J. L. Erskine

Femtosecond thermionic emission from metals in the space-charge-limited regime

We study femtosecond-laser-pulse-induced electron emission from W(100), Al(110), and Ag(111) in the subdamage regime (1–44 mJ/cm2 fluence) by simultaneously measuring the incident-light reflectivity, total electron yield, and electron-energy distribution curves of the emitted electrons. The total-yield results are compared with a space-charge-limited extension of the Richardson–Dushman equation for short-time-scale thermionic emission and with particle-in-a-cell computer simulations of femtosecond-pulsed-induced thermionic emission. Quantitative agreement between the experimental results and two calculated temperature-dependent yields is obtained and shows that the yield varies linearly with temperature beginning at a threshold electron temperature of ~0.25 eV The particle-in-a-cell simulations also reproduce the experimental electron-energy distribution curves. Taken together, the experimental results, the theoretical calculations, and the results of the simulations indicate that thermionic emission from nonequilibrium electron heating provides the dominant source of the emitted electrons. Furthermore, the results demonstrate that a quantitative theory of space-charge-limited femtosecond-pulse-induced electron emission is possible.

Epitaxial growth of fcc Fe on Cu(100)

Abstract Layer-by-layer epitaxial growth of Fe on Cu(100) is reported. The epitaxy is characterized using Auger electron spectroscopy and low energy electron diffraction intensity analysis. Good quality epitaxial Fe films having thicknesses ranging from one to four monolayers are stabilized by the Cu(100) substrate. The overlayer structure is shown to be nearly identical to a continuation of the fcc lattice of the substrate.

Exploring Magnetic Properties of Ultrathin Epitaxial Magnetic Structures Using Magneto-Optical Techniques

We describe magneto-optic Kerr effect studies of ultrathin Fe and Ni films on single crystal surfaces of Ag and Cu. Monolayer Fe films on Ag(100) exhibit the theoretically predicted spin-orbit anisotropy, but also yield some interesting discrepancies between behavior predicted by Kerr effect and by spin-polarized photoemission experiments. Layer-dependent studies of the magnetic moment of Ni on Ag(111) and Ag(100) suggest sp-d hybridization effects quench the first layer magnetic moment on Ag(111) but not on Ag(100). Temperature dependent studies of thin film magnetization obtained from Kerr effect measurements yield thickness dependent Curie temperatures, and critical exponents for several thin film systems.

Angle-resolved photoemission evidence for a Gd(0001) surface state

Abstract From angle resolved photoemission we have observed a surface state on Gd(0001) near the Fermi energy in the vicinity of Γ in agreement with a recently calculated band structure. This surface state is of prominent character (Δ 1 ) at Γ . The observation of this surface state can be correlated with the development of the gadolinium bulk band structure which occurs with increasing film thickness as gadolinium films are grown on W(110).

The electronic structure and orientation of the surface methoxy species on Ni(111)

Abstract Photoelectron spectra of the methoxy species formed by the decomposition of methanol on nickel(111) indicate that the C-O-nickel bond is normal or nearly normal to the metal surface. This structural assignment for the adsorbate complex is consistent with new photoelectron data using linearly polarized synchrotron radiation.

Adsorbate structure modeling based on electron energy loss spectroscopy and lattice dynamical calculations: Application to O/A1(111).

Abstract High-resolution electron energy loss spectroscopy (EELS) and lattice dynamical calculations based on pair interactions are used to investigate oxygen chemisorption on Al(111). The O/Al(111) System is complicated by the simultaneous formation of an oxygen overlayer and underlayer. Oxygen atoms at overlayer and underlayer sites near the Al(111) surface produce well-defined vibrational loss peaks in EELS spectra, however, dynamical coupling between the oxygen atoms and with the host lattice cause vibrational energies to shift with overlayer and underlayer concentrations. These shifts as well as structural parameters of the O/Al(111) complex can be deduced from a slab model of the surface lattice dynamics.

Image properties of the hemispherical analyzer applied to multichannel energy detection

Abstract Electron trajectories through a hemispherical analyzer are studied in relation to applications using high spatial resolution position sensitive devices for multichannel detection. Criteria are established for optimizing detection efficiency, choosing various parameters and analyzing effects of fringing electric fields and magnetic fields on analyzer performance.

Investigation of underlayer formation by oxygen on Al(111) and Ti(0001)

High‐resolution electron energy loss spectroscopy is used to investigate the initial stage of oxide formation on Al(111) and Ti(0001) surfaces. Analysis of the O/Al(111) vibrational data based on lattice dynamical slab calculations confirms underlayer formation as a precursor to oxidation. These results help account for some of the novel properties associated with oxygen chemisorption on Al(111) and Ti(0001) surfaces and also illustrate the ability of vibrational spectroscopy to provide surface structure information which complements results of other structure sensitive techniques.

Electron energy loss spectroscopy studies of nitrogen adsorption on W(100)

Abstract Vibrational excitations of nitrogen on W(100) are investigated over the 100–300 K temperature range using elastic and inelastic electron scattering. New vibrational modes of nitrogen are identified that require different mode assignments from previous work. Experimental evidence for a molecular precursor to the atomic β 2 phase of adsorbed nitrogen is presented. Coverage dependent studies of vibrational modes suggests conversion between two different molecular surface phases and between atomic and molecular phases. A new ordered nitrogen phase characterized by a (4 × 1) LEED pattern is observed. The new phase appears to consist of orthogonal domains of p(4 × 1) symmetry that contain atomic nitrogen at the four fold sites (the β 2 atomic phase) with additional bridge-bonded nitrogen atoms in the unit cell.

Angle-resolving photoelectron energy analyzer designed for synchrotron radiation spectroscopy

Abstract This paper describes design considerations, input lens analysis, ray-tracing studies, construction details and initial tests of a Kuyatt—Simpson-type photoelectron energy analyzer. The analyzer has been designed specifically for angle-resolved photoemission studies using synchrotron radiation. Design features include input and output lens systems which establish virtual slits and apertures which define the input solid angle and source region. Constant angular resolution, constant energy-resolution and constant transmission are achieved by the analyzer. The performance of the analyzer has been checked analytically using computer ray-tracing techniques and experimentally. Initial tests have verified the ray-tracing results and have shown that all the analyzer design specifications have been realized.