W-doped Films Research Articles

W doping effect on the dielectric properties of amorphous Ga2O3 films grown on Si substrate for low-k applications

Tungsten doped gallium oxide (Ga2O3:W) thin films were prepared by vacuum evaporation method on glass and silicon substrates. The W doping level was measured by the energy dispersive X-ray fluorescence (EDXRF) analysis. The molar ratio of W to Ga was 9.6%, 13.4%, 18.2%, 22.7%, and 30.4%. The crystalline state of the prepared oxide films was determined by the X-ray diffraction method. The oxide films deposited on silicon substrate have amorphous structure while those oxide films deposited on glass substrate show crystalline structure of β-Ga2O3, which confirms that the WO3 oxide was totally doped in the lattice of Ga2O3 forming solid solution (SS). The electrical properties of the prepared amorphous W-doped films were studied for samples made in form of MOS: Au/Ga2O3:W/Si configuration. It was observed that W doping of certain level reduces the effective dielectric constant of Ga2O3:W film to less than that of SiO2, i.e. the doping with WO3 turns the high-k gallium oxide dielectric into low-k insulator. The dielectric relaxation of the doped films was studied through the complex dielectric modulus M*, from which the high-frequency dielectric constant ε∞′ and the most probable relaxation time (τ) as a function of W-doping level was determined. The temperature dependent of the dc-current passes through Au/Ga2O3:W/Si arrangement predicts the red shift of the bandgap due to W doping.

Erosion of tungsten-doped amorphous carbon films in oxygen plasma

Tungsten-doped amorphous carbon films with 0–9 at.% W concentration were produced by magnetron sputtering and eroded in oxygen plasmas applying different bias voltages and substrate temperatures. The partial C and W erosion rates were determined from the C and W areal density changes measured by Rutherford backscattering spectrometry (RBS). The initial C removal rate increases with increasing ion energy and temperature and decreases with increasing W concentration. For W-doped films the erosion rate decreases with increasing plasma exposure duration. At low bias voltages the erosion process stops after W accumulation at the surface, which protects the carbon underneath from further erosion. RBS and X-ray photoelectron spectroscopy suggest that the W-rich layer at the surface is carbon free and consists of porous WO 3. Biasing to 200 V leads to removal of W by physical sputtering and, therefore, inhibits the formation of the protecting W oxide layer and the C erosion proceeds.

Highly Improved Quantum Efficiencies for Thin Film BiVO4 Photoanodes

BiVO4 has received much recent interest as a promising photocatalyst for oxygen evolution from water, but little is known about the factors that limit its performance as a photoanode. In this article, we report on highly efficient and reproducible BiVO4 photoanodes prepared by a new spray pyrolysis recipe. For undoped films deposited on a transparent conducting substrate (F-doped SnO2, FTO), electron transport and charge collection at the back-contact were found to limit the photoresponse. Electron transport could be greatly enhanced by donor-doping with 1% W, while the charge collection problem has been solved by introducing a thin (∼10 nm) interfacial layer of SnO2 in between the FTO and the BiVO4. This layer presumably acts as a hole mirror that prevents recombination via FTO-related defect states at the FTO/BiVO4 interface. By addressing these two issues, the external quantum efficiency (IPCE) of spray-deposited BiVO4 films was improved by a factor of ∼7, leading to an unprecedented IPCE of 46% (at 450 nm) at 1.63 VRHE for 1% W-doped BiVO4 films deposited on FTO/SnO2.

Fabrication and study of laser-damage-resistant transparent conductive W-doped In2O3 films

We report that In1.97W0.03O3 (IWO) transparent conductive oxide films grown on quartz glass substrates by laser ablation show good polycrystalline properties, with a preferential orientation of (2 2 2), and excellent optical transmittance in the visible range, with a direct allowed band gap of 4.2 eV. A laser-induced damage study is carried out at 1064 nm with a 15 ns laser pulse in one-on-one mode. It is revealed that IWO films not only possess good electronic conductivity with a low resistivity of 7.85 × 10−4 Ω cm, but also have a laser-induced damage threshold of more than 2.2 J cm−2 which is 2.4 times more than that of a In1.8Sn0.2O3 film deposited by laser ablation with approximately the same resistivity. Weak laser absorption due to low carrier density and low free-electron excitation in the near-infrared region are the primary reasons for the high laser damage resistance of the IWO films.

