Intensity and structure of the energy spectra of Na+ and Ne+ ions scattered from a Cu(110) surface are governed by multiple scattering and neutralization effects. These were studied for ion energies between 600 eV and 1 keV and in the temperature range from 100 to 600 K in the experiment and by computer simulation. Na+ scattering directly reflects the crystallographic structure of the (110) surface. The temperature effects can be used to analyze thermal motions of surface atoms in terms of a surface Debye temperature for specific vibrational directions. The contributions of single and multiple scattering events to the energy spectra are analyzed and for Ne+ a strong trajectory-dependent neutralization is found. The comparison of the neutralization of Ne+ and Na+ leads to a Ne+ ion survival probability of a few percent for single scattering, less than 1% for double scattering, and a value of less than 10−3 for scattering from atoms below the top atomic layer. A simple neutralization model is developed to explain the observed survival probabilities.

The scattering of 1 keV Ne+ and Na+ from a Cu(110) surface in the temperature range from 100 K to 600 K has been investigated experimentally and by using the numerical code ARGUS. The intensity of Ne+ single collisions can be explained with a two-atom model, using a surface Debye temperature of 150 K for vibrations perpendicular to the surface. For Na+ various trajectories contribute to the intensity at a single collision peak. These results are corroborated by three dimensional computer calculations from which the contributions of various scattering classes can be identified. For Ne+ a trajectory dependent neutralization has to be taken into account, yielding an ion survival probability between 2 and 6%, depending on the scattering geometry.

We have measured the specific energy loss, ΔE / ΔX , for 23 projectiles in carbon targets at low velocity, v < v 0 . We have used a Monte Carlo calculation to determine the elastic energy loss appropriate to the experimental conditions. The electronic stopping values derived from our measurements show a marked oscillation in Z 1 , the projectile atomic number, and depend on the target thickness. Our data are compared to other measurements in the same velocity regime.

We have measured the specific energy loss, ΔE/ΔX, for 23 projectiles in carbon targets at low velocity, v < v0. We have used a Monte Carlo calculation to determine the elastic energy loss appropriate to the experimental conditions. The electronic stopping values derived from our measurements show a marked oscillation in Z1, the projectile atomic number, and depend on the target thickness. Our data are compared to other measurements in the same velocity regime.

The depth profiles of 3He implanted at 35 keV energy into Al, Ti, V, Ni, Cu, Zn, Zr, Nb, Ag, Sn, Ta, W, Au and Bi targets have been measured using the thermal neutron reaction 3He(n, p)3H. The profiles obtained from the energy distribution of the emitted protons show a marked Z2-oscillation in both the most probable depth and depth straggling. The measured values are compared to Monte Carlo computer simulation results.

The backscattering of Ne+ and Na+ ions from Cu(110) surface was investigated in the temperature range from 100 to 600 K. For Ne+ scattering from the topmost atomic layer an increase or decrease of the scattering intensity with increasing temperature is found, depending on the scattering geometry chosen. This result can be quantitatively explained using a two-atom model and a surface Debye temperature of 150 K for vibrations perpendicular to the surface. Na+ shows basically the same temperature dependence, the scattering intensity being determined by the smaller neutralization probability. These results are supported by three-dimensional calculations using the computer code ARGUS.

Energy-angle distributions have been measured for 0.8 v 0 , ( v 0 = Bohr velocity) Ne and Bi ions penetrating through carbon foils. Comparing the results with a Monte Carlo computer simulation that included an angle dependence only for the elastic collisions, we have observed for Ne projectiles an angle-dependent inelastic loss which, for small angles, is much larger than the elastic contribution in the case of thin foils. In the case of Bi, the energy loss distribution is dominated by elastic collisions. The calculations of Meyer, Klein and Wedell, and Ellmer and Wedell cannot describe the experimental results. The multiple scattering distributions are in agreement with both analytical and Monte Carlo calculations.

A series is derived for the laboratory Rutherford cross-section in powers of the mass ratio and laboratory scattering angle; the series converges rapidly and the first five terms are sufficient for mass ratios up to 0.6 with errors less than 0.1%. This formulation is particularly convenient for the analysis of scattering cross-section data for light ions in low-Z targets.

