The Macroscope: A Macroscopic Tool for Validating Microscopic Force Relationships
- PDF / 135,655 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 107 Downloads / 199 Views
THE MACROSCOPE: A MACROSCOPIC TOOL FOR VALIDATING MICROSCOPIC FORCE RELATIONSHIPS Claudio Guerra-Vela1, Fredy R. Zypman2 1
University of Puerto Rico at Humacao Department of Physics 100 Tejas Street Humacao, PR 00791-4300 2
Yeshiva University Department of Physics New York, NY 10033 ABSTRACT The Force Macroscope (FM) was presented at the MRS-Spring-2000 as a laboratory teaching tool to introduce students to concepts of Scanning Force Microscopy (SFM). It is a macroscopic version of the SFM. The FM pedagogical advantage over the SFM is its size: students relate to the FM, only a few grasp at once the concepts for the 100 µmlong SFM cantilever. In this work we will show how we take advantage of the FMs large size to teach concepts of force reconstruction. INTRODUCTION Scanning Force Microscopy (SFM) has proven to be the most successful analytical technique to obtain topographical information of non-conducting surface samples. In addition, SFM is today routinely used to measure the force-separation, F(z), curve at a given surface location to gain information about the chemical environment. At the heart of the SFM, is the cantilever-tip system. The cantilever comes in a variety of shapes (rectangular, triangular, etc). It is about 100 µm long, and it is typically made of carbon or silicon nitride. At one of its extremes, it supports a pyramidal tip that, when in operation, points downward. The tip is the sensing component of the microscope. When, for example, there is a region of free charge on the surface under study, then this charge will induce an electric polarization in the tip, which in turn, will interact with the sample via charge-image attractive forces. Force-separation curves provide specific chemical information of the neighboring environment around the pixel underneath the SFM tip. As the tip interacts with the sample, it tends to move towards or away the surface. During this process, the cantilever vibrates and bends. In order to obtain the F(z) curves, it is necessary to use reliable data processing algorithms. Three algorithms are currently in use by the scientific community as well as by the commercial manufacturers: Hooke-Law’s, Simple Harmonic Oscillator, and Beam Model [1] (BM). One of the problems in evaluating the validity of the extant algorithms with SFMs, lies in the impossibility to access atomic-range F(z) curves by “direct” GG6.8.1
means. The SFM is set to collect information about the tip kinematics and, from it, with the aid of a theoretically based algorithm, it produces an F(z) curve. The goodness of the curve has only been assessed either on theoretical grounds, or heuristically, but never experimentally. Regardless of the degree of sophistication of the data reconstruction program, SFM cannot gauge its accuracy because the microscopic forces cannot be measured directly. For the FM, the situation is completely different: any load at its free end (magnets, in our case) that simulates the tip-sample interaction forces, and that can significantly perturb the kinematics of the aluminum b
Data Loading...
