Thickness induced metal to insulator charge transport and unusual hydrogen response in granular palladium nanofilms.

This work reports a systematic study of the evolution of charge transport properties in granular ultra-thin films of palladium of thicknesses varying between 6 nm and 2 nm. While the films with thickness >4 nm exhibit metallic behaviour, that at 3 nm thickness undergoes a metal-insulator transition at 19.5 K. In contrast, the 2 nm thick film remained insulating at all temperatures, with transport following Mott's variable range hopping. At room temperature, while the thicker films exhibit resistance decrease upon H2 exposure, the insulating film showed an anomalous initial resistance increase before switching to a subsequent decrease. The nanostructure dependent transport and the ensuing H2 response is modeled on a percolation model, which also explores the relevance of film thickness as a macroscopic control parameter to engineer the desired system response in granular metal films.

Tomonaga-Luttinger liquid and quantum criticality in spin- 1 2 antiferromagnetic Heisenberg chain C 14 H 18 CuN 4 O 10 via Wilson ratio.

The ground state of a one-dimensional spin- 1 2 uniform antiferromagnetic Heisenberg chain (AfHc) is a Tomonaga-Luttinger liquid which is quantum-critical with respect to applied magnetic fields up to a saturation field µ 0 H s beyond which it transforms to a fully polarized state. Wilson ratio has been predicted to be a good indicator for demarcating these phases [Phys. Rev. B 96, 220401 (2017)]. From detailed temperature and magnetic field-dependent magnetization, magnetic susceptibility and specific heat measurements in a metalorganic complex and comparisons with field theory and quantum transfer matrix method calculations, the complex was found to be a very good realization of a spin- 1 2 AfHc. Wilson ratio obtained from experimentally obtained magnetic susceptibility and magnetic contribution of specific heat values was used to map the magnetic phase diagram of the uniform spin- 1 2 AfHc over large regions of phase space demarcating Tomonaga-Luttinger liquid, saturation field quantum critical, and fully polarized states. Luttinger parameter and spinon velocity were found to match very well with the values predicted from conformal field theory.

Feedback based gas sensing setup for ppb to ppm level sensing.

Sensing and quantification of gas at low concentrations is of paramount importance, especially with highly flammable and explosive gases such as hydrogen. Standard gas sensing setups have a limit of measuring ultra-low concentrations of few parts per billion unless the external gas cylinders are changed to ones with low concentrations. In this work, we describe a home-built resistance based gas sensing setup that can sense across a wide concentration range, from parts per billion to parts per million, accurately. This was achieved using two dilution chambers: a process chamber and a feedback assembly where a part of the output gas from the dilution chamber is fed back to the inlet mass flow controller, enabling enhanced dilutions without increasing the number of mass flow controllers. In addition, the gas-sensing setup can measure across a large temperature range of 77-900 K. The developed setup was then calibrated using palladium thin films and ZnO nanoparticle thin films. The setup was tested for reproducibility, concentration response, temperature response, etc. Corresponding sensitivity values were calculated and found to be in good agreement with published values, validating our setup design.

Charge transport variation from Bloch-Grüneisen to Mott variable range hopping and transport change due to hydrogenation in Palladium thin films.

We report a systematic investigation of the differences in charge transport mechanism in ultra-thin nano-island like films of palladium with thickness varying between 5 nm and 3 nm. The thicker films were found to be metallic in a large temperature range with a dominant Bloch-Grüneisen mechanism of charge transport arising due to electron-acoustic phonon scattering. These films were also found to exhibit an additional electron-magnon scattering. At temperatures below 20 K, the two films displayed a metal-insulator transition which was explained using Al'tshuler's model of increased scattering in disordered conductors. The thinner films were insulating and were found to exhibit Mott's variable range hopping mechanism of charge transport. The thinnest film showed a linear decrease of resistance with an increase in temperature in the entire temperature range. The island-like thin films were found to display very different response to hydrogenation at room temperature where the metallic films were found to display a decrease of resistance while the insulating films were found to have an increase of resistance. The decrease of resistance was ascribed to a hydrogen induced lattice expansion in the thin films that were at the percolation threshold while the resistance increase to an increase in work function of the films due to an increased adsorption of the hydrogen atoms at the surface sites of palladium.

