Showing papers by "Samit K. Ray published in 2016"
TL;DR: Fabricated n-MoS2/p-Si 0D/3D heterojunctions exhibiting excellent rectification behavior have been studied for light emission in the forward bias and photodetection in the reverse bias and are found to be superior to the reported results on large areaPhotodetector devices fabricated using two dimensional materials.
Abstract: Silicon compatible wafer scale MoS2 heterojunctions are reported for the first time using colloidal quantum dots. Size dependent direct band gap emission of MoS2 dots are presented at room temperature. The temporal stability and decay dynamics of excited charge carriers in MoS2 quantum dots have been studied using time correlated single photon counting spectroscopy technique. Fabricated n-MoS2/p-Si 0D/3D heterojunctions exhibiting excellent rectification behavior have been studied for light emission in the forward bias and photodetection in the reverse bias. The electroluminescences with white light emission spectra in the range of 450–800 nm are found to be stable in the temperature range of 10–350 K. Size dependent spectral responsivity and detectivity of the heterojunction devices have been studied. The peak responsivity and detectivity of the fabricated heterojunction detector are estimated to be ~0.85 A/W and ~8 × 1011 Jones, respectively at an applied bias of −2 V for MoS2 QDs of 2 nm mean diameter. The above values are found to be superior to the reported results on large area photodetector devices fabricated using two dimensional materials.
137 citations
TL;DR: In this paper, a solution-processed few-layer molybdenum disulfide (MoS2) was used to synthesize a p-type silicon (p-Si)/n-MoS 2 heterostructure for visible light driven photocatalytic Rhodamine B dye degradation.
Abstract: The present low yielding growth techniques of semiconducting 2H phase molybdenum disulfide (MoS2) hamper its widespread applications. In this article, we report a novel hydrothermal chemical approach to synthesize micron sized few layer 2H-MoS2 on a large scale. Sodium molybdate and ammonium thiocyanate have been used as precursors to obtain template-free 2H-MoS2 in solution. Detailed microscopic and spectroscopic characterizations reveal that the bottom-up synthesized few layer MoS2 flakes are highly crystalline having the hexagonal 2H phase. Photodetector devices comprising a p-type silicon (p-Si)/n-MoS2 heterostructure have been fabricated for the first time using solution processed 2H-MoS2 synthesized by the bottom up approach. The heterojunction diode exhibits a high rectification ratio (>103) with broad band photoresponse over the visible range. Because of the visible light photoresponse, as-synthesized MoS2 along with reduced graphene oxide (MoS2–RGO hybrids) have been utilized to study the potential of this two dimensional (2D) heterostructure for visible light driven photocatalytic Rhodamine B dye degradation. This study demonstrates the potential of solution processed MoS2 for integration with silicon and growth of 2D heterostructures for visible light induced multifunctional applications.
120 citations
TL;DR: The simultaneous mechanical energy harvesting and visible-light detection capabilities of the PNG are attractive for futuristic self-powered optoelectronic smart sensors and devices.
Abstract: Plasmonic characteristics of graphene-silver (GAg) nanocomposite coupled with piezoelectric property of Poly(vinylidene fluoride) (PVDF) have been utilized to realize a new class of self-powered flexible plasmonic nanogenerator (PNG). A few layer graphene has been prepared in a facile and cost-effective method and GAg doped PVDF hybrid nanocomposite (PVGAg) is synthesized in a one-pot method. The PNG exhibits superior piezoelectric energy conversion efficiency (∼15%) under the dark condition. The plasmonic behavior of GAg nanocomposite makes the PNG highly responsive to the visible light illumination that leads to ∼50% change in piezo-voltage and ∼70% change in piezo-current, leading to enhanced energy conversion efficiency up to ∼46.6%. The piezoelectric throughput of PNG (e.g., capacitor charging performance) has been monitored during the detection of the different wavelengths of visible light illumination and showed maximum selectivity to the green light. The simultaneous mechanical energy harvesting a...
