Increase In Interplanar Spacing Research Articles

Evolution of spectroscopy features in layered MoSxSe(2-x) solid solutions

In this work we report the structural and spectroscopic characterization of the bulk MoSxSe2-x solid solutions synthesized by chemical vapor transport. The bulk crystals were analyzed by scanning electron microscopy (SEM), x-ray diffraction (XRD), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Electron microscopy evaluation of the layered materials shows two distinct types of crystals: flat and easily cleavable hexagonal microcrystals up to 50 μm in size, and agglomerated irregular crystals of 5–10 μm in size. XRD shows a consistent increase in interplanar spacing as the Se content is increased in the sample series. Raman spectra of bulk MoSxSe2-x obtained with three different excitation energies revealed first order phonon modes associated with pure MoS2 (x = 2) and MoSe2 (x = 0) along with a complex behavior of vibrational modes when x had intermediate values. XPS Mo3d line scans indicate a slight shift towards lower binding energies as the Se/S ratio increases, consistent with the expected energies of MoSe2. A simple and direct relationship can be established between the characteristic Raman peaks and the value of x, which can be useful for identifying the compositions of TMD crystals.

Ultrafine-grained microstructure and controllable magnetic domains in Fe-based nanocrystalline alloys with excellent magnetic properties induced by hot isostatic pressing

The coarsening and inhomogeneous distribution of nano-grains caused by traditional heat treatment processes are the biggest obstacles for obtaining ultrahigh permeability and excellent comprehensive soft magnetic properties in Fe-based nanocrystalline alloys. Here, we propose a new strategy to control grain growth and magnetic anisotropy, by introducing isotropic compressive stress field in the annealing process to optimize the magnetic properties. Compared with conventional isothermal annealing, the coupling of stress-temperature field generated by hot isostatic pressing (HIP) induced the microstructure, magnetic domain evolution and magnetic properties in Si-rich Fe73.5Si15.5B7Nb3Cu1 amorphous ribbons have been systematically investigated. We demonstrate that HIP treatment promotes more Si atoms to dissolve in Fe unit cell to form Fe(Si) solid solution causing an increase in interplanar spacing. Also, the high-density Cu clusters precipitate in the amorphous matrix upon HIP serving as nucleation sites for α-Fe(Si) grains, which facilitate a high volume fraction, uniform and ultrafine-grained microstructure. Moreover, the existence of stress field introduces induced anisotropy effectively controls the magnetization mechanism and magnetic structure evolution. Furthermore, the Fe73.5Si15.5B7Nb3Cu1 nanocrystalline alloy treated by HIP exhibit excellent comprehensive magnetic properties, such as high Ms, high μe, low Pcv, low AC Hc and high Br/Bm.

UV sensitivity enhancement in Fe-doped ZnO films grown by ultrafast spray pyrolysis

The effect of Fe dopant on structural and photosensitivity properties of ZnO thin films have been studied. The Fe-doped ZnO films were fabricated by ultrafast spray pyrolysis for 30 s. As a result, X-ray diffraction analysis demonstrates that the deposited films are polycrystalline with the hexagonal wurtzite structure. Fe doping in the ZnO system provokes not only the decrease of crystallinity and crystallite size (~50% for Fe concentration of 0.5%) but also the increase of interplanar spacing and strain. Surface morphology images show that the grain size of 3% Fe-doped ZnO (67 nm) is smaller than that of the pure ZnO (114 nm). Based on I–V characterizations, Fe doping increases photocurrent as well as UV sensitivity up to 21 times (1.5% Fe) and 70 times (3% Fe) than that of the undoped ZnO. This study is important to improve the functionality of ZnO as a UV photodetector. • ZnO thin films are fabricated using ultrafast spray pyrolysis for 30 s. • Fe doping decreases the crystallinity and crystallite size of ZnO. • Fe concentration of 3% has the highest UV sensitivity. • Lower dark current and higher photocurrent are found in Fe concentration of 3%.

