Variation Of Band Gap Energy Research Articles

Theoretical studies on B, N, P, S, and Si doped fullerenes toward H2S sensing and adsorption

Abstract Computational methods in materials design can lead to significant progresses toward optimization of novel responsive adsorbents and sensors. In this regard, in current research for the first time, Density Functional Theory (DFT) method has been utilized to tune the properties of C60 fullerene for better adsorptive and detection capability. The DFT calculations were performed on various types of C60, where, to enhance the end properties of the C60 various dopants were imbedded in its structure. The effects of different dopants including B, N, P, S and Si on adsorptive and sensing capability of the C60 were elucidated. Regarding the effect of Nitrogen, it was found that pyrrolic and pyridinic nitrogen can enhance the adsorption energy of C60 considerably. The other dopants could also improve the interaction energy of C60, where, the highest adsorption energy was obtained for B-doped C60 (−32.2973 kj/mol) followed by pyrrolic nitrogen (−17.4745 kj/mol), Si-doped C60 (−10.6411), S-doped C60 (−9.3903 kj/mol) and P-doped C60 (−8.1723 kj/mol). The sensing capability of the proposed structures was evaluated in terms of variation of band gap energy after adding H2 S molecule in which the pyridinic oxide nitrogen in C60 had the highest electrical response to presence of H 2S. Moreover, Natural Bond Orbital (NBO) analysis was performed and then stabilization energies, electron occupation at each bond and hybridization character around each atom were evaluated. Consequently, appropriate synthesis methods can be used to prepare the doped-C60 materials as effective H2S adsorbents and sensors.

Formation and Encapsulation of All-Inorganic Lead Halide Perovskites at Room Temperature in Metal-Organic Frameworks.

Improving the stability and tuning the optical properties of semiconducting perovskites are vital for their applications in advanced optoelectronic devices. We present a facile synthetic method for hybrid composites of perovskites and metal-organic frameworks (MOFs). A simple two-step solution-based method without organic surfactants was employed to make all-inorganic lead-halide perovskites (CsPbX3; X = Cl, Br, I, or mixed halide compositions) form directly in the pores of MIL-101 MOF. That is, a polar organic solution of lead halide (PbX2) was impregnated into the MOF pores to give PbX2@MIL-101, which was then subjected to a perovskite-formation reaction with cesium halide (CsX) dissolved in methanol. The compositions of the halogen anions in the perovskites can be modulated with various halide precursors, leading to CsPbX3@MIL-101 composites with X3 = Cl3, Cl2Br, Br2Cl, Br3, Br2I, I2Br, and I3 that exhibit gradual variation of band gap energies and tuned emission wavelengths from 417 to 698 nm.

Influence of bath temperature on microstructure and NH3 sensing properties of chemically synthesized CdO thin films

Abstract Cadmium oxide (CdO) thin films were synthesized using chemical bath deposition (CBD) method from aqueous cadmium nitrate solution. The bath temperatures were maintained at room temperature (25 °C) and at higher temperature (80 °C). The structural studies revealed that the films showed mixed phases of CdO and Cd(OH)2 with hexagonal/monoclinic crystal structure. Annealing treatment removed the hydroxide phase and the films converted into pure CdO with cubic, face centered crystal structure. SEM micrographs of as-deposited films revealed nanowire-like morphology for room temperature deposited films while nanorod-like morphology for high temperature deposited films. However, cube-like morphology was observed after air annealing. Elemental composition was confirmed by EDAX analysis. Band gap energies of the as-deposited films varied over the range of 3 eV to 3.5 eV, whereas the annealed films showed band gap energy variation in the range of 2.2 eV to 2.4 eV. The annealed films were successfully investigated for NH3 sensing at different operating temperatures and at different gas concentrations. The room temperature synthesized film showed a response of 17.3 %, whereas high temperature synthesized film showed a response of 13.5 % at 623 K upon exposure to 24 ppm of NH3.

