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KONTAKT

Gruppenleiter:

Prof. Dr. Arno Rauschenbeutel
Tel.: +43-1-58801-141761
Fax: +43-1-58801-9141761
Raumnummer: ZB 01 01

TU Wien - Atominstitut
Stadionallee 2
1020 Wien
Austria

Surface Adsorbed Molecules

The guided modes of sub-wavelength-diameter optical nanofibres exhibit a pronounced evanescent field. The absorption of light by particles covering the nanofibre surface is therefore readily detected via the fibre transmission. We have shown that the resulting absorption for a given surface coverage can be orders of magnitude higher than that for conventional surface spectroscopy. As a demonstration, we carried out measurements on sub-monolayers of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) molecules at ambient conditions, revealing the agglomeration dynamics on a second to minutes timescale. PTCDA thin films are excellent indicators for the sensitivity because their spectral properties highly depend on the detailed arrangement of the molecules on the surface.

The experiments were carried out with a simple experimental setup, see Fig. 1. A tapered fibre with a 500-nm diameter waist of 3 mm length was used in a conventional absorption spectrometer configuration with a tungsten white light source and a commercial CCD spectrograph. The molecules were deposited on the fibre waist by placing a heated crucible with PTCDA crystals below the fibre.

 

Figure 1:  Schematic experimental setup for surface absorption spectroscopy of PTCDA molecules adsorbed on an optical nanofibre.

 

The findings of this work are of relevance for a large variety of fields ranging from sensorial applications in industry, environmental studies, and bio-technology to fundamental research concerning thin film growth as well as the controlled interaction of light and matter at the ultimate, microscopic scale.

Recently, we have set up a new experimental apparatus in order to deposit molecules onto the nanofibre under ultra-high vacuum (UHV) conditions. This allows us to carry out spectroscopy on a much larger variety of molecules including those not stable when sublimated at ambient conditions. Secondly, we have full control on the flux of molecules impinging onto the fibre. And finally, in vacuum, we can desorb pollutants (water etc.) from the fibre and work with a much better defined surface.

Furthermore, we will explore the potential of our method for single molecule detection, manipulation, and functionalisation. For this purpose, we will deposit suitable chosen molecules on the fibre in a cryogenic UHV-environment. The molecules will thermalise with the fibre surface and will thus be in their electronic and vibrational ground state. Estimations based upon the results in promise a detectable effect (of order percent) on the transmission of the guided fibre mode from a single molecule. The dispersive effect of single molecules on the fibre mode should be detectable as well. An important goal will then be to store and to manipulate (classical) information in suitably chosen conformation states of the molecules.

 

F. Warken, E. Vetsch, D. Meschede, M. Sokolowski, and A. Rauschenbeutel
Ultra-sensitive surface absorption spectroscopy using sub-wavelength diameter optical fibers
Optics Express, Vol. 15, 19, 11952-11958 (2007)

A. Stiebeiner, O. Rehband, R. Garcia-Fernandez, and A. Rauschenbeutel
Ultra-sensitive fluorescence spectroscopy of isolated surface-adsorbed molecules using an optical nanofiber
Optics Express, Vol. 17, 24, 21704-21711 (2009)

 

We gratefully acknowledge financial support by:

Volkswagen Foundation (Lichtenberg Professorship)

European Science Foundation (European Young Investigator Award)

European Commission (STREP "CHIMONO")

Team

Senior / Post-Doc

Prof. Arno Rauschenbeutel
Dr. Sarah Skoff

PhD Students

Hardy Schauffert

Arno Rauschenbeutel, Hardy Schauffert