chemical mechanical polishing methods to enhance surface morphology and remove material damage free. Growth of both gallium and nitrogen polar films is discussed with key issues identified regarding polarity inversion during growth and impurity incorporation along the -c growth direction. These are illustrated with examples that emphasize the growth of material with low threading dislocation density.

Conventional epitaxial techniques requires single crystalline substrates to form semiconductor material of desired material quality for device applications. The use of amorphous substrates, in many applications, provides an opportunity to consider new materials and designs, which can fundamentally alter the performance, functionality and/or cost limitations of many optoelectronic devices. Here, a growth process is described to achieve single crystalline GaN material on amorphous SiO₂. The evolutionary selection principle in crystal growth is the basis of this technique, and the mechanism is described and analyzed in detail. It is expected that this process can be extended to other semiconductor and substrate combinations, allowing heterogenous integration with functional substrates to produce new classes of semiconductor devices.

Crystals of MnSi_1.73 were prepared by Spark Plasma Sintering (SPS) technique, analyzed by X-ray diffraction (XRD), and invested by metalogragh and scanning electron microscopy (SEM). The growth processes of the samples were studied. It was found that the Mn–Si powders partly formed MnSi_1.73 crystals at 912–937 K under the mechanical pressure of 20 MPa in low vacuum (about 5.0 Pa), and fully formed MnSi_1.73 crystals after sintered at 1173 K for 15 minutes under 40 MPa.

The growth mechanism of coiled carbon whiskers was thoroughly studied. The carbon whiskers were prepared by chemical vapor deposition (CVD) at high temperature (500-650 °C) using acetylene as the carbon source and metal powder as the catalyst. The results show that the shape, diameter and pitch of the coiled carbon whiskers are dependent on the particle size of metal powder: when the sizes of metal powder particles are in the range of tens of microns, carbon whiskers have twisted string shape with diameters between 130 nm and 180 nm and a pitch of 100 to 350 nm. When the diameters of metal powder particles are about several hundred microns, tube shape of carbon whiskers with diameters between 280nm and 350 nm and a pitch between 150nm and 180nm are obtained. The range of temperature for the preparation of coiled carbon whiskers by the CVD method follows Quasi-VLS theory.

The influence of different concentrations of Mg²⁺ ions doping on the structure, morphology and phase transition of LiIO₃ crystal was investigated. The best Mg²⁺-doped alpha-lithium iodate (Mg:α-LiIO₃) crystals for potential optical applications can be successfully grown by the aqueous solution method when the concentration of Mg²⁺ ions in the initial mother solutions C_m< 0.001 M. Chemical component analysis shows the Mg:α-LiIO₃ crystal is a new system with the segregation coefficient k>1. The polarized Raman results are consistent with our conclusions that the Mg²⁺ ion substitutes for the host Li⁺ cation in the pure α-LiIO₃ crystals and results in the corresponding cation vacancies. As C_m increases, inclusions, spontaneously crystalline grains, β phase of LiIO₃ and hillock-shape Mg:α-LiIO₃ crystals are induced respectively by different concentrations of Mg²⁺ ions doping under the same crystal growth conditions. When C_m>0.1 M, the polarized Raman results indicate that larger amounts of Mg²⁺ ions incorporated inhibit LiIO₃ growth and result in the hillock-shape morphology by destabilizing the crystal lattice and inducing lattice distortion.

This paper discusses the optical and mechanical properties of triglycine sulphate (TGS) and MgCl₂ added TGS single crystals (McTGS) grown from aqueous solution at room temperature using slow evaporation solution growth technique. The grown crystals were characterized by powder X-ray diffraction technique and the cell parameter values are found to be a = 9.405 Å, b = 12.623 Å and c = 5.721 Å; β = 110.347° with V = 637.001 ų. UV-Vis-NIR study shows the direct type transition is involved in these materials and indirect, phonon energy gap of McTGS crystals have also been calculated, and these values are less than the TGS crystals. Refractive index and real and imaginary part of the dielectric constant have been discussed for grown crystals. The value of interband optical transition and oscillator energy has been determined by analyzing refractive index with incident energy. Vickers microhardness test was used to determine hardness number, fracture toughness, brittleness index, yield strength and types of crack formed in the crystals.

