Diamond-like hydrocarbon

In the present paper, the term DLC refers to amorphous, pure carbon coatings with diamond like properties while DLHC indicates the amorphous diamond-like hydrocarbon form. Both types contain a significant amount of sp carbon sites. There is little or no hydrogen present in the former type while the latter type contains 17 to 60 atomic percent of hydrogen. 

In the course of the research into the synthesis of diamond under metastable conditions, a new class of materials, diamond-hke carbon and hydrocarbon phases, have been discovered. The diamond-like hydrocarbons (aC H) are generated by the RF self-bias method, a technique derived from RF sputtering, developed by L. Holland [61,62]. The molecular ions, derived from the particular hydrocarbon used in the plasma, disintegrate upon colliding with the substrate surface resulting in the formation of diamond-like hydrocarbon films [63]. The main structural feature of diamond-like hydrocarbons is the presence of both sp - and sp -carbon. Solid-state NMR-investigations revealed that the material contains sp -carbon atoms of the form -C-H or H-C-H [6]. 

Diamondoids can also be seen as cage-like saturated hydrocarbon molecules that possess a rigid carbon framework of diamond-like sp -bonded carbon atoms. Lower-order... 

The adsorption of hydrocarbon molecules on Si surfaces is an interesting topic of study under various viewpoints. For example, a thin hydrocarbon film coating Si may be applied as a low dielectric in microelectronics and may passivate the surface if covalent bonds are formed between Si atoms and the adsorbate species. Further, unsaturated hydrocarbons play an important role as precursor species for chemical vapor deposition (CVD) of diamond - like films on the Si surface, and of silicon carbide (SiC). 

Many new phases of carbon have been discovered as an offshoot of attempts of artificial synthesis of diamond. Among these, a class of amorphous carbon and hydrocarbon phases exhibits properties close to those of diamond. These diamond-like phases are therefore considered to be promising technological materials. 

Because diamond like materials contain a mixture of both sp and sp sites and hydrogen, they can therefore be considered to be an intermediate between diamond, graphite and polymeric hydrocarbon. The mixed bonding means that the properties of diamond like materials are generally inferior to those of diamond. However, these materials have certain advantages that make them competitive to diamond coatings in a number of applications. These advantages are listed below. 

In ion assisted deposition, there are two methods one is decomposition of hydrocarbon oil using energetic ions and the other is evaporation of graphite with eoncurrent bombardment of the growing film with energetic ions. With these methods, diamond like films with reasonably good properties can be deposited over large areas (1 m ) at low temperatures (< 140°C). 

This termed is frequently deployed in the literature to describe ill-defined and unwelcome substances deposited during hydrocarbon reactions on metals, leading to loss of catalytic activity. The work on hydrocarbon adsorption which we have reviewed has shown that, in almost every case, adsorbed species when heated decompose first to Ci species (e.g. =CH2 or H), and that these then lose their hydrogen atoms to form carbon atoms, which on Ir( 100) have been shown by LEED (and DFT) to reside in fourfold sites in a (2 x 2) overlayer. Further heating may lead to their polymerisation to graphite or to a diamond-like structure. Carbon... 

The Lewis-acid-catalysed rearrangement of polycyclic hydrocarbons C H2 4 c (x = 1,2,3,...) into their thermodynamically more stable diamond-like isomers is usually referred to as the adamantane rearrangement . The archetype of this unique isomerization is the AlCl3-catalyzed transformation of en /o-tricyclo[5.2.1.0 ]decane (11) (tetrahydrodicyclopentadiene) into adamantane (Ad-H) (Scheme 4), which was first discovered by Schleyer " more than 30 years ago. This process is thermodynamically controlled and it involves carbenium ion intermediates which rearrange via successive 1,2-C bond and 1,3 hydride shifts. Numerous theoretical and experimental investigations have established the most direct thermodynamically feasible pathway (exo-11 -> 12 13 -> 14 -> 15 Ad-H) for the isomerization of endo-11 to adamantane. 

While metallic solids are deposited by reactions that involve metallic intermediates and ionic solids result from ionic reactions, the solids with covalent bonds grow by means of radical surface reactions. Examples of such materials are diamond, amorphous diamond-like carbon, silicon, and silicon carbide. Diamond and diamond-like carbon can be deposited if hydrocarbon and hydrogen radicals are available at the growing surface. Silicon carbide and boron nitride growth has also been modeled in terms of radical reactions at the surface. 

As for the first topic, methane and other light hydrocarbon plasmas are of great interest in industrial applications, in particular in the chemical vapor deposition ptrocesses. Amorphous carbon and diamond-like thin films, suitable for mechanical and electronic applications can be prepared using low pressure discharges of hydrocarbon gases. The research in this field is mainly devoted to the understanding of the nature of the film growing mechanism but in spite of intense experimental and theoretical work it is not yet fully understood which species are responsible for the deposition process. 

New data concerning the interaction of ions and hydrocarbon radicals allow to have a quite complete mapping of the relevant reaction rates in an Ar/CH4 plasma by now and it is possible to investigate the effect of the chemical kinetics in such a system and eventually to identify the gaseous precursor of the chemical species incorporated in the deposited film. We have modeled the gas-phase chemistry of a typical radio frequency CH4/ Ar plasma used for the deposition of diamond and diamond-like carbon films, with the aim of understanding the effects of the chemical kinetics of argon ions and metastables. 

Hydrocarbons Fluorocarbons Acetone, etc. Diamond-like carbon Polycrystalline diamond... 

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