Vanadium Metal Target Research Articles

Local structure and structural properties of vanadium oxide thin films prepared by radio-frequency reactive magnetron sputtering at various oxygen flow rate

In this work, vanadium oxide thin films were prepared by using radio frequency reactive magnetron sputtering with vanadium metal target. The effect of O2 flow rate was investigated in terms of vanadium oxide thin films by varying O2/Ar flow rate at 1/20, 2/20, 3/20, 4/20, 5/20, 6/20 (in sccm unit) with fixed RF power at 200 W and sputtering time at 80 minutes. The surface morphology and crystal structure of V2O5 thin films were investigated by scanning electron microscope (SEM), atomic force microscope (AFM), and X-Ray Diffractometer (XRD) respectively. The influence of the O2/Ar ratio on a local structure of vanadium oxide thin films was studied by the Synchrotron x-ray absorption spectroscopy (XAS) technique. The oxidation states of vanadium oxide thin films were measured at V K-edge by the x-ray absorption near-edge structure (XANES). The results of XANES spectra at the V K-edge showed that the prepared films under the O2/Ar flow rate at 1/20 sccm contained the vanadium with the oxidation states of V3+ and V5+ while the others contained only V5+. This is because the higher O2/Ar flow rate possibly causes an increase in energy flux at the substrate and the 1s→3d transition peak’s intensity, which could lead to a higher deposition rate. To achieve the desired V2O5 structure, the gas flow rate could be adjusted properly. The evolution of the local structure around V atoms was studied using the extended x-ray absorption fine structure (EXAFS) which supported the XANES results indicating that the structural environment around V atoms is in good agreement with the V2O5 orthorhombic structure. Finally, XANES and EXAFS fitting results confirmed that the O2 flow rate affected the local structure of vanadium oxide thin films.

Characteristics of Vanadium Oxide Thin Films Fabricated by Unbalanced Magnetron Sputtering for Smart Window Application.

Vanadium oxide (VOx) thin films were deposited by an unbalanced magnetron (UBM) sputtering system with a vanadium metal target and O₂ reaction gas, and thermally treated at various annealing temperatures. In this work, the structural, electrical, and optical properties of the fabricated VOx films with various annealing temperatures were experimentally investigated. The UBM sputter grown VOx thin films exhibited amorphous structure, and had a very weak peak of V₂O5 (002) owing to very thin films. However, the crystallite size of VOx films increased with increasing annealing temperature. The surface roughness of VOx films and average transmittance decreased with increasing annealing temperature. The resistivity of VOx films also decreased with increasing annealing temperature, while the electrical properties of films improved.

Synthesis of phase pure vanadium dioxide (VO2) thin film by reactive pulsed laser deposition

Thin films of phase pure VO2 (M1 phase) are deposited on thermally grown oxide (Si/SiO2) substrate by reactive pulsed laser deposition of vanadium metal target. The influence of deposition parameters is studied by varying oxygen partial pressure while keeping other parameters constant. A thin film obtained at 50 mTorr is found to be phase pure by XRD and Raman spectral studies. SEM and AFM studies show smooth morphology with a surface roughness of 3–5 nm. The quality of the thin film was further established by characterizing the 68 °C (TSMT) transition by 2–3 orders of jump in resistance and a 60% change in reflectivity with minimum hysteresis. This single step process of deposition would be a suitable method for fabricating devices for smart window and metamaterial applications.

Influence of Heat Treatment Conditions on the Properties of Vanadium Oxide Thin Films for Thermochromic Applications.

In present work, the effects of the heat treatment on the structural, optical, and thermochromic properties of vanadium oxide films were investigated. Vanadium dioxide (VO2) thin films were deposited on glass substrate by reactive pulsed DC magnetron sputtering from a vanadium metal target in mixture atmosphere of argon and oxygen gas. Various heat treatment conditions were applied in order to evaluate their influence on the crystal phases formed, surface morphology, and optical properties. The films were characterized by an X-ray diffraction (XRD) in order to investigate the crystal structure and identify the phase change as post-annealing temperature of 500-600 degrees C for 5 minutes. Surface conditions of the obtained VO2(M) films were analyzed by field emission scanning electron microscopy (FE-SEM) and the semiconductor-metal transition (SMT) characteristics of the VO2 films were evaluate by optical spectrophotometry in the UV-VIS-NIR, controlling temperature of the films.