Ion-Implantation-Induced Disorder in FePt-C Thin Films

The effects of ion implantation through a mask on the structural and magnetic properties of FePt-C films were investigated. The mask pattern was fabricated using self-assembly of di-block copolymers. For implantation, high- (40 keV for 14N+ and 100 keV for 40Ar+) and low- (7.5 keV for 14N+ and 4.5 keV for 40Ar+) energy 14N+ and 40Ar+ ions were used to modify the structural and magnetic properties of these films. The X-ray diffraction and transport of ions in matter simulations were performed for understanding the structural changes due to the ion implantations. These results revealed the conversion of face-centered tetragonal phase to face-centered cubic (FCC) phase for 40Ar+ ion implantations and increase in inter-planar spacing of FCC FePt (111) planes for 14N+ ion implantations. Magnetic properties were then probed by using a vibrating sample magnetometer (VSM), torque magnetometer, and magnetic force microscopy (MFM). The results from VSM and torque magnetometer showed a change in anisotropy from out-of-plane to in-plane directions for all the implantation cases except for low-energy 40Ar+ ion implantations. The MFM images also showed an absence of stripe domains confirming the above-mentioned effects.

Ag and Cu doped ZnO nanowires: A pH-Controlled synthesis via chemical bath deposition

Synthesizing and doping process of p-type zinc oxide (ZnO) nanowire arrays (NWAs) through chemical bath deposition is still a challenge. We systematically investigate the growth of ZnO NWAs in a pH-controlled aqueous media. This study helps us to successfully grow copper (Cu) and silver (Ag) incorporated NWAs. The optimum pH values for NWA growth and doping are 6.8 and 10.8. Field emission scanning electron microscopy (FESEM) images reveal the finest ZnO NWAs with the length of 1.3 µm (70 nm in diameter) for pH = 6.8 and 8.2 µm (170 nm in diameter) for pH = 10.8, respectively. Moreover, high-resolution X-ray photoelectron spectroscopy (HRXPS) demonstrates the peaks of Cu and Ag at their specific binding energies especially in pH of 6.8. A slight shift to lower angles of (002) peak in X-ray diffraction (XRD) pattern of doped samples is also detected relative to the presence of Ag+ (rAg+ = 115 pm) and Cu+ (rCu+ = 77 pm) which have higher ionic radii than Zn2+ (rZn2+ = 74 pm). A lattice expansion is also observed by high-resolution transmission electron microscope (HRTEM) confirming an average increase in interplanar spacing of 5 pm and 20 pm for copper and silver-doped samples, respectively. Finally, diffused reflectance spectroscopy (DRS) graphs show a red-shift in the UV-absorption of doped samples regarding to obtaining Ag or Cu doped NWAs.

Structure-property correlations in thermally processed epitaxial LSMO films

Mixed-valence perovskites have drawn significant research interest in the past due to their exotic properties. Lanthanum Strontium Manganese Oxide (LSMO) shows a ferromagnetic ordering that can be tuned with the control of defects and strain. Here, experiments were performed to decouple the effects of strain and oxygen content, which together control the magnetic properties of the LSMO (La0.7Sr0.3MnO3). In this work, thermal treatments show promise in effectively controlling the ferromagnetic response of LSMO films. A set of three samples were grown on the same substrate-buffer (Al2O3/MgO) platform with different oxygen partial pressures and annealed above their deposition temperature (∼900 °C) in air. The physical and structural properties were measured and showed overall decrease in magnetization saturation as well as decrease in out-of-plane lattice spacing with decreasing oxygen partial pressure. A second anneal at lower (∼700 °C) temperature with flow of pure oxygen was performed for six hours to allow for defect annihilation and grain growth. All three films remained epitaxial allowing for direct correlation of magnetic measurements with defect concentration. Partial recovery of the magnetic properties and a slight increase in interplanar spacing was observed. The inability of the films to fully recover their original magnetic properties suggests irreversible strain relaxation during the initial, high-temperature air anneal. This hypothesis was further supported by the in-situ XRD that showed a linear increase in the interplanar spacing with temperature until ∼520 °C for LSMO and ∼690 °C for MgO. With further increase in temperature, the films experienced both loss of oxygen and irreversible defect nucleation and recombination. High resolution high-angle annular dark field (HAADF) images showed uniform thickness and no interfacial mixing with subsequent annealing treatments while electron energy loss spectroscopy (EELS) showed a loss of characteristic pre-peak A in oxygen indicating formation of oxygen vacancies. Parallel annealing experiments in high vacuum instead of atmosphere were performed, which showed complete loss of crystal structure in the LSMO films due to significant loss of oxygen in the lattice that irreversibly collapsed the perovskite structure. Furthermore, a low-temperature (∼500 °C) oxidation anneal was performed on a pristine sample with no change in the interplanar spacing observed indicating no change in the strain state of the film due to annealing below the deposition temperature. The reversibility of magnetic properties, which is observed as long as the crystal structure of the films is preserved, indicates the importance of bridging oxygen in controlling the magnetic behavior of mixed valence perovskites. Finally, it was determined that the highest magnetization saturation in the films is achieved with a high oxygen partial pressure during growth and subsequent thermal annealing below the deposition temperature.

