ICMCTF2008 Session DP: Symposium D Poster Session

Diamond-like carbon film incorporating silicon as well as hydrogen (DLC:Si:H) was prepared in T-shape filtered arc deposition system (T-FAD). Clean carbon plasma beam was extracted from the cathodic vacuum arc with graphite cathode by passing it through a T-shape droplet-filtering duct. Tetramethylsilane (TMS) vapor was introduced into the process chamber to incorporate Si in the film. Thus, the film was deposited physically by the cathodic carbon plasma and chemically by plasma enhanced CVD mechanism with TMS as the precursor source gas.

DLC:Si:H was then deposited at various process conditions, such as arc current, gas flow rate, process pressure, and substrate bias. These conditions were as follows. Cathode, graphite; arc current, 30 A or 50 A: TMS vapor flow rate, 5 to 40 sccm; process pressure, 0.05 to 0.2 Pa; substrate bias, pulse -100 V, 10 kHz, duty 20%. The substrate was super hard alloy (tungsten carbide with cobalt binder; WC). The substrate was not heated and the substrate temperature was less than 60°C. The deposition rate was obtained from the film thickness. The film was analyzed by micro-Raman spectroscopy, X-ray diffractometry (XRD), and stylus surface profiler and optical reflectometry. Raman spectroscopy and XRD revealed that the film was amorphous. The G-band peak in Raman spectra was found to shift to the lower wavenumber and the deposition rate increased as increasing the flow rate.

Solid surface wettability could be controlled by a chemical treatment of the material surface or modification of the surface topology. The super-hydrophobic surface, having the water contact angle of over 150 ~170 degree, has drawn much attention owing to its potential applications such as a water repellent self cleaning surface, surface energy induced drop motion or flow channel of low resistance for microfluidic devices. In the previous work, by combining the nanoscale double-rough surface with a hydrophobic DLC coating, we have shown the superhydrophobic wetting behaviour of a water droplet on various surface structures on DLC coated dual rough surface^[1]. Compared to single roughness surfaces with a wetting angle ~120 degree and with high wetting angle hysteresis (difference between forwarding and receding angle) ranging from 40 to 60 degrees, the dual roughness surface were achieved of 160 degree in wetting angle and less than 5 degree in hysteresis. Here we have further examined the superhydrophobic behavior on dual rough surfaces as improved the hydrophobic nature of dual surfaces by varying the deposition condition of DLC coating. Especially we have performed the systematic experiment that a water droplet, placed between the dual rough surfaces, was gradually pressed and we have monitored the variation in contact angle of the droplet from the hydrophobic to hydrophilic state with respect to hydrophobicity of dual rough surfaces.

^[1]T. –Y. Kim, B. Ingmar, K. Bewilogua, K. H. Oh, K.-R. Lee , Chem. Phys. Lett. 436 (2007) 199.

To better understand the formation of Ti₂AlN when titanium aluminides are used as templates, we studied by X-Ray diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM), Scanning Electron Microscopy (SEM) and Glow Discharge Optical Spectroscopy (GDOS) the first stages of the nitride formation when plasma nitridations of bulk TiAl and Ti₃Al samples, but also of Ti_xAl_1-x thin films (0,47 ≤x ≤0,66) deposited onto Si(100) substrates or bulk TiAl, were achieved between 600°C and 900°C.

XRD and cross-sectional TEM observations clearly indicate that this nitridation process first leads in almost all cases to the growth of a Ti₂AlN thin layer instead of TiN, this result being attributed to the very low solubility of nitrogen into TiAl but also to the relationships between the structures. Furthermore, in the case of Ti_xAl_1-x thin films deposited onto bulk TiAl or silicon substrates, strongly textured (0002) Ti₂AlN thin films were obtained. On the contrary no nitride formation was achieved when Ti₃Al was used as a template, a result that explains why a complete transformation of Ti₂Al thin films into Ti₂AlN is not achieved after the nitridation treatment. Our results strongly suggest that a rapid formation of Ti₂AlN is obtained when very fine grains of TiAl are submitted to the nitrogen plasma. This was confirmed by HRTEM cross-sectional observations of nitrided TiAl thin films or by GDOS characterizations that clearly indicate the low diffusion of nitrogen into large TiAl grains.

Recently, field emission (FE) properties of AlN thin films have called attention because the similar properties to diamond. Moreover, their high mechanical strength and excellent chemical stability are favourable for construction of long lifetime FE-based devices.

In this work, low temperature (less that 75°C) AlN thin films were deposited on Si(100) substrates by DC sputtering technique under various applied negative bias voltage ranging from 0 to -200V. The influence of negative substrate bias on the surface morphology and FE properties of as-deposited films has been studied and correlated. For this, AFM measurements were realized for analysis of surface morphology. The FE properties were investigated by measurements of FE characteristics curves and Fowler-Nordheim plots of the films. The measurements showed that low values of turn-on field (approx. 0.4 V/µm) can be obtained. From these results, we have observed that the negative dc bias voltage improves the crystallinity level and orientation for AlN films grown under low substrate temperature. Furthermore, we observed that this technique allows us to control the RMS roughness and the peaks density on the film surface, giving rise the possibility of growing AlN films with high emission current densities.