Grazing Incidence X-ray Diffraction Investigations Research Articles

Grazing-incidence X-ray diffraction investigation of the coincidence site lattice of the Ge/Si(001) system.

The Ge/Si(001) system has been analysed by grazing-incidence X-ray diffraction on a standard laboratory X-ray diffraction tool. A periodic array of interfacial edge dislocations forms a coincidence site lattice (CSL) which yields equidistantly spaced satellite peaks close to Bragg peaks of the Ge layer and Si substrate. The diffraction behaviour of the CSL was analysed using 2θ/φ scans along [100], [110] and [310] directions as well as azimuthal φ scans which revealed a 90° angular symmetry of the CSL. Additionally, different layer thicknesses, from 10 to 580 nm, were analysed, focusing on the dependence of layer thickness on the glancing angles of the satellite peaks. This method provides the ability to analyse whether or not epitaxially grown layers exhibit a periodic array of dislocations, and gain information about the orientation of the interfacial edge dislocations.

Surface morphology effects on Li ion diffusion toward CeO 2 :Cu nanostructured thin films incorporated in PEG matrix

Undoped and Cu-doped CeO2 (2.5, 5, 7.5 mol%) thin films were prepared by modified Pechini process. Grazing incidence X-ray diffraction investigations of the films revealed that the ceria thin film has a cubic structure and Cu doping inhibited the crystal growth. The presence of predominant of Ce4+ oxidation state (CeO2) and Cu2+ in the films was approved by X-ray photoelectron spectroscopy. The fourier transform infrared spectra confirmed the metal-oxygen (Ce–O) bonding. Scanning electron microscopy images of the films displayed a crack free surface and the nano-grains regularly distributed on the surface. Atomic force microscopy analyses indicated that roughness parameters changed by Cu incorporation and 5 mol% Cu-doped CeO2 is the smoothest surface. Fractal dimensions of surface were calculated by box counting and triangulation method. The fractal dimension increased by Cu doping up to 5 mol% and then reduced. The optical transmittance was enhanced and the absorption edge was shifted to lower wavelength by Cu doping. The refractive indices and extinction coefficients which were determined using theoretical approach were decreased by Cu doping. Photoluminescence emission intensity of CeO2 thin film was quenched by Cu doping. The electrochemical behavior of the films was examined in 1 M LiClO4/propylene carbonate electrolyte. The total charge density of ceria thin film increased by Cu doping and 5 mol% Cu-doped CeO2 film had the highest ion storage capacitance. The fractal analyses showed that the surface morphology affected the Li ion diffusion behavior of CeO2:Cu thin films.

Titanium implants’ surface functionalization by pulsed laser deposition of TiN, ZrC and ZrN hard films

Thin films of TiN, ZrC, and ZrN were deposited at room temperature on highly polished Ti and Si samples using the pulsed laser deposition technique. Grazing incidence X-ray diffraction investigations showed that films were nanocrystalline, with grain sizes from 5 to 12nm and under compression. Simulations of X-ray reflectivity curves acquired from the samples indicated that the deposited layers were dense and smooth. Electrochemical tests performed in simulated body fluid showed that the deposited coatings significantly improved the corrosion resistance of Ti samples. The comparative study found out that the best sample was ZrN/Ti, its corrosion current after 32 days immersion in simulated body fluids being half of that measured for the bare Ti sample and in the same time almost unchanged from the initial value.

