K.H. Lai

Wear-resistant multilayered diamond-like carbon coating prepared by pulse biased arc ion plating

Diamond-like carbon coatings have been deposited by a pulse biased arc ion plating. In order to improve their adherence to metal substrate, two systems of graded transition layers, namely Ti/TiN/TiC and Ti/TiCN/TIC, have been applied. The structure and composition of the diamond-like carbon/transition composite coatings were studied by scanning electron microscopy, Raman spectroscopy and energy dispersive X-ray spectroscopy. The total thickness of the coatings was within a range of 1.0-2.0 mum. Such multi-layer coatings showed excellent properties including high hardness, low friction coefficient and long wear-resistant lifetime. Diamond like carbon coatings as well as their wear tracks developed by sliding steel balls have been investigated by scanning electron microscopy. The results of the analysis, particularly that of the tribological study showed that the wear resistance and film-to-substrate adherence of diamond like carbon coatings with stainless steel surface were dramatically improved by using a graded transition layer and pulse biased arc ion plating

Mechanical properties of DLC films prepared in acetylene and methane plasmas using electron cyclotron resonance microwave plasma chemical vapor deposition

Abstract Diamond-like carbon (DLC) films were deposited on silicon using methane and acetylene plasma induced by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-MPCVD). The mechanical properties of DLC films were characterized by micro-Raman system, atomic force microscope, tribometer, nano-indenter used for both hardness and nano-scratch test measurements. The mechanical properties of both DLC films, prepared in methane and acetylene plasmas, respectively, strongly depended on the kinetic energy of impinging particles. The deposition at −120 V substrate bias gave rise to DLC films with the best mechanical properties for both methane and acetylene plasmas. The hardness measurements with variable indentation depth showed the characteristic changes in hardness values implying elastic deformations of supporting substrates. The maximum hardness value of DLC M films was 20 GPa while that of DLC A films was 28 GPa. However, the hardness dropped when DLC films were prepared at substrate biases more negative than −120 V due to the thermal graphitization. The improvement in DLC properties usually provided the films with smaller hydrogen content and higher density of sp 3 bondings. These parameters were engineered through controlling the deposition parameters. Particularly, the bombardment of growing DLC films by energetic ions showed to be extremely important to yield films with lower internal stress.

Efficient green organic light-emitting devices with a nondoped dual-functional electroluminescent material

An efficient nondoped green organic light-emitting device was demonstrated by using a dual-functional electroluminescent material, 4,4′,4″-tris[8-(7,10-diphenylfluoranthenyl)] phenylamine (TDPFPA). TDPFPA was shown to be a good hole transporting [with a mobility of (1.1–1.2)×10−4cm2V−1s−1 at (1.8–5.6)×105Vcm−1] and efficient fluorescent material with an exceptionally high glass transition temperature of 237°C. The device with a simple structure of indium tin oxide/TDPFPA/4,7-diphenyl-1,10-phenanthroline/LiF∕Al showed green emission with Commission Internationale de L’Eclairage coordinates of (0.24, 0.54), a current efficiency of 9.9cd∕A, and power efficiency of 10.6lm∕W.

Mechanical properties of a-C:H multilayer films

Abstract Multilayered amorphous hydrogenated carbon (a-C:H) films consisting of alternating sublayers with different mechanical properties have been deposited by an electron cyclotron resonance microwave-plasma chemical vapor deposition (ECR MP-CVD) system and modulating substrate bias voltage. The mechanical properties of the multilayer films were determined using nanoindentation and nanoscratch experiments with reference to single a-C:H layers of which the multilayer structure were composed. In nanoindentation tests, the relationship between the film hardness and indentation depth has been obtained over an indentation depth range of 20–500 nm. Since the films tend to fracture under high load in nanoindentation tests, their critical fracture loads were determined. The critical loads for fracturing the multilayered a-C:H films were higher than those of single a-C:H layers. The nanoscratch tests also showed that the multilayered a-C:H films required a higher critical load for scratching fracture. This study implies that the mechanical properties of a-C:H film can be improved by engineering suitable multilayer structures.

Mechanical properties and corrosion studies of amorphous carbon on magnetic disks prepared by ECR plasma technique

Abstract Diamond-like carbon (DLC) films were prepared on magnetic disk surfaces using an electron cyclotron resonance assisted microwave plasma chemical vapor deposition (ECR-MPCVD) system with variable radio-frequency (r.f.) substrate bias. Surface roughness of DLC deposited on hard disks was investigated by atomic force microscopy (AFM), which revealed that the DLC coated surfaces are smoother than those of the uncoated disks. Nitrogen incorporation into the films (a-C:N) further reduced the root-mean-square (RMS) roughness to 2.5 A for films prepared at a substrate bias of −120 V. Scratch resistance was improved when the DLC coatings were deposited at bias voltages greater than −90 V. However, the nitrogen introduction into the films deteriorated their scratch resistance. When the DLC films were subjected to an accelerated corrosive environment, pinhole density remarkably varied with the deposition conditions. The DLC films deposited with lower substrate biases and nitrogen incorporation resulted in poorer corrosion resistance. Internal stress, hydrogen content and graphitic cluster size of these films were correlated with data acquired by Raman analysis.

