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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.


Papers
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Journal ArticleDOI
02 Jan 2020
TL;DR: In this article, an easy, fast, scalable and controlled solgel method is devised for GO-TiO2 nanocomposites growth from different amounts of graphene oxide and titanium isopropoxide at atmospheric pressure.
Abstract: Fabrication of flexible solid-state supercapacitor is a field of paramount importance because of its potential application in portable devices. In this article, graphene oxide and titanium dioxide hybrid (GO-TiO2) nanocomposites of different compositions are employed for the fabrication of flexible solid-state supercapacitors. An easy, fast, scalable and controlled sol-gel method is devised for GO-TiO2 nanocomposites growth from different amounts of graphene oxide and titanium isopropoxide at atmospheric pressure. Highly monodispersed rutile TiO2 nanospindle is homogenously grafted on GO by a controlled HCl catalyzed reaction. BET N2 adsorption desorption isotherm analysis confirms formation of the mesoporous structure having a large specific surface area favourable for faster reversible adsorption and desorption of ions. An optimum composition of GO-TiO2 nanocomposite (TG25) exhibits a high areal specific capacitance of 73.43 mF/cm2 at a current density of 0.5 mA /cm2 due to formation of electrical double layer in a solid-state supercapacitor. The fabricated device shows high power density (3.5 mW/ cm2), a high energy density (0.007 mWh/ cm2), good flexibility and excellent cycling stability, 92% specific capacitance retention after 10,000 continuous charge-discharge cycles. Finally, three supercapacitors in a series have illuminated a red LED, indicating the nanocomposite as a potential candidate for energy storage technology.

20 citations

Journal ArticleDOI
TL;DR: In this article, photoluminescence (PL), optical absorption and sheet resistance measurements on poly and single crystalline ZnO samples irradiated with 700 keV O ions were performed.
Abstract: It is well known that energetic oxygen ions induce heavy crystalline disorder in ZnO, however, systematic study on this regard is very much limited Here, we present photoluminescence (PL), optical absorption and sheet resistance measurements on poly and single crystalline ZnO samples irradiated with 700 keV O ions Results have been compared with the effects of 12 MeV Ar irradiation on similar ZnO target Colour change of the samples with increasing O irradiation fluence has also been noted Non-monotonic variation of room temperature sheet resistance with the increase of fluence has been observed for polycrystalline ZnO Such an outcome has been understood as point defects transforming to bigger size clusters Near band edge (NBE) PL emission is largely reduced due to O ion irradiation However, at 10 K NBE emission can be observed for irradiated polycrystalline samples Irradiated ZnO single crystal does not show any band to band transition even at 10 K It is evident that dynamic recovery of defects is more effective in polycrystalline samples Ultraviolet–visible absorption spectrum of the irradiated ZnO crystal show pronounced sub-band gap absorption Oxygen irradiation generated new absorption band in ZnO is at 305 eV In the light of earlier reports, this particular band can be ascribed to absorption by neutral oxygen vacancy defects

20 citations

Journal ArticleDOI
TL;DR: This work reports on the synthesis and UV-vis photodetection application of p-type MoO2 nanostructures (NSs) on Si substrate and fabricated a p-MoO2/n-Si heterojunction Photodetector device with Au as the top and Al as the bottom contacts, which shows good self-powered high-speed photodetsection performance.
Abstract: We report on the synthesis and UV-vis photodetection application of p-type MoO2 nanostructures (NSs) on Si substrate. β-MoO2 NSs have been synthesized from previously grown α-MoO3 structures/n-type Si via a hydrogenation process at 450 °C. After hydrogenation, the α-MoO3 structures were completely converted into β-MoO2 NSs without the presence of sub-oxidized phases of molybdenum oxide. The as-grown NSs exhibited very good p-type electrical conductivity of ≈2.02 × 103 S-cm-1 with hole mobility of ≈7.8 ± 1.3 cm2-V-1-Sec-1. To explore optoelectronic properties of p-type β-MoO2 NSs, we have fabricated a p-MoO2/n-Si heterojunction photodetector device with Au as the top and Al as the bottom contacts. The device exhibits peak photoresponsivity of ≈0.155 A W-1 with maximum detectivity ≈1.28 × 1011 cm-Hz1/2-W-1 and 44% external quantum efficiency around ≈436 nm, following the highest photoresponse (I ph/I d ≈ 6.4 × 102) and good response speed (rise time ∼29 ms and decay time ∼38 ms) at -1.5 V. Importantly, this device also shows good self-powered high-speed (rise time ∼47 ms and decay time ∼70 ms) photodetection performance with peak responsivity and detectivity of ≈45 mA W-1 and ≈4.05 × 1010 cm-Hz1/2-W-1, respectively. This broadband UV-visible light detection feature can be attributed to the coordinated effects of MoO2 band-edge absorption, interfacial defects and self absorption in Si. The photodetection behavior of the device has been understood by proposed energy-band diagrams with the help of an experimentally derived work function, band gap and valence band maximum position of MoO2 NSs.

