Y.P Wu

On the deposition mechanism of a-C:H films by plasma enhanced chemical vapor deposition

Abstract Amorphous hydrogenated carbon (a-C:H) films were deposited from a mixture of C2H2 and Ar, by a radio frequency direct current (r.f.-d.c.) plasma-enhanced chemical vapor deposition technique. The effect of process parameters on the deposition rate of the a-C:H films was systematically studied. It was found that the deposition rate increased initially and then decreased after passing a maximum with the increase of bias voltage and deposition pressure. The deposition rate increased gradually with increasing C2H2 content. However, a-C:H films could not be prepared at C2H2 contents lower than 10%. A simple phenomenological surface model, which takes into account the sputtering effect of a-C:H films by energetic Ar ion bombardment, is proposed on the basis of these results to describe the deposition mechanism of a-C:H films.

Study on functionally gradient coatings of Ti–Al–N

Abstract Functionally gradient coatings of Ti–Al–N were deposited on the 5CrNiMo steel substrate by multi arc ion deposition (MAID) technique by gradually increasing the nitrogen pressure during the deposition process. Scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to investigate the composition, microstructure and phases of coatings. Thermal shock resistance tests were carried out in a resistance furnace. The adhesion strengths of Ti–Al–N functionally gradient coatings were tested by an automatic scratch tester. It was shown that there are three phases, (Ti,Al)N, (Ti 2 ,Al)N and Al, in the coatings. Along the thickness direction of Ti–Al–N functionally gradient coatings, the content of ceramic phase increases and the content of metal phase decreases gradually. The hardness distributed along the thickness direction increases with increasing the N 2 pressure, namely increasing the content of ceramic. It is found that the adhesion strength and the thermal shock resistance property of Ti–Al–N functionally gradient coatings are better than that of homogeneous (Ti,Al)N coatings and increase with decreasing the composition gradient.

Influence of nitrogen ion energy on the Raman spectroscopy of carbon nitride films

Abstract Carbon nitride films were deposited by filtered cathode vacuum arc combined with radio frequency nitrogen ion beam source. Both visible Raman spectroscopy and UV Raman spectroscopy are used to study the bonding type and the change of bonding structure in carbon nitride films with nitrogen ion energy. Both C–N bonds and CN bonds can be directly observed from the deconvolution results of visible and UV Raman spectra for carbon nitride films. Visible Raman spectroscopy is more sensitive to the disorder and clustering of sp 2 carbon. The UV (244 nm) Raman spectra clearly reveal the presence of the sp 3 C atoms in carbon nitride films. Nitrogen ion energy is an important factor that affects the structure of carbon nitride films. At low nitrogen ion energy (below 400 eV), the increase of nitrogen ion energy leads to the drastic increase of sp 2 /sp 3 ratio, sp 2 cluster size and CN bonds fraction. At higher nitrogen ion energy, increase leads to the slight increase of CN bonds fraction and sp 2 cluster size, slight decrease of CN bonds fraction and sp 2 /sp 3 ratio.

Synthesis of Superhard and Elastic Carbon Nitride Films by Filtered Cathodic Vacuum arc Combined with Radio Frequency Ion Beam Source

Superhard and elastic carbon nitride films with hardness and elastic recovery of 47 GPa and 87.5%, respectively, were synthesized by using a double-bend filtered cathodic vacuum arc combined with radio-frequency nitrogen ion beam source. The bombardment of energetic nitrogen atom onto the growing film surface results in the high atomic ratio of N/C (0.4), which contributes to the high sp 2 content and the formation of a five-membered ring structure in the carbon nitride film at room temperature. The buckling of the five-membered ring basal planes may facilitate cross-linking between the planes through sp 3 coordinated carbon atoms. A rigid three-dimensional network is formed, which contributes to the high hardness and elastic recovery of the deposited films.

Influence of deposition parameters on the internal stress in a-C:H films

Abstract Amorphous hydrogenated carbon (a-C:H) films were deposited from a mixture of C 2 H 2 and Ar by the r.f. plasma-enhanced chemical vapor deposition technique. The internal stress was measured by the substrate bending method. The films were characterized by IR and positron annihilation spectroscopies. The influence of substrate bias and C 2 H 2 content in the feedgas on the internal stress and structure were studied. It was found that the hydrogen content and sp 3 /sp 2 ratio decrease with an increase in substrate bias and a decrease in C 2 H 2 content in the feedgas. However, the variations in H content and sp 3 /sp 2 ratio with C 2 H 2 content are much less than that with substrate bias. The void density, which increases monotonically with the increase of C 2 H 2 content, initially decreases and then increases with the increase of substrate bias. The internal stress in a-C:H films decreases with the increase of substrate bias and C 2 H 2 content in the feedgas. The decreases of the H content and sp 3 /sp 2 ratio in the films are the main factors that cause the reduction in internal stress. The void density has a minor effect on the internal stress.

Deposition of carbon nitride films by filtered cathodic vacuum arc combined with radio frequency ion beam source

Abstract Atomically smooth carbon nitride films were deposited by an off-plane double bend filtered cathodic vacuum arc (FCVA) technique. A radio frequency nitrogen ion source was used to supply active nitrogen species during the deposition of carbon nitride films. The films were characterized by atomic force microscopy (AFM), XPS and Raman spectroscopy. The internal stress was measured by the substrate bending method. The influence of nitrogen ion energy (0–1000 eV) on the composition, structure and properties of the carbon nitride films was studied. The nitrogen ion source greatly improves the incorporation of nitrogen in the films. The ratio of N/C atoms in the films increases to 0.40 with an increase in the ion beam energy to 100 eV. Further increase in the ion beam energy leads to a slight decrease in the N/C ratio. XPS results show that nitrogen atoms in the films are chemically bonded to carbon atoms as CN, CN, and CN bonds, but most of nitrogen atoms are bonded to sp 2 carbon. The increase in nitrogen ion energy leads to a decrease in the content of nitrogen atoms bonded to sp 2 carbon, and an increase in the content of nitrogen atoms bonded to sp 3 and sp 1 carbon. Raman spectra indicate an increase in the sp 2 carbon phase in carbon nitride films with an increase in nitrogen ion energy. The increase in sp 2 carbon fraction is attributed to the decrease in internal stress with increasing nitrogen ion energy.

Effect of laser fluences on the structure of carbon nitride films deposited by direct current plasma assisted pulsed laser ablation

Abstract Carbon nitride films were deposited by direct current plasma assisted pulsed laser ablation of a graphite target under a nitrogen atmosphere at room temperature. The surface morphology, composition and bonding structure of the deposited films were characterized by atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, Raman, and X-ray photoelectron spectroscopy (XPS). The effect of laser fluences in the range 0.5–3 J/cm 2 on the surface morphology, composition and bonding structure of the carbon nitride films were systematically studied. As laser fluence is increased, AFM results show a great decrease in the surface roughness of carbon nitride films. FTIR and XPS results indicate an increase in the N/C ratio and the content of N atoms bonded to sp 3 C, as well as a decrease in the content of H atoms and the content of N atoms boned to sp 2 C in the deposited films, and Raman spectra indicate an increase in the content of disordered sp 2 C atoms and the sp 2 cluster size. The increase in the film density and the decrease in the particle fraction contribute to the decrease of surface roughness with increasing laser fluence.