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We present and analyze isothermal adsorption and desorption measurements for methane physisorbed on a Cu(100) surface to characterize the interplay between molecule–surface and molecule–molecule interactions. A 2D gas–liquid phase boundary for the methane layer is observed and partially mapped in coverage and temperature. Comparing our measured critical temperature of 66 K ±2 K to previous work on related systems implies an attractive well between physisorbed molecules of ∼130 K. This reduction compared to the gas phase well can be adequately understood in terms of dielectric screening of the dispersion interaction. By contrast, analyzing the low‐coverage adsorption and desorption isotherms using a quasiequilibrium model and imperfect gas statistics, we deduce a lateral attractive intermolecular potential well of only 40–50 K. This drastic reduction of the attractive well from the gas phase value is not consistent with image charge screening, and is difficult to reconcile with the observed critical temper...

We report time‐resolved electron energy loss spectroscopy results for the thermal desorption of CO physisorbed onto Ag(011). The measurements were performed isothermally and effectively at constant coverage. We observe that the logarithm of the measured pseudo‐first‐order desorption rate constant increases approximately linearly with coverage over the temperature and coverage ranges accessible to our measurements. The results are analyzed in terms of a quasiequilibrium model in which the desorption rate constant is expressed analytically as a virial expansion. Using this analysis, we determine that at low coverage the molecules adsorb with their axes parallel to the surface plane and are oriented with respect to the crystalline axes. We find that long‐range interactions extending out to 7–8 neighbor shells must be included to fit our results. The magnitude of these long‐range interactions is reasonably well described by the gas phase intermolecular potential if screening by substrate image charges is incl...

We present time‐resolved electron energy loss spectroscopy measurement of isothermal desorption of NH3 and ND3 from Cu(001) as a function of coverage. The desorption process is characterized by pseudo‐first‐order kinetics. The pseudo‐first‐order rate constant increases approximately exponentially as a function of adsorbed ammonia coverage. The results of an analysis based on a quasiequilibrium approximation which expresses the desorption rate in terms of a virial expansion in adsorbate coverage are reported. This demonstrates that the intermolecular interactions are dominated by short range repulsive lateral interactions, in qualitative accord with expectations of dipolar interactions. The results also suggest the existence of longer‐range attractive interactions.

The kinetics of NH3 and ND3 desorption from Cu(001) surface have been measured by time‐resolved electron energy loss spectroscopy. The desorption precess is observed to be characterized by pseudo‐first‐order kinetics. The desorption energy and the prefactor have been determined for both NH3 and ND3. The prefactors are unusually low as compared to those observed for simple diatomic molecules. Moreover, we observed an unusual behavior consistent with an isotope kinetic compensation effect. Both of these observations can be explained within the context of transition state theory by the interplay between isotopic masses and the shifts of frustrated vibrational modes of adsorbed molecules. Our results imply that the conventional Arrhenius form would not be precisely applicable to molecular desorption, if a large enough temperature range could be measured, particularly for hydrogen‐containing molecules.

We report time‐resolved electron energy loss spectroscopy results for the desorption of CO from Cu(001) and Cu(011). The measurements were performed isothermally and effectively at constant coverage. We present an analysis based on a quasiequilibrium model that expresses the pseudo‐first‐order desorption rate constant in terms of a virial expansion. The results of this analysis demonstrate the existence of small, long‐range attractive interactions as well as the expected short‐range repulsive interactions between adsorbed molecules. The interplay between these two types of interactions leads to a kinetic compensation effect that can be easily understood in terms of vanishing virial coefficients. Thus, in these simple systems, the origin of the kinetic compensation effect lies in the statistical thermodynamics of the adsorbed phase, while the dynamical events associated with the desorption event apparently play a lesser role. The relationship of this analysis technique to others is investigated, and its generality is emphasized.

