C.S. Xie

UV Nd:YAG laser ablation of copper: chemical states in both crater and halo studied by XPS

Abstract Laser ablation of pure copper was performed using a pulsed Nd:YAG laser operating at 355xa0nm in air. Oxide nanoparticles redeposited near the edge of the crater results in the formation of the halo. Chemical states in both crater and halo were measured by X-ray photoelectron spectroscopy (XPS). After UV laser ablation, there are an obvious shoulder around 934.4xa0eV and a shake up satellite around 942.5xa0eV for the Cu 2p3/2 spectra in both crater and halo. Deconvoluting the Cu 2p3/2 spectra, a component was detected at 933.7xa0eV corresponding to CuO in both crater and halo as expected. Also, another component at 935.1xa0eV can be assigned to Cu(OH)2. The formation of CuO and Cu(OH)2 is probably due to the reactions of copper with O2 and water vapor in air. This suggest that the ablation atmosphere plays an important role for the formation of chemical species in both crater and halo. Moreover, an enhanced oxidation in the halo was found at higher fluence: the FWHM of the Cu 2p3/2 spectra and the peak areas of CuO and Cu(OH)2 were significantly higher than those in the crater. This is probably due to the formation of the laser-induced plasma. In addition, peak areas of CuO and Cu(OH)2 in the halo markedly increase with increasing the laser fluence.

XPS investigation of the chemical characteristics of Kapton films ablated by a pulsed TEA CO2 laser

Laser ablation of 125-μm-thick Kapton polyimide films was carried out in air using a pulsed TEA CO2 laser at 9.3 μm. Laser-produced fibers protruding from the ablated surface results in a bad surface quality. Changes in the composition and the chemical characteristics of the ablated surfaces were identified by X-ray photoelectron spectroscopy (XPS). The C/O and C/N atomic ratios as well as the peak area of the C 1s spectra at 284.7 eV in the ablated area increase, while the peak areas of the C 1s spectra corresponding to the carbonyl groups (Cue5fbO) in the imide system and the ether groups (Cue5f8O) decrease. These suggest that the fiber bundles consist mainly of carbon. Moreover, the amide groups, nitrile groups (ue5f8Cue5fcN) and the benzene derivatives were detected after laser irradiation due to the breakage of the Cue5f8N bonds in the imide ring and ether groups. Upon increasing the fluence to 10.6 J/cm2, the shake up at 537.6 eV decreases further, yet the amide groups as well as the shake up at 291 eV almost disappeared. This is because benzene derivatives decompose completely and the carbonyl groups are eliminated from the aromatic systems due to a large temperature rise. Therefore, the increase in fluence may improve the thermal decomposition during the TEA CO2 laser ablation of the Kapton films.

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.

Dependence of the composition and bonding structure of carbon nitride films deposited by direct current plasma assisted pulsed laser ablation on the deposition temperature

Abstract Carbon nitride films were deposited by direct current plasma assisted pulsed laser ablation of a graphite target under nitrogen atmosphere. Atomic force microscopy (AFM), Fourier transform infrared (FTIR), Raman, and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface morphology, bonding structure, and composition of the deposited films. The influence of deposition temperature in the range 25–400xa0°C on the composition and bonding structure of carbon nitride films was systematically studied. AFM images show that surface roughness and cluster size increase monotonically with deposition temperature. XPS, FTIR, and Raman spectra indicate directly the existence of Cue5f8N, Cue5fbN, and Cue5fcN bonds in the deposited films. The increase of deposition temperature results in a drastic decrease in the N/C ratio, the content of Cue5fcN bond and N atoms bonded to sp3 C atoms, in addition to the increase in the content of disorder sp2 C atoms and N atoms bonded to sp2 C atoms in the deposited films. Raman spectra show that the intensity ratio of D peak over G peak increases with increasing deposition temperature to 200xa0°C, then decreases with the further increase of deposition temperature, which results from the continuous growth of sp2 cluster in the films.

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 Cue606N 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 Cue5f8N bonds fraction. At higher nitrogen ion energy, increase leads to the slight increase of Cue606N bonds fraction and sp 2 cluster size, slight decrease of Cue5f8N bonds fraction and sp 2 /sp 3 ratio.

Internal stress of a-C:H(N) films deposited by radio frequency plasma enhanced chemical vapor deposition

Abstract Amorphous hydrogenated carbon nitride [a-C:H(N)] films were deposited from the mixture of C2H2 and N2 using the radio frequency plasma enhanced chemical vapor deposition technique. The films were characterized by X-ray photon spectroscopy, infrared, and positron annihilation spectroscopy. The internal stress was measured by substrate bending method. Up to 9.09xa0at% N was incorporated in the films as the N2 content in the feed gas was increased from 0 to 75%. N atoms are chemically bonded to C as C–N, Cue605N and Cue606N bond. Positron annihilation spectra shows that density of voids increases with the incorporation of nitrogen in the films. With rising nitrogen content the internal stress in the a-C:H(N) films decrease monotonically, and the rate of decrease in internal stress increase rapidly. The reduction of the average coordination number and the relax of films structure due to the decrease of H content and sp3/sp2 ratio in the films, the incorporation of nitrogen atoms, and the increases of void density in a-C:H(N) films are the main factors that induce the reduction of internal stress.

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 Cue5f8N, Cue5fbN, and Cue5fcN 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.

Influence of deposition pressure on the composition and structure of carbon nitride films deposited by direct current plasma assisted pulsed laser ablation

Abstract Carbon nitride films were deposited by pulsed laser ablation of graphite target under nitrogen atmosphere at room temperature. A direct current discharge apparatus was used to supply active nitrogen species during the deposition of carbon nitride films. FTIR and X-ray photoelectron spectroscopy (XPS) were used to characterize the composition and bonding structure of the deposited films. The influence of deposition pressure in the range 1–20xa0Pa on the composition and bonding structure of carbon nitride films was studied. The composition and structure are strongly depended on the deposition pressure. The N/C ratio in the deposited films increases linearly with increasing deposition pressure to 10xa0Pa, further increase of the deposition pressure results in the slight increase of N/C ratio. FTIR spectra indicate the existence of Cue5f8N, Cue605N and Cue606N bonds in the deposited films. Increasing deposition pressure results in the increase of Cue605C, Cue605N and Cue606N bonds fraction and decrease of the Cue5f8N bonds fraction in the deposited films. XPS results are consistent with FTIR results, which indicate that increasing deposition pressure leads to the increase in the fraction of N atoms bonded to sp 2 C atoms and the fraction of sp 2 C atoms bonded to N atoms, and the decrease in the fraction of N atoms bonded to sp 3 C atoms and the fraction of sp 3 C atoms bonded to N atoms.