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Novel electronic structures and enhanced optical properties of boron phosphide/blue phosphorene and F4TCNQ/blue phosphorene heterostructures: a DFT + NEGF study
摘要： Blue phosphorene (Blue-p), an allotrope of black phosphorene, has attracted extensive interest due to its hexagonal crystal with a flat arranged layer of phosphorus atoms. However, the indirect band gap of Blue-p greatly hinders its applications in optoelectronics. By stacking both boron phosphide (BP) and the organic molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) with Blue-p, we construct BP/Blue-p and F4TCNQ/Blue-p heterostructures. We reveal that the BP/Blue-p heterostructure possesses a direct band gap of 0.605 eV and is tunable via in-plane strain and an external electric field. Moreover, it also has remarkable optical absorption in the UV region and enhanced transport properties. Furthermore, by doping with F4TCNQ, the F4TCNQ/Blue-p heterojunction displays type-II semiconducting properties with a flat valence band and Van Hove singularities at the Fermi level, which can be used to achieve extremely low in-band tunneling, yielding low static power dissipation and large drive currents in the ON regime of transistors. Due to the superior electronic, optical and transport properties, Blue-p-based heterostructures are promising candidates for electronic and optical device applications.
关键词： DFT,optical properties,electronic properties,transport properties,Blue phosphorene,heterostructures,boron phosphide,F4TCNQ,NEGF
更新于2025-09-23 15:19:57
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Controlled optoelectronic properties and abrupt change in photosensitivity by suppressing density of oxygen vacancies in SnO <sub/>2</sub> nanocrystalline thin films prepared at various spray-deposition temperatures
摘要： Nanostructured SnO2 thin films were synthesized at various substrate temperatures using a modified chemical spray pyrolysis (MCSP) technique. The x-ray diffraction (XRD) patterns confirmed the presence of a rutile SnO2 with tetragonal structure for all the resultant film samples. The XRD results ascertained increase in the grain growth rate and consequent enhancement in crystallinity with increasing the spray-deposition temperature. The optical spectroscopic analysis revealed a significant increase in the optical transmission within the visible region as well as a considerable increase in the optical bandgap by increasing the deposition temperature. However, the spectral distribution of the absorption coefficient ascertained the dominance of direct allowed transition for the SnO2 film samples. The analysis of the current-voltage characteristic curves revealed that the variation of the spray-deposition temperature strongly influences the photosensitivity of the film samples. Based on the electrical results, these film samples reveal a semiconductor behaviour of the transport property over the entire investigated range of the working temperature, with two different conduction mechanisms. The optical and electrical results were combined to evaluate the influence of varying the deposition temperature on the figure of merit (FOM) factor for the SnO2 film samples.
关键词： MCSP technique,optical spectroscopic analysis,electrical transport properties,figure of merit,structural properties,spray deposition temperature
更新于2025-09-23 15:19:57
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Phosphorene as H <sub/>2</sub> S and CH <sub/>4</sub> Gas Sensor
摘要： First-principle calculations within density functional theory are carried out to investigate the adsorption of various gas molecules, including hydrogen sulfide and methane on two-dimensional monolayer phosphorene in order to fully exploit the gas sensing capabilities. The adsorption properties of different molecules in the environment on monolayer phosphorene base material is discussed in terms of the Mulliken charge transfer, energy band gap, adsorption energy. The prominent adsorption sites of methane, hydrogen sulfide, water, and oxygen on monolayer phosphorene are investigated at an atomistic level. Based on the results the transport properties of monolayer phosphorene exposed to these gas molecules are investigated both in zigzag and armchair direction using non-equilibrium Green function tuned with density functional theory. The results show that using both directions simultaneously as gas sensing can be an effective technique to distinguish hydrogen sulfide and methane gas molecules from others and demonstrate great selectivity.
关键词： phosphorene,methane,Green function,density functional theory,transport properties,device,hydrogen sulfide,gas sensors
更新于2025-09-23 15:19:57
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Investigation of Conductivity Characteristics of Zn-In-Se Thin Films
摘要： Zn-In-Se thin films were fabricated on the ultrasonically cleaned glass substrates masked with clover-shaped geometry by thermal evaporation of its elemental sources. Temperature dependent conductivity characteristics of the films were investigated under dark and illuminated conditions. The semiconductor type of the films was found as n-type by thermal probe test. According to the van der Pauw technique, the dark electrical conductivity analyses showed that the variations of conductivity of unannealed and annealed at 300°C samples are in exponential dependence of temperature. These conductivity profiles were found to be dominated by the thermionic emission at high temperature region whereas their behaviors at low temperatures were modeled by hopping theory. On the contrary, as a result of the further annealing temperatures, the surface of the samples showed semi-metallic characteristics with deviating from expected Arrhenius behavior. In addition, the temperature dependent photoconductivity of the films was analyzed under different illumination intensities and the results were explained by the supra-linear characteristic based on the two-center recombination model.
