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Chemisorption and sensitivity at semiconductor sensors revisited
摘要： In this work we derived the adsorption isotherms for non-dissociative and dissociative chemisorption of oxygen on a semiconductor surface. We extended the Wolkenstein theory for dissociative chemisorption and re-examined the basis that led to currently accepted formalisms in the literature. In particular, we correctly incorporated dissociative chemisorption as a second-order reaction. We determined band bendings and adsorbate coverages for different gas pressure and doping for a typical metal-oxide used in gas sensing. Finally, consequences for the sensor conductivity and sensitivity are discussed.
关键词： Chemisorption,Conductivity,Adsorption isotherms,Semiconductor gas sensors
更新于2025-09-19 17:15:36
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Photoluminescence, conductivity and structural study of terbium doped ZnO films grown on different substrates
摘要： The effect of substrate material (Si, SiO2, Al2O3) on structural, optical and electrical properties of terbium doped ZnO films (Tb-ZnO) has been investigated by the X-ray diffraction, Raman scattering, atomic force microscopy, photoluminescence and infrared reflection methods. All films consist of micron size clusters of closely packed ZnO grains separated by deep trenches. The width of the trenches depends on the substrate material, being the largest in the Tb-ZnO/Al2O3 one. It is shown that the film on Al2O3 substrate contains the largest amount of extended and point defects. This film also demonstrates the highest intensity of Tb3+-related photoluminescence, while the film on Si substrate shows the lowest. On the contrary, the largest free carrier concentration evaluated from the infrared reflection spectra is found for Tb-ZnO/Si film and the lowest one is for the Tb-ZnO/Al2O3 film.
关键词： Luminescence, Raman spectroscopy,Doping,ZnO, terbium,Conductivity
更新于2025-09-19 17:15:36
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Thermal properties of high purity zinc-tellurite glasses for fiber-optics
摘要： The thermal properties of the series glasses (TeO2)(0.86-x)(ZnO)x(La2O3)0.04(Na2O)0.1 were studied. The heat capacity and characteristics of transitions between aggregative states were determined by the method of differential scanning calorimetry (DSC) in the temperature range 320-950 K. The experimentally obtained values of thermal conductivity, density and coefficient of thermal expansion at room temperature are as follows: 1.14 ± 0.06 W/(m?K), 5.20 ± 0.02 g/cm3 and (54.6 ± 1.2)?10-6 K-1, respectively. The model-statistical processing of calorimetric data was used to determine the complete set of standard thermodynamic functions together with their approximation to the unexplored low-temperature region by means of parametric similarity. The approach allows predicting the functions for unexplored intermediate glasses compositions.
关键词： heat capacity,thermal conductivity,thermodynamic functions,coefficient of thermal expansion,density,Zinc-tellurite glasses
更新于2025-09-19 17:15:36
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Thickness-controlled synthesis of CoX2 (X = S, Se, Te) single crystalline 2D layers with linear magnetoresistance and high conductivity.
摘要： Two-dimensional (2D) materials especially transition metal dichalcogenides (TMDs) have drawn intensive interests owing to their plentiful properties. Some TMDs with magnetic elements (Fe, Co, Ni, etc.) are reported to be magnetic theoretically and experimentally, which undoubtedly provide a promising platform to design functional devices and study physical mechanisms. Nevertheless, plenty of the theoretical TMDs remain unrealized experimentally. In addition, the governable synthesis of these kinds of TMDs with desired thickness and high crystallinity poses a tricky challenge. Here, we report a controlled preparation of CoX2 (X = S, Se, Te) nanosheets through chemical vapor deposition (CVD). The thickness, lateral scale and shape of the crystals show great dependence with temperature and the thickness can be controlled from monolayer to tens of nanometers. Magneto-transport characterization and Density Function Theory (DFT) simulation indicate CoSe2 and CoTe2 are metallic. Besides, unsaturated and linear magnetoresistance have been observed even up to 9 Tesla. The conductivity of CoSe2 and CoTe2 can reach 5 × 106 and 1.8 × 106 S/m respectively, which is pretty high and even comparable with silver. These cobalt-based TMDs show great potential to work as 2D conductors and also provide a promising platform for investigating their magnetic properties.
