Papers by Keyword: Energy Gap

Abstract: The optical properties of CdZnS nanofilms are studied in this paper in relation to the deposition time. Deposition times ranged from 15 to 60 minutes for the CdZnS thin films, which had been developed on surface of glassy substrates. The other factors, such as reactant concentration, solution pH, and bath temperature, were held constant throughout the deposition process. The films were annealed at 200 °C for 120 minutes in a thermal furnace after the deposition process. Measurements of absorbance, transmission spectrum, and direct and indirect energy gaps were made using UV-VIS spectrophotometers. Transmittance in the 400-1000 nm range was 70-90 percent for all of the prepared films. With a wavelength of 600 nm and higher, transmittance was around 90%. CdZnS films have bandgap energies ranging from 2.4–2.15 eV for direct transitions and from 2.1–1.97 eV for indirect band gaps.

Abstract: In the current study, the density function theory (DFT) is used to investigate the chemical adsorption strength of NO₂ gas molecule. The relaxation structure, molecular orbital energy, energy gap and adsorption energy are calculated at ground state. The time dependent DFT (TD-DFT) used to simulate excitation provides UV-Visible spectrum. There was a perpendicular geometrical orientation of the gas molecule around the surface and an adsorption distance of 2.58 Å. The adsorption distance shows the chemical reaction between the gas molecule and the surface. The result of adsorption energy indicates that the gas molecule that closed to the surface has high interaction and it decreases gradually when gas molecule goes further from the graphene nano-ribbon surface. The UV-Visible measurement indicates that the system interaction with gas molecule has red shifting in electromagnetic radiation. The final result concludes that graphene nano-ribbon has high reactivity for NO₂ gas molecule. The theoretical calculations provide the ability to design optical sensor which has useful applications in an environmental monitoring.

Abstract: Nanocomposites were prepared by the method of solution casting with different proportions of magnesium oxide nanoparticles (0, 1, 3, 5, 7 and 9) wt%. The structural and optical properties of nanocomposites of CMC/MgO have been studied. It was well known that the increased content of MgONPs in the method contributes to the peaks of MgONPs being completely integrated and/or disappearing within the CMC diffraction halos in the experimental results of XRD study. The differences in the XRD spectrum indicate that doping with nanoparticles induced a disparity in the microstructure of the polymer. Nanocomposite film scanning electron microscopy (SEM) reveals that MgONPs appear to form aggregates and scatter well in (CMC/MgO) nanocomposite films and at apply 9 wt. It forms a continuous network within the polymer for the percentage of MgONPs to (CMC) polymer. FTIR spectrum revealed the MgONPs has no destructive influence on the polymer structure as no covalent bonds formed between CMC and MgONPs. The optical properties of CMC/MgO nanocomposites were measured in wavelength range (200–900) nm. Experimental studies have shown that the absorbance, absorption coefficient, extinction coefficient, refractive index, actual and imaginary dielectric constant of CMC polymer is improved with an increase in concentrations of MgONPs in nanocomposites. The transmittance and energy gap of CMC polymer are decreased with the increase in the concentrations of MgONPs.

Abstract: In present work, the structure, absorption and energy gap of films prepared from biodegradable polymer doped ZrO₂-SiC NPs for UV-shielding, biomedical fields and optoelectronics approaches were investigated. The nanocomposites films were fabricated by casting method. The absorption spectra was measured in range (200-800) nm. Results indicated to enhance in absorption and energy gap of biopolymer by adding of ZrO₂-SiC NPs ratios, this behavior make it suitable for various applications like antibacterial films, anti-UV light, diodes, solar cell, transistors and other fields. Keywords: biodegradable polymer, UV-shielding, absorption, energy gap, ZrO₂.

