Interaction of graphite with atomic hydrogen

The kinetics of sorption of atomic hydrogen by pyrolytic, quasi-single-crystal, and RGT commercial-grade graphite was studied. The processes of sorption and subsequent thermal outgassing are shown to proceed in a similar manner for all the three types of graphite. Thermal desorption spectra obtained during linear heating of hydrogen-saturated samples have two peaks. A mathematical model including features of the thermal desorption kinetics that are observed when heating is terminated is suggested. According to this model, two types of traps with binding energies of 2.4 and 4.1 eV are present in graphite. The physical justification of the model is given.     

Interaction of atomic hydrogen with the graphite single-crystal surface

We have studied the chemisorption of atomic hydrogen on the basal plane of natural graphite single crystals. LEED and angle-resolved photoemission were used to characterize the clean surface. The adsorption of H saturates at rather low exposures, accompanied by a decrease of the work function by =(100±20) meV. The photoemission spectra indicate a clear carbon-hydrogen interaction, leading to shifts of substrate bands by up to about 200 meV. No detectable etching of the surface occurs at room temperature, in agreement with earlier work. Our results are qualitatively consistent with theoretical considerations about a strong H(1s)-C(2p _z) chemical bond.     

Reaction of thermal atomic hydrogen with carbon

The reaction of thermal atomic hydrogen, produced at the surface of a hot tungsten filament, with evaporated carbon films leads to the production of a number of gaseous products. At least 12 have been identified with the largest number of these being cyclic compounds consistent with the structure of graphite. Methane, the major gas phase product (74% partial pressure), is produced with a stoichiometric reaction probability of 0.002. Although the relative reaction rates decrease rapidly with increasing product mass, the total rate of carbon transport is 60% greater than the rate of methane production. Activation energies obtained for 10 of the products by varying the carbon temperature are the same within experimental error. These features are discussed in terms of a highly simplified model of the reaction with the actual reaction following a complicated branching free radical mechanism.     

Interaction of atomic hydrogen with metal surfaces

Received: 23 March 1998/Accepted: 21 August 1998     

Interaction of atomic hydrogen with the graphite single-crystal surface

The reaction of atomic hydrogen (or atomic deuterium) with highly orientated pyrolytic graphite surfaces has been studied by means of thermal desorption spectroscopy. In some cases atomic deuterium instead of atomic hydrogen, was used solely to assign the desorbed masses unambiguously to the different hydrocarbons. The desorption of D₂ and fourteen hydrocarbons was observed. D₂ desorbed at higher temperatures than the CH-(CD) compounds, the desorption spectra of the hydrocarbons contained two peaks. The dependence of the desorption spectra of several hydrocarbons on the heating rate, the atomic hydrogen exposure and the composition of the desorption products was investigated in detail. The kinetic parameters of the desorption process were determined for CH, C₂H₂, and CD₄. The spectra showed that there must be a first order desorption process for all the hydrocarbons, the values for the activation energy and the frequency factor were the same within experimental errors. The results were discussed by means of a simple model.     

Spectroscopy of atomic hydrogen

This article presents a review of the most recent theoretical and experimental results in hydrogen. We particularly emphasize the methods used to deduce the Rydberg constant R _∞ and we consider the prospects for future improvements in the precision of R _∞.     

Discrete solitons in the bigraphene with adsorbed atomic hydrogen

The propagation of discrete solitons in the bigraphene waveguides was calculated according to the Anderson model. An effective equation analogous to the classical sine-Gordon formula was obtained. The dependence of energy distribution between the waveguides of the graphene bilayers with adsorbed atomic hydrogen on the initial pulse width was studied.     

Experimental ionization of atomic hydrogen with few-cycle pulses

We present experimental data on strong-field ionization of atomic hydrogen by few-cycle laser pulses. We obtain quantitative agreement at the 10% level between the data and an ab initio simulation over a wide range of laser intensities and electron energies.     

Oxidation of silicon surface with atomic oxygen radical anions

The surface oxidation of silicon （Si） wafers by atomic oxygen radical anions （O- anions） and the preparation of metal-oxide-semiconductor （MOS） capacitors on the O-oxidized Si substrates have been examined for the first time. The O- anions are generated from a recently developed O- storage-emission material of [Ca24Al2sO64]^4＋·4O^- （Cl2A7-O^- for short）. After it has been irradiated by an O- anion bean： （0.5 μA/cm^2） at 300℃ for 1-10 hours, the Si wafer achieves an oxide layer with a thickness ranging from 8 to 32 nm. X-ray photoelectron spectroscopy （XPS） results reveal that the oxide layer is of a mixture of SiO2, Si2 O3, and Si2O distributed in different oxidation depths. The features of the MOS capacitor of 〈Al electrode/SiOx/Si〉 are investigated by measuring capacitance-voltage （C - V） and current-voltage （I - V） curves. The oxide charge density is about 6.0 × 10^1 cm^-2 derived from the （C - V curves. The leakage current density is in the order of 10^-6 A/cm^2 below 4 MV/cm, obtained from the I - V curves. The O- anions formed by present method would have potential applications to the oxidation and the surface-modification of materials together with the preparation of semiconductor devices.     