Evaluation of the nanomechanical properties of vanadium and native oxide vanadium thin films prepared by RF magnetron sputtering

Polycrystalline vanadium thin films of 50, 75, and 100nm thickness were deposited by magnetron sputtering of a vanadium metal target of 2 inch diameter with 99.9% purity on native oxide covered Si substrates. One set of the fabricated samples were kept in moisture free environment and the other set was exposed to ambient air at room temperature for a long period of time that resulted in formation of native oxide prior to testing. The crystal structure and phase purity of the vanadium and the oxidized vanadium thin films were characterized by X-ray diffraction (XRD). The XRD results yield a preferential (110), and (200) orientation of the polycrystalline V films and (004) vanadium oxide (V3O7). The vanadium films thickness were verified using field emission scanning electron microscopy and the films surface morphologies were inspected using atomic force microscopy (AFM). AFM images reveal surface roughness was observed to increase with increasing film thickness and also subsequent to oxidation at room temperature. The nanomechanical properties were measured by nanoindentation to evaluate the modulus and hardness of the vanadium and the oxidized vanadium thin films. The elastic modulus of the vanadium and the oxidized vanadium films was estimated as 150GPa at 30% film thickness and the elastic modulus of the bulk vanadium target is estimated as 135GPa. The measured hardness of the vanadium films at 30% film thickness varies between 9 and 14GPa for the 100 and 50nm films, respectively, exhibiting size effects, where the hardness increases as the film thickness decreases. The hardness of the oxidized films depicted less variation and is reported as ∼10GPa at 30% film thickness for the three oxides. The scanning electron microscopy (SEM) imaging depicted a gradual progression of pile up as the film thickness increased from 75 to 100nm. It is noticed that as the film thickness increases the films experience softening effect due to grain coarsening and the hardness values depict the hardness of the Si substrate at deep indents.

DC Magnetron Sputtering Deposition of Room-Temperature Phase Transition Vanadium Oxide Film

Low valence vanadium oxide thin film was deposited on ordinary glass substrates by direct current (DC) magnetron sputtering from a vanadium metal target. And then it was annealed in an atmosphere of oxygen/argon mixture at the temperature of 450°C for 2hours to obtain VO2thin film possessing the ability of phase transition. The XRD patterns and resistance-temperature (R-T) curves of the film before and after the annealing were given. The results show that: the as-deposited film, whose main component is V2O3, presents no phase transition and its resistance changes from 1.26 kΩ~1.01kΩ while its temperature rising from room temperature to 80°C; the annealed film, whose main component is VO2, presents a phase transition when its temperature rising from room temperature to 80°C and its resistance changes from 10kΩ to 60Ω, more than two orders. And the phase transition temperature of the film deposited is only 30°C.

Fabrication of low phase transition temperature vanadium oxide films by direct current reactive magnetron sputtering and oxidation post-anneal method

Vanadium oxide thin films were deposited on ordinary glass substrates by direct current (DC) magnetron sputtering from a vanadium metal target and subsequent oxidation annealing. The deposition and annealing parameters were given in detail. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM). The phase transitions of films were observed by measuring their electrical and optical property variations at different temperature. The results indicated that the films fabricated had a semiconductor–metal phase transition temperature of about 30°C.

The Fabrication of High Resistance-Temperature-Coefficient Vanadium Oxide Film by Magnetron Sputtering Method

Direct current (DC) magnetron sputtering method was used to deposit vanadium oxide thin films on ordinary glass substrates from a vanadium metal target and a five factors four levels orthogonal experimental method was used to find the best combination of sputtering pressure, sputtering power, oxygen/argon flow ratio, substrate temperature and deposition time for fabricating high temperature coefficient of resistance (TCR) vanadium oxide film. The results indicate that a good combination of these parameters should be 1Pa, 160W, 1.5/25, 280°C and 60 minutes. And the film fabricated using this parameters combination is mainly composed of V2O5and has a resistance range of 80.3kΩ to 40kΩ while its temperature changed from 20°C to 80°C.

