High-resolution X-ray Diffraction Studies Research Articles

Strong visible and near infrared photoluminescence from ZnO nanorods/nanowires grown on single layer graphene studied using sub-band gap excitation

Fabrication and optoelectronic applications of graphene based hybrid 2D-1D semiconductor nanostructures have gained tremendous research interest in recent times. Herein, we present a systematic study on the origin and evolution of strong broad band visible and near infrared (NIR) photoluminescence (PL) from vertical ZnO nanorods (NRs) and nanowires (NWs) grown on single layer graphene using both above band gap and sub-band gap optical excitations. High resolution field emission scanning electron microscopy and X-ray diffraction studies are carried out to reveal the morphology and crystalline quality of as-grown and annealed ZnO NRs/NWs on graphene. Room temperature PL studies reveal that besides the UV and visible PL bands, a new near-infrared (NIR) PL emission band appears in the range between 815 nm and 886 nm (1.40–1.52 eV). X-ray photoelectron spectroscopy studies revealed excess oxygen content and unreacted metallic Zn in the as-grown ZnO nanostructures, owing to the low temperature growth by a physical vapor deposition method. Post-growth annealing at 700 °C in the Ar gas ambient results in the enhanced intensity of both visible and NIR PL bands. On the other hand, subsequent high vacuum annealing at 700 °C results in a drastic reduction in the visible PL band and complete suppression of the NIR PL band. PL decay dynamics of green emission in Ar annealed samples show tri-exponential decay on the nanosecond timescale including a very slow decay component (time constant ∼604.5 ns). Based on these results, the NIR PL band comprising two peaks centered at ∼820 nm and ∼860 nm is tentatively assigned to neutral and negatively charged oxygen interstitial (Oi) defects in ZnO, detected experimentally for the first time. The evidence for oxygen induced trap states on the ZnO NW surface is further substantiated by the slow photocurrent response of graphene-ZnO NRs/NWs. These results are important for tunable light emission, photodetection, and other cutting edge applications of graphene-ZnO based 2D-1D hybrid nanostructures.

Emission characteristics of self-assembled strained Ge1−xSnx islands for sources in the optical communication region

Self-assembled strained Ge1−xSnx islands on Si (100) have been grown at a low temperature using molecular beam epitaxy. The in-built strain and fraction of Sn in the islands have been estimated using x-ray photoelectron spectroscopy and high resolution x-ray diffraction study of grown samples. No-phonon assisted transition in the optical communication wavelength range of 1.4–1.8 μm has been observed in the Ge1−xSnx island samples. The direct band gap transition intensity is found to increase with a growth in Sn concentration, with this increase in intensity sustained up to a temperature of 130 K in Ge1−xSnx islands. The observed electroluminescence in p-i-n devices fabricated on Ge1−xSnx island samples above a threshold bias of 4 V makes them attractive for future Si based optical devices.

High resolution X-ray diffraction studies of epitaxial ZnO nanorods grown by reactive sputtering

Vertically aligned and highly c-axis oriented ZnO nanorods were epitaxially grown on c-sapphire by dc reactive sputtering of zinc target in argon-oxygen atmosphere. Scanning electron microscopy shows that substrate temperature critically controls the morphology of sputtered ZnO films, eventually causing the formation of laterally oriented ZnO nanorods at higher temperatures (700 °C–750 °C), as confirmed by ϕ-scan measurements. High resolution X-ray diffraction was used to obtain the micro-structural parameters of ZnO columnar films/nanorods from Williamson-Hall plots of ω and ω-2θ scans, and rocking curves of asymmetric reflections. These results show that epitaxially grown ZnO nanorods exhibit substantially superior micro-structural parameters, namely, tilt (0.4°), twist (0.5°), and micro-strain (4 × 10−4), compared to columnar ZnO films grown at 500 °C–600 °C. The reciprocal space maps of (0002), (0004), 101¯1, 101¯4, and (112¯0) planes of ZnO nanorods were carried out to obtain the lattice parameters of epitaxial ZnO nanorods and calculate lattice strain (9 × 10−4, for both “a” and “c”), which indicates the absence of biaxial strain. Room temperature photoluminescence of epitaxial ZnO nanorods shows a strong near-band-edge emission along with negligible defect emission, owing to their high crystalline quality and micro-structural parameters.

