L. P. Sukhanov

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.

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.

EPR and photoluminescence spectra of smooth CDx films from T-10 tokamak: The effect of iron impurity

The electron and spin structure of thick smooth hydrocarbon CDx films (“flakes”) with a high relative deuterium concentration of x ~ 0.5, redeposited from deuterium plasma discharge onto the walls of the vacuum chamber of the T-10 tokamak and containing ~1 at % of 3d-metal impurities due to erosion of the chamber walls, are studied using electron paramagnetic resonance (EPR) and photoluminescence (PL). The resulting spectra are compared for the first time to the EPR and photoluminescence spectra of polymer (soft) a-C:H(D) films (H(D)/C ~ 0.5), which are considered model analogues of smooth CDx films. A certain similarity of the CDx films with a-C:H films was found in the electronic structure of the valence band. At the same time, the differences in the EPR and photoluminescence spectra were observed due to the presence of 3d-metal impurities in the CDx samples, contributing to the conversion of sp3 → sp2 in the formation of films in the tokamak and upon heating and thermal desorption. An impurity of, presumably, 3d metals was detected for the first time by EPR in the a-C:H films in an amount of approximately 0.2 ppm, related to the evaporation of graphite.

OBSERVATION OF NANOSTRUCTURAL ELEMENTS OF THICK HOMOGENOUS HYDROCARBON FILMS REDEPOSITED FROM T-10 TOKAMAK PLASMA DISCHARGE

Гомогенные углеводородные плёнки могут накапливать изотопы водорода (тритий и дейтерий), которые будут использоваться в качестве топлива термоядерных реакторов. Так как насыщенные тритием плёнки представляют большую радиационную опасность для эксплуатационного персонала будущих термоядерных реакторов, то необходимо знать свойства и структуру таких продуктов эрозии. В работе приводятся результаты исследования структуры толстых гомогенных углеводородных плёнок с большим значением атомного отношения дейтерия к углероду D/C, осаждённых после рабочих разрядов дейтериевой плазмы и чистящих разрядов в токамаке Т-10. Исследования проводились с применением малоуглового рентгеновского рассеяния (МУРР), широкоуглового рентгеновского рассеяния (ШУРР) и дифракции нейтронов. Плёнки содержат имеющие фрактальную структуру элементы размером в несколько десятков нм, которые образуют очень пористые взаимносвязанные кластеры. В области меньших размеров выявлена квазипериодическая углеродная сетка, состоящая из фрагментов углерода С13, которая может альтернативно рассматриваться как сильно повреждённый слой графена с большой концентрацией вакансий.

ELECTRONIC STRUCTURE INVESTIGATIONS OF HYDROCARBON FILMS OBTAINED UNDER CONTROLLABLE PLASMA CONDITIONS OF T-10 TOKAMAK

Впервые обнаружено изменение электронной структуры гладких углеводородных плёнок с высоким атомным соотношением D/C в зависимости от контролируемых условий осаждения токамака Т-10. Эти условия включают в себя стабильные рабочие плазменные разряды, разряды со срывом плазмы, а также тренировочные индукционные (Тейлоровские) разряды. Исследования с помощью рентгеновской фотоэмиссионной спектроскопии проводились впервые для валентной зоны с определением величины запрещённой зоны Eg вместе с «традиционными» измерениями остовных уровней C1s, O1s и обзорных спектров — с оценкой относительного вклада химических элементов и примесей, а также рентгеновской оже-электронной спектроскопии, позволяющей оценить вклад углеродных состояний sp и sp. Электронная структура плёнок показала заметные различия в зависимости от типа формирующих их разрядов. Метод исследования оказался информативным для исследования разных типов плёнок, которые, по существу, являются паспортом процессов, происходящих в токамаках. Кроме того, подобная процедура характеризации электронной структуры может оказаться полезной для исследования других осаждаемых материалов, включая смешанные плёнки и металлы (Be, W, Fe и т.д.), в рамках проектов ИТЭР и ДЕМО.