This study explores the structural, electronic, and optical properties of sandwich-structured thin films composed of WO3, MoWO3, and MoO3 as window layers on VO2/WO3 via a physical vapor deposition method. Morphological analysis demonstrates the evolution of distinct nanowires, offering insights into the lattice strain of the VO2 layer toward high-performance thermochromatic devices. Temperature-dependent sheet resistivity is investigated, showcasing significant improvements in conductivity for samples with MoO3 as a window layer. The electrical and optical properties of the MoO3/VO2/WO3 device showed a phase transition temperature (Tc) of 36.8 °C, a transmittance luminous (Tlum) of 54.57%, and a solar modulation ability (ΔTsol) of 12.43. This comprehensive analysis contributes to understanding the growth of nanowires on multi-layered thin films, offering valuable insights into potential applications in bright windows.@en

This study was on the optoelectronic properties of multilayered two-dimensional MoS₂ and WS₂ materials on a silicon substrate using sputtering physical vapor deposition (PVD) and chemical vapor deposition (CVD) techniques. For the first time, we report ultraviolet (UV) photoresponses under air, CO₂, and O₂ environments at different flow rates. The electrical Hall effect measurement showed the existence of MoS₂ (n-type)/Si (p-type) and WS₂ (P-type)/Si (p-type) heterojunctions with a higher sheet carrier concentration of 5.50 × 10⁵ cm⁻² for WS₂ thin film. The IV electrical results revealed that WS₂ is more reactive than MoS₂ film under different gas stimuli. WS₂ film showed high stability under different bias voltages, even at zero bias voltage, due to the noticeably good carrier mobility of 29.8 × 10² cm²/V. WS₂ film indicated a fast rise/decay time of 0.23/0.21 s under air while a faster response of 0.190/0.10 s under a CO₂ environment was observed. Additionally, the external quantum efficiency of WS₂ revealed a remarkable enhancement in the CO₂ environment of 1.62 × 10⁸ compared to MoS₂ film with 6.74 × 10⁶. According to our findings, the presence of CO₂ on the surface of WS₂ improves such optoelectronic properties as photocurrent gain, photoresponsivity, external quantum efficiency, and detectivity. These results indicate potential applications of WS₂ as a photodetector under gas stimuli for future optoelectronic applications.

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Vanadium oxide (VO₂) is considered a Peierls–Mott insulator with a metal–insulator transition (MIT) at T_c = 68^◦ C. The tuning of MIT parameters is a crucial point to use VO₂ within thermoelectric, electrochromic, or thermochromic applications. In this study, the effect of oxygen deficiencies, strain engineering, and metal tungsten doping are combined to tune the MIT with a low phase transition of 20^◦C in the air without capsulation. Narrow hysteresis phase transition devices based on multilayer VO₂, WO₃, Mo_0.2W_0.8O_3, and/or MoO₃ oxide thin films deposited through a high vacuum sputtering are investigated. The deposited films are structurally, chemically, electrically, and optically characterized. Different conductivity behaviour was observed, with the highest value towards VO_1.75/WO_2.94 and the lowest VO_1.75 on FTO glass. VO_1.75/WO_2.94 showed a narrow hysteresis curve with a single-phase transition. Thanks to the role of oxygen vacancies, the MIT temperature decreased to 35^◦C, while the lowest value (T_c = 20^◦C) was reached with Mo_0.2W_0.8O₃/VO₂/MoO₃ structure. In this former sample, Mo_0.2W_0.8O₃ was used for the first time as an anti-reflective and anti-oxidative layer. The results showed that the MoO₃ bottom layer is more suitable than WO₃ to enhance the electrical properties of VO₂ thin films. This work is applied to fast phase transition devices.

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Effect of in-/ex-situ annealing on the structure, optical, photoluminescence, electrical characterization and gas sensing dynamics on CdS thin films are presented. Raman characterizations showed an increase in the peak intensity with increasing the annealing temperature under ex-situ, while a lower peak intensity observed through the in-situ annealing condition. No shift was observed in the Photoluminescence peaks through the yellow band peaks of in-situ annealed samples, however, a slightly blue shift was observed through the ex-situ annealed samples. High conductivity was observed for all samples, while in the case of in-situ RT, in-situ 100 °C, ex-situ 200 °C and ex-situ 300 °C, a CO₂ and O₂ gas sensing activity have been tested. The ex-situ 300 °C sample shows a higher response towards CO₂ compared with the ex-situ 200 °C film. While, both in-situ RT and 100 °C sensors show the same response towards CO₂ with a high gas response. However, the in-situ 100 °C sensor has the highest response compared to in-situ RT film with a high response of 25% at 50 sccm towards O₂.

