An effective use of VO2 and Ag2O thin films prepared by simple chemical method in different proportion as antibacterial

Vanadium dioxide (VO2) is one of the most attractive thermochromic materials, which show large changes in optical and electrical properties at the transition temperature (Tt) close to the atmospheric temperature (approximately 340 K). We already reported for VO2 deposition by rf magnetron sputtering using V2O3 or V2O5 targets that VO2 films thicker than 400 nm showed high thermochromic performance, whereas the VO2 films thinner than 200 nm did not show such performance because of their poor crystallinity and off-stoichiometry. In this study, very thin thermochromic VO2 films with thicknesses of about 50 nm were successfully deposited using highly <001>-preferred oriented ZnO polycrystalline films as a buffer layer between the VO2 film and glass substrate (VO2/ZnO/glass) because of the heteroepitaxial growth of VO2 polycrystalline films. W-doped VO2 films were also deposited on the ZnO-coated glass substrates (ZnO/glass) by cosputtering. It was confirmed that W doping for thin VO2 films deposited on the ZnO/glass can decrease Tt systematically. Such very thin VO2 films should have high potential for application in “smart windows”.

Vanadium oxide thin films were successfully prepared hydrothermally and deposited on a substrate using the drop casting method. Analytical techniques such as XRD, AFM, (SEM) analyses, Ultraviolet-Visible (UV-Vis), PL, and FTIR measurements were used to confirm the characterization of the prepared vanadium oxide NPs. The XRD measurements show that the VO2 thin film was polycrystalline, with a (monoclinic) phase and crystallite size calculated using Scherrer’s equation, as well as dislocation density and microstrain. The optical properties show that the energy gap (4.49) eV, and depending on PL, a single sharp emission peak was found at location 350 nm (3.54 eV). The Antibacterial activity of the vanadium oxide nanoparticles were investigated, with inhibition zone Escherichia coli (17) mm, Staphylococcus aureus 20 mm, Bacillus subtilis 18 mm, and Klebsiella pneumonia 19 mm and Candida isolates 15 mm. The study confirms that the prepared VO2 samples can be used as an antibacterial agent. The results suggest that proper tuning can make them a good antimicrobial agent.

This work shows the fabrication of Bi2O3/PSi heterojunction for solar cell applications prepared by simple chemical method. Bi2O3 nanoparticles were deposited on the n-type porous silicon and glass substrates by drop casting method. The structural and optical properties of bismuth oxide thin film were studied by XRD, SEM, UV-VIS and FTIR analysise. XRD investigation showed that the thin film is polycrystalline and the optical properties stated that bismuth oxide thin film has direct optical band gap of 2.5 eV in addition to the study of I-V in dark and under illumination and finally. The results indicate a significant improvement in the properties of porous silicon, and thus an increase in the conversion efficiency, as the calculated efficiency values for (Al/Bi2O3/PSi/Si/Ag) heterojunction.

Copper oxide was prepared by simple chemical method and deposited on quartz glass and single crystal PSi for solar cell and Photodetector applications by drop casting method. XRD measurements reveal that the film was polycrystalline in nature. The average crystalline size of film was (17.46) nm. In order to investigate the optical characteristics of CuO, researchers took a recording of the transmittance against wavelength. It was determined that the optical energy gap of CuO is equal to 3.5 electron volts. The efficiency of solar cell was (0.27)% and the maximum value of spectral detectivity was 5*10[Formula: see text] (cm Hz[Formula: see text] W[Formula: see text].

