High-resolution X-ray Diffractometry Research Articles

Structure-Independent Proton Transport in Cerium(III) Phosphate Nanowires.

Understanding of water-related electrical conduction is of utmost importance in applications that utilize solid-state proton conductors. However, in spite of the vast amount of theoretical and experimental work published in the literature, thus far its mechanism remained unsolved. In this study, the structure-related ambient temperature electrical conduction of one-dimensional hydrophilic nanostructures was investigated. Cerium phosphate nanowires with monoclinic and hexagonal crystal structures were synthesized via the hydrothermal and ambient temperature precipitation routes, and their structural and surface properties were examined by using high-resolution transmission electron microscopy, X-ray diffractometry, nitrogen and water sorption, temperature-programmed ammonia desorption, and potentiometric titration techniques. The relative humidity (RH)-dependent charge-transport processes of hexagonal and monoclinic nanowires were investigated by means of impedance spectroscopy and transient ionic current measurement techniques to gain insight into their atomistic level mechanism. Although considerable differences in RH-dependent conductivity were first found, the distinct characteristics collapsed into a master curve when specific surface area and acidity were taken into account, implying structure-independent proton conduction mechanism in both types of nanowires.

Investigation on nucleation kinetics, structural and dielectric properties of an organic NLO single crystal—l-Histidinium maleate (LHM)

An organic nonlinear optical (NLO) material, l-histidinium maleate, was synthesized, and subsequently a single crystal was grown from aqueous solution by slow evaporation technique. The solubility of the material was determined gravimetrically. The metastable zonewidth was studied to observe the stability of the material using the polythermal method. The induction period was experimentally determined, and various nucleation parameters such as interfacial energy, Gibbs free energy change, critical volume free energy change and radius of critical nuclei of LHM crystals were estimated based on classical theory of nucleation. The grown crystals were characterized by powder X-ray diffraction. The crystalline perfection of the grown crystal was assessed with the help of a high-resolution X-ray diffractometry. The stoichiometric form of LHM was confirmed by a CHN analysis. The dielectric measurement was carried out as a function of frequencies at different temperatures.

Enhancement of thermoelectric figure of merit in Bi2Se3crystals through a necking process

The growth of good quality bulk single crystals of bismuth selenide by employing a high-temperature vertical Bridgman technique with a specially designed ampoule having a provision for a necking process is reported. Several growth experiments were performed and reproducible results were obtained. The crystal structure and lattice dimensions were confirmed by powder X-ray diffraction (PXRD), the bulk crystalline perfection was assessed using high-resolution X-ray diffractometry and the good bulk crystalline perfection with an indication of layered structure was confirmed. Transmission electron microscopy (TEM) was carried out for the grown single crystal and confirmed the layered structure. High-resolution TEM (HRTEM) was also used to further assess the crystalline perfection. The direct measurement ofdspacing obtained from HRTEM imaging was found to be in good agreement with the data obtained from PXRD. The thermal behavior was examined by differential scanning calorimetry and a sharp melting was found at 983 K, which revealed the purity of the bismuth selenide. The Seebeck coefficient and electrical and thermal conductivities were measured, and a thermoelectric figure of merit was calculated in order to assess the suitability of the crystal for thermoelectric applications such as refrigeration and portable power generation. Nanoindentation analysis was also performed for the first time.

Microstructure and properties of epitaxial Sr2FeMoO6 films containing SrMoO4 precipitates

Thin films of Sr2FeMoO6 (SFMO) were grown by pulsed laser deposition in non-optimized argon ambient pressures. The films were found to contain a high number of precipitates of foreign phases. The nature and microstructure of these phases were investigated in detail by high-resolution scanning transmission electron microscopy (STEM) and X-ray diffractometry (XRD). We found out that the dominant foreign phase embedded in the SFMO film matrix was SrMoO4 (SMO). Through STEM and XRD analysis, we determined that the SMO phase grows epitaxially with respect to the surrounding SFMO matrix and has a fairly good crystallinity. Although the SFMO films include many foreign precipitates, they still exhibit good conducting properties and moderate magnetization values. Tuning the growth of the SMO phase on top of SFMO films to obtain a natural tunnel barrier might pave the way for future applications of SFMO in spintronic devices.

