Papers by Keyword: Energy Gap

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Authors: M.H. Abdi, N.B. Ibrahim, M.M. Bagheree Mohagheghee
Abstract: Emergenceof innovative technological deposition technique of spray pyrolysis enabled the enhancement of structural, optical, and electrical properties of Sn1-xCrxO2 (x=0.0, 0.02, 0.04, 0.06, 0.10, 0.15) transparent semiconductors thin films in the present study. To evaluate these properties, X-Ray diffraction (XRD) spectroscopy were usedto study the elemental component and the crystalline nature of the materials while the optical properties and structure of the samples were evaluated using UV—vis spectroscopy and field emission scanning electron microscopy (FE-SEM).Finding showed that the Cr-doped SnO2 films were tetragonal in shape. Transmission spectra of the deposited films showed high transparency of ~ 70-90% in visible region with optical edge of 3.7eVfor SnO2. Resistivity of pure tin oxide samples was 0.01 Ω-Cm and increases with increase in dopant level. The Hall voltage showed that the type of semiconductor changed with increasing of dopant.
Authors: Mohammad Hafizuddin Haji Jumali, K. Mohamad Al Asfoor Firas, Shahidan Radiman, Akrajas Ali Umar
Abstract: Optical properties of TiO2 dressed on the surface of MWCNTs have been investigated. The samples were prepared using modified microwave method and characterized using TEM, XRD and UV-Vis spectroscopy. A clear interface between MWCNT and TiO2 indicated strong attachment between these two nanostructures. Significant change in absorption spectra proved the absorption wavelength and band gap energy of TiO2 nanostructures can be controlled via dressing of MWCNT.
Authors: S.A. Aly
Abstract: The optical properties of cobalt oxide samples prepared by spray pyrolysis technique on glass substrates with different film thicknesses have been studied. The structural characteristics of the samples were investigated using X-ray diffraction. The optical properties of the prepared films were studied by transmittance and reflectance measurements, and the integrated transmittance (TVIS, and TNIR) and absorptance (AVIS and ANIR) in VIS and NIR regions was calculated and found to be affected by film thickness. The dependence of absorption coefficient on wave length was also reported. The energy gap was calculated and two energies have been observed at 2.15 and 1.5 eV suggesting that the deposited films are semi-conducting with allowed direct transitions.
Authors: Xiang Gao, Peng Wan Chen, Jian Jun Liu, Hao Yin, Feng Lei Huang
Abstract: In this paper, nitrogen-doped titania was achieved by detonation-driven flyer impacting on the mixtures of TiO2 and different nitrogen precursors. XRD、UV-Vis and XPS spectra were employed to characterize the phase composition, N doping concentration and energy gap of recovered samples. N doping concentration can be effectively regulated by choosing different doping nitrogen resources, changing initial content of doping nitrogen resources and flyer velocity in order to regulate the energy gap of TiO2. The maximum concentration of nitrogen of doped TiO2 by shock loading at 3.37 km/s is 13.45 at%. The results show that anatase transforms to rutile and srilankite appears at a higher flyer velocity (1.9-2.52km/s), the concentration of doped nitrogen in the recovered samples increases with increasing flyer velocity, the maximum concentration of nitrogen is 13.45 at%. The edge adsorption wavelength of nitrogen-doped titania induced by shock wave is shifted from 435nm to 730 nm and the corresponding energy gap is reduced from 2.85 eV to 1.73 eV.
Authors: Ting Zhang, Ming He, Tao Chen, Guang Chang Wang
Abstract: First principle calculations are performed on the structure, energy band gap, and dielectric properties of wurtzite and hexagonal BN by using a plane-wave pseudopotential method. It is found that h-BN has much narrower VB (valence band ) width and much sharper band edge than those of w-BN. And the N 2s states of the two phases of BN are dominant below 30.03 eV and the N 2p states are dominant in the range between −20.62 and 20.32 eV.
