Force-balancing microforce sensor with an optical-fiber interferometer

Abstract

A microforce sensor with a force feedback method for scanning force microscopy is presented. The force sensor is constructed by using an optical fiber and a microcantilever. The facet of the optical fiber is coated with a gold thin film 15 Å thick. This gold film acts not only as a partially reflected mirror but also as an electrode of the electrostatic actuator. The interaction force between a probe tip and a sample is balanced by the electrostatic force. The deflection of the cantilever is measured by an interferometer consisting of the facet of the optical fiber and the cantilever surface. We have made the force sensor and measured some force curves of a mica surface with a SiN probe tip. The force curves obtained by this sensor are quite different from the curves by a conventional measurement without a feedback system. The force resolution of the system is 10−10 N with a bandwidth of dc∼1 kHz.

Modeling and experimentation of a passive low frequency nanoforce sensor based on diamagnetic levitation

“…Most of the time, the uncertainty associated with calibrations is not provided in experiments requiring micro or nanoforce measurements (for instance the nanotribology field with AFM) because there is no way to validate it. Calibration remains an open problem in the scientific community which is using or designing such sensors [4]. One of the questions which arises is about the fact that even if a calibration seems cor-rectly done, it will be illustrated that micro and nanoforce measurements cannot be guaranteed in all circumstances with actual sensors designs.…”

“…The majority is based on monolithic elastic microstructures which are most of the time microcantilevers [1] coupled or not with a mechanical deformation amplifier : AFM based microforce sensors using two or four quadrants photodetectors [2] [3] or the interferometry principle [4], piezoresistive microforce sensors which use the variation of the piezoresistive layer resistance when a force is applied [5] [6], capacitive microforce sensors which make use of change in capacitance between two metal plates when their distance changes during force application [7] [8], piezoelectric microforce sensors which generate a voltage when they are stressed by a force [9], etc. Because maximum microstructure deformations are usually small, these sensors are mostly limited in range of force measurement but have a large frequency bandwidth.…”

Feedback stabilized force-sensors: a gateway to the direct measurement of interaction potentials

“…This has indeed been implemented in probe microscopy using both electrostatic forces (e.g. [8][9][10][11][12]) and magnetic forces [4,13].…”

Micro-Force sensor by active control of a comb-drive

“…Most designs are based on elastic microstructures such as microcantilevers [5], piezoresistive sensors using the variation of resistance on a piezoelectric layerb [6], capacitive sensors based on the variation between two armatures over distance [7], direct piezoelectric sensors through the correlation between their deformation and produced current [8] Nevertheless, the most widespread approach is the Atomic Force Microscopy (AFM) [9] [10]. The deflection of a cantilever of known characteristics is measured by a two or four quadrants photodectectors [11] or by interferometry [12]). The applied force is then deduced using the measured deflection and the stiffness of the cantilever.…”