Stable ferroelectric perovskite structure with giant axial ratio and polarization in epitaxial BiFe0.6Ga0.4O3 thin films.

Ferroelectric perovskites with strongly elongated unit cells (c/a > 1.2) are of particular interest for realizing giant polarization induced by significant ionic off-center displacements. Here we show that epitaxial BiFe0.6Ga0.4O3 (BFGO) thin films exhibit a stable super-tetragonal-like structure with twinning domains regardless of film thickness and substrate induced strain, evidenced with high resolution X-ray diffractometry (HR-XRD), transmission electron microscopy (TEM) and piezoresponse force microscopy (PFM). The origin of the structural stability of BFGO is investigated by the first-principles calculation. The ferroelectric properties of BFGO are studied by PFM, first-principles calculation and macroscopic polarization-electric field (P-E) hysteresis measurement. A giant ferroelectric polarization of ∼150 μC/cm(2) is revealed by the first-principles calculations and confirmed by experiments. Our studies provide an alternative pathway of employing Ga-substitution other than the extensively studied strain engineering to stabilize the supertetragonal structure in BiFeO3-based epitaxial thin films.

A simple method to control the formation of cerium phosphate architectures

Growth of cerium phosphate microstructures was examined under mild conditions using a flow reaction system. Two entirely different development pathways were identified by which the formation of architecturally different cerium phosphate spherulites could be triggered. The selection between these mechanisms could readily be achieved by the reverse addition of precursors. Structural differences were examined by using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffractometry and nitrogen sorption measurement. The precipitate flow profiles were examined comprehensively and taken into consideration to interpret the spherulite formation process. The presumed formation mechanisms were approved by time monitored synthesis and HRTEM investigation. Terbium-doped counterparts of the pristine spherulites were used to assess the structure-related photoluminescence properties. Regardless of the identical crystal phase and chemical composition, a 30–35% difference in photoluminescence intensity was found between the two types of spherulites, suggesting strong architecture-dependent physical properties.

Formation of unusual nonferroic domains in TeO2 single crystals under external electric field

The formation of unusual slowly relaxing domains under an external dc electric field has been revealed in paratellurite (TeO2) crystals. These domains differ from those arising in ferroics (ferromagnets, ferroelectrics, ferroelastics, etc.). The effect is characterized by the existence of a threshold field strength (at which domains begin to be formed) and long equilibrium settling times (up to a few hours, depending on the electric field strength). A crystal returns to the initial single-domain state also after a few hours after the field is switched off. High-resolution triple-crystal X-ray diffractometry has revealed that domains retaining the paraelastic tetragonal phase rotate with respect to each other in space without changing their lattice parameter. The domain sizes are 2–4 mm, depending on the field strength. Currently, the exact mechanisms of domain formation are unclear. Possible reasons for the formation of these defects and an analogy of the observed effects with the behavior of liquid crystals under electric field are discussed.

In situ study of the growth and degradation processes in tetragonal lysozyme crystals on a silicon substrate by high-resolution X-ray diffractometry

The results of an in situ study of the growth of tetragonal lysozyme crystals by high-resolution X-ray diffractometry are considered. The crystals are grown by the sitting-drop method on crystalline silicon substrates of different types: both on smooth substrates and substrates with artificial surface-relief structures using graphoepitaxy. The crystals are grown in a special hermetically closed crystallization cell, which enables one to obtain images with an optical microscope and perform in situ X-ray diffraction studies in the course of crystal growth. Measurements for lysozyme crystals were carried out in different stages of the crystallization process, including crystal nucleation and growth, developed crystals, the degradation of the crystal structure, and complete destruction.

