Shear Force Microscopy

At present the most-used method of probe-sample distance regulation relies on the detection of shear forces between the end of near-field probe and the sample [1]. Shear force based system allows Shear Force Microscopy alone, or simultaneous Shear Force and Near-Filed imaging, including Transmission mode for transparent samples, Reflection mode for opaque samples and Luminescence mode for additional characterisation of samples.

To hold the optical probe near surface nonoptical scheme with quartz tuning fork as sensor is used. It allows to increase ratio of useful signal to noise in comparison with optical holding schemes. It is very important at operations with limiting resolution. Also photoinduced carriers does not appear. It is necessary requirement when some properties of semiconductor are investigated.

At the heart of nonoptical method for obtaining of information about surface lies idea to use response of quartz tuning fork attached to optical fiber on interaction with surface. System fiber-quartz is excited in transverse vibrations with help of external feed element on quartz resonance frequency. Further piezoeffect is used: in the presence of mechanical oscillations electrical outputs of quartz have voltage response, which is used as information signal about amplitude of fiber oscillation.

Shear Force Microscopy is realized in the following way. Piezodriver via quartz tuning fork excite oscillations of the fiber probe with some initial amplitude. Suitable output value of quartz is Ao. After approaching sample surface the amplitude of fiber probe oscillations reaches some set-point value and quartz output reaches value A. After that scanning of the sample surface is conducted with maintaining this value by the feedback system.

References

1. Appl. Phys. Lett. 60, 2484 (1992).