Showing papers by "Samit K. Ray published in 2007"
TL;DR: In this article, the growth of Cadmium sulfide (CdS) nanowires on porous alumina template has been investigated using dc electrochemical method, and the micro-structural study of the CdS nano-structures has been carried out using atomic force microscopy, field-emission scanning electron microscopy and transmission electron microscope.
71 citations
TL;DR: In this paper, a two-cell chemical method using a porous alumina template was used to grow CdS nanowires with diameters ranging from 100 to 110 nm and 50 to 60 nm for two different templates.
Abstract: CdS nanowires have been grown by a two-cell chemical method using a porous alumina template. Field-emission scanning and transmission electron microscopy show the growth of nanowires of diameters ranging from 100 to 110 nm and 50 to 60 nm for two different templates. The surface topography of the template filled with CdS has been studied using atomic force microscopy. The microstructural properties of the nanowires have been studied by high resolution x-ray diffraction. UV–visible spectroscopy of nanowires exhibits a clear blue shift due to quantum confinement. The photoluminescence spectra show green emission due to the defect states of the nanowires and the resonance Raman spectra revealed the stoichiometric phase of CdS with good crystallinity.
51 citations
TL;DR: Pentacene based junctions with Al on both p-Si(1 0 0) and indium tin oxide (ITO) substrates have been analyzed using impedance spectroscopy (100 Hz-20 MHz) and dc-current versus voltage measurements.
Abstract: Pentacene based junctions with Al on both p-Si(1 0 0) and indium tin oxide (ITO) substrates have been analysed using impedance spectroscopy (100 Hz–20 MHz) and dc-current versus voltage measurements. Conduction mechanisms match well with the space charge limited current model with exponential trap charge distributions. Impedance studies reveal the Schottky behaviour for both the devices. The differences between p-Si/pentacene/Al and ITO/pentacene/Al devices have been explained by modelling equivalent circuits, with one and two RC elements, respectively. The switch-over field from ohmic conduction to space charge limited conduction, charge concentration as a function of voltage and bias dependent series resistance have been estimated for both the cases.
44 citations
TL;DR: In this paper, a metal-oxide-semiconductor capacitors with a trilayer structure consisting of Ge+HfO2 layers sandwiched between HfO 2 tunnel and cap oxides were fabricated on p-Si substrates.
Abstract: Metal-oxide-semiconductor capacitors with a trilayer structure consisting of Ge+HfO2 layers sandwiched between HfO2 tunnel and cap oxides were fabricated on p-Si substrates. Ge nanocrystals embedded in SiO2 were also studied for comparison. Cross-sectional transmission electron micrographs revealed the formation of spherical shaped Ge nanocrystals. The optical and charge storage characteristics of trilayer structures were studied through photoluminescence spectroscopy and capacitance-voltage measurements, respectively. An enhancement of the charge injection capability into nanocrystals was observed for the device with HfO2 as tunnel and cap oxide. The optical emission characteristics support the carrier confinement in Ge nanocrystals embedded in oxide matrices.
43 citations
TL;DR: In this article, CdS nanocomposites have been grown in a polymer (polyvinyl alcohol) matrix using a simple chemical bath deposition process Transmission electron micrographs of nanocom composites grown at different solution temperatures revealed the formation of isolated as well as junctionlike structures.
Abstract: CdS nanocomposites have been grown in a polymer (polyvinyl alcohol) matrix using a simple chemical bath deposition process Transmission electron micrographs of nanocomposites grown at different solution temperatures revealed the formation of isolated as well as junctionlike structures X-ray and selected area electron diffraction patterns show that the nanocomposites are polycrystalline with cubic CdS phase Optical band gaps of nanocomposite films are found to decrease (326–286eV) with the increase in bath temperature from 70to90°C Photoluminescence spectra show strong green emission attributed to the Cd2+ or Cd+ ion-related recombination via moderately deep trap states The nanocomposites show an enormous enhancement of dielectric constant in polyvinyl alcohol matrix over a frequency range of 40Hz–10MHz
36 citations
TL;DR: In this paper, the formation of Ge clusters on the Si and within the SiO2 matrix, respectively, has been studied using infrared and x-ray photoelectron spectroscopy.