Rigid Amorphous Phase: Mechanical and Transport Properties of Nitrile Rubber/Clay Nanocomposites

The present study has been focused on the preparation of nitrile rubber/ organoclay nanocomposites containing 0–10 wt% Cloisite 93A by mechanical mixing on a two-roll mill. The rubber samples were vulcanized by accelerated sulfur vulcanization process. The role of nanoclay on the curing process has been carefully studied. The clay dispersion in the rubber matrix was analyzed by high resolution transmission electron microscopy (TEM) and X-ray diffraction studies. Both XRD and electron microscopic analyses indicated that the nanocomposites exhibit partly intercalated and exfoliated structure. However, the nanocomposites showed better exfoliation at lower clay loading (2 wt percent) as evident by TEM and XRD. At higher clay loading the clay tend to form aggregates. The correlation distance and the length and thickness of the clay platelets in the rubbery matrix have been deduced from the TEM micrographs as a function of clay loading. The nanoclay-rubber interaction has been quantified by Kraus analysis. The nanocomposites exhibited improved mechanical properties which include tensile strength, modulus, tear strength and resistance to abrasion. The solvent resistance of the nanocomposite increased with the increase in dosage of the nanofiller. Finally, the properties have been modeled using Guth and Halpin-Tsai equations.

Emission and elastic strain study in GaAs/In0.15Ga0.85As/InxGa1−xAs/GaAs quantum wells with embedded InAs quantum dots

GaAs/In0.15Ga0.85As/InxGa1−xAs/GaAs quantum wells (QWs) with embedded InAs quantum dots (QDs) and with variable In compositions in capping InxGa1−xAs layers (0.10 ≤ x ≤ 0.25) have been studied by means of photoluminescence, X ray diffraction (XRD) and high resolution XRD (HR-XRD) methods. InxGa1−xAs composition varying is accompanied by changing no monotonically the PL spectrum parameters of InAs QDs and by decreasing the InAs QD sizes. XRD and HR-XRD studies permit to control the InGaAs layer compositions and elastic strains in QWs. The analysis of HR-XRD results has shown that the level of elastic strain varies no monotonically in studied QD structures as well. The physical reasons of mentioned optical and structural effects and their dependences on capping layer compositions have been discussed.

TiO2 Nanoparticles Incorporated Peptide Appended Perylene Bisimide-Based Nanohybrid System: Enhancement of Photo-Switching Behavior

A peptide appended perylene bisimide (PBI)-based new hydrogel has been discovered in phosphate buffer medium having the pH ranging from 7.00 to 9.00. This peptide appended PBI-derivative shows interesting photoswitching property in the aggregated state. This gel is thoroughly characterized by UV–visible absorption and fluorescence spectroscopy, field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), and rheological studies. TiO2 nanoparticles are also prepared by using a protein amino acid, glutamic acid, in water medium. The as-synthesized TiO2 nanoparticles exhibit usual photoswitching behavior. An organic–inorganic hybrid nanomaterial is prepared by incorporating the as-synthesized TiO2 nanoparticles into the fibrillar gel network of the native gel. This TiO2–PBI-based hybrid soft material shows a characteristic of nanofiber and nanoparticle combination in their nanoscale coassembled state as it is evident from the respec...

A high-voltage rechargeable magnesium-sodium hybrid battery

Growing global demand of safe and low-cost energy storage technology triggers strong interests in novel battery concepts beyond state-of-art Li-ion batteries. Here we report a high-voltage rechargeable Mg–Na hybrid battery featuring dendrite-free deposition of Mg anode and Na-intercalation cathode as a low-cost and safe alternative to Li-ion batteries for large-scale energy storage. A prototype device using a Na3V2(PO4)3 cathode, a Mg anode, and a Mg–Na dual salt electrolyte exhibits the highest voltage (2.60V vs. Mg) and best rate performance (86% capacity retention at 10C rate) among reported hybrid batteries. Synchrotron radiation-based X-ray absorption near edge structure (XANES), atomic-pair distribution function (PDF), and high-resolution X-ray diffraction (HRXRD) studies reveal the chemical environment and structural change of Na3V2(PO4)3 cathode during the Na ion insertion/deinsertion process. XANES study shows a clear reversible shift of vanadium K-edge and HRXRD and PDF studies reveal a reversible two-phase transformation and V–O bond length change during cycling. The energy density of the hybrid cell could be further improved by developing electrolytes with a higher salt concentration and wider electrochemical window. This work represents a significant step forward for practical safe and low-cost hybrid batteries.

Study of cubic GaN clusters in hexagonal GaN layers and their dependence with the growth temperature

The inclusion of cubic phase in MOVPE-grown hexagonal GaN on GaAs substrate and its dependence with the growth temperature are investigated by high-resolution X-ray diffraction (HR-XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and cathodoluminescence (CL). It is observed that the GaN layers surface exhibits 3D-grains structure. The density and shape of these grains are largely dependent on the growth temperature. HR-XRD study reveals the presence of cubic GaN clusters in the hexagonal GaN layer. Using CL we show that the cubic inclusions are not localized at the substrate/epilayer interface but propagate throughout the film.