Fabrication of Vanadium Oxide Film with Low Phase Transition Temperature by Magnetron Sputtering and Reduction Post-Anneal Method

Vanadium oxide thin films were deposited on ordinary glass substrates by direct current (DC) magnetron sputtering from a vanadium metal target and subsequent reduction annealing. The deposition and annealing parameters were given in detail. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). The phase transition of the film was observed by measuring its resistance-temperature (R-T) characteristic curve. The results indicated that the film fabricated had a semiconductor-metal phase transition temperature of about 52°C, which is 16°C lower than the common phase transition temperature of vanadium dioxide film.

Enhanced electrical and noise properties of nanocomposite vanadium oxide thin films by reactive pulsed-dc magnetron sputtering

Thin films of VOx (1.3 ≤ x ≤ 2) were deposited by reactive pulsed-dc magnetron sputtering of a vanadium metal target while RF-biasing the substrate. Rutherford back scattering, glancing angle x-ray, and cross-sectional transmission electron microscopy measurements revealed the formation of nanocolumns with nanotwins within VOx samples. The resistivity of nanotwinned VOx films ranged from 4 mΩ·cm to 0.6 Ω·cm and corresponding temperature coefficient of resistance between −0.1% and −2.6% per K, respectively. The 1/f electrical noise was analyzed in these VOx samples using the Hooge-Vandamme relation. These VOx films are comparable or surpass commercial VOx films deposited by ion beam sputtering.

Process-structure-property correlations in pulsed dc reactive magnetron sputtered vanadium oxide thin films

Cathode hysteresis in the reactive pulsed dc sputtering of a vanadium metal target was investigated to correlate the structural and electrical properties of the resultant vanadium oxide thin films within the framework of Berg’s model [Berg et al., J. Vac. Sci. Technol. A 5, 202 (1987)]. The process hysteresis during reactive pulsed dc sputtering of a vanadium metal target was monitored by measuring the cathode (target) current under different total gas flow rates and oxygen-to-argon ratios for a power density of ∼6.6.W/cm2. Approximately 20%–25% hysteretic change in the cathode current was noticed between the metallic and oxidized states of the V-metal target. The extent of the hysteresis varied with changes in the mass flow of oxygen as predicted by Berg’s model. The corresponding microstructure of the films changed from columnar to equiaxed grain structure with increased oxygen flow rates. Micro-Raman spectroscopy indicates subtle changes in the film structure as a function of processing conditions. The resistivity, temperature coefficient of resistance, and charge transport mechanism, obeying the Meyer–Neldel relation [Meyer and Neldel, Z. Tech. Phys. (Leipzig) 12, 588 (1937)], were correlated with the cathode current hysteric behavior.

Pulsed DC reactive magnetron sputtering of vanadium dioxide thermochromic thin films

<title/>Vanadium oxides are an important class of materials with a large diversity of physical and chemical properties which derive from a range of single or mixed valences and a large variety of structures. They are already being used in many technological applications such as electrical and optical switching devices, light detectors, temperature sensors, etc. There has been a great interest in a particular phase, VO2(M), due to its thermochromic behaviour near room temperature which allows the development of smart windows with active control of the solar spectrum, for energy efficiency purposes. However, stoichiometric VO2 is difficult to deposit because of a narrow stability range due to the complex vanadium-oxygen reactive system. In this work, vanadium oxide thin films were synthesised on glass substrates by reactive pulsed direct current magnetron sputtering from a vanadium metal target in an O2/Ar atmosphere. Different processing conditions have been chosen in order to evaluate their influence on the crystal phases formed, surface morphologies and thicknesses and optical performance. The films were characterised by X-ray diffractometry in order to examine the crystal structure and identify the phases present in different films. The obtained VO2(M) films were thereafter analysed in terms of surface morphology by scanning electron microscopy and the characteristic reversible semiconductor-metal transition of the VO2 films was evaluate by optical spectrophotometry in the ultraviolet-visible-near infrared.

