Dresden 2011 – scientific programme
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O: Fachverband Oberflächenphysik
O 66: Plasmonics and Nanooptics VI
O 66.5: Talk
Thursday, March 17, 2011, 12:15–12:30, WIL A317
Hotspot related plasmon assisted multiphoton photocurrents in metal-insulator-metal junctions — •Dominik Differt1, Detlef Diesing2, and Walter Pfeiffer1 — 1Universität Bielefeld, Universitätsstr. 25, 33615 Bielefeld, Germany — 2Universität Duisburg-Essen, Universitätsstr. 5, 45117 Essen, Germany
Scanning photocurrent microscopy of metal-insulator-metal junctions (MIM) is used to investigate the mechanisms of femtosecond multiphoton photocurrent injection at liquid nitrogen temperature. The locally induced multiphoton photocurrent in a Ag-TaO-Ta MIM junction is measured in a scanning microscope cryostat under focused illumination (5µm focus diameter, 800nm, 30fs, 80MHz repetition rate). The intensity dependence reveals a mixture of two-photon and three-photon processes that are responsible for the photocurrent. Its lateral variation shows hotspot-like behaviour with significant magnitude variations on a 100 to 200nm length scale. Assuming an injection current duration of 40fs the peak injection current density of about 104 A cm−2 is estimated - 106 times higher than that for 400nm continuous wave illumination slightly below the damage threshold. The simultaneously measured extinction of the incident radiation reveals a 20 to 30% increased absorption at the hotspots. We attribute the local photocurrent enhancement to the defect-assisted excitation of surface plasmon polaritons at the silver electrode leading to an enhanced local excitation.