Optimized opto-electronic and mechanical properties of orthorhombic methylamunium lead halides (MAPbX3) (X = I, Br and Cl) for photovoltaic applications

Organometallic halide perovskites (OMHPs) are absorbent materials, and can thus be employed in solar cells with power conversion efficiency (PEC) of 22% or higher. Using calculations, this work confirms earlier experimental findings and determines optimal properties to achieve maximum conversion efficiency for OMHPs. Values of energy band gap, density of states, absorption coefficient, refractive index, dielectric constant and elastic constants of orthorhombic methylamunium lead halides (MAPbX3) (X = I, Br and Cl) family are all calculated using Density Functional Theory (DFT) method with generalized gradient approximation (GGA). The stiffness of (MAPbX3) (X = I, Br and Cl) is investigated by calculating Young’s moduli E constants. Among the series, MAPbI3 is the stiffest material with Ex = 57.24 GPa. The perovskite family members are characterized by their energy band gap variation as: Eg MAPbI3, MAPbBr3, MAPbCl3 = 1.626, 2.207 and 2.748 eV, respectively. They also exhibit a remarkable absorption coefficient (α MAPbX3 = 105 cm−1) over a wide energy range particularly the visible spectrum [1.65–3.26 eV: 380–750 nm]. The anisotropy of optical properties (MAPbX3) (X = I, Br) is proven in the near and middle ultraviolet [3.1–5 eV] energy band.

Correlated quartic variation of band gap and NBE energy in sol-gel derived Zn1−Co O nanoparticles

Abstract Zn1−xCoxO (x = 0.0, 0.01, 0.03, 0.05, 0.07) nanoparticles were synthesized via sol-gel method. For structural parameters like lattice constants, bond length and particle size, XRD patterns have been analyzed. The particle sizes lie between 15.75 and 35.31 nm. The Williamson-Hall analysis has been performed for strain calculation. The UV–Visible spectra show high transparency in visible range with a dip in near UV region. The band gap calculation has been done using Tauc's plot method. The band gap values show a quartic variation with x. PL emission spectra exhibit NBE emission that too undergoes quartic variation with x. The correlation between both the quartic variations has been analyzed and it has been established that the B-M effect and sp-d exchange interaction both play their role alternately. M-H curves of the Co doped nanoparticles show room temperature ferromagnetism whereas the undoped one have the diamagnetic character. The electrical resistivity has been found to be high; in the range of 4.81 × 104 to 7.26 × 104 Ω-m. A increasing trend in resistivity is noticed with increasing the Co concentration in ZnO matrix.

Interaction Behavior of Cyanogen Fluoride and Chloride Gas Molecules on Red Phosphorene Nanosheet: A DFT Study

The adsorption of cyanogen fluoride and chloride gas molecules on red phosphorene (RP) nanosheet was investigated using the first-principles calculation. We confirmed the geometric solidity of RP nanosheet using the formation energy and the energy band gap is detected to be 0.72 eV. The most stable adsorption configurations of cyanogen halides are studied by energy band gap variation, Bader charge transfer, and adsorption energy. We observed the physisorption type of interaction upon exposure of cyanogen halides on RP nanosheet. Furthermore, the band gap structure along with the density of states spectrum indicates the physisorption of cyanogen halide on RP nanosheet. The variation in the band gap upon adsorption leads to modify the resistance of RP nanosheet. The findings show that RP nanosheets can be used to detect the presence of cyanogen chloride and fluoride.

Computational Study of Perovskite Structured CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> and CH<sub>3</sub>NH<sub>3</sub>SnI<sub>3</sub>

Nowadays, Hybrid Perovskite materials perform a major role in solar cell industry due to their superior power conversion ability. CH3NH3PbI3is the prominent material in hybrid perovskite, where they comprised with advanced photovoltaic properties. But considering the toxicity, it’s more important to observe the role of metal atom in hybrid perovskite. Therefore, this research is basically focused on the objective of figuring out the fundamental properties of CH3NH3PbI3and CH3NH3SnI3with the idea of replacing Pb to Sn in future. Ab-Initio Simulation has been used throughout this research along with basic density function theories (DFT) like Exchange correlation functional, Local-density approximation of Kohn-Sham theory. Moreover, the research was also focused upon the Energy band gap variation, crystallographic orientations, density of states in P, S orbitals of cubic and tetragonal phases in CH3NH3PbI3and CH3NH3SnI3.

