Papers by Keyword: Band Gap

Abstract: Since the C₂N-h2D crystal was efficiently synthesized, this study aims to investigate bandgap modulation of nanoribbons and nanotubes. Appling Density Functional Theory (DFT), the band-gap modulation of C₂N-h2D nanomaterials is researched under elastic strains. The results of the current study indicate that the band gap of C₂N-h2D nanoribbons and nanotubes can be tuned along two directions, namely, stretching or compressing nanoribbons and nanotubes when ɛ is changed from -10% to 10% in zigzag and armchair, respectively. This study also finds that the band gap of the C₂N-h2D nanoribbons and nanotubes change with increase of widths or the radii of nanotubes. Therefore, the great potential applications of the C₂N-h2D nanomaterials have been predicted in strain sensor and optical electronics at nanoscale.

Abstract: The influence of oxygen flow rate is examined on structural, optical and tribological properties of molybdenum oxide films deposited by reactive magnetron sputtering. The films were characterized by X-ray diffraction, scanning electron microscope (SEM), and contact angle measurement system. The optical properties of the films were measured by UV-Vis-NIR spectrophotometer and transmittance of ∼73% in the visible region of the spectrum was achieved. The band gap increases with increases in oxygen gas flow rate. AFM figure illustrates that the roughness of surface increases as oxygen flow rate increases. As oxygen increases wear rate and COF decreases while at the 18 sccm the lowest wear rate found.

Abstract: The wave propagation in a two-dimensional bio-inspired phononic crystal (PC) is analysed. When composite materials and structures consist of two or more different materials periodically, there will be stop band characteristic, in which there are no mechanical propagating waves. These periodic structures are known as PCs. PCs have shown an excellent potential in many disciplines of science and technology in the last decade. They have generated lots of interests due to their ability to manipulate mechanical waves like sound waves and thermal properties which are not available in nature. The physical properties of PCs are not essentially determined by chemical elements and bonds in the materials, but rather on the internal specific structures. Structures of this type have the ability to inhibit the propagation of vibrational energy over certain ranges of frequencies forming band gaps. The main purpose of this study is to investigate the band structure and especially the location and width of band gaps. For this analysis, it is used the finite element method (FEM) and plane wave expansion (PWE). The results are shown in the form of band structure and wave modes. Band structures calculated by FEM and PWE present good agreement. We suggest that the bio-inspired PC considered should be feasible for elastic vibration control.

Abstract: Pure and copper doped tin oxide nanoparticles were synthesized by co-precipitation method and are characterized by XRD, SEM, EDAX, UV-Visible, photoluminescence, and FT-IR analysis techniques. Tetragonal rutile structure is confirmed from XRD and the crystallite size is found to be between 3.8nm and 4.8nm. The optical band gap is observed from UV-Vis spectrum and is found to be 3.99eV and 3.93eV for tin oxide and copper doped tin oxide respectively. The optical band gap of pure and Copper doped tin oxide were blue shifted due to quantum confinement. Photoluminescence spectrum shows UV, blue and green emission peaks.

Abstract: Amorphous carbon (a-C) film is a unique material that attracts the attention of scientists to be investigated. Nitrogen- and boron- doped amorphous carbon (a-C:N and a-C:B) have been deposited on ITO glass substrates by using nanospray method. Palmyra sugar is heated at temperature 250^o C for 2.5 hours to obtain a-C. Boric acid (H₃BO₃) and amonium hidroxide (NH₄OH) are used as the sources of boron doping and nitrogen doping. a-C:N and a-C:B are made by the variations of mole ratio for doping and amorphous carbon, that are 1:15 and 1:20. Then, these samples are dissolved into mixed dymethyl sulfoxide (DMSO) and aquades. The exfoliation process of samples has been done by applying ultrasonic cleaner for 2 hours and also centrifugated at 4000 rpm for 45 minutes. Electrical conductivity and band gap are measured by using four point probe and UV Vis. The results show that electrical conductivity increases but band gap decreases than pure a-C. Furthermore, the larger mole ratio of a:C-N and a-C:B also increases conductivity and decreases band gap, resulting between 5.5×10^-1S/cm – 6.1×10^-1 S/cm and 1.43 eV – 1.71 eV.

