304 research outputs found
Quantitative analysis of ferroelectric domain imaging with piezoresponse force microscopy
The contrast mechanism for ferroelectric domain imaging via piezoresponse
force microscopy (PFM) is investigated. A novel analysis of PFM measurements is
presented which takes into account the background caused by the experimental
setup. This allows, for the first time, a quantitative, frequency independent
analysis of the domain contrast which is in good agreement with the expected
values for the piezoelectric deformation of the sample and satisfies the
generally required features of PFM imaging
Crosstalk Correction in Atomic Force Microscopy
Commercial atomic force microscopes usually use a four-segmented photodiode
to detect the motion of the cantilever via laser beam deflection. This read-out
technique enables to measure bending and torsion of the cantilever separately.
A slight angle between the orientation of the photodiode and the plane of the
readout beam, however, causes false signals in both readout channels, so-called
crosstalk, that may lead to misinterpretation of the acquired data. We
demonstrate this fault with images recorded in contact mode on ferroelectric
crystals and present an electronic circuit to compensate for it, thereby
enabling crosstalk-free imaging
Impact of Electrostatic Forces in Contact Mode Scanning Force Microscopy
In this contribution we address the question to what extent surface
charges affect contact-mode scanning force microscopy measurements. % We
therefore designed samples where we could generate localized electric field
distributions near the surface as and when required. % We performed a series of
experiments where we varied the load of the tip, the stiffness of the
cantilever and the hardness of the sample surface. % It turned out that only
for soft cantilevers could an electrostatic interaction between tip and surface
charges be detected, irrespective of the surface properties, i.\,e. basically
regardless its hardness. % We explain these results through a model based on
the alteration of the tip-sample potential by the additional electric field
between charged tip and surface charges
Sol-Gel Derived Ferroelectric Nanoparticles Investigated by Piezoresponse Force Microscopy
Piezoresponse force microscopy (PFM) was used to investigate the
ferroelectric properties of sol-gel derived LiNbO nanoparticles. To
determine the degree of ferroelectricity we took large-area images and
performed statistical image-analysis. The ferroelectric behavior of single
nanoparticles was verified by poling experiments using the PFM tip. Finally we
carried out simultaneous measurements of the in-plane and the out-of-plane
piezoresponse of the nanoparticles, followed by measurements of the same area
after rotation of the sample by 90 and 180. Such
measurements basically allow to determine the direction of polarization of
every single particle
Contrast Mechanisms for the Detection of Ferroelectric Domains with Scanning Force Microscopy
We present a full analysis of the contrast mechanisms for the detection of
ferroelectric domains on all faces of bulk single crystals using scanning force
microscopy exemplified on hexagonally poled lithium niobate. The domain
contrast can be attributed to three different mechanisms: i) the thickness
change of the sample due to an out-of-plane piezoelectric response (standard
piezoresponse force microscopy), ii) the lateral displacement of the sample
surface due to an in-plane piezoresponse, and iii) the electrostatic tip-sample
interaction at the domain boundaries caused by surface charges on the
crystallographic y- and z-faces. A careful analysis of the movement of the
cantilever with respect to its orientation relative to the crystallographic
axes of the sample allows a clear attribution of the observed domain contrast
to the driving forces respectively.Comment: 8 pages, 8 figure
Precision nanoscale domain engineering of lithium niobate via UV laser induced inhibition of poling
Continuous wave ultraviolet (UV) laser irradiation at lambda=244 nm on the +z face of undoped and MgO doped congruent lithium niobate single crystals has been observed to inhibit ferroelectric domain inversion. The inhibition occurs directly beneath the illuminated regions, in a depth greater than 100 nm during subsequent electric field poling of the crystal. Domain inhibition was confirmed by both differential domain etching and piezoresponse force microscopy. This effect allows the formation of arbitrarily shaped domains in lithium niobate and forms the basis of a high spatial resolution micro-structuring approach when followed by chemical etching
Impact of the tip radius on the lateral resolution in piezoresponse force microscopy
We present a quantitative investigation of the impact of tip radius as well
as sample type and thickness on the lateral resolution in piezoresponse force
microscopy (PFM) investigating bulk single crystals. The observed linear
dependence of the width of the domain wall on the tip radius as well as the
independence of the lateral resolution on the specific crystal-type are
validated by a simple theoretical model. Using a Ti-Pt-coated tip with a
nominal radius of 15 nm the so far highest lateral resolution in bulk crystals
of only 17 nm was obtained
Nanoscale surface domain formation on the +z face of lithium niobate by pulsed UV laser illumination
Single-crystal congruent lithium niobate samples have been illuminated on the +z crystal face by pulsed ultraviolet laser wavelengths below (248 nm) and around (298-329 nm) the absorption edge. Following exposure, etching with hydrofluoric acid reveals highly regular precise domain-like features of widths ~150-300 nm, exhibiting distinct three-fold symmetry. Examination of illuminated unetched areas by scanning force microscopy shows a corresponding contrast in piezoelectric response. These observations indicate the formation of nanoscale ferroelectric surface domains, whose depth has been measured via focused ion beam milling to be ~2 micron. We envisage this direct optical poling technique as a viable route to precision domain-engineered structures for waveguide and other surface applications
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