Investigation of metal distribution and carbide crystallite formation in metal-doped carbon films (a-C:Me, Me = Ti, V, Zr, W) with low metal content

Metal-doped amorphous carbon films (a-C:Me) were deposited at room temperature by magnetron sputtering using a metal (Me = Ti, V, Zr, W) and a graphite target. The metal distribution and the temperature-induced carbide crystallite formation were analyzed by X-ray diffraction (XRD), electron microscopy (TEM, STEM) and X-ray absorption spectroscopy (EXAFS, XANES), focusing on low metal concentrations between 6.5 and 9.5%. In as-deposited samples, the metal atoms are atomically distributed in the carbon matrix without significant formation of carbide particles. With annealing to 900K the local atomic environment around the metal atoms becomes similar to the carbide. The carbide crystallites grow with annealing up to 1300K, their size is dependent on the metal type: V > Ti > Zr≈W. W2C and WC1−x crystallites were identified for W-doped films, whereas the monocarbides are formed for the other metals. It is demonstrated, that EXAFS and high resolution electron microscopy are required to get a correct picture of the structure of the analyzed a-C:W films.

W-Doped DLC Films by IBD and MS

W-doped DLC films were synthesized from ethyne and tungsten by ion beam deposition and magnetron sputtering, and the influence of W target current on the structures and the properties of W-doped DLC films were studied. There exist some defects smaller than 3micron in W-doped DLC films and the influence of W target current on the defects is unobvious. The W content in the films is tardily increased with W target current below 3.5A, and then acutely rises with W target current. When target current is below 3.5A, the ratio of sp3-C to sp2-C is first decreased and then increased with the rise of target current, and the ratio of WC-C to sp2-C is close to 0; but when the target is above 3.5A, the ratio of sp3-C to sp2-C is decreased and the ratio of WC-C to sp2-C is augmented with further increasing target current. The hardness and the modulus is first decreased with target current and the minimum value is reached for the W-doped DLC films deposited with a target current of 2.6A. The W-doped DLC films deposited with a target current of 2.6A exhibit the best film-substrate adhesion. The W-doped DLC films deposited with a low target current exhibit a friction coefficient while the wear resistance of the W-doped DLC films deposited with a medium target current of 2.6A is best.

Tribological Behaviors of W-Doped DLC Films

W-doped DLC films were synthesized from CH4 and W by ion beam deposition and magnetron sputtering, and the influence of W target current on the surface morphology and the mechanical properties of W-doped DLC films deposited were studied. The W-doped DLC films in the study have a smooth dense surface with several particles of about 2micron. The hardness, the modulus, and the film-substrate adhesion of the films are increased with the rise of W target current and the critical load of the scratch test for all the W-doped DLC films is above 70N. The friction coefficient of W-doped DLC films is increased with the increase of W target current while the lowest wear rate is obtained when W target current is 1A.

Electroless deposition of W-doped Ag films onto p-Si(100) from diluted HF solution

Tungsten-doped silver films were prepared by immersing hydrogen-terminated silicon wafers into the solution of 2.5 mmol/L [Ag 2WO 4]+0.1 mol/L HF at 50 °C. Their growth and composition were characterized with atomic force microscopy and X-ray photoelectron spectroscopy, respectively. The effect of tungstate ions on the deposition of silver was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) by comparing W-doped Ag film with Ag film. It is found that the molar fraction of tungsten in the deposits is about 2.3% and the O to W molar ratio was about 4.0 and W-doped Ag films have good anti-corrosion in air at 350 °C. The doping of tungsten cannot change the deposition of silver.

Raman study of W-doped diamond-like carbon films

Amorphous diamond-like carbon (DLC) films prepared by the plasma chemical method on glass substrates SiO2-Al2O3-TiO2 have been studied by Raman spectroscopy. W-doped DLC films show a considerable increase in the G-band frequency up to 1592 cm−1 and an enhanced surface hardness. The DLC films doped with W and atoms of semiconductors exhibit high transparency and a higher G-band shift to the high-frequency range (up to 1611 cm−1).

Characteristics of W-Doped (Pb[sub 0.8]Sr[sub 0.2])TiO[sub 3] Thin Films

Undoped, 0.5%, and 1% W-doped (Pb 0.8 Sr 0.2 )TiO 3 (PST) thin films were deposited on Pt/Ti/SiO 2 /Si substrates by radio frequency magnetron sputtering. X-ray diffraction shows that the cla ratio of PST films decreases with increasing W content. The remnant polarization and coercive field decrease with increasing W content. The W doping exhibits remarkable improvement of fatigue endurance. The degradation of polarization after 10 10 cycles is only 25% for W-doped PST films, and that of the undoped film is 75%. The dielectric properties as analyzed by the Rayleigh law reveal that pinning of the domain wall motion is decreased by W doping.

