Variation Of Band Gap Research Articles

Insights into Selective Sensitivity of In2O3-CuO Heterojunction Nanocrystals to CH4 over CO and H2: Experiments and First-Principles Calculations.

Metal oxide semiconductor gas sensors have demonstrated exceptional potential in gas detection due to their high sensitivity, rapid response time, and impressive selectivity for identifying various sorts of gases. However, selectively distinguishing CH4 from those of CO and H2 remains a significant challenge. This difficulty primarily stems from the weakly reducing nature of CH4, which results in a low adsorption response and makes it prone to interference from stronger reducing gases in the surroundings. Herein, we synthesized In2O3-xCuO nanocomposites using a hydrothermal method to explore their gas sensing properties toward CH4, CO, and H2. Characterization tests confirmed the successful preparation of In2O3-xCuO nanocomposites with different In:Cu molar ratios and the formation of a p-n heterojunction. The gas sensing test results indicated that the In2O3-2.1CuO nanocomposites calcined at 500 °C and measured at 350 °C displayed a p-type response for CH4 and an n-type response for CO and H2, allowing for accurate differentiation of CH4 from CO and H2. Moreover, the In2O3-2.1CuO sensor also showed excellent stability and reproducibility across all three gases. First-principles calculations revealed distinct changes in the electronic structure of the In2O3-CuO heterojunction upon adsorption of CH4, CO, and H2, a finding that aligns with empirical evidence. The gas selectivity mechanism was effectively explained by variations in the energy band gap, driven by electrical behavior during the adsorption process. This work suggests a promising approach for developing selective gas sensors capable of detecting weakly reducing gases.

Nanoscale mapping of local intrinsic strain-induced anomalous bandgap variations in WSe2 using selective-wavelength scanning photoconductivity microscopy

Nanoscale defects can locally tailor the optoelectronic properties of two-dimensional materials such as bandgap. However, it is still challenging to directly map and analyze the defect-induced bandgap variations in a quantitative manner. Here, we report the nanoscale mapping of local intrinsic strain-induced anomalous bandgap variations in as-grown WSe2 by using a selective-wavelength scanning photoconductivity microscopy. In this method, a conducting nanoprobe is utilized to map the spatial distributions of strain, sheet-conductance, and charge trap density (Neff) of epitaxially-grown WSe2 on sapphire while illuminating monochromatic light of selective wavelengths. Under un-illuminated conditions, the maps showed WSe2 domain structures with boundaries having slightly lower sheet-conductance and higher Neff than those in domains, presumably due to low misorientation angles between adjacent epitaxially-grown domains. By measuring wavelength-dependent photoconductance maps and fitting each pixel value of the maps, we could successfully obtain the map of local bandgap. The map clearly showed bandgap variations inside domains as well as rather low bandgaps at boundaries. By comparing with local strain map, we found that tensile strain effectively reduced bandgap following two different power-law relationships. Such anomalous bandgap variations in WSe2 could be explained by strain-induced weakening of d-orbital couplings. Furthermore, in a monolayer-bilayer WSe2 interface, bilayer WSe2 exhibited lower bandgap than the underlying monolayer WSe2, while interfacial boundaries exhibited the strain-induced bandgap values in between those of monolayer and bilayer WSe2. Since our method allows us to directly map the intrinsic strain-induced bandgap variations with a nanoscale resolution down to tens-of-nm, it can be a powerful tool for basic research and practical applications of optoelectronic devices based on two-dimensional materials.

Optimization of CTS thin film solar cell: A numerical investigation based on USP deposited thin films

CTS (Cu2SnS3) can be used in the next generation of thin-film solar cells due to its non-toxicity, affordability, and natural availability. CTS has a direct bandgap, high absorption coefficient, making it an attractive and environmentally friendly choice for fabrication of solar cells. Ultrasonic spray pyrolysis is used to deposit CTS (absorber layer) and ZnS (buffer layer) films and they are characterized by XRD, SEM and UV–Vis spectroscopy. Based on experimental results, numerical simulation has been performed using SCAPS 1D. FTO/CTS/ZnS/Ag is the structure of device, where Ag act as an electrode. In this paper, a study is carried out to investigate the effects of thickness, doping concentrations in CTS and ZnS layer, working temperatures, bandgap variations, and defect densities on these solar cells. At the temperature of 300K, the proposed cell exhibits a power conversion efficiency of 8.25 %, open circuit voltage 0.4252V, short circuit current 24.82 mA/cm2, FF 78.18 % respectively.

