Design of a sample approach mechanism for a metrological atomic force microscope

In order to obtain the high accuracy required for a metrological atomic force microscope, the sample approach mechanism meets strict specifications. The design presented in this paper offers a stiff construction, which limits the influences of floor vibrations on the measurement. Next to this, thermal considerations in the design decrease the uncertainties introduced by temperature variations of the environment. Uncertainties can also be caused by misalignment of the sample holder with respect to the measurement system of three interferometers. To limit these uncertainties, the approach mechanism provides sufficient alignment possibilities. The performance of the sample approach mechanism was evaluated by means of a finite element simulation of its dynamic stiffness. A series of experiments provide the unknown parameters to the simulation model. The dynamic stiffness lies around 395Hz, which is sufficiently high to provide accurate measurements.