Vanadium Films Research Articles

Locally manufactured films for neutron flux measurement in the MNSR type reactor

Metal films deposited on Teflon are used in the Miniature Neutron Source Reactor (MNSR) for the first time to study their usability as neutron activation detectors for the thermal neutron flux measurements in the reactor. For this purpose Titanium, Aluminum, Vanadium, and Silver films deposited on Teflon have been locally prepared at room temperature using two methods: the vacuum arc deposition and DC Magnetron sputtering techniques. The thermal neutron flux in the MNSR inner irradiation site was measured using the prepared metal films. The results at the 95% level of confidence of the neutron flux using the metal films deposited on Teflon by the vacuum arc deposition for Titanium, Aluminum, and Vanadium were: (9.9±0.3)×1011, (1.4±0.3)×1012, (1.2±0.2)×cm−2s−1, respectively. The result at the same level of confidence of the neutron flux using the metal films deposited on Teflon by the DC Magnetron sputtering for Silver was: (1.5±0.2)×1011cm−2s−1. Good agreements are noticed between our obtained mean value (9.3±0.9)×1011cm−2s−1 and the previous published results.

Thermally grown vanadium oxide films and their electrical properties

A metal–insulator transition (MIT) occurring in vanadium oxide films prepared in different ways has been widely studied in many laboratories. It consists of a resistive change of various orders of magnitude taking place while traversing a temperature close to 67°C. In this work the properties of VOx films synthesized by thermal treatment of vanadium films which were vacuum-evaporated on an oxidized silicon substrate are shown. Such thermal oxidizing treatment was performed under atmospheric air at different temperatures during distinct times. Ellipsometry measurements allowed determining the thickness and optical constants of the layers after the oxidation process. From XRD, Raman and FTIR measurements, several phases with distinct oxygen content, V2O3, V3O5, VO2 and V2O5, were found in the films, depending on the oxidation time and temperature. Current–temperature measurements across the films were carried out by using sandwich-type metal–insulator–metal structures. Unlike former studies on similar structures, no MIT was observed from these measurements. On the other hand, from room-temperature current–voltage measurements a well defined memristive behavior was found as a regular result in most of our structures. This memristive behavior is ascribed to the complex defect structure in the films, including the variable amount of oxygen vacancies in the lattice, rather than to the above-mentioned metal–insulator transition in vanadium oxide.

Polarized neutron reflectivity from monolayers of self-assembled magnetic nanoparticles

We prepared monolayers of iron oxide nanoparticles via self-assembly on a bare silicon wafer and on a vanadium film sputter deposited onto a plane sapphire substrate. The magnetic configuration of nanoparticles in such a dense assembly was investigated by polarized neutron reflectivity. A theoretical model fit shows that the magnetic moments of nanoparticles form quasi domain-like configurations at remanence. This is attributed to the dipolar coupling amongst the nanoparticles.

Room temperature gas sensing properties of porous silicon/V2O5 nanorods composite

Here we prepare a composite of porous silicon (PS)/V2O5 nanorods synthesized by a heating process of pure vanadium film on PS. Vanadium films were deposited on PS by DC magnetron sputtering, and then long striped V2O5 nanorods were synthesized with subsequent annealing process in air. Numerous analytical techniques, such as field emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM), have been employed to characterize their feature. The as-prepared composite structure of PS/V2O5 nanorods shows favorable microstructure features for gas sensing application. The gas sensing properties of PS/V2O5 nanorods sensors were investigated at 25°C up to 250°C toward NO2 gas of 0.25–3ppm, and ethanol over concentration of 50–250ppm. The results indicated that the PS/V2O5 structure exhibits perfect reversibility, high response value and good selectivity to NO2 at room temperature (25°C). In addition, we propose a qualitative explanation for the low operating temperature (25°C) of the composite structure. These results are significant from the standpoint of applications requiring room temperature gas sensing.

Mechanical and optical properties of vanadium under shock picosecond loads

The evolution of compression pulses generated by a femtosecond laser in micron-thick vanadium film samples has been studied by the interferometric method with continuous recording of motion in the picosecond range. The relation of the velocity of a shock wave and the particle velocity behind its front indicates the elastic character of shock compression at pressures up to 46 GPa, for which the shear stress is 15.8 GPa. The measured spall strength reaches 21.8 GPa at a strain rate of ∼109 s−1. The picosecond dynamics of the reflection coefficient of vanadium, which indicates the excitation of its electronic subsystem under “cold” compression by an ultrashort shock wave, has been detected.