Exploring the cytotoxic and antioxidant properties of lanthanide-doped ZnO nanoparticles: a study with machine learning interpretation

BackgroundLanthanide-based nanomaterials offer a promising alternative for cancer therapy because of their selectivity and effectiveness, which can be modified and predicted by leveraging the improved accuracy and enhanced decision-making of machine learning (ML) modeling.MethodsIn this study, erbium (Er3+) and ytterbium (Yb3+) were used to dope zinc oxide (ZnO) nanoparticles (NPs). Various characterization techniques and biological assays were employed to investigate the physicochemical and optical properties of the (Er, Yb)-doped ZnO NPs, revealing the influence of the lanthanide elements.ResultsThe (Er, Yb)-doped ZnO NPs exhibited laminar-type morphologies, negative surface charges, and optical bandgaps that vary with the presence of Er3+ and Yb3+. The incorporation of lanthanide ions reduced the cytotoxicity activity of ZnO against HEPG-2, CACO-2, and U87 cell lines. Conversely, doping with Er3+ and Yb3+ enhanced the antioxidant activity of the ZnO against DPPH, ABTS, and H2O2 radicals. The extra tree (ET) and random forest (RF) models predicted the relevance of the characterization results vis-à-vis the cytotoxic properties of the synthesized NPs.ConclusionThis study demonstrates, for the first time, the synthesis of ZnO NPs doped with Er and Yb via a solution polymerization route. According to characterization results, it was unveiled that the effect of optical bandgap variations influenced the cytotoxic performance of the developed lanthanide-doped ZnO NPs, being the undoped ZnO NPs the most cytotoxic ones. The presence alone or in combination of Er and Yb enhanced their scavenging capacity. ML models such as ET and RF efficiently demonstrated that the concentration and cell line type are key parameters that influence the cytotoxicity of (Er, Yb)-doped ZnO NPs achieving high accuracy rates of 98.96% and 98.67%, respectively. This study expands the knowledge of lanthanides as dopants of nanomaterials for biological and medical applications and supports their potential in cancer therapy by integrating robust ML approaches.Graphical abstract

Synthesis and characterization of MoO3/PEDOT:PSS nanocomposite for flexible photodetector and nonlinear optical applications

We present our findings on the preparation, UV photoresponse of nanocomposite films(NCF) on a flexible substrate consisting of orthorhombic molybdenum oxide (α −MoO3) and the conducting polymer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS). We also studied the nonlinear optical properties of prepared NCF on glass substrate. The pristine MoO3 was synthesized using a direct precipitation method which is followed by annealing to ensure the formation of high quality orthorhombic MoO3. MoO3/PEDOT:PSS nanocomposite films with varying MoO3 concentrations were fabricated and employed in photodetector devices to investigate the influence of MoO3 content on photoresponse behaviour. Comprehensive structural investigations were conducted using X-ray diffraction (XRD), revealing minor variations in structural parameters like crystallite size, microstrain, and dislocation density, indicative of the interaction between MoO3 and the polymer matrix. Scanning electron microscopy (SEM) provided detailed insights into the morphological characteristics, showing uniform distribution. UV–visible (UV–vis) spectroscopy demonstrated bandgap variations correlated with the MoO3 concentration in the nanocomposites, highlighting the tunability of optical properties through compositional adjustments. Fourier-transform infrared (FTIR) spectroscopy elucidated the vibrational properties of the nanocomposites, confirming the successful incorporation of MoO3 within the polymer matrix and its impact on vibrational modes. The fabricated photodetectors exhibited a negative photoresponse at low MoO3 concentrations, characterized by a decrease in current under UV illumination, indicative of unique charge trapping and recombination mechanisms. However, as the concentration of MoO3 in the nanocomposite increased, the photoresponse transitioned to a positive mode, reflecting a decrease in resistance upon UV exposure. This tunable photoresponse behaviour underscores the potential of MoO3/PEDOT:PSS nanocomposites for flexible UV photodetector applications. Nonlinear optical studies show the enhanced saturable absorption in NCFs. These findings underscore the significant saturable absorption properties and negative photoresponse, indicating promising avenues for further investigation into the photoresponse and nonlinear optical characteristics of NCFs.

