R. A. Khmelnitskii

Formation of amorphous carbon and graphite in CVD diamond upon annealing : A HREM, EELS, Raman and optical study

Polycrystalline diamond thick films were subjected to annealing in vacuum at temperatures of 1350-1450°C. The films were examined by optical absorption, Raman spectroscopy, transmission electron microscopy and electron energy loss spectroscopy. The formation of amorphous carbon and/or of well-crystallized graphite layers up to 20 nm thick was evidenced along grain boundaries. Intra-granular nanometer-sized graphite islands were also observed, sometimes as transformed micro-twin bands. The diamond-to-graphite transition occurs in such a way that three (111) diamond planes transform into two (0002) graphitic sheets. The internal graphitization causes a severe degradation of the optical quality of the diamond films.

Structure and properties of high-temperature annealed CVD diamond

Abstract Effects of high temperature, up to 1700 °C, annealing in vacuum of CVD diamond on its structure, optical and mechanical properties are investigated. Translucent polycrystalline diamond films of thickness 0.06–1.0 mm were grown by microwave plasma CVD method, and examined with transmission electron microscopy, optical absorption spectroscopy, and three-point bending technique to measure the fracture strength. A progressive darkening of the samples, with appearance of absorption features specific for graphite-like material, was observed upon annealing at temperatures above 1300 °C. The formation along grain boundaries of amorphous carbon and/or well crystallized graphite layers, 5–20 nm thick, as well as intra-granular graphite islands, was directly observed with TEM. This internal diamond-graphite transformation process can be described by two activation energies, both values being much less than those known for the surface graphitization of diamond. The fracture strength of the diamond films increases up to 50% with annealing temperature (1460–1640 °C), this being ascribed to a build up of compressive stress as a result of local diamond-graphite conversion.

Relative Abundance of Single and Vacancy‐Bonded Substitutional Nitrogen in CVD Diamond

Relations between the concentrations of neutral (N0) and charged (N+) single-substitutional nitrogen and of nitrogen–vacancy (N–V) complexes in chemical vapour deposited diamond films of ≈0.2 mm thickness with nitrogen impurity concentration levels of 10 ppm are studied. For this purpose the films were subjected to 8 MeV electron irradiation at room temperature and subsequent annealing at 800 °C. The samples were analysed by micro-photoluminescence, visible and IR absorption, and Electron Spin Resonance techniques. It was found that the concentration of nitrogen in the (N–V) and N+ forms, in as-grown films, is less than 0.1% and 10% of the neutral substitutional nitrogen N0, respectively.

Nonlinear absorption mechanisms during femtosecond laser surface ablation of silica glass

Spatial profiles of single-shot microcraters produced by tightly focused femtosecond laser pulses with variable pulse energies are measured by means of a laser confocal microscope. Dependences of crater depth on laser intensity at different pulse energies appear as overlapping saturating curves with the same threshold, indicating the presence of nonlinear absorption and absence of nonlocal ablation effects. A monotonic twofold increase in absorption nonlinearity is related to the transition from minor defect-band absorption to fundamental band-to-band absorption.

Background-free, highly sensitive surface-enhanced IR absorption of rhodamine 6G molecules deposited onto an array of microholes in thin silver film

Selective IR absorption at 1261 cm−1 enhanced by 455 times, was demonstrated for rhodamine 6G molecules, covering a 2D-photonic crystal, represented by a regular array of 4-micron wide holes in a 30 nm thick silver film on a CaF2 substrate. The reference absorption lines were taken near 2900 cm−1, where the IR radiation is freely channeling through the microholes, indicating the reference substrate coverage by the dye molecules for its relative internal calibration. The limit of background-free detection for the analyte was determined at the level ~10−2 monolayer.

Diffraction microgratings as a novel optical biosensing platform

Using a micro-hole grating in a supported silver film as a laser-fabricated novel optical platform for surface-enhanced IR absoprtion/reflection spectroscopy, characteristic absorption bands of Staphylococcus aureus, in particular, its buried carotenoid fragments, were detected in FT-IR spectra with 10-fold analytical enhancement, paving the way for the spectral express-identification of pathogenic microorganisms.

Microstructures as IR-sensors with Staphylococcus aureus bacteria

Using a micro-hole grating in a supported silver film as a laser-fabricated novel optical platform for surface-enhanced IR absoprtion/reflection spectroscopy, characteristic absorption bands of Staphylococcus aureus, especially – its buried carotenoid fragments – were detected in FT-IR spectra with 10-fold analytical enhancement, paving the way to spectral express-identification of the pathogenic microorganisms.