Scanning Force Microscopy in the Classroom
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SCANNING FORCE MICROSCOPY IN THE CLASSROOM
Fredy R. Zypman Yeshiva University Department of Physics New York, NY 10033-3201 ABSTRACT
We describe a strategy to efficiently introduce concepts of scanning force microscopy in introductory science and engineering classes. Particular emphasis is placed in qualitative understanding via intuition building with numerical trial and error. In addition, model development is introduced and used to perform quantitative predictions of force-separation curves. I. INTRODUCTION
Scanning Force Microscopy (SFM), also known as AFM, has been in use in Materials Science and Engineering for almost two decades to obtain sub micrometric topographic information of surface samples. In addition, it has been used to measure interaction forces between varieties of small objects. In topographic mode a tip is raster scanned on a surface. The tip, at the end of a flexible cantilever, induces torsions and flexions on the latter. These elastic deformations are detected via laser deflection monitoring. In force mode detection, called spectroscopic mode, the tip is approached toward or retracted from the surface, and cantilever deflections are measured. These deflections, when the elastic constants of the cantilever are taken into consideration, give information about stresses, particularly tip-surface force interactions. Detailed descriptions of the operation of the SFM have been published, and we direct the interested reader to some of them . The development of instructional materials to introduce SFM to students for the first time started appreciably less than ten years ago. For example, Sarid produced a book that brings in SFM concepts by symbolic programming. Another example is the development of the Macroscope5, a cm—size apparatus that models, at a larger scale, the dynamics of the SFM. To contribute to the development of instructional materials in SFM, this paper describes the creation of a new course in which first-year students of science and engineering learn the basic concepts of SFM and reconstruction algorithms via familiarization with the Macroscope, and the development of computer code to perform SFM force-distance reconstruction. The organization of this paper is as follows. In section II, we describe the Macroscope and how students use it. In section III, we describe the course itself. Section IV presents an example of the material developed for this class. Finally, section V presents the conclusions. 1,2,3
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II. MACROSCOPE
The Macroscope (Figure 1) consists of a metal bar, the cantilever, at which end is attached a magnet, the tip, with its magnetization directed in the vertical direction. In one of the possible implementations, the other end of the bar is fixed to a heavy frame, and therefore immobile for all practical purposes.
Figure 1. View of the “free” extreme of the cantilever. A magnetic tip interacts with a magnetic sample via nonlinear forces. The absolute height of the sample is adjusted with a micrometer. Also shown above the cantile
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