Change In Band Gap Research Articles

A Theoretical Examination of Various Complexes of a Proposed Novel Chemosensor Material—Graphene/SiC

The potential of semiconducting, corrugated graphene, grown on silicon carbide, as an active element in chemosensors is studied in the present work. For this purpose, the adsorption of benzene, diazepam and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the material’s surface was modeled. According to the graphene sheet bending and adsorbate–adsorbent distances, the heterostructure favors the ligands in the order of diazepam < benzene < TCDD. The apparent ambiguity in the results for diazepam is easy to explain. The abundance of lone pairs and π-electrons compensates for the low-symmetry, non-planar, far from optimal (adsorption-wise) geometry. The maximum band gap change in the heterostructure, caused by adsorption, is 0.02 eV. Intermolecular binding does not alter the HOMO–LUMO difference in benzene and TCDD by more than 0.01 eV. The completely planar molecules are not expected to undergo significant geometrical changes; hence, the alteration in their frontier orbitals is also minimal. The adsorption of diazepam, however, causes significant changes in the projected density of states of both structures in the complex. In conclusion, corrugated graphene is applicable as an active material in selective chemosensors for non-planar aromatic molecules.

Humidity tolerant enhanced hydrogen gas sensing using MoSe[formula omitted]-WSe[formula omitted] heterostructures: An experimental and computational insights

In recent times, air pollution’s threat to humanity highlights the urgent need for advanced sensors to monitor harmful gases, essential for industrial regulation, gas leak detection, and air quality surveillance. Two-dimensional transition metal dichalcogenides (TMDCs) has garnered noteworthy attention as potential materials for gas sensing. This paper investigates the synthesis and characterization of a heterostructure composed of molybdenum diselenide with tungsten diselenide (MoSe2-WSe2) nanomaterials using a liquid phase exfoliation technique and it’s H2 sensing performance. The material characterisations confirmed the successful exfoliation into a hexagonal sheet-like, nanocrystalline MoSe2-WSe2 nanostructure. The study further assessed the sensor’s response to H2 gas, for concentrations of 5–25 ppm at room temperature, comparing the performance of MoSe2-WSe2 sensor with a pristine WSe2 sensor. The MoSe2-WSe2 sensor outperformed the pristine WSe2 sensor with a response of 59.57%, rapid response times and recovery times (16 s and 30 s respectively), low detection limit of 5.55 ppm, good repeatability, and high durability (30 days). Additionally, the impact of humidity was evaluated at 25 ppm H2 (at relative-humidity from 40% to 90%). The hydrophobic nature of MoSe2-WSe2 (CA = 141.4°) aligns with the first principle studies, showing almost no change in bandgap when exposed to humidity. These findings emphasize the potential of MoSe2-WSe2 heterostructure sensors for detecting H2 in humid conditions, filling a gap in research and advancing gas sensing technology for environmental safety.

Dopant effects on the environment-dependent chemical properties of NiO(100) surfaces

NiO is a promising material for applications such as electronic devices and catalysts due to its low cost, environmental friendliness, and optimal chemical and electronic properties. Inclusion of a dopant element into the NiO near surface structure can further tune material properties. Despite extensive studies on doped NiO (M−NiO) materials, there remains a lack of knowledge regarding the connection between dopant, environment-dependent dominant near surface structures, and overall chemical properties. Here, the dopant effects on the near surface structure and electronic properties on M−NiO(100) are systematically examined using a combination of density functional theory (DFT) and ab initio phase diagrams. The simultaneous factors tested include dopant element (Al, Mo, Nb, Sn, Ti, V, W, or Zr), dopant placement (surface or subsurface), Ni/O vacancies (surface or subsurface), and oxygen species (O* or O2*) adsorption. The results reveal the dominant structures and compositions of M−NiO(100) under a wide range of environmental conditions (i.e. varying temperature and pressure). Subsequent electronic analyses of the dominant M−NiO(100) structures shows non-uniform changes in charge redistribution, band gap, work function, and d-band center with dopant and near surface structure, emphasizing the role of dopants in tuning M−NiO(100) both geometric and electronic properties. Overall, these multiscale modeling results enable a rapid, effective, and a priori prediction of dominant M−NiO(100) structures with distinct chemical properties, crucial for guiding NiO-based materials design with enhanced performance for advanced electronics, energy storage, and catalytic systems.