Abstract: Ge nanocrystals of different sizes and densities have been grown on p-Si(100) substrates by radio-frequency magnetron sputtering. We have also synthesized Ge nanocrystals embedded in a SiO2 matrix, using a suitable target, followed by post-deposition annealing at 900 °C in a N2 atmosphere. Atomic force and transmission electron micrographs revealed the formation of Ge clusters on the Si and within the SiO2 matrix, respectively. Infrared and x-ray photoelectron spectroscopy were used to study the chemical bonding in the deposited films. Raman spectra for Ge embedded in the SiO2 matrix show a peak at 300 cm−1 corresponding to the Ge–Ge phonon mode. A photoluminescence study has been performed at room temperature to detect the light emission from the Ge nanocrystals.
25 citations
TL;DR: In this article, polycrystalline Ba1−xSrxTiO3 (BST) thin films with three different compositions have been deposited by radiofrequency magnetron sputtering technique on platinum coated silicon substrates.
Abstract: Polycrystalline Ba1−xSrxTiO3 (BST) thin films with three different compositions have been deposited by radio-frequency magnetron sputtering technique on platinum coated silicon substrates. Samples with buffer and barrier layers for different film thicknesses and processing temperatures have been studied. Crystallite size of BST films has been found to increase with increasing substrate temperature. Thickness dependent dielectric constant has been studied and discussed in the light of an interfacial dead layer and the finite screening length of the electrode. Ferroelectric properties of the films have also been studied for various deposition conditions. The electrical resistivity of the films measured at different temperatures shows a positive temperature coefficient of resistance under a constant bias voltage.
24 citations
01 Mar 2007
TL;DR: Among sapropzoic nematodes, rhabditids, dorylaimids and diplogasterids are the most prominent members of soil nematode community diversity and primarily play significant role in ecosystem processes of soil for making availability of plant nutrients.
Abstract: Survey on plant and soil nematodes associated with rhizosphere of guava (Psidium guajava L.) from Baruipur, 24-Paraganas(south) and Mondouri (Haringhata) and Ghoragachha (Chakdaha), Nadia, West Bengal, India revealed the occurrence of ten genera, viz. Meloidogyne, Pratylenchus, Hoplolaimus, Rotylenchulus, Helicotylenchus, Tylenchorhynchus, Criconemoides, Xiphinema, Longidorus and Aphelenchus. Altogether thirteen species of eight plant parasitic genera identified which were Meloidogyne incognita, M. javanica, M. graminicola, Pratylenchus coffeae, P. brachyurus, Hoplolaimus indicus, Rotylenchulus reniformis, Helicotylenchus goodi, H. indicus, H. abunamai, Tylenchorhynchus mashhoodi, T. nudus and Aphelenchus avenae. The estimation of population density from rhizospheric soil indicated more number of R. reniformis (1052/200cm 3 soil) and Helicotylenchus (233/200cm 3 soil). Community analyses of plant and soil nematodes from the guava rhizosphere further revealed that R. reniformis ranked first in prominence followed by Helicotylenchus and Tylenchorhynchus. Among the less prominent plant parasitic species present as in guava rhizosphere, Pratylenchus, Meloidogyne, R. reniformis, Xiphinema and Longidorus were the potential pathogens to cause decline of yield either alone or in association with soil pathogens. Some ectoparasitic nematodes genera were also prominent members of soil nematode community but less important as plant pathogens. Among sapropzoic nematodes, rhabditids, dorylaimids and diplogasterids are the most prominent members of soil nematode community diversity and primarily play significant role in ecosystem processes of soil for making availability of plant nutrients.
22 citations
TL;DR: In this paper, a vapor-liquid-solid method has been used to study the temperature dependent growth mechanism of Ge nanostructures on Au-coated Si (100) substrates.
Abstract: A vapor-liquid-solid method has been used to study the temperature dependent growth mechanism of Ge nanostructures on Au-coated Si (100) substrates. The formation of Ge nanodots, nanorods, and nanowires has been observed at different growth temperatures. The diameter of grown nanowires is found to be varying from 40 to 80 nm and that of nanorods from 70 to 90 nm, respectively. A comparative study has been done on three types of samples using x-ray diffraction and Raman spectroscopy. Photoluminescence spectra of grown nanostructures exhibit a broad emission band around 2.6 eV due to oxide related defect states.
18 citations
TL;DR: In this article, a set of symmetric and asymmetric superlattices with ferromagnetic and ferroelectric layers were fabricated using pulsed laser ablation, and the properties of all the layers were studied.
