Change Of Gap Energy Research Articles

Understanding of the Effect of the Adsorption of Atom and Cluster Silver on Chitosan: An In Silico Analysis.

In this work, the structural, electronic, and optical stability properties of the chitosan monomer (M-Ch) and atomic silver complex are reported, as well as a unitary cell of a silver cluster in the gas phase and acetic acid. The generalized gradient approximation HSEh1PBE/def2-TZVPP50 results established the structures' anionic charge (Q = -1|e|) and the doublet state (M = 2). The high cohesive energy indicates structural stability, and the quantum-mechanical descriptors show a high polarity and low chemical reactivity. Also, the quantum-mechanical descriptors present a low work function that shows the structures are suitable for applications in light-emitting diodes. Finally, the electronic behavior observed by the |HOMO-LUMO| gap energy changes depending on the atomic silver incorporated into the complex.

Enhanced Wettability, Hardness, and Tunable Optical Properties of SiCxNy Coatings Formed by Reactive Magnetron Sputtering.

Silicon carbonitride films were deposited on Si (100), Ge (111), and fused silica substrates through the reactive magnetron sputtering of a SiC target in an argon-nitrogen mixture. The deposition was carried out at room temperature and 300 °C and at an RF target power of 50-150 W. An increase in the nitrogen flow rate leads to the formation of bonds between silicon and carbon atoms and nitrogen atoms and to the formation of SiCxNy layers. The as-deposited films were analyzed with respect to their element composition, state of chemical bonding, mechanical and optical properties, and wetting behavior. It was found that all synthesized films were amorphous and represented a mixture of SiCxNy with free carbon. The films' surfaces were smooth and uniform, with a roughness of about 0.2 nm. Depending on the deposition conditions, SiCxNy films within the composition range 24.1 < Si < 44.0 at.%, 22.4 < C < 56.1 at.%, and 1.6 < N < 51.9 at.% were prepared. The contact angle values vary from 37° to 67°, the hardness values range from 16.2 to 34.4 GPa, and the optical band gap energy changes from 1.81 to 2.53 eV depending on the synthesis conditions of the SiCxNy layers. Particular attention was paid to the study of the stability of the elemental composition of the samples over time, which showed the invariance of the composition of the SiCxNy films for five months.

Engineering the band gap and optical properties of a two-dimensional molybdenum carbon fluoride MXene

Using first-principles density functional theory, we investigated the electronic and optical properties of monolayer and multilayer nanosheets of molybdenum carbon fluoride (Mo2CF2), a two-dimensional (2D) transition-metal carbide MXene. The indirect band gap of the Mo2CF2 semiconductor can be engineered by controlling the number of layers where the band gap energy changes from 0.278 eV for the monolayer to 0.249 eV for the trilayer nanosheet. The decrease in band gap energy in the multilayer is due to interlayer coupling, which splits the bands according to the number of layers. Mo2CF2 behaves as a metal with an anomalous dispersion and high optical conductivity at incident photon energies of 0.68–2.19, 3.49–6.68 and 7.30–8.31 eV. It has a relatively low reflectivity and is absorbing over a broad range of photon energies from about 0.429 (2890), 0.387 (3204) and 0.345 eV (3594 nm) for the monolayer, bilayer and trilayer nanosheets, respectively, achieving peak absorption in the vacuum ultraviolet region at about 7.9 eV (157 nm). The optical properties of Mo2CF2 can likewise be tuned by varying the number of layers. The unique behavior of its optical properties along with the ability to control its electronic and optical properties enhances the potential of 2D Mo2CF2 for various applications in the fields of electronics and energy storage.

Size dependent polaritonic effects in GaN microrod studied through optical property investigation

We have investigated the optical properties of gallium nitride microrods systematically by spatially resolved cathodoluminescence, Raman and photoluminescence measurements. Blueshifting in near band gap energy with the decrease in diameter of studied microrods has been observed from cathodoluminescence and is attributed to the formation of whispering gallery mode polaritons in microrod cavity. Raman spectra along the length of the tapered microrod shows no noticable shifting in Raman mode positions confirm that the band gap energy changes with the decrease in diameter is not due to the stress/strain or different doping concentration. PL was carried out to look at the probable possibilities of polariton formation in microrod cavity. Exciton photon coupling strength depends on the diameter of the microrods and the coupling strength decreases with the decrease in diameter as studied from spatial-resolved photoluminescence spectra. Rabi splitting energy of nearly 300 ± 40 meV and so polariton lasing was observed from the wide end but that gradually decreases with the decrease in diameter.

Synthesis and temperature-tuned band gap characteristics of magnetron sputtered ZnTe thin films

Zinc telluride (ZnTe) is one of the attractive semiconducting compounds used in various optoelectronic devices. The usage of ZnTe in optoelectronic applications directs researchers to search its optical characteristics in great detail. For this purpose, structural and optical properties of magnetron sputtered ZnTe thin films were studied by means of x-ray diffraction and transmission spectroscopy measurements. Structural analyses indicated that ZnTe thin films having cubic crystalline structure were successfully grown on soda-lime glass substrates. Transmittance spectra in the 400–1000 nm were recorded in between 10 and 300 K temperature region. The analyses of absorption coefficient spectra resulted in band gap energies decreasing from around 2.31 (10 K) to 2.26 eV (300 K). Temperature dependency of gap energy was studied by Varshni and O'Donnell-Chen relations to determine various optical parameters like absolute zero temperature band gap energy, change of gap energy with temperature, phonon energy.