Modeling for calculation of vanadium oxide film composition in reactive-sputtering process

A modified model describing the changing ratio of vanadium to oxide on the target and substrate as a function of oxygen flow is described. Actually, this ratio is extremely sensitive to the deposition conditions during the vanadium oxide (VOx) reactive magnetron-sputtering process. The method in this article is an extension of a previously presented Berg’s model, where only a single stoichiometry compound layer was taken into consideration. This work deals with reactive magnetron sputtering of vanadium oxide films with different oxygen contents from vanadium metal target. The presence of vanadium mixed oxides at both target and substrate surface produced during reactive-sputtering process are included. It shows that the model can be used for the optimization of film composition with respect to oxygen flow in a stable hysteresis-free reactive-sputtering process. A systematic experimental study of deposition rate of VOx with respect to target ion current was also made. Compared to experimental results, it was verified that the theoretical calculation from modeling is in good agreement with the experimental counterpart.

Vanadium oxide thin films for bolometric applications deposited by reactive pulsed dc sputtering

Vanadium oxide (VOx) thin films were deposited by reactive pulse dc magnetron sputtering process using a pure vanadium metal target. The structural, microstructure, and electrical properties were correlated as a function of processing parameters such as substrate temperature, Ar:O partial pressures ratios, and pulsed dc power to fabricate these films. The VOx films deposited at various substrate temperatures between 30 and 300°C using a range of oxygen to argon partial pressure ratios exhibited huge variation in their microstructure even though most of them are amorphous to x-ray diffraction technique. In addition, the electrical properties such as temperature coefficient of resistance (TCR), resistivity, and noise levels were influenced by film microstructure. The TCRs of the VOx films were in the range of −1.1%to−2.4%K−1 having resistivity values of 0.1–100Ωcm. In particular, films grown at lower substrate temperatures with higher oxygen partial pressures have shown finer columnar grain structure and exhibited larger TCR and resistivity.

Influence of film thickness on texture and electrical and optical properties of room temperature deposited nanocrystalline V2O5 thin films

Nanocrystalline V2O5 thin films have been grown at low temperature on glass substrates by dc magnetron sputtering using a vanadium metal target. Film thickness was found to have a great impact on the orientation, shape, and size of the crystallites of these films. X-ray diffraction (XRD) patterns of the films with a thickness of 110nm show a strong c-axis orientated crystal structure with a preferred (001) orientation, while those with a thickness of 315nm show mixed orientations (a-axis+c-axis). With further increase in film thickness, an a-axis orientation with predominant (200) reflection was observed in the XRD pattern. The shape of the crystallite changes from a rodlike to a bricklike structure with change in crystallographic orientation from (001) to (200). Atomic force microscopy results were also in agreement with the field emission scanning electron microscopy and XRD results. A direct correlation has been established between the semiconductor to metal transformation of V2O5 films and their crystallite size and orientation. The optical measurement also revealed a systematic band gap variation (from 2.50to2.20eV) with variation in film thickness.

X-ray diffraction studies of the growth of vanadium dioxide nanoparticles

We have characterized for the first time in situ the growth of vanadium dioxide nanoparticulate films prepared by pulsed-laser deposition, using a five-circle x-ray diffractometer, in order to provide structural information as the films are grown. A vanadium metal target was ablated in the presence of a pulsed N2O reactive gas source, and films were grown on Si(001) and Al2O3(0001) substrates. Optical measurements confirmed that the films deposited in this way exhibit the well-known VO2 metal–insulator transition at approximately 70 °C. The VO2 films grown at room temperature on silicon substrates are amorphous and extremely smooth. These become considerably rougher upon thermal annealing, as the VO2 phase crystallizes out in the form of hemispherical islands. These films also contain traces of a V2O5 nanoparticle phase in the first few monolayers, although the degree of VO2 crystallinity in the nanoparticles is quite high. In contrast, the VO2 nanoparticles grown on the sapphire substrates are in the form of preferentially oriented rodlike islands, with a maximum rod width of about 100 nm. This in-plane texture is in keeping with the relatively good lattice match between film and substrate, indicating good potential for the growth of VO2 epitaxial films and single-crystal nanoparticles on such substrates.