Experimental evidence of charge transfer in a functionalized hexavanadate: a high resolution X-ray diffraction study.

A high resolution X-ray diffraction study has been carried out on [(C4H9)4N]2 [V6O13{(OCH2)3CCH2OCCH2CH3}2] (V6-C3) at 100 K. The V6 core possesses a negative charge, leading to a strong polarization of the anion. A nucleophilic region localized near the organic moiety and an electrophilic region in the vicinity of the V6 core provide an overall description of charge-transfer behavior.

In situ high-resolution powder X-ray diffraction study of UiO-66 under synthesis conditions in a continuous-flow microwave reactor

Large scale synthesis of metal–organic frameworks (MOFs) is of high interest, due to their potential for industrial applications. The capacity to synthesize large amounts of MOFs should be combined with the ability to control their properties. Understanding how process parameters influence the formation of the product is necessary to synthesize tailor-made materials. The crystallization process of a MOF from the reaction mixture can be conveniently monitored in real time by performing in situ studies using synchrotron radiation. This yields insight into the formation of the product under the actual reaction conditions. In this work, we performed an in situ high-resolution powder X-ray diffraction study of the crystallization of UiO-66 in a recently developed continuous-flow microwave reactor that provided excellent performances in terms of space-time yield and atom economy. The effect of the addition of different amounts of water and acetic acid to the reaction mixture on the yield and crystallite size of the product was investigated over a range of residence times. UiO-66 was the only crystalline phase observed and two stages of the process were identified, namely, a preliminary stage, where the crystallite size of the MOF increases, and a steady state one where the quality of the product is constant. The yield and crystallite size of the product primarily depended on the water/acetic acid ratio, which was the most important parameter determining the rate of product formation. Increasing the absolute amounts of additives at fixed ratios led to a higher yield of larger crystallites, whereas aging of the metal stock solution led to a higher yield of smaller crystallites. Selected experiments were performed offline isolating the solid at the steady state and characterizing it after workup. In this way, we demonstrated that large scale synthesis of UiO-66 with controlled properties can be performed with a continuous-flow microwave reactor.

Study of Antioxidant Property of the Endosperm Extract of Borassus flabellifer (Taal) and its use in the green synthesis of Gold nanoparticles

The antioxidant activity of the endosperm extract of Borassus flabellifer (commonly known as Taal) has been studied against a long lived 2,2-diphenylpicrylhydrazyl (DPPH) radical at room temperature. The phytochemicals present in the endosperm extract have been utilized for the synthesis of stable gold nanoparticles at room temperature under very mild conditions. The synthesized gold nanoparticles were characterized by Surface Plasmon Resonance spectroscopy, High resolution transmission electron microscopy, X-Ray diffraction and FTIR studies and a mechanism for the synthesis of stabilized gold nanoparticles has been proposed.

Optical emissions of Ce3+ doped Sulphamic acid single crystals by low temperature unidirectional growth technique

Cerium doped Sulphamic acid (SA) single crystal was synthesized and grown in large size for its cerium ion optical emissions. The photoluminescence emission of unidirectional grown crystals was found to have a broad band from 300 nm to 400 nm, centered at 318 nm (5d → 4f (2F5/2, 2F7/2), due to ground state crystal field splitting. The respective excitation spectra show peak at 273 nm, which is attributed to transitions from the 4f(2F5/2) ground state to first and second excited level of 5d configuration of Ce3+. The nature of decay curve is bi exponential with an average decay life time (τavg) of 20.12 ns. The lattice parameters were determined by X-ray diffraction analysis and the crystalline perfection of grown single crystals have been checked by High Resolution X-ray Diffraction (HRXRD) studies. The vacancy defects are predominant and causes tensile stress in the lattice by incorporation of Ce3+ ions. Functional group analysis and SEM with EDAX reveals that Ce3+ ion is incorporated in the crystal system. The lower cutoff wavelength found at 340 nm and the respective band gap was calculated as 4.6eV. The dielectric measurements were done at different temperatures and the nonlinear optical efficiency was observed as 3.5 times that of standard potassium dihydrogen phosphate (KDP) single crystals. In the present study, sulphamic acid acts as a prominent host material for probing Ce3+ ion emissions for optical device applications.

