Sarfus is an optical quantitative imaging technique based on the association of: *an upright or inverted

optical microscope The optical microscope, also referred to as a light microscope, is a type of microscope that commonly uses visible light and a system of lenses to generate magnified images of small objects. Optical microscopes are the oldest design of microsc ...

in crossed polarization configuration and *specific supporting plates – called surfs – on which the sample to observe is deposited. Sarfus visualization is based on the perfect control of the reflection properties of polarized light on a surface, which leads to an increase in the axial sensitivity of

by a factor of around 100 without reducing its lateral resolution. Thus this new technique increases the sensitivity of standard

to a point that it becomes possible to directly visualize thin films (down to 0.3 micrometer) and isolated nano-objects in real-time, be it in air or in water.

Principles

A recent study on polarized light coherence leads to the development of new supports – the surfs – having contrast amplification properties for standard optical microscopy in cross polarizers mode. Made of optical layers on an opaque or transparent substrate, these supports do not modify the light polarization after reflection even if the numerical aperture of the incident source is important. This property is modified when a sample is present on a surf, a non-null light component is then detected after the analyzer rendering the sample visible. The performances of these supports are estimated from the measurement of the contrast (C) of the sample defines by: C = (I₁-I₀)/(I₀+I₁) where I₀ and I₁ represent the intensities reflected by the bare surf and by the analyzed sample on the surf, respectively. For a one nanometer-film thickness, the surfs display a contrast 200 times higher than on silicon wafer. This high contrast increase allows the visualization with standard optical microscope of films with thicknesses down to 0.3 nm, as well as nano-objects (down to 2 nm diameter) and this, without any kind of sample labelling (neither fluorescence, nor radioactive marker). An illustration of the contrast enhance is given hereafter with the observation in optical microscopy between cross polarizers of a Langmuir-Blodgett structure on a silicon wafer and on a surf. In addition to visualization, recent developments have allowed accessing to the thickness measurement of the analyzed sample. A colorimetric correspondence is carried out between a calibration standard made of nano-steps and the analyzed sample. Indeed, due to optical interference, a correlation exists between RGB (red, green, blue) parameters of the sample and its optical thickness. This leads to 3D-representation of the analyzed samples, the measurement of profile sections, roughness and other topological measurements.

Experimental setup

The experimental set-up is simple: the sample to be characterized is deposited by usual deposit techniques such as dip-coating, spin-coating, deposit pipette, evaporation... on a surf instead of the traditional microscope slide. The support is then placed on the microscope stage.

Synergy with existing equipment

The sarfus technique can be integrated in existing analysis equipment (

atomic force microscope Atomic force microscopy (AFM) or scanning force microscopy (SFM) is a very-high-resolution type of scanning probe microscopy (SPM), with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the op ...

(AFM), Raman spectroscopy, etc.) to add new functionalities, such as optical image, thickness measurement, kinetic study, and also for sample pre-localization to save time and consumables (AFM tips, etc.).

Applications

Life sciences

*Biological films * Biochip *

Phospholipids Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids t ...

* Soft lithography * Cell adhesion

Thin films and surface treatment

Polymers A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...

films * Langmuir-Blodgett films *

Liquid crystals Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. The ...

*Plasma treatment *

Self-assembled monolayer Self-assembled monolayers (SAM) of organic molecules are molecular assemblies formed spontaneously on surfaces by adsorption and are organized into more or less large ordered domains. In some cases molecules that form the monolayer do not interact ...

Nanomaterials

Carbon nanotubes A scanning tunneling microscopy image of a single-walled carbon nanotube Rotating single-walled zigzag carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with diameters typically measured in nanometers. ''Single-wall carbon na ...

* Nanoparticles *

Nanowires A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre (10−9 metres). More generally, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less ...

Graphene Graphene () is an allotrope of carbon consisting of a single layer of atoms arranged in a hexagonal lattice nanostructure.

* DNA molecules

Advantages

Optical microscopy has several advantages compared to the usual techniques of nanocharacterization. It is easy-to-use and directly visualizes the sample. The analysis in real-time allows kinetic studies (real-time crystallization, dewetting, etc.). The broad choice of magnification (2.5 to 100x) allows fields of view from several mm² to a few tens µm². Observations can be performed in controlled atmosphere and temperature.

References

{{Optical microscopy Nanotechnology Microscopy Laboratory techniques Scientific techniques Biological techniques and tools Laboratory equipment Optical microscopy