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

Raman microspectroscopy of soot and related carbonaceous materials: Spectral analysis and structural information

As the technology for diamond film preparation by plasma-assisted CVD and related procedures has advanced, Raman spectroscopy has emerged as one of the principal characterization tools for diamond materials. Cubic diamond has a single Raman-active first order phonon mode at the center of the Brillouin zone. The presence of sharp Raman lines allows cubic diamond to be recognized against a background of graphitic carbon and also to characterize the graphitic carbon. Small shifts in the band wavenumber have been related to the stress state of deposited films. The effect is most noticeable in diamond films deposited on hard substrates such as alumina or carbides. The Raman line width varies with mode of preparation of the diamond and has been related to degree of structural order. The Raman spectrum of hexagonal diamond (lonsdaleite) is distinct from that of the cubic diamond and allows it to be recognized.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400004441

Characterization of diamond films by Raman spectroscopy

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

The origin and interpretation of the Raman features of amorphous (hydrogenated) carbonfilmsdeposited at room temperature in the region of 1000–1700 cm−1 is discussed in this paper. Possible interpretations of the linewidths, positions of the ‘‘G’’ graphite peak and ‘‘D’’ disordered peak, and their intensity ratios are examined using results obtained from magnetron sputtered and magnetic field enhanced plasmadepositedfilms. It is shown that even small ‘‘clusters’’ of condensed benzene rings (cluster size below 20 A) in carbonfilms can explain the observed Raman scattering. Besides the care that should be taken in the correct interpretation of Raman results, the utility of Raman scattering in obtaining an estimate of cluster sizes in amorphous (hydrogenated) carbonfilms is discussed. Carbonfilms prepared by magnetron sputtering show two additional Raman features at 1180 and 1490 cm−1 in addition to the G and D peaks. It is shown that a correlation exists between the 1180 cm−1 peak and the sp 3 content in the films.

Raman spectroscopy on amorphous carbon films

Structure and morphology of polycrystalline diamond films prepared by chemical vapor deposition (CVD) have been studied using x‐ray texture analysis, angle‐resolved optical reflection, and scanning electron microscopy. The films under investigation exhibit a pronounced 110 fiber texture, i.e., a preferential alignment of {110} planes perpendicular to the growth direction. By thinning a 180‐μm‐thick CVD diamond film in an oxygen discharge the dependence of the degree of 110 texture on the film thickness has been investigated. It was found that the crystals formed at the beginning of the film growth are randomly oriented, and that a preferential orientation of {110} planes develops with increasing film thickness. Computer simulations show that this behavior can be explained by evolutionary selection, i.e., competing growth of differently oriented crystals, which implies that 〈110〉 is the direction of fastest growth. In addition, angle‐resolved optical reflection and scanning electron micrographs show that t...

Texture formation in polycrystalline diamond films

Resonant Raman scattering has been used to study amorphous carbon and polycrystalline diamond films. The incident photon energies were varied over the range 2.2--4.8 eV. In hydrogenated amorphous carbon films containing both ${\mathrm{sp}}^{3}$- and ${\mathrm{sp}}^{2}$-bonded carbon, a high-frequency shift is observed for the main Raman peak with increasing photon energies up to 3.5 eV. This shift is interpreted in terms of scattering from \ensuremath{\pi}-bonded carbon clusters which is resonantly enhanced for photon energies approaching the \ensuremath{\pi}-${\ensuremath{\pi}}^{\mathrm{*}}$ resonance of ${\mathrm{sp}}^{2}$-bonded carbon. In polycrystalline diamond films excitation with photon energies \ensuremath{\ge}3.0 eV enhances the Raman signal from the ${\mathrm{sp}}^{3}$-bonded diamond phase relative to the scattering by ${\mathrm{sp}}^{2}$-bonded carbon and with respect to the underlying broadband luminescence. The Raman band arising from scattering by ${\mathrm{sp}}^{2}$-bonded carbon shows a high-frequency shift with increasing photon energy for energies \ensuremath{\ge}3.0 eV. Possible models for the structure of this ${\mathrm{sp}}^{2}$-bonded carbon phase are discussed on the basis of the present Raman data.

Resonant Raman scattering of amorphous carbon and polycrystalline diamond films.

Plasma Deposition, Properties and Structure of Amorphous Hydrogenated Carbon Films

Hydrogenated amorphous carbon (a‐C:H) films, deposited onto negatively biased substrates in a 13.56‐MHz hydrocarbon glow discharge system, have been investigated by mass spectroscopic thermal effusion measurements. Depending on the bias voltage UB as the most important deposition parameter, hydrocarbons and/or H2 molecules are desorbed at threshold temperatures between 300 and 600 °C. The threshold temperature increases with increasing bias voltage while the mass of the desorbed molecules decreases. a‐C:H films deposited at low bias release H2, CH4, and higher hydrocarbons whereas from hard a‐C:H films deposited at UB≳500 V, only H2 is released. Using double‐layer a‐C:H/a‐C:D films, it is shown that H2 and CH4 molecules are formed in the volume of the film followed by molecular diffusion through the a‐C:H network. For high‐bias voltages (UB≳500 V), the reduced pore size of the strongly crosslinked a‐C:H network is shown to prevent diffusion of hydrocarbon molecules, while the films are still permeable for...

Thermal gas effusion from hydrogenated amorphous carbon films

We report on a Raman spectroscopic study of polycrystalline diamond films using a wide range of incident photon energies (1.16–4.82 eV). The scattering intensity of amorphous sp2‐bonded carbon is found to vary considerably as a function of the incident photon energy as compared to the strength of the 1332 cm−1 Raman line from sp3‐bonded diamond. There is also a frequency downshift of the apparent peak position for scattering from the sp2‐bonded carbon with decreasing photon energy. Excitation in the infrared range is shown to give a high sensitivity to scattering from amorphous sp2‐bonded carbon whereas ultraviolet excitation enhances the 1332 cm−1 signal from crystalline diamond considerably even in nanocrystalline films.

Ch. Wild

Papers

Texture formation in polycrystalline diamond films

Resonant Raman scattering of amorphous carbon and polycrystalline diamond films.

Plasma Deposition, Properties and Structure of Amorphous Hydrogenated Carbon Films

Thermal gas effusion from hydrogenated amorphous carbon films

Resonance effects in Raman scattering from polycrystalline diamond films