The total spectra, ions plus neutrals, of 5.0 keV and 9.5 keV Ne+ ions backscattered from an ordered Cu3Au(100) surface were measured by the time-of-flight technique (LEIS-TOF). Good agreement between these results and computer simulations was obtained. From detailed analysis of the trajectories comprising the simulated spectra it is inferred that layers deeper than the first three contribute a secondary structure to the backscattered spectra.

An approximation method is given which permits rapid calculation of the surface backscattering yield from an atomic row with correlated thermal vibrations. The method has been tested by comparison with computer simulations for low index directions in Pt, Au, Mo and Si for He+ beam energies between 0.5 and 2.0 MeV over the temperature range 50–500 K. Agreement was found to be good in those cases where shadow cone scaling of the yields is valid.

The time-of-flight version of low energy ion scattering LEIS (TOF), avoids uncertainties in quantitative analysis due to neutralization in scattering. However, some other factors to consider are: a) accuracy of the scattering cross-sections employed, b) enhancement of scattering yields from sub-surface layers by focusing effects, c) dependence of detector efficiency on scattered energy, and d) background subtraction in integration of single-scattering peaks. We have investigated these problems using 2.4–10 keV Ne+ beams scattered from a Cu3Au (100) ordered surface in conjunction with computer simulation of the energy spectra and have found c) to be the most important potential source of error. Correction factors are derived from measurements of scattering yield vs E0.

Rutherford backscattering measurements (RBS) of Pt(110) and Au(l10) surfaces, both of which exhibit a (1×2) reconstruction, have been made over the temperature range 160–600 K (Pt) and 150–1000 K (Au). Angular scans about the [110] and [100] directions have been measured for the (1×2) phase on both materials. Detailed Monte Carlo simulation studies, including the effects of equal-time displacement correlations, have been used to interpret the vibrational properties of this surface phase. The Pt [110] surface peak data provide clear evidence that correlations of the atom vibrations exist and are consistent with those expected from bulk inelastic neutron scattering measurements. This was not the case for the Au [110] surface peak which exhibited higher yields than predicted.

The reconstruction exhibited by clean Pt(100) surfaces [(5 × 20) LEED pattern] is removed by the adsorption of CO. Rutherford backscattering (RBS) indicates that 1.65 ± 0.05 × 1015 Pt atoms cm−2 move into registry with the bulk upon adsorption of 6.4 ± 0.4 × 1014 CO molecules cm−2 (θ = 0.50 ± 0.03 monolayers). The data indicate that some atoms in the second and perhaps even subsequent layers must be displaced by ≳0.01 nm in the reconstructed surface. By contrast, only 1.3 ± 0.1 × 1015 Pt atoms cm−2 move back into registry upon adsorption of H2 or D2, and the LEED pattern also indicates that residual reconstruction remains. The stability of the CO-covered, H-covered and “almost clean” (1 × 1) surfaces (the latter prepared by NO and H2 treatments with a residual H-coverage of ∼1 × 1014 H atoms cm−2) was investigated by RBS. The CO-covered surface starts to reconstruct only when the CO coverage drops below 0.5 monolayers (T ≳ 450 K) while the H-covered surface (produced by adsorption on the (5 × 20) surface) reconstructs rapidly at T ≳ 350 K, by which temperature the adsorbed hydrogen coverage drops below ∼0.2 monolayers. The “almost clean” surface reconstructs at T ≳ 390 K and the data indicate that the process exhibits an activation energy of 88 ± 17 kJ mol−1. The absolute coverages of CO and D were determined by nuclear microanalysis (NMA) and excellent agreement was achieved between the LEED and NMA data. The saturation CO coverage was found to be 0.77 ± 0.03 monolayers, consistent with the observed c(4 × 2) LEED pattern. Deuterium (and hence hydrogen) coverages of 1.54 ± 0.1 × 1015 D (H) atoms cm−2 (θ = 1.20 ± 0.08) were found at saturation at ∼150 K and the hydrogen adsorbed on the (1 × 1) surface was more strongly bound than that resulting from adsorption on the (5 × 20) surface.

