Schottky junction devices by using bio-molecule DNA template-based one dimensional CdS-nanostructures.

Creating a well-defined nanostructure through de-oxyribo nucleic acid (DNA)-nanotechnology, and specifically the development of metal/inorganic semiconductor junctions on DNA-assembled nanostructures, is an emerging research area. Herein, we investigate the electrical properties of biomolecule DNA-template based one-dimensional nanowires (NWs)-CdS/Au and without-template based nanoparticles (NPs)-CdS/Au devices grown on the Indium Tin Oxide (ITO) glass substrates. More importantly, the NWs-CdS/Au device displays a dramatic augmentation of current flow and also a striking change in threshold voltage (~55 mV) in comparison to NPs (~190 mV) and reported bulk-CdS/Au (~680 mV) devices. Albeit the manifestation of non-linear/asymmetric current-voltage (I-V) characteristic establishes the CdS/Au junction as Schottky device, but captivatingly, the large ideality factor of about 24 found in NWs-CdS/Au device could be due to the DNA-assembled based organic process CdS-semiconductor. Capacitance-voltage (C-V) measurements of the NWs-CdS/Au divulge a remarkable hump-like feature at lower frequency owing to the frequency dispersion effect. In contrast, the effect appears to be enfeebled with increasing frequency. We conjecture that the density of surface/interface traps materialises at the interface of nanostructures-CdS/metal-Au results in the changes in underlying electrical properties. The observation of significant differences in the electrical properties of DNA-assembled NWs-based Schottky junctions could possibly be helpful for the fabrication of more sophisticated and higher multispecificity biosensors for medical applications.

Augmentation of the step-by-step Energy-Scanning EXAFS beamline BL-09 to continuous-scan EXAFS mode at INDUS-2 SRS.

An innovative scheme to carry out continuous-scan X-ray absorption spectroscopy (XAS) measurements similar to quick-EXAFS mode at the Energy-Scanning EXAFS beamline BL-09 at INDUS-2 synchrotron source (Indore, India), which is generally operated in step-by-step scanning mode, is presented. The continuous XAS mode has been implemented by adopting a continuous-scan scheme of the double-crystal monochromator and on-the-fly measurement of incident and transmitted intensities. This enabled a high signal-to-noise ratio to be maintained and the acquisition time was reduced to a few seconds from tens of minutes or hours. The quality of the spectra (signal-to-noise level, resolution and energy calibration) was checked by measuring and analysing XAS spectra of standard metal foils. To demonstrate the energy range covered in a single scan, a continuous-mode XAS spectrum of copper nickel alloy covering both Cu and Ni K-edges was recorded. The implementation of continuous-scan XAS mode at BL-09 would expand the use of this beamline in in situ time-resolved XAS studies of various important systems of current technological importance. The feasibility of employing this mode of measurement for time-resolved probing of reaction kinetics has been demonstrated by in situ XAS measurement on the growth of Ag nanoparticles from a solution phase.

Investigation of alterations in multifractality in optical coherence tomographic images of in vivo human retina.

Optical coherence tomography (OCT) enables us to monitor alterations in the thickness of the retinal layer as disease progresses in the human retina. However, subtle morphological changes in the retinal layers due to early disease progression often may not lead to detectable alterations in the thickness. OCT images encode depth-dependent backscattered intensity distribution arising due to the depth distributions of the refractive index from tissue microstructures. Here, such depth-resolved refractive index variations of different retinal layers were analyzed using multifractal detrended fluctuation analysis, a special class of multiresolution analysis tools. The analysis extracted and quantified microstructural multifractal information encoded in normal as well as diseased human retinal OCT images acquired

Annealing effects on microstructure and laser-induced damage threshold of HfO2/SiO2 multilayer mirrors.

HfO2/SiO2 periodic multilayer high reflection mirrors have been prepared by a reactive electron-beam evaporation technique. The deposited mirrors were annealed in the temperature range from 300°C to 500°C. The effects of annealing on optical, microstructural, and laser-induced damage characteristics of the mirrors have been investigated. The high reflection band of the mirror shifts toward a shorter wavelength with increasing annealing temperature. As-deposited and annealed mirrors show polycrystalline structure with a monoclinic phase of HfO2. Crystalinity and grain size increase upon annealing. The laser-induced damage threshold (LIDT) has been assessed using a 532 nm pulsed laser at a pulse width of 7 ns. The LIDT value of the multilayer mirror increases from 44.1 J/cm2 to 77.6 J/cm2 with annealing up to 400°C. The improvement of LIDT with annealing is explained through oxygen vacancy defects as well as grain-size-dependent thermal conductivity. Finally, the observed laser damage morphology, such as circular scalds and ablated multilayer stacks with terrace structure, are analyzed.

Optical properties and laser damage threshold of HfO(2)-SiO(2) mixed composite thin films.

HfO(2)-SiO(2) mixed composite thin films have been deposited on fused silica substrate by co-evaporation of HfO(2) and SiO(2) through the reactive electron-beam evaporation technique. The composition-dependent refractive index and the absorption coefficient have been analyzed using different effective medium approximation (EMA) models in order to evaluate the suitability of these models for such mixed composite thin films. The discrepancies between experimentally determined and EMA-computed values are explained through microstructural and morphological evolutions observed in these mixed composite films. Finally, the dependence of the laser damage threshold as a function of silica content has been investigated, and the improved laser-induced damage threshold for films having more than 80% silica content has been explained through the defect-assisted multiphoton ionization process.

Postanalyses of an optical multilayer interference filter using numerical reverse synthesis and Rutherford backscattering spectrometry.

Post nondestructive analyses of an all-dielectric multilayer Fabry-Perot interference filter developed through a reactive electron beam deposition process have been carried out through numerical reverse engineering of transmission spectra, Rutherford backscattering spectroscopy and quartz crystal monitoring data to derive multilayer geometry, deposited layer thicknesses, densities, refractive indices, compositions, and stoichiometry. These techniques are collectively used to fulfill the missing links with complementary and some supplementary information to inverse synthesize the multilayer geometry. During this investigation it is distinctly understood that the factors associated with real-time deposition have significantly influenced the microscopic parameters, namely, the densities and refractive indices of TiO2 and SiO2 layers. This in turn influenced the layers' geometric (physical) thicknesses during automated quarter-wave optical layer monitoring and consequently affected the experimental spectral characteristics. The role of oxygen has been observed to be significant in controlling the mass densities of these refractory oxide layers. It is further noticed that the layer density values have been significantly perturbed whether the associated TiO2 or SiO2 oxide dielectric films are substoichiometric (oxygen-deficient), stoichiometric, or superstoichiometric (oxygen-enriched).