Characteristics of W- and Ti-Doped VO[sub 2] Thin Films Prepared by Sol-Gel Method

W- and Ti-doped thin films were deposited onto sapphire by the sol-gel method. Both films were grown with (020)-preferred direction. Doping of W had a great effect on the transition behaviors. A 1.2 atom % W-doped film showed a largely reduced resistance in the insulator state and decreased the transition temperature to . However, Ti-doped film had a little change of the transition temperature, and it was , even for the 20 atom % Ti doping. The resistance in the metal state was very large, which means a markedly small change of the resistance at the transition temperature. Further study is required for understanding the effects of doping film with metal ions.

A Study on Metal-Doped Diamond-Like Carbon Film Synthesized by Ion Source and Sputtering Technique

DLC (diamond-like carbon) has many excellent properties similar to diamond, which make it an attractive film in industrial applications. However, the large residual stress of DLC films limits the maximum film thickness because it reduces the adhesion of the DLC film to substrate causing delamination and cracking of the film. Metal-doped DLC (Me-DLC) has been studied extensively to avoid these disadvantages. Both large area Ti-doped and W-doped DLC films have been synthesized by a hybrid of ion source technique and unbalanced magnetron sputtering. The microstructure and mechanical properties have been analyzed by SEM, Raman, and XPS. A wear tester was used to evaluate the tribiological behavior of Me-DLC. Experimental results demonstrated that a smooth large area DLC film with good mechanical properties could be prepared by this hybrid technology, thick Me-DLC could be deposited with good adhesion and excellent wear resistance.

Characterization of magnetron co-sputtered W-doped C-based films

In this paper, W-doped C-based coatings were deposited on steel and silicon substrates by RF magnetron sputtering, using W and C targets, varying the cathode power applied to the W target and the substrate bias. The chemical composition was varied by placing the substrates in a row facing the C and W targets. W content in the films increased from 1 to 2 at.% over the C target to ∼ 73 at.% over the W target. The coatings with W content lower than ∼ 12 at.% and ∼ 23 at.%, for biased and unbiased conditions, respectively, showed X-ray amorphous structures, although carbide nanocrystals must exist as shown by the detection of the WC 1− x phase in films with higher W content. C-rich films were very dense and developed a columnar morphology with increasing W content. An improvement in the hardness (from 10 GPa, up to 25 GPa) of the films was achieved either when negative substrate bias was used in the deposition, or when the WC 1− x phase was detected by X-ray diffraction. The adhesion of the coatings is very low with spontaneous spallation of those deposited with negative substrate bias higher than 45 V. Varieties in cathode power (90 W or 120 W) applied to the W target showed no observable influence on the characteristics of the films.

Polycrystalline films of tungsten-doped indium oxide prepared by d.c. magnetron sputtering

Electrical and optical properties of polycrystalline films of W-doped indium oxide (IWO) were investigated. These films were deposited on glass substrate at 300 °C by d.c. magnetron sputtering using ceramic targets. The W-doping in the sputter-deposited indium oxide film effectively increased the carrier density and the mobility and decreased the resistivity. A minimum resistivity of 1.8 × 10 − 4 Ω cm was obtained at 3.3 at.% W-doping using the In 2O 3 ceramic targets containing 7.0 wt.% WO 3. The 2.2 at.% W-doped films obtained from the targets containing 5.0 wt.% WO 3, showed the high Hall mobility of 73 cm 2 V − 1 s − 1 and relatively low carrier density of 2.9 × 10 20 cm − 3 . Such properties resulted in novel characteristics of both low resistivity (3.0 × 10 − 4 Ω cm) and high transmittance in the near-infrared region.

Microwave dielectric properties of W-doped Ba 0.6Sr 0.4TiO 3 thin films grown on (001) MgO by pulsed laser deposition with a variable oxygen deposition pressure

