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It has been demonstrated previously that electrons interact differently with chiral molecules depending on their polarization. For enantiomeric pure monolayers of heptahelicene, opposite asymmetries in spin polarization were reported and attributed to the so-called chirality-induced spin selectivity effect. However, these promising proof-of-concept photoemission experiments lack the angular and energy resolution that could provide the necessary insights into the mechanism of this phenomenon. In order to fill in the missing gaps, we provide a detailed spin- and angle-resolved photoemission spectroscopy study of heptahelicene layers on a Cu(111) substrate. Throughout the large accessible energy and angle range, no chirality induced spin asymmetry in photoemission could be observed. Possible reasons for the absence of signatures of the spin-dependent electron transmission through the chiral molecular layer are briefly discussed. [ABSTRACT FROM AUTHOR]

In this paper, we present experimental results on the effect of space charging in photoelectron spectroscopy from a surface using a pulsed and intense femtosecond light source. We particularly focus on a quantitative evaluation of the induced spectral broadening. Our results are compared with analytic calculations based on energy conservation considerations as well as with experimental results from measurements using picosecond pulses for the excitation process. As a measure of space charge effects, we monitored the angular and energy distributions of the photoemission from the occupied Shockley surface state of Cu(111) as a function of the total number N of the photoemitted electrons per laser pulse. Our results show that spectral distortions exist for the entire laser fluence regime probed. The energetic broadening of the surface state peak can be fitted with remarkable accuracy by a √N dependence, in agreement with the theoretical predictions and different from the experimental picosecond results, where a dominating linear dependence has been reported. In addition to a pure energetic broadening of the photoemission spectra, we also identify modifications in the angular distribution of the photoemitted electrons due to space charge effects. [ABSTRACT FROM AUTHOR]

Investigates domains written thermomagnetically in terbium-iron-cobalt thin films. Application of Lorentz transmission electron microscopy and scanning electron microscopy with polarization analysis (SEMPA); Relationship between the magnetic contrast in the SEMPA measurements and the magnetization of the transition-metal subnetwork; Temperature dependence of the coercive field.

Photoelectrons with excess kinetic energy corresponding to several absorbed photons above the work function have been measured from atomically clean Cu(110) and Cu(100) surfaces under ultrahigh vacuum conditions. The power dependence of the photoemission yield does not follow a simple power law dependence corresponding to the number of photons absorbed. This behavior is reminiscent of other above threshold ionization (ATI) or tunnel ionization (TI) processes observed for atoms in the gas phase. The photoelectrons are generated with laser pulsewidths less than 100 fs in duration and peak powers as low as 100 MW/cm2. These intensities are on the order of 105 times lower than that required to observe similar phenomena in the gas phase. The relatively low intensities and correlation with surface roughness suggests a contribution from a surface enhancement mechanism. Thermal heating and space charge effects have been ruled out, and the possibility of electric field enhancement at the surface due to the coupling of photons into surface plasmons is discussed. The nonlinear yield and enhancement of the photoemission produced by short pulse excitation needs to be considered when discussing photoinduced hot electron reaction channels at metal surfaces. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the magnetic properties of thin fcc iron films on copper(001). Method used in the preparation of the iron films; Analysis of the magnetization curves for different fcc iron films; Temperature dependence of the coercive field.

Presents a study which investigated ultrafast thermomagnetic writing processes in rare-earth transition-metal thin films. Experimental details; Discussion; Conclusions.

Presents a study that used the technique of spin-polarized photoemission to investigate electron-lattice relaxation in tin and the spin-lattice relaxation in iron. Measurement of the spin polarization of the photoelectrons emitted from tin and iron during picosecond and nanosecond laser pulses; Determination of the spin polarization of the photoelectrons.

Focuses on a study that investigated the magnetic properties of epitaxial bcc iron films on silver(001) by spin-polarized photoemission. Description of the epitaxy of iron/silver(001) system; Measurement of the spin polarization of the photoemitted electrons; Magnetization curves for iron films on silver (001) for various film thicknesses.