Effect of Ni doping on the acetone vapor sensing performance of ZnO nanofibers

Nickel-doped zinc oxide (NiZ) nanofibres (NFs) were fabricated using sol-gel electrospinning (ES) technique followed by pyrolysis from an aqueous solution of polyvinyl alcohol/zinc acetate/nickel acetate tetrahydrate. The morphology of the NiZ NFs was analyzed using Scanning Electron Microscopy (SEM), which revealed a uniform and well-defined fibrous structure. X-ray diffraction (XRD) results indicated complete removal of the organic phase from NiZ NFs during pyrolysis. The structural analysis confirmed the incorporation of Nickel (Ni) into the Zinc oxide (ZnO) lattice without altering its wurtzite crystal structure. The optical properties and bandgap variations were evaluated using UV–visible spectroscopy, which indicated a bandgap narrowing with increasing Nickel doping. The Photoluminescence (PL) spectroscopy confirmed the presence of defect states and recombination processes in the NFs. The gas sensing performance was investigated by measuring the response to various analytes at a concentration of 50 ppm with varying operating temperatures. The results indicated that the highest response was observed for 5 w% NiZ NFs towards acetone vapors. The response and recovery time were recorded at 80 s and 60 s. The enhanced sensitivity is attributed to the optimal doping concentration, which significantly improves the surface reaction and charge carrier mobility.

Influence of isochronal heat treatment on spray-deposited mixed phase tin based thin films for ammonia gas sensor applications

The current work applied the spray pyrolysis (SP) approach to coat mixed-phase SnS thin films at 3500C, and then air annealed at 400,450,5000C for use in sensor and solar cells applications. A variety of methods were employed to evaluate the structural, morphological, compositional, optical, and electrical characteristics of synthesized mixed-phase films. Films annealed at 5000C are reported to have bigger crystal sizes, and all deposited SnS films exhibit the orthorhombic phase in addition to tetragonal phase of SnO2, with other visible secondary phases like SnS2,Sn2S3. Fourier transform infrared spectroscopy and Raman analyses verified the molecular structure and vibrational mode of SnS films. The Scanning electron microscopy tests reveal a consistent, size-varying two-dimensional flake like grain structure, while the optical studies show a variation in optical direct band-gap from 1.79-2.75eV. The Hall-effect shows that films subsequently annealed at 4000C have improved electrical properties. An efficient metal oxide semiconductor gas sensor was developed by applying mixed-SnS film on the conducting side of an indium tin oxide coated glass plate. To examine the sensor selectivity at room temperature, a variety of test gases, such as NO2, H2S, C2H5OH, NH3, were purged at different concentrations. The optimum working temperature and concentration for NH3 selective gas have been determined to be 3500C and 5ppm. The sensor sensitivity is found to be maximum at operating temperature of 2000C towards NH3 gas. An inexpensive, fabricated MOS-gas sensor based on mixed-phase SnS can be easily mass produced and may find potential applications in industrial and environmental monitoring.

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.

Unveiling Structural Variations in Armchair-Edge Coronoids by Spectroscopies.