The microwave dielectric properties of Ba 0.6Sr 0.4TiO 3 1 mol% W-doped thin films deposited using pulsed laser deposition, are improved by a novel oxygen deposition profile. The thin films were deposited onto (001) MgO substrates at a temperature of 720 °C. A comparison is made between three different oxygen ambient growth conditions. These include growth at a single oxygen pressure (6.7 Pa) and growth at two oxygen pressures, one low (6.7 Pa) and one high (46.7 Pa). Films were deposited in a sequence that includes both a low to high and a high to low transition in the oxygen deposition pressure. Following deposition, all films were post-annealed in 1 atm of oxygen at 1000 °C for 6 h. The dielectric Q (defined as 1 / tan δ) and the dielectric constant, ε r, were measured at room temperature, at 2 GHz, using gap capacitors fabricated on top of the dielectric films. The percent dielectric tuning (defined as ( ε r(0 V) − ε r(40 V)) / ε r(0 V) × 100) and figure of merit (FOM) (defined as percent dielectric tuning × Q(0 V)) were calculated. The film deposited using the two-stage growth conditions, 6.7 / 46.7 Pa oxygen, showed a maximum Q(0 V) value with high percent dielectric tuning and gave rise to a microwave FOM twice as large as the single stage growth condition. The improved dielectric properties are due to initial formation of a film with reduced interfacial strain, due to the formation of defects at the film/ substrate interface resulting in a high Q(0 V) value, followed by the reduction of oxygen vacancies which increases the dielectric constant and tuning.

Electrical properties of W-doped (Ba 0.5Sr 0.5)TiO 3 thin films

Ba 0.5Sr 0.5TiO 3 (BST) thin films doped with W were deposited on LaNiO 3 (LNO) electrode by RF-magnetron sputtering. The microstructure and electrical properties of BST thin films were studied as a function of W content. W-doped BST films show smoother surface and smaller grain size in comparison with the undoped BST film. With increasing W content, the dielectric constant, tunability, dissipation factor, and leakage current decrease while the figure of merit (FOM) and breakdown strength increase. Doping with the optimal content of 1% W, the BST film has a dielectric constant of 239, a tunability of 30%, a dissipation factor of 0.0066, a FOM value of 45.2, a leakage current density of 16 nA/cm 2, and a breakdown strength of 500 kV/cm.

Photocatalysis and hydrophilicity of doped TiO 2 thin films

TiO 2 thin films were prepared using the dip-coating method with a polymeric sol including additives such as Al, W, and Al+W to examine two major properties: photocatalysis and hydrophilicity. W-doped films showed the best photocatalytic efficiency, while Al-doped film was poorer than undoped samples. However, good hydrophilicity in terms of saturation contact angle and surface conversion rate was found in Al- and (Al+W)-mixed-doped films. It was found that deep electron-hole traps and high surface acidity of W-doped TiO 2 thin film were the major factors in high photocatalytic efficiency. In addition, low surface acidities of Al- and (Al+W)-doped films provided better hydrophilicity than W-doped ones. However, the amount of [Ti 3+] point defects on the surface was another major factor, probably the most important, in getting the best hydrophilicity. Conclusively, it seemed that many parts of the photocatalysis mechanism depend more on bulk-related properties than do those of hydrophilicity, which can be defined as an interfacial (surface) or near-surface-restricted process.

Plasma-facing materials mixing and mixed material properties

Tungsten-doped amorphous carbon films with 0–9.5 at.% W concentration were produced by magnetron sputtering and exposed to deuterium plasmas applying different ion energies and fluences. The partial C and W erosion rates were determined from the C and W areal density changes, respectively, measured by Rutherford backscattering spectrometry. For W-doped films the erosion rate decreases with increasing W concentration and incident fluence. During deuterium plasma exposure carbon is preferentially eroded while tungsten atoms accumulate at the surface leading to the formation of a W-rich layer, which decreases the removal efficiency and leads to a continuous decrease of the erosion rate. At 30 eV/D incident energy a relatively compact W-rich layer is formed on films with higher (⩾5%) W concentration which protects the carbon underneath from further erosion. For films with lower (⩽2.5%) W concentration the erosion rate decreases, but the erosion process does not stop because the W-rich layer has a high porosity. Reactive neutral species can penetrate through this porous layer and react with carbon atoms below it. At 100 eV/D incident energy the erosion rate is significantly higher compared with 30 eV/D. In addition, slight tungsten sputtering is observed due to the presence of a small fraction of D+ plasma ions which impinge with 300 eV/D.

Microstructure and NO<sub>2</sub> Sensing Properties of Fe<sub>2</sub>O<sub>3</sub> Thin Films

W-doped Fe2O3 films have been fabricated on polycrystalline alumina substrates by the RF magnetron sputtering method, and effects of annealing temperature on the NO2 sensing properties have been examined. The crystal structure of the obtained film changed from Fe3O4 to α-Fe2O3 after annealing at temperatures of 500 to 500°C in air. An increase in the annealing temperature increased the particle size, resulting in a decrease in the NO2-gas sensitivity. These results suggest that the NO2 sensitivity of W-doped Fe2O3 film depends on the particle size.