Vanadium Pentoxide Thin Films Research Articles

XAS studies of vanadium pentoxide thin films

Thin films of 200 nm of VOx RF magnetron sputtered on the SiO2 glass and Si substrates were studied with X-ray Absorption Spectroscopy in the XANES range of the oxygen K and vanadium L2,3 edges. The total electron yield (TEY) detection mode was used. The spectra were collected at several temperatures between room temperature and 300 °C for the unpolarized and linearly polarized beam to study polarization effects. The experimental data were compared with the theoretical model based on DFT-ROCIS (Density Functional Theory, Restricted Open shell Configuration Interaction with Singles) from the literature. Changes in the spectra with temperature, particularly visible at the oxygen K edge are attributed to the loss of surface oxygen and the corresponding changes of population of the single- double- and triple vanadium coordinated oxygen. The corresponding decrease of the surface stoichiometry leads to formation lower than V5+ valency of vanadium ions such as V4+ or V3+ i.e., containing d-electrons. It gives a tentative explanation for the occurrence of metallicity attributed in the literature to a metal–insulator transition (MIT).

Fast optoelectronic gas sensing with p-type V2O5/WS2/Si heterojunction thin film

The efficiency of ultraviolet (UV) illumination in gas adsorption/desorption is remarkable due to its capacity to activate and energize CO2 molecules, rendering them more reactive and prone to surface interactions. A heterojunction device for room-temperature optoelectronic gas sensing has been fabricated. This was achieved through the deposition of an orthorhombic vanadium pentoxide (V2O5) thin film onto a wafer scale 2D p-type tungsten disulfide (WS2)/silicon (Si). The incorporation of the V2O5 layer brings about alterations in WS2's electronic properties, resulting in increased energy states for photo-generated carriers and a promising approach to enhance the intensity of exciton and trion peaks. Specifically, the WS2 film exhibits a carrier concentration of 3.67 × 1018 cm−3, while incorporating the V2O5 layer significantly raises this concentration to 1.20 × 1020 cm−3. The experiments reveal a rapid response time of 0.4 s and a recovery time of 0.2 s, respectively, demonstrating the swift desorption capability of the device in a CO2 environment. Remarkably, this device exhibits high optoelectronic performances, boasting a detectivity of 1.22 × 1013 Jones and a responsivity of 177.21 A/W. These findings have the potential to advance the development of improved gas-sensing devices, offering heightened sensitivity and selectivity in diverse optoelectronic applications.

Gas sensing performance of Tungsten doped V2O5 nanorod thin-films deposited by hot filament CVD combined with DC sputtering

High-quality polycrystalline tungsten doped vanadium pentoxide thin-films were prepared using Hot Filament Chemical Vapor Deposition technique (HFCVD) combined with sputtering by changing target to substrate distance and reaction duration. Scanning electron microscopy and X-ray diffraction revealed that the morphologies and crystalline structures of the films are depending on the deposition parameters such as target to substrate distance and deposition time. Raman spectroscopy is also used to analyse the oxidation states of the vanadium-based films. The deposited nanorod thin-film was exposed to ammonia and ethanol gases to test their gas sensing performance. It exhibits a sensing response of 1.8 and 1.65 at a concentration of 200 ppm ammonia and ethanol and has a recovery time of 44 and 31 s, respectively.

Tuning of Structural and Morphological Characteristics of V2O5 Thin Films Using Low Energy 16 keV N + for Optical and Wetting Applications

Effect of nitrogen (N+) ion implantation on the morphological, structural, optical, and compositional properties of vanadium pentoxide (V2O5) thin films grown on glass substrates is studied. Surface morphology shows the formation of grains and the growth dynamics is governed by roughness (α) and growth (β) exponents. X-ray diffraction studies reveal that V2O5 exists in a hybrid form, with properties of both the orthorhombic and tetragonal phases. Ion implantation induces defects and strain in V2O5 thin films causing a reduction in crystalline properties and deformation in the β-phase with a corresponding change in crystallite size. Contact angle wetting properties are found to be co-related with fractal growth of the films under ion implantation. Oxygen vacancies and electron scattering/trapping centres are revealed to have increased after N+ implantation, leading to a smaller bandgap in the thin films. The benefits of decreasing the optical band-gap of V2O5 thin films for optical applications are outlined in the present work.