Role of PEG2000 on sol-gel preparation of porous La2Ti2O7 for enhanced photocatalytic activity on ofloxacin degradation

Polyethylene glycol (PEG2000) was used as pore forming reagent in a sol-gel route to synthesize porous lanthanum titanate photocatalyst. All the samples are composed of perovskite La2Ti2O7 in monoclinic system with a reducing tendency for crystallite size and cell volume after adding PEG2000. The addition of 3.0 g of PEG2000 in the precursor can lead to the maximum specific surface area of 52.4 m2/g and the largest pore volume of 0.10762 cm3/g. The application of PEG2000 in sol-gel synthesizing of porous La2Ti2O7 can hardly put effect on the variation of bandgap energy, and the chemical environment for each of the elements in La2Ti2O7 does not noticeably change. The addition of PEG2000 in the precursor can apparently enhance photocatalytic activity of the materials, and the maximum photocatalytic activity is achieved on the porous La2Ti2O7 sample obtained using 3 g of PEG2000. UV–Vis spectra of ofloxacin solution during degradation prove the decomposition of the major organic groups in ofloxacin molecule. Photocatalytic oxidation can lead to a constant reducing TOC amount in the ofloxacin solution while the reducing rate depends on the activity of the materials.

Optical properties and radiative rates of Nd3+ doped zinc-sodium phosphate glasses

Preparation using melt quenching technique and optical characterizations of Nd3+ doped Zn-Na phosphate glasses are presented. The structure of the present glasses was studied using X-ray diffraction and FT-IR spectroscopy. UV-vis spectra of the present glasses were analyzed at different concentrations of Nd2O3. The effect of neodymium concentration on the density and energy band gap was investigated. The density of the present glasses slightly increases with the increasing of Nd2O3. A small variation of energy band gap with the increasing of neodymium content is observed as well, while Eg values decrease with the increase of Nd2O3 content. The Eg values lie between 4.36 and 4.69 eV. Based on the measured optical spectra, Judd-Ofelt theory was used to determine the optical parameters such as line strengths, optical intensity parameters (Ωt), transition probabilities, and transition lifetimes. Hypersensitive transitions were identified in the absorption spectrum, the greatest line strengths are recorded at the transitions 2G7/2 + 4G5/2, 4S3/2 + 4F7/2 and 4D1/2 + 4D3/2 + 4D5/2 + 2I11/2 with wavelengths of 580, 475 and 355 nm, respectively. Lifetimes of the important 4F3/2 laser-level were determined; which show decreasing trend with the increasing of Nd2O3 content and are found to be between 0.838 and 1.595 ms. The uncertainty of the present results was estimated. The RMS deviations were determined, which show lower values than those in the literature.

Serine adsorption through different functionalities on the B12N12 and Pt-B12N12 nanocages

The present work reports the adsorption of serine in the neutral and zwitterionic forms on the pure and Pt-decorated B12N12 fullerenes by means of density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. The binding energy of serine over the fullerene has been studied through its hydroxyl (-OH), carboxyl (-COOH), and amine (-NH2) functional groups. Based on our analysis, the binding energy of serine in zwitterionic form (F: −1.52 eV) on B12N12 fullerene is less stable than that of the neutral form (C: −1.61 eV) using the M06-2X functional. Our results indicated that the most stable chemisorption state for serine is through its amine group (I: −2.49 eV) interacting with the Pt-decorated B12N12 fullerene in comparison with the carbonyl group (J: −1.92 eV). The conductivity of the B12N12 and Pt-decorated B12N12 fullerenes is influenced by the energy band gap variation when serine is adsorbed upon the outer surface of fullerenes. Understanding the adsorption of serine on B12N12 and Pt-decorated B12N12 fullerenes provide fundamental knowledge for future applications in biomolecules and metal surfaces.

