Best practices for real-time in situ atomic force and chemical force microscopy of crystals

The characterization of dynamic crystal surfaces with their surroundings can be elusive because their growth and dissolution usually occur at length scales and in environments that are incompatible with most microscopy methods. Real-time in situ atomic force microscopy (AFM) and chemical force microscopy (CFM) have emerged over the past two decades as powerful tools for the investigation of crystal growth in environments of interest, enabling quantitative characterization of dynamic growth processes at the near-molecular level as well as surface adhesion. Herein, we describe protocols that we view as best practices for these measurements, which permit substantial insight into crystal growth mechanisms and phenomena that often govern aggregation and adhesion of crystals. These protocols are illustrated with a focus on soft organic crystals relevant to human health, such as the pathological crystal L-cystine, which forms kidney stones in patients suffering from cystinuria. This manuscript also describes challenges and obstacles often encountered and some tricks of the trade, while illustrating typical results and data interpretation.