This study explores the electronic and vibrational properties of armchair coronoids (ACs), a unique class of polycyclic aromatic hydrocarbons with varying molecular and cavity sizes. Through density functional theory simulations, we investigated the X-ray photoelectron spectroscopy (XPS) and Raman spectra of C222, C114, C42, and their derivatives with different cavity sizes. The results reveal that band gaps and electronic properties of ACs can be precisely tuned by adjusting the molecular and cavity dimensions. XPS spectra demonstrated shifts in binding energy correlating with bandgap variations, while Raman spectra exhibited distinct C-C stretching and breathing modes. Notably, the introduction of cavities led to shifts in the breathing mode band, providing insights into the structural identification of ACs through Raman spectroscopy. The findings suggest that combining XPS and Raman spectroscopy can effectively characterize ACs, offering a comprehensive understanding of their structure-property relationships. This research lays the groundwork for future experimental and theoretical studies on the potential applications of ACs in electronic materials.

Band Gap Variation and Structural Disorder in the Two-Dimensional Mixed-Halide Hybrid Lead Perovskites

Band Gap Variation and Structural Disorder in the Two-Dimensional Mixed-Halide Hybrid Lead Perovskites

Deposition of Nb-doped TiO2 thin films for electrochromic applications with high durability and stability

Although pure TiO2 has no significant electrochromic properties, it is used to investigate the electrochromic properties after the doping process. In this paper, TiO2 thin film was doped with Nb, and its surface and electrochromic properties were subsequently investigated. A thermionic vacuum arc deposition system was used to deposit the doped thin film, which was then annealed. Field emission scanning electron microscopy and atomic force microscopy were employed to obtain the surface morphology of the films. The Ti/Nb ratio was found to be 0.033. After annealing, the transparency value of the thin film increased to 85 %. The coloration efficiency was determined to be 375 cm2/C. The band gap of Nb2O5 was found to be in the range of 3.1–4.0 eV. For TiO2, the band gap was found to be 3.2 eV. Transmittance variation is about 3 %, and band gap variation in colouring and bleaching states is about 0.5 eV. During the colouring and bleaching states, the band gap value of the sample changed from 3.5 eV to 3.0 eV. The specific capacitance is 3 F/g for the thin film. Finally, the results show that Nb-doped TiO2 is a promising candidate for high-performance and long-life electrochromic material.

Sol gel fabrication of CeO2/SnO2 nanocomposite films for habilitation in optoelectronic and sensing properties

This study investigated the synthesis and characterization of CeO2/SnO2 composite powders and films by varying CeO2 concentration ranging from 2 to 10 mol%. The sol-gel process was utilized to create composites. X-ray diffraction demonstrated that the resulting CeO2/SnO2 powders were polycrystalline, whereas the composite films had amorphous structures. The morphology of the produced samples was studied with SEM and TEM. Also the specific surface area was measured using the Brunauer-Emmett-Teller (BET) technique and the optical characteristics were assessed using a UV–Vis spectrophotometer. The absorption coefficients, energy gaps, and refractive indices of the composite films were determined. Direct and indirect energy gaps were from 3.71 to 3.27 eV and 2.70 to 2.26 eV, respectively. The refractive index increases from 1.61 to 1.7 as the CeO2 concentration increases. The variation in the energy band gap and refractive index values indicate that CeO2/SnO2 nanocomposite films are a viable composite film for optoelectronic devices. The investigated films have electrical conductivity values ranging from 10−2 to 10−8 Ω−1 cm−1. The gas sensing test was studied using different gases as liquid petroleum gas (LPG), carbon monoxide (CO), and Hydrogen sulfide (H2S). CeO2/SnO2 films demonstrated the highest sensitivity for hydrogen sulfide (H2S), with a sensitivity of 0.988 % and a response time of 40 s.

