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Unformatted text preview: CHAPTER 1 Introduction 1 FIGURE 1-1 In the AFM, a sharp probe is scanned across a surface, left, and by monitoring the motion of the probe from each pass across the surface, a 2-D line pro¡le is generated. Then the line pro¡les are combined to create a three dimensional image of the surface, right. Typically, when we think of microscopes, we think of optical or electron microscopes. Such microscopes create a magniFed image of an object by focusing electromagnetic radiation, such as photons or electrons, on its surface. Optical and electron microscopes can easily generate two- dimensional magniFed images of an object’s surface, with a magniFcation as great as 1000X for an optical microscope, and as large as 100,000X for an electron microscope. Although these are powerful tools, the images obtained are typically in the plane horizontal to the surface of the object. Such microscopes do not readily supply the vertical dimensions of an object’s surface, the height and depth of the surface features. Unlike traditional microscopes, the A¡M does not rely on electromagnetic radiation, such as photon or electron beams, to create an image. An A¡M is a mechanical imaging instrument that measures the three dimensional topography as well as physical properties of a surface with a sharpened probe, (see ¡igure 1-1). Chapter 1 • INTRODUCTION 2 Te sharpened probe is positioned close enough to the surface such that it can interact with the force Felds associated with the surface. Ten the probe is scanned across the surface such that the forces between the probe remain constant. An image of the surface is then reconstructed by monitoring the precise motion of the probe as it is scanned over the surface. ¡ypically the probe is scanned in a raster-like pattern. In an A¢M the probe is very sharp, typically less than 50 nanometers in diameter and the areas scanned by the probe are less than 100 um. In practice the heights of surface features scanned with an A¢M are less than 20 um. Scan times can range from a fraction of a second to many 10’s of minutes depending on the size of the scan and the height of the topographic features on a surface. MagniFcations of the A¢M may be between 100 X and 100,000,000 X in the horizontal (x-y) and vertical axis. ¢igure 1-2 illustrates the block diagram of an atomic force microscope. In the microscope, the force between a nanoscopic needle and the surface is measured with a force sensor, the output of the force sensor is then sent to a feedback controller that then drives a Z motion generator. Te feedback controller uses the force sensor output to maintain a Fxed distance between the probe and the sample. X-Y motion generators then move the probe over the surface in the X and Y axis. Te motion of the probe is monitored and used to create an image of the surface....
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- Fall '07
- Electron, Orders of magnitude, Scanning Tunneling Microscope, Scanning electron microscope