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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
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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.
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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.
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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
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osom
e
Pro
tein
Sm
all
Mol
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e
Ato
m
TEM
5-2nm
max 0,1nm
10nm
SEM
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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
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SNOM: Working principles
Visible light
Far field
Scattered Far field
Near field
sample
Tip Aperture
d <<
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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
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3D layout of the MO-SNOM
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Side view of MO-SNOM
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Detail of the sample holder and tip stage
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Snom probesFabbrication of an aperture Snom probe
Toshiharu Saiki and Yoshihito Narita - JSAP International, n.5, January 2002
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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
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How to avoid depolarization effects?
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Applications: magnetic study on the nanometer lateral scale.E.g.: magnetization reversal of single nano-structures in MR devices
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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 ?