Modulation of intrinsic defects in vertically grown ZnO nanorods by ion implantation.

Intrinsic defects created by chemically inert gas (Xe) ion implantation in vertically grown ZnO nanorods are studied by optical and X-ray absorption spectroscopy (XAS). The surface defects produced due to dynamic sputtering by ion beams control the fraction of O and Zn with ion fluence, which helps in tuning the optoelectronic properties. The forbidden Raman modes related to Zn interstitials and oxygen vacancies are observed because of the weak Fröhlich interaction, which arises due to disruption of the long-range lattice order. The evolution of the lattice disorder is identified by O K-edge and Zn K-edge scans of XAS. The hybridization strength between the O 2p and Zn 4p states increases with ion fluence and modulates the impact of intrinsic defects. The ion irradiation induced defects also construct intermediate defects bands which reduce the optical bandgap. Density functional theory (DFT) calculations are used to correlate the experimentally observed trend of bandgap narrowing with the origin of electronic states related to Zn interstitial and O vacancy defects within the forbidden energy gap in ZnO. Our finding can be beneficial to achieve enhanced conductivity in ZnO by accurately varying the intrinsic defects through ion irradiation, which may work as a tuning knob to control the optoelectronic properties of the system.

Phase evolution in thermally annealed Ni/Bi multilayers studied by X-ray absorption spectroscopy.

The thin films of Ni and Bi are known to form NiBi3 and NiBi compounds spontaneously at the interface, which become superconducting below 4.2 K and show ferromagnetism either intrinsically or due to Ni impurities. Formation of NiBi3 and NiBi is a slow diffusion reaction, which means the local environment around Ni and Bi atoms may vary with time and temperature. In this report, we assess the feasibility of using X-ray Absorption Spectroscopy (XAS) as a tool to track the changes in local bonding environment in NiBi3 and NiBi. Thermal annealing at temperatures up to 500 °C was used to induce changes in the local environment in NiBi3 system. Consequent decomposition of NiBi3 into NiO and Bi has been tracked through changes in structural and magnetization behavior, which matched well with the findings of XAS. In addition, the magnetic hysteresis measurements indicated that NiO should be the dominant phase when NiBi3 is annealed at 500 °C. This was corroborated from XAS and was found to be >90%. The shift in K-edge of Ni in annealed samples was attributed to increasing charge state on Ni atom, which was ascertained by Bader charge analysis using Density Functional Theory (DFT). This study correlating macroscopic properties of NiBi3 with local bonding environment of the system indicates that XAS can be a very reliable tool for studying dynamics of diffusion in the NiBi3 system.

Interface of GO with SnO2 quantum dots as an efficient visible-light photocatalyst.

Graphene oxide (GO) with beneficial functional groups regulates the surface chemistry for catalytic applications. However, the low electrical conductivity of GO invokes further treatments that compromise the above-valued properties. We report an interfacial engineering of GO decorated with SnO2 quantum dots (QDs) for the visible-light-driven catalysis of dye degradation. Retention of beneficial functional features of GO and QDs in the GO-SnO2 composite is established by using TEM, FTIR, and Raman spectroscopy techniques. Further, investigations with EXAFS and lifetime-measurements provide the local structure and defects distributions in QDs which are correlated with the improved conductivity. PL and electrochemical impedance spectroscopic measurements help unraveling the charge-transfer across the interface of the GO-SnO2 composite. The unique ability of ∼94% degradation of MB using only 0.5 mg of GO-SnO2 catalyst within half an hour under the visible light is demonstrated for the first time with insights on the photocatalytic mechanism.

Structural studies of spray pyrolysis synthesized oxygen deficient anatase TiO2 thin films by using X-ray absorption spectroscopy.

The present work focuses on synthesis and X-ray absorption studies of single phase oxygen deficient anatase TiO2 thin films. These films are prepared in a two-step method viz. the synthesis of near stoichiometric anatase TiO2 films using an open atmospheric spray pyrolysis method followed by vacuum annealing at their corresponding synthesis temperatures (Ts = 450 °C, 500 °C) for different time durations (t = 2, 4, 6, 8 hours). XRD and Raman studies of these films ascertained the formation and retention of the anatase phase post annealing, indicating that there was no phase change due to prolonged annealing. Extended X-ray absorption spectra (EXAFS) and X-ray absorption near edge spectra (XANES) revealed the presence of an oxygen vacancy and its effect on the local co-ordination. The co-ordination number obtained from EXAFS analysis revealed that the number density of the oxygen vacancy is higher in the case of thin films synthesized at 450 °C than in the case of the films synthesized at 500 °C. As the oxygen vacancy leads to changes in local co-ordination, which in turn have a profound effect on the pre-edge features of the X-ray absorption spectra (XAS), theoretically simulated XAS spectra of pure anatase TiO2 and oxygen deficient anatase TiO2 were generated using FEFF and were found to match with the experimentally observed spectra. In addition, the ambiguities in whether a change in the metal-oxygen bond length has any effect on the pre-edge features or not were delineated in the present study by comparing the pre-edge peak positions of the oxygen deficient TiO2 films. Our results matched with those of some of the researchers who have studied the rutile phase TiO2, wherein it was concluded that in the case of the titanium-oxygen system, the mean Ti-O bond length does have an effect on the pre-edge peak position. It was observed that as the Ti-O mean bond length increases, the pre-edge peak positions shift towards lower energy, which is in concurrence with the literature available for other Ti-O systems with similar geometry. The second pre-edge peak intensity, which is a measure of disorder, is higher for TiO2450 °C-2 h and TiO2500 °C-2 h thin films. This is attributed to the annealing effect, which suggests that TiO6 octahedrons are the most disordered for thin films annealed for 2 h and become more ordered upon annealing for longer times.