Investigating the photocatalytic efficacy of a porous cuprous gallate (CuGa2O4) thick film

Abstract The study aimed to investigate the photocatalytic activity of porous copper gallate (CuGa2O4) thick film with significant wall dimensions. The thick film was meticulously fabricated using tape casting systems, with CuGa2O4 nanoparticles synthesized by Sol–Gel technique and subsequently transformed into gels for the tape casting process. Rietveld refinements were employed to elucidate the crystal structure and lattice parameters of the CuGa2O4 spinel oxide lattice. Moreover, electronic energy configurations and optical transmittance measurements were acquired through UV-visible spectrophotometry. The correlations between the crystal structure, band gap change and formation of electronic energy levels in relation to the photocatalytic performance of CuGa2O4 were explored. The comprehensive examination provides valuable insights into the complex interaction between material properties and photocatalytic behavior, offering a nuanced understanding of the potential applications of porous CuGa2O4 thick films in various technological fields.

A Discovery of Pressure-Induced New Semiconductor Electronic Phase Transitions by DFT Calculations: Introducing a Glimpse of a Novel Semiconductor Family.

This study introduces a discovery of pressure-induced new semiconductor electronic phase transitions. A novel semiconductor family that exhibits pressure-induced nonmonotonic changes in band gaps was found and meets the definition of phase transitions, challenging the traditional understanding of linear and monotonic band gap modification through pressurization. Our findings suggest a complex interplay of atomic spacing and electron orbital contributions under varying pressure conditions, resulting in the variation of band gaps. This behavior, which includes three distinct steps: first, narrowing, second, broadening, and third, narrowing again and ultimately metalizing; some compounds could bypass step 1, has potential applications in piezoelectric and semiconductor technologies. We propose two new semiconductor electronic phase transitions (SEPT) associated with specific inflection points in the pressure-dependent band gap curve. Our results open avenues for further research into the electronic properties of crystals under high pressure, with the ultimate goal of uncovering the more profound physical principles governing these phenomena.

Synthesis and Characterization of TiO2 Thin Films Modified with Anderson-Type Polyoxometalates (Ni, Co, and Fe)

In this work, TiO2 and Anderson-type polyoxometalates (Ni, Co, and Fe) thin-film composites were fabricated. The composites were characterized by FTIR and Raman spectroscopy, diffuse reflectance, and scanning electronic microscopy. The methylene blue (MB) photocatalytic degradation on the composites under UV irradiation was studied. Spectroscopic results verified the modification of TiO2 thin films. Optical and morphological properties changed after TiO2 modification. The largest change in the optical band gap was observed for the FePOM/TiO2 system, which reported a value of 3.05 eV. The POM/TiO2 systems were more efficient in methylene blue (MB) adsorption than bare TiO2. Furthermore, the modified films were more efficient than bare TiO2 during MB photodegradation tests. The NiPOM/TiO2 and the CoPOM/TiO2 were the most efficient in the MB adsorption, reaching ~20%. The NiPOM/TiO2 and the CoPOM/TiO2 composites were the most efficient in the photodegradation process, reaching ~50% of MB removal. The stability tests indicated that composite films were moderately stable after the three performed reusability cycles. Thus, these results suggest that POM modification of TiO2 can improve the adsorption and photodegradation capacity of semiconductors.

Biodetector for chlordane using doped InP3 monolayers: a density functional theory study.

