Tungsten Carbide Thin Films Research Articles

Deposition of tungsten in methane atmosphere using a low energy plasma focus device

Deposition of tungsten in methane atmosphere was performed using a low energy plasma focus device. The resulting compounds were synthesized and investigated during the deposition process. Carbon-rich contamination was identified as an organic viscous liquid crystal defect. Tungsten carbide (W2C) and dark-black oxygen-deficient tungsten trioxide (WO3-x) thin films were synthesized by plasma focus device using different number of focused shots. The synthesis of each thin film, which was dependent upon operation of plasma focus device was verified and discussed. Tungsten carbide W2C was synthesized during the deposition process while the dark-black WO3-x was created after the deposition process in atmosphere. All compounds were investigated by spectroscopy, crystalline, and microscopy methods. Nano indentation test disclosed higher value of hardness for the film containing tungsten carbide compound (10.01 GPa) compared to both pure tungsten (5.72 GPa) and the dark-black WO3-x thin film (6.83 GPa). The verified band gap energy of dark-black WO3-x was around 1.475 eV.

Analysis of the Properties of Tungsten Carbide Thin Films According to the Sputtering Radio Frequency Power

In this study, we investigated characteristics of tungsten carbide thin film according to carbon and tungsten ratio. Tungsten carbide thin film was co-sputtered on silicon substrate and glass substrates using an RF magnetron sputtering system. To analyze the characteristics according to the composition ratio of the tungsten carbide thin film, the RF powers of carbon/tungsten target were divided into 100 W/100 W, 125 W/75 W, 150 W/50 W, and 175 W/25 W, respectively. Hall measurement and 4 points probes were used to measure electrical properties of the tungsten carbide thin films. Raman and field emission scanning electron microscope (FE-SEM) analysis were performed.

Fabrication and mechanical properties of tungsten carbide thin films via mist chemical vapor deposition

Tungsten carbide thin films are used as wear-resistant coatings. For such applications, it is industrially advantageous to form high-quality thin films on substrates with large areas or complex shapes under atmospheric pressure. Herein, we investigated the feasibility of forming tungsten carbide thin films using a mist chemical vapor deposition method. WC1-x thin films with smooth surfaces were obtained at growth temperatures of 650 °C or above, and the elemental composition ratios of C/W and N/W gradually approached 1 and 0, respectively, with increasing growth temperature. The hardness and Young’s modulus of the film obtained at 750 °C were 25 GPa and 409 GPa, respectively. The grown WC1-x films have potential for use as hard coatings.

Deposition of thin tungsten carbide films by dual ion beam sputtering deposition

Hard materials coating fabricated by physical vapor deposition techniques methods are wildly used because of their excellent mechanical strength, stability and chemical resistivity. In this article, compact and high Young's modulus tungsten carbide films with ∼100 nm thickness were prepared on Si (100) substrates by dual ion beam sputtering deposition method, and elucidates the influence of deposition temperature and assistant ion source on the adhesion strength and Young's modulus of tungsten carbide thin films. Morphological analysis, composition, and structure of tungsten carbide films were investigated by Atomic force microscope, X-ray photoelectron spectrometry, Scanning electron microscope. The X-ray diffraction analysis shows that the thin films comprise of hexagonal structure W2C. The adhesion strength is improved due to ion beam source bombardment and elevated deposition temperature. The Young's modulus of the film is codetermined by the density, microstructure and crystal structure. The influence of density, microstructure and crystal structure on Young's modulus was discussed in detail. The Young's modulus is improved due to the more compact structure caused by appropriate assistant source bombardment and elevated deposition temperature, and gets degradative due to the disorganized, coarse and granular structure caused by overlarge assistant source bombardment.

(Invited) Atomic Layer Deposition of Tungsten-Rich Tungsten Carbide Films Using WCl6 and AlH2(tBuNCH2CH2NMe2) as Precursors

The thermal atomic layer deposition (ALD) of tungsten-rich tungsten carbide thin films is described using WCl6 and the aluminum dihydride co-reactant AlH2(tBuNCH2CH2NMe2). Smooth and stable films were grown at temperatures >200 °C. An ALD window was observed between 275-350 °C with a growth rate of 1.6 Å/cycle, according to SEM and XRR. Self-limiting growth was demonstrated at 300 °C for both precursors. XPS analysis showed that high purity tungsten-rich tungsten carbide (WxC, x = 2.8-3.7) films were deposited at 300 °C, with low levels of nitrogen (< 4 at.%), oxygen (< 4 at.%), chlorine (< 3 at.%), and aluminum (< 1 at.%). The as-deposited films were nanocrystalline and converted to the non-stoichiometric β-WC1-x phase above 600 °C. Film densities of the as-deposited films according to XRR were 50-60% of bulk values, which may explain the relatively high film resistivities (1140 mΩ·cm at 300 °C) despite the high film purity.