Prediction of first-order martensitic transitions in strained epitaxial films

Coherent epitaxial growth allows us to produce strained crystalline films with structures that are unstable in the bulk. Thereby, the overlayer lattice parameters in the interface plane, (a, b), determine the minimum-energy out-of-plane lattice parameter, . We show by means of density-functional total energy calculations that this dependence can be discontinuous and predict related first-order phase transitions in strained tetragonal films of the elements V, Nb, Ru, La, Os, and Ir. The abrupt change of can be exploited to switch properties specific to the overlayer material. This is demonstrated for the example of the superconducting critical temperature of a vanadium film which we predict to jump by 20% at a discontinuity of .

Optical modulation characteristics of VO2 thin film due to electric field induced phase transition in the FTO/VO2/FTO structure

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.

Microstructure and corrosion resistance of vanadium films deposited at different target-substrate distance by HPPMS

High power pulsed magnetron sputtering (HPPMS), a novel physical vapor deposition technology, was applied to prepare vanadium films on aluminum alloy substrate in this paper. The influence of target–substrate distance (D t–s) (ranging from 8 to 20 cm) on phase structure, surface morphology, deposition rate, and corrosion resistance of vanadium films was investigated. The results show that the vanadium films are textured with a preferential orientation in the (111) direction except for that fabricated at 20 cm. With D t–s increasing, the intensity of (111) diffraction peak of the films decreases and there exists a proper distance leading to the minimum surface roughness of 0.65 nm. The deposition rate decreases with D t–s increasing. All the V-coated aluminum samples possess better corrosion resistance than the control sample. The sample fabricated at D t–s of 12 cm demonstrates the best corrosion resistance with the corrosion potential increasing by 0.19 V and the corrosion current decreasing by an order of magnitude compared with that of the substrate. The samples gain further improvement in corrosion resistance after annealing, and if compared with that of annealed aluminum alloy, then the corrosion potential of the sample fabricated at 20 cm increases by 0.415 V and the corrosion current decreases by two orders of magnitude after annealed at 200 °C. If the annealing temperature further rises to 300 °C, then the corrosion resistance of samples increases less obviously than that of the control sample.

Preparation and modification of VO2 thin film on R-sapphire substrate by rapid thermal process

The VO2 thin film with high performance of metal–insulator transition (MIT) is prepared on R-sapphire substrate for the first time by magnetron sputtering with rapid thermal process (RTP). The electrical characteristic and THz transmittance of MIT in VO2 film are studied by four-point probe method and THz time domain spectrum (THz-TDS). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and search engine marketing (SEM) are employed to analyze the crystalline structure, valence state, surface morphology of the film. Results indicate that the properties of VO2 film which is oxidized from the metal vanadium film in oxygen atmosphere are improved with a follow-up RTP modification in nitrogen atmosphere. The crystallization and components of VO2 film are improved and the film becomes compact and uniform. A better phase transition performance is shown that the resistance changes nearly 3 orders of magnitude with a 2-°C hysteresis width and the THz transmittances are reduced by 64% and 60% in thermal and optical excitation respectively.

Conductive and transparent V-doped ZnO thin films grown by radio frequency magnetron sputtering

Transparent conductive films of vanadium (V)-doped zinc oxide (VZO) were deposited by radio frequency magnetron sputtering on quartz substrates using a ceramic ZnO target with V chips. The electric, optical and structural properties of VZO thin films (V concentration of 0–4at.%) were investigated at various substrate temperatures (TSUB) from 200 to 600°C. The resistivity sharply decreased by V doping, and the resistivity reached a minimum of about 5×10−4Ωcm and 1×10−3Ωcm for TSUB=200°C and 600°C, respectively. It was almost constant up to V concentration of 1.0–1.5% and gradually increased at higher V concentration. The optical transmittance (λ=500nm) of VZO films (V=0.9–1.1%) drastically degraded from about 80% to 40% for TSUB of below 225°C while that of ZnO films was over 83% for TSUB of over 200°C. From the dependence of growth rate and the expansion of c-axis lattice constant in the VZO film, the V configuration was considered to have a charge number of 3.