108 citations
TL;DR: A comparative study of the reported results on 2D transition metal chalcogenides indicates the superior characteristics of WS2/n-Si heterostructures for future photonic devices.
Abstract: We report for the first time, the fabrication of novel two-dimensional (2D) p-WS2/n-Si vertical heterostructures with superior junction and photoresponse characteristics. Few layer WS2 has been synthesized by a lithium-ion intercalation technique in hexane and coated on Si substrates for realization of CMOS compatible devices. Atomic force microscopy and Raman spectroscopy have been used to confirm the 2D nature of WS2 layers. Sharp band-edge absorption and emission peaks have indicated the formation of mono-to-few-layers thick direct band gap WS2 films. The electrical and optical responses of the heterostructures have exhibited superior properties revealing the formation of an abrupt heterojunction. The fabricated photodetector device depicts a peak responsivity of 1.11 A W−1 at −2 V with a broadband spectral response of 400–1100 nm and a moderate photo-to-dark current ratio of ∼103. The optical switching characteristics have been studied as a function of applied bias and illuminated power density. A comparative study of the reported results on 2D transition metal chalcogenides indicates the superior characteristics of WS2/n-Si heterostructures for future photonic devices.
85 citations
TL;DR: In this article, the white luminescence from heterojunctions based on two dimensional graphitic carbon nitride (g-C3N4) nanosheets and ZnO nanorods was reported.
62 citations
TL;DR: Photodetector devices comprising solution proccessed p-WS2/n-Si heterojunctions, which behave as diodes with a high rectification ratio (>10(2)) exhibiting a broad band photoresponse over the entire visible region are successfully demonstrated.
Abstract: Lithium halide assisted high yield synthesis of few layers of 2H phase semiconducting WS2 in organic solvents is reported. A group of lithium halides (LiCl, LiBr and LiI) has been employed for the first time to intercalate WS2 by using Li, followed by mild sonication to exfoliate in dispersive polar solvents. In contrast to the n-butyllithium (n-BuLi) assisted exfoliation method, which yields only the metallic 1T phase on prolonged reaction (3-7 days) at higher temperatures, the proposed exfoliation method produces only semiconducting 2H WS2 in a much shorter time (5 minute sonication). A very high yield of 19 mg ml(-1) has been obtained using LiI as an exfoliating agent due to its lower lattice energy compared to other alkali halides and the smaller size of the cation. Detailed microscopy and spectroscopic characterization reveals exfoliation of few layered WS2 with stoichiometric composition. Absorption and emission characteristics of the 2D WS2 layer exhibit a characteristic band edge and quantum confined transitions. As a proof-of-concept, we have successfully demonstrated photodetector devices comprising solution proccessed p-WS2/n-Si heterojunctions, which behave as diodes with a high rectification ratio (>10(2)) exhibiting a broad band photoresponse over the entire visible region.
58 citations
TL;DR: Selectivity measurements showed that the sensors were selective towards ethanol when they were exposed to acetone and toluene, and the devices were characterised by exposure to ethanol vapour in humid air in the concentration range of 100-1000 ppm.
Abstract: Here we report on the mask-less deposition of Au-SnO2 nanocomposites with a silicon-on-insulator (SOI) complementary metal oxide semiconductor (CMOS) micro electro mechanical system (MEMS) platform through the use of dip pen nanolithography (DPN) to create a low-cost ethanol sensor. MEMS technology is used in order to achieve low power consumption, by the employment of a membrane structure formed using deep reactive ion etching technique. The device consists of an embedded tungsten micro-heater with gold interdigitated electrodes on top of the SOI membrane. The tungsten micro-heater is used to raise the membrane temperature up to its operating temperature and the electrodes are used to measure the resistance of the nanocomposite sensing layer. The CMOS MEMS devices have high electro-thermal efficiency, with 8.2 °C temperature increase per mW power of consumption. The sensing material (Au-SnO2 nanocomposite) was synthesised starting from SnO nanoplates, then Au nanoparticles were attached chemically to the surface of SnO nanoplates, finally the mixture was heated at 700 °C in an oven in air for 4 h. This composite material was sonicated for 2 h in terpineol to make a viscous homogeneous slurry and then 'written' directly across the electrode area using the DPN technique without any mask. The devices were characterised by exposure to ethanol vapour in humid air in the concentration range of 100-1000 ppm. The sensitivity varied from 1.2 to 0.27 ppm(-1) for 100-1000 ppm of ethanol at 10% relative humid air. Selectivity measurements showed that the sensors were selective towards ethanol when they were exposed to acetone and toluene.
