D. R. Jander

Amorphic diamond films produced by a laser plasma source

Recently, attention has been focused upon laser plasma sources of thin‐film diamond. These depend upon laser‐ignited discharges in which intense pulsed currents flow through the small volume of carbon plasma ablated from graphite feedstock by a focused laser beam. The materials produced in this way generally resemble the hard amorphic films deposited by ion beams. This paper reports a detailed characterization of these films which we call amorphic diamond. The combination of an optical band gap of 1.0 eV with a grain size of 100–200 A places this material far outside the range of possibilities available to the model of graphitic islands. A structure of very fine grained diamond would more readily explain the hardness of 13 GPa determined in the absence of any measurable fraction of hydrogen. Such amorphic diamond films have been grown uniformly on 100‐cm2 areas at ambient room temperatures with no seeding or abrasion of the substrate.

Laser plasma source of amorphic diamond

Amorphic diamond films characterized by a high percentage of sp3 bonds have been prepared in an UHV environment with a laser plasma source of carbon ions. Peak power densities in excess of 1011 W/cm2 were found necessary to produce films at growth rates of 0.5 μm/h over areas of 20 cm2 having optical quality sufficient to show bright interference colors.

MICROSTRUCTURE OF AMORPHIC DIAMOND FILMS

It has been previously reported that layers of amorphic diamond can be grown in a UHV environment free from hydrogen with a laser plasma source. Some advantages are offered by this technique which produces films that adhere more readily to materials for which there are important applications. Theory has recently suggested a structure for amorphic diamond that comprises nodules of carbon atoms linked by sp3 bonds in a matrix of other polytypes and the purpose of this article is to communicate strong evidence in support of that hypothesis. Extensive examinations of a variety of films with a scanning tunneling microscope show a clearly prevalent structure composed of dense nodules. Grain size is about 1000 A and the diamond character is attested by the agreement of morphology, high density, optical properties, soft x‐ray spectroscopy, hardness, and lack of appreciable hydrogen. Measurements agree in supporting a fraction of about 75% diamond contents. The principal conclusion is that this material prepared w...

Adhesion and mechanical properties of amorphic diamond films prepared by a laser plasma discharge source

Amorphic diamond films can be grown in an ultrahigh vacuum environment free from hydrogen with a laser plasma discharge source. This technique produces films that adhere more readily to materials for which there are important applications as protective coatings. In this work adhesion and mechanical properties of amorphic diamond films have been examined. A beam bending method has been used to measure the internal stress and a relatively low value of compressive stress was found. The dependence of stress on the laser intensities at the graphite ablation target has been studied. Analyses of these films on silicon, SiO2, ZnS, and TiAl6V4 by Rutherford backscattering spectrometry show significant interfacial layers with compositions of SiC, C0.5SiO2, C2.5ZnS, and C0.62Ti0.35Al0.05V0.02, respectively. Adhesion properties on ZnS and other substrates have also been examined for harsh environments. The mechanical properties of hardness, Young’s modulus, and stiffness have been obtained with a nanoindentation tech...

The bonding of protective films of amorphic diamond to titanium

Films of amorphic diamond can be deposited from laser plasma ions without the use of catalysts such as hydrogen or fluorine. Prepared without columnar patterns of growth, the layers of this material have been reported to have ‘‘bulk’’ values of mechanical properties that have suggested their usage as protective coatings for metals. Described here is a study of the bonding and properties realized in one such example, the deposition of amorphic diamond on titanium. Measurements with Rutherford backscattering spectrometry and transmission electron microscopy showed that the diamond coatings deposited from laser plasmas were chemically bonded to Ti substrates in 100–200‐A‐thick interfacial layers containing some crystalline precipitates of TiC. Resistance to wear was estimated with a modified sand blaster and in all cases the coating was worn away without any rupture or deterioration of the bonding layer. Such wear was greatly reduced and lifetimes of the coated samples were increased by a factor of better th...

