Papers by Keyword: Band Gap Energy

Abstract: In this work 3,5 Bis(Tri fluro methyl)Benzyl amine phenyl alanine a monmer molecule is DFT theoretically optimized to get the structural insight of the molecule. Band gap energy, Mullikan atomic charges, DOS spectral analysis, HOMO - LUMO, Electrostatic surface potential , molecular electrostatic potential and theoretical Raman spectral analysis is computed and compared with the experimental data .Since this molecule shows self assembly similar to peptide molecules it is quite interesting to analyze its structure based on theory and experimental the results suggests the H –boding interactions between the molecules is the key mechanism. The band energy from DOS plots suggests the molecular interactions through π-π .The possibility of the self assembly is explained further from Raman spectral studies that tells the mode specific interaction among the molecules..

Abstract: TiO₂ nanofibers were synthesised by means of the electrospun technique, which were annealed at high temperatures to achieve the crystalline phase transformation from amorphous to rutile through anatase and the phase mixture. The chemical stoichiometry of electrospun TiO₂ nanofibers was estimated by EDS, finding that at low annealing temperatures excess of oxygen was detected and at high temperatures excess of titanium that originates oxygen vacancies. The TEM images showed clearly the formation of TiO₂ nanofibers (NF’s) that exhibit a homogeneous and continuous aspect without the presence of crystalline defects, whose surface morphology depends strongly on the annealing temperature. The crystalline phase transformation was studied by Raman spectroscopy, which revealed that annealed TiO₂ NF’s showed a crystalline phase transformation from amorphous, pure anatase, anatase-rutile mixed, to pure rutile as the annealing temperature increased, which was corroborated by X-ray diffraction and high-resolution TEM. The average grain size, inside the NF´s, increased with the crystalline phase transformation from 10 to 24 nm for anatase-TiO₂ and from 30 to 47 nm for rutile-TiO₂, which were estimated by using the Scherrer-Debye equation. By absorbance measurements at room temperature the band gap energy (E_g) was obtained, which is ranged in 3.75-2.42 eV, caused by the amorphous → anatase → anatase-rutile mixed → rutile crystalline phase transformation.

Abstract: Zinc oxide (ZnO) thin films were coated onto Indium Tin Oxide (ITO) glass substrate using spin coating technique as a function of annealing temperature. The thin film preparation was undertaken by utilising zinc acetate dihydrate, ethanol and diethanolamine as the precursors. The films were coated at room temperature prior to being annealed at temperatures ranging from 300 °C to 450 °C. The resulting crystalline structure and surface morphology of the thin films were then examined using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). UV-visible spectrophotometer was also used to record the optical absorbance in wavelengths ranging from 200 to 800 nm. The findings revealed that the ZnO thin films showed a single phase of wurtzite with n-type semiconductor, with the lowest value of band gap energy of 3.28 eV for ZnO thin films annealed at 350 °C. FESEM results showed that the ZnO nanoparticles were very compact on the surface, whereby the average particle size was equivalent to 108.5, 115.3, 108.2 and 107.8 nm at the temperatures 300 °C, 350 °C, 400 °C, and 450 °C, respectively. Additionally, the highest photoconversion efficiency (0.11%) recorded for the sample was annealed at 350^◦C. Thus, annealing temperature was found to significantly affect the optical and electrical properties of ZnO nanoparticle seed layer, as well as its band gap energy and surface morphology.

Abstract: Glass substrates are used to deposit thin films utilizing basic and value effective chemical bath deposition (CBD) technique. The films were prepared from the mixture as solutions of manganous acetate tetrahydrate [C₄H₆MnO₄4H₂O] as a manganese source, thiourea [(H₂ N) ₂ CS] as a sulfur source and triethanolamine (TEA) [(HOC₂H₄)₃N] as a complexing agent.In the present paper the deposition was successfully done at 60 °C temperature. The absorption properties and band gap energy were determined employing double beam spectrophotometer. The optical band gap value calculated from absorption spectra of MnS thin film is found to be about 3.1eV.The MnS thin film was structurally characterized by X-ray Diffraction (XRD). The MnS thin film was morphologically characterized by Scanning Electron Microscopy (SEM) and elemental analysis was performed using EDS to confirm the formation of MnS.

