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This article deals with surface loss on quartz of atomic hydrogen (H) and its isotope deuterium (D) in a low-pressure (10 Pa) pulsed inductively coupled plasma. The atomic temporal decay in the post discharge is measured by two-photon absorption laser-induced fluorescence (TALIF). From the loss rate, the atomic surface loss probability is determined. In pure hydrogen or pure deuterium gas, no isotopic effect on surface kinetics has been observed and the surface loss probabilities of H and D were found to be almost identical and equal to ∼1.8%. However, despite the lack of difference in surface loss probability, a net isotopic effect on surface loss rate due to the mass difference between the isotopes is measured. Hydrogen atoms diffuse faster and have higher flux to the plasma chamber walls than deuterium atoms. Hydrogen atoms are therefore lost at higher rate than deuterium atoms. Based on the observed isotopic difference and on the comparison between H and D TALIF signals, the isotopic effects on H and D atom production are discussed. [ABSTRACT FROM AUTHOR]

We present a comparative high-resolution electron energy-loss spectroscopy study on the interaction of atomic hydrogen and deuterium with various reconstructions of SiC(0 0 0 1). We first show that on both the (3 × 3) and reconstructions, deuterium atoms only bind to silicon atoms, thereby confirming the silicon-rich appellation of these reconstructions. Deuterium passivation of the (3 × 3) is only reversible when exposed to atomic deuterium at a surface temperature of 700 K since tri- and dideuterides, necessary precursors for silicon etching, are not stable. On the other hand, we show that the deuteration of the is always reversible because precursors to silicon etching are scarce on the surface. Then, we demonstrate that hydrogen (deuterium) adsorption at 300 K on both the (buffer-layer) and the quasi-free-standing graphene occurs on carbon atoms justifying their carbon-rich appellation. Comparison of the deuterium binding in the intercalation layer of quasi-free-standing graphene with the deuterated surface provides some indication on the bonding structure at the substrate intercalation layer. Finally, by measuring C–H (C–D) vibrational frequencies and hydrogen (deuterium) desorption temperatures we suggest that partial sp2-to-sp3 rehybridization occurs for the carbon atoms of the buffer-layer because of the corrugation related to covalent bonding to the SiC substrate. In contrast, on quasi-free-standing graphene hydrogen (deuterium) atoms adsorb similarly to what is observed on graphite, i.e. without preferential sticking related to the underlying SiC substrate. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we study the abstraction of deuterium (D) by hydrogen (H) atoms (respectively H by D) on both perfectly crystalline and ion bombarded graphite surfaces using high resolution electron energy loss spectroscopy. On an initially defect free graphite surface, abstraction of D by H (reciprocally and reversibly H by D) is a quite efficient process at room temperature. Measurements demonstrate that the abstraction occurs almost essentially with the adsorbed atoms on “weakly” reactive sites. Reciprocally, atoms adsorbed on defects with sp3 configuration participate in a much lower extent to the abstraction mechanism. Obviously, this phenomenon always occurs when exposing a surface to an atomic hydrogen beam and illustrates the competition between sticking and molecules formation by abstraction. [Copyright &y& Elsevier]

Abstract: The first steps of structural and electronic modifications of a graphite surface bombarded with argon, hydrogen and deuterium ions were investigated using high resolution electron energy loss spectroscopy (HREELS). The energy and the damping of the low energy plasmon mode of graphite (E//C mode) were studied with respect to the bombardment settings. We show that argon bombardment affects the energy of the plasmon mode, while no similar change is observed after hydrogen (deuterium) bombardments. This can be related to the variation of inter-planar distance between two graphene layers. Moreover, the damping of the plasmon mode can be correlated with the interstitial defect concentration. Concerning the reactivity of the bombarded surfaces, we demonstrate that deuterium bombardment produce a non-deuterated surface. This last is very reactive to a further atomic deuterium exposure, as it is shown by the formation of C–D bondings. The deuterated sites can be removed after thermal annealings between 473 and 783K. The occurrence of a chemical erosion mechanism accompanying this deuteration is discussed. [Copyright &y& Elsevier]

The time evolution of fuel retention in materials relevant for future fusion reactors is compared for two different tungsten microstructures: single-crystal versus recrystallized poly-crystals. The initial retention of both types of sample is similar. It decays exponentially with a time constant of ~18 h at 300 K (the so-called short-term retention). After 48 h at room temperature, a constant deuterium retention is measured (long-term retention) with the single-crystal containing systematically less deuterium than poly-crystals. Macroscopic rate equations models are built with density functional theory inputs to reproduce deuterium desorption observables with the MHIMS-R code. We found that the native oxide layer could explain the desorption peak located at ~450 K as well as most of the short-term retention in the single-crystal. The native oxide together with, dislocations for single-crystal and grain boundaries for poly-crystals, are responsible for the long-term retention. Dislocations should explain the desorption peak located at ~815 K for mechanically polished samples. The dual role of most of tungsten defects is related to their multi-trapping properties with filling-level-dependent detrapping energies. Finally, the use of an effective diffusivity of deuterium through the native oxide layer, i.e. its diffusion barrier character, is evaluated. [ABSTRACT FROM AUTHOR]

Retention of deuterium ion implanted in polycrystalline tungsten samples is studied in situ in an ultra-high vacuum apparatus equipped with a low-flux ion source and a high sensitivity thermo-desorption setup. Retention as a function of ion fluence was measured in the 10 17 –10 21 D + ·m −2 range. By combining this new fluence range with the literature in situ experimental data, we evidence the existence of a retention ∝ fluence 0.645±0.025 relationship which describes deuterium retention behavior on polycrystalline tungsten on 8 orders of magnitude of fluence. Evolution of deuterium retention as a function of the sample storage time in vacuum at room temperature was followed. A loss of 50% of the retained deuterium is observed when the storage time is increased from 2 h to 135 h. The role of the surface and of natural bulk defects on the deuterium retention/release in polycrystalline tungsten is discussed in light of the behavior of the single desorption peak obtained with Temperature Programmed Desorption. [ABSTRACT FROM AUTHOR]

Relevant parameters for trapping of Hydrogen Isotopes (HIs) in polycrystalline tungsten are determined with the MHIMS code (Migration of Hydrogen Isotopes in MaterialS) which is used to reproduce Thermal Desorption Spectrometry experiments. Three types of traps are found: two intrinsic traps (detrapping energy of 0.87 eV and 1.00 eV) and one extrinsic trap created by ion irradiation (detrapping energy of 1.50 eV). Then MHIMS is used to simulate HIs retention at different fluences and different implantation temperatures. Simulation results agree well with experimental data. It is shown that at 300 K the retention is limited by diffusion in the bulk. For implantation temperatures above 500 K, the retention is limited by trap creation processes. Above 600 K, the retention drops by two orders of magnitude as compared to the retention at 300 K. With the determined detrapping energies, HIs outgassing at room temperature is predicted. After ions implantation at 300 K, 45% of the initial retention is lost to vacuum in 300 000 s while during this time the remaining trapped HIs diffuse twice as deep into the bulk. [ABSTRACT FROM AUTHOR]

Hydrogenation of deuterium-intercalated quasi-free-standing monolayer graphene on SiC(0001) is obtained and studied with low-energy electron diffraction and high-resolution electron energy loss spectroscopy. While the carbon honeycomb structure remains intact, it is shown that a significant band gap opens in the hydrogenated material. Vibrational spectroscopy evidences for hydrogen chemisorption on the quasi-free-standing graphene is provided and its thermal stability is studied. [ABSTRACT FROM AUTHOR]