Microstructural analyses of amorphic diamond, i‐C, and amorphous carbon

Recent experiments have identified the microstructure of amorphic diamond with a model of packed nodules of amorphous diamond expected theoretically. However, this success has left in doubt the relationship of amorphic diamond to other noncrystalline forms of carbon. This work reports the comparative examinations of the microstructures of samples of amorphic diamond, i‐C, and amorphous carbon. Four distinct morphologies were found that correlated closely with the energy densities used in preparing the different materials.

Mass flow in laser-plasma deposition of carbon under oblique angles of incidence

The angular distribution of the mass flow in carbon laser plasmas, generated from graphite targets at laser power densities around 1011 W/cm2 and 1064 nm, was studied. Under oblique angles of incidence the mass flow is not perpendicular to the target surface but rather symmetrical around the bisecting angle between the laser beam and the surface normal. For all angles, however, a cos4ϑ-pattern is observed. Compared to normal incidence the mass flow is weaker by about a factor of 2 to 3 for 30° and 50° angle of incidence. The dependence of film quality on deposition angle with regard to the symmetry axis of the plume is demonstrated.

Preparation an study of laser plasma diamond

Abstract Films of diamond-like material can be deposited with a laser plasma source of carbon ions in an ultrahigh vacuum environment without involving hydrogen in the growth mechanism. These films are distinguished by transparency at visible wavelengths which is a result of a high percentage of sp3 bonds. They resemble materials first quenched from ion beams at very slow deposition rates. In our method an Nd:YAG laser was focused on a graphite feedstock in an ultrahigh vacuum chamber at intensities in excess of 5 × 1011 W cm-2. A high current discharge confined to the path of the laser-ignited plasma provided further heat and aided processing of the ion flux. At a laser repetition rate of 10 Hz, a deposition rate of 0.5 μm h-1 over a 100 cm2 area was attainable with no measurable substrate heating. The substrates required no special preparation or seeding and materials including silicon, fused silica, glass, gold, copper, germanium, InP, ZnS, and polycarbonate and polyimide plastics were readily coated. Complex shapes could be accommodated and spheres of 440C stainless steel were covered successfully. Over 1000 samples were prepared to a variety of specifications with thickness reaching 5 μm and hardness exceeding 37 GPa.

Mechanical and adhesion properties of amorphic diamond films

Abstract Films of amorphic diamond can be deposited with a laser plasma source of carbon ions in an ultrahigh vacuum environment without involving hydrogen in the growth mechanism. This technique produces films that adhere more readily to materials for which there are important applications such as protective coatings. In this study mechanical properties of amorphic diamond films were examined. The hardness and Youngs modulus were obtained using a nanoindentation technique. Analyses of these films on silicon and ZnS by Rutherford backscattering spectrometry (RBS) show significant interfacial layers. The adhesion properties were also studied under harsh environmental conditions.

Textured structure of diamond-like carbon prepared without hydrogen

Abstract Layers of diamond-like material can be grown in a ultrahigh vacuum environment free from hydrogen with a laser plasma source. Substrates require no special preparation or seeding and materials including silicon, fused silica, glass, gold, copper, germanium, InP, ZnS, and polycarbonate and polyimide plastics are readily coated. Generally, our films resemble materials first quenched from ion beams at very slow deposition rates. Although a crystalline structure had been previously inferred, the data were not compelling and this material is generally viewed as a dehydrogenated version of amorphous diamond-like carbon. The purpose of this report is to communicate strong evidence that our diamond-like material prepared with a laser plasma source in the absence of hydrogen is composed of tightly packed diamond clusters. Extensive examinations of a variety of films with scanning tunneling and scanning electron microscopies show the clear prevalence of the structure recently predicted by Angus in which sp 3 clusters are bonded together with other carbon polytypes. Grain size is about 1000 A and the diamond character is attested by the agreement of morphology, density, optical properties and soft X-ray spectroscopy. Measurements agree on supporting a fraction of about 75% diamond bonding.