Tribological properties of diamond-like carbon films deposited bv pulsed laser arc deposition

A novel method, pulsed laser arc deposition combining the advantages of pulsed laser deposition and cathode vacuum arc techniques, was used to deposit the diamond-like carbon （DLC） nanofilms with different thicknesses. Spectroscopic ellipsometer, Auger electron spectroscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy, scanning electron microscopy and multi-functional friction and wear tester were employed to investigate the physical and tribological properties of the deposited films. The results show that the deposited films are amorphous and the sp2, sp3 and C-O bonds at the top surface of the films are identified. The Raman peak intensity and surface roughness increase with increasing film thickness. Friction coefficients are about 0.1, 0.15, 0.18, when the film thicknesses are in the range of 17-21 nm, 30-57 nm, 67-123 nm, respectively. This is attributed to the united effects of substrate and surface roughness. The wear mechanism of DLC films is mainly abrasive wear when film thickness is in the range of 17-41 nm, while it transforms to abrasive and adhesive wear, when the film thickness lies between 72 and 123 nm.

Optical Properties of Tetrahedral Amorphous Carbon Films and Their Potential for Lab-on-a-Chip

In this study, tetrahedral amorphous carbon (ta-C) films with thicknesses between several 100 nm and several micrometers have been deposited onto polished tungsten carbide and steel substrates by pulsed laser deposition (PLD) using an excimer laser (248 nm wavelength). We investigate the optical properties (e.g. the refractive index (n) and extinction coefficient (k) in the visible and near-infrared wavelength range) of these layers in dependence of the used laser ablation fluence on the target. It is shown that n of ~2000 nm thick ta-C films can be tuned, depending on the sp3-content, between n = 2.5 and 2.8 at a wavelength of 632 nm. Besides of this k reduces with the sp3-content and is as low as 0.03 at sp3-contents of more than 75%. We proof that this gives the opportunity to prepare coating with tailored optical properties. Furthermore, it is shown that the ta-C films have low background fluorescence in the wavelengths range of 380 - 750 nm, which make this thin films attractive for certain optical, medical and biotechnological applications. We present for the first time that one possible application is the use in Lab-on-a-Chip-systems (LOC). Within these systems, the ultrasensitive detection of fluorescence markers and dyes is a challenge. In order to increase the signal-to-noise-ratio, a setup was developed, that used the specific optical properties of ta-C films produced by PLD. We used the ta-C film as an integrated reflector that combined low background fluorescence, a low reflectivity at the excitation wavelength and the high reflectivity at the emission wavelength. We prove that this setup improves the detection of fluorescence photons.

Extraordinary self-lubrication properties of non-hydrogenated diamond-like carbon films under humid atmosphere

Tribological properties of non-hydrogenated diamond-like carbon (DLC) films were investigated under humid (RH=80%) and dry (RH=5%) air. These films were deposited by pulsed laser deposition (PLD) at different substrate temperatures. Tribological properties of DLC fabricated by PLD is not sensitive to the relative humidity of testing environment. Because of the unique growth mechanism of DLC pre- pared by PLD, DLC is of "soft-hard" double layers, having a very low friction coefficient and wear rate under humid atmosphere. The minimum coefficient and wear rate of film under humid circumstance are 0.045 and 5.94×10?10 mm3N-1m-1, respectively, just a little bit more than those under dry condition. The root means square roughness of film is less than 1 nm. The sp3 content of film grown at room tem- perature (RT) is 72%, and the sp3 content decreases with temperature. Raman spectrum shows that the micro-structure is amorphous network. The largest hardness and elastic modulus of film are 51 GPa and 350 GPa, respectively and they reduce with increase of deposition temperature too. Water contact angles on surface are more than 90° which indicates that films fabricated by PLD are hydrophobic with low surface energy.