Showing papers by "Samit K. Ray published in 2014"
29 Aug 2014
TL;DR: It appears that the use of molecular markers, though relatively recent in popularity and are not free entirely of flaws, can complement the traditional morphology based method for phylogenetic studies.
Abstract: Uses of molecular markers in the phylogenetic studies of various organisms have become increasingly important in recent times. This review gives an overview of different molecular markers employed by researchers for the purpose of phylogenetic studies. Availability of fast DNA sequencing techniques along with the development of robust statistical analysis methods, provided a new momentum to this field. In this context, utility of different nuclear encoded genes (like 16S rRNA, 5S rRNA, 28S rRNA) mitochondrial (cytochrome oxidase, mitochondrial 12S, cytochrome b, control region) and few chloroplast encoded genes (like rbcL, matK, rpl16) are discussed. Criteria for choosing suitable molecular markers and steps leading to the construction of phylogenetic trees have been discussed. Although widely practised even now, traditional morphology based systems of classification of organisms have some limitations. On the other hand it appears that the use of molecular markers, though relatively recent in popularity and are not free entirely of flaws, can complement the traditional morphology based method for phylogenetic studies.
189 citations
TL;DR: In this paper, the authors reported the development of a highly sensitive, flexible and low-cost ammonia sensor based on the chemically derived multilayered graphene deposited on a 3-inch diameter filter paper.
Abstract: The paper reports the development of a highly sensitive, flexible and low-cost ammonia sensor. The sensing element is based on the chemically derived multilayered graphene deposited on a 3-inch diameter filter paper. The sensing material was deposited on a filter paper because it is a flexible substrate and also reduces cost. Multilayered graphene was obtained by reducing the graphene oxide (GO) using glucose. The fabricated sensor showed sensitivity to detect ammonia concentration as low as 430 ppb. The response characteristics of the sensor as a function of ammonia concentrations (varying from 400 to 4000 ppm) is reported in the paper. It also describes the variation in the response characteristics in flat and bent positions of the sensors. The reproducibility of the sensor performance is also established by the results presented in the paper.
94 citations
TL;DR: The fabrication and optical response of boron-doped single silicon nanowire-based metal-semiconductor-metal photodetector with peak responsivity in the near-infrared region is reported and the observed photoresponse is sensitive to the polarization of exciting light source, allowing the device to act as a polarization-dependent near-Infrared photodetsector.
Abstract: We report the fabrication and optical response of boron-doped single silicon nanowire-based metal–semiconductor–metal photodetector. Typical single nanowire devices with diameter of ∼80–100 nm and electrode spacing of ∼1 μm were made using electron-beam lithography from nanowires, grown by a metal-assisted chemical etching process. A high responsivity, of the order of 104 A W−1, was observed even at zero bias in a single nanowire photodetector with peak responsivity in the near-infrared region. The responsivity was found to increase with increasing bias and decreasing nanowire diameter. Finite element based optical simulation was proposed to explain the diameter dependent performance of a single nanowire. The observed photoresponse is sensitive to the polarization of exciting light source, allowing the device to act as a polarization-dependent near-infrared photodetector.
80 citations
TL;DR: The results suggest the gradual restoration of sp(2) clusters within the sp(3) matrix with an increase of the reduction time and power density, which may lead to the potential application of graphene-based optoelectronic devices.
Abstract: The modification of individual oxygen functional groups and the resultant optical properties of a graphene oxide suspension were investigated using a controlled photothermal reduction by infrared irradiation. The evolution of the structural and optical characteristics of GO suspensions was obtained from Raman spectra, x-ray photoelectron spectroscopy, optical absorption, and steady state and time-resolved photoluminescence spectroscopy. The results suggest the gradual restoration of sp 2 clusters within the sp 3 matrix with an increase of the reduction time and power density. The yellow-red emission (∼610 nm) originated from the defect-assisted localized states in GO due to epoxy/hydroxyl (C-O/-OH) functional groups and that of the blue emission (∼500 nm) was ascribed to the carbonyl (C=O)-assisted localized electronic states. With an increase in the reduction time and IR power density, the intensity of the yellow-red emission was found to decrease, with the blue emission being prominent. These experimental findings open up a new dimension for controlling the optical absorption and emission properties of graphene oxide by tailoring the oxygen functional groups, which may lead to the potential application of graphene-based optoelectronic devices.
