Typical Diffraction Pattern Research Articles

Fabrication of aluminum nitride heterostructures on Si (1 1 1) substrate by plasma-assisted MBE

The aluminum nitride (AlN) heterostructures were successfully grown on silicon substrate by plasma-assisted molecular beam epitaxy. The surface morphology and structural and optical properties of the sample have been investigated by reflection high electron diffraction, scanning electron microscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray, high-resolution X-ray diffraction (HR-XRD), Raman spectroscopy, and photoluminescence, respectively. HR-XRD measurement showed that the sample has a typical diffraction pattern of hexagonal AlN/GaN/AlN heterostructures. The Schottky characteristic of Pt contact on AlN/GaN/AlN heterostructures was also investigated under different annealing temperatures in nitrogen ambient. The temperature dependence and structural evolution of the Schottky barrier height (SBH) of Pt contacts were studied using the current–voltage measurement and FESEM, respectively. Our findings presented that the SBH of the samples change with different annealing temperatures.

AlN/GaN/AlN heterostructures grown on Si substrate by plasma-assisted MBE for MSM UV photodetector applications

The AlN/GaN/AlN heterostructures were successfully grown on silicon substrate by plasma-assisted molecular beam epitaxy (MBE). High purity gallium (7N) and aluminum (6N5) were used to grow GaN and AlN, respectively. The structural and optical properties of the samples have been investigated by high-resolution X-ray diffraction (HR-XRD), photoluminescence (PL), Raman spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED), dark field scanning transmission electron microscopy (DF STEM), and high-angle annular dark field scanning transmission electron microscopy (HAADF STEM). HR-XRD measurement showed that the sample has a typical diffraction pattern of hexagonal AlN/GaN/AlN heterostructures. Raman spectra revealed all four Raman-active modes, i.e., GaN-like E2 (H), AlN-like A1 (TO), AlN-like E2 (H), and AlN-like A1 (LO) inside the AlN/GaN/AlN heterostructures. Good thickness uniformity of the layers and high-quality hetero-structures without cracking were confirmed by TEM, SAED, DF STEM and HAADF STEM. The fabricated AlN/GaN/AlN heterostructures based metal-semiconductor-metal (MSM) for the UV photodetector shows a rise and fall of photoresponses, suggesting that the AlN/GaN/AlN heterostructures have good carrier transport and crystallinity properties.

Structural investigation of SnO2 catalytic nanoparticles doped with F and Sb

Structural and morphological properties of pure and F‐doped or Sb‐doped particles of tin oxide were studied by X‐ray diffraction and transmission electron microscopy (TEM). A typical polycrystalline diffraction pattern corresponding to the tetrahedral phase was obtained for all the particles independently of the doping. No peaks matching any antimony oxide phase were observed; thus, it is probable that Sb replaces Sn in the tin oxide lattice. Doping with antimony results in a lattice parameter increase of the SnO2/Sb phase, which might be related to the geometrical distortion of the lattice due to the replacement of Sn by Sb. Moreover, the SnO2/Sb sample exhibited a preferential orientation in the (110) and (101) planes. The TEM analysis showed that all the tin oxide particles are agglomerated and form aggregates and networks leading to a mesoporous structure with different pore sizes. The particles have a spherical shape and sizes between 5 and 20 nm in average. All particles were well crystallized with nicely visible lattice fringes in the high‐resolution HRTEM images. Copyright © 2014 John Wiley & Sons, Ltd.

Comparison of microporous/mesoporous and microporous HZSM-5 as catalysts for Friedel–Crafts alkylation of toluene with ethene

In this work we investigated the effect of mesopores in a standard zeolite used as a catalyst for Friedel–Crafts alkylation of toluene with ethene. A cationic polymer was used for templating mesopores in a microporous ZSM-5 framework. The mesopore-containing zeolite was compared with a regular zeolite with only micropores with respect to conversion, yield and selectivity. The two NaZSM-5 materials were prepared with the same Si/Al molar ratio and diffuse reflection infrared Fourier transform spectroscopy (DRIFT-FTIR) confirmed that the acidity of the ion-exchanged forms (HZSM-5) were identical. Scanning electron microscopy (SEM) and dynamic light scattering (DLS) were used to determine the particle size of the zeolites, which was similar for the two HZSM-5 materials and nitrogen sorption was used to determine the surface area and pore size distribution. X-ray diffraction (XRD) analysis displayed typical crystalline diffraction patterns for the ZSM-5 framework for both the microporous/mesoporous and the microporous ZSM-5 materials. The results from catalytic testing show an increase in the overall conversion of toluene for the zeolite that contains mesopores. Furthermore, a higher product yield (C9) is obtained for this catalyst. The increase in yield and conversion is most likely due to the mesopores; however, incorporation of mesopores in the microporous ZSM-5 framework gives only minor effects on selectivity with respect to mono- vs. dialkylation, and ortho:meta:para ratio. Consequently, this work shows that the presence of mesopores in a microporous ZSM-5 framework is beneficial for the reaction in terms of conversion of starting material and reaction yield but does not markedly affect the product composition.