Effects of lithium insertion into vanadium pentoxide thin films. Continuum radiation study

Optical emission of Lix(x=0.2,0.7,1.2)V2O5 has been studied during 5 keV Kr+ ions bombardment. Continuous luminescence was observed in a broad wavelength range between 280 and 340 nm. Generally, the emission intensity was influenced by the quantities of lithium giving rise to transient effects as well as an increase in the line intensity. The experimental results suggest that the continuum emission depends on the nature of surface interaction between lithium and vanadium pentoxide and is very probably related to its electronic structure.

Vanadium pentoxide thin films deposited by the thermionic vacuum arc plasma

The Vanadium pentoxide (V2O5) thin films were deposited on glass substrates by a Thermionic vacuum arc (TVA) plasma system. The structural, elemental, surface morphological, and optical properties of the deposited thin films were investigated in detail using X-ray diffraction (XRD), Raman spectroscopy, Fourier Transform Infrared Spectroscopy (FT-IR), Ultraviolet-visible (UV–VIS) spectroscopy, field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), and atomic force microscopy (AFM). In this study, the V2O5 thin films deposited on the glass substrates were produced at three different arc powers at fixed cathode filament current and deposition time, and all characteristics of the deposited thin films were analyzed separately for these three arc powers. The thicknesses of the V2O5 thin films deposited at arc powers of 80, 280, and 640 W were measured as 92, 98, and 204 nm, respectively. The main objective of the research is to show that V2O5 thin films can be deposited by the TVA with the features specified by the technology, which cannot be arranged easily in other methods. While all the deposited thin films have an amorphous structure and roughness as small as 0.4 – 1.8 nm, the arc power did not cause any different bonding in the atomic structure. The transmittance of each film, in the spectral range of 300 to 900 nm, was measured and the optical energy band gap (Eg) was calculated for three films deposited at various arc powers and found to be 3.84, 3.42, and 3.20 eV for the direct allowed transitions respectively.

Comparison of Sputtered and Evaporated Vanadium Pentoxide Thin Films for Resistive Microbolometer Application

V2O5 thin films have made impressive progress in the development of resistive microbolometers. The challenging parameters for microbolometers are the active material selection and the deposition methods. It might be a more promising way to achieve a good performance of the devices. The present work deals with the V2O5 thin films fabricated on soda lime glass substrates by using e-beam evaporation and magnetron sputtering techniques at a substrate temperature of 200 °C. Afterward, samples were annealed at 300 and 400 °C for 1 h to obtain uniform and stoichiometric thin films. X-ray Diffraction (XRD) showed that the thin films deposited by magnetron sputtering were amorphous in nature, even after annealing at elevated temperatures; however, the thin films fabricated by the electron beam evaporation technique show crystalline nature, which was improved by annealing. XRD also revealed various mixed phases of VOx in electron beam-deposited films. Optical properties were determined using UV-Visible spectroscopy, which showed a decrease in transmittance from 81% down to 57% by increasing the annealing temperature. Similarly, the band gap calculated for electron beam evaporated and magnetron sputtered V2O5 thin films was observed in the range of 1.41 to 2.25 eV. Rutherford backscattering (RBS) was performed to determine the thickness and composition of the films. Slight variations have been observed in intended and deposited thicknesses of films fabricated by e-beam and sputtering techniques. Structural properties revealed by Field Emission Scanning Electron Microscope (FESEM) were found to be the uniform, compact and dense surface of the as-deposited and 300 °C annealed samples. However, annealing at 400 °C changed the surface morphology into nanorods in e-beam and plate-like structures in the sputtered film. EDS proved the elemental concentration of vanadium and oxygen in these V2O5 thin films. Electrical properties were investigated using the Hall measurement technique which showed better conductivity of sputtered films than e-beam deposited films. It can be concluded that the cost-effective and reliable microbolometers infrared (IR) sensors can be fabricated using annealed sputtered films.