Study of the Band Gap Changes in Flat Acenes

In the future molecular electronic is substitute the silicon electronic by the organic molecules. Due to p orbital's, upper and lower electron clouds, and resonance phenomenon, the aromatic hydrocarbon from the root of benzene can provide suitable environments for electron transition. A useful approach for this purpose is an appropriate pattern to predict electronic properties by topological indices method (TIM). Therefore, it is first tried to produce a relationship between the topological indices based on the number of rings; then F index values are measured for Circumacenes family. The gap energy changes in the family of C8(n+2)/3H(2n+22)/3 was calculated using Gaussian 09 Software by Hartree–Fock method. The relationships described the gap energy changes in the Circumacenes family achieved by F index. Finally, some heavier members of Circumacenes family are exposed to TIM to predict of Gap energy.

Analysis of temperature-dependent transmittance spectra of Zn0.5In0.5Se (ZIS) thin films

Temperature-dependent transmission experiments of ZnInSe thin films deposited by thermal evaporation method were performed in the spectral range of 550–950 nm and in temperature range of 10–300 K. Transmission spectra shifted towards higher wavelengths (lower energies) with increasing temperature. Transmission data were analyzed using Tauc relation and derivative spectroscopy. Analysis with Tauc relation was resulted in three different energy levels for the room temperature band gap values of material as 1.594, 1.735 and 1.830 eV. The spectrum of first wavelength derivative of transmittance exhibited two maxima positions at 1.632 and 1.814 eV and one minima around 1.741 eV. The determined energies from both methods were in good agreement with each other. The presence of three band gap energy levels were associated to valence band splitting due to crystal-field and spin–orbit splitting. Temperature dependence of the band gap energies were also analyzed using Varshni relation and gap energy value at absolute zero and the rate of change of gap energy with temperature were determined.

High‐efficiency Sb2S3‐based hybrid solar cell at low light intensity: cell made of synthesized Cu and Se‐doped Sb2S3

AbstractCu‐doped (as p‐doped) and Se‐doped (as n‐doped) Sb2S3 were synthesized from undoped Sb2S3 using a newly developed technique, simple colloidal synthesis method. X‐ray diffraction measurements detected no peaks related to any of the Cu and Se compounds in Cu and Se‐doped samples. Energy dispersive X‐ray analysis, however, confirmed the presence of Cu and Se ions in the doped samples. Diffuse reflectance spectroscopy revealed the optical band gap energy changes because of doping effect, as reported for both the p‐type and the n‐type material. The valence‐band X‐ray photoelectron spectroscopy data showed a significant shift in the valence band to higher (Se‐doped; +0.53 eV) and a shift to lower (Cu‐doped; −0.41 eV) binding energy, respectively, when compared with the undoped sample. We report here on an inexpensive solar cell designed and made entirely of a synthesized material (indium tin oxide/p‐doped Sb2S3 + polyaniline (PANI)/amorphous/undoped Sb2S3 + PANI/n‐doped Sb2S3 + PANI/PANI/electrolyte (0.5 M KI + 0.05 M I2)/Al). The cell has a high efficiency of 8% to 9% at a very low light intensity of only 5% sun, which makes it particularly suitable for indoor applications. As found, the cell performance at the intensity of 5% sun is governed by high shunt resistance (RSH) only, which satisfies standard testing conditions. At higher light intensities (25% sun), however, the cell exhibits lower but not insignificant efficiency (around 2%) governed by both the series (RS) and the RSH. Minimal permeability in the UV region (up to 375 nm) and its almost constant value in the visible and the NIR region at low light intensity of 5% sun could be the reasons for higher cell efficiency. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Non-monotonic pressure dependence of band gap in SnTe

The electronic properties of SnTe under pressure are studied using first-principles calculations. The results show that the band gap energy changes non-monotonically with pressure, gradually reducing to zero, then rising. It may be because with pressure the inertia of s state near the bottom of the conduction band is weakened, and the repulsion to p state is enhanced, which pushes the L6+ level down. The work demonstrates an approach for manipulating the electrical properties of SnTe, which is important for future applications based on SnTe.

Improved temperature characteristics of laser diodes with nonidentical multiple quantum wells due to temperature-induced carrier redistribution

Laser diodes with nonidentical multiple quantum wells could have the lasing wavelength very insensitive to temperature variation. For temperature varying from 33 to 260 K, the lasing energy changes less than 5 meV, while the band gap energy changes more than 50 meV. The origin is due to the strongly temperature-dependent Fermi–Dirac distribution, which favors carriers in high-energy states at large temperature. The temperature-induced carrier redistribution could even cause negative characteristic temperature for a certain temperature range because the low-energy quantum wells behave like reservoirs to overcome the detrimental influence of temperature.

Temperature dependence of the fundamental absorption edge in CuGaSe 2

The temperature dependence of the fundamental absorption edge in CuGaSe 2 single crystals was determined in the temperature range from 15 to 300 K. Above about 120 K the gap energy changes linearly with temperature with d E g /d T = − (2.1 ± 0.1) eV K −1. The downshift in d E g /d T of the I–III–VI 2 compounds compared to their II–VI analogs is discussed accounting for the p- d hybridization of the uppermost valence band.