Here, we demonstrate improved NO2 gas sensing properties based on reduced graphene oxide (rGO) decorated V2O5 thin film. Excluding the DC sputtering grown V2O5 thin film, rGO was spread over V2O5 thin film by the drop cast method. The formation of several p–n heterojunctions was greatly affected by the current–voltage relation of the rGO-decorated V2O5 thin film due to the p-type and n-type nature of rGO and V2O5, respectively. Initially with rGO decoration on V2O5 thin film, current decreased in comparison to the pristine V2O5 thin film, whereas depositing rGO film on a glass substrate drastically increased current. Among all sensors, only the rGO-decorated V2O5 sensor revealed a maximum NO2 gas sensing response for 100 ppm at 150 °C, and it achieved an approximately 61% higher response than the V2O5 sensor. The elaborate mechanism for an extremely high sensing response is attributed to the formation and modulation of p–n heterojunctions at the interface of rGO and V2O5. In addition, the presence of active sites like oxygenous functional groups on the rGO surface enhanced the sensing response. On that account, sensors based on rGO-decorated V2O5 thin film are highly suitable for the purpose of NO2 gas sensing. They enable the timely detection of the gas, further protecting the ecosystem from its harmful effects.

Observation of reduced phase transition temperature in N-doped thermochromic film of monoclinic VO2

The stoichiometric vanadium(IV) oxide thin films were obtained by controlling the temperature, time and pressure of annealing. The thermochromic phase transition and the IR thermochromic property of 400 nm and 900 nm VO2 thin films in the 7.5 μm-14 μm region were discussed. The derived VO2 thin film samples were characterized by Raman, XRD, XPS, AFM, SEM, and DSC. The resistance and infrared emissivity of VO2 thin films under different temperature were measured, and the thermal images of films were obtained using infrared imager. The results show that the VO2 thin film annealed at 550 °C for 10 hours through aqueous sol-gel process is pure and uniform. The 900 nm VO2 thin film exhibits better IR thermochromic property than the 400 nm VO2 thin film. The resistance of 900 nm VO2 film can change by 4 orders of magnitude and the emissivity can change by 0.6 during the phase transition, suggesting the outstanding IR thermochromic property. The derived VO2 thin film can control its infrared radiation intensity and lower its apparent temperature actively when the real temperature increases, which may be applied in the field of energy saving, thermal control and camouflage.

Post-deposition annealing of thin RF magnetron sputter-deposited VO2 films above the melting point

VO2 thin films have been studied for their semiconductor-metal reversible transition from the monoclinic to the rutile structure, where the electrical and optical properties undergo a drastic change by increasing the temperature or by applying a voltage. VO2 film is becoming a promising material for optical switch, optical storage, optical modulator, smart window, and micro-bolometer. The preparation procedures of the FTO/VO2/FTO structure in detail are as follows: First, the F-doped SnO2 conductive glass (FTO) substrates are cleaned sequentially in acetone, ethanol, and deionized water for 10 min using an ultrasonic cleaning equipment at a frequency of 20 kHz. When the FTO substrates was cleaned, they are dried with nitrogen. Second, the dried FTO substrates are placed in the chamber of a DC magnetron sputtering system equipped with a high-purity metal target of V (99.9%). After argon (99.999%) of 80 sccm flux was discharged with the current of 2 A and the voltage of 400 V for 2 min, the vanadium films are deposited on the FTO substrates. Third, the prepared vanadium films are annealed for different annealing time in an atmosphere composed of different proportions of nitrogen-oxygen. Then another layer thickness of 350 nm of FTO conductive film is deposited on the VO2 thin film by using the plasma enhanced chemical vapor deposition method. Finally, different sizes of the FTO/VO2/FTO structure are prepared by using photolithography and chemical etching processes. The effect of different annealing time and different proportions of nitrogen-oxygen atmosphere on the VO2 thin films has been studied. X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and spectrophotometer are then used to test and analyze the crystal structure, surface morphology, surface roughness, the relative content of the surface elements, and transmittance of the VO2/FTO composite films. Results show that a relatively single component VO2 thin film can be obtained under the optimum condition. The current abrupt change can be seen at the threshold voltage when the FTO/VO2/FTO structure is applied to voltage on both the transparent conductive films of the VO2 thin film. The threshold voltage is 1.7 V when the contact area is 3 mm×mm, and the threshold voltage increases as the contact area increases. When the contact area is 6 mm × 6 mm, the threshold voltage of the thin film phase transition is 4.3 V; when the contact area is 8 mm × 8 mm, the threshold voltage of the thin film phase transition is 9.3 V. Compared with the no voltage situation, the infrared transmittance difference of the FTO/VO2/FTO structure under the effect of voltage is up to 28% before and after the transition. The structure remains stable with a strong electrochromic capacity when it is applied with voltage repeatedly. This brings about many new opportunities for optoelectronic devices and industrial production.

