Papers by Keyword: Band Gap

Abstract: We present the rational synthesis of novel nanocrystals CuS (nc-CuS) by single source molecular precursor (SSMP) method. Among the present materials synthetic routes, the SSMP route is high efficient and comfortable way to construct nanostructured materials. Both CuS nanocrystals capped with hexadecylamine (HDA) and trioctylphosphine oxide (TOPO) have been synthesized by thermolysing bis (N-diisopropyldithiocarbamate)Cu (II) complex at 180 °C. Various physicochemical characterizations such as SEM images of nc-CuS exhibited uniform exfoliated surface morphologies with uniform continuous network of about 50 μm agglomerated particles. Our method could be broadly applicable for the preparation of other high quality yield metal sulfide nanostructures

Abstract: During the last few decades many researchers have been interested in acoustic wave propagation in artificial periodic composites known as sonic crystals. Sonic crystals have received renewed attention because they exhibit acoustic band gaps where there are only evanescent waves. Sonic crystals consist of a periodic array of scatterers embedded in a host medium. The host medium and/or scatterers are fluids. We investigate the band structure of acoustic waves propagating in a sustainable sonic crystal composed by miriti fibers and air, regarding square and triangular lattices. Miriti fibers are extracted from buriti palm petiole (Mauritia flexuosa Mart.), which is a typical specie that grows in Amazonian region. We also study the influence of miriti fiber cross section, i.e. circular, hollow circular, square and rotated square with a 45° angle of rotation with respect to x, y axes. Plane wave expansion method is used to solve the wave equation. Acoustic band gaps are observed for all miriti fiber cross sections and lattices. The best performances of the sustainable sonic crystal are for triangular lattice, regarding circular and rotated square miriti fiber cross sections, and for square lattice with circular miriti fiber cross section. We suggest that the sustainable sonic crystal should be feasible for noise management.

Abstract: Doping of the materials with other metals or transition metals will modify the properties of the nanomaterials. In this work, MgO and Cu doped MgO which are Mg_0.95Cu_0.05O and Mg_0.90Cu_0.10O nanomaterials are synthesized using a self-propagating combustion method. The samples are annealed at 900 °C for 24 hours. The phase and purity of the synthesized samples are studied using X-Ray Diffraction (XRD) and the result revealed that the samples are pure and single phase. The morphology and crystallite size of the pure samples are examined using Field Emission Scanning Electron Microscope (FESEM). The result shows polyhedral morphology with agglomeration of crystallite and average crystallite size of the samples is between 40 to 210 nm. The band gap obtained for MgO nanostructures is 6.38 eV which is lower than bulk MgO of 7.8 eV. The presence of Cu causes the narrowing the band gap energy of Mg_0.95Cu_0.05O and Mg_0.90Cu_0.10O samples to 4.28 eV and 3.35 eV respectively.

Abstract: Pulsed laser deposition (PLD) method has the advantages of high quality mirror finish, good densification and uniform thickness. In this work, Al₂O₃ thin films with different thicknesses were fabricated via the PLD method. The characteristics of the thin film samples were investigated using Grazing Incidence Diffraction (GID) technique and Field Emission Scanning Electron Microscope (FESEM). For the band gap studies, measurements were done using a UV-Vis NIR spectrophotometer. The deposition was done in the presence of oxygen gas with partial pressure of 2.66 Pa. FESEM images showed high quality, smooth and dense films obtained using the PLD method. The Al₂O₃ thin films have thicknesses of between 71.2 nm to 176 nm. The band gap energies obtained were in the range of 6.29 eV to 6.49 eV. It was observed that the band gap of the thin films increases as the thickness decreases due to the defects in the films.

Abstract: Lanthanum and silver co-doped zinc borotellurite glasses having chemical composition of [{[(TeO₂)_0.7(B₂O₃)_0.3]_0.7(ZnO)_0.3}_0.96 (La NPs)_0.04]_1-x(Ag₂O)_x with 0.02 ≤ x ≤ 0.10 molar fraction were fabricated via melt-quenching technique. X-ray diffraction (XRD) analysis confirmed the amorphous nature of the samples through the presence of broad hump instead of sharp peaks. Optical properties of the samples were determined through ultraviolet-visible spectroscopy (UV-Vis) in the range of 220 to 800 nm. Fundamental absorption edge observed in the optical absorption spectra shifts to longer wavelength as the concentration of silver in the glass system increases. Decreasing trend for indirect energy band gap and increasing trend of Urbach energy values with the increment of Ag content suggest the contribution of Ag to the formation of nonbridging oxygen. Enhanced optical properties of the prepared glass hints the possible application of the glass material as optical fiber in photonic field.