73 citations
TL;DR: In this article, brush-like SnO2 nanowires have been grown by pulsed laser deposition on ZnO nanorods synthesized by the hydrothermal method.
Abstract: Brush-like SnO2 nanowires have been grown by pulsed laser deposition on ZnO nanorods synthesized by the hydrothermal method. SnO2 nanowire/ZnO nanorod heterostructures have been used for sensing several volatile organic compounds (VOCs). The heterostructure sensor exhibits higher response compared to that of control ZnO nanorods. The potential barriers formed at the SnO2–ZnO and SnO2–SnO2 interface are proposed to be responsible for an improved sensing performance over the pure ZnO nanorods. The effect of the length of SnO2 nanowires on the performance of triethylamine, toluene, ethanol, acetic acid, acetone, and methanol sensing has been studied. It is found that the response to the VOCs greatly depends on the length of the brush-like SnO2 nanowires. The SnO2/ZnO heterostructures can be successfully used to discriminate acetone from other VOCs.
60 citations
TL;DR: Three novel luminescent nanofibrous metal-organic gels (MOGs) have been synthesized by the reaction of 1,3,5-tris(3-pyridylmethoxyl)benzene (L) with chloride salts of Cd(II, Hg(II), and Cu(II).
Abstract: In this study, three novel luminescent nanofibrous metal–organic gels (MOGs) have been synthesized by the reaction of 1,3,5-tris(3-pyridylmethoxyl)benzene (L) with chloride salts of Cd(II), Hg(II), and Cu(II). The metal–ligand coordination, intermolecular π–π stacking and several other weak interactions found to play an important role in the formation of nanofibrous materials. The gel materials are characterized by rheology, diffuse reflectance spectra and various microscopic techniques such as TEM, FESEM, and AFM. The gels MOG-1 and MOG-2 were found to exhibit significant white photoluminescence, whereas the MOG-3 exhbits green emission upon excitation at 325 nm. Furthermore, the MOG-1 has shown its application as a chemosensor for the remarkable detection of nitroaromatics such as nitrobenzene (NB), 2,4-dinitrophenol (DNP). The significant quenching response for NB and DNP is attributed to the strong charge-transfer interactions between the electron-deficient aromatic ring of NB and the electron rich ar...
58 citations
TL;DR: In this article, the flat band voltage shift and depletion width of ZnO nanorods/electrolyte interface have been estimated from Mott-Schottky (MS) characteristics.
Abstract: ZnO nanorods have been grown on indium-tin-oxide coated glass substrates by a low cost chemical process Current-voltage characteristics have been studied using ZnO nanorods as photoanode in an electrochemical cell The flat band voltage shift and depletion width of ZnO nanorods/electrolyte interface have been estimated from Mott-Schottky (MS) characteristics The electrochemical impedance measurements have been carried out to study the charge transport mechanism at the semiconductor-electrolyte interface under dark and white light (100 mW/cm2) illumination The doping concentration of nanorods has been extracted from MS plot Photoresponse behavior of ZnO nanorods is found to be enhanced than seed layers with the incident of white light Spectral dependent photovoltage of ZnO nanorods has been carried out using monochromatic light of wavelength 250–600 nm The photopotential recovery time has been estimated for nanorods and seed layers The stability of ZnO nanorods as a photoanode has been investigated
54 citations
TL;DR: The observed white light emission from the Si/ZnS nanowire heterojunction could open up the new possibility to integrate Si-based optical sources on a large scale.
Abstract: Well-separated Si/ZnS radial nanowire heterojunction-based light-emitting devices have been fabricated on large-area substrates by depositing n-ZnS film on p-type nanoporous Si nanowire templates. Vertically oriented porous Si nanowires on p-Si substrates have been grown by metal-assisted chemical etching catalyzed using Au nanoparticles. Isolated Si nanowires with needle-shaped arrays have been made by KOH treatment before ZnS deposition. Electrically driven efficient white light emission from radial heterojunction arrays has been achieved under a low forward bias condition. The observed white light emission is attributed to blue and green emission from the defect-related radiative transition of ZnS and Si/ZnS interface, respectively, while the red arises from the porous surface of the Si nanowire core. The observed white light emission from the Si/ZnS nanowire heterojunction could open up the new possibility to integrate Si-based optical sources on a large scale.
38 citations
TL;DR: In this article, structural, optical and electrical properties of the as-deposited and post-annealed thin films were investigated and X-ray diffraction patterns suggest that the films transform from crystalline to amorphous state with increasing aluminium content.