Growth, structural and mechanical analysis of a single crystal ofl-prolinium tartrate: a promising material for nonlinear optical applications

A single crystal of L-prolinium tartrate (LPT), which is an organic non linear optical material, was successfully synthesized and grown using a slow evaporation solution growth technique (SEST). The crystal structure and lattice parameters of the crystal were confirmed by powder X-ray diffraction and it was found that it belongs to the monoclinic crystal system with β = 100.380 and a noncentrosymmetric space group. The presence of strain in the grown ingot was calculated from powder X-ray diffraction measurements. The crystalline perfection was examined by high resolution X-ray diffractometry, which revealed that the crystal contained structural grain boundaries. The optical behavior of the grown specimen was analyzed by photoluminescence (PL) spectroscopy and its time resolved PL decay was calculated. The grown crystal adopted a step wise growth pattern with parallel striations, which was confirmed from the etching technique. Its ferroelectric and piezoelectric properties were also assessed. Its third order non linearity was assessed using an open aperture Z-scan technique. The thermal parameters of the LPT single crystal were calculated using a photopyroelectric technique. The mechanical strength of the single crystal at the micro level was observed by nanoindentation using the Oliver–Pharr method.

On the doping limit for strain stability retention in phosphorus doped Si:C

Strain stability of phosphorus doped pseudomorphically strained Si:C alloy is investigated via high-resolution X-ray diffractometry, Fourier transform infrared spectroscopy, and Hall measurement. Significant strain relaxations are found under post-annealing treatment far below β-SiC precipitation threshold temperature, especially for the highest phosphorus doped case. Most of the substitutional carbon is retained and no further β-SiC formation can be found for all samples investigated. Volume compensation through gettering of interstitial atoms around substitutional carbon is considered as a probable mechanism for the observed strain relaxation. The strain relaxation effect can be further reduced with HF treatment prior to post-annealing process. We found an upper limit for ion implant dose (<1 × 1014 atom/cm2) for the retention of strain stability in phosphorus doped Si:C.

Hydrothermal epitaxy and resultant properties of EuTiO3 films on SrTiO3(001) substrate.

We report a novel epitaxial growth of EuTiO3 films on SrTiO3(001) substrate by hydrothermal method. The morphological, structural, chemical, and magnetic properties of these epitaxial EuTiO3 films were examined by scanning electron microscopy, transmission electron microscopy, high-resolution X-ray diffractometry, X-ray photoelectron spectroscopy, and superconducting quantum interference device magnetometry, respectively. As-grown EuTiO3 films with a perovskite structure were found to show an out-of-plane lattice shrinkage and room-temperature ferromagnetism, possibly resulting from an existence of Eu3+. Postannealing at 1,000°C could reduce the amount of Eu3+, relax the out-of-plane lattice shrinkage, and impact the magnetic properties of the films.PACS81.10.Aj; 81.15.-z; 61.05.-a

Unidirectional growth of l-alanine single crystal: NLO material from the amino acid family

Single crystal of l-alanine (LALA) has been grown by using the Sankaranarayanan and Ramasamy (SR) method. The identity of the crystal was confirmed using single crystal X-ray diffraction. The crystalline perfection was evaluated using high-resolution X-ray diffractometry (HRXRD). Infrared (IR) spectroscopic, UV–vis–NIR spectral and second harmonic generation (SHG) conversion efficiency studies were carried out. Microhardness measurements and thermal studies of the compound were made and reported.

Unit-cell determination of epitaxial thin films based on reciprocal-space vectors by high-resolution X-ray diffractometry

A new approach, based on reciprocal-space vectors (RSVs), is developed to determine Bravais lattice types and accurate lattice parameters of epitaxial thin films by high-resolution X-ray diffractometry. The lattice parameters of single-crystal substrates are employed as references to correct the systematic experimental errors of RSVs of thin films. The general procedure is summarized, involving correction of RSVs, derivation of the raw unit cell, and subsequent conversion to the Niggli unit cell and the Bravais unit cell by matrix calculation. Two methods of this procedure are described: in three-dimensional reciprocal space and in six-dimensionalG6space. The estimation of standard error in the lattice parameters derived by this new approach is discussed. The whole approach is illustrated by examples of experimental data. The error of the best result is 0.0006 Å for the lattice parameter of indium tin oxide film. This new RSV method provides a practical and concise route to the crystal structure study of epitaxial thin films and could also be applied to the investigation of surface and interface structures.

