Electron stimulated desorption of H− and H+ from hydrogen covered tungsten

Electron stimulated desorption from a hydrogen covered polycrystalline tungsten surface has been investigated. The H^? and H⁺ desorption current as a function of incident electron energy was measured in both the low and high energy region. Some threshold-like structures appear in the curve of the desorption current versus incident electron energy; however, no threshold structures have been observed for H^? desorption in the high energy region. The experimental results obtained and the desorption process are discussed in some detail, including initial excitation, charge transfer and ultimate desorption.     

Ejection of H2O,O2, H2 and H from water ice by 0.5–6 keV H+ and Ne+ ion bombardment

The ejection of H₂O, O₂, H₂ and H from water ice at 30–140 K, bombarded by 0.5–6 keV H⁺ and Ne⁺ was studied experimentally. Neon ions in this energy range deposit their energy in the ice by nuclear collisions, whereas with protons of 0.5 to 6 keV the energy deposition mechanism shifts gradually from predominantly nuclear collisions to predominantly electronic processes. The existing theory of nuclear sputtering predicts very well the yield of ejected water molecules and the experimental results in the region of electronic processes agree well with the experimental results of Lanzerotti, Brown and Johnson. However, the major mass loss from water by ion bombardment is via the ejection of O₂, H₂ and H atoms, which exceed the ejection of water molecules. O₂ and H₂ production is markedly enhanced at temperatures exceeding ~100 K, whereas H₂O and H production are temperature independent, suggesting that O₂ and H₂ are produced in the bulk of the ice whereas H₂O and H atoms are ejected from the surface or near surface layers.     

On the origin of electron stimulated desorption of H+ from metal surface

The emission of hydrogen ESD ions from polycrystalline Nb is studied experimentally. The results demonstrate clearly that no ESD emission of H⁺ occurs from a pure H adsorbate. However, adsorption of H₂O, present as an impurity in H₂, and H₂ adsorption on Nb preceded by O adsorption, produce strong H⁺ ESD emission. It is shown that Auger ionization of O can account for the increased H⁺ yield and it is postulated that similar effects also occur on other metal surfaces.     

Infrared study of H+(H2O)nβ″ alumina

Infrared spectra of H⁺(H₂O)_nβ″ alumina show than the dehydrated samples contain H₃O⁺ ions as dominant species while the hydrated ones consists mainly of H₃O⁺ and H₅O⁺₂ entities. Oxonium ions can occupy many different positions more or less distant form the ideal prismatic sites. This structural disorder in the conductivity plane is believed to be the main factor responsible for the high conductivity of the material.     

Core polarization of Cu2+ ions in [Cu(H2O)6]2+ complexes

An alternative interpretation of the experimental spin-Hamiltonian of Cu²⁺: LMN on the basis of M.O. theory is proposed. The calculated value for the core polarization of Cu²⁺ is 20% higher than the one previously assumed.     

TDS and LEED studies of H2O adsorption on GaAs(110)

The UHV cleaved (110) face has been exposed to water in the range from 10 L to 2 × 10⁴ L. The main TDS peak in H₂O desorption appears at 350 K, independent of coverage. The low desorption energy of 0.7 eV (16 kcal/mol) is reasonable for oxygen atoms bound via the lone pair orbital to As as was earlier derived from UPS measurements. A broad spur between 450 and 600 K may be related to O-Ga bonds. The sticking probability shows values below 10^-4; only near 4.8 × 10³ L (6 × 10¹⁵ cm^-2 s^-1 H₂O molecules for 300 s) corresponding to a coverage of about 0.4 monolayes a steep maximum appears. At about one monolayer saturation is observed. Exposures to more than 10⁴ L of water quench the intensity of the (10) LEED spot considerably stronger than the intensity of the (11) spot. A comparison of the I(E) curves with existing model calculations suggests that the observed behaviour of the LEED spots is caused by a change in surface structure towards the unrelaxed configuration. The higher sticking coefficient observed near 0.4 monolayers may be connected with this rearrangement of surface atoms.     