Atomic layer deposition was adopted to deposit VOx thin films using vanadyl tri-isopropoxide {VO[O(C3H7)]3, VTIP} and water (H2O) at 135 °C. The self-limiting and purge-time-dependent growth behaviors were studied by ex situ ellipsometry to determine the saturated growth conditions for atomic-layer-deposited VOx. The as-deposited films were found to be amorphous. The structural, chemical, and optical properties of the crystalline thin films with controlled phase formation were investigated after postdeposition annealing at various atmospheres and temperatures. Reducing and oxidizing atmospheres enabled the formation of pure VO2 and V2O5 phases, respectively. The possible band structures of the crystalline VO2 and V2O5 thin films were established. Furthermore, an electrochemical response and a voltage-induced insulator-to-metal transition in the vertical metal-vanadium oxide-metal device structure were observed for V2O5 and VO2 films, respectively.

Vanadium dioxide (VO2) is an archetypal metal-insulator transition (MIT) material, which has been known for decades to show an orders-of-magnitude change in resistivity across the critical temperature of approximately 340 K. In recent years, VO2 has attracted increasing interest for electronic and photonic applications, along with advancement in thin film growth techniques. Previously, thin films of VO2 were commonly grown on rigid substrates such as crystalline oxides and bulk semiconductors, but the use of transferrable materials as the growth substrates can provide versatility in applications, including transparent and flexible devices. Here, we employ single-crystalline hexagonal boron nitride (hBN), which is an insulating layered material, as a substrate for VO2 thin film growth. VO2 thin films in the polycrystalline form are grown onto hBN thin flakes exfoliated onto silicon (Si) with a thermal oxide, with grains reaching up-to a micrometer in size. The VO2 grains on hBN are orientated preferentially with the (110) surface of the rutile structure, which is the most energetically favorable. The VO2 film on hBN shows a MIT at approximately 340 K, across which the resistivity changes by nearly three orders of magnitude, comparable to VO2 films grown on common substrates such as sapphire and titanium dioxide. The VO2/hBN stack can be picked up from the supporting Si and transferred onto arbitrary substrates, onto which VO2 thin films cannot be grown directly. Our results pave the way for new possibilities for practical and versatile applications of VO2 thin films in electronics and photonics.

Evolution of polymorph and photoelectric properties of VO2 thin films with substrate temperature

Study of rectifying properties and true Ohmic contact on Sn doped V2O5 thin films deposited by spray pyrolysis method

The resistive switching temperature associated with themetal–insulatortransition (MIT) of epitaxial VO2 thin films grown on flexiblesynthetic mica was modulated by bending stress. The resistive switchingtemperature of polycrystalline VO2 and V2O5 thin films, initially grown on synthetic mica without a bufferlayer, was observed not to shift with bending stress. By insertinga SnO2 buffer layer, epitaxial growth of the VO2 (010) thin film was achieved, and the MIT temperature was foundto vary with the bending stress. Thus, it was revealed that the bendingresponse of the VO2 thin film depends on the presence orabsence of the SnO2 buffer layer. The bending stress applieda maximum in-plane tensile strain of 0.077%, resulting in a high-temperatureshift of 2.3 °C during heating and 1.8 °C during cooling.After 104 bending cycles at a radius of curvature R = 10 mm, it was demonstrated that the epitaxial VO2 thin film exhibits resistive switching temperature associatedwith MIT.

The synergistic effect of Ta-doping and antireflective TaOx layer on the thermochromic VO2 thin films for smart windows