Samit K. Ray

Bio: Samit K. Ray is an academic researcher from Indian Institute of Technology Kharagpur. The author has contributed to research in topics: Photoluminescence & Thin film. The author has an hindex of 44, co-authored 507 publications receiving 8085 citations. Previous affiliations of Samit K. Ray include University of Delaware & Indian Institute of Technology Kanpur.

Highly Responsive, Polarization Sensitive, Self-Biased Single GeO2-Ge Nanowire Device for Broadband and Low Power Photodetectors

Abstract: Highly uniform and dense GeO2 nanowires with Ge as the core were grown on Si (001) substrates by vapor–liquid–solid technique with an aim to utilize GeO2 as the active material for photodetectors. X-ray photoelectron spectroscopy was carried out to investigate the composition and interfaces of the resultant Ge/GeO2 NWs. The observed broad and visible photoluminescence emission from as-grown core–shell NW heterostructure is attributed to oxygen-related defect states in the GeO2 shells. Single Ge-GeO2 NW based metal–semiconductor–metal photodetectors were fabricated using nanolithography techniques. Self-driven (zero bias) detectors have been found to be responsive to a broadband spectrum from 350 to 900 nm with a peak responsivity (∼0.6 × 104 A/W) and detectivity (∼3.8 × 1012 Jones). The high gain in photocurrent has been explained using a back-to-back metal–semiconductor junction model in single NW. The device also shows sensitivity to polarization-dependence of light source. Finite element method (FEM) b...

Resistive switching memory characteristics of Ge/GeOx nanowires and evidence of oxygen ion migration

Abstract: The resistive switching memory of Ge nanowires (NWs) in an IrO x /Al2O3/Ge NWs/SiO2/p-Si structure is investigated. Ge NWs with an average diameter of approximately 100 nm are grown by the vapor–liquid-solid technique. The core-shell structure of the Ge/GeO x NWs is confirmed by both scanning electron microscopy and high-resolution transmission electron microscopy. Defects in the Ge/GeO x NWs are observed by X-ray photoelectron spectroscopy. Broad photoluminescence spectra from 10 to 300 K are observed because of defects in the Ge/GeO x NWs, which are also useful for nanoscale resistive switching memory. The resistive switching mechanism in an IrO x /GeO x /W structure involves migration of oxygen ions under external bias, which is also confirmed by real-time observation of the surface of the device. The porous IrO x top electrode readily allows the evolved O2 gas to escape from the device. The annealed device has a low operating voltage ( 103), long pulse read endurance of >105 cycles, and good data retention of >104 s. Its performance is better than that of the as-deposited device because the GeO x film in the annealed device contains more oxygen vacancies. Under SET operation, Ge/GeO x nanofilaments (or NWs) form in the GeO x film. The diameter of the conducting nanofilament is approximately 40 nm, which is calculated using a new method.

Optical and dielectric properties of junctionlike CdS nanocomposites embedded in polymer matrix

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

Hierarchical growth of ZnFe2O4 for sensing applications

Abstract: Mesoporous ZnFe2O4 nanoflowers (NFs) have been prepared using a modified hydrothermal (MHT) technique, developed in our laboratory. Urea has been brought in for hydrolysis of FeCl3 and ZnSO4 in solution to homogeneously precipitate ZnFe2O4. The precipitated product upon annealing at 450 °C results in mesoporous ZnFe2O4 NFs. Important physical methods have been used to characterize the NF material in the solid state. The growth mechanism of mesoporous NFs of evolution is confirmed by the adopted reaction strategy. The ZnFe2O4 NF finds application in peroxidase mimicking activity which in turn helps the selective naked eye detection of H2O2 and Hg2+ ions in solution. However, spectrophotometric detection limit goes down to 0.1 mM and 2.58 × 10−3 mM for H2O2 and Hg2+, respectively. To contemplate peroxidase like activity, colorless 3,3′,5,5′-tetramethylbenzidine (TMB) is employed which in turn oxidized to a blue solution by H2O2 in the presence of ZnFe2O4 rendering H2O2 sensing. It has been discovered that the blue color development is selectively held up by Hg2+ ion causing Hg2+ sensing possible. Judicious selection of Hg2+ ions once again indicates strong affinity of the nitrogen donor towards Hg2+. This makes Hg2+ sensing possible without the use of any noble metal. A strong and definite ‘–N–Hg–N’ binding interaction with nitrogen donors of the TMB substrate causes blue color bleaching. Herein we report the usefulness of an under-rated ZnFe2O4 nanoflower for the first time to detect Hg2+ spectrophotometrically and in a cost-effective way. On the other hand, a highly mesoporous nanoflower has been shown to be a selective sensor for acetone also. Based on the above reaction/interaction strategies it is expected that the as-synthesized ZnFe2O4 NFs would stand as cost effective sensor materials for biological applications and environmental remediation.

Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Abstract: Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

Principles Of Fluorescence Spectroscopy

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Nanoscale metal oxide-based heterojunctions for gas sensing: A review

Abstract: Metal oxide-based resistive-type gas sensors are solid-state devices which are widely used in a number of applications from health and safety to energy efficiency and emission control. Nanomaterials such as nanowires, nanorods, and nanoparticles have dominated the research focus in this field due to their large number of surface sites facilitating surface reactions. Previous studies have shown that incorporating two or more metal oxides to form a heterojunction interface can have drastic effects on gas sensor performance, especially the selectivity. Recently, these effects have been amplified by designing heterojunctions on the nano-scale. These designs have evolved from mixed commercial powders and bi-layer films to finely-tuned core–shell and hierarchical brush-like nanocomposites. This review details the various morphological classes currently available for nanostructured metal-oxide based heterojunctions and then presents the dominant electronic and chemical mechanisms that influence the performance of these materials as resistive-type gas sensors. Mechanisms explored include p–n and n–n potential barrier manipulation, n–p–n response type inversions, spill-over effects, synergistic catalytic behavior, and microstructure enhancement. Tables are presented summarizing these works specifically for SnO2, ZnO, TiO2, In2O3, Fe2O3, MoO3, Co3O4, and CdO-based nanocomposites. Recent developments are highlighted and likely future trends are explored.

Diversity of life

Abstract: It is clear that the above can lead to confusion when scientists of different countries are trying to communicate with each other. Another example is the burrowing rodent called a gopher found throughout the western United States. In the southeastern United States the term gopher refers to a burrowing turtle very similar to the desert tortoise found in the American southwest. One final example; two North American mammals known as the elk and the caribou are known in Europe as the reindeer and the elk. We never sing “Rudolph the Red-nosed elk”! Confused? This was the reason for creating an internationally recognized system of naming organisms. To avoid confusion, living organisms are assigned a scientific name based on Latin or Latinized words. The English sparrow is Passer domesticus or Passer domesticus (italics or underlining these two names is the official written representation of a scientific name). Using a uniform naming system allows scientists from all over the world to recognize exactly which life form a scientist is referring to. The naming process is called the binomial system of nomenclature. Passer is comparable to a surname and is called the genus, while domesticus is the specific or species name (like your given name) of the English sparrow. Now scientists can give all sparrow-like birds the genus Passer but the species name will vary. All similar genera (plural for genus) can be grouped into another, “higher” category (see below). Study the following for a more through understanding of taxonomy. Taxonomy Analogy Kingdom: Animalia Country

Environmental applications of graphene-based nanomaterials.

Abstract: Graphene-based materials are gaining heightened attention as novel materials for environmental applications The unique physicochemical properties of graphene, notably its exceptionally high surface area, electron mobility, thermal conductivity, and mechanical strength, can lead to novel or improved technologies to address the pressing global environmental challenges This critical review assesses the recent developments in the use of graphene-based materials as sorbent or photocatalytic materials for environmental decontamination, as building blocks for next generation water treatment and desalination membranes, and as electrode materials for contaminant monitoring or removal The most promising areas of research are highlighted, with a discussion of the main challenges that we need to overcome in order to fully realize the exceptional properties of graphene in environmental applications