A. M. Lebedev

Temperature and spectroscopic characteristics of homogeneous co-deposited carbon–deuterium films produced in the T-10 tokamak

Homogeneous carbon–deuterium (C‒ D) films with a high [D]/[C] ratio, redeposited on deuterium-plasma discharge in the T-10 tokamak, have been studied by means of thermogravimetric analysis, spectroscopy based on electron paramagnetic resonance, Fourier-transform infrared spectroscopy and photoluminescence spectroscopy. Deuterium was found to be accumulated only in the C‒ D2, 3 sp3 vibrational modes, including 633 and 1090 cm−1 deformation modes, and 2100–2200 cm−1 stretching modes, the intensity of which slightly diminished on annealing at 450 °C. Photoluminescence of an excitonic nature was found at 390–530 nm related to the C 2p π−π* transitions within the aromatic rings, and luminescence quenched at 450 °C. The luminescence excitation spectra at 3–10 eV showed similarity in peak positions to the luminescence excitation spectra of thin C60 films. Possible physical reasons explaining the effect of H‒ D‒ T isotopes on the accumulation and desorption of hydrogen are considered.

Adsorption States of Protium and Deuterium in Redeposited Polymer Hydrocarbon Films from a T-10 Tokamak

Free redeposited hydrocarbon films (flakes) with a high content of deuterium and hydrogen formed in the T-10 tokamak operating at the Russian Research Centre (RRC) “Kurchatov Institute” are studied using thermal desorption spectroscopy (TDS), infrared (IR) spectroscopy, and X-ray diffraction (XRD) analysis. According to the XRD data, the films contain scattering elements with dimensions of about 1 nm and weakly ordered structures. The TDS curves for D2 (H2) consisting of two groups of peaks at 450–800 and 900–1000 K turn out to be sufficiently similar to the spectra of nanographite obtained by milling graphite mechanically. Two main adsorption states with activation energies of ≈0.65 and ≈1.25 eV/N corresponding to hopping diffusion and resonance mechanisms, respectively, were discovered. The difference between the IR spectra of reddish-gold and dark-brown films is due to both a weaker degree of C-H hybridization of dark films and their disordered carbon network whose ends are connected to CD2,3 fragments.

Study of microimpurities and charge states in homogeneous hydrocarbon films (Redeposited from a T-10 tokamak deuterium plasma discharge) using XRF analysis, IR spectroscopy, EPR, and I-V characteristics

Microimpurities and charge states of homogeneous deuterated hydrocarbon films redeposited from a T-10 tokamak deuterium plasma discharge are studied spectroscopically using x-ray fluorescence (XRF) analysis, electron paramagnetic resonance (EPR), infrared (IR) spectroscopy; current-voltage (I-V) charachteristics are also measured. Twelve microimpurities (mainly, those of transition metals Fe, Mo, Cr, Ni, Ti, etc., with relative concentrations of 50–7000 ppm) have been discovered. The resulting broad EPR (9.9 GHz, 6000 G) line with g-factors of g = 2.053–2.093 and g = 4.3 assigned to paramagnetic impurities confirms their presence. The presence of different charge states on two sides of the film (one facing the plasma and another facing the vacuum-chamber wall) and the difference in the IR spectra of these states are established. This can be explained by the process of film formation under the influence of the tokamak plasma.

Spectroscopy of Homogeneous Deuterated Hydrocarbon Films Redeposited from a T-10 Tokamak Plasma Discharge

Homogeneous deuterated hydrocarbon films redeposited from a deuterium plasma discharge inside the T-10 tokamak vacuum chamber are studied using photoluminescence methods; EXAFS, EPR, and IR spectroscopies; and temperature measurements. The photoluminescence excitation spectra of sp3-sp2 nanostructures of tokamak films are compared with those of sp2 nanostructures of C60 fullerite films. The effect of defect states on photoluminescence and its temperature quenching is discussed. It is concluded that the model of temperature luminescence quenching for homogeneous deuterated tokamak films is similar to that for amorphous a-C:H films.

