Berlin 2005 – wissenschaftliches Programm

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DS: Dünne Schichten

DS 23: Postersitzung I

DS 23.2: Poster

Freitag, 4. März 2005, 16:00–18:30, Poster TU B

Statistical approach in description of electron emission from nanoparticles under femtosecond laser radiation — •D.A. Valdaitsev, A. Gloskovskii, S.A. Nepijko und G. Schönhense — Institut für Physik, Johannes Gutenberg - Universität, 55099 Mainz

Intense electron emission from Ag particle films deposited onto a Si substrate under 400 and 800 nm laser radiation has been investigated. The observed electron emission enhancement in a particle film with few-nanometer size can not be explained only by multiphoton photoemission occurring through particle plasmon excitation. We consider the effect of a deviation of the number of photons absorbed in one laser pulse by a given particle from its mean value. In the conditions where the mean statistical number N of absorbed photons is in the range of a few or even <1 per pulse the quantum character of energy absorption can not be ignored. This circumstance is found to play an important role for particles with sizes <10nm. In the consideration of the absorption by a particle of this size a statistical approach with N = 0, 1, 2,... has been used. It is demonstrated that taking into account the probability of each statistical event results in an increase of the electron emission due to anomalously high energy density in particles of few nm of size that have absorbed one or a few photons. In certain cases after the thermalization of the electron gas its temperature becomes high enough to give rise to thermionic electron emission. For example, for a particle of 2nm size the absorption of two 3eV photons leads to a transient electron gas temperature of 2000K. The probability to achieve the same temperature for a 5nm particle (absorption of 31 photons) is 25 orders of magnitude lower.