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Bulk and surface states of a clean and Cs-doped surface of a Co film grown on Cu͑001͒ have been studied by spin-resolved photoemission ͑SR-PE͒ and compared with band structure calculation results. One-photon ͑1PPE͒ and two-photon ͑2PPE͒ photoemission spectra from clean Co films are found to be dominated by a peak located at a binding energy of about 0.4 eV with respect to E F , which is assigned to the spin up 3d bulk state. Slight Cs-doping of a Co͑001͒ surface shifts an image potential state in resonance with the sp-states of the conduction band. SR-2PPE study of the optically-induced electron population in such an image resonance reveals a strong dependence on the set polarization of the laser light. We are able to directly detect the spin polarization of electrons photoemitted from the image resonance state, which can be varied from highlypolarized ͑about bulk values͒ to almost unpolarized when tuning light polarization of the pump laser pulse from s to p.

Electron emission from Ag and Au nanoparticle films was studied under excitation with femtosecond-laser pulses with photon energies of 1.55 and 3.1 eV. Films were grown on a glass substrate with particle sizes from the nanometer range to a continuous layer. The transition from a continuous film to a nanoparticle film is accompanied by an increase in photoemission current by more than an order of magnitude. Pump-and-probe experiments with variable delay gave information on the lifetime of the intermediate states. At a fixed pulse power, the emission yield increases as the temporal width of the laser pulses is decreased. Experimental results are interpreted in terms of two different electron emission mechanisms, i.e., multiphoton photoemission and thermionic emission or thermally assisted multiphoton photoemission. The first mechanism prevails for continuous films and larger particles with sizes above several tens of nanometers; the second one prevails for smaller nanoparticles with sizes of a few nanometers.

Electron-spin relaxation at different surfaces of p-doped GaAs is investigated by means of spin, time and energy resolved 2-photon photoemission. These results are contrasted with bulk results obtained by time-resolved Faraday rotation measurements as well as calculations of the Bir-Aronov-Pikus spin-flip mechanism. Due to the reduced hole density in the band bending region at the (100) surface the spin-relaxation time increases over two orders of magnitude towards lower energies. At the flat-band (011) surface a constant spin relaxation time in agreement with our measurements and calculations for bulk GaAs is obtained. PACS numbers: 72.25.Mk,72.25.Rb,78.47.+p In recent years, much experimental and theoretical work has been focused on the control and manipulation of the electronic spin degree of freedom independently of its charge, with the ultimate goal of spintronics devices, in which the electron spins are the carriers of the information [1]. The limiting factor for the usefulness of the information encoded in a spin-polarized current in a non-ferromagnetic semiconductor is the relaxation of the spin polarization, which is caused by a variety of interaction mechanisms [2]. In bulk GaAs, the relaxation of optically induced spin polarizations has been studied intensely for more than 30 years. Early work has led to the identification of several mechanisms that destroy the spin polarization, and good agreement between experiment and theory was found on the level of numerical and experimental accuracy available at that time [3]. In recent years, there has been renewed experimental and theoretical interest in spin relaxation, with many experimental studies focusing on undoped and n-doped semiconductors [4,5]. Early results for p-doped GaAs were obtained by means of hot photon luminescence and the Hanle effect [6]. Surfaces and interfaces, such as Schottky barriers, originally received comparatively little attention [7,8]. More recently, however, interfaces have been studied because of their importance for spintronics device applications where efficient electrical spin injection from a ferromagnetic metal or half-metal through a Schottky barrier into the semiconductor is of utmost importance [9]. The difficulty of efficient spin injection has stimulated interest in a fundamental understanding of spin-flip scattering at semiconductor surfaces and interfaces, e. g., at step edges [10].The purpose of this paper is the investigation of electron spin-relaxation in p-doped GaAs and the unambiguous identification of surface effects on the electron spin-relaxation. Using a spin, energy and time-resolved photoemission technique [11] we study the room-temperature spin-dependent electron dynamics at two surfaces with different characteristics [12]: the (100) surface with pronounced band-bending and the cleaved (011) surface, for which we expect flat-band conditions. To obtain a complete picture of the spin relaxation at surfaces as compared to the bulk we have also measured bulk spin relaxation-times by time-resolved Farada...