Diamond-like carbon: state of the art

Diamond-like carbon (DLC) films have been deposited onto mirror-finish silicon surfaces using three different techniques: (a) RF glow discharge from methane, (b) DC magnetron sputtering from a graphite target, with substrate RF bias; and (c) an ion beam generated from a cathodic arc discharge. Nanoscale atomic force microscopy (AFM) (tapping mode) surface roughness analysis has been carried out on as-deposited and post-deposition treated DLC films. It was found that, in terms of the effect on surface roughness, there is a threshold value of the ion impingement energy. Below this ion energy, which has a value of approximately 50 eV for each of the three techniques studied, the DLC surface is very rough on a nanoscale, while above it the roughness drops sharply. This threshold is close to previously reported atomic displacement threshold energies for graphite and diamond. These observations have been explained in terms of the tendency for surface diffusion to generate sp 2 -rich surface clusters which roughen the surface, whereas high impingement energies lead to ion implantation, and hence less efficient surface diffusion, and to preferential sputter removal of protruding regions, which also favours low roughness. Observed effects of substrate temperature and exposure to atomic hydrogen have also been explained in terms of these mechanisms of roughening and smoothing.

Surface roughness of diamond-like carbon films prepared using various techniques

This article discusses the current status of the rapidly evolving area of field emitter arrays. The development of field emitter arrays is reviewed in the context of major applications of the devices, such as flat panel displays and cathodes for microwave power amplifiers. State-of-the art technologies for fabrication of field emitter arrays as well as recently reported results on electrical performance of the devices are reviewed. Remaining challenges in the major applications in conjunction with some of the potential pathways to device improvement are discussed.

Recent progress in field emitter array development for high performance applications

The application of diamond like carbon (DLC) coatings in tribological applications, the range of deposition methods employed and techniques for characterising the structure and properties of the films produced are reviewed. Thus far, DLC coatings have found broad industrial application, particularly in optical and electronic areas. In tribological applications, DLC coatings are used successfully as coatings for ball bearings where they decrease the friction coefficient between the ball and race; in shaving applications where they increase the life of razor blades in wet shaving applications; and increasingly in automotive applications such as racing engines and standard production vehicles. The structure and mechanical properties of DLC coatings are dependent on the deposition method and the incorporation of additional elements such as nitrogen, hydrogen, silicon and metal dopants. These additional elements control the hardness of the resultant film, the level of residual stress and the tribologic...

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Diamond like carbon coatings for tribology: production techniques, characterisation methods and applications

Quantitative assessment of surface roughness as measured by AFM: application to polished human dentin

The surface morphologies of diamondlike carbon (DLC) films with atomic force microscopy (AFM) are reported. The films were prepared by laser ablation with tuning power densities range from 3×108 to 1×1010 W/cm2. For power densities above 2×109 W/cm2, the films reveal smooth surfaces with uniform shapes of nanometer sized carbon clusters (sp3 bonding) and retain the surface roughness of the silicon substrate. For power densities below that, graphitic films are formed, and the surface roughness increases with decreasing laser intensity. The present AFM studies confirm that there exists a clear correlation between surface morphologies and the degree of diamondlike qualities.

Surface morphology of laser deposited diamondlike films by atomic force microscopy imaging

Diamond like carbon (DLC) films are deposited on silicon substrates by the pulsed laser ablation technique. The surface morphology of the DLC film, studied by atomic force microscopy (AFM), shows a strong dependence on the power densities of the laser pulses. The degree of diamond-like properties of the films, which were studied using Raman spectroscopy and Auger electron spectroscopy, shows close correlation with the surface morphology. Electron emission characteristics of the films are measured and their correlations with the surface morphology and bonding structure are investigated. Variation of these structural and electron emission characteristics of the films on the deposition conditions such as substrate temperature and flow rate of atomic hydrogen during the process of laser ablation is also studied.

Electron emission characteristics of diamond like carbon films deposited by laser ablation technique

We have investigated field electron emission properties of diamondlike carbon films deposited by a laser ablation method. Emission properties of diamondlike carbon films show a strong correlation with surface roughness of the films which varies as a function of laser power densities. The threshold emission voltage of films turns out to be critically dependent on the surface morphology. Measurement of electrical resistivity shows that the density of states near the Fermi level is strongly localized. The major carrier transport occurs not by the activation to the conduction band but by hopping between the localized defect states near the Fermi level. The existence of localized defect bands in the intrinsic gap can also make it possible to emit electrons with a relatively small activation energy.

Field electron emission of diamondlike carbon films deposited by a laser ablation method

We have successfully introduced nitrogen into diamond-like-carbon films by evaporating carbon and nitrogen ions simultaneously from a carbon target dipped in hexamethylenetetramine solution with a laser. Nitrogen content in the film was changed by varying the molar concentration of hexamethylenetetramine solution. This method needs no vacuum arc and provides a simple effective way of nitrogen addition. The resistivity measured as a function of nitrogen content decreases up to a certain nitrogen content and then increases at higher nitrogen content, suggesting that nitrogen act as a true dopant. Atomic force microscopy and Raman spectroscopy studies also suggest that no graphitization whatsoever occurs in the films after nitrogen addition. Although no structural change in the films was found with nitrogen addition, the emission threshold field decreased by ∼4–5 V/μm depending on nitrogen content. The nitrogen-added diamond-like-carbon film was found to have a typical threshold field of ∼10 V/μm at optimal composition.

Properties of nitrogen-doped diamond-like-carbon films prepared by a laser ablation

We have investigated field electron emission properties of diamond-like-carbon films deposited by a laser ablation method. Emission properties of diamond like carbon films show a strong correlation with sut$ace roughness of the films which varies as a function of laser power densities. The surface morphology tums out to be critically dependent on the threshold emission voltage of the films. Measurement of electrical resistivity shows that the density of states near the Fermi level is strongly localized. The major carrier transport occurs not by the activation to the conduction band hut by hopping between the localized defect states near the Fermi level. The existence of localized defect bands in the intrinsic gap can also make it possible to emit electrons with a relatively small activation energy.

http://ieeexplore.ieee.org/iel3/4954/13634/00627643.pdf

Jin Seung Kim

Papers

Surface morphology of laser deposited diamondlike films by atomic force microscopy imaging

Electron emission characteristics of diamond like carbon films deposited by laser ablation technique

Field electron emission of diamondlike carbon films deposited by a laser ablation method

Properties of nitrogen-doped diamond-like-carbon films prepared by a laser ablation

Field electron emission of diamond-like-carbon films deposited by a laser ablation method