Local crystal structure in the vicinity of Cr in doped AlN thin films studied by X-ray absorption spectroscopy.

This article reports the detailed X-ray absorption spectroscopy (XAS) study of Al1-xCrxN (x = 4, 6, 11%) thin films synthesized by the reactive magnetron co-sputtering technique. All these films were crystallized with a hexagonal wurtzite structure with preferential orientation along the a-axis without the formation of any secondary phases. Surface chemical analysis to evaluate the Cr concentration was carried out using X-ray photoelectron spectroscopy. The study confirmed the presence of AlN and Cr in bonding with N. The local crystal structure around the Cr dopant in the as-synthesized and annealed thin films has been analyzed by both the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) techniques. From XAS, it was found that Cr replaced the Al atom in the AlN lattice and led to a localized CrN species with distorted tetrahedral AlN in the absence of Cr clustering. The bond lengths of (Cr-N)ax, (Cr-N)bs and Cr-Al, extracted from the EXAFS fitting, were found to decrease with the Cr concentration for both the as-synthesized and annealed thin films due to the enhancement of p-d hybridization between the dopant and the host atoms. However, in the annealed 11% Cr film, the bond lengths are larger than the other and tend to match the Cr-N geometry in CrN.

Ketamine, Transcranial Magnetic Stimulation, and Depression Specific Yoga and Mindfulness Based Cognitive Therapy in Management of Treatment Resistant Depression: Review and Some Data on Efficacy.

Depression affects about 121 million people worldwide and prevalence of major depressive disorder (MDD) in US adults is 6.4%. Treatment resistant depression (TRD) accounts for approximately 12-20% of all depression patients and costs $29-$48 billion annually. Ketamine and repetitive transcranial magnetic stimulation (rTMS) have useful roles in TRD, but their utility in long term is unknown. As per the latest literature, the interventions using Yoga and meditation including the mindfulness based cognitive therapy (MBCT) have been useful in treatment of depression and relapse prevention. We present a review of rTMS, ketamine, and MBCT and also report efficacy of a depression specific, innovative, and translational model of Yoga and mindfulness based cognitive therapy (DepS Y-MBCT), developed by the first author. DepS Y-MBCT as an adjunctive treatment successfully ameliorated TRD symptoms in 27/32 patients in an open label pilot trial in TRD patients. Considering the limitations of existing treatment options, including those of ketamine and rTMS when used as the sole modality of treatment, we suggest a "tiered approach for TRD" by combining ketamine and rTMS (alone or along with antidepressants) for rapid remission of acute depression symptoms and to use DepS Y-MBCT for maintaining remission and preventing relapse.

Physico-chemical processes and kinetics of sunlight-induced hydrophobic ↔ superhydrophilic switching of transparent N-doped TiO2 thin films.

Sunlight-responsive anatase N-doped TiO2 thin films undergoing reversible and switchable hydrophobic to superhydrophilic transition were synthesized by ultrasonic spray pyrolysis in a single step. Film thickness, roughness, surface morphology, crystal structure, composition, band gap, and wetting properties were studied using surface profilometry, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis spectroscopy, and water contact angle measurements, respectively. Surface X-ray photoelectron spectroscopy before and after sunlight irradiation revealed the major physicochemical process responsible for the hydrophobic → hydrophilic transition as surface hydroxylation and that responsible for hydrophilic → superhydrophilic transition as destruction of surface adsorbed organic species. The kinetic rates of the hydrophobic → superhydrophilic transition under sunlight and superhydrophilic → hydrophobic transition when kept under dark are found to be 0.215 min(-1) and 2.03 × 10(-4) min(-1), respectively.

Development and validation of a HPTLC method for simultaneous estimation of lornoxicam and thiocolchicoside in combined dosage form.

AIM: To develop a simple, precise, rapid and accurate HPTLC method for the simultaneous estimation of Lornoxicam (LOR) and Thiocolchicoside (THIO) in bulk and pharmaceutical dosage forms. MATERIALS AND METHODS: The separation of the active compounds from pharmaceutical dosage form was carried out using methanol:chloroform:water (9.6:0.2:0.2 v/v/v) as the mobile phase and no immiscibility issues were found. The densitometric scanning was carried out at 377 nm. The method was validated for linearity, accuracy, precision, LOD (Limit of Detection), LOQ (Limit of Quantification), robustness and specificity. RESULTS: The Rf values (±SD) were found to be 0.84 ± 0.05 for LOR and 0.58 ± 0.05 for THIO. Linearity was obtained in the range of 60-360 ng/band for LOR and 30-180 ng/band for THIO with correlation coefficients r(2) = 0.998 and 0.999, respectively. The percentage recovery for both the analytes was in the range of 98.7-101.2 %. CONCLUSION: The proposed method was optimized and validated as per the ICH guidelines.

Psychiatric manifestations of Wilson's disease and treatment with electroconvulsive therapy.

Wilson's disease is a rare genetic disorder involving the liver and brain, with onset frequently in adolescence. Psychiatric symptoms are often the first manifestation of the disease and can obscure the diagnosis. Although such patients are more commonly seen in neurological and hepatological settings, mental health professionals must keep in mind a high level of suspicion, once first presentations may be of psychiatric nature. We present the case of a 20-year-old female patient who initially presented with psychiatric symptoms. The neuropsychiatric manifestations and treatment of this patient with electroconvulsive therapy is presented.