Effect of variation in band gap via carbon doping in ZnO NPs on its photocatalytic activity in Pb ion removal from water

Effect of variation in band gap via carbon doping in ZnO NPs on its photocatalytic activity in Pb ion removal from water

Tuning of optical, thermodynamic, and thermoelectric properties of Cs2CuBiX6 (X = Cl, Br, I) halide perovskites for solar cells and energy harvesting applications

The double perovskites are outstanding materials for solar cells and transport applications to clean harvest energy. Therefore, the Cs2CuBiX6 (X = Cl, Br, I) are discussed comprehensively for energy harvesting by modified Becke and Johnson (mBJ) potential. The studied DPs fit the structural, mechanical, and dynamic stability scale by tolerance factor, Born–Huang criteria, and phonon dispersion band structures. The band gaps (1.20, 1.0, 0.70) eV for (Cl, Br, I) based DPs ensure the Cs2CuBiCl6 has an absorption band in the visible region while Cs2CuBiBr6 and Cs2CuBiI6 has an absorption band in the infrared region. Heavy elements’ spin–orbit coupling effect (Cs, Bi) reduces the band gap to 0.08 eV. Thermoelectric behavior regarding the merit scale against dopant carriers and temperature has been elaborated. The ultralow lattice thermal conductivity, large Debye temperature, hardness, and melting temperature increase their implication for thermoelectric and other thermodynamic applications. The variation in band gap makes them important for diverse optoelectric and thermoelectric applications. The Cs2CuBiCl6 with a band gap of 1.20 eV is suitable for solar cells, while Cs2CuBiBr6 and Cs2CuBiI6 with band gaps of 1.0 eV and 0.70 eV are significant for thermoelectric generators.

A theoretical investigation into the impact of temperature and band gap variation of La2NiMnO6 oxide double perovskite nanostructures on the performance of La2NiMnO6/MASnI3 based hybrid solar cells

The study aimed at simulating a model of bilayer La2NiMnO6/MASnI3 hybrid perovskite solar cell having a potential benefit of better stability at higher operating temperature with higher band gap of LNMO. This numerical analysis of La2NiMnO6/MASnI3 based hybrid solar cell performance parameters has been carried out as a function of temperature and optical band gap (Eg) of La2NiMnO6 (LNMO). The analysis reveals that the fill factor of solar cells operated at room temperature has not been affected too much on varying Eg of LNMO and decreases non-linearly with increasing operating temperature. The open circuit voltage of solar cells operated at room temperature increases with increasing Eg of LNMO and drops linearly with increasing operating temperature. The short-circuit current density (JSC) increases non-linearly at different rates with increasing the operating temperature. The value of dη/dT increases up to a critical temperature (Tc) and then decreases in the solar cells comprised with higher Eg of LNMO (Eg ∼ 1.50 eV–1.60 eV). The Tc value was shifted towards higher operating temperature in the higher Eg of LNMO (Eg ≥ 1.50 eV), enabling more stable solar cell at higher operating temperature.

The effect of quantum confinement and the role of electron-phonon interaction on the band gap shrinkage of some II-VI semiconductors

The role of electron-phonon interaction in band gap shrinkage for some II-VI bulk and low-dimensional semiconductors is investigated in this work. The variation of the energy band gap is studied as a function of temperature using Varshni's, Vina's, and Passler's relations. It is observed that the change in the energy band gap is affected due to the quantum confinement as the dimensionality of these semiconductors is decreased.

Hex-star phosphorene nanosheets as sequencing material for DNA/RNA strands – A first-principles investigation

In this study, we utilised hex-star phosphorene as the main detecting material to identify the nucleobases. Nucleobases, being crucial carriers of hereditary information are identified through specific hydrogen bonding and steric interactions such as adenine pairing with thymine (or) uracil and guanine pairing with cytosine. The stable hex-star phosphorene possesses negative formation energy of −5.194 eV. The hex-star phosphorene exhibits a semiconductor nature with an energy band gap of 1.658 eV, which is deployed as the adsorbing substrate for nucleobases. Based on the Mulliken charge analysis, adsorption energy, relative band gap variation, and the detection efficiency of hex-star phosphorene towards nucleobases are examined. The outcome confirms the physisorption of nucleobases on hex-star phosphorene and strongly supports that hex-star phosphorene can be used as sequencing material for DNA and RNA.