High spatial resolution magnetic x-ray spectromicroscopy at x-ray photon energies near the cobalt L3 resonance was applied to probe an amorphous 50 nm thin SmCo5 film prepared by off-axis pulsed laser deposition onto an x-ray transparent 200 nm thin Si3N4 membrane. Alternating gradient magnetometry shows a strong in-plane anisotropy and an only weak perpendicular magnetic anisotropy, which is confirmed by magnetic transmission soft x-ray microscopy images showing over a field of view of 10 μm a primarily stripe-like domain pattern but with local labyrinth-like domains. Soft x-ray ptychography in amplitude and phase contrast was used to identify and characterize local magnetic and structural features over a field of view of 1 μm with a spatial resolution of about 10 nm. There, the magnetic labyrinth domain patterns are accompanied by nanoscale structural inclusions that are primarily located in close proximity to the magnetic domain walls. Our analysis suggests that these inclusions are nanocrystalline Sm2...

We report a simple and nondestructive method to determine directly the spatial profiles of the constituent elements in a synthetic multilayered material with a resolution of 10–20 A. This has been accomplished by measuring the x‐ray diffraction Bragg peak intensities over a large range of energies, and interpreting these data using a dynamical theory to deduce the first few Fourier coefficients of the relevant spatial profiles. We present initial results for Ti‐Si multilayer samples grown by thermal deposition. These results demonstrate extensive interdiffusion of the silicon into the titanium layers, even without annealing.

We have used resonant, coherent soft x-ray scattering to measure wave vector re- solved magnetic domain memory in Co/Pd multilayers. The technique uses angular cross correlation functions and can be applied to any system with circular annuli of constant values of scattering wave vector q. In our Co/Pd film, the memory exhibits a maximum at q = 0.0384 nm-1 near initial reversal that decreases in magnitude as the magnetization is further reversed. The peak is attributed to bubble domains that nucleate reproducibly near initial reversal and which grow into a labyrinth domain structure that is not reproduced from one magnetization cycle to the next.

Emerging interest in utilizing the transverse coherence properties of thermal energy atomic and molecular beams motivates the development of ionization detectors with near unit detection efficiency and adequate spatial resolution to resolve interference fringes of submicron dimension. We demonstrate that a field ionization tip coupled to a charged particle detector meets these requirements. We have systematically studied the current-voltage relationship for field ionization of helium using tungsten tips in diffuse gas and in a supersonic helium beam. For all 16 tips used in this study, the dependence of ion current on voltage for tips of fixed radius was found to differ from that for tips held at constant surface electric field. A scaling analysis is presented to explain this difference. Ion current increased on average to the 2.8 power of voltage for a tip at fixed field and approximately fifth power of voltage for fixed radius for a liquid nitrogen cooled tip in room temperature helium gas. For the heli...

An angle‐resolving electron energy analyzer capable of operating at an energy resolution of ≲20 meV and an angular resoltuion of ≲1/4° has been designed, constructed, and tested. A novel input lens allows independent control over both the energy and angular resolution. A series of tests has been performed which indicates that the analyzer operates at the theoretical resolution limit for the lowest values used.

A new high‐resolution electron‐energy‐loss spectrometer (EELS) based on dispersion compensation has been designed, built, and tested. A detailed analysis indicates that this system should yield two to three orders of magnitude more signal than conventional spectrometers operating at comparable energy resolution. Second‐order imaging aberrations have been calculated and shown to be consistent with this expectation. A specific design is presented which will allow studies of the vibrations of transient species on a surface. Initial tests on the chemisorption of CO on Cu (100) indicate the applicability of this new technique.

We present time‐resolved electron energy loss spectroscopy (EELS) results for the desorption of submonolayer coverages of H2O and D2O from Ag(011). The measurements were performed isothermally and effectively at constant coverage. At coverages above a few percent of a monolayer, we observe that the desorption is characterized by zero‐order kinetics. That is, the desorption rate is independent of coverage. We hypothesize that this results from the formation of two‐dimensional water islands on the surface at all coverages and temperatures measured. The desorption process is governed in part by the dissociation of water from the edges of these islands. Rapid diffusion on the surface maintains a quasiequilibrium between the molecules bound to islands and isolated adsorbed water molecules, thereby leading to pseudo‐zero‐order kinetics. This result is interpreted upon general thermodynamic grounds, and also using a simple kinetic model which leads to pseudo‐zero‐order desorption kinetics. An unusual hydrogen ki...