Pulsed laser deposited Zn1-xTixO (0.000≤x≤0.050) thin films for tunable refractive index and nonlinear optical applications

In the present paper, a systematic study on the structural, linear and nonlinear optical properties of Zn1-xTixO (0 ≤ x ≤ 0.050) thin films is documented. The thin films are grown onto fused silica substrate via pulsed laser deposition technique employing 2nd harmonic of a Q-switched Nd:YAG laser (532 nm, 10ns, 10 Hz). The crystallinity of the film is observed to be increased initially up-to x = 0.02 and then decreased for higher values of x. A small variation in band gap energy is observed in the Zn1-xTixO thin films with x which is mainly due to the Burstein Moss effect followed by the weak quantum confinement effect. The third order optical nonlinearities in the films are experimentally recorded using modified z-scan technique under cw He:Ne laser (λ = 632.8 nm) illumination. The nonlinear optical coefficients; β and n2, are observed to be in the range of 1.1–6.0 cm/W and (1.0–4.1) × 10−4 cm2/W, respectively. The maximum value of β (6.0 cm/W) and n2 (4.1 cm2/W) are observed in the Zn1-xTixO film having x = 0.02. These studies suggest that an optimum concentration of Ti content in ZnO is required for the enhancement in nonlinear optical behavior.

CuBi2O4 Prepared by the Polymerized Complex Method for Gas-Sensing Applications.

Multicomponent oxides can be extensively explored as alternative gas-sensing materials to binary oxides with their structural and compositional versatilities. In this work, the gas-sensing properties of CuBi2O4 have been investigated toward various reducing gases (C2H5OH, NH3, H2, CO, and H2S) and oxidizing gas (NO2) for the first time. For this, the powder synthesis has been developed using the polymerized complex method (Pechini method) to obtain a single-phase polycrystalline CuBi2O4. The defect, optical, and electronic properties in the prepared CuBi2O4 powder were modulated by varying the calcination temperature from 500 to 700 °C. Noticeably, a high concentration of Cu+-oxygen vacancy ([Formula: see text]) defect complexes and isolated Cu2+ ion clusters was found in the 500 °C-calcined CuBi2O4, where they were removed through air calcination at higher temperatures (up to 700 °C) while making the compound more stoichiometric. The change in the intrinsic defect concentration with the calcination temperature led to the variation of the electronic band gap energy and hole concentration in CuBi2O4 with the polaronic hopping conduction (activation energy = 0.43 eV). The CuBi2O4 sensor with 500 °C-calcined powder showed the highest gas responses (specifically, 10.4 toward 1000 ppm C2H5OH at the operating temperature of 400 °C) with the highest defect concentration. As a result, the gas-sensing characteristics of CuBi2O4 are found to be dominantly affected by the intrinsic defect concentration, which is controlled by the calcination temperature. Toward reducing H2S and oxidizing NO2 gases, the multiple reactions arising simultaneously on the surface of the CuBi2O4 sensor govern its response behavior, depending on the gas concentration and the operating temperature. We believe that this work can be a cornerstone for understanding the effect of chemical defect on the gas-sensing characteristics in multicomponent oxides.

