E.N. Loubnin

D.c. arc plasma deposition of smooth nanocrystalline diamond films

We report on chemical vapour deposition growth of nanocrystalline (grain size 30–50 nm) diamond films of 100 nm to 2 μm thickness in methane-rich mixtures. A d.c. arc discharge in CH4H2Ar gas mixtures with a methane percentage CH4(CH4 + H2) varied from 10% to 100% was used for diamond deposition on Si substrates seeded with ultrafine (5 nm) diamond particles. The films obtained were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray excited Auger electron spectroscopy. Remarkably well-crystallized diamond films were produced even in hydrogen-free gas mixtures. Raman spectra confirmed the nanocrystalline structure of all the films examined. The film hardness measured with a nanoindenter was in the range 70–85 GPa typical for diamond, the highest values corresponding to 100% methane content. The films were very smooth with surface roughness Ra < 20 nm. The essential improvement in surface smoothness was obtained by means of laser-induced disintegration of coalesced seeding particles.

Optical monitoring of nucleation and growth of diamond films

Early stages of diamond film deposition on molybdenum substrates using dc arc discharge in CH4/H2 gas mixtures were studied by in situ measurements of optical reflectivity of growing film. Ultrafine diamond grit of ≊200 A size was used for seeding to increase nucleation density up to 2×109 cm−2 and to produce smooth thin films. Evolution of He‐Ne laser beam reflection at 0.63 μm wavelength is described in terms of Mie scattering by nonabsorbing dielectric spheres in the case of nucleated film and of light interference in the system of continuous diamond film on a metal substrate. During the deposition process the growth rate passes through a minimum at the moment when a minimum roughness is supposed to be achieved.

Laser ablation of metals and ceramics in picosecond–nanosecond pulsewidth in the presence of different ambient atmospheres

Abstract Ablation tests of AlN, Si3N4, SiC, Al2O3 ceramics, steel and aluminum have been carried out in vacuum, air and argon atmospheres using UV (270 nm), visible (539 nm) and IR (1078 nm) picosecond (100÷150 ps) and nanosecond (6÷9 ns) laser pulses. Ablation rate dependencies have been measured in the range of laser energy densities varied from (2÷5)×101 J/cm2 to (5÷10)×103 J/cm2. Peculiarities of laser ablation processes at different wavelengths, pulsewidths and ambient gases are discussed. In particular, the efficiencies of laser ablation in picosecond and nanosecond regions are compared. The scanning electron microscope (SEM) pictures of high quality microstructures, deep and narrow cuts and holes produced in ceramics with typical size of tens microns and aspect ratio as high as 20, are demonstrated.

Catalytic interaction of Fe, Ni and Pt with diamond films: patterning applications

Abstract Diamond films were patterned using thin films of Fe, Ni and Pt for catalytic etching at temperatures of 850–950°C in an H2 atmosphere. The diamond etching mechanism involves carbon dissolution in metal, diffusional transport to the metal-gas interface and carbon desorption in the form of methane. Iron films have shown the highest catalytic activity of the metals examined, providing etch rates up to 8 μm min−1. An effect of catalyst deactivation was observed and assigned to graphite-like carbon accumulation on the outer surface of the metal. Several methods for the patterning of iron films are described.

Fine patterning of diamond films by laser-assisted chemical etching in oxygen

Abstract We report on the use of low power (~2 W) continuous wave Ar+ laser for etching (engraving) of diamond films via a laserinduced local oxidation (burning) reaction. Smooth fine-grained diamond films of about 10 μm thickness have been grown on Mo and Si substrates in a d.c. arc discharge using CH 4 H 2 gas mixtures. The sharply focused laser beam was scanned under computer control over the film surface causing fast diamond oxidation in air or pure O2 atmosphere. The dependence of etch rate on laser power, beam scanning velocity and film quality was examined. Various grooves and holes of a few micrometres in size have been produced with etch rate of tens of micrometres per second.