43 citations
TL;DR: In this article, the authors reported precise control of nonlinear optical properties of reduced graphene oxide in femtosecond regime with increased degrees of IR reduction measured by open aperture z-scan technique.
Abstract: Simultaneous occurrence of saturable absorption nonlinearity and two-photon absorption nonlinearity in the same medium is well sought for the devices like optical limiter and laser mode-locker. Pristine graphene sheet consisting entirely of sp2-hybridized carbon atoms has already been identified having large optical nonlinearity. However, graphene oxide (GO), a precursor of graphene having both sp2 and sp3-hybridized carbon atom, is increasingly attracting cross-discipline researchers for its controllable properties by reduction of oxygen containing groups. In this work, GO has been prepared by modified Hummers method, and it has been further reduced by infrared (IR) radiation. Characterization of reduced graphene oxide (RGO) by means of Raman spectroscopy, X-ray photoelectron spectroscopy, and UV-Visible absorption measurements confirms an efficient reduction with infrared radiation. Here, we report precise control of non-linear optical properties of RGO in femtosecond regime with increased degrees of IR reduction measured by open aperture z-scan technique. Depending on the intensity, both saturable absorption and two-photon absorption effects are found to contribute to the non-linearity of all the samples. Saturation dominates at low intensity (∼127 GW/cm2) while two-photon absorption becomes prominent at higher intensities (from 217 GW/cm2 to 302 GW/cm2). The values of two-photon absorption co-efficient (∼0.0022–0.0037 cm/GW for GO, and ∼0.0128–0.0143 cm/GW for RGO) and the saturation intensity (∼57 GW/cm2 for GO, and ∼194 GW/cm2 for RGO) increase with increasing reduction, indicating GO and RGO as novel tunable photonic devices. We have also explained the reason of tunable nonlinear optical properties by using amorphous carbon model.
40 citations
TL;DR: The negative photoconductive response of hybrid Au-silk under UV illumination may pave the way towards the utilization of silk for future bio-photonic devices using metal nanoparticle platforms.
Abstract: Silk protein is a natural biopolymer with intriguing properties, which are attractive for next generation bio-integrated electronic and photonic devices. Here, we demonstrate the negative photoconductive response of Bombyx mori silk protein fibroin hydrogels, triggered by Au nanoparticles. The room temperature electrical conductivity of Au–silk hydrogels is found to be enhanced with the incorporation of Au nanoparticles over the control sample, due to the increased charge transporting networks within the hydrogel. Au–silk lateral photoconductor devices show a unique negative photoconductive response under an illumination of 325 nm, with excitation energy higher than the characteristic metal plasmon resonance band. The enhanced photoconductance yield in the hydrogels over the silk protein is attributed to the photo-oxidation of amino groups in the β-pleated sheets of the silk around the Au nanoparticles followed by the breaking of charge transport networks. The Au–silk nanocomposite does not show any photoresponse under visible illumination because of the localization of excited charges in Au nanoparticles. The negative photoconductive response of hybrid Au–silk under UV illumination may pave the way towards the utilization of silk for future bio-photonic devices using metal nanoparticle platforms.
39 citations
TL;DR: In this article, mesoporous ZnFe2O4 nanoflowers (NFs) have been prepared using a modified hydrothermal (MHT) technique, developed in our laboratory.
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.
36 citations
TL;DR: The presence of Au nanostructures on top of O-deficient and sharp-tipped TNFs results in enhanced FE performance following their reduced tunneling barrier via pinning of effective Φ.