Na+ doped CuO: A new paradigm electrode material for high performance supercapacitors

This study investigates the influence of sodium doping on the properties of cupric oxide (CuO) thin films synthesized via spray pyrolysis. Comprehensive characterization was conducted using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDAX), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Raman spectroscopy, Hall effect measurements, and electrochemical studies. All films exhibited p-type conductivity, with an optical band gap variation from 1.53 to 1.73 eV. XRD analysis confirmed the dominance of monoclinic CuO, with minor phases of Cu2O and Cu4O3. EDAX and XPS verified the incorporation of Cu, O, and Na elements. FESEM revealed a densely packed morphology with uniform particle distribution and rough surfaces in the electrically optimized film. The Raman spectra of doped samples showed increased intensity and sharpness, attributed to Na + ion-induced polarizability enhancement. Hall effect measurements indicated a tenfold decrease in carrier concentration and a more than tenfold increase in mobility upon sodium doping. Films doped with 4 at.% sodium exhibited the lowest resistivity. Additionally, Na doping enhanced the electrochemical performance of CuO. These findings demonstrate that sodium doping significantly enhances the electrical, optical and electrochemical properties of CuO thin films, making them suitable for applications in optoelectronic devices and supercapacitors.

Correlating the electronic structures of β-Ga2O3 to its crystal tilts induced defects at nanoscale

Crosslinking structural transformation mechanism at nanoscale to the corresponding anisotropically electronic properties is essential to both the atomic-level controlled synthesis and extreme-conditional applications of the ultrawide bandgap semiconductors. Here, we report the first direct observation of bandgap variation at certain microstructural flaws in monoclinic crystal β-Ga2O3 via scanning transmission electron microscopy-electron energy loss spectrum (STEM-EELS) technology with both high energy and spatial resolution. Atomic-scale tilt of the Mosaic blocks relative to [010] zone axis is demonstrated to cause specific point defects accumulation at block boundaries, resulting in the formation of vacancy lines (or clusters) and then the crystal deformation induced flaws. These as-formed tiny Mosaic tilts observed from both in-plane and out-of-plane geometry are correlated to the corresponding electronic structure obtained by density functional calculations, indicating the carrier mobility limits transferred from intrinsic polar optical phonon scattering to the ionized oxygen atoms scattering in the defective monoclinic crystal. These findings provide a new insight on these anisotropic defect formation induced electronic structural variation, paving the way for precise synthesis and development of high-performance ultra-wide bandgap materials.

Dichloro-tin (IV) hexadeca-fluoro-phthalocyanine (F16PcSnCl2) thin film on porous silicon layers by ultrasonic spray pyrolysis, for possible application in optoelectronics devices

Phthalocyanines represent a significant class of organic semiconductors that have garnered attention for their potential applications in conducting polymers and organic electronics. The unique structural characteristics of phthalocyanines, coupled with the intriguing chemical behavior and variations in bandgap associated with different substitution sites, offer exciting prospects for designing novel application devices. In this study, we have successfully fabricated a heterostructure incorporating dichloro tin (IV) hexa deca fluoro phthalocyanine (F16PcSnCl2) on both porous silicon (PS) and crystalline silicon (c-Si). The PS substrate was prepared using metal-assisted chemical etching. To explore the optoelectronic applications, we thoroughly characterized the optical, electrical, and morphological properties of the heterostructure. F16PcSnCl2 exhibits the lowest reflectance within the visible light spectrum, making it highly advantageous for photosensitive applications that necessitate efficient light absorption, diffusion, or scattering. The morphological analysis of the F16PcSnCl2 film reveals the presence of nanosphere-type structures uniformly distributed on both PS and c-Si substrates. The absorbance spectrum exhibits three distinct bands, which serve as typical indicators of the F16PcSnCl2 complex. Several hybrid heterostructures were fabricated for electrical characterization, displaying rectifying ohmic behavior and demonstrating a photocurrent effect in the I-V curves. Notably, when the heterostructures were polarized at 1 V, a pronounced response to pulses of white light was observed in the current–time curves. Overall, the integration of organic and inorganic materials in heterostructures holds great promise for innovative applications in optoelectronics.