High-resolution X-ray Diffraction Methods Research Articles

Synthesis of Carbon Nanotube-CuxO(x=8, 64) Nanocrystal Composites

A simple, rapid and eco-friendly method has been introduced to prepare suboxide Cu(x)O(x = 8, 64) nanocrystals on multiwall carbon nanotube (MWCNT) composites. The structural characterization by using high-resolution transmission electron microscopy and X-ray diffraction methods indicates that Cu(x)O(x = 8, 64) can be uniformly grown on the sidewalls of carbon nanotube under direct copper deposition at room temperature. Our results suggest that the growth method of nano-Cu(x)O (x = 8, 64) crystals could be used to synthesize other nano-metal suboxides, such as M(x)O [M=metal; x = 1, 2, 4, 8 and 64]

Enhancement of SHG efficiency by urea doping in ZTS single crystals and its correlation with crystalline perfection as revealed by Kurtz powder and high-resolution X-ray diffraction methods

The enhancement of second-harmonic generation (SHG) efficiency by urea doping in tristhioureazinc(II) sulfate (ZTS) single crystals and its correlation with crystalline perfection have been investigated. ZTS is a potential semiorganic nonlinear optical material. Pure and urea-doped single crystals of ZTS have been successfully grown by the slow evaporation solution technique. The presence of dopant has been confirmed and analysed by Fourier transform infrared spectrometry. The influence of urea doping at different concentrations on crystalline perfection has been thoroughly assessed by high-resolution X-ray diffractometry (HRXRD). HRXRD studies revealed that the ZTS crystals could accommodate urea up to a critical concentration without any deterioration in crystalline perfection. Above this concentration, very low angle structural grain boundaries developed and it seems the excess urea above the critical concentration was segregated along the grain boundaries. At very high doping concentrations, the crystals were found to contain mosaic blocks. The SHG efficiency has been studied using the Kurtz powder technique. The relative SHG efficiency of the crystals was found to increase substantially with the increase in urea concentration. The correlation found between crystalline perfection and SHG efficiency is discussed.

Effect of Reinforcement Volume Fraction on the Mechanical Properties of Al—SiC Nanocomposites Produced by Mechanical Alloying and Consolidation

Al—(1, 3, 5, 7, 10 vol%) SiC nanocomposites were produced by mechanical alloying (MA) and double pressing/sintering route. The characteristics of the milled powders and the consolidate specimens were examined using high resolution scanning electron microscopy and X-ray diffraction method. Compression and hardness tests were used to study the effect of SiC volume fraction on the strength of Al—SiC nanocomposites. It was shown that with increasing the SiC volume fraction, finer particles with narrower size distribution and smaller crystallite size are obtained after MA. During sintering close to the melting point of aluminum, the presence of nanometer-scaled SiC particles was found to hinder the grain growth significantly. The Al matrix with a higher SiC content exhibited more potential for grain boundary pinning, i.e., smaller grain size was obtained at higher SiC volume fractions. Consequently, an improved mechanical strength was obtained. The processing method (MA/pressing/sintering) can be used for fabrication of near-net shape Al matrix nanocomposites.

Aging of MEMS – Correlation of Mechanical and Structural Properties

Related to the dramatically smaller volume of microelectromecanical systems (MEMS), new methods in testing and qualification are needed. In single crystal silicon (SCSi) based devices, stress and loading in operation introduces defects during the MEMS life time and increases the risk of failure. Reliability studies on potential failure sources have an impact on MEMS design and are essential to assure the long term functioning of the device. In this paper, a comprehensive approach is proposed for assessing the resistance of SCSi structures under conditions of accelerated aging. Defects introduced by DRIE, thermal annealing, dicing and bonding and also the device environment (radiations, temperature) influence the crystalline perfection and have a direct impact on the mechanical properties of MEMS and their aging behavior. Defects and deformations are analyzed using High Resolution X-ray Diffraction Methods (HRXRD) and supporting simulations are done by Finite Element Method (FEM). MEMS reliability is assessed. Preliminary results indicate a decrease in lifetime and strength of SCSi devices with defect density enhanced by irradiation.

Defects in Czochralski-grown Si–Ge annealed under high hydrostatic pressure

Defect structure of Czochralski-grown oxygen-containing silicon–germanium (Si–Ge) samples with Ge content 1.5×10 18 cm −3, subjected to processing for 5 h at up to 1400 K under hydrostatic Ar pressure up to 1.1 GPa, has been investigated by synchrotron topography (at HASYLAB), high-resolution X-ray diffraction, photoluminescence and related methods. Ge admixture prevents formation of extended defects at processing done under 10 5 Pa. Such defects are created, however, in Si–Ge processed at 1400 K under high pressure (1.1 GPa).