Chlordane is a serious pollutant in the environment, and it is necessary to monitor chlordane levels using biodetectors. We performed first-principles calculations to investigate the adsorption of chlordane on Ag, Pd, and Au doped InP3 semiconductor monolayers. The results indicated that the adsorption energies of chlordane adsorbed on Ag, Pd, and Au doped InP3 are -7.961 eV, -6.328 eV, and -7.889 eV respectively. The band gaps of the doped InP3 monolayers underwent drastic changes after coming in contact with chlordane, the largest change in band gap occurred for Pd-doped InP3, where the band gap changed from 0.024 eV to 0.335 eV. The large change in band gap shows that the monolayer is sensitive to the molecule, making it a good biodetector. Our results conclude that Pd-doped InP3 stands out as the most promising biodetector for chlordane. This result will benefit environmental experimentalists in their further research.

Pressure-induced band gap enhancement and temperature-dependent thermoelectric characterization of semiconducting Transition Metal Chalcogenides LiMS (M = Cu, Ag)

The first principles study of Transition Metal Chalcogenides LiMS (M = Cu, Ag) has been conducted utilizing the concepts of Density Functional Theory (DFT). Both the compounds possess a cubic structure with space group F-43m. The mechanical stability of LiCuS and LiAgS has been predicted based on the values of elastic tensor. These Chalcogenides possess an interesting electronic band structure which reveals their semiconducting nature with a direct band gap. The electronic structure is further subjected to high pressure and the changes in band gap are deeply observed. For these materials, the changes in band gap in response to applied pressure suggest the possibility of their use in band gap engineering. The phonon curves are investigated over the Brillouin zone's high symmetry directions which reveal the lattice dynamical stability of the presently studied compounds. Moreover, the atoms present at different positions inside a crystal lattice exhibit vibrations of different intensities and in different directions which have been studied through the Eigenvector representations. The thermoelectric properties of LiCuS and LiAgS have been characterized using Boltzmann's theory over the range of temperature between 100 K and 1600 K. The calculated thermoelectric parameters reveal the high thermoelectric efficiency of these materials with excellent values of the figure of merit. The interesting properties of ternary Chalcogenides LiMS (M = Cu, Ag) make them promising candidates for thermoelectric applications.

Cerium-infused tungstate nanocrystals: Illuminating the future of solid-state lighting

Rare earth based luminescent materials have emerged as a focal point of the scientific investigation owing to their remarkable optical behaviour and potential applications. An effort has been made to develop a series of Ce3+ doped CaWO4 nano-phosphors using an ethylene-glycol assisted reflux route. The detailed structural and morphological properties have been examined through various analytical techniques. The +3-oxidation state of the activator ion Ce has been verified through the XPS study. The change in optical band gap due to the substitution is well discussed using diffuse reflectance spectroscopy. In Photoluminescence study, a broad emission centred at 465 nm is observed due to the 5D3/2→2FJ transitions (J = 7/2 and 5/2) and a significant enhancement in the emission peak is obtained for the optimized phosphor. Concentration quenching phenomenon, observed after 3 mol% of Ce3+ is mainly mediated by the electric multipole-multipole type interaction. The CIE diagram indicates the tuning of emission colour from blue to white region and the emission near white region for the optimized phosphor is further authenticated by its low colour purity value (43 %). The effective tunability of photo-physical properties and colorimetric parameters suggest the applicability of the optimized nano-phosphor in solid state lighting especially for outdoor illumination.

CsPbBr3 and Cs2AgBiBr6 Composite Thick Films with Potential Photodetector Applications

This paper investigates the optoelectronic properties of CsPbBr3, a lead-based perovskite, and Cs2AgBiBr6, a lead-free double perovskite, in composite thick films synthesized using mechanochemical and hot press methods, with poly(butyl methacrylate) as the matrix. Comprehensive characterization was conducted, including X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), UV–visible spectroscopy (UV–Vis), and photoluminescence (PL). Results indicate that the polymer matrix does not significantly impact the crystalline structure of the perovskites but has a direct impact on the grain size and surface area, enhancing the interfacial charge transfer of the composites. Optical characterization indicates minimal changes in bandgap energies across all different phases, with CsPbBr3 exhibiting higher photocurrent than Cs2AgBiBr6. This is attributed to the CsPbBr3 superior charge carrier mobility. Both composites showed photoconductive behavior, with Cs2AgBiBr6 also demonstrating higher-energy (X-ray) photon detection. These findings highlight the potential of both materials for advanced photodetector applications, with Cs2AgBiBr6 offering an environmentally Pb-free alternative.

