Atomic force microscopy has been the primary workhorse for imaging and manipulating samples with sub-nanometer resolution and pico-Newton scale force resolution. It has found applications in such diverse fields as biology, chemistry, engineering, medicine, and physics. The central feature of atomic force microscopy (AFM) is its probing system that detects the near-field physical interactions between the probe tip and the sample. In principle, 3D forces can be detected and controlled. However, the overwhelming majority of the applications of AFM, in every field where it is used, are on samples which are very nearly planar and horizontal. The primary reason for this severe constraint on the possible samples that can be imaged or manipulated by AFM is due to the geometry of the probe.
In this research, the design, actuation, and control of a novel multi-axis probing system, which can simultaneously control the tip position and tip orientation, and which enables imaging and manipulation of samples having three-dimensional geometries, is investigated. It can change the orientation of the tip according to the surface normal of the sample, and thus precisely control the tip-sample interaction point when imaging surfaces having large topographic variations. It leads to the creation of a multi-axis probing system for nano-metrology, which is a three-dimensional (3D) surface tool rather than a two-dimensional (2D) planar surface tool. In order to fully develop the probing system, two more innovations are proposed. Firstly, a multi-axes scanning scheme is developed in order to align the directions of scanning and interaction control depending on the local surface orientation. Secondly, a tip-sample interaction scheme is proposed that regulates the direction of the tip-sample interaction while minimizing the effect of lateral friction. A robust control scheme is implemented in combination with these proposed developments, which commands the tip to track orientation changes of the sample surface when imaging 3D samples. The integrated system possesses two unique features, namely, multi-axis control of tip and scanning operation and the capability to interact with 3D surfaces in a gentle, controlled manner. The probing system is evaluated by imaging a variety of engineered 3D surfaces. The result of scanning a micro-pipette of diameter 2.4µm using this tool is presented and discussed.