Growth of GaN films on silicon (1 1 1) by thermal vapor deposition method: Optical functions and MSM UV photodetector applications

In this study, gallium nitride (GaN) films were grown on n-Si (111) substrate by thermal vapor deposition method in quartz tube furnace for different growth duration. Gallium metal mixed with GaN powder and aqueous ammonia (NH3) solutions were used as sources of Ga and N. Structural, elemental, and optical characterizations were carried out using various techniques in order to investigate the properties of the films. Scanning electron microscopy images showed that the films surface have self-textured morphology, which was introduced during the growth process. Moreover, further deposition resulted in the formation of heterogeneous film. X-ray diffraction (XRD) measurements reveal in all samples a typical diffraction pattern of hexagonal GaN wurtzite structure. Raman spectra demonstrated redshifts in E2-high with increasing deposition time due to tensile stress inside the GaN films, confirmed by XRD. The photoluminescence spectra of the films demonstrated strong near band edge emission at about 363nm. The fabricated GaN films based metal–semiconductor-metal (MSM) UV photodetector shows a contrast ratio of ∼240–40 at +5V and responsivity in the range of 0.28–0.01A/W for the UV photodetectors. This study shows the possibility of synthesizing GaN films on Si wafers at low-cost and has potential applications in UV photodetection.

Fabrication and electrical properties of La8.33Sb(SiO4)6O2 thick films for solid oxide fuel cells

In this study, Sb-substituted La8.33Sb(SiO4)6O2 apatite thick films were fabricated by using a screen printing method and the structural and electrical properties of these materials, with variation in sintering temperature for solid oxide fuel cells were investigated. With increased sintering temperatures, the second phase La2SiO5 phase decreased and the specimens sintered at over 1350 °C showed typical X-ray diffraction patterns of apatite polycrystalline structure. The grain size increased and porosity decreased, with increasing sintering temperatures. The thickness of all films was approximately 25–30 μm. La8.33Sb(SiO4)6O2 thick films, sintered at 1350 °C, showed good conductivity and activation energy characteristics at 9.87 × 10−5 S cm−1and 1.24 eV, respectively.

Physicochemical properties and in vitro digestion of starches from different Dioscorea plants

Physicochemical properties (paste clarity, water-binding capacity, swelling power, solubility and thermal properties) and in vitro digestion of starches isolated from ten different Dioscorea plants were investigated. Moisture content ranged from 7.52% to 15.75% and protein content varied between 0.010% and 0.028%. All of the starches gave a typical C-type X-ray diffraction pattern except D.BY (CA-type pattern) and Dioscorea persimilis (B-type pattern) starches. The relative crystallinity of them varied from 12.02% to 51.68%. The starches displayed significant variability in thermal transition temperatures and susceptibility to in vitro digestion, and varied in rapidly digestible starch (RDS), slowly digestible starch (SDS), resistant starch (RS) contents, hydrolysis index (HI) and glycemic index (GI). The ten Dioscorea starch samples can be classified into two major clusters by hierarchical cluster analysis: one cluster with more D.PP, D.BY and D.RC, and another cluster with D. XM, D.M-1, D.M-2, D.TG, D.H, D.CJ and D.J.

New ducting model for analyzing the Gaussian beam propagation in nonlinear Kerr media and its application to spatial self-phase modulations

