A preliminary study of the adhesion of polymers to diamond substrates was conducted by examining the wetting characteristics of coupling agents to diamond. The contact angle between several commercial liquid coupling agents and a CVD diamond surface was measured. A silane, Z-6026, was found to wet the diamond surface. Several other coupling agents, including a titanate and an organometallic blend, wet the diamond surface significantly better than most of the other materials in this survey. It was found that water did not wet the diamond.

Diamond-like carbon (DLC) films have been deposited on silicon using two deposition techniques. Both deposition techniques used acetylene (C2H2) plasmas as the carbon/hydrogen source. One technique, that is relatively well known, employs an rf-plasma with an associated self-bias on the substrate. DLC films have also been deposited using a pulsed-bias method. Coatings of various thickness have been deposited using both deposition methods, and various combinations of gas pressure and bias. Coating characteristics, such as composition, density, and sp3 content, of selected films will be presented. For each deposition technique, the correlation between coating characteristics, mechanical properties and tribological behavior is presented.

Low-friction/ultralow-wear coatings allow “surface engineering” for improved performance and durability, and enable use of new light weight or low cost materials. The accepted correlation of wear resistance with hardness suggests use of ceramic carbides and nitrides, with diamond being the ultimate anti-wear coating. While any of these may be deposited by chemical vapor deposition, the high cost (due to low deposition rates and high capital costs) and (usually) high deposition temperatures makes CVD coating impractical for cost-sensitive automotive applications. While rarely as hard as their crystalline counterparts, hard amorphous films exhibit similar (and occasionally superior) tribological properties and may be deposited on virtually any material at low cost. The highly nonequilibrium deposition process - conformal plasma reactive ion plating (CP-RIP) - allows tailoring of film properties and exploration of completely new compositions with no crystalline counterparts. Factors controlling the mechanical and optical properties of amorphous hard coatings, and recent progress in their application will be reviewed.

Amorphous carbon films approximately 20nm thick are used throughout the computer industry as protective coatings on magnetic storage disks. The structure and function of this family of materials at the atomic level is poorly understood. Recently, we simulated the growth of a:C and a:CH films 1 to 5 nm thick using Brenner's bond-order potential model with added torsional energy terms. The microstructure shows a propensity towards graphitic structures at low deposition energy (<1eV) and towards higher density and diamond-like structures at higher deposition energy (>20eV). In this paper we present simulations of the evolution of this microstructure for the dense 20eV films during a simulated indentation by a hard diamond tip. We also simulate sliding the tip across the surface to study dynamical processes like friction, energy transport and microstructure evolution during sliding.

We describe correlations between the atomic-scale structure and the global electronic and vibrational properties in amorphous carbon versus mass density. The model structures have been generated by applying different annealing regimes using a density-functional based molecular-dynamics (DF-MD) method. The stability of the amorphous modifications and the calculated vibrational density of states (VDOS) are strongly affected by the density and the annealing sequences, altering the chemical composition, the sp/sp2/sp3-clustering, the structure and related physical properties. A mass density of 3.0 g/cm3 is confirmed as a magic density favoring the formation of most stable a-C modifications having lowest defect densities and maximum band gap. In analyzing the vibrational spectra and the localization of modes in comparison with crystalline diamond and graphite, we identify the spectral signatures for chemically different bonded species and defects, that may be used for comparison with related Neutron-, Raman- and IR- work.

Nanoindentation and nanoscratching experiments have been performed to assess the mechanical properties of several carbon thin films with potential application as wear resistant coatings for magnetic disks. These include three hydrogenated-carbon films prepared by sputter deposition in a H2/Ar gas mixture (hydrogen contents of 20, 34, and 40 atomic %) and a pure carbon film prepared by cathodic-arc plasma techniques. Each film was deposited on a silicon substrate to thickness of about 300 nm. The hardness and elastic modulus were measured using nanoindentation methods, and ultra-low load scratch tests were used to assess the scratch resistance of the films and measure friction coefficients. The results show that the hardness, elastic modulus, and scratch resistance of the 20% and 34% hydrogenated films are significantly greater than the 40% film, thereby showing that there is a limit to the amount of hydrogen producing beneficial effects. The cathodic-arc film, with a hardness of greater than 59 GPa, is considerably harder than any of the hydrogenated films and has a superior scratch resistance.

Cathodic arc deposition combined with macroparticle filtering of the plasma is an efficient and versatile method for the deposition of amorphous hard carbon films of high quality. The film properties can be tailored over a broad range by varying the energy of the carbon ions incident upon the substrate and upon the growing film by applying a pulsed bias technique. By varying the bias voltage during the deposition process specific properties of the interface, bulk film and top surface layer can be obtained. We report on nanoindentation and transmission electron microscopy studies as well as stress measurements of cathodic-arc amorphous hard carbon films deposited with varied bias voltage. The investigations were performed on multilayers consisting of alternating hard and soft amorphous carbon.

We compare the microstructure of highly tetrahedrally-coordinated-amorphous carbon (atC) films prepared by pulsed laser deposition (PLD), measured using both small angle x-ray scattering (SAXS) and x-ray reflectivity, with other physical properties such as film stress and electrical resistivity. These properties are controlled by the film growth conditions and film thicknesses. Films prepared under vacuum conditions exhibit a shift in the measured mass density, as a function of laser energy density. The density for films approximately 600Å thick approach that of crystalline diamond. The measured densities for thicker, approximately 1000Å films, exhibit a smaller shift, and a lower density value. This shift correlates to observed changes in film stress and electrical resistivity. The small angle signal of the reflectivity spectra suggests the presence of layering, or in-plane density variations or a combination of both within the films.

Amorphous carbon films have been deposited on various grounded substrates by direct current (DC) magnetron sputtering from a graphite target in an argon discharge. The argon pressure and sputtering power density were fixed at 0.25 Pa and 2.65 W cm−2, respectively. The substrate temperature was varied from 50 to 350°C. The hydrogen content determined by ERDA and the electrical resistivity of films were found to be dependent on the base pressure in the deposition chamber and substrate temperature. The mass density of films evaluated from RBS data and compressive residual stresses in the films decreased with increasing substrate temperature from 2.2 to 1.4 g cm−3 and - 0.6 to - 0.2 GPa, respectively. The friction coefficient and wear rate of about 2-μm-thick carbon films deposited on polished stainless steel disks were determined by alumina ball-on-disk tribological measurements conducted in dry air under a load of 4.9 N with a sliding velocity of 10 m min−1 for 105 cycles. The tribological performance of carbon-coated disks are correlated with the deposition temperature and physical characteristics of carbon films.