Band Gap

Materials with the olivine LixMPO4 structure form an important new class of materials for rechargeable Li batteries. There is significant interest in their electronic properties because of the importance of electronic conductivity in batteries for high rate applications. The density of states of LixMPO4 (x = 0, 1 and M = Fe, Mn) has been determined with the ab initio GGA+U method, appropriate for these correlated electron systems. Computed results are compared with the optical gap of LiFePO4, as measured using UV-Vis-NIR diffuse reflectance spectroscopy. The results obtained from experiment (3.8-4.0 eV) and GGA+U computations (3.7 eV) are in very good agreement. However, standard GGA, without the same level of treatment of electron correlation, is shown to make large errors in predicting the electronic structure. It is argued that olivines are likely to be polaronic conductors with extrinsically determined carrier levels and that their electronic conductivity is therefore not simply related to the band gap.

The band gap of Cd1-xMgxTe can be easily tuned from 1.48 to 3.5 eV (x = 0 to 1), and hence this material is a potential candidate for developing the wide band gap top cell in tandem solar cells. In this paper, we present an all-sputtered Cd1-xMgxTe/CdS top cell developed on commercial SnO2:F-coated (Tec-7) glass substrates with sheet resistance of

Thin films of nanocrystalline cubic AlN were synthesized by vapor–liquid–solid (VLS) route on Si and fused silica substrates at appropriate conditions. The formation of cubic AlN was confirmed by X-ray diffraction studies. We also observed that AuCl3 plays an important role as a catalyst in the synthesis of well crystalline cubic phase of AlN. Energy dispersive analysis of X-rays confirmed

Nanostructured metal surfaces comprised of periodically arranged spherical voids are grown by electrochemical deposition through a self-assembled template. Detailed measurements of the angle- and orientation-dependent reflectivity reveal the spectral dispersion, from which we identify the presence of both delocalized Bragg- and localized Mie-plasmons. These couple strongly producing bonding and anti-bonding mixed plasmons with anomalous dispersion properties. Appropriate plasmon engineering of the void morphology selects the plasmon spatial and spectral positions, allowing these plasmonic crystal films to be optimised for a wide range of sensing applications.

Indium tungsten oxide (In6WO12) powders and thin films were prepared from a 2,4-pentanedione solution containing In(NO3)·xH2O and WCl6. X-ray diffraction results indicated that phase-pure In6WO12 powder formed after drying and heating the solution at 900 °C. Glancing X-ray diffraction results indicated that thin-film samples prepared on fused quartz substrates at 600 and 700 °C contained a disordered fluorite-related phase whereas those prepared at 800 °C contained the ordered compound—In6WO12. Films prepared at 900 °C reacted with the substrate to form In2Si2O7. Despite the chemical and structural similarity of In6WO12 to several indium-containing fluorite-related oxides, including In2O3, In3Sn4O12, and Ga3−xIn5+xSn2O16, the resistivity of the films prepared in this study ranged from 70 to 720 Ω cm, which is several orders of magnitude higher than reported for the related oxides (approx. 10−3 Ω cm). The band gaps of the films prepared at 600 and 700 °C were estimated from optical transmittance measurements to be 4.1 and 3.8 eV, respectively. Films prepared at 700 °C exhibited substantial coloration when exposed to n-butyl lithium whereas those prepared at 800 °C did not.

Fluorinated and hydrogenated amorphous silicon‐carbon alloys (a‐SiC:H,F) are produced by glow discharge decomposition of SiF 4 ‐CH 4 ‐H 2 mixture. Small amount of CH 4 in SiF 4 ‐H 2 mixture are enough to produce silicon carbon alloys having optical gap ranging between 1.8 and 2.6 eV. Materials, having 1.95 eV band gap and exhibiting optoelectronic properties typical of state of art a‐SiC:H, are deposited under plasma modulation conditions. © 1996 American Institute of Physics.

The appearance of band gaps in periodic media is a well known phenomenon. In the past 15 years an increasing attention was payed to sonic crystals, as the properties of such arrangements could lead to the design of innovative noise barriers. In fact, sonic crystal barriers exhibit good insulation properties at some frequencies and could be tuned in order to cause stop bands in a frequency range centred at 1 kHz, classic for road traffic noise pollution. In this paper measurements are described that were conducted over an array of cylinders arranged in a square lattice, whose Bragg band gap was centred at about 900 Hz. Measurements were conducted in accordance with EN 1793-6. Together with measurements, FE simulations were carried out in order to address and verify the procedure. In the simulations, cylinders were assumed to be infinitely rigid and the system was investigated in a 2d domain. The first hypothesis is consistent with the high contrast between the acoustic properties of air and PVC. The second one is consistent with the measurement method, as the windowing of the IRs leads to an evaluation of the attenuation due only to the BG without comprising any effect from ground reflections. Simulation and measurements are compared and discussed over a variety of cases.

Abstract: - This paper describes a fully integrated acoustic sensor that combines high sensitivity, wide frequency range and low cost of batch processed miniaturized silicon components. A sputtered piezoelectric ZnO layer transforms the mechanical deflection of ...

In this paper, we report structural and optical properties of nanocrystalline chromium (Cr) doped ZnS particle, which have been synthesized by co-precipitation method. The structural properties of ZnS:Cr nanoparticles have been characterized by X-ray diffraction (XRD) analysis. The XRD patterns show hexagonal structure in nanoparticles without any additional phase. The mean crystallite size calculated from the XRD patterns has been found in the range 2.45-1.50 nm with the increase in molar concentration of doping agent. Absorption spectra have been obtained using UV-Vis spectrophotometer to find the optical direct band gap. The obtained values have been founded to being range 3.82-4.42 eV. It was also found that optical band gap (Eg) increases with the increase in molar concentration of doping agent is attributed to size quantization effect due to the small size of the particles.

We report highly efficient red phosphorescent organic light-emitting diodes with a triplet p-i-n single quantum well (QW) structure. This p-i-n single QW structure is realized using p-doped and n-doped wide band-gap hole and electron injection and transporting layers with narrow band-gap host and dopant materials. The maximum current and power efficiencies of 11.1 cd/A and 14.4 lm/W, respectively, are demonstrated by a good carrier confinement effect of QW. Very low driving voltage characteristics of 3.7 ∼ 3.9 V at 1000 cd/m2 are realized by almost no injection barrier with high conductivity configuration in our p-i-n structure.

Using amino-acid histidine as chelating agent, CdS nanoparticles have been synthesized by sonochemical method. It is found that by varying the ultrasonic irradiation time, we can tune the band gap and particle size of CdS nanoparticles. The imidazole ring of histidine captures the Cd ions from the solution, and prevents the growth of the CdS nanoparticles. The deviation in the linear relation in between cube of radius of nanoparticles and ultrasonic irradiation time confirms the growth of CdS nanoparticles occur via two process; one is the diffusion process of the reactants as well as reaction at the surface of the crystallite. CdS nanoparticles synthesized using histidine as organic chelating agent have band edge emission at ∼481 nm and have greater photoluminescence intensity with blue-shift to higher energy due to typical quantum confinement effect.