关键词： Transition metal dichalcogenides,Magnetoresistance,Conductivity,Two-dimensional materials,Chemical vapor deposition
更新于2025-09-19 17:13:59
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Growth and characterization of ZnxSn1?xSe films for use in thin film solar cells
摘要： We have fabricated ZnxSn1?xSe (ZTSe) ?lms for the ?rst time. Samples were fabricated by chemical molecular beam deposition method at atmospheric pressure in hydrogen ?ow. ZnSe and SnSe powders with 99.999% purity were used as precursors. The temperature of precursors varied in the range of (850–950) °C. Films were deposited at substrate temperature of (500–600) °C. Borosilicate glass was used as a substrate. We have studied ZTSe ?lms by EDS, XRD and SEM. The samples had orthorhombic and cubic structures depending on composition. Results of EDS have shown that stoichiometric composition of samples moved to ZnSe side by increasing with substrate temperature. SEM pictures have shown that samples had polycrystalline structure. The grain size varied in the range of (2–15) μm. The grain size of samples increased from (2–5) μm to (15–20) μm for substrate temperatures of 500 °C and 550 °C respectively. While, at a substrate temperature of 600 °C the grain size decreased up to (3–5) μm, possibly, because of increasing of ZnSe content. XRD analysis has shown that samples have ZnSe, SnSe, Se and Sn phases. The band gap of samples varied in the range of 1.0–2.0 eV depending on the ?lm compositions. An inversion of the conductivity type was found: samples fabricated at 500 °C and 550 °C performed of p-type conductivity; while samples fabricated at 600 °C showed n-type conductivity.
关键词： Grain size,Conductivity,X-ray,ZnXSn1?XSe ?lms,Morphology
更新于2025-09-19 17:13:59
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Improved conductivity of carbonized polyimide by CO <sub/>2</sub> laser graphitization
摘要： Direct laser writing (DLW) is a fast and cost-effective technique for printing conductive structures on flexible substrates such as polyimide (PI) by the conversion of insulative PI to conductive carbon. However, the conductivity (B103 S m?1) obtained by this method needs to be improved to compete with ink-jet printing of carbon-based materials. The reason behind the low conductivity achieved by the DLW process is due to the crystallinity and hybridization of bonding in carbonaceous structures. In this work, the DLW process has been implemented in two steps: the first step called carbonization was performed by writing pulsed CO2 laser on PI to form tracks which consist of amorphous tetrahedral carbon (a mixture of sp2 and sp3 hybridized carbon) having intrinsically low conductivity. The second step called graphitization is overwriting of the laser on the pre-carbonized tracks to convert sp3 hybridized bonds to sp2 hybridized bonds by the process called laser graphitization. The conductivity of tracks carbonized at (0.21 ± 0.02) W and fluence (3.31 ± 0.32) × 103 mJ cm?2 at a repetition rate of 0.1 kHz was 56.1 ± 3.1 S m?1 which increased to 146.7 ± 5.1 S m?1 upon overwriting with the laser at (0.50 ± 0.03) W and fluence (7.88 ± 0.47) × 103 mJ cm?2 at the same repetition rate. The photothermal process of carbonization and graphitization is modeled for the DLW process and the threshold power of both the processes is calculated and validated by Raman spectroscopy. Improved conductivity achieved by detailed understanding of the laser and material parameters involved in this transformation enables process optimization leading to future applications in scalable manufacturing of flexible bio-sensors and electrochemical energy storage devices.
关键词： Direct laser writing,carbonization,graphitization,CO2 laser,polyimide,conductivity
更新于2025-09-19 17:13:59
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The effects of air, oxygen and water exposure on the sub-bandgap absorption, the electronic conductivity and the ambipolar diffusion length in highly crystalline microcrystalline silicon films for photovoltaic applications
摘要： Reversible and irreversible changes due to long term air and short term de-ionized water (DIW) or pure oxygen exposure were investigated in about 1 μm thick hydrogenated microcrystalline silicon (μc-Si:H) films deposited on rough glass substrates, thereby comparing highly crystalline with compact material. Time and temperature dependent dark conductivity, steady-state photoconductivity, the steady-state photocarrier grating and dual-beam photoconductivity methods have been used to study the effects. Standard measurement procedures defined previously have been carefully applied to record the changes after different treatments using the steady-state methods under light. After long term air exposure of highly crystalline μc-Si:H films, a thermal annealing step leads to an increase in dark conductivity (σD) and steady-state photoconductivity (σph) as well as to a significant increase in the sub-bandgap absorption. These effects are likely due to a reversible recovery from surface adsorbents in a porous microstructure after air exposure resulting in surface charge and Fermi level shifts in agreement with earlier results. Compact μc-Si:H films showed only marginal effects upon an annealing after long term air exposure suggesting much reduced susceptibility to surface adsorbent induced by Fermi level shifts. Five hours exposure to de-ionized water at 80 °C caused more than an order of magnitude increase in σD and σph and a substantial decrease in the sub-bandgap absorption spectrum in highly crystalline as well as in compact μc-Si:H films. In addition, minority carrier diffusion lengths measured by the steady-state photocarrier grating method improved significantly. The changes after exposure to water were not reversible upon our standard annealing procedure. Exposure to high purity oxygen gas at 150 °C resulted in similar effects like the exposure to DIW. Also here the changes in material properties were not reversible upon annealing. Results are discussed in terms of adsorption and chemical reactions on surfaces in the porous highly crystalline material versus the materials with more compact structures. Results are compared to earlier observations and consequences for device application will be indicated.