Effect of Annealing on the Microstructure, Opto-Electronic and Hydrogen Sensing Properties of V2O5 Thin Films Deposited by Magnetron Sputtering

This paper reports results of investigations on selected properties of vanadium oxide thin films deposited using gas impulse magnetron sputtering and annealed at temperatures in the range of 423 K to 673 K. Post-process annealing was shown to allow phase transition of as-deposited films from amorphous to nanocrystalline V2O5 with crystallite sizes in the range of 23 to 27 nm. Simultaneously, annealing resulted in an increase in surface roughness and grain size. Moreover, a decrease in transparency was observed in the visible wavelength range of approximately 50% to 30%, while the resistivity of formed vanadium pentoxide thin films was almost unchanged and was in the order of 102 Ω·cm. Simultaneously, the best optoelectronic performance, testified by evaluated figure of merit parameter, indicated the as-deposited amorphous films. Performed Seebeck coefficient measurements indicated the electron type of electrical conduction of each prepared thin film. Furthermore, gas sensing properties towards diluted hydrogen were investigated for annealed V2O5 thin films, and it was found that the highest senor response was obtained for a thin film annealed at 673 K and measured at operating temperature of 623 K.

Tuning of optical properties of doped vanadium pentoxide thin films

Thin films of vanadium pentoxide (V2O5) have been investigated for various technological applications. This article covers new research on the effects of transition and rare earth metal ions doping on the optical characteristics of thin films made of vanadium pentoxide. It has been observed that tuning of optical properties of V2O5 thin films is significantly influenced by size, concentration and filling of empty orbitals of dopant ions. In addition, optical transmittance of has been found to alter due to scattering from the dopants ions into the V2O5 lattice. Dopant induced stress, strain and oxygen defects notably influence the optical transitions from filled oxygen states to empty vanadium 3d states. Additionally, the creation of midgap states inside the forbidden bandgap cause bandgap narrowing at greater doping levels. Annealing of thin films has been found to reduce transmittance more than 50% as compared to pristine V2O5 thin films.

Structural characteristics and gas sensing response of V2O5 nanorod thinfilms deposited by hot filament CVD

Using the novel hot filament chemical vapor deposition (HFCVD) technique, thinfilms of vanadium pentoxide (V2O5) were deposited under various conditions. The structural characteristics and gas sensing response of the thinfilms were investigated. X-ray diffraction shows that the thinfilms are orthorhombic V2O5 with (001) preferred orientation. Scanning electron microscopy observation reveals that nanorod thinfilms could be obtained under optimized oxygen content and substrate to filament distance. The sensing response of the nanorod thinfilm towards ammonia and ethanol were tested. It exhibits a sensing response of 1.557 and 1.721 towards 200 ppm ammonia and ethanol, respectively, with a response time of 14 s and 20 s after the exposure to ethanol and ammonia and a corresponding recovery time of 26 s and 38 s respectively.

In Situ Raman Observation of Dynamically Structural Transformation Induced by Electrochemical Lithium Intercalation and Deintercalation from Multi‐Electrochromic V2O5 Thin Films

AbstractUnderstanding the dynamic nature of electrochemical interface induced by ion transfer is of great significance. Herein, in situ Raman spectroscopy combined with electrochemistry has been developed to real‐time monitor the transfer of lithium ions at electrode‐electrolyte interface and reveal the associated structure and performance variation of the vanadium pentoxide (V2O5) thin films on the indium tin oxide/silver/aluminum zinc oxide/poly(ethylene terephthalate) (ITO/Ag/AZO/PET) substrates. It is demonstrated that the Raman active/silent states of the vibrational modes of VO, V3O, and VO bonds, as well as the transformation of the V2O5 thin films from V2O5 to lithium vanadate (LixV2O5), can be reversibly changed with reversible extraction/insertion of lithium ions. In situ UV‐vis spectroscopy in combination with in situ Raman analysis is applied to show that the reversible evolutions involving V2O5/LixV2O5 and VO bonding characteristic contribute to the multi‐color electrochromic characteristic of the V2O5 thin films enabling a superior optical modulation of up to 75.41%. This experimental approach establishes a significative guideline for the more elaborate research on the dynamic nature of electrochemical interface.

Thermal Annealing Effects of V2O5 Thin Film as an Ionic Storage Layer for Electrochromic Application.