Abstract: A set of symmetric and asymmetric superlattices with ferromagnetic $La_{0.6}Sr_{0.4}MnO_3$ (LSMO) and ferroelectric $0.7Pb(Mg_{1/3}Nb_{2/3})O_3–0.3(PbTiO_3)$ as the constituting layers was fabricated on $LaNiO_3$ coated 100 oriented $LaAlO_3$ substrates using pulsed laser ablation. The crystallinity, and magnetic and ferroelectric properties were studied for all the superlattices. All the superlattice structures exhibited a ferromagnetic behavior over a wide range of temperatures between 10 and 300 K, whereas only the asymmetric superlattices exhibited a reasonably good ferroelectric behavior. Strong influence of an applied magnetic field was observed on the ferroelectric properties of the asymmetric superlattices. Studies were conducted toward understanding the influence of conducting LSMO layers on the electrical responses of the heterostructures. The absence of ferroelectricity in the symmetric superlattice structures has been attributed to their high leakage characteristics. The effect of an applied magnetic field on the ferroelectric properties of the asymmetric superlattices indicated strong influence of the interfaces on the properties. The dominance of the interface on the dielectric response was confirmed by the observed Maxwell-Wagner-type dielectric relaxation in these heterostructures.
16 citations
TL;DR: In this article, Er3+ ions of controlled composition were incorporated into the SiO2 glasses to investigate the emission properties of the 1.54 µm line, where the size of the Ge nanocrystals varied from 5 to 10 nm.
Abstract: Ge nanocrystals embedded in bulk SiO2 glasses were prepared by the sol–gel process. Er3+ ions of controlled composition were incorporated into the glasses to investigate the emission properties of the 1.54 µm line. The size of the Ge nanocrystals was found to vary from 5 to 10 nm. XRD and Raman measurements showed the formation of crystalline Ge in SiO2 matrix. Elemental composition of Ge and Er in the samples was determined by RBS analysis. Various absorption edges in the optical spectra of the samples due to the atomic transition of Er3+ ions were detected. The samples exhibited intense emissions at 1.54 µm in the presence of Ge nanocrystals.
TL;DR: A set of symmetric and asymmetric superlattices with ferromagnetic La 0.6Sr0.4MnO3 and ferroelectric 0.7Pb(Mg0.33Nb0.67)O3 0.3(PbTiO3) as constituting layers were fabricated on LaNiO3 coated (100) oriented LaAlO3 substrates using pulsed laser ablation.
Abstract: A set of symmetric and asymmetric superlattices with ferromagnetic La0.6Sr0.4MnO3 and ferroelectric 0.7Pb(Mg0.33Nb0.67)O3 0.3(PbTiO3) as the constituting layers were fabricated on LaNiO3 coated (100) oriented LaAlO3 substrates using pulsed laser ablation. The crystallinity, magnetic and ferroelectric properties were studied for all the superlattices. All the superlattice structures exhibited a ferromagnetic behavior over a wide range of temperatures between 10K and 300K, whereas only the asymmetric superlattices exhibited a reasonably good ferroelectric behaviour. Strong influence of an applied magnetic field was observed on the ferroelectric properties of the asymmetric superlattices. Studies were conducted towards understanding the influence of conducting LSMO layers on the electrical responses of the heterostructures. The absence of ferroelectricity in the symmetric superlattice structures has been attributed to their high leakage characteristics. The effect of an applied magnetic field on the ferroelectric properties of the asymmetric superlattices indicated strong influence of the interfaces on the properties. The dominance of the interface on the dielectric response was confirmed by the observed Maxwell Wagner type dielectric relaxation in these heterostructures.
TL;DR: In this paper, Ferroelectric SrBi 2 Ta 2 O 9 (SBT) thin films were grown on p-type Si substrates by radio frequency sputtering technique and the crystallinity of the films were studied using grazing incidence X-ray diffraction pattern.
Abstract: Ferroelectric SrBi 2 Ta 2 O 9 (SBT) thin films were grown on p-type (1 0 0) Si substrates by radio frequency sputtering technique. The crystallinity of the films was studied using grazing incidence X-ray diffraction pattern. The spectra showed the films were polycrystalline with dominant orientation along (1 1 5) plane. The surface morphology was investigated by atomic force microscope. The chemical composition was studied by Rutherford back-scattering, which yielded a near stoichiometric composition of SBT. The capacitance–voltage characteristics of Al/SBT/Si capacitors measured at 100 kHz showed a hysteresis nature with a clockwise rotation and the memory window of the hysteresis loop was 0.88 V with the gate voltage ±5 V. The interface trap density was calculated by using Hills method at room temperature and a value in the order of 10 11 –10 12 eV −1 cm −2 was found depending on the crystallization temperature at midgap region.
