The ferroelectric domain structure on a (001) surface of a single crystal prepared under ultrahigh vacuum conditions is imaged by laser-excited photoemission electron microscopy (PEEM). The PEEM images allow for discrimination of three domain types by their different photoemission yields. To characterize the contrast between the different ferroelectric domains of (001) in the region of 4.0–4.6 eV close to the photoemission threshold, the broad wavelength tunability of the femtosecond laser system is used. The femtosecond time resolution within two-photon PEEM experiments, using two fully independently tunable laser beams, is demonstrated for the first image potential state of Ag(001). In a pump-probe setup with a cross-correlation full-width at half-maximum of 70 fs, an angle-integrated apparent lifetime of 40 fs is derived from the PEEM intensities. In contrast with energy-resolved two-photon photoemission measurements, PEEM data reveal a 17-fs shorter lifetime. This difference is discussed by considering the co-excitation of bulk states, which leads to an additional time-dependent photoelectron contribution in PEEM.
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IBM Journal of Research and Development
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18 August 2011
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