Origin of H− in collisions of hydrogen atoms with an adsorbate-covered Cu(100) surface

DeFazio, J N; Peko, B. L.

doi:10.1116/1.1795821

Cited by 2 publications

(2 citation statements)

References 37 publications

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“…This indicates that the sample surfaces are kept clean without contamination such as water. 21 On the other hand, for the carbon surface it seems that the H + (H − ) intensity slightly increases (decreases) with increasing temperature. We have confirmed reproducibility of this trend.…”

Section: Figures 3(a)-3(c) Show the Intensities Of The Reflected H +mentioning

confidence: 96%

Effects of roughness and temperature on low-energy hydrogen positive and negative ion reflection from silicon and carbon surfaces

Tanaka

Kato

Miyamoto

et al. 2014

Review of Scientific Instruments

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Hydrogen ion-solid surface interaction leads to formation of both positive and negative ions at the surface, and is of particular importance in wall conditioning of plasma confinement devices. We have studied the fundamental processes of beam-surface interactions by measuring the positive and negative ions scattered from the solid surface by injecting low-energy (13 keV) light ion beams. 1) Both positive and negative ions from molybdenum, tungsten, vanadium alloy, and carbon nano wall were observed. The intensities of negative ions formed on these samples were the same order of magnitude. The negative ion yields from such high work function surfaces of graphite, Si, and diamond are too large to be explained by conventional surface charge transfer models. We also found that the surface structure affected the reflection property. The results suggest that the surface structure is an important factor determining the intensities of scattered positive and negative ions. On the other hand, most experiments of the beam-surface interaction have been performed at room temperature. Here we report the surface roughness effect on the reflection properties at Si targets for a 1 keV H + beam injection. Reflection from Si and carbon surfaces are measured for comparison. Temperature effects of these materials are also studied.We prepared a Si crystal, a rough-finished Si (a few µm roughness), and a graphite (carbon plate) samples. The H + beam energy was kept at 1 keV and beam current was 10-40 nA at the target throughout this series of the experiment. The reflected ions were measured by a magnetic momentum analyzer consists of a pair of magnetic coils and a multi-channel plate set on a turntable. This analyzer system enables energy and angle resolved measurements of reflected positive and negative ions with single scan.Reflection angle dependence of the reflected ion energy and intensity at several incident angles were measured for Si crystal, rough-finish Si crystal, and carbon plate. 2) FE-SEM images of the rough-finish SI crystal and carbon plate are shown in upper panels in Fig. 1. We define the incident and reflection angles with respect to the sample surface. The reflected ion intensity in the rough-finished Si was largely reduced compared to that in the Si crystal as shown in Figs. 1(a) and 1(b). The angular distribution of the rough-finished Si was slightly broader than that of Si crystal at α = 10 • and that of the graphite was much broader than the others. Figure 1(c) shows result for the carbon plate (graphite). The graphite has a piled-up structure of small pieces horizontally. This result suggests that this structure has a similar effect on the reflected ion intensity angle distribution as the diffuse scattering in the rough-finished Si. Thus the structure and surface roughness affect on the scattering ion intensity and angle distribution particularly at lower incident angles. We also studied temperature dependence of the reflected ion intensity for these samples. Temperature-dependence of the H + ion intensity re...

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Section: Figures 3(a)-3(c) Show the Intensities Of The Reflected H +mentioning

confidence: 96%

Effects of roughness and temperature on low-energy hydrogen positive and negative ion reflection from silicon and carbon surfaces

Tanaka

Kato

Miyamoto

et al. 2014

Review of Scientific Instruments

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“…Consequently, we expect the charge transfer processes and experimental ion/atom fractions obtained during scattering experiments to be very different for the Cu(100) surface with respect to Cu(111). To the best of our knowledge, there are no experimental data available for H − or H scattering and survival on clean Cu(100). Prior experimental studies reported in the literature include (1) Atomic and ionic hydrogen scattered from Cu(100) covered with a residual gas at very low energy (25 to 200 eV) . This study showed that the dominant process leading to the H − formation proceeds through the adsorbed species, with the Cu(100) surface acting as a scattering platform.…”

