The deposition of amorphous hydrogenated hard carbon (a–C:H) thin films from benzene vapor in a rf plasma is described. a–C:H was deposited on glass, quartz, Si, Ge, and GaAs. Negative self‐bias VB and gas pressure P are shown to be the two significant parameters for an accurate control of the deposition process. The dependence of growth rate and deposition temperature on VB and P was determined; this gives an empirical relation for the average energy E of the ions forming the thin films. Refractive index (1.85–2.20 in the IR), optical gap (0.8–1.8 eV) and density (1.5–1.8 g/cm3) of a–C:H was measured. The optical gap varies linearly with the content of bonded hydrogen in the films. The density of a–C:H is proportional to the average ion energy E. We demonstrate the application of a–C:H as antireflective coating on Ge for 10.6 μm (reflection <0.2% at 10.6 μm) and as terminating layer of an optical multilayer stack.

rf‐plasma deposited amorphous hydrogenated hard carbon thin films: Preparation, properties, and applications

Diamond-like carbon (DLC) films combine several excellent properties like high hardness, low friction coefficients and chemical inertness. The DLC coating material can be further classified in two main groups, the hydrogenated amorphous carbon (a-C:H, ta-C:H) and the hydrogen free amorphous carbon (a-C, ta-C). By adding other elements like metals (a-C:H:Me) or non-metal elements like silicon, oxygen, fluorine or others (a-C:H:X), several modifications of the properties can be adjusted according to application requirements. First reports on hard amorphous carbon films were published in the 1950s and about 20 years later there began worldwide intensive research activities on DLC. In the following years the number of publications increased continuously and the importance for industrial applications became more and more evident. Several deposition techniques were applied to prepare a-C:H, ta-C, metal containing a-C:H:Me and non-metal containing a-C:H:X coatings. In parallel the structure and deposition mechanisms of DLC coatings were extensively studied. An essential obstacle for a broad industrial application was the high compressive stress level in a-C:H films causing delamination and limiting the film thicknesses. With metal based intermediate layer systems most adhesion problems could be solved satisfactorily and thus from the mid-1990s the pre-conditions for a broad application especially in the automotive industry were given. With modified a-C:H:X and a-C:X coatings a considerable friction reduction or surface energy adjustments could be achieved.

History of diamond-like carbon films — From first experiments to worldwide applications

The real and imaginary parts, n and k, of the complex index of refraction of a hydrogenated amorphous carbon (a‐C:H) film have been determined for photon energies between 145 and 49 eV from measurements of reflectance R and transmittance T Both n and k, and consequently e1 and e2 (the real and imaginary parts of the dielectric constant), show a considerable variation with subsequent annealing of the a‐C:H film up to Ta=750 °C, with the most rapid changes occurring for Ta=450 °C and above The optical gap Eopt is observed to decrease from 22 eV to 0 as the film is annealed, signaling the development of graphitic short range order in the film Using an effective medium approximation to model the optical properties of the film, we find that the as‐deposited film contains amorphous diamond‐like, graphitic, and polymeric components With annealing, the amorphous diamond‐like and polymeric components decrease, the amorphous graphitic component grows, and a void component appears We discuss the local order 

Optical constants of a hydrogenated amorphous carbon film

Preparation and properties of hard i-C and i-BN coatings

Thin C:N films were prepared by rf diode sputtering of a graphite target in a mixed argon/nitrogen plasma. We have observed a systematic variation of the properties of these C:N films with an increase in the nitrogen partial pressure. XPS, AES, and TEM studies show that nitrogen will stabilize the diamond sp3 bonding. From XPS studies, we found that the density of our C:N films is increased from 1.37 × 1023 atoms/cm3 to 1.63 × 1023 atoms/cm3 using a 100% nitrogen plasma. The energy gap of our nitrogen carbon also shows an increase from 1.1 eV to 1.4 eV using a 100% nitrogen plasma. The mechanical properties also are shown to be enhanced for certain applications. By using the same method, we can also show that it can produce 100% amorphous C:N films which are more diamond-like as compared with other methods.

S Towta

Papers

Properties and coating rates of diamond-like carbon films produced by R.F. glow discharge of hydrocarbon gases