Electron stimulated desorption of H3O from 316L stainless steel

Surface ions generated by electron stimulated desorption from mass spectrometer ion source grids are frequently observed, but often misidentified. For example, in the case of mass 19, the source is often assumed to be surface fluorine, but since the metal oxide on grid surfaces has been shown to form water and hydroxides, a more compelling case can be made for the formation of hydronium. Further, fluorine is strongly electronegative, so it is rarely generated as a positive ion. A commonly used metal for ion source grids is 316L stainless steel. Thermal vacuum processing by bakeout or radiation heating from the filament typically alters the surface composition to predominantly Cr₂O₃. X-ray photoelectron spectral shoulders on the O 1s and Cr 2p_3/2 peaks can be attributed to adsorbed water and hydroxides, the intensity of which can be substantially increased by hydrogen dosing. On the other hand, the sub-peak intensities are substantially reduced by heating and/or by electron bombardment. Electron bombardment diode measurements show an initial work function increase corresponding to predominant hydrogen desorption (H₂) and a subsequent work function decrease corresponding to predominant oxygen desorption (CO). The fraction of hydroxide concentration on the surface was determined from X-ray photoelectron spectroscopy and from the deconvolution of temperature desorption spectra. Electron stimulated desorption yields from the surface show unambiguous H₃O⁺ peaks that can be significantly increased by hydrogen dosing. Time of flight secondary ion mass spectrometry sputter yields show small signals of H₃O⁺, as well as its constituents (H⁺, O⁺ and OH⁺) and a small amount of fluorine as F⁻, but no F⁺ or F⁺ complexes (HF⁺, etc.). An electron stimulated desorption cross-section of σ⁺ ∼ 1.4 × 10⁻²⁰ cm² was determined for H₃O⁺ from 316L stainless steel for hydrogen residing in surface chromium hydroxide.     

Electron-stimulated desorption of D (H) from condensed D2O (H2O) films

The electron-stimulated desorption (ESD) of D⁻ and H⁻ ions from condensed D₂O and H₂O films is investigated. Three low-energy peaks are observed in the ESD anion yield, which are identified as arising from excitation of ²B₁, ²A₁ and ²B₂ dissociative electron attachment (DEA) resonances. Additional structure is observed between 18 and 32 eV, which may be due to ion pair formation or to DEA resonances involving the 2a₁ orbital. The ion yield resulting from excitation of the ²B₁ resonance increases as the film is heated. We attribute the increase in the ion yield to thermally induced hydrogen bond breaking near the surface, which enhances the lifetimes of the excited states that lead to desorption.     

EPR of Fe3+ ion and symmetry of [AIF5·H2O]2? complex ion in (NH4)2AIF5·H2O single crystals

We used the spin-Hamiltonian method for the analysis of the electron paramagnetic resonance (EPR) spectrum of Fe³⁺ as a probe ion in (NH₄)₂AlF₅·H₂O single crystalline basic material. The theoretical expressions for the magnetic field (at which the fine structure transition lines appear) versus the angle between the magnetic field and the axis of symmetry of the magnetic complex are also given. These values were calculated by applying the perturbation theory to the second-order terms. From the experimental results (at 300 K and 9.21 GHz), the spin-Hamiltonian parameters were deduced:D=(668±10)·10⁻⁴ T,E=(−56±10)·10⁻⁴ T,a=(−54±10)·10⁻⁴ T,F=(30±10)·10⁻⁴ T. An isotropic superhyperfine structure was evidenced for the five fluorine ions. The obtained EPR data were used to determine the local symmetry of the Al³⁺ ion. A good agreement with X-ray diffraction measurements was found.     

Channeling of 3 keV H+ ions in copper

Energy spectra and angle dependent yield distributions of 3 keV H⁺ ions scattered from a (001) face of a copper single crystal were measured. The spectra reveal channeling and semi-channeling effects at this relatively low primary energy.     

Molecular effect of Al K α X-ray yields from aluminum oxide films for H+ and H+2 ion bombardments

Al Kα X-ray spectra for equi-velocity H⁺ and H⁺₂ ions of ? 0.9 MeV/amu incident on thin aluminum oxide films with thickness 100 and 300 Å were observed. The intensity ratio of the KL¹ satellite line to the KL⁰ main one for H⁺₂ incident on the films of thickness 100 and 300 Å was about 10% and 4% larger than that for incident H⁺, respectively.     

Effect of H2O on Na+ diffusivity in beta alumina

The effect of H₂O on Na⁺ diffusivity in polycrystalline, and single crystal, beta-alumina was investigated. We found no evidence that water affects the diffusion kinetics and conclude that H₂O is not as easily introduced as a blocking impurity into either the grain boundaries or fast conducting planes, nor is Na⁺ easily removed from the structure by leaching.     