The true structural periodicities and superspace group descriptions of the prototypical incommensurate composite materials: Alkane/urea inclusion compounds

The prototypical family of incommensurate composite materials are the n-alkane/urea inclusion compounds, in which n-alkane guest molecules are arranged in a periodic manner along one-dimensional tunnels in a urea host structure, with an incommensurate relationship between the periodicities of the host and guest substructures along the tunnel. We develop interpretations of the structural periodicities, superspace group descriptions and symmetry properties of the low-temperature phases of n-alkane/urea inclusion compounds, based in part on a high-resolution synchrotron single-crystal X-ray diffraction study of n-nonadecane/urea. Specifically, we prove that, on passing from phase I to phase II, the C-centering of the orthohexagonal unit cell is lost for both the host and guest substructures, and that the symmetries of all phases I, II and III are described completely by (3 + 1)-dimensional superspace groups.

Crystalline perfection, thermal, mechanical and optical investigations on solution grown l-arginine monohydrochloride single crystal

In the present work we report crystallization and detailed analyses on l-arginine monohydrochloride single crystal an efficient material for nonlinear optical applications. The crystal of titled material was grown using slow evaporation solution growth technique using double distilled water as solvent. Single crystal X-ray diffraction technique revealed that lattice dimensions of grown crystal are in good agreement with the reported literature and it crystallised in monoclinic crystal system. High resolution X-ray diffraction study revealed that crystalline perfection is fairly good. Optical homogeneity and variation of birefringence across the sample cross-section was studied using birefringence interferometer. Specific heat and thermal conductivity of grown crystal was measured using photopyroelectric technique and was found to be higher than many organic and inorganic crystals. Its various mechanical properties and resistance toward deformation was examined using nano-indentation technique. Further laser damage threshold value and phase matching angle was also measured.

Glycosyltransfer in mutants of putative catalytic residue Glu303 of the human ABO(H) A and B blood group glycosyltransferases GTA and GTB proceeds through a labile active site.

The homologous glycosyltransferases α-1,3-N-acetylgalactosaminyltransferase (GTA) and α-1,3-galactosyltransferase (GTB) carry out the final synthetic step of the closely related human ABO(H) blood group A and B antigens. The catalytic mechanism of these model retaining enzymes remains under debate, where Glu303 has been suggested to act as a putative nucleophile in a double displacement mechanism, a local dipole stabilizing the intermediate in an orthogonal associative mechanism or a general base to stabilize the reactive oxocarbenium ion-like intermediate in an SNi-like mechanism. Kinetic analysis of GTA and GTB point mutants E303C, E303D, E303Q and E303A shows that despite the enzymes having nearly identical sequences, the corresponding mutants of GTA/GTB have up to a 13-fold difference in their residual activities relative to wild type. High-resolution single crystal X-ray diffraction studies reveal, surprisingly, that the mutated Cys, Asp and Gln functional groups are no more than 0.8 Å further from the anomeric carbon of donor substrate compared to wild type. However, complicating the analysis is the observation that Glu303 itself plays a critical role in maintaining the stability of a strained "double-turn" in the active site through several hydrogen bonds, and any mutation other than E303Q leads to significantly higher thermal motion or even disorder in the substrate recognition pockets. Thus, there is a remarkable juxtaposition of the mutants E303C and E303D, which retain significant activity despite disrupted active site architecture, with GTB/E303Q, which maintains active site architecture but exhibits zero activity. These findings indicate that nucleophilicity at position 303 is more catalytically valuable than active site stability and highlight the mechanistic elasticity of these enzymes.

Polaron-induced lattice distortion of (In,Ga)As/GaAs quantum dots by optically excited carriers

We report on a high resolution x-ray diffraction study unveiling the effect of carriers optically injected into (In,Ga)As quantum dots on the surrounding GaAs crystal matrix. We find a tetragonal lattice expansion with enhanced elongation along the [001] crystal axis that is superimposed on an isotropic lattice extension. The isotropic contribution arises from excitation induced lattice heating as confirmed by temperature dependent reference studies. The tetragonal expansion on the femtometer scale is tentatively attributed to polaron formation by carriers trapped in the quantum dots.

Vertically aligned ZnO nanorods of high crystalline and optical quality grown by dc reactive sputtering

ZnO nanorods were grown on Si and quartz substrates by direct current reactive magnetron sputtering of metallic zinc target in argon–oxygen ambient, without the use of any seed layer or catalyst. A combination of top-down and cross-sectional scanning electron microscopy studies have shown that the substrate temperature critically controls the growth behavior and morphology of ZnO films, eventually resulting in the growth of well aligned and separated ZnO nanorods at substrate temperature of ∼750 °C. High resolution x-ray diffraction studies of ZnO nanorods grown at 750 °C have shown that the nanorods are highly c-axis oriented and vertically aligned perpendicular to both Si and quartz substrates, and display small values of tilt and micro-strain, particularly in the case of Si substrate (1.26° and 4 × 10−4, respectively). Cross-sectional transmission electron microscopy of ZnO nanorods demonstrates their single-crystalline nature and growth along [0002] direction. Room temperature photoluminescence spectra of ZnO nanorods display extremely high near-band-edge emission and weak defect emission due to point defects, compared to that of the ZnO films grown at lower substrate temperatures. The drastic enhancement of near-band-edge emission of ZnO nanorods (over two orders of magnitude) and strong suppression of defect emission are attributed to their high crystalline quality and absence of interface defects due to lateral coalescence.

