Tengcai Ma

SPM investigation of diamond-like carbon and carbon nitride films

Scanning probe microscopy was used to evaluate and compare the surface roughness, mechanical and tribological properties of hydrogenated (a-C:H) and tetrahedral (ta-C) diamond-like carbon (DLC) and amorphous carbon nitride (a-C:N) films. Compared to the a-C:H and a-C:N films, the ta-C films exhibit the lowest surface roughness. The soft surface layers of DLC and a-C:N films were revealed by nanowear tests and their thickness varies over the range of 0.2 to 4.1 nm. The nanoscale friction coefficient measurements from lateral force microscopy shows that these films have obviously different friction coefficients. The lower friction coefficients of ta-C and a-C:N films can be attributed to the existence of soft graphite-like surface structure. We proposed the deposition processes of DLC and a-C:N films, where their surface roughness, structure and mechanical properties were associated with the vapor plasma particle energy distribution.

Characterization of CNx films prepared by twinned ECR plasma source enhanced DC magnetron sputtering

Abstract The DC discharge of a planar magnetron was enhanced by twinned microwave electron cyclotron resonance plasma source. The magnetic cusp geometry formed in the processing chamber was used for plasma confinement. The sputtering discharge characteristics was investigated and a combined mode of voltage and current was observed at a pressure as low as 0.007 Pa. Carbon nitride thin films were synthesized using this method. Characterization of the films showed that the deposition rate was high, and the films were composed of a single amorphous carbon nitride phase with N/C ratio close to that of C3N4, with the bonding mainly of CN type.

Deposition of diamond-like carbon films by barrier discharge plasma with 1.4 and 20 kHz power sources

Hydrogenated diamond-like carbon (DLC) films were deposited on Si substrates at 1.4 and 20 kHz a.c. power frequencies by dielectric barrier discharge (DBD) technology. Atomic force microscope analysis showed that the roughness parameter Rq changed from 0.27 to 0.107 nm with decreasing the deposition pressure from 2.48 to 1.65 Torr. The charge-coupled device camera images and measurements of high-voltage and current waveforms of the DBD plasma indicate that the low-pressure DBD consists of spatially uniform glow-like single breakdowns that contribute to the formation of smooth surfaces of the deposited films. Fourier transform infrared spectroscopy analysis and hardness measurement results showed that the properties of the films deposited at 20 kHz power frequency changed from those of graphite-like to diamond-like to polymer-like with increasing the deposition pressure from 1.12 to 2.48 Torr. Increasing the power frequency from 1.4 to 20 kHz may cause an increase of the deposition rate from 4.5 to 26 nm/min. The higher breakdown voltage at 20 kHz power frequency may produce hydrocarbon ions with higher energies in the cathode sheath near the substrates, which would have much effect on hardness of the deposited DLC films.

CVD of hard DLC films in a radio frequency inductively coupled plasma source

Chemical vapor deposition (CVD) of hard diamond-like carbon (DLC) films on silicon (100) substrates from methane was successfully carried out using a radio frequency (r.f.) inductively coupled plasma source (ICPS). Different deposition parameters such as bias voltage, r.f. power, gas flow and pressure were involved. The structures of the films were characterized by Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The hardness of the DLC films was measured by a Knoop microhardness tester. The surface morphology of the films was characterized by atomic force microscope (AFM) and the surface roughness (Ra) was derived from the AFM data. The films are smooth with roughness less than 1.007 nm. Raman spectra shows that the films have typical diamond-like characteristics with a D line peak at ∼1331 cm−1 and a G line peak at ∼1544 cm−1, and the low intensity ratio of ID/IG indicate that the DLC films have a high ratio of sp3 to sp2 bonding, which is also in accordance with the results of FTIR spectra. The films hardness can reach approximately 42 GPa at a comparatively low substrate bias voltage, which is much greater than that of DLC films deposited in a conventional r.f. capacitively coupled parallel-plate system. It is suggested that the high plasma density and the suitable deposition environment (such as the amount and ratio of hydrocarbon radicals to atomic or ionic hydrogen) obtained in the ICPS are important for depositing hard and high quality DLC films.