Study on Vanadium Films Deposited on Concave Object by Conventional Direct Current and High Power Pulsed Magnetron Sputtering

Abstract High power pulsed magnetron sputtering (HPPMS) is a novel tool to fabricate films with high quality. In this paper, vanadium films on concave object have been deposited by HPPMS and conventional direct current magnetron sputtering (DCMS) under the condition of the same average power. The plasma composition, crystalline structure, surface morphology and film thickness have been investigated. The results show that the plasma produced by HPPMS is composed of Ar(1+), V(0) and a certain amount of V(1+). In contrast, the plasma produced by DCMS is composed of Ar(1+), V(0) and a very small amount of V(1+). Both films fabricated by HPPMS and DCMS demonstrate the similar microstructures. The HPPMS vanadium films are dense and flat on the top surface while the surface of DCMS vanadium films presents very sharp peak with larger height. The DCMS vanadium films exhibit a porous columnar grain structure. In contrast, the HPPMS vanadium films have slightly columnar and denser structure. The thickness of the HPPMS vanadium films is less than that of DCMS vanadium films. Compared with the surface on the top, the thickness of the DCMS vanadium films is decreased to about 32% at the side wall and to about 55% at the bottom. However, the HPPMS vanadium films can reach a thickness of about 35% at the side wall and 69% at the bottom relative to that on the top surface. HPPMS shows a better uniformity in the film thickness on concave object.

Effect of RF power on electrochromic V–Ce mixed oxide thin films

Thin films of vanadium–cerium mixed oxides (molar ratio of V2O5 and CeO2=1:2) were deposited at room temperature by varying the RF power in RF magnetron sputtering in a pure argon atmosphere. The XRD patterns reveal that the prepared thin films are amorphous. With increase in RF power, the transmittance and the optical bandgap of the prepared thin films increase. The structural and optical properties were studied by analyzing XRD patterns and transmittance and absorption spectra. The growth of CeVO4 phase on the surface of the prepared thin films is enhanced by increasing the RF power during deposition and this is confirmed by analyzing the photoluminescence, laser Raman and FT-IR spectra. A three electrode electrochemical cell was designed with these mixed oxide thin films as the working electrode, platinum mesh as counter electrode and the saturated calomel as the reference electrode with 0.01M HCl solution diluted in distilled water as electrolyte. The variation in the electrochemical and the in situ optical properties of the prepared thin films over H+ ion intercalation and de-intercalation with respect to the RF power during deposition are elaborately discussed in this study.

Hydrogen induced changes in the optical properties of Pd capped V thin films

Abstract Optical properties of 50 nm thick single crystal vanadium films deposited on double side polished MgO substrates have been obtained from spectrophotometric measurements. The films were coated with a polycrystalline Pd layer (5 nm thick) to protect them from oxidation and to favor absorption of atomic hydrogen. Electrical resistance was recorded while hydrogen pressure was increased slowly up to 750 mbar keeping temperature constant. Simultaneously, under normal incidence of non-polarized radiation [350–950 nm], transmittance spectra of this Pd/V/MgO system were measured. These were numerically inverted to obtain the spectral behavior of the Pd, V, PdH y and VH x dielectric functions at 22 and 140 °C, and at 750 mbar. Hydrogen concentration in V film was first determined from a resisto-optical method. Finally, we demonstrate the possibility to determine the concentration in the Pd and the V layers independently, solely using the changes in the optical transmission.

Electric field assisted aerosol assisted chemical vapour deposition of nanostructured metal oxide thin films

Nanostructured thin films of tungsten, vanadium and titanium oxides were deposited on gas sensor substrates from the electric field assisted chemical vapour deposition reaction of tungsten hexaphenoxide, vanadyl acetylacetonate and titanium tetraisopropoxide respectively. The electric fields were generated by applying a potential difference between the inter-digitated electrodes of the gas sensor substrates during the deposition. The deposited films were characterised using scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The application of an electric field, encouraged the formation of interesting and unusual nanostructured morphologies, with a change in scale length and island packing. It was also noted that crystallographic orientation of the films could be controlled as a function of electric field type and strength. The gas sensor properties of the films were also examined; it was found that a two to three fold enhancement in the gas response could be observed from sensors with enhanced morphologies compared to control sensors grown without application of an electric field.

