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Cantilever-based Near-Field optical probe

 

General topic : Design and fabrication of optical near field probes - optical near field instrumentation, and characterization in photonics and biology


Focused topic : Implementation of an integrated cantilever SNOM probe on a commercially available microscope

Context :
Scanning Near-field Optical Microscopy (SNOM) makes use of evanescent waves that carry information about sub-wavelength-sized objects or details. Near-field optic probes also offer the possibility to acquire simultaneously topographical and optical images and to mechanically or optically interact with the object, although investigations and interactions are limited to the object surface. This can be either an advantage, for example when studying the cell membrane, or a drawback, for instance when focusing on the cell cytoplasm or nucleus.

We designed a probe that :
• enables either to collect light or to illuminate the object, as the tip is solid
• can be adapted on a SNOM/AFM microscope, as it is a cantilever type
• requires less mechanical and optical adjustments, as it integrates an optical guide and a photodetector
• is low cost, as the material is polymer, the fabrication is parallel and takes advantages of unmoulding to release the cantilever

 

Near-field optic probes also offer the possibility to acquire simultaneously topographical and optical images and to mechanically or optically interact with the object, although investigations and interactions are limited to the object surface. This can be either an advantage, for example when studying the cell membrane, or a drawback, for instance when focusing on the cell cytoplasm or nucleus.

We report the design of a new type of scanning near-field optical microscopy probes combining the advantages of both tapered optical fibers type and cantilever type commercial scanning near-field optical microscopy probes. The material is an organo-mineral synthesized by the sol-gel method.

This material matches mechanical and optical performances for such a scanning near-field optical microscopy probe fabrication. Numerical calculations were carried out using finite element method in order to study the optical transmission of the probe in emission and collection modes. The influence of the probe geometry on the intensity distribution in the vicinity of the aperture and in the extremity of the cantilever is studied in details.

The probe structure is based on a transparent homogeneous material cantilever with a solid pyramidal-shaped tip at the end, see illustration below.

The cantilever is used as an optical guide. This structure is allowed by the fabrication process we developed using an organo-mineral material synthesized by sol-gel process
The mineral network of the material is based on Silica which offers good optical and mechanical properties.
The organic network brings the properties of polymers : ease and simplicity of layer deposition, definition of structures by photo polymerization, composition versatility.


The sol-gel process is based on soft chemistry, and performed at moderate temperature (120°C) and ambient pressure. It thus requires low energy and is low cost.
Moreover, this material, transparent in visible and infrared light, has been used to realize photonic circuits. Such circuits could be integrated to realize a smart probe.

Structure of the probe :

 


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Fabrication of the probe :    

Example of probe and integration of a detector (microSD type) :

Final setup ready to use on the microscope holder :

 

Optical characterization of the probe : test sample 30 nm thick Va array on quartz  :

SIROCO probe

https://anr.fr/Project-ANR-11-EMMA-0008

Commercial probe

 

Mechanical characterization : test sample 30 nm thick Va array on quartz :

Cantilever stiffness 0,04N/m to 0,01 N/m

SIROCO probe

Commercial probe

 

 

For more details, see our following most relevant articles :

* B. Mourched, E. L. Nativel, R. Kribich, P. Falgayrettes, P. Gall-Borrut, J. of Microscopy , Vol.262, Issue 1, 2016, pp.3-11, Study of light emission and collection in a transparent dielectric cantilever based near-field optical probe
* P. Falgayrettes, P. Gall-Borrut, A. Tsigara, B. Belier, F. Maillard, DTIP2015, Montpellier , MOEMS for near field
optical microscopy: from conception to fabrication process challenges
* A.Tsigara, B. Mourched, P. Falgayrettes, B. Belier, E.L. Nativel, R. Kribich, .Etienne, S. Calas, P. Gall-Borrut, Sensors and Actuators A 212, 2014, 12–17, Fabrication and mechanical properties of an organomineralcantilever- based probe for near-field optical microscopy
* A. Tsigara, B. Belier, F. Maillard, P. Falgayrettes, E. Nativel, R. Kribich, P. Gall-Borrut, NSTI-Nanotech 2014,
www.nsti.org, ISBN 978-1-4822-5827-1Vol.2, 2014, AFM/SNOM Cantilever Probe Serial Fabrication Process with Controlled Tip Nanoaperture
* B. Mourched, A. Tsigara, P. Falgayrettes, E.L. Nativel, R. Kribich, B. Belier, S. Etienne-Calas, P. Etienne, P. Gall-Borrut, 12th International Conference Near-Field Optics, Nanophotonics,and Related Techniques, 2012, p128, Collection mode cantilever-based SNOM probe

* Patent : 01/04/2011 n° 11305043.9-1524 « Near-field optical probe manufacturing using organo-mineral material and sol-gel process » Falgayrettes P, Kribich R, Nativel L, Mourched B, Gall-Borrut P, Belier B.