A novel nanoscale SOI MOSFET by embedding undoped region for improving self-heating effect

Because of the low thermal conductivity of the SiO2 (oxide), the Buried Oxide (BOX) layer in a Silicon-On-Insulator Metal-Oxide Semiconductor Field-Effect Transistor (SOI MOSFET) prevents heat dissipation in the silicon layer and causes increase in the device lattice temperature. In this paper, a new technique is proposed for reducing Self-Heating Effects (SHEs). The key idea in the proposed structure is using a Silicon undoped Region (SR) in the nanoscale SOI MOSFET under the drain and channel regions in order to decrease the SHE. The novel transistor is named Silicon undoped Region SOI-MOSFET (SR-SOI). Due to the embedded silicon undoped region in the suitable place, the proposed structure has decreased the device lattice temperature. The location and dimensions of the proposed region have been carefully optimized to achieve the best results. This work has explored enhancement such as decreased maximum lattice temperature, increased electron mobility, increased drain current, lower DC drain conductance and higher DC transconductance and also decreased bandgap energy variations. Also, for modeling of the structure in the SPICE tools, the main characterizations have been extracted such as thermal resistance (RTH), thermal capacitance (CTH), and SHE characteristic frequency (fTH). All parameters are extracted in relation with the AC operation indicate excellent performance of the SR-SOI device. The results show that proposed region is a suitable alternative to oxide as a part of the buried oxide layer in SOI structures and has better performance in high temperature. Using two-dimensional (2-D) and two-carrier device simulation is done comparison of the SR-SOI structure with a Conventional SOI (C-SOI). As a result, the SR-SOI device can be regarded as a useful substitution for the C-SOI device in nanoscale integrated circuits as a reliable device.

Alcohol molecules adsorption on graphane nanosheets – A first-principles investigation

The geometric structure, electronic and adsorption properties of methanol, ethanol and 1-propanol molecules on hydrogenated graphene (graphane) were investigated using first-principles calculations. The stability of graphane base material is confirmed using formation energy and phonon band structures. The adsorption of alcohol molecules on bare graphane and hydrogen vacant graphane nanosheet is found to be prominent and the selectivity of alcohol molecules can be achieved using bare or hydrogen vacant graphane nanosheet. Moreover, the interaction of alcohol molecules on bare and hydrogen vacant graphane nanosheets is studied using the adsorption energy, energy band gap variation, Bader charge transfer and average energy band gap variation. The adsorption energy ranges from -0.149 to −0.383 eV upon alcohol adsorption. The energy gap varies from 4.71 to 2.62 eV for bare graphane and from 4.02 to 3.60 eV for hydrogen vacant graphane nanosheets upon adsorption of alcohol molecules. The adsorption properties of alcohol molecules provide useful information for the possible application of graphane nanosheet as a base material for the detection of alcohol molecules.

Tuning NBE emission and optical band gap of nanocrystalline ZnO thin films using Fe dopant

Tuning of 100meV in optical band gap of nanocrystalline Fe doped ZnO thin films deposited by sol gel spin coating is obtained. Band gap increases monotonically from 3.16 to 3.26eV as dopant is increased. Polycrystalline nature and hexagonal wurtzite structure of undoped and Fe doped films is revealed from XRD. The crystallite size lies between 8 to 15nm. Films are highly transparent and doping increases transmission monotonically. NBE emission occurs at 399 nm which shifts to higher energy with increasing dopant concentration. Defect emission occurs at 486nm. Intensity of the NBE emission is higher for the doped samples and is highest for 2at.% doping. Similar variation in band gap energy and in the NBE emission energy with dopant concentration is obtained.

Effect of Hydrostatic Pressure on the Structural, Electronic and Optical Properties of SnS2 with a Cubic Structure: The DFT Approach

Recently, a cubic structure of polymorphic SnS2 has been synthesized experimentally, which is stable at room temperature. In this paper, we calculated some structural, electronic and optical properties of the cubic SnS2 structure based on the full potential-linearized augmented plane waves method. We also studied the effect of hydrostatic pressure on the physical properties of the cubic SnS2 structure. Structural results show that the compressibility of the cubic SnS2 phase is greater than its trigonal phase and the compressibility decreases with increasing pressure. Investigations of the electronic properties indicate that pressure changes the density of states and the energy band gap increases with increasing pressure. The variation of energy band gap versus pressure is almost linear. We concluded that cubic SnS2 is a semiconductor with an indirect energy band gap, like its trigonal phase. The optical calculations revealed that the dielectric constant decreases with increasing pressure, and the width of the forbidden energy interval increases for electromagnetic wave propagation. Moreover, plasmonic energy and refractive index are changed with increasing pressure.