Tungsten carbide electrocatalysts prepared from metallic tungsten nanoparticles for efficient hydrogen evolution

Pyrolysis of hexacarbonyl tungsten, W(CO)6, in 1-octadecene has been used to prepare colloidal tungsten, W, nanoparticles (NPs). The obtained W NPs has been spin-coated on graphite (C) electrodes. Heat treatment of the W/C electrodes at elevated temperatures (≥900 °C) allows the preparation of metallic W and tungsten carbide (W2C@WC) thin films. The obtained W2C@WC electrodes were used for hydrogen evolution studies (HER) in 0.5 M H2SO4. Cyclic voltammetry tests for 1000 cycles showed that W2C@WC exhibit long term stability without significant drop in current density. The overpotential defined at 10 mA/cm2 is 310 mV vs. RHE giving an excellent catalytic activity for HER. Materials characterization has been achieved using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). Here, EIS studies were used to access the charge-transfer resistance of tungsten carbide electrodes.

Deposition and Characterization of Reactive Magnetron Sputtered Tungsten Carbide Films

Tungsten carbide thin films were deposited on silicon (100) substrates by DC reactive magnetron sputtering using CH4 as a carbon source. The microstructure, compressive stress, hardness and tribological behaviors showed great dependences on the rates of CH4 flow (FCH4). Increasing the FCH4 from 2 to 5 sccm, the film exhibited a phase transition from hexagonal-W2C to cubic-WC1-x. Further increasing the FCH4 larger than 10sccm, the film presented amorphous state. As the FCH4 increased, the Raman revealed that the films showed a graphitization trend, meanwhile, the surface of the films became smoother and smoother. The hardness of tungsten carbide films first increased, and then decreased after reaching the maximum 38.5GPa (FCH4=10 sccm). While the sample deposited at 15 sccm obtained the lowest wear rate (2.17×10-6 mm3/Nm) and low coefficient of friction (CoF, 0.24) and still maintained a high hardness of 32.1 GPa. The lowest wear rate could be ascribed to the highest ratio of H3/E2.

Experimental investigation into tungsten carbide thin films as solid oxide fuel cell anodes

Abstract

Wide band gap and conducting tungsten carbide (WC) thin films prepared by hot wire chemical vapor deposition (HW-CVD) method

In this letter, we report synthesis of tungsten carbide (WC) thin films having wide band gap (3.22–3.3eV) with high electrical conductivity (80–1260S/cm) by HW-CVD using heated W filament and Tetra-fluoro-methane (CF4) gas. Formation of WC was confirmed by low angle XRD, Raman spectroscopy and x-ray photoelectron spectroscopy. UV–Visible spectroscopy analysis revealed that the synthesized films have high transmission at wavelength 500nm. Electrical properties measured using Hall measurement show that these films are semiconductor. The obtained results imply that the growth of WC thin films is mainly from the atomic species (W and C) evaporated from the hot filament. The HW-CVD opens a novel route to synthesize wide band gap and conducting WC at a cost-efficient way for DSSCs and hydrogen evolution reaction (HER).

A controlled growth of WNx and WCx thin films prepared by atomic layer deposition

This work reports a capability for a controlled preparation of tungsten nitride and carbide thin films via an atomic layer deposition (ALD) approach. Those films were deposited by ALD using a fluorine- and nitrogen-free W metallorganic precursor of tungsten tris(3-hexyne) carbonyl [W(CO)(CH3CH2C≡CCH2CH3)] and a N2+H2 mixture plasma as a reactant at a deposition temperature of 250°C. It was found that a phase, microstructure and composition of the films could be controlled in precision by varying a gas flow rate ratio of N2/H2 in the plasma reactant. With the N2/H2 gas ratio of 1:3 and 1:5, W-rich polycrystalline WNx thin films (W/N ratio:~1.39) were deposited with a resistivity of 700–900µΩcm, while nano-crystalline (close to an amorphous) W-rich WCx films (W/C ratio:~1.26) with a much lower resistivity of ~510µΩcm, without any nitrogen incorporation, were formed when H2 gas became extremely rich (N2/H2 gas ratio of 1:10). Both X-ray diffraction and electron diffraction analyses revealed that the ALD-WCx films were composed of hexagonal W2C, WC, and non-stoichiometric cubic β-WCx. while the ALD-WNx films of cubic W2N.

