Abstract
We introduce drive-amplitude-modulation atomic force microscopy as a dynamic mode with outstanding performance in all environments from vacuum to liquids. As with frequency modulation, the new mode follows a feedback scheme with two nested loops: The first keeps the cantilever oscillation amplitude constant by regulating the driving force, and the second uses the driving force as the feedback variable for topography. Additionally, a phase-locked loop can be used as a parallel feedback allowing separation of the conservative and nonconservative interactions. We describe the basis of this mode and present some examples of its performance in three different environments. Drive-amplutide modulation is a very stable, intuitive and easy to use mode that is free of the feedback instability associated with the noncontact-to-contact transition that occurs in the frequency-modulation mode.
Highlights
Dynamic atomic force microscopy [1,2] is a powerful yet versatile tool capable of operating in environments ranging from ultrahigh vacuum (UHV) to liquids [3,4], and imaging samples ranging from stiff inorganic materials [5] to soft biological matter [6], with nanoscale resolution
Amplitude-modulation AFM (AM-AFM) [7] and in particular its large-amplitude version, commonly known as tapping mode [8], is the most extended Dynamic atomic force microscopy (dAFM) mode, but it has limitations: Its application to the vacuum environment is very difficult because of the long scanning times imposed by the high quality factor Q of the cantilevers in vacuum, which present a settling time given by τcl= Q/(πf0)
The oscillation amplitude A is the controlled input for the topography feedback, and the scanner position in the z-direction is the regulated variable; the variation of the phase is recorded in the phase image, which is used as a spectroscopic image
Summary
Dynamic atomic force microscopy (dAFM) [1,2] is a powerful yet versatile tool capable of operating in environments ranging from ultrahigh vacuum (UHV) to liquids [3,4], and imaging samples ranging from stiff inorganic materials [5] to soft biological matter [6], with nanoscale resolution. In this work we present a new AFM scanning mode, which we have called “drive amplitude modulation” (DAM-AFM) [20] and which takes advantage of the aformentioned monotonicity of the dissipation to obtain stable images in all environments from vacuum to liquids.
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