Xing-zhao Ding

Hard carbon nanocomposite films with low stress

Abstract Ti- and Al-containing carbon nanocomposite films were deposited by the filtered cathode vacuum arc technique. The influence of Ti and Al content in the target on the surface morphology, structure, internal stress, hardness and Youngs modulus of the deposited films were studied. The surface of all carbon nanocomposite films was atomically smooth. The incorporation of metal atoms in the films led to an increase in surface roughness and ID/IG ratio. The RMS and ID/IG ratio of ta-C:Al films was higher than that of ta-C:Ti films deposited from a target with the same metal content. The incorporation of both Ti and Al atoms in ta-C films resulted in a decrease in internal stress, hardness and Youngs modulus. The effect of Al on the internal stress, hardness and Youngs modulus of carbon nanocomposite films was more pronounced than that of Ti. For ta-C:Ti and ta-C:Al films deposited from a target with a metal content of 10 at.%, the internal stress was reduced to 4.29 and 1.94 GPa, respectively, whereas the hardness remained at a high level (24 and 18 GPa, respectively). Raman spectra clearly indicate that the Ti atoms in ta-C:Ti films exist as a TiC phase, which contributes to the higher internal stress, hardness, and Youngs modulus of ta-C:Ti films.

Structural and tribological characterization of multilayer ta-C films prepared by filtered cathodic vacuum arc with substrate pulse biasing

Abstract The filtered cathodic vacuum arc (FCVA) technique is reported to be an effective method for producing high quality hard coatings, but has limitations for preparing thick hard tetrahedral amorphous carbon (ta-C) films by the conventional method of floating conditions. Currently, the multilayer approach is the only way to overcome this limitation, and is of great interest because it enables the fabrication of films with varied thickness and properties to suit the application. A multilayer ta-C film of approximately 1 μm thickness is prepared on a silicon substrate by alternate soft (20 nm thick) and hard (100 nm thick) layers of tetrahedral amorphous carbon. The compressive stress of the film measured using the radius of curvature technique, profiled by stylus, is found to be approximately 5.4 GPa. The bond structure of the film is studied using Raman spectroscopy and is typical of films containing reasonably high sp 3 fractions, with an I D / I G ratio of approximately 0.265. The hardness and elastic modulus of the film are approximately 57 and 550 GPa, respectively, which are fairly high for thick ta-C films. The coefficient of friction and wear rate of the ta-C film against a sapphire counter-face are observed to be relatively low. This investigation finds that the ta-C films of relatively high thickness, with favourable hardness and tribological properties, can be prepared by FCVA with alternate substrate pulse biasing.

Ion beam assisted deposition of diamond-like nanocomposite films in an acetylene atmosphere

Abstract In recent years, doped diamond-like carbon (DLC) coatings have been shown to solve some intrinsic application difficulties of DLC, esp. reducing internal stresses and improving thermal stability. Diamond-like nanocomposite (DLN), by incorporating an amorphous Si-O network into the DLC, is a special class of modified DLC coatings, which have many excellent properties and wide applications. In this paper, a diamond-like nanocomposite film was synthesized by an ion beam assisted deposition method in an acetylene atmosphere. The composition and microstructure of the DLN film were investigated by various spectroscopic analyses, including Fourier transform infrared absorption spectroscopy, Rutherford backscattering spectroscopy. Raman scattering spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet-visible absorption spectroscopy.

Preferential orientation of titanium carbide films deposited by a filtered cathodic vacuum arc technique

Abstract Titanium carbide films with a thickness of approximately 100-nm were deposited on Si(100) substrates by a filtered cathodic vacuum arc technique. The composition and microstructure of the films were assessed by Rutherford backscattering spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and atomic force microscopy. A negative bias voltage ( V S 0∼−1000 V) was applied to the substrate during deposition, and the influence of V S on the crystalline orientation of the as-deposited films was investigated. It was found that the crystallites are randomly oriented in the film deposited at V S =0 V. In the bias voltage range of V S =−40∼−500 V, the titanium carbide films exhibited a (111) preferential orientation. When V S was increased to −1000 V, however, the film was (100) preferentially oriented. The compressive internal stress, determined by the radius of curvature technique, in the titanium carbide films exhibited a minimum value at approximately V S =−80∼−120 V. The (111) preferential orientation can be explained by minimization of elastic energy storage in the films; while the (100) preferential orientation in the film deposited at V S =−1000 V is due to the sputter channeling effect, because the (100) direction in the TiC lattice shows the most open channeling direction and therefore the lowest sputtering yield.

Electron field emission from Ti-containing tetrahedral amorphous carbon films deposited by filtered cathodic vacuum arc

Titanium-containing tetrahedral amorphous carbon (ta-C:Ti) films with different titanium content were deposited by a filtered cathodic vacuum arc technique. The microstructure of these films was confirmed to be of ta-C+TiCx(x<1) nanocomposite by Rutherford backscattering spectroscopy, x-ray diffraction, and micro-Raman spectroscopy experiments. With the increase of titanium content, the titanium carbide content increased and the sp3 fraction in the residual ta-C phase decreased gradually. In the electron field emission tests, it was found that proper conditioning processes are necessary for all these films in order to get a steady reproducible emission behavior. After conditioning, the emission threshold field of the films is about the same value, around 10 V/μm, except for the film with the lowest titanium content (∼1.2 at%) of which the threshold field is much higher, around 17–18 V/μm. The optimum titanium concentration in the film for field emission, showing the highest emission current and emission s...

