Working AFM Model Construction

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Labeled AFM

A) Tip and Cantilever

B) Frame and Adjustment

C) Mirrors and Laser

D) Sample(s)

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    A) Tip and Cantilever

     Our tip is a shortened phonograph stylus, specifically an Astatic N52 stylus. We had previously tried bent sheet metal, a thumb tack, and victrola stylus with little luck. Although the small cantilever of the phonograph stylus was rather short to begin with, we found that nearly the entire length of the arm needed to be cut off in order for the tip to be suitably sensitive.

Phonograph Stylus Before Modification
Final Phonograph Stylus
Stylus 
Final Tip

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       B) Frame and Adjustment

     The frame was manufactured by the UVM Physics Dept. Machine Shop using conventional methods and was fabricated almost entirely from 6061 Aluminum stock. The housing for the laser and lense was made from brass telescoping tubing.
     The manual positioners were specifically two 3900 Series (1.25 inches wide) miniature stages from Edmund Optics. A z-axis adapter was also necessary in order to have the x/z axis adjustment we needed rather than the usual x/y. We accidentally ended up with the English version rather than metric, but it turned out to be a lucky mistake simply because the wider spaced lines were easier to read in dim light.

Structure
Mini Stages

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        C) Mirrors and Laser

     Our laser source was a 10 mW laser diode assembled with a small lens. The lens also had a quartz fiber cross-hair attached which made measurements considerably easier. The small mirror on the tip of the AFM phonograph stylus was made from small chips of polished silicon wafer. Our final mirror was simply an adapted round dental mirror.


Laser Lens with Quartz Fiber Cross-Hair
Large Mirror
Small Silicon Mirror
Lens
Large Mirror
Silicon Mirror

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        D) Sample(s)

     Initially, we tried Ronchi gratings and experimented with sandpaper. The 400 grit sandpaper seemed to work best and several graphs were made from the data collected during test runs. However, the irregular sandpaper surface was not ideal for our introductory lab - where we wanted to be able to predict the size and shape of the grooves before scanning - and so we continued to experiment with different materials. By chance, we discovered a holographic post-card whose surface was made of a regularly grooved plastic. The pieces of postcard proved to be the best samples we had tried thus far and so they remained as our primary samples used in classroom labs.


10x Image of Plastic Sample
Sample and Tip
Sample 1
Sample 2

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