An analytic expression is derived for the magnitude of the “surface peak” in the energy spectra of ions backscattering from an atomic string in the regime where more than two string atoms contribute to the backscattering. The thermal amplitudes of the atoms comprising the model string can be varied, thus facilitating calculations relevant to the investigation of the vibrational properties of surfaces by RBS. This aspect of the model is illustrated by comparison wit experimental measurements for the He/Pt system.

A comparison was made of ion scattering and neutralization results obtained by two time-of-flight systems, one neutral-stripping system, and two electrostatic analyzers, using 5 keV H + , He + , Ne + , N 2 + and Ar + beams on polycrystalline gold targets with a scattering angle of 90°. Data presented include energy distributions of ions plus neutrals, ions only, and ion fractions. Computer simulations of the ion plus neutral spectra are also included.

The scattering of hydrogen and helium ions in the energy range 0.1–15 keV from tungsten, tungsten oxide and a tungsten solid with a 2.5 nm oxide surface, was studied using computer simulation. Good agreement with experimental measurements of the particle and energy reflection coefficients was obtained by scaling the Lindhard form of the electronic stopping powers by 1.75 and 2.7 for hydrogen and helium, respectively. Comparisons with the experimental backscattered energy distributions showed excellent agreement in the higher energy portions of the spectra; this agreement was poorer in the lower energy portions. For low ions energies, the influence of the thin oxide layer was pronounced, in particular in the range profiles, energy distributions and reflection coefficients.

The adsorption of CO (or NO) at temperatures below 250K onto the clean reconstructed (1*2) surface of Pt(110) produces a new metastable c(8*4) phase. Rutherford backscattering measurements have shown that the equivalent of an entire monolayer of Pt atoms is displaced during the adsorption.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation W. N. Unertl, T. E. Jackman, P. R. Norton, D. P. Jackson, J. A. Davies; Summary Abstract: Surface phases of clean, CO and NO covered Pt(110). J. Vac. Sci. Technol. 1 March 1982; 20 (3): 607–608. https://doi.org/10.1116/1.571404 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAVS: Science & Technology of Materials Interfaces and ProcessingJournal of Vacuum Science and Technology Search Advanced Search |Citation Search

An analysis of metabolism by measurement of respiratory quotient values indicates that reduced substances, such as lipids and/or amino acids, are the primary respiratory substrates of dormant Dictyostelium discoideum spores. The spores appear to consume both reduced substances and carbohydrates during the swelling stage of germination. The respiration of emerged myxamoebae is again dominated by the consumption of reduced substances. The pool of trehalose remains largely intact during heat-induced activation and also during postactivation lag. The initiation of spore swelling is accompanied by a decrease in the trehalose pool; the majority of trehalose is consumed before late spore swelling. Upon placing heat-activated spores under restrictive environmental conditions, swelling and trehalose hydrolysis are both prevented. Release from these conditions results in rapid swelling and hydrolysis of trehalose. Trehalase, the enzyme responsible for trehalose breakdown, is present in dormant spores at basal levels. This preformed enzyme is responsible for the hydrolysis of trehalose even though there is a significant increase in trehalase activity with the emergence of myxamoebae. RNA and protein synthesis inhibitors do not prevent trehalose hydrolysis or spore swelling. It is concluded that oxidation of reduced substances occurs in dormant, activated, and swollen spores, as well as in emerged myxamoebae of D. discoideum. Carbohydrate utilization dominates over the oxidation of reduced substances only during the swelling stage of germination.

Backscattering of MeV 4He+ ions in conjunction with nuclear microanalysis has been used to study the effect of adsorbed gases on the interplanar spacing between the outermost Pt layers of the Pt(100)−(1 × 1) surface at 175 K. For the “almost clean” surface, the spacing is found to be within ~0.2% of the bulk spacing: i.e. the surface is unrelaxed. Similar measurements on CO- or H2-covered surfaces, however, show that monolayer adsorption of either gas produces a small outward relaxation of ~0.015 nm (i.e. 0.8%). The results also suggest that the surface Debye temperature is considerably lower than that of the bulk.