Design and Development of a Holographic Atomic Force Microscope
Date Issued
2009
Date
2009
Author(s)
Leong, Kuok-Chan
Abstract
This thesis proposes using a holographic pick-up head to build up the measurement unit of the atomic force microscope (AFM), so as to simplify its configuration. The ordinary AFM, which applies the optical lever method, has a large volume and costs much time in tuning. By contrast, the holographic pick-up head, which is under mass production, has a stable performance and can be used to measure the displacement precisely. Using a holographic pick-up head to build up the measurement unit of the AFM can shorten the tuning time and improve the size and the freedom of design. A workable assembly of collimating lens and objective lens is decided by the optical simulation software. Also, the relationship between the output voltage and the displacement of the cantilever beam of the probe can be obtained by the radiant flux shot on the photo-diodes. (The output voltage is also called focus error signal, and the relationship curve is called S-curve.) The practical S-curve is obtained by using a piezo linear stage and a laser interferometer which can acquire the precise displacement. In addition, the tilted mirror moved along perpendicular direction is used to find the influence of tilt-angle mirror to the S-curve. In the last part of the thesis, three given samples are measured by a whole holographic AFM configuration, and the performance and the feasibility are verified. The results indicate that the configuration can measure the 20nm-height and the 2nm-height step of a calibration grating.
Subjects
atomic force microscope
holographic pick-up head
displacement measurement
focus error signal
Type
thesis
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