Thermal-oxidation-induced local lattice distortion at surface of 4H-SiC(0001) characterized by in-plane X-ray diffractometry

Local lattice distortions at the surface of 4H-SiC(0001) after various thermal oxidation processes were investigated by in-plane X-ray diffractometry. Our results showed that dry oxidation induced lattice distortion, observed as the increase of interplanar spacing, became higher with increasing oxidation time. Lattice constant changes of up to ∼0.4% were observed by increasing the oxide thickness to 44 nm. This lattice distortion was not recovered after removal of the SiO2 layer by chemical etching, although it was partially reduced by Ar gas annealing, suggesting that strain relaxation requires removal of oxidation-induced defects in the 4H-SiC surface region.

Microstructure characterization of hydrothermally synthesized PANI/V2O5·nH2O heterojunction photocatalyst for visible light induced photodegradation of organic pollutants and non-absorbing colorless molecules

Polyaniline intercalated vanadium oxide xerogel (PV) hybrid nanocomposite (NC) with novel structure has been successfully synthesized through a simple hydrothermal route. Detailed structure and microstructure characterization of PV NC is illustrated through Rietveld refinement of XRD data and FESEM/HRTEM images. Both FTIR and XPS spectra confirm the presence of PANI and water molecules within the NC and partial reduction of V5+ to V4+, corroborating with the results of XRD pattern analysis. Core-shell structure of PV NC, where PANI sheath layer acts as a shell covering around V2O5·nH2O crystalline core is confirmed from HRTEM images. Successive morphological changes of PV NC with different reaction time have been revealed from FESEM images. UV–vis spectra also confirm the formation of PV NC. Intercalation of water and PANI layers into V2O5·nH2O layer leads to a structural phase transition from orthorhombic to monoclinic phase due to substantial increase in interplanar spacing of (00l) of orthorhombic V2O5. The photocatalytic property of the as synthesized PV NC has been reported for the first time, with a promising photocatalytic activity for the degradation of organic dye, Rhodamine B (RhB) under visible light irradiation. It is attributed to a synergic effect in between PANI and V2O5·nH2O xerogel. The photocatalyst also shows remarkable real visible light photocatalytic activity with non-absorbing colorless test molecules like phenol and antibiotic kanamycin.

Properties of Polyhydroxy Butyrate Polyvalerate Biopolymeric Nanocomposites Reinforced with Natural Halloysite Nanotubes

In this study, the properties of bacterial fermentation based poly(hydroxybutyrate-co-hydroxyvalerate) –PHBV thermoplastic biopolymer was investigated by reinforcing natural halloysite nanotubes (HNTs). At first, HNTs were added to PHBV polymer by melt processing technique. The modified PHBV resin was then used to fabricate films using compression molding process. X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile tests were performed. XRD results showed mixed intercalated and exfoliated behavior of HNTs in PHBV matrix with an increase in interplanar spacing and decrease in peak intensity. DSC analysis showed that the crystallinity of PHBV resin increased with the increase in HNTs concentration. Also, the DSC endotherm curve showed dual melting peaks indicating formation of different crystalline phases. Higher melting and recrystallization temperature was found in nanophased samples in comparison to the pure PHBV counterpart. The thermal stability, activation energy, tensile and viscoelastic properties of nanophased samples were also increased with an optimum at 3 wt. % HNTs loading. Scanning electron micrographs (SEM) revealed river like pattern in neat films indicating a brittle failure in contrast to rougher surfaces observed in nanophased samples.