Characteristics of LaB6 thin films grown by pulsed laser deposition

LaB6 thin films were deposited at a temperature of 500 °C under vacuum or Ar atmosphere by the pulsed laser deposition technique on (100) Si substrates using a KrF laser. Grazing incidence x-ray diffraction investigations found that films were nanocrystalline, with grain size dimensions from 86 to 102 nm and exhibited microstrain values around 1.1%. Simulations of the x-ray reflectivity curves acquired from the deposited films showed that films had a density around 4.55 g/cm3, and were very smooth, with a surface roughness root-mean-square of 1.5 nm, which was also confirmed by scanning electron and atomic force microscopy measurements. All films were covered by a ∼2 nm thick contamination layer that formed when samples were exposed to the ambient. Auger electron spectroscopy investigations found very low oxygen impurity levels below 1.5 at. % once the contamination surface layer was removed by Ar ion sputtering. Four point probe measurements showed that films were conductive, with a resistivity value around 200 μΩ cm for those deposited under Ar atmosphere and slightly higher for those deposited under vacuum. Nanoindentation and scratch investigations showed that films were rather hard, H ∼ 16 GPa, E ∼ 165 GPa, and adherent to the substrate. Thermionic emission measurements indicated a work function value of 2.66 eV, very similar to other reported values for LaB6.

Gamma irradiation effects on the properties of indium zinc oxide thin films

Thin films of amorphous and polycrystalline indium zinc oxide (IZO) having various In/(In+Zn) nominal compositions from 0.3 to 0.9 were grown by the pulsed laser deposition technique at room temperature or at 400°C on oxidized Si and quartz substrates. After deposition, the films were gamma irradiated at doses of 10, 20 and 30kGy under Ar atmosphere. Grazing incidence X-ray diffraction investigations could not find measurable changes of the structure after irradiation. Simulations of the X-ray reflectivity (XRR) and diffuse scattering curves acquired from the films showed a small density decrease after irradiation, accompanied by an increase of the thickness and surface roughness. Spectroscopic ellipsometry investigations confirmed the increase of the IZO films' thickness after irradiation, being in agreement with the XRR results. Small changes in the refractive index, most probably caused by changes in the film density were also observed. Four point probe measurements showed very small resistivity increases after irradiation, with the films containing higher In concentration presenting negligible changes.

Performance Improvement of CH3NH3PbI3 Perovskite Solar Cell by CH3SH Doping

Organometal halide perovskites have recently emerged as an appealing candidate in photovoltaic devices due to their excellent properties. Therefore, intense efforts have been devoted to find the ideal organics for perovskite solar cells. In response, we investigate the doping effect of CH3SH organic on the structure and related performance of a CH3NH3PbI3 perovskite solar cell, via in situ synchrotron-based grazing incidence X-ray diffraction (GIXRD), together with scanning electron microscopy (SEM). In situ GIXRD investigations clearly illustrated the transformation and modification of the perovskite structure induced by the organic dopant, which subsequently led to the enhancement of the power conversion efficiency of fabricated solar cells. Notably, nanoporous morphology and nanocrystalline structures were discovered in the perovskite film by SEM; they were also confirmed by the increase in broadening peaks/features in the GIXRD measurements. Overall, our study may ultimately result in an attractive st...

Pulsed laser deposition of nanocrystalline SiC films

Abstract Thin SiC films were grown on (1 0 0) Si substrates at temperatures from 400 to 1000 °C under various CH 4 pressures by the pulsed laser deposition (PLD) technique using a KrF excimer laser. After deposition, films were in situ annealed at their deposition temperature under 500 mbar of CH 4 for 1.0–1.5 h. X-ray reflectivity investigations showed that films exhibited mass densities similar to SiC single crystal samples, while symmetrical and grazing incidence X-ray diffraction investigations found that films deposited at 800 °C or higher substrate temperatures were nanocrystalline. Modeling of spectroscopic ellipsometry measurements indicated that the refractive index values were similar to those reported for bulk SiC, while X-ray photoelectron spectroscopy investigations found that films contained in bulk a relatively low oxygen concentration of around 1.0 at.%. Nanoindentation results showed that the deposited SiC films were very hard, with hardness values above 40 GPa for films deposited at temperatures higher than 800 °C.

Grazing Incidence X-ray Diffraction investigation of strains in silicon nanowires obtained by gold catalytic growth

In this paper, we measure experimentally the strains in silicon nanowires using Grazing Incidence X-ray Diffraction. Silicon nanowires have been grown with a gold-catalytic method and have a crystalline character. Bragg's diffraction peak is measured and analyzed. A lattice mismatch parameter between the silicon substrate and silicon nanowires is found and accurately measured. The influence of the presence of the gold catalyst in the wires is investigated, and reveals a small decrease of the lattice mismatch parameter when the gold catalyst is removed. A residual strain is measured and a possible origin is proposed. An estimation of the surface and bulk stress is calculated and presented.