Abstract: Aluminium-doped (Al = 0–5 wt.%) SnO2 thin films with low-electrical resistivity and high optical transparency have been successfully synthesized by pulsed laser deposition technique at 500 °C. Structural, optical and electrical properties of the as-deposited and post-annealed thin films were investigated. X-ray diffraction patterns suggest that the films transform from crystalline to amorphous state with increasing aluminium content. The root mean square (Rq) surface roughness parameter, determined by atomic force microscopy decreases upon annealing of the as-deposited film. While resistivity of the film is the lowest (9.49 × 10−4 Ω-cm) at a critical doping level of 1 wt.% Al, optical transparency is the highest (nearly 90%) in the as-deposited condition. Temperature dependence of the electrical resistivity suggests that the Mott’s variable range hopping process is the dominant carrier transport mechanism in the lower temperature range (40–135 K) for all the films whereas, thermally activated band conduct...
19 citations
TL;DR: In this paper, a floating gate memory using carbon nanotube-CdS nanostructures embedded in Bombyx mori silk protein matrix has been demonstrated, where the enhanced charge injection resulting in increase in memory window is observed at higher sweeping voltages.
14 citations
01 Jan 2014
TL;DR: This is the first report of diversity of cyanobacterial flora present in the microbial mats of an alkaline geothermal spring located at Panifala in Burdwan district of West Bengal.
Abstract: This is the first report of diversity of cyanobacterial flora present in the microbial mats of an alkaline geothermal spring located at Panifala in Burdwan district of West Bengal. Ten species of cyanobacteria belonging to three heterocystous and four non-heterocystous genera from four cyanobacterial orders were isolated and identified by morphological and morphometric studies. The temperature range in the hot spring is 50-61°C. Temperature has been found to be the key factor for the variation of species composition in this spring. In addition to temperature, pH and electrical conductivity were also measured. Various chemical parameters like dissolved oxygen, phosphate, ammonium, bicarbonate, chloride and metals like sodium, potassium and calcium of the hot spring water were measured. An isolated strain of Fischerella thermalis was physiologically characterized with regard to pigment profile. In summer season carotenoid : chl-a ratio is 2.637:1 (highest among 5 sites) while in monsoon carotenoid : chl-a ratio is 0.132:1 (lowest among 5 sites). Species of Synechococcus and Calothrix were dominant in this solitary hot spring. The most abundant species were Synechococcus bigranulatus, S. elongatus and Phormidium laminosum. The genera Synechococcus, Phormidium, Calothrix and Fischerella were isolated from the above mentioned spring using BG-11 medium under 25-30 μmol photons m -2 s -1 light and 37±2oC temperature.
01 Jan 2014
TL;DR: In this article, Indium Tin Oxide (ITO) coated glass was taken as the basic substrate for sensing layer deposition and sensitivity tests for relative humidity (RH) measurements were carried out at five different concentrations of humid air at room temperature.
Abstract: Reduced Graphene Oxide (RGO) has been synthesized chemically by reducing micron-sized Graphene Oxide (GO) flakes using sodium borohydride solution. Indium Tin Oxide (ITO) coated glass was taken as the basic substrate for sensing layer deposition. Sensitivity tests for relative humidity (RH) measurements were carried out at five different concentrations of humid air at room temperature. The response of the sensor was found to vary between 3.8 for 10 % humid air and 20.4 for 100 % humid air. Characterizations of the sensing layer were carried out using Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscopy (FESEM).
TL;DR: In this paper, the authors evaluated the excess free energy of mixing and excess molar polarization in the binary mixtures of ketones (acetone, MIBK, DIBK and acetyl acetone) in nonpolar solvents (carbon tetrachloride, Benzene, cyclohexane and n-heptane) by using the experimental findings of relative permittivity and refractive index.
TL;DR: In this article, the growth process of germanium inverted quantum hut (IQH) structures, which are embedded in a silicon lattice, has been studied using anomalous x-ray scattering techniques.
Abstract: The growth process of germanium inverted quantum hut (IQH) structures, which are embedded in a silicon lattice, has been studied using anomalous x-ray scattering techniques. These self-assembled IQH structures exhibit strong photoluminescence (PL) although the number density of the huts is rather small. We show here that these IQH structures form by the intermixing of germanium with previously deposited silicon producing an intriguing composition variation that keeps the out-of-plane lattice parameter of the alloy almost constant. We have identified a zero strain cubic structure, which extends towards the tip of these IQHs to accommodate large-scale interdiffusion of germanium in silicon lattice. A substantial increase in intensity of the PL peak at around 0.8 eV as the temperature is lowered from 70 to 10 K and a corresponding activation energy of 49 meV indicates that photon induced carriers are predominantly captured at the tip of the embedded quantum hut structures.
