Abstract
The article presents a redesigned sensor holder for an atomic force microscope (AFM) with an adjustable probe direction, which is integrated into a nano measuring machine (NMM-1). The AFM, consisting of a commercial piezoresistive cantilever operated in closed-loop intermitted contact-mode, is based on two rotational axes, which enable the adjustment of the probe direction to cover a complete hemisphere. The axes greatly enlarge the metrology frame of the measuring system by materials with a comparatively high coefficient of thermal expansion. The AFM is therefore operated within a thermostating housing with a long-term temperature stability of 17 mK. The sensor holder, connecting the rotational axes and the cantilever, inserted one adhesive bond, a soldered connection and a geometrically undefined clamping into the metrology circle, which might also be a source of measurement error. It has therefore been redesigned to a clamped senor holder, which is presented, evaluated and compared to the previous glued sensor holder within this paper. As will be shown, there are no significant differences between the two sensor holders. This leads to the conclusion, that the three aforementioned connections do not deteriorate the measurement precision, significantly. As only a minor portion of the positioning range of the piezoelectric actuator is needed to stimulate the cantilever near its resonance frequency, a high-speed closed-loop control that keeps the cantilever within its operating range using this piezoelectric actuator further on as actuator was implemented and is presented within this article.
Highlights
Introduction and Literature ReviewDue to its high structural resolution, the atomic force microscope (AFM) [1] was a prime instrument to obtain qualitative information down to the atomic-scale, but it is a widely used and traceable tool in nanometrology [2]
A different approach to measure vertical or near vertical surface features is to introduce an inclination between the measuring object and the cantilever
In [13] an AFM based on two rotational axes [14] to adjust the probe direction to cover a complete hemisphere has been demonstrated
Summary
Due to its high structural resolution, the AFM [1] was a prime instrument to obtain qualitative information down to the atomic-scale, but it is a widely used and traceable tool in nanometrology [2]. A different approach to measure vertical or near vertical surface features is to introduce an inclination between the measuring object and the cantilever. It has been redesigned to a clamped sensor holder, which will be presented, evaluated and compared to the previous glued sensor holder within this paper Another way to reduce the effects of thermal variations during a measurement is the improvement of the measuring speed. As piezoelectric actuators suffer from hysteresis and creepage [20], provisions have been made to measure the extension of the piezoelectric actuator by a fibre optic distance sensor This highspeed AFM and its limitations will be presented in Sect. All measurements have been conducted within a thermostating housing and the set temperature was 20 ◦C
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