Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 8: Posters Transport

TT 8.33: Poster

Freitag, 4. März 2005, 14:00–18:00, Poster TU C

Multiphoton photofieldemission in electromigrated nanogaps — •S. Dantscher¹, D. Wolpert¹, W. Pfeiffer¹, J. U. Würfel², and H. B. Weber² — ¹Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg — ²FZ Karlsruhe, Institut für Nanotechnologie, PO-Box 3640, 76021 Karlsruhe

The combination of nanocontacts and laser excitation offers the possibility of studying photoinduced nonequilibrium transport phenomena and therefore also electron dynamics on the nanometer scale. Using the method of electromigration, contacts with electrode distances in the range of several nanometers can be produced. For relatively large gaps no tunnel current is detectable, i.e. with a moderate applied DC bias, that avoids field emission, these junctions carry no significant current.

We have investigated photocurrents in such contacts under illumination with ultrashort femtosecond laserpulses. The use of a microscope objective as focusing element provides focal radii down to 2µ m resulting in maximum intensities during the pulses of 10¹⁰W/cm². Under these conditions and with bias voltages in the range of ± 5V photo induced currents are detected. The intensity dependences exhibit power laws with exponents up to 3, indicating that multiphoton excitation is responsible for the detected current. Moreover the multiphoton order depends on the actual junction parameters, such as the applied bias. This suggests that the photocurrent flows in the nanogap. The observed bias dependence is attributed to photofieldemission, i.e. the multiphoton photocurrent is influenced by the static field distribution in the gap. In addition, also dynamic field effects might affect the signals.