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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.
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.
Appl. Surf. Sci. 140, 287 (1999).
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).
Appl. Surf. Sci. 210, 37-42 (2003)
closeness of agreement between quantity values obtained by replicate measurements of a quantity, under specified conditions
Measurement precision is usually expressed numerically by measures of imprecision, such as standard deviation, variance, or coefficient of variation under the specified conditions of measurement. (VIM)
Appl. Surf. Sci. 210, 37-42 (2003)
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).