Rocking Curve Research Articles

Direct Current Reactive Sputtering Deposition and Plasma Annealing of an Epitaxial TiHfN Film on Si (001)

Deposition of a heteroepitaxial TiHfN film with a growth rate of about 1 μm/h was successfully achieved on a Si (001) substrate at a temperature above 700 °C by direct current magnetron reactive sputtering of a Ti0.6Hf0.4 (in atomic fraction) target with an Ar/N2 gas mixture. Annealing of the as-deposited TiHfN/Si sample at a temperature above 1000 °C using microwave plasma with H2/N2 gas was performed to further improve the TiHfN film’s quality. X-ray diffraction results show that the heteroepitaxial TiHfN film on Si exhibits a cube-on-cube relationship as {001}TiHfN//{001}Si and <110>TiHfN//<110>Si. X-ray rocking curve measurements show that the full width at half maximum of (200)TiHfN is 1.36° for the as-deposited TiHfN film, while it is significantly reduced to 0.53° after microwave plasma annealing. The surface morphologies of the as-deposited and annealed TiHfN films are smooth, with a surface roughness of around ~2 nm. Cross-sectional scanning/transmission electron microscopy (S/TEM) shows a reduction in defects in the annealed film, and X-ray photoelectron spectroscopy shows that the film composition remains unchanged. Additionally, S/TEM examinations with atomic resolution illustrate domain matching epitaxy (DME) between TiHfN and Si at the interface. The TiHfN films have good electrical conducting properties with resistivities of 40–45 μΩ·cm.

Fracture Closure Empirical Model and Theoretical Damage Model of Rock under Compression.

The rock or rock mass in engineering often contains joints, fractures, voids, and other defects, which are the root cause of local or overall failure. In response to most of the current constitutive models that fail to simulate the nonlinear fracture compaction deformation in the whole process of rock failure, especially brittle rocks, a piecewise constitutive model was proposed to represent the global constitutive relation of rocks in this study, which was composed of the fracture compaction empirical model and the damage statistical constitutive model. The fracture empirical compaction model was determined by fitting the expressions of fracture closure curves of various rocks, while the rock damage evolution equation was derived underpinned by the fracture growth. According to the effective stress concept and strain equivalence hypothesis, the rock damage constitutive model was deduced. The model parameters of the fracture compaction empirical model and damage statistical constitutive model were all calculated by the geometrical characteristics of the global axial stress-strain curve to guarantee that the models are continuous and smooth at the curve intersection, which is also simple and ready to program. Finally, the uniaxial compression test data and the triaxial compression test data of different rocks in previous studies were employed to validate the models, and the determination coefficient was used to measure the accuracy. The results showed great consistency between the model curves and test data, especially in the pre-peak stage.

Experimental research on influence mechanism of loading rates on rock pressure stimulated currents

The study of pressure stimulated current (PSC) changes of rocks is significant to monitor dynamic disasters in mines and rock masses. The existing studies focus on change laws and mechanism of currents generated under the loading of rocks. An electrical and mechanics test system was established in this paper to explore the impacts of loading rates on PSCs. The results indicated that PSC curves of different rocks had different change laws under low/high loading rates. When the loading rate was relatively low, PSC curves firstly changed gently and then increased exponentially. Under high loading rates, PSC curves experienced the rapid increase stage, gentle increase stage and sudden change stage. The compressive strength could greatly affect the peak PSC in case of rock failure. The loading rate was a key factor in average PSC. Under low loading rates, the variations of PSCs conformed to the damage charge model of fracture mechanics, while they did not at the fracture moment. Under high loading rates, the PSCs at low stress didn’t fit the model due to the stress impact effects. The experimental results could provide theoretical basis for the influence of loading rates on PSCs.

A semiempirical constitutive relationship for rocks under uniaxial compression considering the initial damage recovery

AbstractA better understanding of the constitutive model and damage evolution law is the premise to ensure their feasibility and practicability in rock engineering projects. In this paper, a damage constitutive relationship, which can reflect the initial damage recovery, is established based on the generalized equivalent strain principle and the initial tangent modulus. A Weibull distribution‐based model is also established to represent the deformation after the compaction point. A piecewise expression of the complete stress–strain curve of rocks under uniaxial compression is thereby obtained by the combination of the above two constitutive models. Finally, the effectiveness of the piecewise constitutive relationship is verified using uniaxial compression test data of different types of rocks. The results show that the theoretical curves are in good agreement with the experimental curves. Parameters of the proposed relationship are relatively to be derived, making it convenient for engineering applications.

