NANOSNOM: Near Field Optics for Nanotechnology

• Unité de recherche: PCRD EU
• Numéro de projet: 97.0558
• Titre du projet anglais: NANOSNOM: Near Field Optics for Nanotechnology

Mots-clé (Anglais)

Scanning near field optical microscopy (SNOM); novel optical probes; image formation mechanisms; plasmons; polarisation effects; optical spectroscopies with high spatial resolution

Autre Numéro de projet (Anglais)

EU project number: FMRXCT980242

Programme de recherche (Anglais)

EU-programme: 4. Frame Research Programme - 10.1 Stimulation of training and mobility

Description succincte (Anglais)

See abstract

Autres indications (Anglais)

Full name of research-institution/enterprise:
Universität Basel
Institut für Physik
Experimentelle Physik der kondensierten Materie

Partenaires et organisations internationales (Anglais)

Coordinator: Universität Ulm (D)

Résumé des résultats (Abstract) (Anglais)

A) ELECTRO-CHEMICAL STRUCTURING OF APERTURE SNOM PROBES
Well-defined reliable probes with apertures well below 100 nm in diameter, positioned at the apex of a metal-coated transparent probe tip, are instrumental for routine application oof scanning near-fieldoptical microscopy (SNOM). Manufacturing of such probes represents a considerable (nano-)technological challenge that is not well mastered with established techniques. The development of a new method for routine production of such probes therefore became our main focus of research within the scope of the present project. Our approach is based on aperture formation by controlled all solid state electrolysis (CASSE): The apex of the blank, completely metal-coated illuminated probe is eroded electrolytically until light begins to be transmitted. The SNOM probe is mounted in operating position during this process, pointing towards a chip of solid state electrolyte positioned side by side with the sample on the sample stage. The onset of light transmission is used to terminate the erosion process at minimal aperture size. Integration into the SNOM has the advantage to reduce the risk of aperture damage and corrosion before usage. It furthermore allows to repair small damages of the aperture by re-deposition of metal at the apex. SNOM images with excellent resolution were obtained with the new probes. The resolving power is l/20 at least which is close to the limits of SNOM and a factor 10 better than the resolving power of the best conventional microscopes.
B) SNOM IMAGING OF METAL SURFACES
SNOM images of metal films show intensity modulation patterns under certain conditions that cannot be directly related to existing physical structures. The patterns obscure SNOM images but provide interesting information on surface plasmons (SP). The SNOM probe in fact acts as a SP point source. The SP emission lobes are clearly seen with a conventional microscope integrated into the SNOM setup. The lobes are seen to be partially reflected by the grooves and other irregularities of the film which leads to pronounced interference effects. The latter were found to cause the intensity modulation pattern seen in the SNOM images. The depth of modulation allows to estimate reflectivity and transmissivity of the grooves for SP waves. This may be considered a first step towards an optics of SP waves which, in turn, might lead to new form of nano-scale integrated optics.
C) NEAR FIELD OPTICS SEEN AS AN ANTENNA PROBLEM
The similarities in the electromagnetic properties of fluorescing molecules, small scattering particles, optical resonators on the one hand and of telecommunication antennas and waveguides on the other is suggestive of inspecting antenna theory for concepts applicable and useful to near field optics problems. In a preliminary study, we found that (i) the criteria for field confinement at the feed point of an antenna and at a SNOM probe are essentially the same, (ii) some antenna designs, downscaled to (sub-)micron size may be suitable as SNOM probes and (iii) hold promise for improved resolving power and illumination efficiency.

Références bases de données (Anglais)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 97.0558