Regensburg 2002 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 11: Poster 1

HL 11.60: Poster

Montag, 11. März 2002, 17:00–19:30, Poster A

Confocal Microscopy and Spectroscopy on Silicon Nanocrystals — •Jörg Martin, Frank Cichos, and Christian von Borczyskowski — Institut für Physik 122501, TU Chemnitz, 09107 Chemnitz

Silicon nanoparticles are of currently of considerably interest since they seem to explain certain, unexplained features in the emission of interstellar matter. With respect to this background we investigate silicon nanocrystals by spectrally resolved confocal laser microscopy.

Silicon nanocrystals are prepared by laser pyrolysis and size selected with a time of flight method. The obtained particles show a broad luminescence which is blue shifted compared to bulk silicon emission according to the theoretical predictions of quantum confinement. The studied particle ensembles of approximately 100000 nanocrystals show rapid photobleaching under irradiation with the 514 nm line of an argon ion laser (>10 kW/cm²). All photobleaching decays have a stretched exponential charateristic with decay times in the range of some 100 to 1500 ms depending on the laser intensity. The nonlinear dependence of the decay time on the laser intensity points to a crossover between different bleaching mechanisms. Along with bleaching a shift of the peak wavelength of the luminescence band to the red spectral region occurs, which is appearently connected with different bleaching times for particles of different size. Since heating effects can be ruled out photoinduced ionisation or creation of defect centers are possible sources for the observed photobleaching.