Physical, physicochemical and nutritional characteristics of Bhoja chaul, a traditional ready-to-eat dry heat parboiled rice product processed by an improvised soaking technique

Bhoja chaul is a traditional whole rice product processed by the dry heat parboiling technique of low amylose/waxy paddy that is eaten after soaking in water and requires no cooking. The essential steps in Bhoja chaul making are soaking paddy in water, roasting with sand, drying and milling. In this study, the product was prepared from a low amylose variety and a waxy rice variety by an improvised laboratory scale technique. Bhoja chaul prepared in the laboratory by this technique was studied for physical, physicochemical, and textural properties. Improvised method shortened the processing time and gave a product with good textural characteristics. Shape of the rice kernels became bolder on processing. RVA studies and DSC endotherms suggested molecular damage and amylose–lipid complex formation by the linear B-chains of amylopectin, respectively. X-ray diffractography indicated formation of partial B-type pattern. Shifting of the crystalline region of the XRD curve towards lower values of Bragg’s angle was attributed to the overall increase in inter-planar spacing of the crystalline lamellae. Resistant starch was negligible. Bhoja chaul may be useful for children and people with poor state of digestibility.

Preparation and investigation of the physical and chemical properties of clay-based polyacrylamide/Cr (III) hydrogels as a water shut-off agent in oil reservoirs

The effects of clay (montmorillonite and kaolinite) in the hydrogels were investigated on various properties such as syneresis and strength of thermal and salinity situations in one of the southern Iranian oil reservoirs. The X-ray diffraction (XRD) patterns exhibited a significant increase in interplanar spacing between the montmorillonite clay layers, varying from the initial value of 12.43 °A to 19.45 °A, which evidences the intercalation formation. It was revealed that even increasing of the interlayer spacing due to kaolinite modification had no effect on the clay compositions. Formation water was used to study the strength of the hydrogel in the presence of ions. The results indicated that 15 wt% increase of kaolinite clay (modified and non-modified) leads to 20% decrease of the hydrogels’ syneresis. The diffusion of polymer chains between the clay layers increased the elastic modulus (G′) of the prepared hydrogels with modified kaolinite and montmorillonite, where the maximum value of G’ was observed in 3 wt% of montmorillonite. Finally, the thermogravimetric analysis (TGA) indicated an increase in the thermal stability of the mentioned hydrogels.

Carbon fibers derived from UV‐assisted stabilization of wet‐spun polyacrylonitrile fibers

ABSTRACTA rapid, dual‐stabilization route for the production of carbon fibers from polyacrylonitrile (PAN) precursor fibers is reported. A photoinitiator, 4,4′‐bis(diethylamino)benzophenone, was added to PAN solution before the fiber wet‐spinning step. After a short UV treatment that induced cyclization and crosslinking at a lower temperature, precursor fibers could be rapidly thermo‐oxidatively stabilized and successfully carbonized. Scanning electron microscopy micrographs show no deterioration of the microstructure or hollow‐core formation in the fibers due to UV treatment or presence of photoinitiator. Fast‐thermally stabilized pure PAN‐based carbon fibers show hollow‐core fiber defects due to inadequate thermal stabilization, but such defects were not observed in carbon fibers derived from fast‐thermally stabilized fibers that contained photoinitiator and were UV treated. Tensile testing results confirm that fibers containing 1 wt % photoinitiator and UV treated for 5 min display higher tensile modulus than all other sets of thermally stabilized and carbonized fibers. Wide‐angle X‐ray diffraction results show a higher development of the aromatic structure and molecular orientation in thermally stabilized fibers. No significant increase in interplanar spacing or decrease in crystals size were observed within the UV‐stabilized carbon fibers containing photoinitiator, but such fibers retain a higher extent of molecular orientation when compared with control fibers. These results establish for the first time, the positive effect of the external addition of photoinitiator and UV treatment on the properties of the PAN‐based fibers, and may be used to reduce the precursor stabilization time for faster carbon fiber production rate. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40623.

