1. Scanning near-field optical microscopy (SNOM) for magneto-optics Paolo Vavassori INFM - National Research Center on nanoStructures and Biosystems at Surfaces (S3), Dipartimento di Fisica, Universita` di Ferrara, Italy

2. SPM: main components All Scanning Probe Microscopes contain some main components: - a probe tip; - a piezoelectric scanner to move the tip (or the sample); - the acquisition system to measure and convert the data into an image.

3. SPM: Scanning Probe Microscopy The piezoelectric scanner moves the sample under the tip (or the tip on the sample) in a raster pattern. A feedback system controls the distance tip-sample. A computer system measures in each points the different interactions between the tip and the surface of the sample.

4. Optical microscopy Electronic microscopy : Scanning Probe Microscopy (SPM): 2Å AFM STM 0,1Å SNOM 10nm 0,4-0,7 m* * The diffraction limit depends on used wavelength ( Resolution 1 cm| 1mm| 100 m| 10 m| 1 m| 100nm| 10nm| 1nm| 1Å| 0,1Å| | | | | | | | Plant Cell Animal Cell Bacterium Viral ribosome Protein Small Molecule Atom TEM 5- 2nm max 0,1nm 10nm SEM

5. Snom is a scanning microscopy that use an optical fiber as a probe. SNOM: Near-Field Scanning Optical Microscopy The tip is a Metal-Covered Optical Fiber with aperture d << 1

6. SNOM: Working principles Visible light Far field Scattered Far field Near field sample Tip Aperture d <<

7. An electromagnetic wave, when interacts with an object, is diffracted into two components: a propagating component (Far field) an evanescent component (Near field), which decays exponentially with the distance from the object SNOM use the near field component, which make possible to overtake this diffraction limit and obtain better resolution Conventional optics microscope use far field components of the light. But there is a far field diffraction limit: Abbe barrier /2, where is a wavelength of the incident ligth. Near-Field

8. 3D layout of the MO-SNOM

9. Side view of MO-SNOM

10. Detail of the sample holder and tip stage

11. Snom probes Fabbrication of an aperture Snom probe Toshiharu Saiki and Yoshihito Narita - JSAP International, n.5, January 2002

12. Snom Probes Transmission coefficient of aperture probe as a function of aperture diameter for single-tappered and double- tappered probes (with various cone angles). Toshiharu Saiki and Yoshihito Narita - JSAP International, n.5, January 2002

13. How to avoid depolarization effects?

14. Applications: magnetic study on the nanometer lateral scale. E.g.: magnetization reversal of single nano-structures in MR devices

15. Schedule SNOM convenzionale nel layout che permette di applicare campi H esterni, verra` consegnato da APE research entro la fine di Ottobre. In collaborazione con APE si effettueranno i test di funzionamento e si comincera` a lavorare sulla realizzazione di fibre ottiche adatte e alla loro caratterizzazione in termini di polarizzazione. Successivamente lo strumento vera` completato con stadi di movimentazione piu` precisi. Lo strumento sara` operativo a partire da ?