These additional imaging techniques are based on one of the three basic modes of operation. They help extract additional information about the sample surface simultaneously with its topography. Some of these modes such as e. Lift Mode or Hover Mode. In Lift Mode the AFM acquires topography data and electric or magnetic data on the same scan line independently. The first pass is a regular topographic scan.
During the second pass, second line scan or retrace scan, the AFM tip traces the surface topography at a preset vertical distance, usually nm, gathering information about the long-range electrostatic, magnetic, etc.
More recently developed Single-Pass Methods allow gathering topographic and other data simultaneously in a single pass with the help of lock-in amplifiers with improved sensitivity and higher resolution.
Phase Imaging: Recording the phase difference between the drive signal and the AFM cantilever oscillation in dynamic mode gives additional information about material properties such as elasticity, adhesion, etc. For applications in liquids, silicon nitride probes are commonly used. High-Speed Scanning HSS : By increasing the scanning speed and the feedback speed up to video rates with the help of AFM cantilevers with megahertz resonance frequencies and high-speed electronics, dynamic processes in bioresearch can be visualized.
Lateral Force Microscopy LFM : By using a four-segment photodetector and scanning in Contact Mode, the microscope is capable of detecting not only the vertical deflection of the AFM cantilever but also its torsional twisting due to lateral forces usually friction acting on the AFM probe tip. Electrostatic Force Microscopy EFM : The variations of the electric field gradient across the sample surface can be analyzed in Non-Contact Mode by applying a voltage bias to intermediately stiff AFM probes with an electrically conductive coating.
Piezoresponse Force Microscopy PFM : This mode exploits the reverse piezoelectric effect to investigate piezoelectric and ferroelectric materials by scanning a conductive AFM tip in Contact Mode and simultaneously applying an alternating voltage bias to induce mechanical deformation from the surface domains.
A voltage difference is applied between the AFM probe and the sample the resulting electrical current is recorded. Scanning Spreading Resistance Microscopy SSRM is a closely related technique that scans a cross-sectional device area for determining dopant concentrations in semiconductors. Both techniques are very demanding on the AFM tip and require AFM probes with highly wear-resistant electrically conductive coatings.
I-V Spectroscopy allows examining the bias dependent resistivity by ramping the voltage bias in Point-Contact Mode over a sample location of interest. Force-distance F vs d Measurements: In this technique the AFM cantilever deflection is monitored as a function of piezo-displacement as the AFM probe tip approaches the sample, presses against it and then retracts from the surface.
In Nanoindentation the approach curve is analyzed and in Adhesion Testing - the retract curve. Another related technique, Force Volume Mode takes a force-distance measurement at a predefined set of measurement point during a scan.
AFM cantilevers with different stiffness can be used depending on the stiffness of the sample and the tradeoff between higher force sensitivity and higher maximum force.
Pulsed Force Mode PFM : By introducing an oscillation at a much lower frequency than the resonance frequency of the AFM cantilever, force-distance curves are taken at every point of an intermittent contact scan, thus mapping sample adhesion and stiffness.
Nanolithography: Modifications of the sample surface can be obtained by applying sufficiently strong forces with the AFM probe tip Scratch Lithography , by local oxidation of specific substrates such as titanium or silicon or by etching. To put the nanoscale in a more understandable perspective, consider that the size of an atom relative to an apple is similar to the size of an apple relative to the planet Earth!
As the tip approaches the surface, the close-range, attractive force between the surface and the tip cause the cantilever to deflect towards the surface. However, as the cantilever is brought even closer to the surface, such that the tip makes contact with it, increasingly repulsive force takes over and causes the cantilever to deflect away from the surface.
By reflecting an incident beam off the flat top of the cantilever, any cantilever deflection will cause slight changes in the direction of the reflected beam.
A position-sensitive photo diode PSPD can be used to track these changes. Thus, if an AFM tip passes over a raised surface feature, the resulting cantilever deflection and the subsequent change in direction of reflected beam is recorded by the PSPD. The raised and lowered features on the sample surface influence the deflection of the cantilever, which is monitored by the PSPD.
By using a feedback loop to control the height of the tip above the surface—thus maintaining constant laser position—the AFM can generate an accurate topographic map of the surface features. By clicking "Submit", you agree to the privacy policy of Park Systems. Park NX-Hivac. Park 3DM Series. Park Wafer Series. Sustainability Investors Careers News Events en. Investors Careers. Case Studies. About Us. Sales Inquiries.
Customer Support. Probe Selection Guide. The Underlying Principle of AFM AFM microscopes operate on the principle of surface sensing using an extremely sharp tip on a micromachined silicon probe.
Additional AFM Microscope Principles AFM microscopes are extremely versatile tools that are not limited to topographical measurements and imaging applications. Find out more. How can we help you? By submitting this form I agree that Oxford Instruments will process my data in the manner described in the Privacy Policy.
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