In situ determination of effective tip radius in dynamic atomic force microscopy
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In situ determination of effective tip radius in dynamic atomic force microscopy C. Maragliano, A.Glia, M.Stefancich and M.Chiesa LENS Laboratory @ Institute Center for Future Energy Systems (iFES), Masdar Institute of Science and Technology, P.O.Box 54224, Abu Dhabi, UAE
Abstract Atomic force microscopy (AFM) suffers from an important limitation: it does not provide quantitative information about the scanned sample. This is because too many unknowns come into play in AFM measurements. The shape of the tip is probably the most important. A technique able to characterize in situ the shape of the tip apex would represent an important step ahead to turn the AFM into a quantitative tool. Standard methods can be destructive to the tip and are time consuming. Two main methods are currently used to characterize the tip radius in situ without affecting its shape. The first consists of characterizing the tip radius by monitoring the dynamics of the cantilever. The value of free amplitude, for which transitions from the attractive to repulsive force regimes are observed, strongly depends on the curvature of the tip. The second method to characterize the tip radius consists instead on fitting the capacitance curve of the tip-sample system with an analytical function. In this work we compare the two methods to characterize in situ the tip radius and results are verified with SEM images. The value of the free amplitude is correlated with the value of R while the capacitance curve is derived with a method we proposed. Tips with different tip radii are used. The investigation is conducted with the aim of determining the most reliable technique for characterizing the tip radius for both sharp and blunt tips.
Introduction Since it was first proposed in 1986[1], AFM has been extensively used for imaging surfaces, achieving sub-nanometric spatial resolution under specific conditions[2]. Recently, the scientific community has witnessed an evolution of AFM into a versatile instrument able to quantify sample properties [3, 4]. This is made possible combining experimental results with accurate models of the tip-sample system[5]. It is therefore evident that knowing the shape of the tip, and in particular the dimension of the tip apex, is crucial in order to accurately quantify sample
properties. The importance of knowing the tip size is confirmed also by the numerous manifestations in literature where expressions for tip-sample forces generally have a term, the tip radius , accounting for the effective curvature of the tip [6-8]. Current standard methods to quantify the tip radius make use of Scanning Electron Microscope (SEM) images of the tip[9] or rely on combining theoretical models with measurements of topographical sample features[10]. Despite their good reliability, the applicability of these techniques is nevertheless limited. They are indeed generally destructive, time consuming, and in the case of using SEM, require removing the tip from the AFM chamber. Two promising methods have been proposed in the last years capable of o
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