GetPDFServlet - Calibration of atomic-force microscope tips...

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Calibration of atomic-force microscope tips Jeffrey L. Hutter and John Bechhoefer Department of Physics, Simon Fraser University, Burnaby, British Columbia, VSA 235, Canada (Received 29 March 1993; accepted for publication 12 April 1993) Images and force measurements taken by an atomic-force microscope ( AFM) depend greatly on the properties of the spring and tip used to probe the sample ’s surface. In this article, we describe a simple, nondestructive procedure for measuring the force constant, resonant frequency, and quality factor of an AFM cantilever spring and the effective radius of curvature of an AFM tip. Our procedure uses the AFM itself and does not require additional equipment, 1. INTRODUCTION check, for example, whether a tip has been blunted after crashing into a sample surface. Since its invention in 1986, the atomic-force microscope ’ (AFM) has become an increasingly impor- In this article, we describe a nondestructive procedure for calibrating individual cantilevers and tips for use in tant tool for studying surfaces at the atomic level. Beyond microscopy. In Sec. II, we review the two the often spectacular and occasionally informative images common AF?vi imaging modes. In Sec. III, we show that obtained of surfaces, the AFM has the potential to give measurements of thermal fluctuations of the cantilever can quantitative information about focal forces and interactions.26 The accuracy of such measurements de- yield its spring constant, resonant frequency, and the qual- ity factor of the resonance. In Sec. IV, we show that mea- pends upon a knowledge of the physical properties of the surements of van der Waals forces on the tip allow an spring and tip that probe these forces. In particular, one effective tip radius to be inferred. In Sec. V, we present needs estimates of the size of the tip and the force constant representative data from the calibration of a silicon-nitride of the cantilever spring to which the tip is attached. cantilever with an integral pyramidal Despite this need for calibration of individual tips and cantilevers, measurements of these properties have either been based on theoretical estimates or have been made only on supposedly representative samples. Typically, the radius of an AFM tip is taken from manufacturer ’s specifications or, rarely, measured by electron microscopy.7-9 In the former case one uses a nominal figure that represents an average for a batch of microfabricated tips, while, in the latter, measurements are difficult and are likely to destroy the tip. ” In either case, only the average macroscopic ra- dius of curvature will be measured. However, the tip- sample interaction is dominated by the small portion of the tip closest to the sample. Since the tip is not likely to end in a perfect sphere, particularly in the case of pyramidal tips, such an average value will not serve as a very useful calibration. II. THE ATOMIC-FORCE MICROSCOPE The AFM probes the surface of a sample by moving the sample beneath a tip attached to a weak cantilever
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GetPDFServlet - Calibration of atomic-force microscope tips...

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