Orthorhombic crystal structure and oxygen deficient cluster distribution model for YBa2Cu3-xAlxO6+δ superconductor.

Single crystal x-ray diffraction measurements on both as-grown as well as oxygenated single crystals of an aluminium doped high temperature superconductor YBa2Cu3-xAlxO6+δ revealed the crystal structure to be orthorhombic with space group Pmmm, in contrast to, tetragonal crystal structures corresponding to space group P4/mmm, previously reported for as-grown YBa2Cu3-xAlxO6+δ, and conflicting structures on oxygenated YBa2Cu3-xAlxO6+δ. The orthorhombic crystal structure was confirmed by powder x-ray diffraction that showed the presence of two peaks corresponding to (020) and (200) reflections associated with orthorhombic structures of space group Pmmm, instead of a single (200) reflection corresponding to tetragonal crystal structures with space group P4/mmm. All the as-grown crystals were found to be superconducting. An oxygen-vacancy cluster distribution model is proposed to explain the differences in the obtained magnetisation hysteresis loop and the broad superconducting transition temperature. The model proposes the existence of two oxygen deficient clusters of (Al-..-Cu-O-Cu)n and (Cu-O-Cu-..)n juxtaposed with each other whose number and size vary as the as-grown single crystals of YBa2Cu3-xAlxO6+δ are subjected to oxygenation. X-ray photoelectron spectroscopy measurements showed the existence of two distinct peaks in each of the spectrum of O, Cu, Y and Ba in YBa2Cu3-xAlxO6+δ crystals corresponding to the two different types of clusters. The relative intensities of each XPS peak was found to decrease in the oxygenated crystals as compared to the as-grown ones confirming the change in the number and size of clusters in the as-grown crystals after oxygenation.

Investigations of vibrational spectra and bioactivity of novel anticancer drug N-(6-ferrocenyl-2-naphthoyl)-gamma-amino butyric acid ethyl ester.

The bioactivity of compounds is mainly dependent on molecular structure and the present work aims to explore the bonding features responsible for biological activity of novel anticancer drug N-(6-ferrocenyl-2-naphthoyl)-gamma-amino butyric acid ethyl ester (FNGABEE). In the present study, we investigate the molecular structural properties of newly synthesized title compound through experimental and quantum chemical studies. The detailed vibrational analysis has been performed using FT IR and FT Raman spectrum, aided by DFT computed geometry, vibrational spectrum, Eigen vector distribution and PED, at B3LYP/6-311++G(d,p) level. The resonance structure of naphthalene, different from that of benzene, revealed by molecular structure has been investigated using CC and CC stretching modes. The proton transfer in amide has been analyzed to obtain spectral distinction between different carbonyl and CN groups which point to the reactive sites responsible for binding with DNA and bovine serum albumin (BSA). The spectral distinction between eclipsed and staggered form of ferrocene has been analyzed. The molecular docking of FNGABEE with BSA and DNA has been performed to find the strength of binding and the moieties responsible for the interactions. The experimental binding studies of FNGABEE with BSA and DNA has been performed using UV absorption spectroscopy and fluorometric assay, to find the nature and strength of binding.

Evidence of gap anisotropy in superconducting YNi2B2C using directional point-contact spectroscopy.

We present a study of the anisotropy in the superconducting energy gap in a single crystal of YNi2B2C (T(c) approximately 14.6 K) using directional point-contact spectroscopy. The superconducting energy gap at 2.7 K, when measured for I||c, is 4.5 times larger than that for I||a. The energy gaps in the two directions also have different temperature dependences. Our results support a scenario with s + g like symmetry.