Abstract: Thin films Tin sulfide SnS pure and doped with different ratios of Cu (X=0, 0.01, 0.03 and 0.05) were prepared using thermal evaporation with a vacuum of 4*10^-6 mbar on two types of substrates n-type Si and glass with (500) nm thickness for solar cell application. X-ray diffraction and AFM analysis were carried out to explain the influence of Cu ratio dopant on structural and morphological properties respectively. SnS phase appeared forming orthorhombic structure with preferred orientation (111), increase the crystallinity degree and surface roughness with increase Cu ratio. UV/Visible measurement revealed the decrease in energy gap from 1.9eV for pure SnS to 1.5 for SnS: Cu (0.05) making these samples suitable for photovoltaic application. On the other hand, Hall Effect indicated the high percentage of Cu increased carrier concentration and mobility. Current-voltage characteristics of p-SnS: Cu / n-Si demonstrate good photovoltaic effect as ratios of Cu increased and the contact parameters which obtained from these measurement show good dependence on doping concentration. In addition, 0.05 of Cu doping was an optimum level of concentration doping increase the efficiency of SnS: Cu /Si solar cell to 3.5%.

Abstract: A p-type thin film of hydrogenated amporphous silicon (a-Si:H) has successfully been fabricated by radio frequency-plasma enhanced chemical vapor deposition (RF-PECVD) technique. Substrate used in the deposition process is indium tin oxide (ITO) layer coated having size of 10 x10 cm² and being cleaned with 97% alcohol using ultrasonic bath. According to Atomic Force Microscope (AFM) observation, the layer thickness of p-type a-Si: H film was 150 nm. The Transmission spectrum at room temperature obtained from UV-Vis measurement demonstrates a large period modulation, which is due to the interference within the film. At wavelength longer than 1000 nm (or energy <1 eV), the interference modulation in the transmission spectrum of the film is seen to broaden. It is shown in a zoomed - scale around the related band gap area that one may find an exciton structure.

Abstract: Cubic phase of silver antimony sulfide (AgSbS₂) nanostructures were successfully synthesized from silver nitrate (AgNO₃)_, antimony acetate (CH₃CO₂)₃Sb, and sodiumthiosulphate pentahydrate (Na₂S₂O₃.5H₂O) in propylene glycol (PG) without using any surfactants or splitting agents by a facile wet chemical route at 160 ^OC for 30 min. The XRD, SEM and TEM reveal AgSbS₂ nanostructures forming the clusters. Due to the UV-visible absorption shows its direct band gap, is 1.80 eV, AgSbS₂ is found to be the excellent material for the solar energy converters. And the possible formation of AgSbS₂ nanostructured cluster was also discussed.

Abstract: The objectives of this study were to mix TiO₂ and SiO₂ gel for photo catalyzing in methylene blue and calculated energy gap of TiO₂- SiO₂ gel composite. Nanoparticles of TiO₂-doped SiO₂ gels have been synthesized for use as composites in photodegradation of methylene blue. SiO₂ gel was synthesized by a sol-gel method from rice husk ash. TiO₂ was synthesized by microwave method from TiOSO₄. The composite of TiO₂-SiO₂ was prepared by mixing of 25% wt TiO₂ and 75% wt SiO₂ gel and SiO₂ gel bead. This work can be dived into two kinds of TiO_­2 sources were TiO₂ from microwave synthesis (MW) and TiO₂ from P25. The UV absorption values of methylene blue after used TiO₂-SiO₂ composite were measured. Wavelengths of composites were measured by Uv-vis reflectometer and energy gap were calculated.

Abstract: Modifying the optical properties of rare earth doped phosphate glasses in a tunable fashion via the embedment of magnetic nanoparticles (NPs) is challenging for magneto-optic devices. Glasses with compositions (69-x)P₂O₅-30ZnO-1Er₂O₃-(x)Fe₃O₄, where x = 0 to 1.5 mol% are prepared by conventional melt quenching method. The Fe₃O₄ NPs concentration dependent density, molar volume, refractive index and optical properties are determined. Density and molar volume shows strong correlation with structural alteration in the presence of NPs. The XRD spectra confirm the disordered nature of the glass and TEM micrograph display the presence of spherical NPs with average size ~26 nm. The optical band gap and Urbach energy calculated from the room temperature absorption spectra recorded in the range of 350-1700 nm reveal significant improvement. The density and refractive index increases and the molar volume decreases with the increase of Fe₃O₄ contents. The energy band gap for direct and indirect transitions varies in the range of 4.47-3.64 eV and 4.27-3.53 eV, respectively. The Urbach energy increases from 0.15 to 0.19 eV as the NPs concentration increases from 0 to 1.5 mol%.

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.