Development of a flexure-based nano-actuator for high-frequency high-resolution directional sensing with atomic force microscopy

Scanning probe microscopies typically rely on the high-precision positioning of a nanoscale probe in order to gain local information about the properties of a sample. At a given location, the probe is used to interrogate a minute region of the sample, often relying on dynamical sensing for improved accuracy. This is the case for most force-based measurements in atomic force microscopy (AFM) where sensing occurs with a tip oscillating vertically, typically in the kHz to MHz frequency regime. While this approach is ideal for many applications, restricting dynamical sensing to only one direction (vertical) can become a serious limitation when aiming to quantify the properties of inherently three-dimensional systems, such as a liquid near a wall. Here, we present the design, fabrication, and calibration of a miniature high-speed scanner able to apply controlled fast and directional in-plane vibrations with sub-nanometer precision. The scanner has a resonance frequency of ∼35 kHz and is used in conjunction with a traditional AFM to augment the measurement capabilities. We illustrate its capabilities at a solid-liquid interface where we use it to quantify the preferred lateral flow direction of the liquid around every sample location. The AFM can simultaneously acquire high-resolution images of the interface, which can be superimposed with the directional measurements. Examples of sub-nanometer measurements conducted with the new scanner are also presented.