A Monte Carlo simulation model for plasma source ion implantation

Plasma source ion implantation is a process in which a target is immersed in a plasma and a series of large negative‐voltage pulses are applied to it to extract ions from the plasma and implant them into the target. A Monte Carlo simulation model is developed to study the energy and angle distributions of ions at the planar target for higher pressures of the neutral gas. Cross sections of the charge exchange and momentum transfer that depend on the ion energy are taken into account precisely. The energy and angle distributions of N2+ at the target during the sheath edge evolution for the different pressures are determined.

Investigation on properties of ceramic coatings of ZrN

Abstract The ceramic coatings of zirconium nitride were deposited on M2 high speed steel by reactive magnetron sputtering ion plating. The microhardness and the scratch critical load (Lc) of the coatings with different nitrogen partial pressures have been discussed. The adhesion and toughness of the coatings as well as the scratch failure have also been studied by means of the scratch test.

Surface and structural properties of ultrathin diamond-like carbon coatings

Abstract Nanoscale wear resistance, friction, and electrical conduction tests using atomic force microscope (AFM) have been conducted on ultrathin diamond-like carbon (DLC) coatings, including tetrahedral amorphous carbon (ta-C) deposited using pulsed cathodic arc (PCA) and filtered-PCA, and hydrogenated amorphous carbon (a-C:H) deposited using electron cyclotron resonance—chemical vapor deposition (ECR-CVD). The low-resistant layers at the surfaces of these thin DLC coatings were revealed by AFM-based nanowear tests. Their thickness is mainly determined by the deposition methods and does not show an obvious variation with the coating thickness decreasing from tens of nm to a few nm. The ∼3 nm ta-C coatings from PCA and filtered-PCA deposition were found to have the stable bulk structure beneath the thin (0.3–0.95 nm) surface layers. The ∼3 nm a-C:H coating from ECR-CVD had the extremely low load-carrying capacity and exhibited the evidence of coating delamination, which can be related to the thicker (1.5±0.1 nm) soft surface layers of a-C:H coatings. The results from conducting-AFM measurements indicate that a-C:H coatings have H and sp3 C enrichment surface layers while the soft surface layers of ta-C coatings have graphite-like structure. The nanoscale friction coefficients of these thin ta-C and a-C:H coatings were compared by AFM-based lateral force microscope. The lower friction coefficient of ta-C coatings can be attributed to the existence of graphite-like surface structure.

ENERGY AND ANGLE DISTRIBUTIONS OF IONS STRIKING A SPHERICAL TARGET IN PLASMA SOURCE ION IMPLANTATION

Plasma source ion implantation is a process in which a target is immersed in a plasma and a series of large negative‐voltage pulses is applied to it to extract ions from the plasma and implant them into the target. A Monte Carlo simulation model is developed to study the energy and angle distributions of ions striking the spherical target for high pressures of the neutral gas. The ion‐neutral charge exchange and momentum‐transfer cross sections that depend on the ion energy are taken into account precisely. The energy and angle distributions of Ar+ at the spherical target during the sheath edge evolution after the ion matrix sheath for different pressures are investigated in detail.

Rotational temperature of nitrogen glow discharge obtained by optical emission spectroscopy.

Measurements of rotational temperature as low as several hundred Kelvin have been measured using optical emission spectroscopy (OES) in nitrogen direct current (DC) glow discharge. The strongest band of the first negative system of nitrogen was chosen to deduce the rotational temperature at four different positions in nitrogen DC glow discharge, the back of cathode; cathode sheath; positive column; and anode glow. In positive column the rotational temperature increased apparently with the increasing discharge voltage from 500 to 1000 V when the pressure was 10 Pa. But with pressure of 20 Pa the rotational temperature in positive column increased slightly with the increase of discharge voltage. On the contrary, the rotational temperature in cathode sheath took reverse tendencies when the discharge voltage varies from 500 to 1000 V. As regard the anode glow, the rotational temperature at 10 Pa decreased with the increase of discharge voltage, but that at pressure of 20 Pa increased. We attribute the different tendencies of the rotational temperature to the different discharge statues at different pressures. When the discharge voltage varies from 500 to 1100 V, the discharge with pressure of 10 Pa is normal glow and that with 20 Pa is abnormal glow.

Model of collisional sheath evolution in plasma source ion implantation

A model is developed to study the temporal evolution of the sheath during a pulse of high negative voltage applied to a target immersed in a plasma, such as that present in plasma source ion implantation. This model covers the whole range from collision free to collision dominated sheaths. The sheath expansion velocity and the position of the sheath edge as a function of time in planar geometries for various pressures are obtained.