Structural and mechanical properties of Ti-containing diamond-like carbon films deposited by filtered cathodic vacuum arc

Abstract Titanium-containing diamond-like carbon films were deposited on silicon wafer substrates at room temperature by the filtered cathodic vacuum arc technique. A wide range of negative bias voltage from 0 to 500 V was applied to the substrates during film deposition. The structural and mechanical properties of the films were analysed by Rutherford backscattering spectroscopy, Raman spectroscopy, surface profilometry, the scratch test, and nanoindentation. For comparison, a set of pure diamond-like carbon films were also deposited and analysed. Raman spectra showed that all the samples had the lowest intensity ratio of the D peak to G peak ( I D / I G ) at a bias voltage of approximately 80 V, which normally represents the highest sp 3 -bonded carbon components in the films. Correspondingly, the highest internal stress (σ), hardness ( H ) and Youngs modulus ( Y ), and the lowest scratch critical load ( L c ) were observed at the bias voltage of approximately 80 V. With the increase of titanium content in the films, I D / I G increased, while σ, H , and Y reduced, and L c increased. The results demonstrate that the addition of titanium into the diamond-like carbon films could significantly reduce the internal stress and, as a consequence, effectively improve the adhesion properties of these films.

Field emission from cobalt-containing amorphous carbon composite films heat-treated in an acetylene ambient

Cobalt-containing amorphous carbon composite films have been prepared by the filtered cathodic arc technique using a cobalt-containing graphite target at room temperature. After heat treatment at 550 °C in a mixture of acetylene and nitrogen gases, the field emission properties were significantly improved. A threshold electric field of 1.7 V/μm and an emission site density of 105/cm2 were obtained without conditioning. The composite films, which can be deposited with a high rate at room temperature and require a relatively low temperature heat-treatment process to enhance electron emission, are promising for practical applications in field emission display.

Field emission from metal-containing amorphous carbon composite films

Metal-containing (Co, Al and Ti) amorphous carbon composite films (a-C:Me) have been prepared by the filtered cathodic arc technique using metal-containing graphite targets at room temperature. Field emission properties of the heat-treated a-C:Me films were improved and were found to be dependent on the metal content and variety of metals. After heat-treatment at 550°C in a mixture of acetylene and nitrogen gases, the field emission properties of a-C:Co films were significantly improved, in which Co acted as catalysts to enhance graphitization as well as formation of carbon nanotubes during heat-treatment. A threshold electric field of less than 2 V/μm was obtained from the heat-treated a-C:Co composite films without conditioning. The heat-treated a-C:Al and a-C:Ti films, though the conditioning step could be avoided and relatively low threshold fields could be obtained, exhibited relatively low emission site densities, however. The a-C:Me films, which can be deposited with a high rate at room temperature and require a relatively low temperature, heat-treatment process to enhance electron emission, are promising for practical applications in field emission display.

Characterization of ta-C films prepared by a two-step filtered vacuum arc deposition technique

Abstract Adhesive strength is one of the most important properties of a coating, and one which could be improved by preparing an interface layer with increased ion energy, i.e. by applying high substrate-bias voltage. Hence, an investigation has been carried out to study the effect of substrate-bias voltage, and of the interface layer on the mechanical and tribological properties of ta-C films. In this presentation, the films are prepared by a two-step process. A relatively thick, hard layer of ta-C film is deposited on top of a relatively thin soft adhesive (interface) layer, which is deposited on a silicon substrate. The thin soft adhesive (interface) layer was prepared with a different ion energy, by controlling the high voltage negative substrate-bias. The thick hard layer on the top was prepared without any substrate-bias. The influence of substrate-bias during the preparation of the interface layer on the properties (structural, mechanical and tribological) of the ta-C films was investigated. The results show that the adhesive strength can be improved to a great extent, without much damage to the mechanical and tribological properties of the coating.

Magnetic properties of Fe+-implanted silica films after post-implantation annealing

Magnetic properties of Fe-implanted silica films after different annealing processes were studied. The magnetization of the samples annealed at Ta⩽600 °C was very weak, and hard to saturate due to the superparamagnetic effect. At Ta=800 °C, the saturation magnetization increased significantly, but still much lower than that of bulk Fe. The coercivity of the films, either as-implanted or annealed, was much higher than that of bulk Fe. No evident magnetic domain structure can be observed for the as-implanted and 600 °C annealed samples, which implied that the magnetic particles at lower temperatures were small and deeply embedded in the film. During the annealing process at 800 °C, the implanted Fe atoms gradually diffused outward with the formation of islands on the film surface. These islands were demonstrated to be ferromagnetic. At the initial stage of annealing (ta⩽1 h), all the islands were of a single-domain magnetic structure. Besides these islands, some embedded magnetic particles could also be det...