TL;DR: In this article, the formation of strained Ge islands has been found for film with higher thickness following Stranski-Krastanov growth mechanism and the variation of strain with changing Ge layer thickness has been analyzed using Raman spectroscopy and high resolution X-ray diffraction techniques.
Abstract: Strained Ge islands have been grown on fully relaxed Si0.5Ge0.5 substrate by pulsed laser ablation technique. The formation of strained Ge islands has been found for film with higher thickness following Stranski–Krastanov growth mechanism. The variation of strain with changing Ge layer thickness has been analyzed using Raman spectroscopy and high-resolution X-ray diffraction techniques. X-ray photoelectron spectra have shown the absence of any Si-Ge intermixing and oxidation of Ge films. A strong no-phonon photoluminescence emission from Ge islands has been observed, showing the superior optical characteristics of the islands grown on relaxed substrate.
TL;DR: In this paper, a resistive single wall carbon nanotubes (SWCNTs) sensor was developed based on a CMOS substrate that responds at ambient temperature to ppm levels of ammonia.
TL;DR: In this paper, the growth temperature dependent phase formation and its magnetic property in Mn-doped Ge nanowires (NWs) fabricated at temperature (TG) varying from 600 to 900 C using vapor-liquid-solid technique.
Abstract: We report a study on the growth temperature dependent phase formation and its magnetic property in Mn-doped Ge nanowires (NWs) fabricated at temperature (TG) varying from 600 to 900 °C using vapor–liquid–solid technique. Structural and magnetic measurements on the nanowires reveal that Mn are not homogeneously distributed in Ge-matrix, but atomic clusters (Mn-rich regions) are formed in lightly doped Ge matrix (GeMn-matrix) at 600 °C. Upon increasing TG, Ge3Mn5 compound starts to nucleate in expense of atomic clusters following the migration of Mn from GeMn-matrix. At 900 °C, only precipitates of Ge3Mn5 in cluster-free Ge-matrix are found.
TL;DR: In this article, structural characterizations on as-grown, UV-irradiated, and as-annealed samples were performed and they showed no measurable difference in X-ray diffraction profiles and field-emission scanning and transmission electron microscopy images.
Abstract: Nonferromagnetic ${\rm SnO}_{2}$ nanowires show ferromagnetism at room temperature, which is significantly enhanced upon irradiation by ultraviolet (UV) light of wavelength 365 nm. The structural characterizations on as-grown, UV-irradiated, and ${\rm O}_{2}$ -annealed samples show no measurable difference in X-ray diffraction profiles and field-emission scanning and transmission electron microscopy images. But optical absorption, photoluminescence, and X-ray photoelectron spectroscopy reveal a significant effect of UV irradiation and establish a remarkable enhancement of O vacancies in ${\rm SnO}_{2}$ nanowires upon UV light irradiation, which diminishes after annealing in the presence of ${\rm O}_{2}$ gas. The as-grown and ${\rm O}_{2}$ -annealed nanowires show weak ferromagnetism at room temperature, but the UV-irradiated nanowires show strong ferromagnetism. The origin of such ferromagnetism in pure (undoped) ${\rm SnO}_{2}$ is attributed to the presence of oxygen vacancies, which is tunable externally using UV irradiation.
01 Jan 2014
TL;DR: In this article, thin amorphous diamond-like nanocomposite (a-DLN) films are deposited on p-type crystalline silicon (c-Si) by plasma assisted chemical vapour deposition (PACVD) technique to use it as an ammonia (NH3) gas sensor operable at room temperature.
Abstract: Thin amorphous diamond-like nanocomposite (a-DLN) films are deposited on p-type crystalline silicon (c-Si) by plasma assisted chemical vapour deposition (PACVD) technique to use it as an ammonia (NH3) gas sensor operable at room temperature. The non-linear current–voltage (I–V) characteristic of a-DLN/c-Si heterojunction shows a very good rectifying property of the junction in air and quick sensitivity in NH3 gas at room temperature. The current output in reverse biased condition of the a-DLN/c-Si heterojunction is ~ 15 times higher in NH3 than in air. Sensor also shows a good recovery property to the original state, even at room temperature. Sensing material is characterized by using Field Emission Scanning Electron Microscope (FESEM), Fourier Transform Infrared Spectroscopy (FTIR) and UV–VIS Near-IR Spectroscopy, to understand the sensing behaviour.