Studies of the structural and third-order nonlinear optical properties of solution grown 4-hydroxy-3-methoxy-4′-N′-methylstilbazolium tosylate monohydrate crystals

An organic nonlinear optical crystal, 4-hydroxy-3-methoxy-4′-N′-methylstilbazolium tosylate monohydrate (VMST) was grown from methanol:water mixed solvent by slow cooling method. The crystal structure, morphology, composition and melting point of grown crystals were studied through single crystal X-ray diffraction, infrared spectrum and differential scanning calorimetry analyses respectively. The crystalline perfection of grown crystal was evaluated by high-resolution X-ray diffractometry. The cut-off wavelength, optical transmission, refractive index and band gap energy of grown crystal were determined from UV–Visible spectral analysis. The photoluminescence spectral study revealed the transition mechanism of ions. The self-focusing Z-scan technique and degenerate four wave mixing technique have been employed to observe the third-order nonlinear optical property of the grown crystal. The surface laser damage threshold value of VMST crystal was measured by using Nd:YAG laser.

Effect of low-temperature annealing on the electronic- and band-structures of (Ga,Mn)As epitaxial layers

The effect of outdiffusion of Mn interstitials from (Ga,Mn)As epitaxial layers, caused by post-growth low-temperature annealing, on their electronic- and band-structure properties has been investigated by modulation photoreflectance (PR) spectroscopy. The annealing-induced changes in structural and magnetic properties of the layers were examined with high-resolution X-ray diffractometry and superconducting quantum interference device magnetometry, respectively. They confirmed an outdiffusion of Mn interstitials from the layers and an enhancement in their hole concentration, which were more efficient for the layer covered with a Sb cap acting as a sink for diffusing Mn interstitials. The PR results demonstrating a decrease in the band-gap-transition energy in the as-grown (Ga,Mn)As layers, with respect to that in the reference GaAs one, are interpreted by assuming a merging of the Mn-related impurity band with the GaAs valence band. Whereas an increase in the band-gap-transition energy caused by the annealing treatment of the (Ga,Mn)As layers is interpreted as a result of annealing-induced enhancement of the free-hole concentration and the Fermi level location within the valence band. The experimental results are consistent with the valence-band origin of itinerant holes mediating ferromagnetic ordering in (Ga,Mn)As, in agreement with the Zener model for ferromagnetic semiconductors.

Crystallographically tilted and partially strain relaxed GaN grown on inclined {111} facets etched on Si(100) substrate

High resolution X-ray diffractometry (HR-XRD), Photoluminescence, Raman spectroscopy, and Transmission electron microscope measurements are reported for GaN deposited on a conventional Si(111) substrate and on the {111} facets etched on a Si(100) substrate. HR-XRD reciprocal space mappings showed that the GaN(0002) plane is tilted by about 0.63° ± 0.02° away from the exposed Si{111} growth surface for GaN deposited on the patterned Si(100) substrate, while no observable tilt existed between the GaN(0002) and Si(111) planes for GaN deposited on the conventional Si(111) substrate. The ratio of integrated intensities of the yellow to near band edge (NBE) luminescence (IYL/INBE) was determined to be about one order of magnitude lower in the case of GaN deposited on the patterned Si(100) substrate compared with GaN deposited on the conventional Si(111) substrate. The Raman E2(high) optical phonon mode at 565.224 ± 0.001 cm−1 with a narrow full width at half maximum of 1.526 ± 0.002 cm−1 was measured, for GaN deposited on the patterned Si(100) indicating high material quality. GaN deposition within the trench etched on the Si(100) substrate occurred via diffusion and mass-transport limited mechanism. This resulted in a differential GaN layer thickness from the top (i.e., 1.8 μm) of the trench to the bottom (i.e., 0.3 μm) of the trench. Mixed-type dislocation constituted about 80% of the total dislocations in the GaN grown on the inclined Si{111} surface etched on Si(100).