Section: Introductionmentioning

confidence: 99%

Charge transfer during H/H⁻ collisions with Cu(100) and Cu(111) surfaces

Bahrim

Stafford

Makarenko

2017

Surface & Interface Analysis

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We study the H and H − survival probabilities during collisions with Cu(100) and Cu(111) surfaces, at energies ranging from 0.5 to 5 keV and exit angles ranging from 20°to 90°. Calculations are performed with the Wave-Packet Propagation method adapted to ion-surface interactions. The projectile survival probability depends on the perpendicular velocity and the copper face being investigated. Projectile's interaction time with the surface and the distance of closest approach are important factors that influence the survival. The H − survival on Cu(100) is much smaller than on Cu(111) but only at low velocities, while becoming higher or comparable to Cu(111) for higher velocities. For very fast collisions, the copper surface behaves like a jellium, and the electron involved in charge transfer does not "feel" the particularities of the surface band structure anymore. While the H survival on Cu(100) seems to not depend on energy and exit angle, the H survival on Cu (111) is both energy and angle dependent, and it is smaller. The study of partial density of states indicates that strong atom-surface interactions at short distances and the role played by surface states are important factors in determining the neutral fractions obtained after scattering. KEYWORDS charge transfer, ion fractions, ion/atom scattering, ion-surface interactions, survival probability 1 | INTRODUCTION Charge transfer processes during the interaction between atomic projectiles and metal surfaces are of both fundamental and practical interest. Such studies are crucial for progress in various applied fields, such as plasma wall interactions in fusion devices, catalysis, space science, and film deposition. 1-5 In addition, charge transfer is essential in adsorption and desorption processes, chemical reactions, quenching of metastable states, and in the ion formation during scattering and sputtering experiments. 6-10The most efficient type of charge transfer is the one-electron transfer between energetically degenerate electronic levels of the atom and the solid, also called resonant charge transfer. The atomsurface resonant charge transfer processes are very sensitive to several parameters, such as the projectile energy, exit angle, distance of closest approach to surface, and surface band structure. [11][12][13][14][15][16] In particular, it has been shown that these processes are strongly influenced by the presence of a band gap in the direction normal to the surface, such as the L-gap in the Cu(111) surface. The presence of a projected band gap in the direction normal to the surface forbids electrons with energies in that particular energy range to be transferred into the metal along the surface normal, thus strongly affecting the charge transfer processes that occur at the surface. 17,18 Our previous studies have been devoted to H − formation and survival on clean and adsorbate-covered Cu(111) surfaces. These studies have been focused on understanding the physics involved in such complex many-body systems. [18][19][20] In this work, we are inte...

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Origin of H− in collisions of hydrogen atoms with an adsorbate-covered Cu(100) surface

Cited by 2 publications

References 37 publications

Effects of roughness and temperature on low-energy hydrogen positive and negative ion reflection from silicon and carbon surfaces

Effects of roughness and temperature on low-energy hydrogen positive and negative ion reflection from silicon and carbon surfaces

Charge transfer during H/H⁻ collisions with Cu(100) and Cu(111) surfaces

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Origin of H− in collisions of hydrogen atoms with an adsorbate-covered Cu(100) surface

Cited by 2 publications

References 37 publications

Effects of roughness and temperature on low-energy hydrogen positive and negative ion reflection from silicon and carbon surfaces

Effects of roughness and temperature on low-energy hydrogen positive and negative ion reflection from silicon and carbon surfaces

Charge transfer during H/H− collisions with Cu(100) and Cu(111) surfaces

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Charge transfer during H/H⁻ collisions with Cu(100) and Cu(111) surfaces