IBM1
TL;DR: In this paper, a multi-step reactive ion etching (MS-RIE) process for silicon was developed for the fabrication of deep anisotropic, closely packed structures with vertical sidewalls.
Abstract: A multi-step reactive ion etching (MS-RIE) process for silicon was developed for the fabrication of deep anisotropic, closely packed structures with vertical sidewalls. This process used repeated cycles of etching and the replenishment of masking layers, similar to the Bosch process (Laermer and Schilp 1996 US Patent 5,498,312) [1] that is employed in specialized etching tools. The process described here, however, can be used on conventional RIE tools, and is based on the isotropic deposition of an etch-inhibiting polymer to protect sidewalls, its anisotropic removal from the bottom etch front, and a subsequent isotropic etch into deeper layers. A conventional parallel plate etcher without fast gas management, cryogenic substrate cooling, or inductively coupled plasma density enhancement, produced these steps. Each process step was optimized for the maximal etch rate, minimal mask erosion, deposition of the thinnest polymer required to protect the sidewalls, and was tailored for use with 2 µm thick photoresist as the initial mask layer. This cyclic RIE process was used to fabricate photonic devices with high aspect ratios of etched depths over 100 µm and etch widths near 1 µm.
01 Dec 2007
TL;DR: In this article, the properties of ITO/pentacene/Al diode have been investigated by current voltage, capacitance frequency, and capacitance voltage measurements in the framework of space charge limited current.
Abstract: Eelectrical properties of ITO/pentacene/Al diode have been investigated by current - voltage (I-V), capacitance - frequency (C-f), and capacitance - voltage (C- V) measurements The current-voltage characteristics at different temperatures are analyzed in the framework of space charge limited current (SCLC) model From the measured diode capacitances, it is revealed that the frequency-dependent properties are related to the localized traps in the band gap of pentacene The C-V characteristics at different test frequencies have been presented From the capacitance-voltage data the ionized acceptor density, the diffusion potential, and the width of the depletion region are calculated to be 40 x 1017 respectively
01 Dec 2007
TL;DR: The effect of annealing temperature on the structural and photoluminescence properties of nanocrystalline ZnO films deposited by sol-gel process has been investigated in this paper.
Abstract: The effect of annealing temperature on the structural as well as photoluminescence (PL) properties of the nanocrystalline ZnO films deposited by sol-gel process has been investigated The as-deposited film is amorphous in nature, and the crystallinity as well as grain sizes have been found to increase on post-deposition annealing PL intensity is greatly improved with the increase in annealing temperature, and the band gap of ZnO films is red-shifted A correlation between the structural and optical properties has been investigated in detail
01 Dec 2007
TL;DR: Using vapour-liquid-solid mechanism, the authors has grown Ge and composition modulated Ge:SnO2 nanowires on gold-coated silicon substrates with diameter distribution ranging from 30-100 nm, and length more than tens of micrometers.
Abstract: Using vapour-liquid-solid mechanism, we have grown Ge and composition modulated Ge:SnO2 nanowires on gold coated silicon substrates with diameter distribution ranging from 30-100 nm, and length more than tens of micrometers. The outer sheath of pure Ge nanowires consists of GeO2 as revealed from the XRD and TEM analyses. Raman spectra of the as-grown nanowires exhibit a blue shift, which is attributed to the compressive strain in the wires. The formed T-junction Ge:SnO2 axial nanowire heterostructure is attractive for novel optical and electronic devices.
TL;DR: In this paper, the authors reported the self-assembled growth of Ge islands of different shapes and sizes on p-Si (001) by r.f. magnetron sputtering by varying the power, growth temperature and postdeposition annealing condition.
Abstract: We report the self-assembled growth of Ge islands of different shapes and sizes on p-Si (001) by r.f. magnetron sputtering by varying the r.f. power, growth temperature and postdeposition annealing condition. The well known Stranski-Krastanov growth mechanism due to lattice mismatch between Si & Ge leads to the formation of Ge islands, similar to a more sophisticated MBE growth, albeit at a much higher pressure in our study. Ge nanocrystals embedded in SiO2 matrix have also been grown. Optical properties of nanocrystals exhibiting visible luminescence at room temperature are presented.