Optimization of Maximum VO<sub>2</sub> Content in Polymorphous Oxides of Vanadium

Optical properties of thin films of vanadium thermally oxidized at air were studied by ellipsometric method using wavelength of He-Ne laser. Multipart composition of these films was revealed and method of optimization of technological conditions based on dynamic of changing optical constants near 68°C was developed.

Using light transmission to watch hydrogen diffuse.

Because of its light weight and small size, hydrogen exhibits one of the fastest diffusion rates in solid materials, comparable to the diffusion rate of liquid water molecules at room temperature. The diffusion rate is determined by an intricate combination of quantum effects and dynamic interplay with the displacement of host atoms that is still only partially understood. Here we present direct observations of the spatial and temporal changes in the diffusion-induced concentration profiles in a vanadium single crystal and we show that the results represent the experimental counterpart of the full time and spatial solution of Fick's diffusion equation. We validate the approach by determining the diffusion rate of hydrogen in a single crystal vanadium (001) film, with net diffusion in the [110] direction.

Magnetic maps of ultrathin Vanadium (V) film on Ni/Cu(1 0 0) and Co/Cu(1 0 0) systems

The magnetic maps of ultrathin V film on Ni/Cu(1 0 0) and Co/Cu(1 0 0) systems were studied using in situ surface magneto-optical Kerr effect (SMOKE). Vanadium atom has large magnetic moment nearly—1.9 μ B where antiferromagnetic coupling occurs with ferromagnetic materials generally. It was found that V film epitaxially grows on ultrathin Co/Cu(1 0 0) and Ni/Cu(1 0 0) systems where magnetic anisotropy energy decreases in Co/Cu(1 0 0) system and increases in Ni/Cu(1 0 0) system. It was well known that Ni/Cu(1 0 0) shows thickness dependent magnetization reversal process, in which a sharp transition occurred from in plane to perpendicular magnetization at 7 ML Ni thickness. However, wedge shaped sample of Ni/Cu(1 0 0) system showed perpendicular magnetization at 6 ML Ni due to 1 ML V effect.

Recording of laser irradiation by reversible film media on the basis of vanadium dioxide

This paper is devoted to reversible film media on the basis of vanadium dioxide Al-VO2-D (dielectric) and VO2-D (dielectric), completing the change in optical and electrical properties, respectively, during the photoinduced semiconductor-to-metal phase transition (SMPT). The media were obtained by the air oxidation of vanadium films sputtered in vacuum. The optical and photometric parameters, as well as resolving power, diffraction efficiency, and energy sensitivity of the medium Al-VO2-D (depending on the laser radiation character) are presented, and possible fields of the medium application are outlined. Possible application fields include character indicators, irradiation visualizers, and transparencies for holographic recording. The thermal hysteresis of SMPT in VO2-D media (resistance jump and hysteresis loop width values) was determined depending on the production technology variation. The possibility of applying the VO2-D medium as a thermally sensitive layer of the thermal radiation receiver was demonstrated. The receiver time constant, sensitivity, and fundamental noises imposing limitations on the sensitivity were determined. Different designs of thermal radiation receivers are presented.

Corrosion protection properties of vanadium films formed on zinc surfaces

Vanadium films were prepared on zinc surfaces by using a solution containing vanadate. Corrosion protection properties of vanadium-treated (V-treated), chromium-treated (Cr-treated), and untreated zinc surfaces in contact with a 3.5 wt.% NaCl solution were studied using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and neutral salt spray (NSS) tests. According to these results, the V-treated layer significantly improved the corrosion resistance of zinc surfaces. In comparison with the Cr-treated layer, the V-treated layer exhibited a better corrosion resistance. The composition of the V-treated layer was studied using X-ray photoelectron spectroscopy (XPS). XPS measurements indicated that the vanadium layer formed on zinc surfaces and the vanadium-rich coating was a hydrated oxide with a composition of V2O5, VO2, and its hydrates such as V2O5·nH2O and VO(OH)2.

Combined light and electron scattering for exploring hydrogen in thin metallic films

We present a method, combining optical transmission with electrical resistance, to study the hydrogen uptake in thin transition metal films. The change in optical transmission is used to determine the hydrogen concentration, while the change in resistance serves as an indicator for the ordering of hydrogen. We identify phase boundaries and regions of high and low orders as well as changes in the ordering temperature. As a demonstration of this approach we compare the hydrogen uptake of 50 and 10 nm single-crystal vanadium films. The ordered phase is found to be extended to higher temperatures in the thinner sample.