Optical properties of textured V2O5/Si thin films deposited by reactive magnetron sputtering

Thin films of V2O5 were deposited on Si substrates by reactive DC magnetron sputtering of vanadium metal target in Ar/O2 low-pressure gas mixture. The phase composition of the films was examined with reflection high-energy electron diffraction (RHEED) at 65keV. The presence of V2O5 textured polycrystal with preferencial orientation of [100] was found for the range of 32.7–40.8% O2/(O2+Ar) ratio. The films are polycrystal without pronounced ordering for the range of 40.8–48.9% O2/(O2+Ar) ratio. Optical characterization of the films was produced with laser ellipsometry (λ=0.6328μm) and reflection spectra measurements. For V2O5 film deposited at 32.7 O2/(O2+Ar) ratio a uniform refractive index profile was found with n=2.67, optical absorption coefficient k=0.0011 and thickness d=165.0nm. These optical parameters are very reproducible and weakly dependent on gas mixture composition within the range pointed above. Optical anisotropy of V2O5 film has not been detected. The thickness of the transition layer at the V2O5/Si interface has been estimated to be ∼20nm. The wear resistance of the oxide films was tested with sand-bombardment method and good mechanical stability of the samples has been confirmed.

Fabrication of VO2 films with low transition temperature for optical switching applications

Vanadium dioxide films for optical switching applications have been prepared on Si3N4-film-coated silica substrates by ion beam sputtering from a vanadium metal target in an atmosphere of argon and oxygen and subsequent heat treatment. The as-fabricated VO2 films exhibit a nanocrystalline structure and undergo abrupt changes in electrical and optical properties with an abnormal low transition temperature of 34°C. Using micromachining technology, applications of the films as thermo-optical switches are also demonstrated. The measured average optical isolation for the switches is 15dB with a −2dB insertion loss at a wavelength of 1.55μm.

Electrochemical and structural properties of V 2O 5 thin films prepared by DC sputtering

Vanadium pentoxide thin films have been prepared by reactive DC magnetron sputtering from a vanadium metal target without annealing posttreatment. XRD, Raman and electrochemical experiments on 800 nm thin films show a high crystallinity of the deposits. Chronopotentiometric measurements performed in the two voltage range 3.8–2.8 and 3.8–2.15 V have demonstrated the promoting effect of the h 0 0 preferred orientation of V 2O 5 films in terms of polarization, kinetics and rate capability. The same reproducible deposition method is successfully applied to get films thicker than 1 μm in order to optimize the specific capacity. Effective high specific capacities can be then obtained with films 2.4 μm thick tested at high constant current density (100 μA cm −2): a stable capacity of 75 μAh cm −2 is available over 100 cycles in the 3.8–2.8 V potential range and 130 μAh cm −2 are still recovered in the range 3.8–2.15 V. These results indicate a promising cycling behaviour can be expected with thick films exhibiting a preferred orientation corresponding to V 2O 5 planes perpendicular to the substrate.

Optical and electrical properties of sputtered vanadium oxide films

Thin films of vanadium oxide with thickness of 0.1 to 0.2 μm were deposited on Si3N4/Si substrate by reactive rf magnetron sputtering. The oxide films were sputtered using a vanadium metal target in various ratios of Ar and O2 gases. The O2 content in the mixed atmosphere has a significant influence on the metal-insulator transition characteristics of the oxide films. The oxide film deposited in an Ar/O2 ratio of 98/2 exhibited high optical transmission of 70% to 80% in wavelength from 2 to 10 μm in insulating state while very low transmission of less than 5% in metallic state. Films prepared with higher O2 concentration showed no metal-insulator transition. In low O2 concentration, films showed characteristics of having both a broader transition region spanning over 30 °C and a lowered transition temperature which are similar to those of doped vanadium oxide films.