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Molybdenum - tungsten oxide (Mo_1-xW_xO₃, x = 1, 0.8, and 0.6) nanostructured thin films-based room temperture (RT) gas sensors are prepared by means of reactive RF magnetron co-sputtering at 400 °C. The structural, morphology, topography, optical, and electrical characterizations of the prepared sensors are carried out by XRD Rietveld structure refinement analyses, SEM, AFM, UV-VIS spectrophotometer, and source meter. By controlling the deposition temperture of 400 °C, a co-existing phase of MoO₃ and MoO₂ in WO₃ matrix is presented with high oxygen vacancies concentration as calculated from the XRD Rietveld Refinement analyses. By increasing the Mo content, the calculated oxygen vacancies concentration increases by factor of 1.36. The optical characterization of Mo_0.2W_0.8O₃ thin film shows a high transparent of 99.6% at 500 nm. The prepared thin films have successfully tested to detect carbon dioxide (CO₂) at RT (20 °C) with high selectivity and repeatability. The Mo_0.4W_0.6O₃ sensor film shows an electrical Schottky contact with fast response and recovery times towards CO₂ under UV light activation. Mo_0.4W_0.6O₃ thin film under dark and UV conditions were able to detect low CO₂ concentration of 2 and 0.5 sccm CO₂ at RT, respectively. Under UV illumination, Mo_0.4W_0.6O₃ film shows a fast response and recovery time of 6.53 and 8.05 s at 0.5 sccm with sensitivity of 29.19%. Under UV photonic activation, higher electron concentration is presented in the oxide surface, which leads to high probability for reaction with CO₂ molecules, and consequently enhanced the chemisorption of CO₂. The enhanced CO₂ gas sensitivity and fast response may refer to the high oxygen vacancies concentration and the active role of the grain boundaries in MoO₂, MoO₃ and WO₃ mixed-valence nanostructured under UV activation.

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The negative charge trapped in the oxygen species present in metal oxides like Tin Oxide (SnO₂) caused an upward band bending and makes these materials as promising sensing materials for CO₂ detection. However, sensors based on pure SnO₂ may only detect CO₂ at high temperature making them un-sensitive at room temperature (RT) (20 °C). In this study, SnO₂ and Cobalt doped SnO₂ (Co:SnO₂) thin films of varying thickness were successfully synthesized by sol-gel spin coating technique, followed by annealing. The highly active surface due to high number of divided layers has been determined by X-ray diffraction (XRD) for neat and doped SnO₂ deposition. Moreover, the effect of increasing the annealing from 400 to 500 °C has been evaluated. The calculated band gap of the multilayer sample annealed at 500 °C blue shifted from 3.55 to 3.81 eV with the Co doping. Therefore, the Co doped SnO₂ can detect CO₂ as low as 30 vol% in atmosphere at RT, meanwhile the un-doped SnO₂ coating shows a weak response. Moreover, at high CO₂ concentration the recovery time decreases due to the high desorption kinetic. The obtained results illustrate the control of the film's properties gives the opportunity to manage the sensing and optoelectronic performance.

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The distinctive properties of strongly correlated oxides provide a variety of possibilities for modulating the properties of 2D transition metal dichalcogenides semiconductors; which represent a new class of superior optical and optoelectronic interfacing semiconductors. We report a novel approach to scaling-up molybdenum disulfide (MoS₂) by combining the techniques of chemical and physical vapor deposition (CVD and PVD) and interfacing with a thin layer of monoclinic VO₂. MoWO₃/VO₂/MoS₂ photodetectors were manufactured at different sputtering times by depositing molybdenum oxide layers using a PVD technique on p-type silicon substrates followed by a sulphurization process in the CVD chamber. The high quality and the excellent structural and absorption properties of MoWO₃/VO₂/MoS₂/Si with MoS₂ deposited for 60 s enables its use as an efficient UV photodetector. The electronically coupled monoclinic VO₂ layer on MoS₂/Si causes a redshift and intensive MoS₂ Raman peaks. Interestingly, the incorporation of VO₂ dramatically changes the ratio between A-exciton (ground state exciton) and trion photoluminescence intensities of VO₂/(30 s)MoS₂/Si from < 1 to > 1. By increasing the deposition time of MoS₂ from 60 to 180 s, the relative intensity of the B-exciton/A-exciton increases, whereas the lowest ratio at deposition time of 60 s refers to the high quality and low defect densities of the VO₂/(60 s)MoS₂/Si structure. Both the VO₂/(60 s)MoS₂/Si trion and A-exciton peaks have higher intensities compared with (60 s) MoS₂/Si structure. The MoWO₃/VO₂/(60 s)MoS₂/Si photodetector displays the highest photocurrent gain of 1.6, 4.32 × 10⁸ Jones detectivity, and ~ 1.0 × 10¹⁰ quantum efficiency at 365 nm. Moreover, the surface roughness and grains mapping are studied and a low semiconducting-metallic phase transition is observed at ~ 40 °C.

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The greenhouse effect is involving global heating and climate change within the world. Carbon dioxide (CO₂)is one of the major gas at the origin of this effect, but also the byproduct of human activity. Therefore, monitoring the indoor/outdoor CO₂ emission by gas sensors is one of the priorities for environmental preservation. In this paper, the sensing performance of CO₂ towards two different O-rich films have been studied; graphene oxide (GO)and vanadium dioxide (VO₂). The preparation of GO film has been carried out by spray pyrolysis on fluorine tin oxide (FTO)prepared by the modified Hummers method. While the VO2 film has been sol-gel spin-coated on a glass substrate. Both films have been characterized using XRD, SEM and electrical properties. The CO₂ gas sensing mechanism and the role of oxygen vacancies in VO₂ are addressing. The oxygen functional groups in GO play a main role in the CO₂ gas the sensitivity level and response time. Their gas sensing performances have been investigated based on measuring the response vs recovery time, dynamic response curve analysis and sensitivity. In order to better understand the sensing mechanism, characterization has been done with different gas concentrations. Both GO and VO₂ based CO₂-sensors are acted as an n-type sensor. Sensing behavior of GO at RT has explained to be mainly mediated by the oxygen functional groups and a wide range of active sites. In the other hand, VO₂ contains oxygen vacancies and more defect sites which play a main role in the RT sensing activity and low recovery time.

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