Deposition of ultra-thin diamond-like carbon protective coating on magnetic disks by electron cyclotron resonance plasma technique

Abstract Diamond-like carbon (DLC) films were prepared on Si and magnetic disks using an electron cyclotron resonance assisted microwave plasma chemical vapour deposition system with variable radio-frequency (rf) substrate bias. Surface morphology of disks deposited with 10 nm DLC was observed under atomic force microscopy (AFM), which revealed surfaces smoother than the uncoated disk. The root-mean-square roughness decreased with increasing substrate bias and reduced to 0.23 nm for film prepared at a bias of −150 V. Internal stress and hardness of the resulting films deposited on Si were investigated by curvature measurement and nano-indentation, respectively. Both internal stress and hardness increased with increasing ion energies. At a bias beyond −120 V, the film structure changed from diamond-like to graphite-like. There was also an improvement of scratch resistance of the DLC coatings deposited at bias >−90 V.

Deposition and properties of tetrahedral amorphous carbon films prepared on magnetic hard disks

The areal density of information stored on the hard disk has doubled every two years. This substantial increase in disk storage has resulted from the application of giant magnetoresistance heads, new thin film media, and better electronic recording channels. However, such an increase cannot be easily attained without reducing the separation between the magnetic read-write head and magnetic recording medium surfaces. This can be achieved by using a thinner protective overcoat. In this study, ultrathin tetrahedral amorphous carbon (ta-C) films were deposited on magnetic hard disks (CoCrTa/Cr/NiP/Al–Mg) by a magnetic filtered cathodic arc deposition under different substrate bias voltages. The obtained films exhibited smoother surfaces than the uncoated disks as indicated by the atomic force microscopic measurement. The Raman spectra acquired showed a single asymmetric Lorentzian curve shape. Tetrahedral amorphous carbon coatings were subjected to an accelerated corrosion test in vapors of concentrated hydro...

Effects at reactive ion etching of CVD diamond

Polycrystalline diamond chemical vapor deposition (CVD) films have been etched in both microwave and hot filament direct current plasmas. Hydrogen, hydrogen/argon and hydrogen/oxygen mixtures were used as reactive gases. Our results showed that bias-induced electron bombardment in hydrogen plasma did not enhance the etching yield. In contrast, bias-induced ion bombardment in hydrogen promoted the increase of etching yield through the graphitization of diamond surface. Introduction of argon to the reactant precursors increased the ion bombardment, which in turn, led to higher defect density and the formation of non-diamond phase. The oxygen addition into hydrogen gas reverted the etching mechanism. In addition, oxygen acted as a medium for material transport in the case of hot filament plasma.

Formation of cubic boron nitride films on nickel substrates

Abstract Cubic boron nitride (c-BN) films were synthesized by radiofrequency (r.f.) magnetron sputtering at a frequency of 13.56 MHz from an h-BN target. The substrate used was high-purity polycrystalline nickel foil (0.125 mm thick). The deposition process was carried out in an Ar–N 2 gas mixture (in a ratio of 5:1) at a total pressure of 10–15 mTorr. The ion flux impinging on the substrate was enhanced by an auxiliary electrode placed between the magnetron and the substrate. The main deposition parameters included substrate temperature and negative bias voltage. The films were characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). By the proper cleaning procedure of substrate and parameter optimization, stable and adherent films with a c-BN fraction above 90% have been achieved. The substrate surface state and energetic bombardment, including the ion flux and energy, were essential factors controlling the formation of sp 3 -bonded cubic phase during deposition. It was found that the application of a negative bias voltage higher than 150 V at substrate temperature of 400–500°C promotes the growth of c-BN phase. The present experiment showed that nickel may also be a promising substrate material for the preparation of high quality and well adherent c-BN films under physical vapor deposition (PVD) conditions.

Fracture resistance enhancement of diamond-like carbon/nitrogenated diamond-like carbon multilayer deposited by electron cyclotron resonance microwave plasma chemical vapor deposition

Diamond-like carbon (DLC), nitrogenated diamond-like carbon (CNx) and multilayered DLC/CNx films of 350 nm overall thickness were deposited on Si (100) substrates by using an electron cyclotron resonance microwave plasma chemical vapor deposition system. The deposited films were investigated for the fracture resistance using nanoindentation and nanoscratch methods in combination with scanning electron microscopy. In nanoindentation fracture tests, the film fracture was detected by the discontinuities in the load-displacement curves. The abrupt increase in the friction force between the tip and films during nanoscratch fracture tests was taken as a criterion for film fracture. Both the nanoindentation and nanoscratch fracture tests revealed that the DLC/CNx multilayer exhibited substantially higher critical load than that measured for either DLC or CNx films, though there was no obvious enhancement in the multilayer hardness and elastic modulus while the multilayer internal stress was between that of DLC a...