Deposition and Characterization of Tungsten Carbide Thin Films by DC Magnetron Sputtering for Wear-Resistant Applications

In this study, WC (tungsten carbide) thin films were deposited on high-speed steel (AISI M2) and Si (100) substrates by direct current magnetron sputtering of a tungsten carbide target having 7% cobalt as binding material. The properties of the coatings have been modified by the change in the bias voltages from grounded to 200 V. All the coatings were deposited at 250°C constant temperature. The microstructure and the thickness of the films were determined from cross-sectional field-emission gun scanning electron microscope micrographs. The chemical composition of the film was determined by electron probe micro analyzer. The x-ray diffractometer has been used for the phase analyses. Nanoindentation and wear tests were used to determine the mechanical and tribological properties of the films, respectively. It is found that the increase in the bias voltages increased drastically the hardness and elastic modulus, decreased the friction coefficient values and increased the wear resistance of tungsten carbide thin films by a phase transformation from metallic W (tungsten) to a nonstoichiometric WC1−x (tungsten carbide) phase.

756 炭化タングステン薄膜の形成および機械的特性に及ぼす熱処理条件の影響(材料力学IV)

756 炭化タングステン薄膜の形成および機械的特性に及ぼす熱処理条件の影響(材料力学IV)

Cis‐(1,3‐Diene)2W(CO)2] Complexes as MOCVD Precursors for the Deposition of Thin Tungsten – Tungsten Carbide Films

AbstractTungsten ‐ tungsten carbide thin films are deposited by metal‐organic (MO)CVD on silica‐coated silicon wafers using [cis‐(1,3‐butadiene)2W(CO)2] and [cis‐(1,3‐cyclohexadiene)2W(CO)2], respectively, as tunable precursor complexes. The compounds are prepared through photochemical ligand exchange reactions from [W(CO)6] and fully characterized, including X‐ray structure determination and detailed differential thermal analysis (DTA)/thermogravimetry (TG) investigations. Gas‐phase diffusion coefficients and the vapor pressure of the compounds are calculated. The MOCVD experiments are performed in a vertical cold‐wall reactor and the exhaust gas is analyzed by gas chromatography (GC). X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) measurements are utilized for film characterization. Consequences of the high oxophilicity of freshly formed tungsten surfaces, consecutive surface reactions of the complex ligands, film growth, and film properties are discussed. Inside the layers, tungsten carbide is identified as the main component.

Relatively low temperature synthesis of hexagonal tungsten carbide films by N doping and its effect on the preferred orientation, phase transition, and mechanical properties

The authors deposited N-doped tungsten carbide thin films on Si(100) substrates at 500°C using direct-current reactive magnetron sputtering in a mixture of CH4∕N2∕Ar discharge and explored the effects of N doping on the preferred orientation, phase transition, and mechanical properties of the films by using x-ray diffraction, x-ray photoelectron spectroscopy, and nanoindentation measurements. They found that N doping significantly influenced the compressive stress, which led to a pronounced change in the preferred orientation, phase structure, and hardness for the tungsten carbide film. A phase transition from β-WC to α-WC occurred when N doping was in the range of 2.9 and 4.7at.%, meaning that α-WC can be obtained at relatively low temperature (500°C). To reveal the relationship between the stress and phase transition, as well as preferred orientation, the density-functional theory based on first principles was used to calculate the elastic constants and shear modulus for tungsten carbide with a structure of β-WC or α-WC. The calculated results showed that the preferred orientation depended on the competition between strain energy and surface energy, as well as the grains competitive growth, and the phase transition can be attributed to a decrease in the strain energy. The hardness of α-WC was harder than β-WC because the shear modulus for α-WC was larger than that of β-WC, whereas the bulk modulus for α-WC was almost equal to that of β-WC.

Structural investigation by the Rietveld method of sputtered tungsten carbide thin films

Thin films of tungsten carbides deposited by reactive radio-frequency sputtering were investigated by X-ray diffraction using the Rietveld method. Two films were selected for the structural refinement. One was biased, the other unbiased. The unbiased film was found to consist of a cubic phase WC 1 − x (C 0.9) in the space group Fm3 m with a lattice parameter of 4.263 (5) Å. A negative substrate bias of − 40 V leads to a multiphasic film: a cubic phase WC 1 − x with a lattice parameter of 4.301 (6) Å and a hexagonal phase W 2C ( P-3 m1) with lattice parameters of a = b = 2.787 (1) and c = 4.549 (2) Å. The domain size was found to be of ~ 5 nm. The coexistence of nanocrystalline phases WC 1 − x and W 2C is in accordance with the decrease of the carbon content (WC 0.7) in the biased film.