关键词： microcrystalline silicon,electronic conductivity,sub-bandgap absorption,photovoltaic applications,ambipolar diffusion length
更新于2025-09-19 17:13:59
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Solvent-free and large-scale preparation of silver@polypyrrole core@shell nanocomposites; structural properties and terahertz spectroscopic studies
摘要： There is a growing interest over the environmental safety and mass-production of polymer nanocomposites. Solvent-free synthetic pathways are considered as promising alternative green techniques because of their high efficiency, simplicity and negligible liberation of hazardous waste. A new synthetic route has been developed to synthesize silver@polypyrrole core@shell nanocomposites at ambient condition. The silver nanoparticles are directly synthesized via solid-state reaction with poly(vinylpyrrolidone) and then pyrrole is polymerized in Ag/PVP powder. The band gap value decreases with the increased addition of pyrrole in the preparation step due to the formation of more silver nanoparticles. Scanning and transmission electron microscope confirm the formation of core@shell structure. The negatively charged carbonyl group of poly(vinylpyrrolidone) can bind to polycationic polypyrrole by an electrostatic effect to form the core@shell structure. The terahertz spectroscopy characterizes the prepared core@shell nanocomposites that are well fit to the Drude-Smith model. The DC optical conductivity in the terahertz range (0.3–2 THz) is increased with increasing Py addition.
关键词： Core@shell,Solvent-free method,Silver,Polypyrrole,Optical conductivity
更新于2025-09-19 17:13:59
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High performance carbon-based planar perovskite solar cells by hot-pressing approach
摘要： A simple yet effective method based on hot-pressing a free-standing carbon film onto adjacent hole transport layer (HTL) is used to fabricate carbon electrode for planar perovskite solar cells (C–PSCs). Due to the thermoplasticity of as-prepared carbon film, the conductivity of the carbon electrode is enhanced by over ten-fold and the adhesion to adjacent layer is dramatically strengthened via this hot-pressing process. By optimizing the pressing temperature, 15.3% of power conversion efficiency (PCE) is obtained for CuSCN based C–PSCs, which is 70% high than the device without heating at the same pressing pressure. The device demonstrates 93% performance retention after being stored in a humid environment (55–70%) without encapsulation over 80 days. This facile fabrication process of PSCs paves a way to facilitate commercialization of the new PV technology.
关键词： Carbon electrode,Hot-pressing,Perovskite solar cells,Conductivity,Temperature
更新于2025-09-19 17:13:59
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Synthesis of silicon carbide nanocrystals and multilayer graphitic carbon by femtosecond laser irradiation of polydimethylsiloxane
摘要： Laser-based modification of polymer materials has been emerging as a versatile and efficient technique to simultaneously form and pattern electrically conductive materials. Recently, it has been revealed that native polydimethylsiloxane (PDMS) can be modified into electrically conductive structures using femtosecond laser irradiation; however, the details regarding the structures formed by this method have yet to be revealed. In this work, structures were fabricated by focusing and scanning femtosecond laser pulses onto the surface of PDMS. Raman Spectroscopy and Transmission Electron Microscopy (TEM) analyses revealed the formation of silicon carbide (SiC) nanocrystals, as well as multilayer graphitic carbon, in the modified regions of PDMS. The state of the formed material differed depending on the distance from the focal spot, suggesting that photo-thermal effects contributed to the degradation of PDMS into conductive material. Electrical conductivity measurements, in addition to Raman results, indicated that the amount of disorder in the formed graphitic carbon contributes to the electrical conductivity of the fabricated structures.
关键词： PDMS,femtosecond laser,graphitic carbon,electrical conductivity,silicon carbide
更新于2025-09-19 17:13:59