20 citations

Journal ArticleDOI
TL;DR: The efficacy of MoS2 nanocrystals for their size tunable properties for optical and photocatalytic applications is reported and the effect of size variation of NPs in the dye degradation process is reported.
Abstract: While two-dimensional (2D) layered MoS2 nanosheets have been extensively studied owing to their fascinating optoelectronic properties, less attention has been paid to the corresponding zero-dimensional nano-crystals. In this contribution, we report the efficacy of MoS2 nanocrystals for their size tunable properties for optical and photocatalytic applications. We have synthesized differently sized (10-70 nm) crystalline, hexagonal 2H-MoS2 nanoparticles (NPs) dispersed in DMF solvent using a simple exfoliation technique. Synthesized NPs are found to exhibit size-dependent optical properties and excitation-dependent fluorescence characteristics in the visible region, which are otherwise not observed in bulk or 2D MoS2 layers. Size tunable bandgap and broad absorbance and emission spectrum covering the visible range could be exploited in the fabrication of various opto-electronic devices. Charge carrier emission dynamics of differently sized MoS2 NPs are investigated using time correlated single photon counting (TCSPC) spectroscopic technique. We found two time components, one in the order of several hundreds of ps, which arises due to the radiative recombination of charge carriers, while the other one is of the order of a few ns, which emanates from the defect states of MoS2 NPs. The average time constants are found to decrease with increase in particle size. A noticeable photocatalytic activity of the synthesized MoS2 NPs under visible light illumination for the degradation of brilliant green dye is also demonstrated for the first time and the effect of size variation of NPs in the dye degradation process is reported.

20 citations

Journal ArticleDOI
TL;DR: In this article, the structural, optical, and electrical properties of the composite films have been studied as a function of SnO2 content, and it is revealed from X-ray diffraction analysis that films are crystalline in nature and the crystallite size decreases from 20-23nm to 5-7nm with increase of Sn O2 content.
Abstract: ZnO-SnO2 composite thin films have been deposited at 400 °C on glass substrates using targets of different SnO2 content (1 to 40 wt. %) by pulsed laser deposition technique. The structural, optical, and electrical properties of the composite films have been studied as a function of SnO2 content. It is revealed from X-ray diffraction analysis that films are crystalline in nature and the crystallite size decreases from 20–23 nm to 5–7 nm with increase of SnO2 content. X-ray photoelectron spectroscopy analysis indicates that Sn is predominantly doped into the ZnO lattice upto a SnO2 content of 15 wt. % in the composite. For higher concentration, a separate SnO2 phase is segregated in the composite. The band gap energy as well as the electrical conductivity can be tuned by varying the SnO2 content in the composite. Low temperature electrical conductivity measurements show three dominant conduction mechanisms in the temperature range of 20–300 K. At high temperature range of 200–300 K, thermal activation condu...

20 citations


Cited by
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Journal ArticleDOI
TL;DR: Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each that are among the hottest research topics of the last decades.
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

3,720 citations

01 Jan 2016
TL;DR: The principles of fluorescence spectroscopy is universally compatible with any devices to read and is available in the digital library an online access to it is set as public so you can download it instantly.
Abstract: Thank you very much for downloading principles of fluorescence spectroscopy. As you may know, people have look hundreds times for their favorite novels like this principles of fluorescence spectroscopy, but end up in malicious downloads. Rather than reading a good book with a cup of tea in the afternoon, instead they cope with some harmful bugs inside their desktop computer. principles of fluorescence spectroscopy is available in our digital library an online access to it is set as public so you can download it instantly. Our digital library spans in multiple locations, allowing you to get the most less latency time to download any of our books like this one. Kindly say, the principles of fluorescence spectroscopy is universally compatible with any devices to read.

2,960 citations

Journal ArticleDOI
TL;DR: In this paper, the dominant electronic and chemical mechanisms that influence the performance of metal-oxide-based resistive-type gas sensors are discussed, including p-n and n-n potential barrier manipulation, n-p-n response type inversions, spillover effects, synergistic catalytic behavior, and microstructure enhancement.
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.

1,392 citations

Journal ArticleDOI
01 Mar 1994-Nature
TL;DR: It is clear that the above can lead to confusion when scientists of different countries are trying to communicate with each other, so an internationally recognized system of naming organisms is created.
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

1,305 citations

Journal ArticleDOI
TL;DR: 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.
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

1,158 citations