Ultra Small Surface Force Measurements in Vacuum

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Profound understanding of adhesive interactions on the nanoscale is important for a variety of applications as for example for handling of particles and building blocks during micro- and nanoassembly, for industrial cleaning processes and for medical drug delivery.Atomic force microscope based force spectroscopy with the colloidal probe technique and other force measurement tools have led to great advances in the understanding of fundamental adhesive interactions and verified theoretical considerations in this field. However, force spectroscopy in ambient atmosphere always yields only a superposition of van der Waals, electrostatic and capillary effects. Moreover, colloidal probe studies with particles below 1 micrometer in diameter are rare due to the limited ability to fabricate such small probes without a complicated wet-chemical process and restrictions regarding geometry and material selection. Measurements in an aqueous medium reduce the capillary forces, but at the same time they can introduce new force contributions and alter the chemical environment. Furthermore, data gained in ambient or an aqueous medium is not fully applicable to handling processes inside the scanning electron microscope, which has become a preferred environment for nanomanipulation and nanoassembly, as they do not take into account the influence of the electron beam and the vacuum environment.This project aims at two main objectives: directly investigating the van der Waals and electrostatic interactions without the influence of capillary forces and the need for an aqueous medium, and exploring the influence of electron beam induced effects on adhesion and stiction inside a scanning electron microscope. Furthermore, the common adhesion theories and approximations will be validated in the force range that is normally superimposed by capillary interaction and jump to contact effects. To achieve this goals a dedicated force spectroscopy setup surpassing the current force resolution limits will be combined with a high resolution scanning electron microscope/focused ion beam instrument. In this way, systematic adhesion force studies inside the vacuum chamber of the scanning electron microscope employing tailored substrates and colloidal probes with hitherto unachievable variety regarding size, geometry, and material will be feasible, thus allowing for deeper understanding of capillary forces and adhesive interactions in general, and making way for new micro- and nanohandling strategies.