Effects of substrate temperature, substrate orientation, and energetic atomic collisions on the structure of GaN films grown by reactive sputtering

The combined effects of substrate temperature, substrate orientation, and energetic particle impingement on the structure of GaN films grown by reactive radio-frequency magnetron sputtering are investigated. Monte-Carlo based simulations are employed to analyze the energies of the species generated in the plasma and colliding with the growing surface. Polycrystalline films grown at temperatures ranging from 500 to 1000 °C clearly showed a dependence of orientation texture and surface morphology on substrate orientation (c- and a-plane sapphire) in which the (0001) GaN planes were parallel to the substrate surface. A large increase in interplanar spacing associated with the increase in both a- and c-parameters of the hexagonal lattice and a redshift of the optical bandgap were observed at substrate temperatures higher than 600 °C. The results showed that the tensile stresses produced during the film's growth in high-temperature deposition ranges were much larger than the expected compressive stresses caused by the difference in the thermal expansion coefficients of the film and substrate in the cool-down process after the film growth. The best films were deposited at 500 °C, 30 W and 600 °C, 45 W, which corresponds to conditions where the out diffusion from the film is low. Under these conditions the benefits of the temperature increase because of the decrease in defect density are greater than the problems caused by the strongly strained lattice that occurr at higher temperatures. The results are useful to the analysis of the growth conditions of GaN films by reactive sputtering.

Substrate and buffer layer effect on the structural and optical properties of graphene oxide thin films

Graphene oxide (GO) thin films on various substrates show surprising variations of their structural and optical properties. These variations were also studied by depositing GO via introducing a gold nanoparticles buffer layer on quartz substrate. The effect of the substrate as well as buffer layer results in short range order crystallization in deposited GO films with an increase in inter-planar spacing. XPS analysis shows that GO undergoes reduction when spin coated on ITO/glass substrate. The deposited GO films exhibit luminescence emission, and the introduction of gold buffer layer results in a blue shift of the photoluminescent emission spectra. The GO on gold buffer layer shows almost constant optical absorption in the whole visible spectral region like graphene. The present study indicates that buffer layer effects and the interaction between different substrates and GO is strong enough to affect the oxygen linkages in GO which in turn changes its structural and optical properties, which may find potential application in graphene based optoelectronic device fabrication.

Epoxy to Carbonyl Group Conversion in Graphene Oxide Thin Films: Effect on Structural and Luminescent Characteristics

The conversion of epoxy to carbonyl group in graphene oxide (GO) thin films has been carried out via oxygen plasma treatment, and the effects of this conversion on structural and optical properties were investigated. Hydrophilicity of the prepared GO solution allows it to be uniformly deposited onto substrates in the form of thin films. High-resolution transmission electron microscopy and electron diffraction analysis confirmed 4–5 layers of the graphene oxide layers which are polycrystalline in structure, and the oxygen plasma treatment results in short-range order crystallization in graphene oxide films with an increase in interplanar spacing which can be attributed to the presence of oxygen functional groups on the graphene oxide layers. Electron energy loss spectroscopy (EELS) and Raman spectroscopy confirm the presence of the sp2 and sp3 hybridization due to the disordered crystal structures of the carbon atoms results from oxidation, and XPS analysis shows that epoxy pairs convert to more stable C═O and O–C═O groups with oxygen plasma treatment. The broad energy level distribution resulting from the broad size distribution of the sp2 clusters produces excitation-dependent photoluminescent (PL) emission in a broad wavelength range from 400 to 650 nm. Our results suggest that as oxygen pressure increases, there is a change from epoxide to carbonyl linkages which also resulted in variation in PL emission.

Durability study of neat/nanophased GFRP composites subjected to different environmental conditioning

Experimental investigations on the durability of E-glass/nanoclay–epoxy composites are reported. SC-15 epoxy system was modified using 1–2 wt.% of nanoclay. Extent of clay platelet exfoliation in epoxy was evaluated using X-ray diffraction (XRD). Glass fiber reinforced plastic (GFRP) composite panels were fabricated using modified epoxy and exposed to four different conditions, i.e. hot (elevated temperature-dry, wet: 60 and 80 °C) and cold (subzero-dry, wet) for 15, 45 and 90 days. Weight change due to conditioning, quasi-static flexure and micrographic characterization were studied on the conditioned samples. Room temperature samples were also tested for baseline consideration. XRD results showed exfoliation of clay platelets in nanoclay–epoxy samples with decrease in peak intensity and increase in interplanar spacing. Samples subjected to hot-wet conditions showed higher percentage weight gain with a maximum of 4.25% in neat and 3.1% in 2 wt.% samples. Flexural tests results showed degradation with increasing time. Maximum degradation were observed for hot-wet (80 °C) for 90 days neat samples, i.e. 22.6% and 29.8% reduction in flexural strength and stiffness, respectively. However, less degradation was noticed for nanophased composites under similar conditions. Scanning electron microscopy (SEM) results of failed samples showed better interfacial bonding in nanophased composites.