Van der Waals ZnO/HfSn2N4 Heterojunction with Exceptional Photoresponse for Photodetectors.

Two-dimensional van der Waals heterojunctions represent a promising avenue for a spectrum of optoelectronic endeavors. Nonetheless, their deployment has been somewhat constrained by the suboptimal efficiency of the photocurrent generated. In this article, a ZnO/HfSn2N4 heterojunction is proposed to achieve high photoresponse efficiency. First-principles calculations are utilized to confirm that this heterojunction possesses thermal stability with a direct bandgap (1.36 eV). It exhibits a high light absorption coefficient and high carrier mobility (2.51 × 103 cm2 V-1 s-1), and biaxial strain has a significant effect on the modulation of the band structure. As the tensile strain increases, the bandgap changes nonlinearly, transitioning from a type-II to a type-I heterojunction. When compressive strain increases, the bandgap decreases. Quantum transport simulations are employed to calculate the density of states and transmission spectrum of the ZnO/HfSn2N4 model, verifying its excellent photoresponse (a photocurrent peak reaching 4.93 a02/photon and an extinction ratio peak of 75.1). It shows that the ZnO/HfSn2N4 heterojunction is a potentially efficient photodetector.

Laser-engraved defects in TiO2 support: Enhancing reducibility and redox capability of Pt/TiO2 catalyst for reactive and selective hydrogenation

Titanium dioxide (TiO2) has been studied as catalyst or catalyst support in catalysis. Its synthesis or modification approach controls the structural, optical, and electronic properties. Here we applied laser engraving to the anatase TiO2 and studied the consequent changes in its structure and property as well as the properties of TiO2 supported platinum (i.e., Pt/TiO2) catalyst. The laser engraving enlarged the particle size, formed rutile phase and created defects (i.e., oxygen vacancy (Ov) and Ti3+) in anatase TiO2. This induced band gap change and enhanced visible light absorption. The defects created by laser engraving are stable and more reducible than those existed in the pristine TiO2. The defective TiO2 is structurally stable and has great redox properties. The metal-support interaction in the Pt/defective TiO2 catalyst is stronger than that of the pristine Pt/TiO2 catalyst, which enabled higher reactivity and selectivity in hydrogenation of 3-nitrostyrene and furfuryl alcohol. Laser-engraved TiO2 has been rarely studied for thermal catalysis. This work provides basic understanding of material properties and catalysis application of laser-engraved catalyst supports and catalysts in field of thermal catalysis.

Adsorption mechanism of CO, CO2, NO, NO2, and SO2 gases onto AlNNT(m,n)_k, (m = 5, 7; n = 0, 5, 7; k = 3–9)

This study provides valuable insights into two key areas. First, we conduct a detailed examination of aluminum nitride nanotubes (AlNNT (m,n)_k), where m = 5,7; n = 0,5,7; and k = 3−9, focusing on their electronic properties across different lengths and diameters. We then investigate how these nanotubes interact with various gases, including CO, CO2, NO, NO2, and SO2. To determine the most energetically favorable configurations, we use the bee colony algorithm for global optimization. Our computational approach employs several Density Functional Theory (DFT) methods, such as PBE0, B3LYP(GD3BJ), CAM-B3LYP, HSE06, M06–2X, TPSSh, and ωB97XD functionals, in combination with the Def2svpp basis set. We prioritize the optimization of structural configurations and analyze the changes in energy band gaps within the nanotubes using conceptual DFT analysis. Additionally, we examine charge transfer mechanisms during gas/nanotube interactions through Natural Bond Orbital (NBO) analysis and assess the nature of these interactions with the Quantum Theory of Atoms in Molecules (QTAIM) framework. Our findings reveal that the interaction with SO2 tends to be slightly stronger compared to the other gases, as evidenced by various analytical techniques. This comprehensive analysis enhances our understanding of gas interactions with aluminum nitride nanotubes and provides insights into their practical applications.