Epitaxial Growth of GaN/AlN on h-BN/Si(111) by Metal–Organic Chemical Vapor Deposition: An Interface Analysis

Among III-nitride semiconductors, hexagonal boron nitride (h-BN) has a two-dimensional crystal structure and can be used as an insulator for nanotransistors or a substrate release layer for flexible electronics, which heavily rely on its interface properties. In this study, h-BN films were successfully grown on 150 mm Si(111) substrates by metal–organic chemical vapor deposition using AlN as a nucleation layer, and van der Waals epitaxy of GaN on the h-BN films was investigated, including the challenges of exfoliation of epilayers. As a result of the accumulated stress in GaN films during growth, self-exfoliation of GaN films was observed on GaN of thickness 1 μm and more. This issue was resolved by decreasing the h-BN thickness from 8 to 3 nm and lower, which results in improved crystal quality as evidenced by the smaller linewidth of the (0002) GaN X-ray rocking curves. Based on the exfoliation behavior of a series of GaN grown with different thicknesses, a self-exfoliation mechanism was proposed and an interface binding energy of 54 meV was estimated for the h-BN/AlN interface.

Optimization of chemical mechanical polishing of (010) β-Ga2O3

Smooth (< 0.5 nm rms) and subsurface damage-free (010) β-Ga2O3 was achieved with low-pressure chemical mechanical polishing. An applied pressure of 1 kPa along with colloidal silica and poromeric polyurethane polishing pads rotating at 30 rpm was found to be the optimal polishing parameters for (010) β-Ga2O3. Using higher pressures typically employed in the current literature induced subsurface damage in the substrates. Diffuse scatter intensity of triple-axis x-ray rocking curves was used to determine the presence of subsurface lattice damage, which was quantified by measuring peak widths below the half maximum (i.e., FWXM where X < 0.5). The initially rough surfaces of (010) β-Ga2O3 substrates due to wafer slicing and grinding were lapped and polished. A 5 μm Al2O3 slurry followed by a 0.3 μm Al2O3 slurry was used as the primary lap material removal step. The material removal rates were ∼20 and ∼9 μm/h, respectively. Then, chemical mechanical polishing was performed using colloidal alumina followed by colloidal silica. The removal rates were ∼1.3 and ∼0.4 μm/h, respectively. Only colloidal silica showed the complete removal of subsurface damage. The final (020) β-Ga2O3 rocking curve FWHM was ∼13″ and FW(0.001)M was ∼120″, which matches the widths of commercially available pristine (010) β-Ga2O3. A final cleaning step using dilute bleach and dilute citric acid to remove residual silica slurry particles from the surface was demonstrated.

AN ANALYSIS ON IMPROVEMENT OF X-RAY DIFFRACTOMETER RESULTS BY CONTROLLING AND CALIBRATION OF PARAMETERS

The X-ray diffractometer in the laboratory is a crucial instrument for analyzing materials in science. It can be used on almost any crystal material, and if the machine parameters are appropriately controlled, it can offer a lot of information about the sample’s characteristics. Nevertheless, the data obtained from these machines are complicated by an aberration function that can be resolved through calibration. In this study, a powder comprising of Barium Sulfate (BaSO4), Zinc Oxide (ZnO) and Aluminum (Al) was used as the first sample and a single crystal sample comprised of Gallium Nitride (GaN) and Aluminum Oxide (Al2O3). The required calibration parameters of the X-ray diffractometer namely: Straight Beam Alignment, Beam Cut Alignment and Sample Tilt Alignment for two samples were analyzed and carried out. Using the results of the X-ray spectrum, important parameters such as corresponding planes for peak positions, d-spacing of planes, intensities, smallest crystallite sizes and lattice parameters, and a comparison with the reference data were all carried out. As another result, the out-of-plane alignment and Full-Width- at Half-Maximum (FWHM) value for GaN could be determined using the rocking curve.