Abstract: Preparation of MgO and Mg_0.95Zn_0.05O nanomaterials using self-propagating combustion method are done to investigate the effect of doping on the band gap energy. The synthesis condition has been optimized to obtain pure MgO and Mg_0.95Zn_0.05O materials which confirmed by XRD. FESEM results shows agglomeration of crystallite with average crystallite size of samples between 30 nm to 125 nm. The band gap obtained from the measurement of UV-Vis NIR spectrophotometer for MgO nanostructure is 6.36 eV which is lower than bulk MgO of 7.8 eV. The presence of Zn in Mg_0.95Zn_0.05O sample causes the narrowing of band gap to 5.33 eV.

Abstract: Preparation of MgO and Mg_0.9Li_0.2O materials using self-propagating combustion method are done to investigate the effect of substitution doping on the band gap energy. The synthesis condition has been optimized to obtain pure and single phase of MgO and Mg_0.9Li_0.2O materials and was confirmed by X-Ray Diffraction (XRD). The morphology obtained from field emission scanning electron microscopy (FESEM) is spherical and rounded polyhedral shape with agglomeration of crystallites for MgO and Mg_0.9Li_0.2O materials respectively. The crystallite size of MgO and Mg_0.9 Li_0.2O samples is between 50 nm to 120 nm and 200 nm to 1500 nm respectively. The band gap was determined by UV-Vis NIR spectrophotometer and it was found that the band gap obtained for MgO nanostructure is 6.10 eV which is lower than bulk MgO of 7.8 eV. The presence of Li in the MgO had caused changes in morphology, crystallite size and band gap narrowing to 3.83 eV.

Abstract: In the proceeding way of material research in the field of manganites, LCMO micro and nanoparticles are synthesized via. the solid-state reaction route, glycine-nitrate combustion method respectively. The phase confirmation is done by XRD, FT-IR technique and the surface morphology viewed by Scanning Electron Microscope (SEM). The energy band gap obtained from Diffuse Reflectance Spectroscopy clearly suggests that the band gap of nanoparticles (2.06eV) is larger than that of the microparticles (1.58eV). Both samples comprise of wide band-gap semiconductor, so the refractive index is calculated using Herve and Vandamme relation. The impedance spectroscopy and dielectric properties of the two samples are studied from room temperature to 100oC over the frequency range 10²-10⁶ Hz. The Cole-Cole plot of impedance is fitted using the RC-Circuit R(Q_gR_g)(Q_gbR_gb)(CR_in). The dielectric property is found to be enhanced in nanoparticles as compared to the microparticles. The findings suggest the nanoparticles be promising candidates in the field of high frequency devices as compared to micro.

Abstract: In this work, ZnO thin films grown on heated glass substrates in a temperature range of 300 to 500 °C with a 50°C step. The prepared solution is composed of methanol and zinc acetate Zn(CH₃COO)₂.2H₂O. ZnO thin films are deposited by pyrolysis spray technique, our work focuses on the study of the substrate temperature influence on the structural and optical properties of these layers. Therefore, The X-ray diffraction, showed a Wurtzit hexagonal structure of elaborated films, with (002) as a preferred orientation, and a grain size of 64 to 74 nm. The optical transmission spectroscopy UV-Visible, illustrated an increase of optical band gap from 3.19 to 3.25 eV, proportionally with the substrate temperature.

Abstract: Cadmium sulphide nanocrystallites have been synthesized using precipitation method. The average sizes of the prepared samples is determined by XRD (x-ray diffraction) method. Morphological studies are carried out by SEM (scanning electron microscopy) measurement. Necesssary elements present in prepared samples, are confirmed by EDAX (energy dispersive analysis of x-ray spectroscopy) method. By Ultraviolet visible spectroscopy measurement, the value of absorption wavelength, band gap values are calculated in optical method. The electrical properties are analysed using impedance analyser measurement for the Nanocrystallites.