Effect of substrate temperature variation on nanostructured WC films prepared using HFCVD technique

Nanocrystalline tungsten carbide thin films are deposited on quartz substrates using hot-filament chemical vapor deposition technique. The influence of the substrate temperature on the nanostructured WC films is studied. The scanning electron microscopy indicates that the size of nanoparticles increases from 50 to 150 nm with an increase of substrate temperature from 400 °C to 800 °C. The crystalline structures, chemical bonds, and nanocomposition of WC films are characterized using X-ray diffraction, X-ray photoelectron spectroscopy, Raman scattering, and energy dispersion spectroscopy. The evolution of crystalline structures from α-WC to α-W 2C following variation of substrate temperature is observed.

Deposition of Tungsten Carbide Thin Films by Simultaneous RF Sputtering

Tungsten carbide (WC1-x) thin films were deposited by simultaneous sputtering. Tungsten and carbon solid materials were simultaneously sputtered by argon ion bombardment and deposited on substrates. Argon plasma was triggered using an RF (13.56 MHz) power source. The aim of this study is to apply this sputtering technique in a plasma-based ion implantation and deposition (PBII&D) system for the surface modification of three-dimensional workpieces. The films' surfaces in both the presence and absence of tungsten were very smooth, and only a few metal droplets were seen. An in-depth X-ray photoelectron spectroscopy profile revealed the following: (1) the films deposited contain approximately 30% tungsten in the most-to-least film; (2) carbon atoms bonded to tungsten (C–W) as well as those bonded to carbon (C–C) are detected in the C 1s spectra; (3) the stoichiometry of the film for an argon ion sputter time between ∼400 and ∼1600 s is deduced as WC0.73±0.10. The Raman spectra and Tauc plot from the optical transparency showed that the films contain approximately 10% sp3 with a band gap of 1.1 eV.

Influence of CH4 partial pressure on the microstructure of sputter-deposited tungsten carbide thinfilms

Tungsten carbide thin films have been prepared by reactive rf sputtering from a tungsten target in variousAr–CH4 mixtures. The composition, structure, microstructure and chemical state ofthe films have been investigated by the complementary use of RBS, NRA,XRD, GIXRD, TEM and XPS analyses. These characteristics of the filmswere then correlated to their mechanical properties determined by hardness(H), Young’smodulus (Er) and friction coefficient measurements. Under lowCH4 pressures, the formation of a mixture of nanocrystallineWC1−x andW2C phases has beenobserved. A pure WC1−x phase was observed in films having a composition close toW1C0.9. Withincreasing CH4 pressure, the amount of carbon in the films increases, leading to a progressive amorphization oftungsten carbide deposited layers. Nanocomposite films appeared to be formed, withWC1−x nanograins(<3 nm) dispersed in an amorphous carbon matrix. The film deposited at 30% ofCH4 exhibits a-C:H phase. The nature of the phases present in the films plays an important roleon their mechanical properties, as shown by the wide domain of variation of thefilms’ hardness (between 22 and 5.5 GPa) and the plastic deformation parameterH3/Er2 (between 0.08 and 0.04).

Crystallographic and electrical characterization of tungsten carbide thin films for Schottky contact of diamond photodiode

Tungsten carbide (WC) thin films are sputter deposited using a WC target on different substrates such as Si (111), Si (100), sapphire (0001), and Si (111) coated with Ti thin film. These films are characterized for their crystallographic structure, composition, electrical resistivity, optical transmittance and oxidation resistance in order to use WC as thermally stable electrodes for diamond devices. Preferentially (100) oriented cubic WC1−x thin films are obtained at room temperature, irrespective of the various deposition conditions and substrates. The electrical resistivity of the films is about 200–300μΩcm. No deterioration of the properties occurs after annealing at 500°C in argon ambient. However, the films suffer from decomposition at 800°C with the depletion of carbon. The well characterized WC and Ti∕WC bilayer are used as Schottky and ohmic contacts of diamond photodiodes, respectively. The excellent Schottky properties with rectifying ratio of 108 and reverse leakage current lower than 10−14A are maintained upon annealing at 500°C for 4h. This work indicates that the WC-based Schottky and ohmic contacts are promising in diamond optoelectronic devices for high-temperature applications.

Microstructural and mechanical investigations of tungsten carbide films deposited by reactive RF sputtering

Tungsten carbide thin films were deposited on (100) Si single crystal substrates by reactive RF sputtering from a tungsten target in Ar–CH 4 mixture. Under 1% of methane, the formation of a mixture of nanocrystalline WC 1− x presenting a partial (200) texture and W 2C phases was observed. The film deposited under 2% of CH 4 shows a maximum hardness of 22 GPa (a value comparable to the bulk WC reference material), these coatings also exhibit the lowest friction coefficient of 0.1. For coatings performed with CH 4 percentage higher than 3%, a progressive amorphization of the layers was observed. At 5% of CH 4 concentration, the films become essentially amorphous. Simultaneously the hardness decreases continuously to achieve a minimum value of 13 GPa.