Multiple sensor stabilization system for local probe microscopes

We introduce the concept of a multiple sensor stabilization system (MSS) applicable to all local probe microscopes. With this it is possible to separate distance control and sensor-sample-interaction signals with unprecedented stability. The MSS uses two or more sensors of an array of local probe sensors, which are coupled via rigid low-mass short-distance connections. At least one of these sensors is employed to always provide a continuous and independent feedback signal. Using this, the distance between any other sensor of the array and the sample surface can be controlled, under ambient and in situ conditions, with the resolution and range of the designated sensors on time scales of up to hours. The concept of MSS is applicable to the whole range and any conceivable combination of local probe techniques, especially all other scanning near field probes. MSS offers particularly large advantages for spectroscopic applications. We demonstrate its utility by the example of an atomic force microscope using a commercially available array of cantilevers. By using two cantilever sensors for position control it is possible to eliminate all drift between the sample and the tip's position. The high potential of the MSS is illustrated by two applications: a thermal noise-reduction based approach with minimal contact forces and the first pN-"force clamp" for single molecule force spectroscopy. (C) 2001 American Institute of Physics.