Structural and photoluminescence properties of tin oxide and tin oxide: C core–shell and alloy nanoparticles synthesised using gas phase technique

In the present study, we report a controlled growth of tin oxide and tin oxide: carbon nanoparticles by an integrated method comprising of the gas phase agglomeration, electrical mobility based size selection, and in–flight sintering steps. The effect of in-flight sintering temperature and variation in growth environment (N2, H2 and O2) during nanoparticle formation, morphology and composition has been investigated by carrying out High Resolution Transmission Electron microscopy and X-Ray diffraction studies. The results highlight the novelty of the present technique to grow alloy and core-shell nanoparticles in which the stoichiometery (x) of SnOx and the mode of incorporation of carbon into the tin oxide lattice (alloy or core-shell structure), along with well-defined size can be controlled independently. Detailed Photoluminescence (PL) studies of well sintered monocrystalline SnO, SnOx and SnO2 nanoparticles along with SnOx:C and SnO2:C alloy and C@SnO core-shell nanoparticle has been carried out. The shift in the position and nature of PL peaks due to band edge, Sn interstitials and oxygen vacancy defect level energy states has been understood as a function of stoichiometery and nanoparticle structure (alloy and core-shell). These results suggest the possibility of tailoring the position of these levels by controlling the size, composition and alloying which is potentially important for gas sensing, photoconductivity and photo-electrochemical applications.

Novel nitrogen/gallium precursor [Ga(bdma)H2] for MOVPE

Dilute nitrogen (N) containing III/V semiconductors are promising candidates for solar cell and laser applications. The N incorporation efficiency of 1,1-dimethylhydrazine (UMDHy) in metal organic vapor phase epitaxy (MOVPE), however, happens to be only in the one percentage range and below. This leads to an extremely high offer of UDMHy in the MOVPE reactor and, therefore, a drastic change in the growth conditions. Furthermore, the device efficiency of dilute nitride materials is currently hampered by carbon (C) incorporation, which is believed to be incorporated either jointly with the N from the dimethylamine radical of the UMDHy or from short hydrocarbon radicals originating from the decomposition of the other metal organics. Therefore, this work presents a novel N precursor N,N'-Bis(dimethylamino)acetamidinato-galliumdihydride [Ga(bdma)H2], which provides not only N but also gallium (Ga) during MOVPE. The direct N–Ga bond in this molecule might facilitate the N incorporation and hence increase the efficiency. For a systematic N incorporation study Ga(NAs)/GaAs heterostructures were grown by MOVPE. The N content was determined via high resolution X-ray diffraction and photoluminescence (PL) studies. Good structural quality and as grown room temperature PL were obtained. It will be also shown that the N incorporation efficiency in GaAs using [Ga(bdma)H2] is significantly higher than for growths using UDMHy under comparable conditions, making this class of molecules promising candidates for the growth of dilute nitride materials.

Growth and X-ray Diffraction Study and Specific Features of Thermal Expansion of Ba3NbFe3Si2O14 Single Crystal from the Langasite Family

Ba3NbFe3Si2O14 single crystals of promising multiferroic properties from the langasite family have been grown by floating zone melting. The accurate high-resolution X-ray diffraction studies of this crystal were performed on a diffractometer with a two-dimensional CCD detector at 293 and 90.5 K. To compensate systematic measurement errors, two data sets were obtained independently for different sample orientations at each temperature. The structure refinement was performed based on averaged data sets with the following results: space group P321, Z = 1; a = 8.52421(8), c = 5.23372(5) A at 293 K; and a = 8.5211(2), c = 5.2243(7) A, at 90.5 K. The R factors of the model structure refinement were found to be R/wR = 1.15/1.29% for 4396 independent reflections at 293 K, and R/wR = 1.13/1.35% for 4203 reflections at 90.5 K. A displacement of magnetic ion Fe3+ in the 3f site was found with reducing temperature. It was also established from comparison of the structures of Ba3NbFe3Si2O14 and Ba3TaFe3Si2O14 that the...