Temperature dependence of the energy bandgap of multi-layer hexagonal boron nitride

The temperature dependence of the energy bandgap of hexagonal boron nitride (h-BN) has been probed via photoluminescence emission characteristics of a donor-to-acceptor pair transition in a 20-layer h-BN epilayer. The results indicate that the universal behavior of bandgap decreasing with temperature is absent in multi-layer h-BN. Below 100 K, the bandgap energy variation with temperature, Eg vs. T, is dominated by the electron-phonon coupling and conforms to the common behavior of redshift with an increase in temperature. At T > 100 K, the bandgap shows an unusual blueshift with temperature, which can be attributed to the unique behavior of the in-plane thermal expansion coefficient of h-BN that becomes negative above around 60 K. Although both graphite and h-BN have negative thermal expansion coefficients in a broad temperature range, graphite has a zero energy bandgap, which makes h-BN a unique semiconductor to exhibit this unusual temperature dependence of the energy bandgap.

Structural, vibrational and band gap tunability of lead-free (1 − x)NaBiTO3–xBiMnO3 ceramics

We report the band gap tunability of (1 − x)Na0.5Bi0.5TiO3–xBiMnO3 (x = 0.00, 0.05, 0.10 and 0.15) ceramics by a solid-state reaction method. X-ray diffraction (XRD) analysis confirmed the phase formation of rhombohedral structure with the space group of R3c. Rietveld refinement of XRD data revealed that the structural symmetry as a function of x composition. Raman analysis exhibited the vibrational phonon frequencies associated with Bi–O, Na–O, and TiO6 octahedral vibrations. The realized band gap energy variations (3.35–2.53 eV) suggesting that the synthesized ceramics materials are promising for photovoltaic and photocatalytic applications.

Effects of microwave-assisted hydrothermal treatment and of use of capping reagent on the photophysical properties of SrMoO4 phosphors

Strontium molybdate particles (SrMoO4) with uniform shapes have applications in various fields such as phosphors, optical fibers, scintillators, magnets, sensors, and catalysts. SrMoO4 were prepared by Microwave-Assisted Hydrothermal (MAH) method with variations in applied experimental parameters. The effect of the applied synthesis methodology and experimental parameters on the morphology, particle size, sample uniformity and optical properties of the SrMoO4 were studied. In this study, was observed that the microwave radiation favors an organization of material and that this organization can be changed with a capping agent, which provokes alterations in morphology, a disorder-order degree of material and variations of band gap energy. This study indicates that surface defect states favor an alteration in properties of the PL emission. The control of a surface state, the particle size and morphology can be a form to modify the property in accordance with optics characteristics the desired one.

Efficient diagnostics of the electronic and optical properties of defective ZnO nanoparticles synthesized using the sol–gel method: experimental and theoretical studies

ZnO nanoparticles were synthesized using the sol–gel method with a variation on the sol aging time and refined structural data were taken to simulate the synthesized sample in a first-principles calculation. The ZnO nanoparticles aged at 36 h and showed profound properties with high crystallinity and good visual fit in a Rietveld analysis. Optical analysis revealed only small variation in energy band gap for all samples, ranging between 3.08–3.12 eV, with the presence of oxygen vacancy defects. In first-principles calculation, several exchange-correlation functionals, including LDA, GGA-PBE, GGA-PBESol, LDA + U, GGA-PBE + U and GGA-PBESol + U, were tested to converge with the lowest optimized lattice deviation. GGA-PBE + U (Ud,Zn = 10 eV and Up,O = 6.1 eV) showed the lowest lattice deviation and reproduced the experimental band gap. The ZnO supercell structure with an oxygen vacancy showed that a defect state appears in the valence band and acts as a deep donor.