A vanadium pentoxide (V2O5) thin film with thermal annealing as an ionic storage layer for electrochromic devices is presented in our study. The V2O5 thin film was deposited on an ITO glass substrate by an RF magnetron sputtering. The electrochromic properties of the film were evaluated after various thermal annealing temperatures. The structural analysis of the film was observed by X-ray diffraction (XRD), field emission electron microscopy (FE-SEM), and atomic force microscopy (AFM). The structure of the V2O5 thin film transformed from an amorphous to polycrystalline structure with directions of (110) and (020) after 400 °C thermal annealing. The electrochromic properties of the film improved compared with the unannealed V2O5 thin film. We obtained a charge capacity of 97.9 mC/cm2 with a transparent difference ΔT value of 31% and coloration efficiency of 6.3 cm2/C after 400 °C thermal annealing. The improvement was due to the polycrystalline orthorhombic structure formation of V2O5 film by the rearrangement of atoms from thermal energy. Its laminate structure facilitates Li+ ion intercalation and increases charge capacity and transparent difference.

Performance of RF sputtered V2O5 interface layer in p-type CdTe/Ag Schottky diode

In this work, vanadium pentoxide (V2O5) thin films were successfully grown on soda-lime glass by RF magnetron sputtering technique under an oxygen partial pressure of 10−6 m-bar at room temperatures. Systematically, the characterization of V2O5 films was carried out to study the impact of different sputtered power on the growth, structural and optical properties. XRD results revealed that films exhibit a preferred orientation along with the (001) plane, including an orthorhombic structure at the low RF power. The crystal growth corresponding (001) and (110) planes were suppressed as well as the intensity of peak (003) and (401) planes increased with increasing RF power. It was examined that at the high RF power, thin films show mixed oxide of VO2 and V2O5. A uniform spherical grains morphology was observed by FESEM micrographs. The thin films exhibited good transmittance above 80%, and a sharp absorption edge was found for all samples about 412 nm. Moreover, Two Schottky structures, Ag/V2O5/CdTe and Ag/CdTe were fabricated to investigate the performance of Schottky diode (SD) with the V2O5 interface layer between metal and semiconductor junctions for solar cell applications. The SD parameters such as ideality factor, barrier height, and interface resistance were also calculated. It was found that Ag/V2O5/CdTe diode performs well at room temperature. The saturation current increases from 1.03 μA to 8.39 μA with the insertion of the V2O5 interface layer (IF). Consequently, the V2O5 layer plays a vital role in enhancing the diode's performance.

Defect structure and electrical properties of vanadium pentoxide thin films

Defect structure and electrical properties of vanadium pentoxide thin films

Solution-processed light-emitting diodes consisting of metal-oxide and organic–inorganic hybrid emissive thin films

We prepared organic–inorganic hybrid emissive thin films using a simple sol-gel method containing an emissive polymer for improving the operating lifetime of organic materials. The hybrid films can be developed using a precursor solution of tetraethoxysilane (TEOS) and an emissive polymer. In the films, the emissive polymer is encapsulated in SiO2 and not exposed to the atmosphere, thus improving the photoluminescence lifetime of the hybrid films with this sealing effect. We also prepared vanadium pentoxide (V2O5) thin films using a vanadium(V) oxytriisopropoxide (VTIP) precursor solution for application to hole-injection layers in light-emitting diodes (LEDs). The fabricated LEDs consisting of a solution-processed bilayer (hybrid and V2O5) showed improved operating lifetime. These results clearly demonstrate that a good sealing effect on the emissive polymer can be realized in hybrid films using a simple sol-gel method and that V2O5’s hygroscopicity and strong acidity are better than those of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS).

Effect of fluorine doping on the structural and gas sensing property of V2O5 thin films

Pristine and fluorine doped vanadium pentoxide (V2O5) thin films are prepared by spray pyrolysis technique at different molar, dopant concentrations at a substrate temperature of 450 ˚C. The structural, optical, morphological, electrical and ethanol sensor studies are then carried out for these films. The band gap of the prepared host film at 0.03 M concentration has a lowest value of 2.43 eV and the 3 % of F doped V2O5 thin film has a lowest value of 2.39 eV. Morphological studies reveal that the film prepared at 0.03 M and 3 % doped films have good crystallinity. The electrical studies like I-V and Hall measurement on the host film has a conductivity of 245 Ω−1 m−1 and the carrier concentration of 4.74 × 1018 cm−3 where as for the doped film they are 253 Ω−1 m−1 and 7.25 × 1018 cm−3 respectively. Ethanol sensing property of these doped and un-doped V2O5 thin films are then studied. It is observed that F doped V2O5 thin films have higher sensitivity compared to the pure V2O5 thin films.