Knowing the Gaussian beam parameters, such as its radius of curvature and spot size during propagation in nonlinear Kerr media, is of paramount importance in describing the observable far-field diffraction ring patterns as well as in design and stability analysis of Kerr-lens mode-locked resonators. Specifically, the sign of the beam radius of curvature after exiting these media has been proposed to be of assistance in recognizing their optical nonlinearity sign through determining the type of diffraction ring pattern in the far field. In order to be able to trace the evolution of the beam parameters in the Gaussian beam formalism, we have used the common aberration-free theory. We have shown that the nonlinear propagation problem of a fundamental Gaussian beam in a Kerr medium with an intensity-dependent index of refraction can be handled by assuming a ducting index profile along the propagation direction. Knowing the familiar ABCD matrix of a duct, the evolution of the mentioned beam parameters can be traced during propagation using the ABCD law in Gaussian beam theory. We have validated our ducting model by comparing its results with the outcomes of one widely used and accepted model which has been known to yield consistent results when electronic optical nonlinearity prevails. We have shown that when thermal optical nonlinearity is dominant, as in diffraction ring observation experiments, our ducting model yields sensible results and should be used. Our model predicts that when the sign of the thermal nonlinearity and the beam radius of curvature on the entrance plane of the medium are positive, the sign of the beam radius of curvature on the exit plane may have either sign, depending on the medium thickness used in the experiment. Hence, two types of diffraction ring pattern may be obtained using the same medium with two different thicknesses and this may cast doubt on the validity of the methods proposing the detection of the optical nonlinearity signs by observing these patterns. We have proposed a simple procedure for experimentally obtaining the two different types of diffraction pattern from the same medium.

Orientation and diffraction patterns of δ-Ni2Si precipitates in Cu–Ni–Si alloy

Morphology, orientation and diffraction patterns of δ-Ni2Si precipitates in a Cu–Ni–Si alloy are investigated by TEM and HREM. Many disk-shaped nanosized δ-Ni2Si precipitates are uniformly distributed in Cu–1.5wt%Ni–0.34wt%Si alloy in an over-aging condition. The δ-Ni2Si precipitates preserve an orthogonal structure with a=0.708±0.005nm, b=0.504±0.005nm, and c=0.364±0.005nm. The orientation relationships of six variants of δ-Ni2Si precipitates with Cu-matrix can be determined as (100)p||{001}Cu, [100]p||〈110〉Cu and [010]p||〈110〉Cu. Two typical diffraction pattern models under [001]Cu and [111]Cu zone axis are simulated according to diffraction effects of multiple variants, secondary diffraction and the size of particles, which coincide with the experimental results perfectly.

Effects of Different Drying Conditions on Water Absorption and Gelatinization Properties of Pasta

Three flat pasta types dried by low temperature (LT), high temperature (HT), and very high temperature (VHT) drying profiles were analyzed. The starch properties of these pastas, cooked at different temperatures for different times, were investigated. The starch properties were examined by observing starch swelling with a scanning electron microscope (SEM), identifying the phase difference with an ultrasonic device, and determining the water absorption and gelatinization rate with the BAP method and X-ray diffraction. The SEM images revealed expanded and gelatinized starch granules during cooking pasta and increased with drying temperature. The water absorption of pasta increased with cooking temperatures and times, and the trend was LT > HT > VHT-dried pasta. The gelatinization rate of pasta increased with cooking time and temperature. The X-ray diffractograms of pasta cooked less than 12 min showed typical A-type X-ray diffraction patterns, while in pasta cooked for 12 min, V-type diffraction was observed. Uncooked pasta showed an enhanced peak at about 2θ = 20°, which indicated the generation of high levels of amylose–lipid complexes. The present study found that these changes occurred during drying and may affect pasta starch characteristics.

Comparative study on the properties of ZnO nanowires and nanocrystalline thin films

The microstructural, morphological, optical and water-adsorption properties of nanocrystalline ZnO thin films and ZnO nanowires were studied and compared. The ZnO thin films were obtained by a sol–gel process, while the ZnO nanowires were electrochemically grown onto a ZnO sol–gel spin-coated seed layer. Thin films and nanowire samples were deposited onto crystalline quartz substrates covered by an Au electrode, able to be used in a quartz crystal microbalance. X-ray diffraction measurements reveal in both cases a typical diffraction pattern of ZnO wurtzite structure. Scanning electron microscopic images of nanowire samples show the presence of nanowires with hexagonal sections, with diameters ranging from 30 to 90nm. Optical characterization reveals a bandgap energy of 3.29eV for the nanowires and 3.35eV for the thin films. A quartz crystal microbalance placed in a vacuum chamber was used to quantify the amount and kinetics of water adsorption onto the samples. Nanowire samples, which have higher surface areas than the thin films, adsorb significantly more water.