The fundamental mechanism responsible for optically induced magnetization dynamics in ferromagnetic thin films has been under intense debate since almost two decades. Currently, numerous competing theoretical models are in strong need for a decisive experimental confirmation such as monitoring the triggered changes in the spin-dependent band structure on ultrashort time scales. Our approach explores the possibility of observing femtosecond band structure dynamics by giving access to extended parts of the Brillouin zone in a simultaneously time-, energy- and spin-resolved photoemission experiment. For this purpose, our setup uses a state-of-the-art, highly efficient spin detector and ultrashort, extreme ultraviolet light pulses created by laser-based high-order harmonic generation. In this paper, we present the setup and first spin-resolved spectra obtained with our experiment within an acquisition time short enough to allow pump-probe studies. Further, we characterize the influence of the excitation with femtosecond extreme ultraviolet pulses by comparing the results with data acquired using a continuous wave light source with similar photon energy. In addition, changes in the spectra induced by vacuum space-charge effects due to both the extreme ultraviolet probe- and near-infrared pump-pulses are studied by analyzing the resulting spectral distortions. The combination of energy resolution and electron count rate achieved in our setup confirms its suitability for spin-resolved studies of the band structure on ultrashort time scales. [ABSTRACT FROM AUTHOR]

Optimized-quality monoenergetic target surface electron beams at MeV level with low normalized emittance (0.03p mm mrad) and high charge (30 pC) per shot have been obtained from 3 TW lasersolid interactions at a grazing incidence. The 2-Dimension particle-in-cell simulations suggest that electrons are wake-field accelerated in a large-scale, near-critical-density preplasma. It reveals that a bubble-like structure as an accelerating cavity appears in the near-critical-density plasma region and travels along the target surface. A bunch of electrons are pinched transversely and accelerated longitudinally by the wake field in the bubble. The outstanding normalized emittance and monochromaticity of such highly collimated surface electron beams could make it an ideal beam for fast ignition or may serve as an injector in traditional accelerators. [ABSTRACT FROM AUTHOR]

In order to explore the role of enhanced spin-orbit interactions on the laser-induced ultrafast magnetization dynamics, we performed a comparative study on cobalt thin films and Co/Pt multilayers. We show that the presence of the Co/Pt interfaces gives rise to a three-fold faster demagnetization upon femtosecond laser heating. Experimental data for a wide range of laser influences are analyzed using the Microscopic 3-Temperature Model. We find that the Elliott-Yafet spin-flip scattering in the multilayer structure is increased by at least a factor of four with respect to the elementary Co film. [ABSTRACT FROM AUTHOR]

An experimental setup for time- and angle-resolved photoemission spectroscopy using a femtosecond 1 kHz high harmonic light source and a two-dimensional electron analyzer for parallel energy and momentum detection is presented. A selection of the 27th harmonic (41.85 eV) from the harmonic spectrum of the light source is achieved with a multilayer Mo/Si double mirror monochromator. The extinction efficiency of the monochromator in selecting this harmonic is shown to be better than 7:1, while the transmitted bandwidth of the selected harmonic is capable of supporting temporal pulse widths as short as 3 fs. The recorded E(k) photoelectron spectrum from a Cu(111) surface demonstrates an angular resolution of better than 0.6° (=0.03 Å-1 at Ekin,e=36 eV). Used in a pump-probe configuration, the described experimental setup represents a powerful experimental tool for studying the femtosecond dynamics of ultrafast surface processes in real time. [ABSTRACT FROM AUTHOR]

Describes theoretical and experimental investigations for a design of an ultrashort pulsed laser activated electron gun for time-resolved surface analysis. Design methodology; Electrode configuration; Calculated electron trajectories and field distribution; Laser system; Electron gun performance; Time-resolved electron diffraction.

We describe the growth of high quality tetrathiofulvalene tetracyanoquinodimethane (TTF-TCNQ) organic charge-transfer thin films which show a clear non-Fermi liquid behavior. Temperature dependent angle resolved photoemission spectroscopy and electronic structure calculations show that the growth of TTF-TCNQ films is accompanied by the unfavorable presence of neutral TTF and TCNQ molecules. The quality of the films can be controlled by tuning the evaporation temperature of the precursor in physical vapor deposition method. [ABSTRACT FROM AUTHOR]

Examines the magnetization reversal of amorphous GdTbFe films. Use of spin-polarized photoemission with a pulsed laser; Correlation between compensation temperature and laser pulse duration; Dependence of magnetization reversal on temperature.

Studies the time resolution in photoemission using pulsed lasers as light sources. Results of the study.

We have found that ion bombardment produces dramatic changes in the surface magnetism of Fe3O4. The surface layer with irregular magnetic behavior is more than 50 Å thick. These findings are of importance for current studies of ferritelike sputtered thin films as well as magnetic alloys in general. [ABSTRACT FROM AUTHOR]

A custom-made Omicron-compatible sample holder for time-resolved photoelectron emission microscopy experiments is presented. It comprises a sample plate with four contacts that hosts a chip carrier where the semiconductor substrate is mounted. Covering the sample holder, a 6 mm diameter mask protects electrostatically the sample from the extractor lens voltage while keeping the imaging quality unperturbed. The improvements are a greater sample lifetime and the ability to withstand much higher currents in the stripline that provides the magnetic pulse to the magnetic microstructure.