Arnab Sankar Bhattacharyya; Ritambhara Dash
Abstract
The rGO-ZnO composite was found promising improvement over the photocatalytic ability of pure ZnO and is useful for other Opto-chemical applications. ZnO/rGO composite was synthesized by the sol-gel method. The morphology of rGO caused better dispersion of the ZnO crystallites The reducing agent ammonia ...
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The rGO-ZnO composite was found promising improvement over the photocatalytic ability of pure ZnO and is useful for other Opto-chemical applications. ZnO/rGO composite was synthesized by the sol-gel method. The morphology of rGO caused better dispersion of the ZnO crystallites The reducing agent ammonia was varied in concentration during the synthesis. A reduction in the crystallization was observed for lower concentrations (0 – 1%) of ammonia which got stabilized in higher concentrations (>1%). The crystalline morphology showed variations from being close to amorphous to 38 nm. The average crystallite size was 15 nm. The rGO induced nonradiative phononic modes in the optical transition process when present in lower concentration but interestingly aided the crystallization process in a preferential crystallographic orientation which however got lowered in intensity for >2% ammonia concentration. The defect states formed in the rGO/ZnO composite in the form of oxygen vacancies, zinc interstitials, and vacancies caused a decrease in band gap due to indirect transitions. The role of ammonia in the performance of the composites was found to be significant
Ramakanta Naik; C. Sripan; R. Ganesan
Abstract
In this manuscript, the As40Se60 and As50Se50 samples of 800nm thickness were deposited onto glass substrate by thermal evaporation technique. The as-deposited films were characterized using X-ray diffraction (XRD) and FTIR Spectrophotometer. The prepared samples are amorphous type. The transmission ...
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In this manuscript, the As40Se60 and As50Se50 samples of 800nm thickness were deposited onto glass substrate by thermal evaporation technique. The as-deposited films were characterized using X-ray diffraction (XRD) and FTIR Spectrophotometer. The prepared samples are amorphous type. The transmission is found to be decreased for As50Se50 film. The indirect optical transition mechanism for the photon absorption happens inside the studied film. The optical band gap is decreased with change in As and Se content. The density of state model and increase in disorder is responsible for the reduction of optical band gap in the studied films. The addition of more % As creates localised states in the gap which results the tailing of the band edges. The Urbach energy which gives the degree of disorder changes that indicates the more disorderness of As50Se50 than As40Se60 film. The XPS As3d, Se3d core level spectra variation infers the optical changes in the film and such type of film can be used for optical materials and optoelectronics.
Manpreet Kaur; Akshay Kumar; Manoj Sharma
Abstract
Composition regulation of semiconductors can engineer the band gap and thus tune the optical properties. For effective utilization of orange emitting phosphors in color conversion applications blue excitation is necessary. Here in this work, absorption and photoluminescence spectroscopic measurements ...
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Composition regulation of semiconductors can engineer the band gap and thus tune the optical properties. For effective utilization of orange emitting phosphors in color conversion applications blue excitation is necessary. Here in this work, absorption and photoluminescence spectroscopic measurements have been done to study the variation in band gap energy by changing the composition of ZnxCd1-xS nanocrystals. Further, ternary Mn doped ZnxCd1-xS semiconductor nanocrystals have been synthesized via an aqueous route over a wide composition range by adjusting the molar ratio of precursors which leads to tunable bandgap, thus propagate the progressive growth of light absorption and photoluminescence spectra. The variation in tunability of bandgap is due to the change in Cd/Zn ratio. By changing Cd/Zn ratio excitation wavelength shifts from UV to blue colour. Copyright © 2017 VBRI Press.
Shahjad .; Ranoo Bhargav; Dinesh Bhardwaj; Asit Patra
Abstract
Currently significant progress has been made for the small molecules, indeed, achieved comparable performance compared to polymer in electronic devices mainly due to the many advantages of small molecules over the polymers. Designing better small molecules for electronic applications are required a comprehensive ...
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Currently significant progress has been made for the small molecules, indeed, achieved comparable performance compared to polymer in electronic devices mainly due to the many advantages of small molecules over the polymers. Designing better small molecules for electronic applications are required a comprehensive understanding of the structure-properties relationship and the factors affecting it. Valuable information can be generated directly toward understanding by systematically theoretical and experimental studies (band gap, HOMO, LUMO energy levels and geometry). Hybrid density functional B3LYP level of theory is a very good method for predicting the reliable geometry, electronic structure and properties of conjugated systems. In the present work, we have calculated the band gaps, highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and geometry of a series of small molecules based on oligothiophene, benzodithiophene and dithienosilole unit using the hybrid density functional (B3LYP/6-31G(d)) level of theory and correlated with experimental values. The study provides details for the effect of the extended conjugation, two-dimension conjugation, substitution on geometry, HOMO, LUMO and band gaps of the small molecules. Copyright © 2017 VBRI Press.
Elangbam C. Devi; Ibetombi Soibam
Abstract
Manganese ferrite nanoparticles with chemical formula MnFe2O4 have been synthesized by low temperature chemical co-precipitation method. The structural and optical properties of the nanoparticles were studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray ...