Abstract: The lowering of the work function (Φ) can lead to a better field emission (FE) behavior at lower threshold fields. We report on enhanced FE from randomly oriented and faceted Au-capped ZnO hetero-nanostructures (HNs) having more oxygen defects. Large-area arrays of non-aligned, faceted Au-capped ZnO HNs, such as nanowires (NWs) and triangular nanoflakes (TNFs) are grown using the chemical vapor deposition (CVD) method. Enhanced FE properties from the TNF sample resulted in a turn-on field as low as 0.52 V μm(-1) at a current density of 0.1 mA cm(-2) and a field enhancement factor (β) as high as ≈5.16 × 10(5). Under similar experimental conditions, drawing the same current density from an NW specimen needs a higher turn-on field (0.86 V μm(-1)) and to exhibit nearly four times less field enhancement factor compared to the TNFs samples. X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) measurements confirm the presence of more oxygen defects in the TNF samples compared to the NW samples. Kelvin probe force microscopy (KPFM) measurements show the average local work function to be 4.70 ± 0.1 eV for the TNF sample, which is ≈ 0.34 eV lower than the NW sample. Using density functional theory (DFT) calculations, the estimated Φ values are found to be 4.98 eV for ZnO(0001), 4.17 eV for Au(001)/ZnO(0001) and 3.91 eV for Au(001)/Ovac-ZnO(0001) surfaces. The DFT results are qualitatively in agreement with our experimental results. The presence of Au nanostructures on top of O-deficient and sharp-tipped TNFs results in enhanced FE performance following their reduced tunneling barrier via pinning of effective Φ.
TL;DR: In this paper, the authors reported the thermal quenching of carbon nanodots (CNDs), synthesized by a simple solvothermal method, at varying temperatures in an ambient atmosphere, attributed to varying fractions of the core sp 2 moiety and the surrounding surface chemical groups.
TL;DR: In this article, an in-depth study using low temperature PL and room temperature Raman spectroscopy was conducted to shed light on the widely discussed issue of defects and photoluminescence (PL) from ZnO material.
TL;DR: In this article, a novel graphene-Ag0 hybrid plasmonic nanostructure-based photodetector exhibiting moderately high responsivity and spectral selectivity in the visible wavelength.
Abstract: We report the fabrication and characteristics of a novel graphene-Ag0 hybrid plasmonic nanostructure-based photodetector exhibiting moderately high responsivity (∼28 mA/W) and spectral selectivity (∼510 nm) in the visible wavelength. The formation of highly stable Ag0 nanoparticles with an average size of 40 nm is observed within the graphene layers, resulting in n-type doping of hybrid material. The absorption peak of graphene-Ag0 hybrid is redshifted to the visible wavelength (∼510 nm) from the plasmonic Ag peak (∼380 nm) in agreement with the optical simulation results for embedded metal nanoparticles. The study demonstrates the synergistic effect of the graphene-metal nanocomposite, which appears attractive for applications in graphene-based photonic devices.
TL;DR: In this article, a single step process to grow Au capped oxygen deficient GeO2 crystalline nanowires via generation of growth species through the metal induced surface decomposition of Ge substrate is reported.
Abstract: A single step process to grow Au capped oxygen deficient GeO2 crystalline nanowires via generation of growth species through the metal induced surface decomposition of Ge substrate is reported. Without the external source supply, the growth of the Au-GeO2 nanowires on the Ge substrate is addressed with possible mechanism. Despite high band gap, application of GeO2 as a possible new material for visible light photodetection is presented. The as-grown samples were found to have a photo-response of ≥102 with 17% external quantum efficiency at −2.0 V applied bias upon visible-light illumination (λ = 540 nm, 0.2 mW/cm2). This visible-light detection can be attributed to the oxygen vacancy related defect states as well as localized surface plasmon resonance induced absorption and subsequent hot electron injection from Au to conduction band of GeO2. The photodetection performance of the devices has been understood by the proposed energy band diagrams. In addition, ≈4 times enhancement in the efficiency has been ...