Friedel–Crafts acylation of 2-methylindole with acetic anhydride using mesoporous HZSM-5

Mesoporous HZSM-5 was compared with microporous HZSM-5 as catalyst for Friedel–Crafts acylation of 2-methylindole with acetic anhydride. Nitrogen sorption (BET and BJH methods) was used to determine the surface area, pore size and porosity of the materials. The adsorption isotherms showed presence of pores in the size range 6–7nm for the mesoporous HZSM-5 and X-ray diffraction displayed a typical crystalline diffraction pattern corresponding to ZSM-5 for both the microporous and the mesoporous material. Dynamic light scattering was used to determine the particle size of the zeolites, which was shown to be approximately the same for the two materials. The mesoporous and the microporous ZSM-5 zeolites were prepared with the same Si/Al molar ratio and diffuse reflection infrared spectroscopy was used to confirm that the acidity of the materials was the same. Reaction over the microporous zeolite was regiospecific, giving acetylation only in the 3-position of 2-methylindole. Reaction over the mesoporous zeolite resulted in a mixture of two isomers, the N-acetylated product and the product with acetylation in 3-position, obtained in a 3:2 ratio. A kinetic model was constructed for the Friedel–Crafts acylation reaction, which correlated well with an Eley–Rideal reaction mechanism. The kinetic model allowed determination of rate constants, adsorption energy and activation energy for the reaction. It was found that the microporous HZSM-5 zeolite gave higher rate constants and lower activation energy compared to the mesoporous HZSM-5 zeolite. However, the mesoporous HZSM-5 zeolite gave lower adsorption energy and a considerably higher yield at the highest reaction temperature used, 89%, compared to 65% for the microporous HZSM-5 zeolite. Consequently, the catalytic material with the larger pore size gave a lower reaction rate but better resistance to poisoning and deactivation of the catalyst compared to its microporous counterpart.

Evaluation of Black Tea Polyphenol Extract Against the Retrogradation of Starches from Various Plant Sources

The effects of black tea polyphenol extract (BTPE) on the retrogradation of starches from different plant sources were studied using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). DSC analysis shows that the gelatinization temperature of maize starch and starches from different rice varieties increased with increasing BTPE level. After storage at 4 °C, BTPE at a concentration of 15% markedly retarded the retrogradation of maize starch and starches from different rice varieties. Native maize starch and starches from different rice varieties showed typical A-type X-ray diffraction patterns, while native potato starch showed a typical B-type X-ray diffraction pattern. Adding BTPE significantly affected the crystalline region and intensities of X-ray diffraction peaks of maize and rice starch granules. It is concluded that adding BTPE markedly inhibits the retrogradation of maize starch and starches from different rice varieties, but has no significant influence on the gelatinization and retrogradation characteristics of potato starch.

Formation of Amyloid-Like Fibrils by Y-Box Binding Protein 1 (YB-1) Is Mediated by Its Cold Shock Domain and Modulated by Disordered Terminal Domains

YB-1, a multifunctional DNA- and RNA-binding nucleocytoplasmic protein, is involved in the majority of DNA- and mRNA-dependent events in the cell. It consists of three structurally different domains: its central cold shock domain has the structure of a β-barrel, while the flanking domains are predicted to be intrinsically disordered. Recently, we showed that YB-1 is capable of forming elongated fibrils under high ionic strength conditions. Here we report that it is the cold shock domain that is responsible for formation of YB-1 fibrils, while the terminal domains differentially modulate this process depending on salt conditions. We demonstrate that YB-1 fibrils have amyloid-like features, including affinity for specific dyes and a typical X-ray diffraction pattern, and that in contrast to most of amyloids, they disassemble under nearly physiological conditions.

Chromatic Properties of Industrial Solid Waste Based Ferrites

The hexaferrite and monoferrite powders were prepared by the common solid state reaction method. Similar formulations have been prepared but using chemically-pure commercial reagents or by using a sludge generated by steel wiredraw process as source of iron oxide. This iron-rich industrial waste is mainly composed of Fe2O3 (62 wt%). Zinc and calcium are present in minor quantities and can form complexes such as franklinite (ZnFe2O4) and apatite (Ca5(PO4)3(OH,F,Cl)). Ni/Cr galvanising sludge was also used to enhance the black coloration of monoferrite. After calcination of the mixtures at 1,000 °C and 1,050 °C, typical X-ray diffraction patterns of the expected SrFe12O19 and NiFe2O4 phases were obtained, together with minor peaks of spinel-type (SrFe2O4 and ZnFe2O4) and Fe2O3 phases. Anyway, this resulted in a black pigment with chromatic properties comparable to those of commercial formulations, such as iron cobalt chromite (Fe,Co)(Fe,Cr)2O4 (DCMA 13-40-9), chrome iron nickel (Ni,Fe)(Fe,Cr)2O4 (DCMA 13-50-9), and manganese ferrite (Fe,Mn)(Fe,Mn)2O4 (DCMA 13-41-9).