Abstract: To reveal the effects of annealing condition on CZTSSe thin film solar cells, co-sputtering and subsequent selenization were used to prepare CZTSSe thin films. Structural, morphological and optical properties of CZTSSe thin films were investigated. CZTSSe thin films with various Se/(S+Se) ratio ranging from 0.69-0.78 were obtained. Representative peaks corresponding to CZTSSe in XRD and Raman results showed a slight shift to lower diffraction angle and wavenumbers. Selenization time significantly influenced the morphologies of CZTSSe films and the gradual grown up grain size was observed. V_OC deficit values down to 839 mV was achieved for the best cell. CZTSSe solar cell with the selenization time of 10 min showed a best conversion efficiency of 5.32%, which presented a 50% enhancement comparing to the solar cells with insufficient and over-selenized absorbers.

Abstract: Thin (200-600 nm) Si-Sn alloy films were grown under ultrahigh vacuum conditions by co-deposition of Si and Sn on the Si (100) substrate at room temperature. Investigations of the film structure by X-ray diffraction showed the preservation of the amorphous structure of Si-Sn films without the contribution of the Si_1-xSn_x alloy with sphalerite lattice at Sn concentration in the range of x=0.14-0.19. Analysis of optical spectra and calculations showed that an amorphous Si-Sn film with a Sn concentration of 19% is a semiconductor with indirect fundamental optical transition with very high absorption at photon energies 0.2 – 1.0 eV. It was found that precipitation of β-Sn occurs with an increase of Sn concentration up to 40%, which is accompanied by an increase in the reflection coefficient to 0.6-0.8 at photon energies below 0.8 eV. The limited temperature stability of amorphous Si-Sn films is shown for high-energy and long-term (10 minutes) laser irradiation due to the formation of metallic precipitates of β-Sn.

Abstract: Solar Energy is an everlasting source of energy with minimal carbon footprint. However, due to lack of reliability and consistency it needs to be converted into more reliable and effective means that can be used to provide energy on demand. Hydrogen is a promising carrier and is thus an efficient mean of energy to be converted in, stored and transported. A more direct approach towards harnessing Solar Energy is by photo-aided generation of hydrogen via splitting of water using photolysis. Photocatalytic water splitting is therefore a promising method for future energy security. On the other hand strain sensing is a useful technique to measure medium range loads in trusses or tension rods & can easily replace the existing fragile & expensive semiconductor based sensors. This was done by using a composite of TiO2 /Reduced Graphene Oxide (RGO); TiO2 (anatase) was synthesized via sol-gel process and the main precursor was titanium tetrapropoxide (Ttip). Titania (anatase) characterized by XRD and photo spectrometry while Graphene oxide was synthesized via modified Hummer’s Method. The obtained Reduce Graphene Oxide was dispersed using Sodium Dodecyl Benzene (SDB) and Hydrazine Hydrate. A drastic synergetic effect was found by simply mixing RGO with TiO2 Solution. This not only broadened the photoactivity spectrum of TiO2 from UV region to the more available visible light radiation but also exhibit strain sensing properties and considerable tunable gauge factor. The photocatalytic effect of our composite was tested by coating it over Polycarbonate & then analyzing emitted gas bubbles in a UV radiation chamber while strain sensing was done by coating it on an elastic substrate & applying loads against values of resistance which were measured. This study will also include the reduction of recombination and band gap of TiO2 in order to synchronize it with the available Solar Spectrum thus maximizing solar-to-hydrogen efficiency.

Abstract: —Density function theory (DFT) based simulation combined with non-equilibrium green function (NEGF) was used to theoretically investigate electrical properties of symmetrical and asymmetrical boron nitride (BN) passivated graphene nanoribbons. Using density function theory method, it is demonstrated that the band gap of armchair (A) graphene nanoribbon (GNR) can be widened with boron nitride passivation. five symmetrical and five asymmetrical structures were considered, for which we obtained band gaps from 0.45 eV to 2 eV for symmetrical structures and 0.3 eV to 1.5 eV for asymmetrical structures. For the same width of graphene nanoribbon, our results showed that asymmetrical structure has a smaller band gap and almost the same conductance in comparison with the symmetrical one. Finally, comparison between the asymmetrical structure and the hydrogenated armchair graphene (h-AGNR) nanoribbon showed that, hBN-AGNR exhibited a higher conductance compared to an h-AGNR for the same width of GNR.

Abstract: High quality (200) and (111) orientations cubic MgZnO thin films were made on (200) and (111) orientations MgO substrates separately under different condition with higher and lower migration energy of reactive atoms separately. The crystal quality of (111) orientation MgZnO thin film is higher than (200) one because of the stronger horizontal migration of atoms on (111) surface under high temperature condition, the surface of (200) orientation MgZnO thin film is smoother than (111) orientation one because of lower vertical growth speed of (200) MgZnO grains. The band gap of (111) orientation MgZnO thin film is smaller than (200) one because of more Zn atoms in (111) orientation MgZnO lattice than that in (200) ones. This paper gives an effective method to improve crystal quality of different orientation MgZnO thin film under different condition, which is meaningful in application of cubic MgZnO in different areas.