Experimentally observed orientation of C 60 F 18 molecules on the nickel single crystal (100) surface

The angular dependence of near edge X-ray absorption fine structure (NEXAFS) spectra has been obtained in the vicinity of carbon and fluorine 1s absorption edges in a monolayer film of polar fullerene fluoride (C60F18) molecules on a Ni(100) substrate. The fine structure of the spectra has been identified according to experimental data via calculations based on the density functional theory, and the angular dependence of the spectra has been explained. The orientations of structural molecular fragments are determined from the angular dependence of the NEXAFS spectra. It is demonstrated that the electric dipole moment of a C60F18 molecule is oriented along the normal to the substrate surface with an accuracy of 5°.

Electron structure investigations of homogeneous hydrocarbon films formed in plasma conditions of T-10 tokamak

Electron structure investigations of smooth hydrocarbon thick films with a high atomic D/C ratio, redeposited from deuterium plasma discharge onto the vacuum vessel regions of the T-10 tokamak, are continued. For the first time, the investigations of both film sides and in a valence band region were performed by X-ray photoemission spectroscopy, combined with “conventional” measurements of survey spectra, C1s, O1s core levels, and by using Auger X-ray electron spectroscopy for sp2/sp3 ratio determination. The distinctions of electron structure of both sides of flakes which were noticed earlier using another techniques, were found, differing from the structure of thin films deposited in cleaning discharges of a low-temperature plasma. It is shown how these differences are connected with different processes of film deposition in tokamaks.

Detection of the iron impurity in CD x films formed in the T-10 tokamak and its influence on the sp 3 → sp 2 conversion

Experimental data on Fe-impurity detection in smooth carbon–deuterium (CDx, x ~ 0.5) films from the T-10 tokamak, which are obtained by means of X-ray diffraction, are presented. Additional analysis and systematization of the results of previous experiments are performed in order to clarify the iron charge state and estimate its influence on the sp3 → sp2 conversion.

Investigating the fine structure of near-edge X-ray absorption in the molecular spectra of C60F18 adsorbed on a single nickel crystal

Angular dependences of the fine structure of near-edge X-ray absorption (NEXAFS) of carbon C1s spectra are obtained for a monolayer film of C60F18 polar molecules on a Ni (100) substrate. The fine structure and angular dependences of these spectra are interpreted using calculation data obtained by the density functional method upon fitting NEXAFS spectra by the set of trial functions. It is shown that during deposition, the dipole moment of molecules is oriented perpendicular to the surface and fluorine atoms are the ones closest to the surface.

Spectroscopy of smooth deuterated carbon films redeposited from plasma discharge in the tokamak T-10

Smooth deuterated carbon films redeposited from a deuterium plasma discharge in the tokamak T-10 vacuum chamber have been investigated by different spectroscopic methods and temperature measurements. The photoluminescence excitation spectra of sp3-sp2 nanostructures of tokamak films and sp2 nanostructures of fullerite C60 films are compared. The effect of defect states on the photoluminescence and its temperature quenching is discussed. It is concluded that the mechanism of thermal luminescence quenching for smooth deuterated tokamak films is close to the corresponding mechanism for amorphous a-C:H films.

On the interaction of self-assembled C 60 F 18 polar molecules with the Ni(100) surface

The current work is dedicated to investigation of the interaction between self-assembled polar molecules of fullerene fluoride C60F18 with the chemically active surface Ni(100) under radiation and heat treatments. X-ray photoelectron spectroscopy is used in combination with quantum-chemical simulation. For the first time, the transformation of an as-deposited dielectric continuous 2D thin film to a 3D island-type assembly with molecular ordering within the islands is shown to take place. The degree of coverage of the Ni surface by C60F18 islands (0.6–0.7) and their height (~6 nm) are estimated. Quantum-chemical simulation shows that the chemisorption energy of the C60F18 molecule on the Ni surface equals ~6.6 eV and fluorine atoms are located at a distance of 1.9 Å above the Ni surface. The results of the investigation provide an opportunity to create nanoscale ordered structures with local changes in the work function.