High Speed Pump-Probe Spectroscopy of Si3N4 Nanostructures

OLIVER RISTOW; MARTIN GROSSMANN; MIKE HETTICH; AXEL BRUCHHAUSEN; ELKE SCHEER; ARTUR ERBE; THOMAS DEKORSY

Paris

Workshop; Phonons and Fluctuations Meeting; 2010

Ecole Centrale Paris

In this work we present time domain all optical investigations of a single Si3N4 nanostructure in the shape of a double-clamped nanomechanical resonator, using high speed asynchronous optical sampling (ASOPS). This method is based on two asynchronously linked femto-secondunidirectional ring lasers of ~1 GHz repetition rate. One laser provides the pump pulse while the other provides the probe pulse. The time delay between pump and probe pulse is realized by introducing a 5 kHz offset in the repetition rates of the two lasers, introducing a linear time delay without the need of a mechanical delay line [1, 2].In order to achieve a high spatial resolution a microscope objective is used which allows for a focal spot size of 1.3 micron. Furthermore, using a CCD camera and a motorized scanning stage, we are able to resolve and address single nanostructures as well as to scan over larger sampleareas with high spatial resolution. Earlier work on thin silicon membranes using the same technology showed conned longitudinalmodes in the GHz range [3] and the possibility of resonant driving of these modes [4]. Further it was shown that silicon membranes are excellent model systems for the studies of thermal properties at the nanoscale [5]. Turning away from one dimensional conned systems we now demonstrate the capabilities to investigate two dimensional conned nanostructures, e.g. nanomechanical systems (NEMS). As an example we show the results of pump probe experiments analyzing the dynamics of nanomechanical resonator beam based on Si3N4. The typical dimensions of such a nanostructure, as shown in Fig.1 left, are 100nm by 100nm in cross section and 2-3 micron in length. These systems are an ideal model system for the investigation of dissipation in NEMS, as they are accessible by this all optical method.