Authors: W. Liu, S. Berko, Allen P. Mills
Authors: Hong Xia Wang, Zi Biao Song, Dai Zhi Liu
Abstract: On the base of the electron energy band structure of graphene obtained by the tight-binding method, the quantized wave vector equation along the circumferential director of the spiral single-walled carbon nanotubes was established through coordinate transformation and periodic boundary condition, and an analytical expression of the electron energy band was derived. MATLAB is used to calculate the energy band curve of spiral single-walled carbon nanotubes with different structural parameters. The characteristic of the energy band curves was analyzed and discussed. The results shows that single-walled carbon nanotubes (n, m) can be identified as metallic with no band gap nearly which satisfies n-m=3q(q is integer), otherwise, the nanotubes is semiconducting and there are band gaps between conduction band and valence band. And the band gap is inversely proportional to diameter approximately for semiconducting tubes.
Authors: Silvana da Dalt, Juliano Schorne Pinto, Felipe Antonio Lucca Sanchez, Annelise Kopp Alves, Carlos Pérez Bergmann
Abstract: Carbon nanotubes (CNT) have been investigated for a wide range of applications. The combination of the CNT structure with semiconductors oxides opens up various application possibilities: water separation for hydrogen generation, degradation of pollutants in aqueous contamination and sewage treatment, photoreduction of CO2 activity in self-cleaning air purification and dyes for solar cells. The junction multi-walled carbon nanotubes with dioxide titanium and zinc oxide (MWCNT-TiO2-ZnO), when used as support, can facilitate a change in electron transfer, increasing the photocatalytic activity. MWCNTs/TiO2/ZnO nanocomposites were prepared by the modified sol-gel method using MWCNTs, titanium (IV) propoxide, commercial TiO2 (P25) as titanium sources, zinc oxide produced in the laboratory by thermal evaporation and commercial ZnO. The composites obtained from the titanium (IV) propoxide were prepared by solution processing followed by thermal treatment at 500° C. The results were associated with the characteristics of the nanocomposites using Raman spectroscopy. The photocatalytic activity on organic dye was associated to energy gap evaluated by diffuse reflectance spectroscopy.
Authors: Chia Cheng Huang, Fang Hsing Wang, Cheng Fu Yang, Hong Hsin Huang, Cheng Yi Chen, Ping Chih Huang
Abstract: W-TiO2 (W, tungsten) dual-layer thin films are deposited by RF magnetron sputtering onto glass substrates and annealed at 150oC~400oC for 4hrs. The crystal structure, morphology, and trans- mittance of annealed W-TiO2 dual-layer thin films are investigated by X-ray diffraction, FESEM, and UV-Vis spectrometer, respectively. The annealing temperatures have large effect on the properties of W-TiO2 dual-layer thin films. The band gap energy values of W-TiO2 dual-layer thin films are evaluated from (h)1/2 versus energy plots. The energy gap for un-annealed W-TiO2 dual-layer thin film is 3.16 eV. As the annealing temperature increases from 150oC to 400oC, the energy gap decreases from 3.16 eV to 3.10 eV.
Authors: Imen Gaied, Abdelaziz Gassoumi, Mounir Kanzari, Noureddine Yacoubi
Abstract: Sulfosalt SnSb2S4 films have been deposited on glass substrates by thermal evaporation and subsequently thermally annealed in vacuum at temperatures from 100 to 250°C. Below a transition temperature of 140°C, the films are highly resistive with a dominant amorphous component, however above this temperature, the samples exhibit p+-type semiconductor behaviour with a dominant crystalline component.In this work we have studied the thermal and optical properties of these films using the photothermal deflection technique. The thermal properties are determined by comparing the experimental amplitude and phase curves variations versus square root modulation frequency of the photothermal signal to the corresponding theoretical ones. The best theoretical fitting curves are obtained for well-defined values of thermal conductivity and thermal diffusivity. The optical absorption spectrum is obtained by comparing the experimental normalized amplitude of the photothermal signal curves variations versus the wavelength to the corresponding theoretical curves variations versus the optical absorption coefficient. We have determined the energy gap by using the Tock law. From a measure of the sample’s resistance, one can deduce the electrical resistivity which may be correlated to the thermal conductivity.
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