TL;DR: In this paper, a new synthesis method to grow Zn-doped CuS (CZS) nanoballs on multi-walled carbon nanotube (MWCNT) surfaces from a single molecular source [Cu(en) 2 ZnCl 4 ]·DMSO complex was reported.
TL;DR: In this article, a detailed evaluation of mechanical, tribological, and high temperature oxidation resistance properties of YSZ, and Al 2 O 3 based thin films developed by pulsed laser deposition technique is presented.
14 Jan 2016
TL;DR: In this article, the authors reported enhanced ammonia sensing using chemically reduced graphene oxide (RGO) and rose bengal (RB) nanocomposite fabricated in a very simple and cost effective manner.
Abstract: Development of chemoresistive ammonia sensor that does not suffer with humidity interference is highly desirable for practical environmental monitoring systems. We report enhanced ammonia sensing using chemically reduced graphene oxide (RGO) and rose bengal (RB) nanocomposite fabricated in a very simple and cost effective manner. The RGO–RB nanocomposites were synthesized using three different concentrations (2 mg mL−1, 5 mg mL−1 and 10 mg mL−1) of RB keeping the RGO concentration same. Ammonia and humidity sensing of these three different composites were explored. Interestingly, it was observed that with increasing concentration of RB, the sensitivity of the sensor towards ammonia was increased but the sensitivity towards humidity was decreased. The response of the nanocomposites varied from ~9–45% against 400−2800 ppm of ammonia whereas intrinsic RGO showed a response of merely 17% against 2800 ppm of ammonia. On the other hand the response of the nanocomposite based sensor was reduced from 18% to 7% against 100% relative humidity. Also, the sensor was found to be selective towards ammonia when tested against other toxic volatile organic compounds. The limit of detection of the RGO–RB based sensor was calculated to be as low as 0.9 ppm. Field emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and UV–vis spectroscopy were carried out for the detailed structural characterizations of the sensing layer. These results are believed to be very useful for the cost effective fabrication of graphene based ammonia sensors which have reduced effects of humidity.
TL;DR: A novel amplified spontaneous emission (ASE) system based on a GO-embedded all-dielectric one-dimensional photonic crystal (1DPhC) micro-resonator and randomness assisted field confinement reduces the ASE threshold of the mono- to few-layered weak emitter making the realization of an ASE source feasible.
Abstract: The realization of optoelectronic devices using two-dimensional materials such as graphene and its intermediate product graphene oxide (GO) is extremely challenging owing to the zero band gap of the former. Here, a novel amplified spontaneous emission (ASE) system based on a GO-embedded all-dielectric one-dimensional photonic crystal (1DPhC) micro-resonator is presented. The mono- to few-layered GO sheet is inserted within a microcavity formed by two 5-bilayered SiO2/SnO2 Bragg reflectors. Significantly enhanced photoluminescence (PL) emission of GO embedded in 1DPhC is explicated by studying the electric field confined within the micro-resonator using the transfer matrix method. The inherent randomness, due to fabrication limitations, in the on-average periodic 1DPhC is exploited to further enhance the PL of the optically active micro-resonator. The 1DPhC and randomness assisted field confinement reduces the ASE threshold of the mono- to few-layered weak emitter making the realization of an ASE source feasible. Consequently, ASE at the microcavity resonance and at the low-frequency band-edge of photonic stop-band is demonstrated. Variation of the detection angle from 5° to 30°, with respect to the sample surface normal allows reallocation of the defect mode ASE peak over a spectral range of 558-542 nm, making the GO-incorporated 1DPhC a novel and attractive system for integrated optic applications.
TL;DR: In this article, the size dependent photoresponse behavior of crystalline Ge quantum dots (QDs) dispersed within the silica matrix was investigated and the effect of Coulomb interaction of photogenerated carriers, QD/silica interface defects and electric field driven carrier separation and tunneling through the oxide barriers.
