- P -
PFM
Piezoresponce
Force Microscopy
In
PFM the tip is brought into contact with the surface
and the piezoelectric response of the surface is detected
as a first harmonic component of bias-induced tip deflection
do+ A cos(wt+f). The phase f yields information on the polarization
direction below the tip. For a polarization vector pointing
downwards (i.e., c- domains), the application of a positive
tip bias results in the expansion of the sample and bias-induced
surface oscillations are in phase with tip voltage f=0.
For polarization pointing up-wards (i.e., c+ domains) f
=180°. The amplitude A defines the local piezoresponse and
depends on the geometry of the system (thin film vs bulk
crystal or ceramics). The numerical value of A under ideal
imaging conditions (perfect contact between the tip and
the surface, no viscous damping) is determined by combination
of a electroelastic constants of material and tip properties.
Phys. Rev. B 63, 125411 (2001).
Pulsed
Force Mode I
At the starting point, the AFM tip is well above the sample
surface. Moving closer to the surface, the tip snaps into
contact due to the negative (attractive) force between tip
and sample surface. As the piezo pushes the tip further
toward the sample, the positive (repulsive) force reaches
a maximum. As the piezo pulls back, the repulsive force
decreases and the force signal changes sign from repulsive
to attractive. Finally, the tip loses contact. The subsequent
free oscillation of the probe is damped towards the baseline.
After this, the cycle starts again. The Pulsed Force Mode
extends the capabilities of an Atomic Force Microscope beyond
simply measuring topography. It allows additional properties
like local stiffness and adhesion to be determined.
http://www.witec.de/pfm.html
Pulsed
Force Mode II
Pulsed Force Mode employs an oscillating cantilever to probe
a sample’s surface and produces simultaneous but separate
maps of sample topography, stiffness, and adhesion. In PFM,
the probe scans the surface in contact mode feedback while
a sinusoidal oscillation, well below the cantilever’s resonant
frequency, is applied to the z-piezo. This oscillation brings
the tip into periodic contact with the surface as it scans
the sample. This scan technique minimizes destructive lateral
forces that may be induced by standard contact mode, and
makes it possible to scan soft samples. Through each oscillation,
the system monitors probe displacement to characterize the
force-distance relationship between the surface and the
probe. This displacement is related to tip force bythe spring
constant of the cantilever.
http://www.topometrix.com/tech/modes/pfm.htm
Phase
Imaging
ph-HFM
PLL
PMFM
potential-correction
MFM
A
scanning probe technique for current-carrying device imaging.
It combines magnetic-force microscopy with surface-potential
nulling measurements. The device is ac biased at an off-resonant
frequency and the current-induced magnetic field results
in cantilever deflection which is detected by a lock-in
amplifier. An ac bias at the resonant frequency is simultaneously
applied to the tip and conventional scanning surface-potential
microscopy feedback is used to match the tip and surface
potentials. This multiple-modulation technique allows electrostatic
and magnetic interactions to be distinguished and surface-potential
and magnetic-force images to be collected simultaneously.
The technique, which is referred to as potential-correction
magnetic-force microscopy, produces force rather than force-gradient
images as in conventional magnetic-force microscopy.
Appl. Phys. Lett. 78, 1005 (2001).
PPM
PSD
PSPD
PSTM
Photon
STM
The
PSTM uses the sample-modulated tunneling of photons
to a sharpened optical-fiber probe tip, the source being
the evanescent field produced by total reflection of a light
beam. This provides an exponentially decaying waveform normal
to the sample surface. As in the case of the STM,
a feedback prevents the tip from contacting the sample.
Phys. Rev. B 39, 767 (1989).
PTR
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