关键词： Photoconductivity,Thin film,Annealing,Transport properties
更新于2025-09-19 17:15:36
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Structure and transport properties of titanium oxide (Ti2O, TiO1+, and Ti3O5) thin films
摘要： Titanium oxides have partially filled or empty d orbital and are stable at various oxidation states with different structures and unique properties. Here, three kinds of titanium oxide thin films of hexagonal Ti2O metal, cubic TiO1+d superconductor, and monoclinic g-Ti3O5 semiconductor, were successfully grown on a-Al2O3 substrates by a pulsed laser deposition technique, through ablating a pure titanium target under different oxygen pressures. The electrical resistivities of these films increase with increasing oxygen content. The metallic behaviors of Ti bulk and Ti2O film can be described by the Bloch-Grüneisen formula, and the semiconducting behaviors of TiO1+d films in normal state and g-Ti3O5 film obey the variable range hopping and the small polaron hopping conduction mechanisms, respectively. For titanium monoxide TiO1+d (1.05 ≤ 1+d ≤ 1.17) films, increasing oxygen content is accompanied by an increase of disorder, a decrease of electron density of states at the Fermi level, and an enhancement of carrier localization, leading to a suppression of superconductivity.
关键词： Electron energy-loss spectroscopy,Oxygen content,Superconductivity,Transport properties,Titanium oxide thin films,Pulsed laser deposition
更新于2025-09-19 17:15:36
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Electronic and optical characterization of 2D Ti<sub>2</sub>C and Nb<sub>2</sub>C (MXene) thin films
摘要： Two-dimensional (2D) transition metal carbides and/or nitrides (MXenes) are emerging as a new class of 2D materials, with extensive opportunities for property tailoring due to the numerous possibilities for varying chemistries and surface terminations. Here, Ti2AlC and Nb2AlC MAX phase epitaxial thin films were deposited on sapphire substrates by physical vapor deposition. The films were then etched in LiF/HCl solutions, yielding Li-intercalated, 2D Ti2CTz and Nb2CTz films, whose terminations, transport and optical properties were characterized. The former exhibits metallic conductivity, with weak localization below 50 K. In contrast, the Nb-based film exhibits an increase in resistivity with decreasing temperature from RT down to 40 K consistent with variable range hopping transport. The optical properties of both films were determined from spectroscopic ellipsometry in the 0.75 to 3.50 eV range. The results for Ti2AlTz films confirm the metallic behavior. In contrast, no evidence of metallic behavior is observed for the Nb2CTz film. The present work therefore demonstrates that one fruitful approach to alter the electronic and optical properties of MXenes is to change the nature of the transition metal.
关键词： transition metal carbide,thin films,MXene,transport properties
更新于2025-09-19 17:15:36
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Nitrogen-doped CQDs to enhance the power conversion efficiency of perovskite solar cells via surface passivation
摘要： In this study, nitrogen doped CQDs (N-CQDs), as a novel additive, were successfully synthesized and characterized by XPS, TEM and UVeVis spectrometry techniques. Importantly, we introduced N-CQDs in CH3NH3PbI3 solar cells. The results indicated that nonradiative charge back recombination decreased and the trap states in the absorber layer were passivated when N-CQDs was used an additive in CH3NH3PbI3 solution. Additionally, the morphological characterization results indicated that the crystallization problems and defects on perovskite surfaces can be easily resolved by N-CQDs additive in perovskite solution. A significant improvement in power conversion efficiency at a yield of 14% is achieved by doping of 3 vol% of N-CQDs, thanks to enhancement of charge transport properties due to the morphological and electrical changes. Herein, we propose an effective and novel additive for the fabrication of high efficiency perovskite solar cell, which can be seen that this method is simple.
关键词： Film coverage,N-CQDs,Perovskite solar cells,Charge transport properties
更新于2025-09-19 17:13:59
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The use of surfactant-filled mesoporous silica as an immobilising medium for a fluorescence lifetime pH indicator, providing long-term calibration stability
摘要： Surfactant filled mesoporous silica is applied as a matrix for immobilizing the fluorescence lifetime pH-indicator acridine. We demonstrate that this type of encapsulation provides a stable and uniform chemical environment for the indicator and has good proton transport properties leading to rapid pH response times. Furthermore, the immobilising medium effectively prevents leaching of the indicator, facilitates high long-term stability and does not influence the pH sensing-range of the indicator.
关键词： acridine,surfactant-filled mesoporous silica,fluorescence lifetime pH indicator,proton transport properties,long-term calibration stability
更新于2025-09-16 10:30:52
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Synthesis of carbon quantum dots in a Nafion matrix: Precursor effect on the ion transport properties
摘要： Carbon quantum dots have been prepared in a Nafion? matrix via the hydrothermal treatment of organic precursors, and the swelling and ion transport properties of the prepared composite materials have been characterized.
关键词： Nafion matrix,ion transport properties,carbon quantum dots,hydrothermal treatment
更新于2025-09-16 10:30:52
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The photocurrent generated by photon replica states of an off-resonantly coupled dot-cavity system
摘要： Transport properties of a quantum dot coupled to a photon cavity are investigated using a quantum master equation in the steady-state regime. In the off-resonance regime, when the photon energy is smaller than the energy spacing between the lowest electron states of the quantum dot, we calculate the current that is generated by photon replica states as the electronic system is pumped with photons. Tuning the electron-photon coupling strength, the photocurrent can be enhanced by the influences of the photon polarization, and the cavity-photon coupling strength of the environment. We show that the current generated through the photon replicas is very sensitive to the photon polarization, but it is not strongly dependent on the average number of photons in the environment.
关键词： photon replica states,transport properties,electron-photon coupling,photon cavity,quantum dot
更新于2025-09-16 10:30:52