HVPE Growth and Characterization of Thick κ-Ga2O3 layers on GaN/Sapphire Templates

Ga2O3 layers with thickness from 10 to 86 μm were grown by halide vapor phase epitaxy (HVPE) on GaN(0001)/sapphire templates in a hot wall reactor at 570 °C, with the growth rate of about 3–4 μm h−1. The grown layers consisted of pure (001)-oriented κ-Ga2O3 polymorph with no admixture of β-Ga2O3 or α-Ga2O3 phases. The narrowest (004) X-ray rocking curves were observed for 13–20 μm thick κ-Ga2O3 layers. A further increase in thickness results in deterioration of the crystal quality which is indicated by the broadening of rocking curves. Electrical measurements of the thick layers revealed that they were n-type, with the concentration of shallow donors gradually decreasing from ∼1016 cm−3 to ∼1015 cm−3. Deep level transient spectroscopy (DLTS) measurements revealed the presence of deep traps with levels near Ec−0.3 eV, Ec−0.6 eV, Ec−0.7 eV, Ec−0.8 eV, Ec−1 eV, with the Ec−0.8 eV being predominant.

An In Situ Detection System for Obtaining IRM Acquisition Curves and Alternating Field Demagnetization Remanence Curves of Rocks

An In Situ Detection System for Obtaining IRM Acquisition Curves and Alternating Field Demagnetization Remanence Curves of Rocks

Oxygen distribution in the structure of YBa-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-7-delta-=/SUB=- thin films after vacuum exposure at 300 K

We have found out that vacuum exposure of YBa2Cu3O7-delta thin epitaxial films at 300 K for 24 hours decreases oxygen content and induces changes in their crystal structure depending on the films synthesis conditions. YBa2Cu3O7-delta films on SrTiO3 (100) substrates were synthesized by pulsed laser deposition. The crystal structure was studied using XRD technique. Additional maxima of diffraction peak (005) before and after vacuum exposure indicate the presence of regions with different oxygen content; and the change in the shape of the rocking curves indicate a change in the crystallites orientation. After vacuum exposure, the oxygen deficiency delta in the films increased from ~0.01 to ~0.6 for films with a crystallites size of 2-10 nm and from ~0.25-0.35 to ~0.6 for crystallites size of 500-1000 nm. The appearance of a residual resistance after the superconducting transition in the dependence R(T) may be explained by the fact that oxygen loss mainly in the boundary regions of the crystallites takes place, so that their boundaries become dielectric, while the crystallites themselves remain superconductive. Based on the data of X-ray diffraction analysis, as well as resistive measurements, we have come to the conclusion about oxygen loss through grain boundaries in films with nanocrystallites of 2-10 nm in size, and also through structural defects in films with larger crystallites. Keywords: pulsed laser deposition, surface relief, transport characteristics of films, film evolution, SrTiO3.

Modelling fine-sliced three dimensional electron diffraction data with dynamical Bloch-wave simulations

Recent interest in structure solution and refinement using electron diffraction (ED) has been fuelled by its inherent advantages when applied to crystals of sub-micrometre size, as well as its better sensitivity to light elements. Currently, data are often processed with software written for X-ray diffraction, using the kinematic theory of diffraction to generate model intensities - despite the inherent differences in diffraction processes in ED. Here, dynamical Bloch-wave simulations are used to model continuous-rotation electron diffraction data, collected with a fine angular resolution (crystal orientations of ∼0.1°). This fine-sliced data allows a re-examination of the corrections applied to ED data. A new method is proposed for optimizing crystal orientation, and the angular range of the incident beam and the varying slew rate are taken into account. Observed integrated intensities are extracted and accurate comparisons are performed with simulations using rocking curves for a (110) lamella of silicon 185 nm thick. R1 is reduced from 26% with the kinematic model to 6.8% using dynamical simulations.