Large-size and high-quality anthracene single crystals were prepared simply by solution technique. The basal planes correspond to (001) face and two large lateral faces of the anthracene crystals determined to be the (100) plane can also be obtained. The optical properties of the obtained anthracene single crystals were studied. The results indicate that anthracene can be a good window material up to 410 nm as the transmittance of the obtained crystal is around 70% from 800 nm to 410 nm and the band gap energy is 3.02 eV. The dielectric components in x-, y- and z-directions of the obtained crystals were extracted by fitting the results from spectroscopic ellipsometry and the results indicate the dielectric anisotropy of anthracene single crystals. The reflectivity calculated from the permittivity is close to the measured results.

An organic nonlinear single crystal of Nitrilotriacetic acid (NTAA) was grown for the first time by employing a simple slow evaporation technique. Single crystal X-ray diffraction (XRD) analysis reveals that the grown crystal belongs to the monoclinic system with noncentrosymmetric space group $C_C$. Fourier transform infrared (FTIR) spectral study ascertains the presence of functional groups in NTAA. The molecular structure of the grown crystal was confirmed by Nuclear Magnetic Resonance (NMR) spectral analysis. The optical parameters such as transmittance, absorption coefficient and band gap were calculated from UV–Visible and fluorescence studies. Dielectric measurements were carried out for different frequency and temperature. The mechanical strength of the grown crystal was measured using Vickers microhardness test. The high thermal stability and the melting point of the grown crystal were also estimated using thermogravimetric (TGA) and differential thermal analyses (DTA). The confirmation of the grown crystals belonging to nonlinear optical crystals was performed by Kurtz–Perry technique and found as suitable candidate for optoelectronics applications.

Mentioned communication explores the modification in properties of Zinc Thiourea Sulphate (ZTS) crystal due to L-Threonine (LT) addition. Superior quality LT-doped ZTS crystal with 0.5 M% concentration of LT was grown by the slow evaporation solution growth technique. Powder X-ray diffraction technique was applied to study the cell parameters which confirmed orthorhombic crystal structure of both pure and LT-ZTS crystal with slight variation in cell parameters. Shimatzu make spectrophotometer confirmed the UV-Visible spectral analysis in the range of 200–900 nm which affirmed the 94% transmittance, enhanced bandgap value (4.72 eV), lower cut-off value (246 nm) and lower optical constants viz. extinction coefficient, polarizability, refractive index, and reflectance of LT-ZTS crystal. The higher second harmonic generation (SHG) efficiency of LT-doped ZTS was pointed by Kurtz Perry powder method (3.06 times of pure ZTS crystal and 3.62 times of KDP crystal) using Nd: YAG laser. The colour centered emission and electronic purity of parent and doped ZTS crystals were examined which resulted in the violet emission in visible region for both pure and LT-ZTS crystals. Z-scan technique is used to identify the Kerr lensing nonlinearity in pure and LT-doped ZTS crystal. Close aperture Z-scan curve demonstrated negative refraction nonlinearity (self-defocusing nature) for pure and positive refraction nonlinearity (self-focusing nature) for LT-ZTS crystal. Calculated value of refraction nonlinearity n2 is −2.2 × 10${}^{-11}$ cm²/W for pure ZTS and $+$4.99 × 10${}^{-12}$ cm²/W for LT-ZTS crystal. Open aperture Z-scan showed reverse saturable absorption effect (RSA) in pure ZTS and saturable absorption effect (SA) in LT-ZTS crystal. The $\beta$ value is 2.85 × 10${}^{-5}$ cm/W for pure ZTS and 3.92 × 10${}^{-5}$ cm/W for LT-ZTS crystal. The $\chi$3 of ZTS crystal is 6.133 × 10${}^{-5}$ cm/W and 1.655 × 10${}^{-4}$ cm²/W for LT-ZTS crystal. The transition in TONLO parameters is observed due to doping of LT in ZTS. The obtained parameters indicated the superiority of LT-ZTS for application in distinct laser stabilization systems, UV shelter and NLO applications.