Yields of H+ and He+ at the energy for elastic scattering from H2+3He+ incident on Ag and Pd

Yields, Y, of H⁺ and He⁺ emerging specularly with the energy for single binary elastic collisions have been measured from polycrystalline Ag and Pd surfaces bombarded with mixed monoenergetic (300 < E₀ < 2600 eV) beams of H₂⁺³He⁺ impinging at an angle of 45° from the surface normal. The surfaces were exposed to H₂⁺ at a dynamic pressure of 8 × 10^?3 Pa (6 × 10^?5 Torr) during the measurements. The He⁺ yields from Pd are slightly larger than from Ag, and the H⁺ yields from Pd are 10 to 40 times as large as those from Ag. These results suggest that differences between Pd and Ag in the amount of hydrogen adsorbed and in the character of the hydrogen-metal bond may be responsible for the yield differences through shadowing by, and possibly the sputtering of, adsorbed hydrogen. The Y versus E₀ curves for all four systems have qualitatively the same singly peaked shape which implies that reactive and noble gas ions undergo similar neutralization processes during elastic surface collisions. The ratios of the yields from Ag and Pd do not exhibit the theoretically expected exponential dependence on collision time over the entire range studied, but at the lowest energies the ratios lead to estimates of the difference of neutralization constants which do agree with theory. The potential utility of the large difference in proton yields from Ag and Pd for studying the Ag-Pd alloy system is noted.     

H+和Ar11+激发Si的K壳层X射线发射研究

测量了50–250 keV H⁺和1.0–3.0 MeV Ar¹¹⁺ 轰击Si表面过程中辐射的X射线. 结果表明, 在Ar¹¹⁺入射的情况下, 引起了Si的L壳层上3, 4个电子的多电离.计算了Si的K壳层X射线产生截面, 并将两体碰撞近似(BEA), 平面波恩近似, ECPSSR理论计算与实验值进行了对比. ECPSSR理论与质子产生的截面数据能够很好地符合; 而考虑多电离后, BEA理论与Ar¹¹⁺的实验结果符合较好. 关键词： X射线 高电荷态重离子 多电离     

EPR of Mn2+ in Cd(COO)2· 3H2O single crystals

The electron paramagnetic resonance spectrum of Mn²⁺ has been investigated in cadmium oxalate trihydrate single crystals at room temperature. The spectrum, recorded in the X-band, consists of a set of lines all of which correspond to a single type of environment. None of the principal axes coincides with any crystallographic axis. The spectrum is satisfactorily described by a spin Hamiltonian with a rhombic crystalline electric field. The separations of the forbidden doublets (Δm = ± 1) in different electronic transitions have been calculated and compared with the observed doublet separations.     

H+5团簇离子及其中性团簇产物H3和H4

报道了H⁺₅的实验结果.分析讨论了H⁺₅的 形成和分解途径.根据理论分析，以稳定的H⁺₃为核心与一个或多个氢分子结合可能形成稳定的H^{+_n氢团簇离子.另一方面，在高频离子源中, 有发生H+₃与H₂反应的条件.实 验中，从高频离子源引出的离子束被静电加速器加速，然后用9 关键词： +}₅团簇离子')" href="#">H⁺₅团簇离子 3中性团簇')" href="#">H₃中性团簇 4中性团簇')" href="#">H_{4中性团簇}     

Infrared absorption of aligned H−Na+H− complexes in Kcl crystals

The localized vibrations of a complex in KCl consisting of a triangular array of two H^? ions and one Na⁺ ion in substitutional, neighboring positions have been observed in infrared absorption. As one would expect for such a molecule, five modes are observed: two longitudinal modes at 365 and 508 cm^-1, two complanar transverse modes along <110> at 459 and 562 cm^?1, and one transverse mode along <100> at 551 cm^?1.     

Electron-induced desorption of O+ ions from W,Mo and Cr

We have studied the electron-induced desorption (EID) of O⁺ ions from oxygen-covered polycrystalline W, Mo and Cr surfaces. As the incident electron energy is increased, desorption begins at about 25 eV, and increases dramatically at the binding energy major low-lying substrate core levels. In the range of electron energy studied, below about 200 eV, there are also other variations in ion yield not associated with known core levels. The peak ion kinetic energy is 7.8, 5.3 and 3.4 eV for W, Mo and Cr respectively, and is independent of incident electron energy. These measurements imply that the desorption is initiated by a core level ionization event, although the subsequent electronic transitions leading to desorption apparently differ from those occurring on metallic oxide surfaces.     

Estimation of T1 for Co2+ ions from the temperature variation of the ESR linewidths for VO2+ in Cs2Co(SeO4)2·6H2O single crystals

The electron spin resonance of VO²⁺ is studied in single crystals of Cs₂M″ (SeO₄)₂·6H₂O (M″ = Zn, Co) from 290 to 77 K at ～ 9.45 GHz. The line broadening of VO²⁺ spectra on cooling the Cs₂Co(SeO₄)₂·6H₂O crystal is explained on the basis of host spin-lattice relaxation narrowing. T₁ for Co²⁺ is estimated to be ≈ 1.7 × 10^?12 sec. at 290 K.