Optical and electrical properties of Sb-doped β-Ga2O3 crystals grown by OFZ method

Sb-doped β-Ga2O3 crystals were grown using the optical floating zone (OFZ) method. X-ray diffraction data and X-ray rocking curves were obtained, and the results revealed that the Sb-doped single crystals were of high quality. Raman spectra revealed that Sb substituted Ga mainly in the octahedral lattice. The carrier concentration of the Sb-doped single crystals increased from 9.55×1016 to 8.10×1018 cm-3, the electronic mobility depicted a decreasing trend from 153.1 to 108.7 cm2 ·V-1 ·s-1, and the electrical resistivity varied from 0.603 to 0.017 Ω·cm with the increasing Sb doping concentration. The un-doped and Sb-doped β-Ga2O3 crystals exhibited good light transmittance in the visible region; however, the evident decrease in the infrared region was caused by increase in the carrier concentration. The Sb-doped β-Ga2O3 single crystals had high transmittance in the UV region as well, and the cutoff edge appeared at 258 nm.

Распределение кислорода в структуре тонких пленок YBa-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-7-delta-=/SUB=- после хранения в вакууме при 300 K

Abstract We have found out that vacuum exposure of YBa2Cu3O7‒δ thin epitaxial films at 300 K for 24 hours decreases oxygen content and induces changes in their crystal structure depending on the films synthesis conditions. YBa2Cu3O7‒δ films on SrTiO3 (100) substrates were synthesized by pulsed laser deposition. The crystal structure was studied using XRD technique. Additional maxima of diffraction peak (005) before and after vacuum exposure indicate the presence of regions with different oxygen content; and the change in the shape of the rocking curves indicate a change in the crystallites orientation. After vacuum exposure, the oxygen deficiency δ in the films increased from ~0.01 to 0.6 for films with a crystallites size of 2-10 nm and from ~0.25−0.35 to 0.6 for crystallites size of 500−1000 nm. The appearance of a residual resistance after the superconducting transition in the dependence R(T) may be explained by the fact that oxygen loss mainly in the boundary regions of the crystallites takes place, so that their boundaries become dielectric, while the crystallites themselves remain superconductive. Based on the data of X—ray diffraction analysis, as well as resistive measurements, we have come to the conclusion about oxygen loss through grain boundaries in films with nanocrystallites of 2-10 nm in size, and also through structural defects in films with larger crystallites.

Synthesis of thin single-crystalline α-Cr-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- layers on sapphire substrates by ultrasonic-assisted chemical vapor deposition

Single-crystalline α-Cr2O3 layers were synthesized on a sapphire substrate with a basal orientation in a laboratory reactor using ultrasonic-assisted chemical vapor deposition in the temperature range of 700-850oC. The influence of the growth temperature on the structural quality of the layer was studied by X-ray diffraction. At a growth temperature of 800oC, continuous layers with a thickness of about 1 μm were obtained. The layers were transparent in the visible region with a slightly greenish tint and showed some light transmission up to wavelengths of ~ 350 nm. The full width at half maximum of the rocking curve for reflection 0006 was ~ 300 arcsec. Keywords: chromium oxide, CVD epitaxy, wide-bandgap semiconductor.

Тонкие монокристаллические слои α-Cr-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-, выращенные на подложках сапфира в реакторе ультразвуковой паровой химической эпитаксии

Single-crystalline α-Cr2O3 layers were synthesized on a sapphire substrate with a basal orientation in a laboratory reactor using ultrasonic-assisted chemical vapor deposition in the temperature range of 700-850°C. The influence of the growth temperature on the structural quality of the layer was studied by X-ray diffraction. At a growth temperature of 800°C, continuous layers with a thickness of about 1 μm were obtained. The layers were transparent in the visible region with a slightly greenish tint and showed some light transmission up to wavelengths of ~350 nm. The full width at half maximum of the rocking curve for reflection 0006 was ~ 300 arcsec.

Improved optoelectronic performance from the internal secondary excitation of MAPbCl3-MAPbBr3 single crystal photodetectors

Single crystal (SC) MAPbBr 3 and MAPbCl 3 perovskite are considered promising materials for fabricating high-performance photodetectors (PDs) due to their impressive optoelectronic properties and good chemical stability. Structural modification of PDs is the fundamental solution to improve performance. In this paper, we designed a simple structure diagram considering photoelectric properties and the possibility of epitaxial crystal growth. Then a solution height restriction method (SHR) was used to grow the crystal and make the internal secondary excitation feasible. X-ray rocking curves (XRC) of MAPbBr 3 -SHR SCs show the quality of crystal under this growth method is excellent. X-ray photoelectron spectroscopy (XPS) measurements and Energy-dispersive X-ray spectroscopy (EDS) indicate element diffusion exists in the interface. Photoluminescence spectra (PL) and the photoelectric performance test have proved the existence and validity of the internal secondary excitation of crystals. Based on the above analysis, it was demonstrated that the inner MAPbCl 3 single-crystal enhances the optoelectronic performance of MAPbCl 3 -MAPbBr 3 crystals by the internal secondary excitation effect.