Tribological properties of smooth polycrystalline diamond films

Abstract We have used a pin-on-disk tribometer with either a monocrystalline ruby or a 100Cr6 steel ball to evaluate the tribological properties of a series of polycrystalline chemical vapour deposition diamond films. Different polishing treatments of the as-grown films resulted in marked differences of their tribological behaviour. The friction and wear of smooth nanocrystalline diamond films was dependent on the surface morphology and roughness as well as the material transfer from the ball to the film. Microcrystalline films polished by laser irradiation, though being substantially rougher, showed a lower friction and minimal ball wear. Films polished by Ar-microwave plasma etching showed a similar behaviour as the laser-irradiated samples. However, the film with roughness comparable with the laser polished samples produced significantly higher ball wear. An unrivalled tribological performance was obtained with mechanically polished diamond films.

Electroless metallization of diamond films

Abstract Experimental studies of area selective metallization of diamond films are presented with emphasis on (i) laser activation of diamond surface for electroless metal plating, (ii) electroless metal deposition onto the activated surface areas, and (iii) diamond growth on the metal-patterned diamond films, encapsulating metal patterns into diamond. The activation of the diamond surface for electroless metal plating was achieved by laser-induced modification of the film surface during ablative etching. Transformations in the valence band structure of diamond upon laser processing were studied by Auger electron spectroscopy and related to a mechanism of activation of the diamond surface for electroless metal plating. It was concluded that the capability of laser-activated diamond surface to reduce metal ions from electroless solution was due to the formation of non-zero density of electronic states in the gap of diamond. Encapsulation of the electroless copper lines into diamond films was performed by means of the diamond growth onto the copper-plated diamond films. The composition and electrical properties of the encapsulated copper lines were studied, revealing high purity and low electrical resistivity of the encapsulated electroless copper.

Laser activation of diamond surface for electroless metal plating

Selective area electroless nickel and copper deposition onto the surface of diamond single crystals and polycrystalline diamond films has been realized. Three methods of laser‐assisted activation of diamond surface were applied: (i) prenucleation of diamond surface with a thin layer of palladium catalyst via laser‐induced decomposition of a palladium acetyl‐acetonate [Pd(acac)2] solid film; (ii) deposition of palladium by means of the decomposition of Pd(acac)2 dissolved in dimethylformamide; (iii) laser‐induced damage of diamond surface.

Excimer laser etching of diamond-like carbon films: spalling effect

Abstract Etching of diamond-like amorphous hydrogenated carbon films by 20 ns pulses of a KrF excimer laser has been investigated. In addition to previously reported etching mechanisms realized via either carbon oxidation or vaporization, a new etching mode based on a spalling effect was observed. It was found that there is a narrow window in laser fluences in which the etch rate of the carbon films examined exceeds by nearly two orders of magnitude the etch rates measured at fluences beyond this interval. The effect of anomalously fast etching occurs below a threshold for normal laser ablation (vaporization), and is ascribed to stress-induced lift-off of the material in the form of 30–60 nm thick macroscopic sheets. Very smooth surface relief in the etched crater and a reduced degree of film graphitization are characteristic features of this new etching mode.

Laser-assisted selective metallisation of diamonds by electroless Ni and Cu plating

Abstract Results are presented on area-selective metallisation of diamond single crystals and CVD diamond films realised by means of electroless metal deposition onto laser-activated diamond surfaces. Two techniques of laser activation of the diamond surface are applied: (1) prenucleation of the surface with a thin layer of Pd catalyst via laser-induced decomposition of a corresponding acetyl-acetonate solid film, and (2) laser-induced damage of the diamond surface. The activated surface is characterised with Auger spectra and X-ray microanalysis techniques. The possible mechanisms of surface activation are discussed along with alternative methods of diamond activation for electroless plating. The adherence strength of the Cu deposit is 1.5–2 N/mm2.