A semi-organic nonlinear optical material L-Arginine tetrafluoroborate (LAFB) was synthesized as single crystal using Slow Evaporation Technique. Various properties of this material were analyzed to make it suitable for NLO applications. The structural behavior of the material was determined by single crystal XRD and found that the crystal has orthorhombic structure and was synthesized with P2₁2₁2₁ space group. The High-Resolution X-Ray Diffraction (HRXRD) study was conducted to determine the change in the lattice parameters resulting from strain, defects or by other means in LAFB material. The diffraction curve analysis show that the grown crystal consisted of interstitial type point defect. The Shock Damage Threshold (SDT) measures the stability of the compound against shock, the analysis exhibits that under Mach number 2.2 up to 10th shock no significant cracks were observed in the crystal but damage area of the crystal was increased. The mechanical behavior of the sample against highly intense laser was analyzed through Laser Damage Threshold (LDT). The calculated value of LDT was to be 0.75GW/cm² for 1 pulse per second whereas it decreased to 0.57GW/cm² for 10 pulse per second. To explore the mechanical properties of the material, Nano indentation was carried out, by which the values of H${}_0=131.548$MPa and E${}_0=4.38769$GPa were obtained.

Ferroelectric triglycine sulphate (TGS) single crystals were grown by slow evaporation technique over a period of 30–40 days. The Vickers microhardness studies have been carried out on (001), (010), (101), ($\bar{1}$$\bar{1}$1) and ($\bar{1}$11) faces of the TGS crystal. The as-grown (001) face and (010) face with the ferroelectric phase were used to study the temperature dependence of hardness. The indentation size effect (ISE) described using the five theoretical models viz., Meyer’s law, Hays–Kendall, elastic/plastic deformation (EPD), proportional specimen resistance (PSR) and modified PSR model has been investigated on all the crystal faces under study. The experimental results show that the modified PSR model is more accurate at generating load-independent hardness data and also for explaining the origin of ISE.

Crystals with different faceting behavior were observed in the strontium titanate borosilicate glass ceramic system with a small amount of bismuth oxide addition and proper heat treatment schedule. These types of faceting morphology were generally observed in phase-separated glasses followed by heterogeneous nucleation. X-ray diffraction and electron microscopic techniques were used to characterize these samples. X-ray diffraction patterns for bulk and pulverized samples were observed to be readily different from each other. Peaks in the X-ray diffraction pattern for bulk samples can be indexed for icosahedral symmetry.

The kinetics of the Ostwald ripening in a homogeneous supersaturated solution is studied both numerically and analytically. The time evolution of the grain-size distribution function in a new phase is theoretically described, taking into account the finite value of the maximal size of a grain. Two situations are considered: the kinetics of grain growth is controlled either by the grain-monomer reaction process (an early stage) or by the monomer diffusion process (a late stage). A transition to the final distribution is shown to take place through an intermediate-asymptotical mode of the Ostwald ripening kinetics, the crossover of the kinetic indices is demonstrated, and the duration of intermediate stage is evaluated.

Single crystals of 2-Naphthalenol (2N), new organic nonlinear optical (NLO) material, have been grown by slow evaporation solution growth technique at room temperature. The crystal system has been confirmed from the single crystal X-ray diffraction analysis. The functional groups were identified using FTIR spectroscopy. UV-vis-NIR spectrum showed absence of absorption in the wavelength region 400–1400 nm. The second harmonic generation efficiency is two times higher than that of standard potassium dihydrogen phosphate (KDP).