Layered Structure and Swelling Behavior of a Multiple Hydrate-Forming Pharmaceutical Compound

Investigation of one anhydrous and four hydrated forms of a pharmaceutical compound (1) using both single-crystal and high-resolution powder X-ray diffraction methods revealed a two-dimensional framework which, upon exposure to moisture, absorbed water between the layers, causing the lattice to expand by as much as 20% of the axial length along a. The single-crystal structure was solved and refined for the pentahydrate form in space group C2 with unit cell parameters a = 36.961(5) Å, b = 7.458(2) Å, c = 20.691(4) Å, β = 99.461(1)°, and V = 5626(4) Å3. In the single-crystal structure the water layers were parallel to the bc plane and sandwiched by the crystalline compound 1 framework. Upon a change of relative humidity, water goes in and out of the interlayer space with the retention of the layer structure of the development compound. Starting from the anhydrous form, each additional water of hydration increased the interlayer spacing of the pharmaceutical solid by ∼1.3 Å, half the size of a water molecule. In an exploratory formulation, this expansion of interlayer spacing caused tablets to crack upon storage at high relative humidity.

Defect reduction of laterally regrown GaN on GaN/patterned sapphire substrates

Structural properties of GaN epilayers on wet-etched protruding and recess-patterned sapphire substrates (PSSs) have been investigated in detail using high-resolution double-crystal X-ray diffraction (DCXRD) and etch-pit density methods. The DCXRD results reveal various dislocation configurations on both types of PSSs. The etch pits of GaN on the recess PSS exhibit a regular distribution, i.e. less etch pits or threading dislocation density (TDD) onto the recess area than those onto the sapphire mesas. On the contrary, an irregular distribution is observed for the etch pits of GaN on the protruding PSS. A higher crystal quality of the GaN epilayer grown onto the recess PSS can be achieved as compared with that onto the protruding PSS. These data reflect that the GaN epilayer on the recess PSS could be a better template for the second epitaxial lateral overgrowth (ELOG) of GaN. As a result, the GaN epilayers after the ELOG process display the TDDs of around ∼10 6 cm −2.

Reliability and failure in single crystal silicon MEMS devices

In single crystal silicon (SCSi) MST devices, crystalline imperfection is recognized to favor failure. Defects are introduced by DRIE etching which is commonly used in SCSi structuring. However, thermal annealing improves the crystal quality. High resolution X-ray diffraction methods such as the rocking curve method and reciprocal space mapping can monitor crystalline imperfection in SCSi devices. A DRIE etched SCSi structure was built to study the crystal strain profile in dependence of the SCSi deformation by applying a mechanical force. Our investigations also include the numerical simulation of deformations.

Effect of CdTe monolayer insertion on CdZnTe/ZnTe quantum well characteristics

The effect of CdTe monolayer (ML) insertion on the structural and luminescence characteristics of ZnCdTe/ZnTe quantum well (QW) was investigated by a high-resolution X-ray diffraction (HRXRD) and photoluminescence (PL) methods. The structures were grown by MBE on just-oriented or 3° off (001) GaAs substrate and contained Zn0.6Cd0.4Te QW with or without CdTe 1ML insertion embedded in the middle of QW. HRXRD(004) diffraction profiles and reciprocal space maps in the vicinity of the (004) reflection were measured. CdTe insertion led to the shift of QW-related peak to larger angels as well as to significant broadening and disappearance of fringes. The low-temperature PL investigations showed that CdTe insertion resulted in a “blue” shift of the QW PL peak position, in the two times narrowing of the QW PL band and one order of value increase of its intensity.

A new type of structural defects in CdZnSe/ZnSe heterostructures

The changes of structural and photoluminescence (PL) characteristics of MBE-grown CdZnSe/ZnSe single quantum well (QW) structures caused by Cd/Zn interdiffusion were studied by high-resolution X-ray diffraction (HRXRD) and low-temperature PL methods. The PL investigations showed that the increase of Cd content in the QW resulted in the increase of the depth of potential fluctuations in the QW as well as in the decrease of ZnSe cap layer band gap (up to several meV). The HRXRD scans as well as reciprocal space maps measured for symmetrical and asymmetrical diffractions revealed the formation of CdZnSe layers near the QW/ZnSe interface with Cd content of order of several percents. It is found that in some samples, the Cd profile in these layers is rather smooth while in others it is quite abrupt. In the latter case, the partial strain relaxation can occur in these layers.

