Scanning force microscopy - Calibrative procedures for 'best practice'

Scanning force microscopy (SFM) is gaining rapidly in popularity as a convenient and versatile tool for characterising and manipulating a great variety of physical and biological systems. In spite of being in the early stages of the learning curve, the SFM family has already made significant contributions to the rapidly expanding body of knowledge about surface structures and properties. However, many of the results emerging from SFM studies are the outcomes of incompletely characterised methodologies, and the reports often do not provide adequate information about instrumental and operational conditions. A typical SFM system consists of the following main elements: a sample stage with x-y-z positional control; a detector/sensor stage containing the optical deflection arrangement and the position-sensitive sensor assembly; and the force-sensing probe which consists of a lever and a tip. The elements will perform according to operational criteria, and their functionalities will be contingent on evaluation of sets of parameters, without which the interpretation of results may be open to questioning and/or be difficult to reproduce. Methodologies for evaluation and calibration of the various elements are now in the process of being developed; these will in due course constitute the basis on which prescriptions will be constructed for “best practice.” The current state of the literature is reviewed, and strengths and weaknesses are identified.