In this paper, experimental data are presented on the synthesis and properties of nanocrystalline diamond (NCD) films grown by a dc plasma CVD technique from various gas mixtures (CH4-H2, CH4-H2-Ar, CH4-Ar, CH4-H2-N2, CH4-Ar- N2). The interrelation between the CVD conditions, the film microstructure and film properties is established using Raman spectroscopy, XRD, XPS, AES, SEM, TEM, AFM/STM, spectroscopic ellipsometry and optical transmission spectroscopy techniques. Experimental methods for laser assisted fabrication of ultrathin and highly smooth NCD films are described. Effects of the deposition parameters (substrate temperature, CH4 content, addition of Ar gas to CH/H2 gas mixtures) on the grain size, surface roughness and optical properties of NCD films are discussed. Results of nitrogen doping of nanocrystalline diamond films are presented and discussed.
We have applied spectroscopic ellipsometry with binary polarization modulation to study the refractive index n(λ) and extinction coefficient k(λ) spectra of as-deposited and irradiated with nitrogen ions polymethylmethacrylate (PMMA) and polystyrene (PS) films in 300-1030 nm range. The results of performed investigation confirmed the possibility and estimate restrictions of the ion implantation for local change the refractive index of polymeric materials.
Raman and optical spectroscopy, conductivity and steady-state photoconductivity measurements, spectroscopic ellipsometry and atomic force microscopy (AFM) techniques were used to determine the properties of microcrystalline (μc-Si:H) and amorphous (a-Si:H) hydrogenated silicon films deposited at low temperatures by a conventional plasma-enhanced chemical vapour deposition (PECVD) reactors from silane-hydrogen mixtures. In order to gain insight into the mechanisms of transport and recombination in μc-Si:H films we study effect of isochronal annealing at 300-600° C on their properties.
Laser-induced structure transformations in diamond single crystals implanted with light ions (H+, D+, He+) are studied by monitoring changes in the material density and optical transmission in dependence on UV laser pulsed irradiation parameters and ion implantation conditions. Characteristic features of the processes of laser annealing, graphitization, low-rate etching and explosive ablation of ion-implanted diamond layers are discussed.
Results are reported on the study of phase transformations in diamonds induced by nano- and picosecond pulses of KrF excimer laser (λ=248 nm) and second harmonic of a YAP:Nd laser (λ=539 nm). Main attention in the research was paid to i) laser-induced graphitization of high-quality CVD diamond plates and ii) laser-induced structure transitions in ion-implanted diamond single crystals. For CVD diamond, the thickness of the laser-graphitized surface layers was measured and the accumulation period for graphitization to occur was found to be longer for lower laser fluences. In the experiments with ion-implanted diamonds, multipulse laser irradiation at fluences lower than the graphitization thresholds resulted in progressive annealing, i.e., in an increase of the optical transmission and surface contraction. Under certain low-intensity irradiation conditions, it was also found that, competing with the annealing process, laser etching of the ion-implanted diamond occurred at extremely low rates of 10-4-10-3 nm/pulse. A correlation between the defect concentration distribution and graphitization thresholds in partially annealed ion-implanted diamonds is discussed.
The results of laser polishing of 350 micrometers thick free- standing diamond films are reported. The polishing was performed with a grazing beam of a copper vapor laser. It is shown that the laser polishing conditions and the resulting surface roughness are controlled by varying an angle of incidence of a scanning laser beam during polishing. The surface roughness of the as-grown films was reduced by an order of magnitude and a minimum roughness of Ra equals 0.38 micrometers was achieved as a result of the two-step polishing. Optical transmission in the UV-visible spectral range of the diamond films polished under the optimized conditions was found to be close to the optical transmission of the mechanically polished diamond film. Properties of the laser-graphitized layer at the diamond surface were studied with optical spectroscopy techniques in the process of oxidative removal of the layer with increasing temperature of the oxidation in ambient air. The optical properties and oxidation stability of the laser-modified surface layer were found to change throughout its thickness from the surface to the diamond interface, depending on the laser polishing regime.
Thermal conductivity perpendicularly to diamond film surface was measured using a laser flash technique. Polycrystalline diamond wafers of up to 500 microns thickness and 2.25 inch diameter were produced in microwave plasma at different deposition conditions. Thermal conductivity (TC) was determined from heat propagation time across the wafer after short pulse of a Nd:YAG laser absorbed at sample surface. Distributions of TC along wafer radius were measured with 1 mm spatial resolution, they correlate to optical absorption, Raman diamond peak width and amorphous carbon concentration in the material. The best TC values of 18 W/cmK were measured for selected samples.
Vitali Konov, E. Obraztsova, Sergej Pimenov, Victor Ralchenko, Andrey Smolin, A. Khomich, Vladimir Polyakov, A. Rukovishnikov, Polievet Perov, E. Loubnin
Thin nanocrystalline diamond films promising for IR optical applications were grown on Si substrates from methane-hydrogen gas mixture in a DC arc plasma CVD reactor. Three stages for the synthesis of the highly smooth noncrystalline diamond films are important: (i) substrate pretreatment with ultrafine diamond powder, (ii) excimer laser irradiation of seeded substrates, and (iii) two-step deposition process. A correlation between optical properties of the films and growth conditions has been established by means of Raman spectroscopy, spectroscopic ellipsometry and optical transmission spectroscopy techniques. Surface roughness, which was Ra equals 8 - 40 nm for the 1 micrometers thick films, significantly decreased the transmission in the visible because of light scattering, but it had a negligible effect in the IR range. The films are transparent in the IR and have optical constants n equals 2.34-2.36 and k equals 0.005- 0.03. The hydrogen incorporation in the films in amounts up to 1.5% have been deduced from intensity of C-H absorption band around 2900 cm(superscript -1.
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