Dresden 2009 – scientific programme

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O: Fachverband Oberflächenphysik

O 38: Nano-optics of metallic and semiconducting nanostructures (experiments I)

O 38.7: Talk

Wednesday, March 25, 2009, 16:30–16:45, SCH A216

20 nm Optical Resolution Using Gold Nanospheres as Near-Field Probes — Hadi Eghlidi, Kwang Geol Lee, Xuewen Chen, Mario Agio, •Stephan Götzinger, and Vahid Sandoghdar — Laboratory of Physical Chemistry and optETH, ETH Zürich, CH-8093 Zürich, Switzerland

Apertureless Scanning Near-Field Optical Microscopy (SNOM) has reported spatial resolution below 20 nm in isolated cases. However, researchers have confronted considerable difficulties in reproducing tips that deliver this performance. Several years ago, we developed reliable and reproducible near-field probes consisting of single gold nanospheres attached to the end of glass tips. It has been also shown that such probes can act as resonant dipole nanoantennas to enhance the fluorescence of single molecules by more than 25 times [1, 2]. We report on experimental images of single molecules obtained using different gold nanoparticle probes with diameters between 40 nm and 100 nm. Resolutions as high as 20 nm were demonstrated at a high yield and with different particle sizes. Furthermore, fluorescence enhancements greater than 30 times were observed. For very small gold particles, the competition between quenching and enhancement of the molecular fluorescence becomes important because the ratio of the absorption to the scattering cross section inverses. We discuss this paradigm shift and its implications for ultrahigh resolution SNOM.

[1] S. Kühn et al., Phys. Rev. Lett. 97, 017402 (2006).

[2] S. Kühn et al., Mol. Phys. 106, 893 (2008).