Effect of native crystalline structure of isolated potato starch on gelatinization behavior and consequently on glycemic response

Effect of crystalline structure of two isolated potato starches on gelatinization and glycemic response was studied. Both starches showed to possess different fine structures. Starch 1 exhibited a typical B-type X-ray diffraction pattern, while Starch 2 exhibited an X-ray diffraction pattern suggesting the presence of imperfections of the general B-type crystalline structure (peak at 5.5° 2θ was absent), hence disarraying the structure order. This difference was reflected in the gelatinization behavior and consequently in the glycemic response. Starch 2 started to melt at lower temperature than Starch 1 (e.g. To was 60.9 and 61.84°C, respectively, to native starches), and residual gelatinization enthalpy (ΔH) of Starch 2 was always smaller than that of Starch 1 when heated at 54–65°C for 10min. Glycemic response was increased as gelatinization degree (DG) increased in starches independent from the native crystalline structure (area under curve=2.59×DG-75.83, R2=0.986; maximum concentration of postprandial blood glucose=0.042×DG-0.23, R2=0.935). Results suggested that native crystalline structure of isolated potato starch affects the glycemic response of heated starches by affecting the gelatinization behavior.

Surface structure, morphology, and growth mechanism of Fe3O4/ZnO thin films

We have investigated the growth mechanism and surface structure of magnetite (Fe3O4) films grown on semiconducting ZnO substrates. Growth proceeds in a wetting layer plus island-mode and a later coalescence of islands, as was verified by electron diffraction, topography measurements of the surface, and the investigation of the microstructure. The typical (111) surface diffraction pattern magnetite is observed already at the early island growth stage. Due to the island-like growth mode, domain boundaries form upon coalescence of the islands. Twin boundaries have been evidenced between neighboring domains. Island growth enables partial relaxation of the misfit strain.

Development and microstructural characterization of microwave cladding on austenitic stainless steel

In the present work microwave cladding was explored as a new processing method for enhancement of surface properties of austenitic stainless steel (SS-316). Cladding of nickel based powder (EWAC) was developed using microwave radiation as the heating source. This paper explains the possible mechanism of clad formation using microwave hybrid heating with the help of a schematic model. The developed clads were characterized using field emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectroscope (EDS), X-ray diffraction (XRD) and measurement of Vicker's microhardness. Typical X-ray diffraction (XRD) pattern of the clad showed the presence of chromium carbide, nickel silicide and nickel iron phases that eventually contribute to enhancement in microhardness of the clads. Clads of approximately 1 mm thickness were developed without any visible interfacial cracking and had significantly less porosity (1.09%). Microstructure of clad transverse section revealed good metallurgical bond with SS-316 substrate by partial mutual diffusion of constituent elements. The microstructure of the clad was found dominantly cellular in nature. Chromium was observed segregated around the cell boundaries while iron and nickel were identified inside the cells. Chromium carbides (Cr 23C 6, Cr 3C 2) were formed during the processing and appeared at the cell boundaries. Vicker's microhardness study revealed that the hardness profile varies within the clad zone and the average microhardness of the developed clad was observed to be 304 ± 48 H v.

Zinc‐oxide nanowires electrochemically grown onto sol–gel spin‐coated seed layers

AbstractThe electrochemical deposition of ZnO nanowires (NW) was optimized by growing onto a previously deposited seed layer. The ZnO seed layer was prepared by a sol–gel process from different precursor solutions and deposited onto FTO/glass by spin coating. Afterwards, NW were electrochemically grown onto those seed layers. The electrolyte was an aqueous solution of the Zn+2 precursor (1 mM zinc acetate) and a supporting electrolyte (0.1 M sodium acetate), saturated with bubbling oxygen. The films were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and optical transmittance. The XRD measurements show typical diffraction pattern of ZnO wurtzite structure. The SEM micrographs show the presence of smooth NW with hexagonal sections with diameters ranging from 40 to 250 nm. The optical transmittance reveals the presence of ZnO with bandgap energy between 3.23 and 3.29 eV. These spectra show a monotonically increasing transmittance from the UV into the red part of the spectrum. This feature may be originated in the dispersion of light at the NW and can be used to enhance below‐gap absorption.magnified image

Bulk Dislocation Core Dissociation Probed by Coherent X Rays in Silicon

We report on a new approach to probe bulk dislocations by using coherent x-ray diffraction. Coherent x rays are particularly suited for bulk dislocation studies because lattice phase shifts in condensed matter induce typical diffraction patterns which strongly depend on the fine structure of the dislocation cores. The strength of the method is demonstrated by performing coherent diffraction of a single dislocation loop in silicon. A dissociation of a bulk dislocation is measured and proves to be unusually large compared to surface dislocation dissociations. This work opens a route for the study of dislocation cores in the bulk in a static or dynamical regime, and under various external constraints.