TL;DR: In this article, Li2MnO3 (layered) and LiMn15Ni05O4 (spinel) composite cathodes have been synthesized using auto-combustion route Rietveld refinements together with analyses of high resolution transmission electron micrographs confirm the structural integration of Li2NO3 nano-domains into the LiNnO4 matrix of the composite cathode.
Abstract: High energy density Li2MnO3 (layered)–LiMn15Ni05O4 (spinel) composite cathodes have been synthesized using auto-combustion route Rietveld refinements together with the analyses of high resolution transmission electron micrographs confirm the structural integration of Li2MnO3 nano-domains into the LiMn15Ni05O4 matrix of the composite cathodes The discharge capacity of the composite cathodes are due to the intercalation of Li+ ion in the tetrahedral (8a) and octahedral (16c) sites of the spinel component and also the insertion of Li+ in the freshly prepared MnO2 lattice, formed after Li2O extraction from the Li2MnO3 domains The capacity fading of the composite cathodes are explained to be due to the layered to spinel transition of the Li2MnO3 component and Li+ insertion into the octahedral site of the spinel lattices which trigger cubic to tetragonal phase transition resulting volume expansion which eventually retard the Li+ intercalation with cycling
25 Apr 2016
TL;DR: In this paper, the authors have demonstrated the enhanced photoluminescence and photoconducting characteristics of plasmonic Ag-ZnO films due to the light scattering effect from Ag nanoislands.
Abstract: We have demonstrated the enhanced photoluminescence and photoconducting characteristics of plasmonic Ag–ZnO films due to the light scattering effect from Ag nanoislands. Ag nanoislands have been prepared on ITO-coated glass substrates by thermal evaporation followed by annealing. Plasmonic Ag–ZnO films have been fabricated by depositing ZnO over Ag nanoislands by sol–gel process. The band-edge emission of ZnO is enhanced for 170 nm sized Ag nanoislands in ZnO as compared to pure ZnO. The defect emission is also found to be quenched simultaneously for plasmonic Ag–ZnO films. The enhancement and quenching of photoluminescence at different wavelengths for Ag–ZnO films can be well understood from the localized surface plasmon resonance of Ag nanoislands. The Ag–ZnO M–S–M photoconductor device showed a tenfold increment in photocurrent and faster photoresponse as compared to the control ZnO device. The enhancement in photoresponse of the device is due to the increased photon absorption in ZnO films via scattering of the incident illumination.
TL;DR: Structural characterization has shown that films grown in the presence of surfactant exhibit very smooth surfaces with a relatively higher strain value in comparison to those grown without any surfactants.
Abstract: Compressively strained Ge films have been grown on relaxed Si0.45Ge0.55 virtual substrates using molecular beam epitaxy in the presence of Sb as a surfactant. Structural characterization has shown that films grown in the presence of surfactant exhibit very smooth surfaces with a relatively higher strain value in comparison to those grown without any surfactant. The variation of strain with increasing Ge layer thickness was analyzed using Raman spectroscopy. The strain is found to be reduced with increasing film thickness due to the onset of island nucleation following Stranski-Krastanov growth mechanism. No phonon assisted direct band gap photoluminescence from compressively strained Ge films grown on relaxed Si0.45Ge0.55 has been achieved up to room temperature. Excitation power and temperature dependent photoluminescence have been studied in details to investigate the origin of different emission sub-bands.
TL;DR: Gold cluster (Au8) coated CdS hybrid nanorods (HNRs), synthesized using a sonication assisted assembly route, exhibit phonon assisted coherent mixing of excitons, effecting enhancement of exciton-phonon (e-p) interactions.
Abstract: Gold cluster (Au8) coated CdS hybrid nanorods (HNRs), synthesized using a sonication assisted assembly route, exhibit phonon assisted coherent mixing of excitons. As observed from optical absorption, Raman scattering, x-ray diffraction and transmission electron microscopic studies, the Au8 modulates the crystal—and electronic—structure of the CdS nanorods, effecting enhancement of exciton–phonon (e–p) interactions. The e–p interaction and entropy effect mediated phase matching of the excitonic transitions, leading—via cooperative and coherent mixing of the excitons' color—to the emission of white light, has been confirmed from room temperature and time resolved photoluminescence measurements.