GaN epilayers on nanopatterned GaN/Si(1 1 1) templates: Structural and optical characterization

Template-based nanoscale epitaxy has been explored to realize high-quality GaN on Si(1 1 1) substrates. We have employed polystyrene-based nanosphere lithography to form the nano-hole array patterns on GaN/Si(1 1 1) template and then, subsequent regrowth of GaN is carried out by metalorganic chemical vapor deposition (MOCVD). During the initial growth stage of GaN on such nanopatterned substrates, we have observed formation of nanoislands with hexagonal pyramid shape due to selective area epitaxy. With further epitaxial regrowth, these nanoislands coalesce and form continuous GaN film. The overgrown GaN on patterned and non-patterned regions is characterized by high-resolution X-ray diffraction (HRXRD) and high-spatial resolution optical spectroscopic methods. Micro-photoluminescence (PL), micro-Raman scattering and scanning electron microscopy (SEM) have been used to assess the microstructural and optical properties of GaN. Combined PL and Raman data analyses show improved optical quality when compared to GaN simultaneously grown on non-patterned bulk Si(1 1 1). Such thicker GaN templates would be useful to achieve III-nitride-based opto- and electronic devices integrated on Si substrates.

Structure and Electrochemical Properties of FeS<sub>x</sub> Nanoparticles Synthesized by Chemical Vapor Condensation Process

FeSx nanoparticles were synthesized by the chemical vapor condensation (CVC) process using the pyrolysis of iron pentacarbonyl (Fe(CO)5) and sulfur (S). The influence of CVC parameter on the formation of nanoparticle and size distribution was studied. The synthesized nanoparticles consisting of FeS, FeS2 and Fe2O3 were nearly spherical shape and 5~40 nm in mean diameter. Obtained particles were studied by applying the field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) methods. Electrochemical properties of the electrode fabricated with synthesized nanoparticles were evaluated.

Effect of growth temperature on the luminescent and structural properties of InGaAsSbN/GaAs quantum wells for 1.3 μm telecom application

Variations of the characteristics of Sb-surfactant assisted grown InGaAsN/GaAs single quantum wells (QWs) in dependence on QW growth temperature ( T GR = 442–505 °C) are investigated by the photoluminescence (PL) and high-resolution X-ray diffraction (HRXRD) methods. The QWs grown at ∼480 °C demonstrated optimal PL characteristics, namely the highest PL intensity and small potential fluctuations. A good quality of heterointerfaces is proved by HRXRD. These structures emit at ∼1.29 μm at 300 K and are promising for application in long wavelength opto-electronic devices. The good structural properties of these QWs are assigned to Sb surfactant effect that allows shifting of the T GR to higher temperatures without significant alloy decomposition. The increase of T GR in its turn results in the decrease of the density of nonradiative defects that are the specific feature of low temperature growth.

Revealing the structural disturbances in Czochralski silicon by high temperature–pressure treatment

High-resolution X-ray diffraction and topographic methods were used to characterize the structural defects in single crystalline Czochralski-grown silicon (Cz-Si) with various oxygen concentrations. Annealing under hydrostatic pressure (HP) was applied for revealing the defects existing in Cz-Si wafers. The high pressure–high temperature treatment of as-grown Cz-Si at 1127 °C under 1.1 GPa resulted in enhanced oxygen precipitation, mostly at the initially existing structural disturbances, while annealing under 10 7 Pa did not affect the defect structure in the sample. The visibility of defects after the treatment under high pressure can be related to HP-induced strain at the boundary between the defect and the Si matrix, to increased defect dimensions due to HP-stimulated oxygen precipitation and to decreased concentration of defects. Precipitation of oxygen on small structural inhomogeneities and agglomeration of small defects assist in revealing the structural disturbances pre-existing in Cz-Si.

Study of strain relaxation in CdSe/ZnSe nanostructures

Strain relaxation in CdSe/ZnSe self-assembled quantum dot (QD) and CdZnSe/ZnSe quantum well (QW) structures have been investigated by the photoluminescence (PL) and high-resolution X-ray diffraction methods. The PL spectra of the QW structures revealed that splitting of free exciton line in ZnSe cap layer is influenced significantly by Cd content in QWs that allows to obtain information about strain in quantum-confinement structures. It is shown that information about strain relaxation mechanism and interdiffusion processes can be obtained from the analysis of the PL spectra of free and bound excitons. It is found that strain relaxation in the QD structures occurs mainly via QD formation in spite of generation of extended defects. Significant doping of ZnSe cap layer with Cd is found both in the QW and QD structures. The data obtained from the simulations of X-ray diffraction profiles qualitatively proved the results obtained from the analysis of ZnSe excitonic spectra. The reasons of quantitative discrepancy are discussed.