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Manganese ferrite nanoparticles with chemical formula MnFe2O4 have been synthesized by low temperature chemical co-precipitation method. The structural and optical properties of the nanoparticles were studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), fourier transform infra-red spectroscopy (FTIR) and UV-visible absorption spectroscopy. XRD confirm pure spinel phase formation of the prepared sample. All the observed peaks correspond to the standard diffraction pattern of manganese ferrite having JCPDS card number 74-2403. From the XRD data, the average crystallite size was calculated and found to be 27.40 nm. The FTIR spectrum shows the characteristic bands of the spinel ferrite. Morphology of the nanoferrites was given by SEM image revealing that the particles are approximately spherical in shape. The elemental composition along with their relative ratios was given by EDAX and was found to be in agreement with their initial calculated values. UV- visible absorption spectrum of the prepared sample shows characteristic absorption in visible range and from the UV-visible absorption data the band gap of the prepared sample was determined. MnFe2O4 nanoparticles were found to possess a narrow band gap of 1.4 eV which may find applications in photocatalytic degradation of pollutants. The simple co-precipitation method proves to be an effective method for synthesis of pure phase manganese ferrite nanoparticles. Copyright © 2017 VBRI Press.
Trilok K. Pathak; L. P. Purohit
Abstract
ZnO and ZnO:N thin films were deposited on plane glass substrate using RF sputtering method. The crystalline structure and surface morphology of the film was investigated using XRD and SEM. The XRD patterns of ZnO thin films have largest crystalline orientation for the (002) peak and shows wurtzite structure. ...
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ZnO and ZnO:N thin films were deposited on plane glass substrate using RF sputtering method. The crystalline structure and surface morphology of the film was investigated using XRD and SEM. The XRD patterns of ZnO thin films have largest crystalline orientation for the (002) peak and shows wurtzite structure. The ZnO thin films composed of dance packing, grains without any cracks indicating uniform grain size distribution. The transmittance and absorbance of ZnO thin film was measured using UV-VIS-IR spectrophotometer in the wavelength range 200 nm-800 nm. The band gap of ZnO film was3.26 eV calculated by Tauc’s plot method. Photoluminescence property was also investigated at the excitation wavelength 325 nm. A.C. conductivity measurements carried out on the ZnO/ZnO:N thin films at room temperature in the frequency range 10 KHz to 0. 1MHz. This measurement also helps to distinguish between localized and free band conduction.The study demonstrated that ZnO and ZnO:N thin films fabricated by RF sputtering method can be used in electronicand optoelectronic applications due to high transmittance in visible region, large bandgap and localized conduction. Copyright © 2016 VBRI Press.
Mukta Behera; Rozalin Panda; Naresh C. Mishra; Ramakanta Naik
Abstract
In the present work, structural, microstructural, compositional and electronic band gap properties of As40Se60 and As40Bi15Se45 bulk and thin films are reported. The films were prepared by thermal evaporation technique under high vacuum. X-ray diffraction (XRD) study indicated amorphous nature of As40Se60 ...
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In the present work, structural, microstructural, compositional and electronic band gap properties of As40Se60 and As40Bi15Se45 bulk and thin films are reported. The films were prepared by thermal evaporation technique under high vacuum. X-ray diffraction (XRD) study indicated amorphous nature of As40Se60 in bulk prepared by melt quenching technique. Bi incorporation in As40Se60 with composition Bi15As40Se45 however led to nucleation of Bi2Se3 nanocrystallites in the amorphous matrix of As40Se60. The films made out of the two targets of composition As40Se60 and As40Bi15Se45 did not show any XRD peak, indicating their amorphous nature. UV-Visible-NIR spectroscopic study indicated a large decrease in the electronic band gap from 1.74 eV in films of composition As40Se60 to 1.28 eV for compositon Bi15As40Se45. This decrease is explained on the basis of a high concentration of defect states leading to the presence of localized states in the band gap due to Bi incorporation. Field emission scanning electron microscopy (FESEM) images show smooth and homogeneous surface for the As40Se60 films, while Bi incorporation led to increases of the surface roughness in the Bi15As40Se45 films. The decreased band gap and increased surface roughness on Bi incorporation in As40Se60 films indicate the suitability of these films for solar cell applications.
Rozalin Panda; Ramakanta Naik; Udai. P. Singh; Naresh. C. Mishra
Abstract
In the present work, Ag/In/Ag/In multilayers were deposited on glass substrates by DC magnetron sputtering and the films were selenized at 350℃. The selenized films were annealed at 450℃ and 500℃. The selenized and annealed films were characterized by X-ray diffraction (XRD), UV-Visible-NIR spectroscopy ...
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In the present work, Ag/In/Ag/In multilayers were deposited on glass substrates by DC magnetron sputtering and the films were selenized at 350℃. The selenized films were annealed at 450℃ and 500℃. The selenized and annealed films were characterized by X-ray diffraction (XRD), UV-Visible-NIR spectroscopy and Field Emission Scanning Electron Microscopy (FESEM). XRD revealed formation of the desired AgInSe2 phase along with Ag2Se as impurity phase. Unlike in previous studies, where conventional approach of optimizing the volume fraction of initial precursor material is adopted to control the phase purity of AgInSe2, we show that annealing highly impure films at 500℃ can suppress the impurity phase and lead to pure AgInSe2 phase. The suppression of the low band gap Ag2Se impurity phase on annealing the films at 500℃ led to increase in the optical band gap. Copyright © 2016 VBRI Press