Journal Article•
TL;DR: In this article, a multilayer of Al2O3-YSZ thin film was applied as thermal barrier coating (TBC) for thermal barrier in thermal barrier coatings.
Abstract: The present study concerns development of yttria stabilized zirconia (YSZ), Al2O3 and a multilayer of Al2O3-YSZ thin film deposition by pulsed laser deposition (PLD) technique for its application as thermal barrier coating (TBC). The detailed study included characterization (microstructure, composition, phase and surface topography) of the thin film. The phase analysis of the YSZ films deposited at room temperature showed amorphous feature, while the film deposited at high temperature showed the formation of tetragonal phase. Residual stress analysis of the coating showed the presence of compressive stress and was maximum at 573 K (σ11 = -8.1 GPa and σ22 = -6.4 GPa). Residual stress was found to decease with increase in substrate temperature and was found to be lowest at 973 K (σ11 = -3.0 GPa and σ22 = -1.7 GPa). The crosssectional morphology of the YSZ and Al2O3 thin films deposited at room temperature showed presence of inter-columnar porosities which changed to a dense structure with increase in substrate temperature.
TL;DR: A hybrid photovoltaic device was demonstrated on polyethylene terephthalate (PET) substrates paving the way to achieve flexible,transparent and printable devices.
Abstract: Hybrid photovoltaic devices were fabricated using different sizes of CdSe quantum dots with different loading concentrations in P3HT matrix. CdSe quantum dots were synthesized chemically using olive oil as the capping agent, instead of toxic phosphine. The efficiency of hybrid poly-(3-hexylthiophene-2,5-diyl) P3HT:CdSe photovoltaic device was found to depend on the size as well as the loading of the nanocrystals. A maximum power conversion efficiency of -0.8% was achieved under AM1.5G solar illumination for the device with -5.3 nm CdSe nanocrystals. A hybrid photovoltaic device was demonstrated on polyethylene terephthalate (PET) substrates paving the way to achieve flexible,transparent and printable devices.
01 Jan 2016
TL;DR: In this article, the two-photon absorption co-efficient and saturation intensity for grown and reduced graphene oxide (RGO) were measured using single beam open aperture Z-Scan technique in femtosecond regime.
Abstract: Graphene Oxide (GO) has been prepared by modified Hummers method and it has been reduced using an IR
bulb (800-2000 nm). Both as grown GO and reduced graphene oxide (RGO) have been characterized using
Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Raman spectra shows well documented Dband
and G-band for both the samples while blue shift of G-band confirms chemical functionalization of
graphene with different oxygen functional group. The XPS result shows that the as-prepared GO contains 52%
of sp 2 hybridized carbon due to the C=C bonds and 33% of carbon atoms due to the C-O bonds. As for RGO,
increment of the atomic % of the sp 2 hybridized carbon atom to 83% and rapid decrease in atomic % of C=O
bonds confirm an efficient reduction with infrared radiation. UV-Visible absorption spectrum also confirms
increment of conjugation with increased reduction. Non-linear optical properties of both GO and RGO are
measured using single beam open aperture Z-Scan technique in femtosecond regime. Intensity dependent nonlinear
phenomena are observed. Depending upon the intensity, both saturable absorption and two photon
absorption contribute to the non-linearity of both the samples. Saturation dominates at low intensity (~ 127
GW/cm 2 ) while two photon absorption become prominent at higher intensities (from 217 GW/cm 2 to 302
GW/cm 2 ). We have calculated the two-photon absorption co-efficient and saturation intensity for both the
samples. The value of two photon absorption co-efficient (for GO~ 0.0022-0.0037 cm/GW and for RGO~
0.0128-0.0143 cm/GW) and the saturation intensity (for GO~57 GW/cm 2 and for RGO~ 194GW/cm 2 ) is
increased with reduction. Increase in two photon absorption coefficient with increasing intensity can also
suggest that there may be multi-photon absorption is taking place.