Defects and stresses in MBE-grown GaN and Al0.3Ga0.7N layers doped by silicon using silane

The electric and structural characteristics of silicon-doped GaN and Al0.3Ga0.7N layers grown by molecular beam epitaxy (MBE) using silane have been analyzed by the Hall effect, Raman spectroscopy, and high-resolution X-ray diffractometry. It is established that the electron concentration linearly increases up to n = 4 × 1020 cm−3 with an increase in the silane flow rate for GaN:Si, whereas the corresponding dependence for Al0.3Ga0.7N:Si is sublinear and the maximum electron concentration is found to be n = 4 × 1019 cm−3. X-ray measurements of sample macrobending indicate a decrease in biaxial compressive stress with an increase in the electron concentration in both GaN:Si and Al0.3Ga0.7N:Si layers. The parameters of the dislocation structure, estimated from the measured broadenings of X-ray reflections, are analyzed.

Microstructural and wear characteristics of HVOF-sprayed nanocrystalline NiAl coating

In this research, the microstructure and dry sliding friction and wear behavior of nanocrystalline NiAl coatings were investigated. Toward this purpose, nanocrystalline NiAl powders were initially prepared by mechanical alloying (MA) and deposited on low carbon steel substrate by high velocity oxygen fuel (HVOF) thermal spray process with two sets of spray parameters. The coatings were characterized with respect to their microstructure and phase compositions using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and X-ray diffractometry (XRD). In addition, the friction and wear behavior of coating were tested under three loads of 30, 60 and 90N. Microstructural observations showed that the as-sprayed coatings include mainly NiAl intermetallic compound with a crystallite size of ~20nm, although there exist some Al2O3 and Ni phases. HVOF spraying at higher fuel/oxygen ratio caused higher amounts of non-NiAl phases and lower hardness and wear resistance. The wear mechanisms and friction behavior of nanocrystalline NiAl coatings were evaluated and discussed in detail.

A novel comparative study of crystalline perfection and optical homogeneity in Nd:GGG crystals grown by the Czochralski technique with different crystal/melt interface shapes

Nd:GGG crystals (GGG is gadolinium gallium garnet) grown with different crystal/melt interface shapes (convex/flat/concave) by varying the seed rotation rate while using the Czochralski technique were studied for their optical homogeneity and crystalline perfection by optical polarization microscopy (OPM) and high-resolution X-ray diffractometry (HRXRD), respectively. It was found that there is a remarkable effect of seed rotation rate, which decides the shape of the crystal/melt interface, on the optical homogeneity and crystalline perfection. It was found experimentally that, as the rotation rate increases, the crystal/melt interface changes from convex to flat. If the rate further increases the interface becomes concave. With a steep convex interface (for low rotation rates), certain facets are concentrated in the small central portion of the crystal, and as the rate increases, these facets slowly move outward, leading to improved optical homogeneity and crystalline perfection as observed from the OPM and HRXRD results. The strain developed in the crystalline matrix as a result of segregation of oxygen in the crystals at low seed rotation rates as observed from HRXRD seems to be the reason for the observed optical inhomogeneity. The correlation between optical inhomogeneity and crystalline perfection for a variety of specimens with different shapes of the crystal/liquid interface obtained at different seed rotation rates is reported.

Synthesis and Optical Characterization of Sulfonated Polyaniline/Single-Walled Carbon Nanotube/Zinc Sulphide Nanocomposite

Polyaniline functionalized with sulfonate groups (SPANI) shows excellent solubility in water. Single-walled carbon nanotubes functionalized with carboxylic groups (f-SWCNTs) and then hybridized with freshly prepared zinc sulphide (ZnS) nanocrystals have been found to be good luminescent material with tuned emission properties. Nanocomposite of sulfonated polyaniline with embedded SWCNT/ZnS nanohybrid fibers has been prepared by a simple solution mixing process and characterized by using high resolution transmission electron microscopy (HRTEM), X-ray diffractometry, Raman spectroscopy, FTIR spectroscopy, and thermogravimetric analysis (TGA). The study of optical properties by UV-vis absorption and photoluminescence spectroscopy reveals that the composite is a luminescent material of enhanced emission intensity in the visible region of the spectrum.