Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

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Diamond-like amorphous carbon

Diamond may be grown at low pressures where it is the metastable form of carbon. Recent advances in a wide variety of plasma and electrical discharge methods have led to dramatic increases in growth rates. All of these methods have certain aspects in common, namely, the presence of atomic hydrogen and the production of energetic carbon-containing fragments under conditions that support high mobilities on the diamond surface. Some understanding of the processes taking place during nucleation and growth of diamond has been achieved, but detailed molecular mechanisms are not yet known. Related research has led to the discovery of a new class of materials, the "diamondlike" phases. Vapor-grown diamond and diamondlike materials may have eventual applications in abrasives, tool coatings, bearing surfaces, electronics, optics, tribological surfaces, and corrosion protection.

https://science.sciencemag.org/content/sci/241/4868/913.full.pdf

Low-Pressure, Metastable Growth of Diamond and "Diamondlike" Phases

Chemical vapour deposition of coatings

The recent development in the field of superhard materials with Vickers hardness of ⩾40 GPa is reviewed. Two basic approaches are outlined including the intrinsic superhard materials, such as diamond, cubic boron nitride, C3N4, carbonitrides, etc. and extrinsic, nanostructured materials for which superhardness is achieved by an appropriate design of their microstructure. The theoretically predicted high hardness of C3N4 has not been experimentally documented so far. Ceramics made of cubic boron nitride prepared at high pressure and temperature find many applications whereas thin films prepared by activated deposition from the gas phase are still in the stage of fundamental development. The greatest progress has been achieved in the field of nanostructured materials including superlattices and nanocomposites where superhardness of ⩾50 GPa was reported for several systems. More recently, nc-TiN/SiNx nanocomposites with hardness of 105 GPa were prepared, reaching the hardness of diamond. The principles of de...

https://mediatum.ub.tum.de/doc/958917/file.pdf

The search for novel, superhard materials

Characterization of amorphous and nanocrystalline carbon films

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

Hydrogenated amorphous (a‐C:H) films were prepared by rf‐plasma deposition from benzene vapor. Complete optical absorption spectra from the UV to the IR (0.2–20.0 μm) have been measured. The optical gap depends linearly on hydrogen content and Eopt can be varied between 0.8 and 1.8 eV. For energies below Eopt the films are almost transparent and absorption is especially low in the 2–6‐μm region (e.g., α=15 cm−1 at λ=2.8 μm). Sharp C–H stretch absorption bands occur near 3.4 μm, giving insight into the microstructure of the films. A newly reported weak band at 3.03 μm is first evidence for C–C triple bonds (sp1 hybridization) in a‐C:H, where sp3 (single) and sp2 (double) C–C bonds dominate.

Hard carbon coatings with low optical absorption

Amorphous carbon films were prepared by radio frequency plasma deposition from benzene and fluorinated benzenes: C6H6−mFm with m=0–6. The films have been characterized spectroscopically. The infrared spectrum shows that besides hydrogen, fluorine is incorporated in the films. With increasing m the concentration of fluorine in the film increases while the amount of chemically bonded hydrogen decreases and vanishes for m>3. The properties of these hydrogenated fluorinated amorphous carbon films (a‐C:H,F) are qualitatively similar to those of hard carbon coatings (a‐C:H) prepared from benzene. However, the deposition rate has been found to rise significantly (up to 900 nm min−1) with increasing fluorine content, m, in the substituted benzene. Optical data and protective properties of the films are reported.

Amorphous carbon coatings prepared by high rate rf plasma deposition from fluorinated benzenes

Amorphous hydrogenated hard carbon (a-C:H) is a promising new optical coating material for passive infrared materials. It offers the rare combination of extreme hardness, chemical inertness, and optical transparency over a wide spectral range. We give an overview of the optical properties of rf-plasma deposited a-C:H coatings and compare them with vacuum-evaporated infrared coatings. For many applications, a-C:H solves the problem of a mechanically and chemically resistant 8 to 12 Am coating despite its moderate absorption in the 6 to 20 Am range. The tunability of the refractive index between 1.8 and 2.2 allows single layer coatings on Si and Ge with zero reflection. State-of-the-art applications, possible future developments, as well as remaining technological problems of a-C:H are discussed.

Role Of Hard Carbon In The Field Of Infrared Coating Materials

Hydrogenated amorphous carbon (a-C:H) thin films were prepared from hydrocarbons such as CH4, C2H4 and C6H6 in a capacitively coupled RF-discharge. a-C:H films which are electrically insulating (10 12 2Ωcm), transparent in the IR and very hard (on the order of 1400 kp/mm2 Knoop hardness) were deposited on glass, quartz, Si, Ge, SiC, GaAs and Gd3Ga5O12. This method allows large area (several inch diameter) homogeneous coatings and using C6H6 also gives high deposition rates on the order of 1000 A/min. The deposition process is described and the influence of various deposition parameters is discussed. It is shown that by means of the two parameters negative self bias and gas pressure coating properties such as refractive index can be easily tuned and controlled. The application of a-C:H as a single layer antireflection coating on Ge for 10.6 [im is demonstrated; the reflection at 10.6 pri is less than 0.2%.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A. Bubenzer

Papers

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

Hard carbon coatings with low optical absorption

Amorphous carbon coatings prepared by high rate rf plasma deposition from fluorinated benzenes

Role Of Hard Carbon In The Field Of Infrared Coating Materials

RF-Plasma Deposition Of Hydrogenated Hard Carbon Thin Films