01 Dec 2007
TL;DR: In this article, structural and electrical properties of metal-ferroelectric-insulator-semiconductor capacitors with 280-nm-thick SrBi2Ta2O9 (SBT) ferroelectric films grown on Si as well as on Si with buffer layer (HfO2).
Abstract: We have investigated the structural and electrical properties of metal-ferroelectric-insulator-semiconductor capacitors with 280-nm-thick SrBi2Ta2O9 (SBT) ferroelectric films grown on Si as well as on Si with buffer layer (HfO2). The SBT thin films and HfO2 buffer layer were fabricated using rf magnetron sputtering method. XRD patterns revealed the formation of well crystallized SBT perovskite thin film on the HfO2 buffer layer which is evident from sharp peaks in XRD spectra. The electrical properties of the metal-ferroelectric-insulator- semiconductor (MFIS) structure were characterized by varying thickness of the HfO2 layer. The width of memory window in the capacitance-voltage curves for the MFIS structure decreased with increasing thickness of HfO2 layer. Leakage current density decreased significantly after inserting HfO2 buffer layer. This shows that the proposed Al/SrBi2Ta2O9/HfO2/Si structure ideally suitable for high performance ferroelectric memories.
TL;DR: A vapor-liquid-solid method has been used to grow Ge nanowires on Au-coated Si(100) substrates with diameters ranging from 30-80 nm.
Abstract: A vapor–liquid–solid method has been used to grow Ge nanowires on Au-coated Si(100) substrates with diameters ranging from 30–80 nm The nanowires have been found to form Y- and T-junctions along with the growth of straight nanowires of length up to 10 μm X-ray diffraction and Raman analyses support the formation of a core-sheath Ge–GeO2 structure in consistent with the observation made by transmission electron microscopy
01 Dec 2007
TL;DR: In this paper, self-assembled nano-sized Ge islands have been grown on Si (001) substrates using a solid source molecular beam epitaxy Detailed island morphological studies at different deposition temperatures and flux rate of as-grown and annealed nanocrystals are reported Both the alloy composition and in-plane strain in the grown islands were determined from high-resolution XRD and Raman study.
Abstract: Self-assembled nano-sized Ge islands have been grown on Si (001) substrates using a solid source molecular beam epitaxy Detailed island morphological studies at different deposition temperatures and flux rate of as-grown and annealed nanocrystals are reported Both the alloy composition and in-plane strain in the grown islands have been determined from high-resolution XRD and Raman study The shape and size of the grown islands and the coarsening mechanism are explicitly discussed with the help of data obtained from AFM topographic images The current-voltage characteristics of a single isolated island exhibits Coulomb blockade behaviour at room temperature
01 Dec 2007
TL;DR: In this paper, pseudomorphic Si1-xGex epitaxial layers have been grown on Si(100) at a low temperature using molecular beam epitaxy and a 5-period SiGe/Si multiple quantum well structure has also been grown for infrared photodetector applications.
Abstract: Pseudomorphic Si1-xGex epitaxial layers have been grown on Si(100) at a low temperature using molecular beam epitaxy. Compressively strained grown layers have been characterized by high-resolution XRD, RBS and Raman spectroscopy. A 5-period SiGe/Si multiple quantum well structure has also been grown for infrared photodetector applications. The simulated and measured temperature dependent dark current behaviour of the multi- quantum well structure is presented.
01 Dec 2007
TL;DR: CdSe nanowires were prepared by a simple DC electrochemical process using porous anodic alumina templates FESEM micrographs demonstrated the growth of CdSe Nanowires of diameter 200-300 nm by filling up the nano-pores in alumina X-ray diffraction patterns revealed the growth with hexagonal phase.
Abstract: CdSe nanowires were prepared by a simple DC electrochemical process using porous anodic alumina templates FESEM micrographs demonstrated the growth of CdSe nanowires of diameter 200-300 nm by filling up the nano-pores in alumina X-ray diffraction patterns revealed the growth of CdSe with hexagonal phase The absorption spectrum showed a band gap value nearer to bulk CdSe Room temperature photoluminescence measurement showed the defect related emission from the nanowires