WHITEPAPER – Ultra-High-Resolution Microscopy in a Modular System
Dipl.-Phys. Gernot Hamann

Piezo-Based Scanning Stages for Precise Sample
Positioning and Measurement
Ultra-High-Resolution Microscopy in a Modular System

Physik Instrumente (PI) GmbH & Co. KG_Auf der Roemerstrasse 1_76228 Karlsruhe, Germany
Tel. +49 721 4846-0, Fax +49 721 4846-1019 Email info@pi.ws, www.pi.ws

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WHITEPAPER – Ultra-High-Resolution Microscopy in a Modular System
Dipl.-Phys. Gernot Hamann

In life sciences, chemical-pharmaceutical analyses orThe same device can then provide and link molecularmodern material sciences, the optical resolution andRaman and structural AFM information from the same

information content of classical microscopy methods aresample region.

no longer sufficient. In order to obtain the mostcomprehensive information on a sample, modular, highresolution microscope systems open up interesting
opportunities, since different microscopy methods can beused either individually or in combination. As highprecision

anddynamic

samplepositioning

isindispensable in most application areas, piezo-based
scanning stages are a good solution. Thanks to theircompact design, they can easily be integrated inmicroscopes.

For high-resolution optical information, the microscope
can also be equipped with SNOM (scanning near field
optical microscopy). As a result, precise optical,
topographical and molecular analyses are possible, justas required by the respective application. This opens up
opportunities for diverse of application areas. The
application

spectrumofmodular

high-precision

microscopes ranges from pharmaceutical research andlive cell analyses, through nanophotonics, forensics up
to analyses in photovoltaic or semiconductor technology

Close-Ups Below the Diffraction
Limit.

With conventional microscopy technology, the position
resolution is limited to half of its wavelength due todiffraction effects on the objective. In contrast, scanningnear-field optical microscopy can show far smaller
structures. Here, a glass fiber couples laser light into ahollow measuring tip. This light emerges through a tiny
opening at the tip with a diameter of less than 100 nm. If
the opening of the measuring tip is brought closely to thesample surface, a spot far below the diffraction limit ofclassical microscopy can be illuminated. Depending onthe geometry of the measuring tip and its opening, alateral position resolution of up to around 60 nm can beattained, while with confocal (light) microscopy the value
would be between 200 to 300 nm.
For scanning the sample point by point, it is moved
under the measuring tip by a piezo-driven, highresolution scanning stage. At each position, the camera

Fig. 1 The modular microscopy systems from WITecmake it possible to combine a confocal Raman
microscope with atomic force microscopy (AFM)(Image: WITec GmbH)
Theultra-high-resolution microscopy systemsintegrated in the microscope records the incoming lightintensity and saves this value together with the position
information, which is used to create the image. Thefromposition resolution and accuracy of the image depend on

WITec have a modular structure (fig. 1). This makes it

the positioning accuracy and stability of the scanningpossible to combine a confocal Raman microscope withstage as well as the optical and mechanical components

atomic force microscopy (ATM), if required.

of the microscope (fig. 2).

Physik Instrumente (PI) GmbH & Co. KG_Auf der Roemerstrasse 1_76228 Karlsruhe, Germany
Tel. +49 721 4846-0, Fax +49 721 4846-1019 Email info@pi.ws, www.pi.ws

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WHITEPAPER – Ultra-High-Resolution Microscopy in a Modular System
Dipl.-Phys. Gernot Hamann

In the case of the AFM method, the measuring tip is also
moved over the sample surface line by line in a definedgrid. Forces are measured between a very thinmeasuring tip and the surface of the object, which thenprovides information on the topology of the surface. Inaddition, sample characteristics such as adhesion,
stiffness or viscosity can be determined. The lateral
resolution is 10 nm and below. The position of thesample is readjusted in the direction of the Z axis hereas well. The variation of the Z position together with therelevant X and Y coordinates for the spatial resolution
Fig. 2 For high-resolution optical information, themicroscope can also be equipped with SNOM (scanningnear field optical microscopy). With SNOM, far smaller
structures can be shown than with conventional
microscope technology (Image: WITec GmbH)

Information on the Surface Topology
SNOM simultaneously provides information on thesurface topology: Since the distance between themeasuring tip and the surface has to be kept constantand practically every surface has a certain roughness,the position of the sample must be readjusted in the Zdirection. This readjustment is carried out by thescanning stage and provides topological information
additionally to the optical SNOM image.

then provide high-precision topology information on thesamples (fig. 3).

The Chemical Fingerprint
Raman microscopy is based on a confocal, optical
microscope combined with a Raman spectrometer. In
the case of a confocal system, apertures are used tosuppress light outside of the focal plane of themicroscope. In this way, only light information from thefocal plane is transferred to the spectrometer. In thespectrometer, this light is spectrally separated anddetected. The sample is scanned point by point and line
by line. The lateral resolution is approximately 200 nm
with green excitation light. During the measurement, acomplete Raman spectrum is recorded for each pixel.
These Raman spectra act like a specific fingerprint foreach type of molecule, so that the chemical components
of a sample can be identified for each pixel and theirdistribution in the sample can be shown.
Combining

Raman

imagingwithAFM

yieldstopographical information with high spatial resolution as
well as molecular information on the sample surface.
Since the corresponding images are recorded insuccession (fig. 4), the requirements for the scanningstage are very high. Any drift would distort the correlation
Fig. 3 Atomic force microscopy (AFM) provides precise
information on the surface topology(Image: WITec GmbH)between the two images. Precise positioning in all threeaxes is indispensable for the accuracy of the image.