Hf:Fe:LiNbO₃ crystals were grown by the Czochralski technique with various ratios of Li/Nb = 0.946, 1.05, 1.20 and 1.38 in the melt. The crystal composition and defect structure were analyzed by XRD, UV-Vis and IR spectroscopy. The results show that the threshold concentration of Hf in LiNbO₃ crystals decrease with the increasing of the Li/Nb ratio; when the Li/Nb ratio is 1.05, the threshold concentration of Hf is less than 2 mol%, largely under the threshold concentration of Hf ions in congruent Hf:Fe:LiNbO₃ crystal (4 mol).^1–3 With the increase of Li/Nb, Hf ions first replace the ; when the concentration of Hf ions is higher than the threshold value, Hf ions occurs on normal Nb and Li sites.

Single crystals of pure and various amount of L-lysine doped KDP crystals were grown from aqueous solution. The doping of L-lysine was confirmed by CHN analysis and FT-IR spectroscopy. Powder XRD was carried out to assess the single phase nature of the samples. The effect of doping on thermal stability of the crystals was carried out by TGA and the kinetic and thermodynamic parameters of dehydration were evaluated. It was found that as the amount of doping of amino acid, L-lysine, increased the thermal stability of the grown crystals decreased. However, the second-harmonic generation (SHG) efficiency of Nd:YAG laser and UV-vis spectroscopy studies indicated that as the L-lysine doping increased in KDP crystals the SHG efficiency and optical transmission percentage increased. The dielectric constant and the dielectric loss of L-lysine doped KDP crystals are lower than the pure KDP crystals. Hence L-lysine doped KDP crystals are found to be more beneficial from an application point of view as compared to pure KDP crystals. The results are discussed.

This paper reports that ZnSnO nanofibers (ZSNFs) were synthesized by thermal oxidation of ZnSn alloys. ZnSn alloys were prepared by cold press and sintering (powder metallurgy). The structure and optical properties were characterized by X-ray diffraction (XRD), micro-Raman scattering technology, field emission scanning electron microscopy (FESEM) and photoluminescence (PL) spectrum. The micro-Raman scattering spectra of ZSNFs show four Raman peaks at 574, 1156, 1729 and 2330 cm^-1. The diameter and length of ZSNFs are about 50 nm and 60 μm, respectively. The room temperature PL spectra of ZSNFs shows the near-band-edge emission at ~391 nm and a broad green emission at ~493 nm.

A novel mixed organic single crystal of glycine thiourea (GTU), which is a potential material for nonlinear optical applications, has been grown by solvent evaporation method at room temperature. The grown single crystal has been analyzed using different characterization methods. X-ray diffraction studies show that it belongs to an orthorhombic crystal system having lattice dimensions a = 5.546 Å, b = 7.774 Å and c = 8.637 Å. The formation of the compound was verified by FTIR analysis. Its optical behavior was analyzed using UV-vis analysis and it was found that it had good optical transmission in the entire visible region. The mechanical properties of grown crystals were studied using Vickers microhardness tester. The surface defects were examined by adopting an etching technique. Its nonlinear optical property was tested using Kurtz powder method and found to have better SHG efficiency than that of potassium dihydrogen phosphate (KDP) single crystal.

A template-free solution method based on solid-liquid interface reaction has been developed for fabricating metal chalcogenide dendritic nanostructures. Well-defined PbSe dendrites with four branches can be large-scale synthesized with metal lead foil as Pb²⁺ source and Na₂SeO₃ as Se²⁺ source in solvothermal conditions. The nanorods in each branch are parallel to each other in the same plane and are perpendicular to the trunk. It was found that PbSe cubes first formed on the lead substrate through a direct surface reaction and that subsequent crystal growth preferentially took place on the vertex of these PbSe cubes, leading to the formation of final branched dendrites. The current solid-liquid interface reaction has been extended to the synthesis of CuS micro-pine dendrites with copper foil and sulfur powder as reaction reagents.