Observation of multifunctional robust topological states based on asymmetric C4 photonic crystals

Recent advancements in high-order topological insulators have heralded new opportunities for the innovation and utilization of optical devices. This paper presents a composite asymmetric C4 photonic crystal to achieve multifunctional, robust topological states. Through detailed analysis of the fine changes in the topological bandgap induced by distortion parameters, we facilitate the realization of topological edge states in wavelength division multiplexing applications. We utilize both trivial and nontrivial properties of the topological bandgap to precisely manipulate zero-dimensional angular states, one-dimensional topological boundary states, and two-dimensional body states. Through simulations and experimental results, our advanced asymmetric C4 photonic crystal structure demonstrates superior robustness for the transmission of topological edge states. Our research paves the way for the deployment of more robust topological boundary state transmission systems and advances the application potential of higher-order topological states.

Production of GeOx Films at Different Oxygen Flow Rates and Different Annealing Temperatures and Examination of Energy Band Gaps using Kubelka Munk Method

In this study, GeOx films were grown on silicon substrates using the Radio Frequency (RF) Magnetron Sputtering method at different oxygen flow rates and annealing temperatures. The films were produced at a substrate temperature of 250°C and a working pressure of 13 mTorr. Subsequently, the films were annealed at temperatures of 300°C, 500°C, 600°C, 700°C, 900°C, and 1000°C. Total and diffuse reflection measurements were performed to investigate the optical properties of the films. Energy band gaps were determined using diffuse reflection measurements and they were calculated using the Kubelka-Munk method. It was observed that the energy band gap increased with increasing oxygen ratio. Additionally, annealing temperatures were found to cause changes in the energy band gaps.

MODELING OF THE GEOMETRY AND ELECTRONIC BANDGAP STRUCTURE OF CHIRAL SINGLE WALLED CARBON NANOTUBES

Carbon Nanotubes (CNTs) are one-dimensional nanostructured materials that will play a key role in future electronics. All properties of the carbon nanotubes are determined by its electronic structure. The main focus of this study has been to investigate the basic electronic bandgap structure of the chiral single walled carbon nanotubes (SWCNTs). A simple algorithm is presented in order to model the geometry of the chiral single-walled CNTs with any desired structure. The electronic bandgap structure of the chiral single-walled carbon nanotubes has been studied by employing an extended tight binding model (TBM). The changes in the energy band gap due to the chirality effect in case of metallic (6, 3) SWCNT and in the semiconducting (12, 7) SWCNT are discussed here. The value of the SWCNTs diameter is calculated also. The computed results indicates that the bandgap depends inversely on the diameter of the tube. The present results were found to be in consistent with those reported in the literature and indicated the correctness of the process of simulation technique process.

Solar driven photocatalytic colored co–TixOyNz amorphous film prepared through air plasma treatment of sputtered titanium film

Colored co–titanium oxides and oxynitride amorphous thin film were fabricated through air plasma treatment of sputtered titanium films. Air plasma treatment led to the removal of the passive film that developed on the titanium film surface, and changes in the structural and optical properties of the films. The amorphous nature, grain size, and thickness of the films remained invariant after the treatment process. The surface roughness of the films increased upon plasma treatment. UV-vis spectroscopy study showed the reduction of the bandgap energy of the films after the air plasma treatment and the maximum reduction was found for the thinner film. The 60min air plasma treatment of the thinner film (AD5: film with 5 min deposition time) leads to the changes in bandgap from 4.11 eV to 3.26 eV, and significant Urbach energy values pointed to the formation of defect states. XPS analysis highlighted that the plasma treatment process led to the formation of titanium oxides (TiO2, Ti2O3) and oxynitrides (TiON), accompanied with Ti2+ defect states in the bandgap. The degradation of methylene blue dye solution with plasma-treated film (PT5) as the photocatalyst resulted in 88% degradation efficiency under 240min irradiation of solar simulator. The degradation has also been checked with natural solar illumination and is found to have a 90% degradation efficiency in 480min.

