Scanning near-field optical microscopy (SNOM) for magneto-optics

Paolo VavassoriINFM - National Research Center on nanoStructures and Biosystems at Surfaces (S3), Dipartimento

di Fisica, Universita` di Ferrara, Italy

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.

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.

Optical microscopy

Electronic microscopy :

Scanning Probe Microscopy (SPM):

2Å

AFM

STM

0,1Å

SNOM

10nm

0,4-0,7m*

* The diffraction limit depends on used wavelength (

Resolution

1 cm| 1mm| 100m| 10 m| 1 m| 100nm| 10nm| 1nm| 1Å| 0,1Å|

| | | | | | |Pla

nt C

ell

Ani

mal

Cel

l

Bac

teriu

m

Vira

l rib

osom

e

Pro

tein

Sm

all

Mol

ecul

e

Ato

m

TEM

5-2nm

max 0,1nm

10nm

SEM

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

SNOM: Working principles

Visible light

Far field

Scattered Far field

Near field

sample

Tip Aperture

d <<

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

3D layout of the MO-SNOM

Side view of MO-SNOM

Detail of the sample holder and tip stage

Snom probesFabbrication of an aperture Snom probe

Toshiharu Saiki and Yoshihito Narita - JSAP International, n.5, January 2002

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

How to avoid depolarization effects?

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

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 ?