Column Control DTX

Intrinsic Contact Noise: Identifying High Resolution AFMs

Application Notes

Introduction

Resolution and sensitivity are two important characteristics by which to judge the performance of an Atomic Force Microscope (AFM), and they are both adversely affected by noise. If the AFM is noisy, a sensitive cantilever or detector, a precisely calibrated piezoelectric scanner, and a whole host of other high-performance elements of an AFM may as well be replaced by lower-performance, cheaper substitutes because, their value is lost in the noise of the AFM.

 

Resolution and sensitivity of an AFM cannot be determined from the performance specifications of a component, or of a collection of components. While tabulated numerical specifications can make one AFM look better than another, the usefulness of a specification, a “spec“, is only validated if it can be shown to directly correlate with better performance, the definition of which we limit here to higher resolution and better sensitivity. For example, one AFM may be specified to allocate two more bits than another AFM, for analog-to-digital (A/D) conversion of the voltage applied to the piezoelectric actuators, thus implying that tip fine positioning resolution is superior in the first AFM. But in fact, when it comes to AFM image resolution, those two extra bits may add nothing of value if the lowest achievable noise level, the noise floor, of the two AFMs are the same, and larger than the equivalent of three digital bits in both AFMs’s A/D converters.

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Column Control DTX