Growth of 2-inch diameter Mg<sub>2</sub>Si crystal by the VGF method under Ar normal pressure

A 2-inch diameter Mg2Si crystal was synthesized via the vertical gradient freeze (VGF) method in an open-tube system using pyrolytic boron nitride crucibles coated with boron nitride. Using this open-tube system, Mg evaporation was significantly prevented under Ar gas flow. Many grain boundaries were observed at the crystal cross section. A 5-mm square wafer without grain boundaries was cut out from the crystal and characterized by X-ray rocking curve (XRC) analysis, exhibiting a sharp single peak with a full width at half maximum (FWHM) of 50.4 arcsec. This indicates good crystallinity of the single crystalline area of the synthesized crystal.

Deposition of Ga2O3 thin films by liquid metal target sputtering

This paper reports on the deposition of amorphous and crystalline thin films of Ga2O3 by reactive pulsed direct current magnetron sputtering from a liquid gallium target onto fused (f-) quartz and c plane (c-) sapphire substrates, where the temperature of the substrate is varied from room temperature (RT) to 800 °C. The deposition rate (up to 37 nm/min at RT on f-quartz and 5 nm/min at 800 °C on c-sapphire) is two to five times higher than the data given in the literature for radio frequency sputtering. Deposited onto unheated substrates, the films are X-ray amorphous. Well-defined X-ray diffraction peaks of β-Ga2O3 start to appear at a substrate temperature of 500 °C. Films grown on c-sapphire at temperatures above 600 °C are epitaxial. However, the high rocking curve full width at half maximum values of ≈2.4–2.5° are indicative of the presence of defects. A dense and void-free microstructure is observed in electron microscopy images. Composition analysis show stoichiometry close to Ga2O3 and no traces of impurities. The optical properties of low absorptance (<1%) in the visible range and an optical band gap of approximately 5 eV are consistent with the data in the literature for Ga2O3 films produced by other deposition methods.

Growth of rare-earth monopnictide DySb single crystal by novel self-flux method

A new method for the single crystal growth of rare-earth monopnictide DySb by self-flux technique is reported. Detailed structural, transport and magnetic characterisation of the crystal has been carried out by using X-ray diffraction (XRD), High resolution X-ray diffraction (HRXRD), resistivity and magnetisation measurements, respectively. The Rietveld refinement of powder XRD pattern reveals that the grown crystal is in single phase and crystallises in space group Fm3̄m (225) of rock- salt type crystal structure. The HRXRD and rocking curve analysis reveals the high-quality of the grown crystal. Temperature dependent resistivity and magnetisation measurements show a transition at 9.7 K from paramagnetic to antiferromagnetic state.

Heterogeneous integration of lithium tantalate thin film on quartz for high performance surface acoustic wave resonator

Surface acoustic wave (SAW) resonator based on the piezo film on a foreign substrate is promising to enhance the performance of radio frequency filters. In this work, the 4 inch wafer-scale lithium tantalate thin film on quartz (LTOQ) heterogenous substrate was fabricated by ion-cut process. The cut angle of quartz was optimized to achieve high-quality factor (Q) based on finite element analysis. The average film thickness and the film nonuniformity for the whole wafer are 602 nm and ±2.2%, respectively. The lithium tantalate film exhibits single-crystalline quality where the full width at half-maximum of high-resolution X-ray diffraction rocking curve is 47.4 arcsec. The shear horizonal surface acoustic wave resonator based on the LTOQ structure exhibits a maximum Bode-Q exceeding 3000 and the electromechanical coupling coefficient of 10.26%. The temperature coefficient of frequency at resonant frequency and anti-resonant frequency are −25.21 ppm °C−1 and −35.22 ppm °C−1, respectively.