Dresden 2003 – scientific programme

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DS: Dünne Schichten

DS 24: Poster

DS 24.35: Poster

Tuesday, March 25, 2003, 14:30–17:00, P2a

TOF-PEEM investigation of photoelectron emission from Ag clusters — •D.A. Valdaitsev, M. Cinchetti, A. Gloskovskii, S.A. Nepijko, and G. Schönhense — University Mainz

A Time of Flight Photoelectron Emission Microscope (TOF-PEEM) has been used to investigate the photoemission properties of Ag clusters. The measurements were carried out on an Ag film deposited on a Si substrate (wedge-shaped thickness profile). To excite the photoelectrons, pulsed laser radiation with a pulse FWHM of 80 fs and average power of 100 mW was used. The photon energy was 3.1 eV that is lower than the work functions of Ag and Si. The image of the sample surface reveals a non-monotonous character of the dependence of the photoelectron emission intensity on the coverage thickness. The emission current is far above in the region where the film is not continuous, but it is formed by clusters. The spectra of electrons emitted from the continuous Ag films and from the cluster film are characterized by different shapes and different maxima position on the energy scale. The photoelectron spectrum measured for the continuous film has features typical for the two-photon photoemission from bulk Ag. The shape of the spectra obtained for the cluster films and their energy position point to a thermoelectron nature. The estimations show that the electron temperature can reach several thousand Kelvin. As this takes place, the clusters are not evaporated that argues in favor of the fact that the electron gas temperature is not transferred to the lattice. The performed study is of practical importance because it shows a possibility of realizing effective pulsed photocathodes as well as emissive coatings with preset emission properties.