Ordering structure along the [formula omitted] direction of InAlAs

We have found a new type ordering structure in materials containing Indium. Generally conventional natural superlattice (NSL) stacks toward to { 1 1 1 } . However, the periodical structure in question stacks along the [ 0 0 1 ] direction, sometimes parallel to the substrate. We have studied the structure in detail as seen in InAlAs-bulk layers on a vicinal ( 0 0 1 ) InP substrate. We investigated the structure using a transmission electron microscope and a high-resolution X-ray diffraction method, and confirmed the structure stacks along [ 0 0 1 ] direction with a pitch three times that of the InP lattice constant. We found a similar structure in InAlGaP-bulk layers on a ( 1 0 0 ) GaAs substrate 10 ∘ tilted toward the 〈 0 1 1 〉 direction. The mechanisms have not been clarified yet, however, we consider that atomic steps on the epitaxial surface could be related.

Valence and structural transitions in the mixed Ru–Ir perovskites Ba2PrRu1−xIrxO6

The valence state of Pr in the B-site ordered double perovskites Ba2PrRu1−xIrxO6 is shown to be sensitive to both the precise Ru:Ir content and temperature. Pr LIII XANES measurements show that at room temperature the Pr is trivalent in the Ru-rich compounds with x<0.25. At higher Ir contents the Pr is tetravalent. High-resolution powder synchrotron X-ray and neutron diffraction methods have been used to study the composition and temperature dependence of the crystal structures of these oxides. The Ru and Ir are statistically distributed on one of the two available B-sites. The oxides undergo an apparently first-order monoclinic P21/n to tetragonal P4/mnc phase transition in response to the change on the Pr and Ru/Ir valence. High temperatures and Ru contents favor the lower symmetry monoclinic structure, that is arises from the presence of the larger PrIII cations. The variations in the observed metal–oxygen bond distances are consistent with a simultaneous change in the valence of the Ru/Ir accompanying the PrIII–PrIV valence transition.

Effect of structural imperfections on luminescence of ZnCdSe/ZnSe quantum wells

The structural and luminescence properties of Zn1−xCdxSe/ZnSe multi-quantum well (MQW) structures with high molar fraction of cadmium (30–50%) and wide ZnSe barriers (50, 100 and 500nm) grown by molecular beam epitaxy (MBE) have been investigated by high-resolution X-ray diffraction (HRXRD) and photoluminescence (PL) methods. It is shown that the fluctuations of composition within the quantum well layer determine the full-width at half maximum (FWHM) of the QW photoluminescence peak. The unusual polarization characteristics of this photoluminescence have been observed. The emission peak in the edge geometry is strongly polarized perpendicularly to the QW plane. This effect is ascribed to the localization of the ground-state heavy-hole-like excitons in the regions with increased cadmium content.

Investigation of intrinsic defects and their distribution in CdSe/ZnSe quantum dot structures

The intrinsic defects and their distribution in CdSe/ZnSe self-assembled quantum dot heterostructures grown under variation of VI/II group beam pressure ratio are investigated by luminescent and high-resolution X-ray diffraction methods. In all samples the self-activated emission connected with donor-acceptor pairs V Zn–D is found. Analysis of excitation spectra of this band shows that vacancy related defects are mainly localised in ZnCdSe wetting layer. It is found that increase of Se beam pressure results in: (i) the increase of the number of metal vacancy related defects and their appearance on nanoisland interface; (ii) enhancement of Cd/Zn interdiffusion process; (iii) the decrease of Cd content in nanoislands and suppression of nanoisland formation. It is proposed that observed transformation of nanoisland emission band is mainly caused by enhancement of interdiffusion process.

Structure and composition of gallium nitride films produced by processing gallium arsenide single crystals in atomic nitrogen

Thin GaN films are grown on (001) single-crystal GaAs substrates processed in an atmosphere of active nitrogen radicals. Auger electron spectroscopy is applied to take the depth profiles of the basic chemical elements that enter into the composition of the epitaxial GaN films and single-crystal GaAs substrates. It is found that the surface composition of the GaN films is characterized by considerable nonstoichiometry (the excess nitrogen achieves ≈9%), which is caused by the presence of atomic nitrogen in the discharge chamber. With a high-resolution X-ray diffraction method, the structural perfection of the epitaxial layers is investigated. It is shown that low-temperature annealing (at temperatures below 700°C) is responsible for the formation of cubic GaN films on the (001) surface of cubic GaAs, whereas higher temperature annealing results in the growth of the hexagonal films.