Effect of substrate temperature on micro-structural, optical and electrical properties of V2O5 thin films

Vanadium pentoxide (V2O5) thin films have been prepared onto ITO coated flexible Kapton substrates by electron beam evaporation technique. The influence of substrate temperature on the structural, morphological, optical and electrical properties has been investigated. The XRD results reveals that the films prepared at lower temperatures are amorphous in nature and the films prepared at 300 oC is exhibited predominant (001) orientation with an orthorhombic crystal structure. AFM study showed that the grain size varies from 80 nm to 150 nm. The optical studies revealed that the transmittance decreased with increasing substrate temperature. The optical absorption coefficient ‘a’ determined from the experimentally measured transmittance and reflectance data for V2O5 films was found to give a better fit for the exponent n = 3/2 suggesting the direct forbidden transitions with an estimated optical band gap of 2.31 eV for the films prepared at 300 oC. The electrical conductivity has been observed to be increased from 2 x 10-6 S/cm to 3 x 10-2 S/cm by varying temperature from 30 oC to 300 oC. The electrochemical experiments exhibited the discharge capacity of about 60 μAh/(cm2-μm) for the films deposited at 300 oC.

Cylindrical model of electrochromic colouration of hydrated vanadium pentoxide thin films with point contacts

This article analyses experiments on the kinetics of the internal electrochromism of thin (micron) films of hydrated vanadium pentoxide xerogel with point contacts. It describes a cylindrical model of electrochromic colouration, which was used to evaluate the concentration of the colour centres in the initial film and after additional hydrogenation of this film by plasmaimmersion ion implantation.When we compared the calculated values of the concentration of colour centres with the equilibrium concentration of protons in the xerogel, we saw that the mobility of the protons migrating from the depth of the film to the cathode region, which are involved in the electrochemical reaction, was not a determinant of the electrochromism kinetics.The rate of electrochromic colouration could be increased by the formation of layered film structures based on hydrated vanadium pentoxide, which have increased overall electron conductivity and, as a consequence, low faradaic resistance of the electrochromic cathodic reaction.

Study of vanadium pentoxide thin film prepared by spin coating method

Attraction towards V2O5 thin film is due to its wide range of applications in the field of opto-electric device, electro-chromic device, as an excellent catalyst, gas sensor etc. Here, we report the deposition of V2O5 thin film using spin coating method. To study the effect of annealing, the prepared films were annealed at 250° C, 350° C and 450° C. To study the structural and optical properties of the prepared films, X-Ray Diffraction (XRD) and UV– Visible spectroscopy were used. XRD reveals the increase in the crystallinity of film with increase in temperature. The film annealed at 450° C has pure β- V2O5 tetragonal phase. The decrease in band gap of the films was also observed with increase in annealing temperature. Moreover, the electrical resistance of films was also measured.

Effects of Annealing on the Structural and Optical Properties of V2O5 Thin Films Prepared by RF Sputtering for Humidity Sensor Application

In this work, vanadium pentoxide (V2O5) thin films were prepared using rf magnetron sputtering on silicon wafer and glass substrates from V2O5 target at 200 °C substrate temperature, followed by annealing at 400 and 500 °C in air for 2 h. The prepared thin films were examined by X-ray diffraction (XRD), forier transform infra-red spectroscopy (FTIR), UV-visible absorbance, and direct current coductivity to study the effects of annealing temperature on their structural and optical properties. The XRD analysis exhibited that the annealing promoted the highly crystallized V2O5 phase that is highly orientated along the c direction. The crystalline size increased from 22.5 nm to 35.4 nm with increasing the annealing temperature to 500 °C. The FTIR spectroscopy showed the enhancement of the characteristics band for the V2O5 with increasing annealing temperature to 500 °C. The optical study showed that the energy gap for the sample deposited on glass slides decreased from 2.85 eV, for as deposited sample, to 2.6 eV upon annealing the sample to 500 °C. There was a linear dependence between sensitivity and relative humidity (RH) at the range from 25% to 70%, while the behavior was exponential at high RH range.