Physik Instrumente (PI) GmbH & Co. KG_Auf der Roemerstrasse 1_76228 Karlsruhe, Germany
Tel. +49 721 4846-0, Fax +49 721 4846-1019 Email info@pi.ws, www.pi.ws

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WHITEPAPER – Ultra-High-Resolution Microscopy in a Modular System
Dipl.-Phys. Gernot Hamann

Fig. 4 Topology of a PEET-PET polymer film on a glass
substrate recorded with AFM (left), the Raman spectrum(right) and the false color representation of the Raman
image (center). Raman spectra act like a specificfingerprint for each type of molecule, so that chemicalcomponents present in a sample can be identified foreach pixel and their distribution in the sample can beshown (Image: WITec GmbH)

Positioning with a Very High
Position Resolution and Dynamics
Since the positioning system used for scanning provides
the spatial resolution, its resolution must be in the sub-For these reasons, WITec decided on a piezo-based
scanning stage (fig. 5) from PI (Physik Instrumente) for
positioning. It is designed for working distances of 100 or
200 µm in the axes of the scanning plane and 30 µm in
the Z axis. It allows a position resolution of better than
2 nm and provides the best conditions for use in modular
microscopes for all three methods. As there are noclassical mechanical components that could cause
friction or mechanical backlash in the drive, very highmotion resolution is possible with the piezo drives.

the dynamics are high: The faster the topography

Capacitive Sensors and Digital
Electronics Ensure Stability

tracking in the Z direction, the faster the positioning in

Stability and path accuracy during scanning are crucial

the X and Y axis can be. Consequently measurement

when combining Raman imaging with AFM, since thetimes are shorter and temperature drift, which wouldmeasurements can take a few minutes and any drift

increase with time, is reduced. So the high dynamics

would distort the recordings. In addition, the active

also benefit the accuracy.

guiding

nanometer range. At the same time, the requirements forusingcapacitive

sensorsincreases

path

accuracy: The sensors measure any deviation in the axis
lateral to the direction of motion. Undesired crosstalk of
the motion (for example from external forces ormechanical crosstalk) into another axis can be detectedin this way and actively compensated in real time.
A digital controller provides the necessary control. It is
specially adapted to the piezo-based scanning stage andguarantees a good linearity, also for dynamic operation.
Fig. 5 The piezo-based scanning stage is essential forsample positioning. It is designed for working distancesof 100 or 200 µm in the axes of the scanning plane and30 µm in the Z axis. It allows a position resolution of
better than 2 nm. Capacitive sensors and digitalelectronics provide maximum stability

The digital electronics work with a high clock rate. This isdecisive for an accurate assignment of the positionvalues of the piezo scanner and the recording camera. If
it were too slow or inaccurate, there would be a loss ofresolution and distortions (jitter) during the assignment.

Physik Instrumente (PI) GmbH & Co. KG_Auf der Roemerstrasse 1_76228 Karlsruhe, Germany
Tel. +49 721 4846-0, Fax +49 721 4846-1019 Email info@pi.ws, www.pi.ws

Page 4 of 5

WHITEPAPER – Ultra-High-Resolution Microscopy in a Modular System
Dipl.-Phys. Gernot Hamann

The piezo-based scanning system is an essential part inmethods,

high-precision microscopes. As a result of its compact

sciences and life sciences. Europe, the USA and thedimensions, the scanning stage can be easily integrated

Asia/Pacific region are the most important sales markets,in microscopes where installation space is usuallywith users coming from research and industry.

limited.

Authorarefoundinnanotechnology,materials

PI (Physik Instrumente) in Brief
In the past four decades, PI (Physik Instrumente) with
headquarters in Karlsruhe, Germany has become theleading manufacturer of nanopositioning systems withaccuracies in the nanometer range. With four company
sites in Germany and ten sales and service offices
abroad, the privately managed company operates
globally. Over 700 highly qualified employees around theworld enable the PI Group to meet almost any

Dipl.-Physicist Gernot Hamann, Business Development

requirementinManager for Microscopy at PI (Physik Instrumente)

positioningtechnology.

WITec in Brief

thefieldofAll

innovative

key

precisiontechnologies

aredeveloped in-house. This allows the company to control
every step of the process, from design right down toSince its foundation in 1997, WITec GmbH (Ulm,shipment: precision mechanics and electronics as wellGermany) has developed into a market leader in high-asresolution microscopy systems (Raman, AFM andelements are manufactured by our subsidiary PI CeramicSNOM) and generated average growth rates of annuallyin Lederhose, Germany, one of the global leaders for

10%. With 52 employees worldwide, the company ispiezo actuator and sensor products. PI miCos GmbH inrepresented by subsidiaries in the USA and Asia, andEschbach near Freiburg, Germany, is a specialist for

has regional offices in Spain and Japan. The main

positioning systems for ultrahigh vacuum applications asapplication areas for the modular high-performancewell as parallel-kinematic positioning systems with six

microscopes, allowing the combination of different

degrees of freedom and custom-made designs.

positionsensors.

ThePI headquarters in Karlsruhe, Germany: More than 350
employees work on high-resolution drive systems andpositioning systems

Physik Instrumente (PI) GmbH & Co. KG_Auf der Roemerstrasse 1_76228 Karlsruhe, Germany
Tel. +49 721 4846-0, Fax +49 721 4846-1019 Email info@pi.ws, www.pi.ws

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requiredpiezoceramic