Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
3 results
Search Results
Item Ultrafast nonlinear optical properties of dye-doped PMMA discs irradiated by 40 fs laser pulses(2009) Xia, Y.; Jiang, Y.; Fan, R.; Dong, Z.; Zhao, W.; Chen, D.; Umesh, G.The two-photon absorption (TPA) characteristics of PMMA discs doped with three different dyes were studied using an fs-pulsed Ti-Sapphire laser as the pump source, and employing the open-aperture Z-scan technique. TPA cross-sections obtained for PMMA doped with the dyes PM597, DCM and rhodamine 6G-rhodamine B (co-doped) were found to be equal to 24.7, 33.3 and 32.3 GM, respectively (1 GM=10-50 cm4 s phot-1 mol-1). Furthermore, two-photon fluorescence was measured for the samples containing DCM and rhodamine 6G-rhodamine B (co-doped). Compared to the one-photon fluorescence spectrum, the peaks in the two-photon fluorescence spectrum were red shifted and the extent of red shift increased with increasing doping concentration. We have also observed that the red shift in the two-photon fluorescence peak of the samples in the solid form is much larger than that in the solution state. This phenomenon could be explained by a twisted intra-molecular charge transfer model. © 2009 Elsevier Ltd. All rights reserved.Item Memory type switching behavior of ternary Ge20Te80-xSnx (0 x 4) chalcogenide compounds(Institute of Physics Publishing michael.roberts@iop.org, 2016) Fernandes, B.J.; Sridharan, K.; Pumlianmunga, P.; Ramesh, K.; Udayashankar, N.K.Chalcogenide compounds have gained huge research interest recently owing to their capability to transform from an amorphous to a crystalline phase with varying electrical properties. Such materials can be applied in building a new class of memories, such as phase-change memory and programmable metallization cells. Here we report the memory type electrical switching behavior of a ternary chalcogenide compound synthesized by doping Tin (Sn) in a germanium-telluride (Ge20Te80) host matrix, which yielded a composition of Ge20Te80-xSnx (0 x 4). Results indicate a remarkable decrease in the threshold switching voltage (V T) from 140 to 61 V when the Sn concentration was increased stepwise, which is attributed to the domination of the metallicity factor leading to reduced amorphous network connectivity and rigidity. Variation in the threshold switching voltage (V T) was noticed even when the sample thickness and temperature were altered, confirming that the memory switching process is of thermal origin. Investigations using x-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed the formation of a crystalline channel that acts as the conduction path between the two electrodes in the switched region. Structural and morphological studies indicated that Sn metal remained as a micro inclusion in the matrix and hardly contributed to the rigid amorphous network formation in Ge20Te80-xSnx. Memory type electrical switching observed in these ternary chalcogenide compounds synthesized herein can be explored further for the fabrication of phase-change memory devices. © 2016 IOP Publishing Ltd.Item Solar-metallicity gas in the extended halo of a galaxy at z ? 0.12(Oxford University Press, 2020) Pradeep, J.; Sankar, S.; Umasree, T.M.; Narayanan, A.; Khaire, V.; Gebhardt, M.; Sameer; Charlton, J.C.We present the detection and analysis of a weak low-ionization absorber at z = 0.121 22 along the sightline of the blazar PG 1424+240, using spectroscopic data from both HST/COS and STIS. The absorber is a weak Mg II analogue, with an incidence of weak C II and Si II, along with multicomponent C IV and O VI. The low ions are tracing a dense (nH ? 10?3 cm?3) parsec-scale cloud of solar or higher metallicity. The kinematically coincident higher ions are either from a more diffuse (nH ? 10?5–10?4 cm?3) photoionized phase of kiloparsec-scale dimensions or are tracing a warm (T ? 2 × 105 K) collisionally ionized transition temperature plasma layer. The absorber resides in a galaxy overdense region, with 18 luminous (>L?) galaxies within a projected radius of 5 Mpc and velocity of 750 km s?1. The multiphase properties, high metallicity, and proximity to a 1.4L? galaxy, at ? ? 200 kpc and separation |v| = 11 km s?1, favour the possibility of the absorption tracing circumgalactic gas. The absorber serves as an example of weak Mg II–O VI systems as a means to study multiphase high-velocity clouds in external galaxies. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society