SEW - New detection system for extremely small vertical cantileversDetection techniques currently used in scanning force microscopy impose limitations on the geometrical dimensions of the probes and, as a consequence, on their force sensitivity and temporal response. We have developed a new technique, based on scattered evanescent electromagnetic waves (SEW), which enables us to detect the displacement of the extreme end of a vertically mounted cantilever in the sample plane (XY). SEW detection system enables the use of force sensors with sub-micron size, opening new possibilities in the investigation of biomolecular systems and high-speed imaging.
 Figure 1. Diagram of the SEW detection system. |
Evanescent electromagnetic field is generated just above the sample surface by using the objective-based total internal reflection. When the tip of a vertically mounted force sensor enters the evanescent field, it causes part of this field to propagate. The scattered electromagnetic radiation is collected with the same objective lens and is projected onto a four-sector photodetector, where either an image of the tip or the interference pattern resulting from the combination of the scattered light from the tip and the reference beam, is produced.
 Figure 2. Optical microscope images of a tipless vertically mounted AFM cantilever positioned: (left) above the evanescent field; (right) in the evanescent field. |
 Figure 3. Cantilevers produced by FIB milling and optimised for high force sensitivity and high temporal resolution. |
SEW detection has been successfully used to monitor the displacement of small custom force sensors fabricated by FIB milling of commercially available AFM cantilever (Veeco Biolever).
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SEW detection system enables the use of novel probes, e.g., directly use nanowires and nanotubes as
force sensors.
For more details, see M Antognozzi et al., Nanotechnology (2008), in press.