Microstructural Investigations of Hafnium Aluminum Oxide Films

ABSTRACTThe crystalline structure, composition, chemical bonding and thermal stability of HfO2-Al2O3 mixtures deposited on Si using a combinatorial pulsed laser deposition technique were investigated. After deposition some films were annealed at temperatures from 850 to 950 °C for 6 or 12 minutes. Grazing incidence x-ray diffraction investigations were performed to asses the crystallinity and thermal stability of the annealed layers. Measurements of the Al to Hf ratios were performed using energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy. From simulations of the x-ray reflectivity and spectroscopic ellipsometry spectra the phase composition and thickness of the films was calculated and then the Al to Hf ratios. Al/Hf values of 1 and 8 were found to be necessary to block the crystallization of the films after anneals at 850 and 950 °C, respectively.

Deviation from the virtual crystal approximation in disordered Au–Cu alloy nanocrystals: EXAFS and GIXRD investigation

The short-range order and the crystalline structure of AuCu and AuAg alloy nanoclusters obtained by sequential ion implantation in silica are investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy and by grazing incidence X-ray diffraction (GIXRD). While in the case of AuAg alloy the nearest neighbor interatomic distances correspond to the lattice parameter, in the case of chemically disordered solid solution AuCu alloy a significant deviation from the virtual crystal approximation is observed: the Au–Au, Cu–Cu and Au–Cu nearest neighbor distances are different, only their average corresponding to the fcc lattice parameter. This result, mainly related to the different atomic radius of the two alloy components, is for the first time reported for nanostructured systems.

X-ray diffraction and foam film investigations of PC head group interaction in water/ethanol mixtures

The influence of ethanol on single phospholipid monolayers at the water/air interface and in foam films has been investigated. Grazing incidence X-ray diffraction investigations (GIXD) of Langmuir monolayers from 1,2-distearoyl-phosphatidylcholine (DSPC) spread on water subphases with different amounts of ethanol were performed. The thickness and free specific energy of formation of foam films stabilized by 1,2-dimyristoyl-phosphatidylcholine (DMPC) at different concentrations of ethanol in the film forming dispersions were measured. The GIXD investigations show that the tilt angle of the alkyl chains in the PC lipid monolayer decreases with increasing concentration of ethanol caused by a decrease of the diameter of the head groups. With increasing ethanol content of the solution also the thickness of the aqueous core of PC lipid foam films decreases. We assume that ethanol causes a decreasing probability for the formation of hydrogen bonds of water molecules to the PC head groups. The distinct difference between the effects of ethanol on lipid bilayers as described in the literature and on monolayers and foam films found in this study is discussed. Whereas PC monolayers at the water/air interface become unstable above 25 vol.% ethanol, the PC foam films are stable up to 50 vol.% ethanol. This is related to the decrease of the surface excess energy per lipid molecule by the interaction between the two film surfaces.

Stress effects induced in SiGe strained layers by low-temperature ultraviolet-assisted oxidation

Low-temperature (550 °C) ultraviolet-assisted oxidation of epitaxially grown Si0.8Ge0.2 strained layers on (100) Si substrates leads to the formation of nanocrystalline Ge (nc-Ge) particles embedded in a SiO2 layer which exhibit visible photoluminescence with an emission maximum situated at around 2.18 eV. Grazing incidence x-ray diffraction investigations of the remaining SiGe layer which was continually rejected by the advancing oxide layer have shown the presence of the (311) diffraction peak. This implies that the unoxidized SiGe layer has been fractured in many regions misoriented with respect to the initial layer. The displacement of the SiGe (311) peak position recorded for samples which had their grown oxide layer stripped away when compared with as-grown samples indicates the presence of a significant stress in these low-temperature grown oxide layers. This stress is believed to explain both the survival of the nc-Ge particles during prolonged oxidation and the fracturing of the buried SiGe layer.