TL;DR: In this paper, a single-silicon-nanowire based photodetectors showed superior response (>10000 A/W) even without external bias in visible-to-near-IR region.
Abstract: Single-silicon-nanowire based MSM photodetectors show superior response (>10000 A/W) even without external bias in visible-to-near-IR region. The responsivity improvement as function of nanowire diameter has been explained by electric-field enhancement using finite-element based optical simulation.
TL;DR: In this paper, the authors presented the continuously tunable optical properties by controlled reduction of graphene oxide (GO) using IR radiation and discussed the application of GO/n-Si heterojunction diode as a broadband photodetector.
Abstract: In this paper, we present the continuously tunable optical properties by controlled reduction of graphene oxide (GO) using IR radiation. The application of GO/n-Si heterojunction diode as a broadband photodetector is discussed.
TL;DR: One-dimensional micro-cavity resonators, constituted of Eu2+,3+ doped silica layer inserted between two SiO2/SnO2 Bragg mirrors, are fabricated by sol-gel method.
Abstract: One-dimensional micro-cavity resonators, constituted of Eu2+,3+ doped silica layer inserted between two SiO2/SnO2 Bragg mirrors, are fabricated by sol-gel method. Spectral management of Eu2+,3+ emission by varying the angle of detection is presented.
01 Jan 2014
TL;DR: In this paper, the effect of encapsulation of SiNW arrays with diamond-like nanocomposite (DLN) deposited by plasma assisted chemical vapor deposition (PACVD) method has been investigated.
Abstract: Silicon nanowire (SiNW) arrays were synthesized using single step metal assisted chemical etching (SSMACE) method on n-type mono crystalline silicon. The effect of encapsulation of SiNW arrays with diamond-like nanocomposite (DLN) deposited by plasma assisted chemical vapor deposition (PACVD) method has been investigated. The structural and optical properties of SiNW and DLN thin film has been studied using FESEM, FTIR and UV–VIS-NIR spectroscopy. A very low (3–4 %) and high broadband (300–1,000 nm) reflection has been achieved from SiNWs array. However, after deposition of DLN thin film on nanowire array, the reflection further reduces significantly to 1.7 %. The SiNW arrays encapsulated with DLN thin film has a great potential to use in solar cell.
TL;DR: In this paper, the room-temperature vertical transport in InAs/AlSb and GaAs/alAs short-period superlattices was studied and the influence of optical cavity on current-voltage characteristics was found in the range of both resonant and nonresonant tunneling.
Abstract: The room-temperature vertical transport in InAs/AlSb and GaAs/AlAs short-period superlattices was studied. The influence of optical cavity on current-voltage characteristics was found in the range of both resonant and nonresonant tunneling. Possible explanations are suggested.
TL;DR: In this paper, Mn0.02Sn0.98O2−δ/p-Si(100) heterojunctions were fabricated varying oxygen pressure on p-Si (100) substrate by pulsed laser deposition technique.
Abstract: Mn0.02Sn0.98O2−δ thin films were fabricated varying oxygen pressure on p-Si (100) substrate by pulsed laser deposition technique. Magnetic moment measurements confirm that the films are ferromagnetic at room temperature. The magnetic moment increases with decrease in oxygen pressure. The Mn0.02Sn0.98O2−δ/p-Si(100) heterojunctions behave well as rectifiers at lower temperature, but not at room temperature. The forward current (I) of the rectifier is drastically reduced at lower temperature on application of a few Oe magnetic field (H), and almost zero current is observed above 0.5 kOe. The I-H curves are symmetric with respect to positive and negative magnetic field. As the temperature increases the dependency of current on magnetic field decreases and becomes null above 70 K.
TL;DR: In this article, near infrared light emission in the range of 1.5-1.8 μm, sustaining upto 110 K temperature has been obtained from direct band gap transition in Ge1-xSnx nanostructures grown by molecular beam epitaxy on P-Si(100) substrates.
Abstract: Near infrared light emission in the range of 1.5-1.8 μm, sustaining upto 110 K temperature has been obtained from direct band gap transition in Ge1-xSnx nanostructures grown by molecular beam epitaxy on P-Si(100) substrates.