Antibacterial activity of silver-carried sodium zirconium phosphate prepared by ion-exchange reaction

Ag+-Na+ exchange equilibrium for carrier (sodium zirconium phosphate) was investigated at 60°C, and the chemical compositions and structure of carrier and silver-carried zirconium phosphate (AgZrP) were investigated by EDX and XRD. The silver valence state and antibacterial activity of AgZrP were also studied. The Ag+ exchange was favorable over the whole Ag+ concentration range. The molecular formulae of carrier [NaZr2(PO4)3.H2O] and AgZrP [Ag0.5Na0.5Zr2(PO4)3.H2O] have been determined, and the silver of AgZrP was in an ionic state. Both carrier and AgZrP displayed hexagonal crystal structures, but Ag+ exchange resulted in the increase of interplanar spacing and lattice parameter c, and the crystal orientation of AgZrP was affected by the existence of Ag+. Moreover, 100 mg.l-1 of AgZrP possessed high antibacterial activity and was capable of killing all the Escherichia coli and more than 99.9% of the Staphylococcus aureus within 8.0 h of contact. Furthermore, AgZrP showed a broad-spectrum and long-acting antibacterial activity.

Transformation of (0002)-oriented Ti film into (111)TiN through nitrogen implantation

Nitrogen implantation into a (0002)-oriented Ti film has resulted in a systematic deformation of the hcp host with implantation dose. Grazing-incidence X-ray diffraction study shows an increase in interplanar spacing of the (0002) and the (10\(\)3) planes as a function of nitrogen concentration. The diffractograms indicate a smooth change of (0002) plane of the host into (111) of the δ-TiN. Strain in the hcp cell was found to be proportional to the nitrogen concentration. The results provide evidence for a strain-driven ‘martensite-like restacking’ formation of TiN compound.

Microstructural Evolution of AI/Ni and Ni/AI Bilayer Thin Films

ABSTRACTThe growth and microstructural evolution of Al/Ni and Ni/AI bilayer thin films have been investigated as a function of Al and Ni layer thickness and thermal treatment by transmission electron microscopy. Studies were also made of Al and Ni single layers of varying thickness. All films were grown by dc magnetron sputtering using carbon coated Cu TEM grids as substrates. For the bilayers, the Al thickness was fixed at either 3.5 or 7.0 nm while the Ni thickness was varied systematically from 3.2 to 12.8 nm. Deposition sequence significantly influenced bilayer microstructure even in as-deposited samples. Al/Ni bilayers generally exhibited a finer microstructure than Ni/AI. In the 3.5 nm Al/Ni bilayers no conclusive electron diffraction evidence was found for elemental Al while for the reverse sequence both Al and NiAl3 diffraction rings were found. In the 7.0 nm Al/Ni bilayers diffraction rings due to Al were observed. The reverse sequence again produced both Al and NiAl3 diffraction rings. Interestingly, diffraction rings due to the Ni layers were found for all samples but were consistently measured at positions corresponding to a 2.5–3.5% increase in interplanar spacing. Annealing at 385°C produced evidence for generalized grain growth and strong accentuation of the electron diffraction rings due to the NiAl3 phase. Again, deposition significantly influenced annealed bilayer microstructure. For the Al/Ni sequence annealing produced polycrystalline N1AI3 island-like structures, while for Ni/AI bilayers, annealing promoted the growth of small NiAl3 crystals uniformly distributed in the film.

A simultaneous study of lattice expansion and swelling in proton-bombarded gap single crystals

Abstract The swelling and the lattice expansion of proton bombarded GaP single crystals are simultaneously measured for different proton doses by the “Talystep” method and by the Kossel technique, resp. The results reveal good agreement between the increase in interplanar spacing and the volume change in the damaged region