Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 15: Methods: Other Experimental Techniques I

O 15.1: Talk

Monday, February 25, 2008, 15:30–15:45, MA 041

Tip-enhanced Raman Spectroscopy with a High NA Parabolic Mirror — •Dai Zhang, Catrinel Stanciu, Markus Sackrow, Kai Braun, and Alfred J. Meixner — Institut für Physikalische und Theoretische Chemie, Auf der Morgenstelle 8, 72076 Tübingen

Tip-enhanced Raman spectroscopy (TERS) allows chemical information collection with a sensitivity reaching single molecule level and a spatial resolution in the range of 10 nm. The efficient excitation and collection of the plasmon-enhanced optical signals of species present in the tip-sample nano-gap between the tip apex and the substrate are crucial for TERS. The optical excitation field has to be polarized along the gap and the field emerging form the gap has to be observed from the side. These geometrical restrictions require the side-illumination and light collection using a low-NA lens, limiting the sensitivity of the measurements. We present a novel method to overcome this problem based on a confocal optical microscope with a high NA parabolic mirror for the excitation and the detection instead of the objective lens. The sample is arranged co-axially with the axis of the parabolic mirror and the gap is centered in the focus. Hence localized plasmons can be efficiently excited parallel to the surface we illuminate the parabolic mirror with a radially polarized doughnut mode and the field developed from the gap can effectively be collected by the rim of the parabolic mirror and directed to the detection system. Examples about tip-enhanced imaging and spectroscopy of nanomaterials and biological systems will be shown to demonstrate the efficiency of this modification.