Thermodynamics of Bose-condensed atomic hydrogen

We study the thermodynamics of the Bose-condensed atomic hydrogen confined in the Ioffe-Pritchard potential. Such a trapping potential, that models the magnetic trap used in recent experiments with hydrogen, is anharmonic and strongly anisotropic. We calculate the ground-state properties, the condensed and non-condensed fraction and the Bose-Einstein transition temperature. The thermodynamics of the system is strongly affected by the anharmonicity of this external trap. Finally, we consider the possibility to detect Josephson-like currents by creating a double-well barrier with a laser beam. Received 15 February 2000     

Interaction of intense laser pulses with hydrogen atomic clusters

The interaction between intense femtosecond laser pulses and hydrogen atomic clusters is studied by a simplified Coulomb explosion model. The dependences of average proton kinetic energy on cluster size, pulse duration, laser intensity and wavelength are studied respectively. The calculated results indicate that the irradiation of a femtosecond laser of longer wavelength on hydrogen atomic clusters may be a simple, economical way to produce highly kinetic hydrogen ions. The phenomenon suggests that the irradiation of femtosecond laser of longer wavelength on deuterium atomic clusters may be easier than that of shorter wavelength to drive nuclear fusion reactions. The product of the laser intensity and the squared laser wavelength needed to make proton energy saturated as a function of the squared cluster radius is also investigated. The proton energy distribution calculated is also shown and compared with the experimental data. Our results are in agreement with the experimental results fairly well.     

Collisional deactivation of atomic and molecular hydrogen

The H_α, H_β and H_γ lines of the Balmer series of atomic hydrogen and the molecular hydrogen emission system G¹Σ_g⁺→B¹Σ_u were produced by impact of 40 keV electrons with ground state H₂ at room temperature. The variation with H₂ pressure of the fluorescence intensity of these radiative transitions was observed, and the collisional quenching cross sections of the excited electronic states H(n = 3, 4 and 5) and H₂G¹Σ_g⁺ were determined. For the atomic hydrogen principal quantum numbers n = 3, 4 and 5, the quenching cross section was found to be 76, 32 and 8.9 ?², respectively. For the H₂G¹Σ_u⁺ state, the quenching cross section was determined to be 100 ?².     

Surface modification of polystyrene with atomic oxygen radical anions-dissolved solution

A novel approach to surface modification of polystyrene (PS) polymer with atomic oxygen radical anions-dissolved solution (named as O⁻ water) has been investigated. The O⁻ water, generated by bubbling of the O⁻ (atomic oxygen radical anion) flux into the deionized water, was characterized by UV-absorption spectroscopy and electron paramagnetic resonance (EPR) spectroscopy. The O⁻ water treatments caused an obvious increase of the surface hydrophilicity, surface energy, surface roughness and also caused an alteration of the surface chemical composition for PS surfaces, which were indicated by the variety of contact angle and material characterization by atomic force microscope (AFM) imaging, field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and attenuated total-reflection Fourier transform infrared (ATR-FTIR) measurements. Particularly, it was found that some hydrophilic groups such as hydroxyl (OH) and carbonyl (CO) groups were introduced onto the polystyrene surfaces via the O⁻ water treatment, leading to the increases of surface hydrophilicity and surface energy. The active oxygen species would react with the aromatic ring molecules on the PS surfaces and decompose the aromatic compounds to produce hydrophilic hydroxyl and carbonyl compounds. In addition, the O⁻ water is also considered as a “clean solution” without adding any toxic chemicals and it is easy to be handled at room temperature. Present method may suit to the surface modification of polymers and other heat-sensitive materials potentially.     

Near-threshold positron-impact ionization of atomic hydrogen

We consider the positron-impact ionization (breakup) of atomic hydrogen utilizing the full and S-wave model calculations, concentrating on the near-threshold energy region. Unlike the corresponding electron-impact case, the S-wave model does support the Wannier-like threshold law predicted by Ihra et al. [Phys. Rev. Lett. 78, 4027 (1997)10.1103/PhysRevLett.78.4027]. It is found that convergent S-wave model cross sections are obtained only if complete expansions are utilized on both the atomic and the positronium centers. Furthermore, we suggest that, in the model and full calculations, the separate contributions to the breakup cross section from both centers become equal at threshold.