Study of carbon monoxide adsorption on the α- and γ-graphyne nanosheets for the sensor applications

Recently, graphyne-based gas sensors have drawn a lot of interest. One kind of graphene with acetylene bonds connecting its hexagons is graphyne. In this study, the density functional theory (DFT) method was used to investigate the physical parameters of the surface adsorption of carbon monoxide on the [Formula: see text]- and [Formula: see text]-graphyne nanosheet, taking into account van der Waals (vdW) interactions through the use of the SIESTA computational code. CO molecule adsorbed and optimized in two vertical and horizontal states from the side of carbon and oxygen atoms, at different distances and sites relative to the graphyne sheet. After optimization and finding the adsorption energy, the best adsorption sites, equilibrium distance of the molecule from the surface, electronic structure, charge transfer rate, and bandgap changes were calculated. It was observed that the changes in the electronic structure after the adsorption of CO molecule are insignificant and the [Formula: see text]- and [Formula: see text]-graphyne nanosheets remained zero-gap and narrow-gap semiconductors, respectively. The adsorption of CO molecule on the [Formula: see text]- and [Formula: see text]-graphyne nanosheets is physisorption. The results show that the [Formula: see text]-graphyne nanosheet has a good potential for adsorbing and detecting CO molecules and sensor applications.

Enhancement of multiferrocity in CuCrO2 compounds through effective doping induced optimization of localized carrier holes and reduction in helical disorder

The bulk pristine CuCrO2, doped CuCr0.96M0.03V0.01O2 (M = Ti, Mn, Ga and Nb), CuCr0.96V0.04O2, CuCr0.97Mg0.03O2, CuCr0.97Ni0.03O2, and CuCr1-xFexO2 (x = 0.03, 0.06, and 0.09) compounds with single rhombohedral phase were investigated through low-temperature dc resistivity, field-dependent magnetization, and dielectric measurements. The room-temperature UV measurements were also carried out to determine possible changes in the optical bandgap due to the dopants mentioned above. The present work provides significant evidence of novel methodology for optimizing the number of localized carrier holes along with a reduction in helical disorder around MO6 octahedra, which leads to enhancement of the double exchange along the Cr-O-M-O linkages or superexchange between M3+/4+-Cr3+ mediated via oxygen. The nonmagnetic substitution in magnetic sublattice disrupts the spin spiral and a net weak component is realized in magnetization measurements.

TB-mBJ for doping concentration effects on magneto-optical properties in [formula omitted] spintronics materials

An investigation for electronic, magnetic, and optical properties of Mn-doped ZnSnAs2 compound performed using advanced computational methods. Using spin-polarized density functional theory (DFT) calculations with local orbital linearized augmented plane wave (lo-LAPW) method and Tran–Blaha’s modified Becke–Johnson (TB-mBJ) functional, Mn-doped n-type chalcopyrite semiconductor ZnMnxSn(1−x)As2, studied within varying Mn doping concentration range 0≤x≤0.5. Doping of Mn to Sn site in pure ZnSnAs2 creates a strong spin effect, which makes it useful spintronic materials. We observed with increase the Mn concentration in ZnSnAs2, energy bandgap changes while the magnetic strength of the unit cell remains unchanged, showing stability of system’s magnetism. Optical properties of the Mn doped ZnSnAs2 compounds analysed in term of dielectric function, absorption spectra, and refractive index. Optical properties show, compound is optically low active in the Infrared (IR) region and more active in visible and ultraviolet (UV) region. The electronic and optical properties of Mn-doped ZnSnAs2, offer potential technological advancements in semiconductor device design technology and engineering.