Almost every specialist in SPM
community has been faced in his (her) experience with failures caused
by mutual displacement of sample and probe. This effect arises either
from mechanical or thermal drifts inside the AFM system. The consequences
could be fatal for whole experiment especially for small scan areas
(less then 1 ìm).
Mechanical Drift Caused by Piezoceramics Properties
Even best piezoceramics devices
suffer from hysteresis, creep and non-linearity. The only way to have
the system with ultimate repeatability is to apply a special software
and closed-loop (CL) correction. In practice CL sensors always put
some noise into the system therefore almost all commercially available
SPMs do not allow working on the fields smaller than 500 nm with closed-loop
Special design of NTEGRA Therma
measuring head gives the opportunity to maintain ultra high stability
and reproducibility of probe movement. Scanner sensors of NTEGRA Therma
have the lowest noise level among commercially available instruments.
The engineering solutions make the
hardware correction possible on the areas as small as 50 nm. In fact
even atomic lattice can be imaged with CL sensors switched on.
Drift Caused by Non-Uniform Thermal Expansion of SPM Parts
One can easily find temperature
noise of 3-5°K magnitude even in the room with climate control.
SPM also produces some heat during
its operation. Typical values of thermal drift in commercially available
SPMs are tens of nanometers per hour. The wider is the temperature
range of experiment the more prominent becomes thermal drift influence.
The drift about hundreds of nanometers per K becomes a rule for usual
incorporates unique design solutions to fight against the thermal
drift. Thoroughly developed system geometry, special combination of
materials with similar coefficients of thermal expansion and conductivity,
precise stabilization of the scanning module temperature, and some
other features enable XY drifts at room temperature as small as 3-5
nm/hour, and about 10 nm/K at changing temperature!
Figure 1. Atomic lattice of HOPG obtained at extremely low scan rate (about
Figure 2. Atomic lattice of mica as imaged with closed loop correction.
Figure 3. Nanotubes and nanoparticles in long-term experiment . Overall displacement
for 7 hours is about 35 nm. Sample courtesy of Dr.H. B. Chan, Department
of Florida, USA.
Based Tomography Using the NTEGRA Tomo
AFM tomography is a method based
on both atomic-force microscopy (AFM) and ultramicrotomy. It allows one to study inner properties of almost
any polymer material including rather hard ones. 3D reconstruction
can be performed after serial AFM imaging of the block face combined
with sectioning by an ultramicrotome.
Figure 4. Principle scheme of the AFM tomography setup: 1 - sample, 2 - sample
holder, 3 - movable ultramicrotome arm, 4 - ultramicrotome knife,
5 - AFM scanner, 6 - probe holder, 7 - AFM probe
Figure 5. Silica nanoparticles within polymer matrix (nanocomposite material).
Each individual image size is 20x40 ìm, spaces are 200 nm. Sample
courtesy of Dr.Aliza Tzur, Technion, Israel.
Figure 6. 3D Model of multicomponent polymer blend. Model size 8.0x5.6x0.6 um,
spaces between sections 40 nm. Sample courtesy of Dr.Christian Sailer,
Institut f. Polymere,ETH-Honggerberg, Switzerland.
Figure 7. AFM tomography of resin embedded cyanobacteria. Photosynthetic membrane
lamellae are clearly seen both on enlarged AFM image and on a 3D model
(4.9x4.6x0.9 um, spaces between sections 50 nm).Sample courtesy of
Dr.N.Matsko, ETH, Zurich, Switzerland.
+ Confocal Microscopy/Spectroscopy
Combination of SPM and confocal
microscopy/spectroscopy allows to carry out simultaneous physical
and chemical characterization of the same area on sample surface.
has successfully integrated AFM, SNOM (near-field optical microscopy),
Raman and fluorescence microscopy and spectroscopy techniques.
Moreover, unique nonlinear optical
effects arising due to interaction of light with an SPM probe produce
giant enhancement of Raman and fluorescence signals. TERS (tip-enhanced
Raman scattering) experiments become possible due to precise spatial
coordination of a special AFM tip and focused laser spot. Optical
characterization can now be performed with resolution far beyond the
Figure 8. Raman microscopy with ultra-high spatial resolution.A - tip enhanced
Raman scattering experiment, B - intensity of carbon nanotube G-band
increases by several orders of magnitude when the probe tip is landed,
C - confocal Raman image of carbon nanotube bundle. D- tip-enhanced
Raman scattering (TERS) image of the same nanotube bundle. Note, TERS
provides more than 4-times better spatial resolution as compared to
confocal microscopy. Data courtesy of Dr. S.Kharintsev,Dr. J. Loos,
TUE, the Netherlands and Dr. P.Dorozhkin,
ISSP RAS, Russia.
Figure 9. Microalgae seen by bright field microscopy (A), Raman microscopy at
beta-carotene line (B), and confocal microscopy of autofluorescence
(C). Sample courtesy of Dr. Don McNaughton, Monash University, Victoria,
Figure 10. SNOM image of mitochondria dyed with FITC-labeled antibodies. Note
XY resolution beyond the diffraction limit.