S.M. Pimenov

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.

Laser treatment of tribological DLC films

The friction and wear reduction in applications that allow only a minimal use of liquid lubricants is done with solid lubricant films or with protective coatings, such as diamond-like carbon (DLC). Further improvements are possible if the geometries of the contact surfaces are modified in a controlled way, as we have already demonstrated it for TiN and TiCN. In this work, the possibilities to generate patterned DLC coated low wear tribological surfaces by means of laser processing were investigated. In the first approach, a two step method was used: steel substrates were laser patterned and subsequently DLC films were deposited on them. The second considered approach was the laser processing of coated surfaces. DLC films were irradiated with laser pulses of different durations and energy densities (100 fs, 800 nm, <4 J/cm2; 150 ns, 1064 nm, <10 J/cm2) and the treated spots were examined using optical microscopy, SEM, AFM and Raman spectroscopy. The graphitisation of a-C:H films under both fs- and ns- regimes was shown as well as a film-peeling phenomenon during the ablation process. Microstructured and DLC coated surfaces obtained in the former approach were used for preliminary tribological tests (oscillation-friction-wear method). The results showed that the friction coefficient did not increase, as compared with the unstructured and DLC coated surfaces, and that the structure pores trapped the debris particles produced when the DLC film eventually broke.

Effects of post-growth treatment and coating with ultrathin metal layers on the band bending and field electron emission of diamond films

Band bending formation on thin nanocrystalline diamond films and field electron emission after post-growth treatments was investigated. It was found that treatment of the diamond surface with hydrogen plasma substantially decreases the density of point defects, forms the downward band bending and enhances the field electron emission from the films. In the case of an argon plasma treated diamond surface, new point defects were induced and their energy distribution was changed. Nevertheless, the downward band bending was formed and the field electron emission was enhanced similar to the H–plasma-treated diamond surface with minor density of defects. These effects were interpreted in terms of the electrical dipole formation on the plasma treated diamond surfaces. Coating the diamond films with ultrathin metal (Ni, Ti) layers revealed the dependence of the band bending and field emission behavior on the type and thickness of the metal used. The deposition of a few monolayers of Ni on the diamond surface was f...

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.

Smoothening of diamond films with an ArF laser

Abstract Polycrystalline diamond films of various microstructures were modified by large-area ArF laser irradiation. The modified film surfaces were characterized employing electron microscopy, mechanical profilometry and optical reflectometry. Laser irradiation was found to smooth the surface finish over a wide range of spatial frequencies covering microroughness imposed by the individual crystallites as well as waviness with periods exceeding the crystal sizes. No smoothening was achieved, however, for chemically non-uniform diamond films. The results can be rationalized in terms of laser-induced surface evaporation. Resistivity measurements revealed the simultaneous formation of a highly stable conductive surface layer upon laser irradiation.

UV laser polishing of thick diamond films for IR windows

Abstract Diamond has very suitable properties for infrared (IR) window applications. The rugged surface of a free-standing 320 μm thick diamond film grown by chemical vapour deposition (CVD) is polished with the UV light of an ArF excimer laser (λ=193 nm). The angle of incidence is 85° and irradiation is subsequently performed at three planar directions around the perpendicular axis. Scanning electron microscopy (SEM) is used to visualise the surface before and after the polishing procedure. With a profilometer (tip radius 5 μm) the improvement of the average roughness of the surface is measured. Polishing is analysed in dependence on the size of surface irregularities by means of fast Fourier transformation (FFT) of the signal of the profilometer. Surface roughness measurements are also performed on the polished surface with an atomic force microscope (AFM). With IR transmittance measurements the optical quality is analysed over a wavelength range of 2.5 to 25 μm before and after polishing. The oxidative removal of the laser induced graphitic layer is studied with optical spectroscopy techniques.

Similarity in field electron emission from nanocrystalline diamond and related materials

Abstract Results on a complex study of macroscopic and microscopic electronic properties of nanocrystalline diamond and related material (BN, GaN, CN) films are presented. It was found that all the samples studied showed similar dependencies of macroscopic emission parameters (the Fowler–Nordheim work function, the effective emitting area) on the film emissivity. Also, some microscopic properties were found to be common for all the films tested. It was generally observed that field electron emission occurred at nanosized regions on the boundary of high and low resistivity areas, and peaks of the emission intensity were associated with a lowered surface electron potential. Based on the experimental data, a mechanism of field electron emission from the surface of nanocrystalline films is proposed. We suppose that electrons are transported from narrow conducting channels into vacuum through specific low-dimensional regions, the electronic properties of which, due to the quantum size effect, are different from the bulk material. In this case the base material grains play a role of the conductive channel-containing matrix as well as a heat sink. Details of the new low-field emission mechanism including the filling of discrete energy states, and the decrease in the work function under the action of electric field are discussed.

Laser-induced forward transfer of ultra-fine diamond particles for selective deposition of diamond films

Abstract A laser-induced forward transfer (LIFT) technique is used for area-selective prenucleation of Si substrates with ultra-fine diamond powder for subsequent diamond film deposition via a conventional CVD process. The influence of the laser parameters (wavelength, energy density, etc.) on the features of the ablation-deposition process is experimentally studied with the aim of improving the spatial selectivity of diamond patterning.

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.

Charge-based deep level transient spectroscopy of undoped and nitrogen-doped ultrananocrystalline diamond films

Abstract A comparative study of electrically active defects has been performed for undoped and nitrogen-doped nanocrystalline diamond thin films deposited on Si substrates from CH 4 /Ar/H 2 and CH 4 /Ar/N 2 gas mixtures using microwave and d.c. plasma CVD techniques. The method of charge-based deep level transient spectroscopy (Q-DLTS) was applied to obtain information on the concentration, activation energy and capture cross-section of native and nitrogen-induced defects. A common feature in Q-DLTS spectra of undoped films was the presence of a deep level with the activation energy of 0.13–0.22 eV. The Q-DLTS spectra of nitrogen-doped films, however, exhibited a shallow level peak with the activation energy of approximately 0.05 eV. The density of the shallow defects was found to increase with increasing concentration of incorporated nitrogen. The photoelectrical properties of the films were also studied. The kinetics of photoresponse to a high intensity light pulse (in open circuit condition at zero bias) was measured. These photoresponse data were obtained at saturation conditions and were used for designing the energy band diagram for the p-Si/UNCD film/metal and n-Si/UNCD film/metal heterostructures studied.