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AFM tool on micron robot

The Atomic Force Microscopy allows imaging and interacting with biological samples in the scale of nanometres and nN. The designed and implemented AFM tool consists in two parts: sensor and actuator. The sensor is a piezo-resistive AFM commercial probe, which is connected to the actuator by means of a specially designed holder. The actuator is a multilayer piezoceramic element, which can be moved in three orthogonal directions.

The actuator consists on four piezoelectric stackers (dimensions: 2mmx2mmx3,5mm) allowing the position control of the AFM tip with a resolution in the range of manometers. The holder allows the coupling among the piezo-actuator and the AFM sensor. This holder is suitable for the space requirements and, in addition, it contacts with the sensor mechanically, without the needle of soldering, allowing an easy interchange of diverse AFM tips. Finally, a cantilever forms the classical AFM sensor with a sharp tip probe at its end and the laser force detection system. In our case we only use a self-sensing cantilever, which has silicon piezo-resistance deposited over it.

When the cantilever bends, the strain over the piezo-resitance changes the resistance value in linear way (this is true only for low variations). With this system we reduce drastically the dimensions and the power consumption comparing to the classical AFMs. The driver and instrumentation for this tool fits in the onboard electronics result, but it's especially important the possibility of externally adjust the instrumentation system in order to allow the AFM tip interchange.

The results of the calibration of the AFM system, comparing it with a typical AFM experience (using a laser for measure the cantilever deflection) making a force curve over a crystal sample are:
- The electronic noise causes a 10% of error, which could be filtered in the software system.
- The non-linearity is lower than 1.2%, which implies the system works with the same accuracy than the laser measurement.

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Reported by

Marti i Franques 1
08028 Barcelona
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