|
|
 (version française)
 Nanostructures, Nanocomposites |
Scanning Near Optical Microscopy  |
Person in charge :
- Guy LOUARN (MC)
Contributor :
- Victor LE NADER (Post graduate student)
Summary :
- Main goal
- Problematic
- Numerical studies
- Microscopy and spectroscopy results
- Publications
| Main goal |
The Institute of Materials
research, in Nantes has various Raman spectrometers (Jobin Yvon T64000 and Brucker RFS 200) with a space resolution limited around the micrometer. Whereas many research in the Institute and more largely in the word are directed towards the characterization of nanomaterials (carbon nanotubes, polymer nanotuwires, nano-bio-materials,…) it seems important to be able to test them individually an optically. To this end, we develops today a Snom-Raman enabling to work under the limit of diffraction.
|
 Sketch of the Snom -Raman developped here
|
From a purely optical point of
view, one of the conditions to exceed the limit of resolution, is to
detect the evanescent field, which is associated with the very fine structures of the objects. These waves can then be “collected” by a fiber optic near the extreme surface of a sample. |
The set up is composed of a near field scanning optical microscope (NSOM or SNOM) in order to maintain the end of the nanoprobe near the surface. The microscope control is based on the Shear forces. An optical measuring equipment is made up of a photomultiplier (Hamamatsu), a photocounter, amplifier and of a discriminator or a Raman spectrometer.
|
"SNOM" head used in this work |
Apex d’une fibre gravée et nettoyée (non métallisée)
|
One of the key points for the
success of this project is the realization of the optical probes. For
that, we set up a precise protocol of manufacture of these tips. The
preparation of fiber optics is a crucial step for this kind of
equipment. The parameters of chemical etching, cleaning, metallization
and nano-opening are now controlled.
|
Les extrémités des sondes sont obtenues par gravure chimique et présentent un angle d’ouverture du cône de 15° à 20° et un diamètre extrême d’environ 50 nm. Un procédé plasma à géométrie originale nous a permis de nettoyer la surface des pointes puis de les métalliser par le dépôt d’une couche ultra-mince métallique, homogène et opaque. L’intérêt de ce procédé de pulvérisation cathodique consiste essentiellement en la suppression du mouvement de rotation de la sonde lors du dépôt, la faible quantité de matière utilisée (Ag, Al, …) et la excellente compacité du film malgré son épaisseur d’environ 50 nm. Pour une utilisation en mode collection, les nanosondes sont alors ouvertes à l’extrémité par érosion électrolytique ou par une décharge électrique très localisée. Le dispositif permet ainsi la réalisation de nanosondes de diamètre d’ouverture à l’extrémité inférieur à 100nm. |
nanoaperture at the apex
of the nanoprobe
|
On the basis of experimental result, we developed a numerical model, based on the transmission of the light through a nanoaperture. We demontrate how the confrontation experiment-modeling is interesting for a better comprehension and a better prediction of the experimental results .
|
Diffracted Field according to the geometry of the nanoaperture |
Power flow through the nano aperture according to its diameter.
|
More precisely, in this work we insist on the influence of the various
geometrical probe parameters according to the properties of the light (polarization, energy).
|
Microscopy and spectroscopy results |
Snom image of polyparaphénylène vinylène nanowires
|
Snom image of carbon nanotubes |
Raman scattering of polydiacétylène obtained with the Snom-Raman.
|
In this project, Materials
intervenes for several reasons. We chose “model” materials which wellknow on a macroscopic scale, and which are also good candidates for a first spectroscopic analysis in near field.). We present some images of the experimental measurements obtained inoptical near field with our set up.
|
| Publications |
- M. Chaigneau, G. Ollivier, T.M. Minea, G. Louarn, "Nano-probes for near-field optical microscopy manufactured by substitute-sheath etching and hollow cathode sputtering", Rev. Sci. Instum. 77, 103702 (2006).
- M. Chaigneau, G. Ollivier, T.M. Minea, G. Louarn,"Comparative study of different process-steps for the near-field optical probes manufacturing", Ultramicroscopy, in press (2007).
- M. Chaigneau, G. Louarn, and T. M. Minea "Nano-aperture formation at metal covered tips by micro-spark optimized for near-field optical probes" Applied Physic Letters (11/2007 accepted)
- "Plasmon resonance micro-sensor for droplets analysis", M. Chaigneau, K. Balaa, T. Minea, and G. Louarn Optic Letters 32 (2007) 2435-2437
- Patent : T.M.
Minea, G. Ollivier, G. Louarn, M. Chaigneau, "Nanometric emitter/receiver guides", WO 2006131639 (14 December 2006)
|
|
© IMN
Phone : +33 2 40 37 39 39
Fax : +33 2 40 37 39 95
|
|
Page updated february, 5, 2008 |
|