Abstract: Tungsten trioxide (WO₃) is an oxygen deficient metal oxide and well known semiconductor with a small band gap of between 2.4 and 2.8 eV. It is also used as a photo-catalyst for degradation of organic pollutants present in aqueous environment. It has stable physico-chemical properties and shows strong absorption of solar spectrum and thus can be used in visible-light driven photocatalysis. WO₃ has a conduction band (E_CB) of +0.4 V versus NHE (normal hydrogen electrode) at pH = 0. Therefore, pure WO₃ has lower light energy conversion efficiency as compared to other widely used photocatalysts such as zinc oxide (ZnO) and titanium oxide (TiO₂). This is because the reduction potential of the electrons in WO₃ is low due to its low conduction band level. O₂ cannot be efficiently trapped in the conduction band electrons to yield superoxide radicals and fast recombination of charge carriers takes place resulting in lesser photocatalytic activity of WO₃. However, holes in the valence band (E_VB = +3.1 V) are energetically favorably situated to oxidize water to hydrogen. To modify the energy band position and reduce the charge carrier recombination, doping or surface modification of WO₃ is necessary. This review article demonstrates the effect of dopants (low band semiconductor catalyst) on the surface modification of WO₃ to enhance the photo catalytic activity which helps in degradation of the organic pollutants present in the wastewater.

Abstract: This work aims to study the effect of ZnO containing in TiO₂/SiO₂ film on the superhydrophilic property after exposed to different types of light. The metal solutions were prepared by sol-gel technique and the film was deposited on glass slides by dip coating method. The parameter studied was the amount of ZnO in the TiO₂/SiO₂ film. The contents of ZnO were 5-20% weight (increased by 5%). The amount of TiO₂ was constant at 30% weight. The obtained films were analyzed for their roughness. The results indicated that film roughness changed according to the ZnO contents. With 5%ZnO in the thin film, the roughness was 0.726 nm while 20%ZnO obtained the roughness of 2.128 nm. UV-Vis spectrophotometer was used for measuring of transmittance of films. At wavelength of 550 nm, the transmittances of each film were greater than 90%. Band gap energy of each film was calculated from the transmittance data. It was found that the average band gap energy of the films was 2.47 eV. Then, the films contained various amount of ZnO were grouped into 2 sets. The first set was exposed to visible light while the other set was exposed to UV. The duration of exposure was 5 hr. Both sets of films after exposed to any light were kept in a black box controlled relative humidity of 85%. Each film was measured contact angle every day. It was found that the 30%TiO₂/5%Zn/SiO₂ film exposed to visible light showed the best superhydrophilic property. The contact angle was about 0-5° within 3 days. This may due to the reduction of band gap energy in the presence of ZnO in TiO₂/SiO₂ films to 2.41 eV and the roughness of the film.

Abstract: Carbon Dots (C-Dots) was successfully prepared by simple heating method. The effect of additional elemental sulfur on the luminiscent performance of C-Dots was investigated. The preparation, chemical composition and optical properties such as absorbance and band gap energy are studied. The C-Dots were prepared with various mass sulfur 0.5-3.0 g and citric acid-urea was constant, i.e. 1.0 g and 4.0 g, respectively. This study used sulfur from natural deposit in Indonesia. The raw materials were prepared by mixing in pure water. The homogeneous solutions were heated at 225°C for 15 minutes under atmospheric pressure. The color emission of C-Dots is found in the visible light spectrum. The addition of sulfur in C-Dots phosphor caused the shifting of absorbance wavelength, i.e. 350-429 nm. By increasing mass of sulfur, the band gap energy of C-Dots decreased from 2.4 eV to 1.8 eV.

Abstract: Under external electric field, a free standing silicene monolayer is investigated for the physical and electronic features using the density functional theory with norm-conserving pseudopotentials and pseudo-atomic localized basis functions. It is found that silicene tends to be flat instead of buckled as applying electric field perpendicular to the surface. We observed on some range magnitude of electric field and noticed that there is a monotonic decreasing in number of DOS near the Fermi level showing the possibility of tunable bandgap on silicene. We also found that in this higher magnitude electric field, the Dirac cone is no longer occurring at K-point while the band gap term remains direct. The asymmetry onsite potential between the Si atom at site A and B spoils the degeneracy at the K point by the presence of external or internal influence. In this work, we try to combine those influences by considering Stone Wales (SW) defect and outer z-direction of electric field as internal and external factors respectively. A non-linear correlation of the result is profoundly becoming more effective way in effort to bring remarkable band-gap in silicene monolayer.