by Hephaestus, published
This is just a placeholder for an ongoing project to cheaply (from 3D printed parts and hardware store parts) make a purely mechanical single wavelength ellipsometer for surface measurement and analysis. Additional wavelengths (as well as angles of incidence or AOI's) could also be sampled by using laser modules of other known wavelengths.
Current BOM is as follows:
- Printed Items
1.1 (10) 90 deg Threaded Rod Connectors
1.2 (2) Eyehole Threaded Rod Connectors
1.3 (1) AOI Arm
1.4 (1) Right AOI ARM
1.5 (1) "ThreadRod_Connect_90deg_0_25in-20-SmoothRodModFront-v2.stl"
1.6 (2) "Spacer_Plates"
1.7 (1) "Optics_Mounts_Photocell"
1.8 (2) "Polarizer_Mounts_Laser_v2", (http://www.thingiverse.com/thing:98556)
1.9 (2) Rotatable Polarizer Mount Assemblies (http://www.thingiverse.com/thing:98556).
- Non-Printed Items
2.1 (1) Protractor
2.2 (13?) 1/4-20 Threaded Rods
2.3 (25) 1/4-20 Hex Nuts
2.4 (10) M3-0.5x16MM Socket Cap Screws
2.5 (8) M3-0.5 Nuts
2.6 (1) Laser Module (http://www.scientificsonline.com/diy-red-laser-pointer.html)
2.7 (2) Polarizing Filters (http://www.sciplus.com/p/POLARIZING-FILTER-IN-REMOVABLE-MOUNT_48927)
2.8 (1) CdS PhotoCell (Radio Shack?)
2.9 (1) Multimeter that measures resistance
2.10 (1) Circular Polarizing Filter (http://www.amazon.com/Tiffen-46CP-46mm-Circular-Polarizer/dp/B00004ZC8Y/ref=sr_1_31?s=electronics&ie=UTF8&qid=1371667297&sr=1-31&keywords=circular+polarizing+filter). This should fill the role of a quarter wave plate compensator
There will also be various tools and craft implements you will need to use.
- Notes on data analysis
5.1.1 A User's Guide to Ellipsometry by Harland G. Tompkins (available on Amazon).
5.1.2 The Measurement, Instrumentation and Sensors Handbook (Electrical Engineering Handbook-CRC), 2 volume set by John G. Webster (Dec 29, 1998)-available on Amazon
* Update 06/20/13 **
Added an extra optic mount on left and right Angle Of Incidence arms to allow for mounting a circular polarizer on either side (depending on the desired configuration). This is to allow for a null ellipsometer configuration.
* Update 06/28/13 **
2nd mechanical mock-up (had to reverse the order of the stack and place the sample behind the main axis), and first light-up test to make sure the laser module works. I decided to switch back to a Stokes polarimeter configuration (Polarizer-Sample-Analyzer). This will require only 4 intensity measurements (0, 90, and +/-45 degrees analyzer rotation only) to solve for Psi/Del.
* Update 07/03/13 **
-Reworked the mechanical stack to hopefully minimize parallax error in measuring AOI. A picture of this mock-up was uploaded. I should probably add more supports to make frame more rigid.
-Completed 1st draft of polarizer calibration procedure. Uploaded pdf print of this.
-Completed 1st draft data sheet for collecting relative intensity measurements that will produce Psi/Del data. Started work on theoretical filmstack sheet (starting with bare substrate) to convert known dispersion to a theoretical Psi/Del trajectory (versus variation in AOI) which measured results can be regressed to.
* Update 07/12/13 **
Took some time out from hardware development to work on some theory. Attached is an updated data spreadsheet that also contains a single-layer Psi/Del model that will allow the user to manually regress their measured results (to minimize the various error measures shown in the sheet) to determine the film optical properties. The data sheet shows SiO2 with no film since I plan next to perform the polarizer calibrations on a glass slide with a black backing (to prevent backside reflections).
Started work again after a significant hiatus (sorry, I have been a little busy). As you can see from the latest picture, the appartus has undegone some evolution that I still need to document. Started Polarizer, "A", calibration. Still need to do Polarizer "B" before I can start 1st real data collection for analysis.
Posted my first test data using a (not clean) microscope coverslip. The data curves appeared similar for +45 degree polarizer position (less so for -45 degrees polarizer position). From this 1st data set, there appears to be significant sources of error and need to better test repeatability (manual data collection is time comsuming). Posted a screen shot of the data compared to model with y-axis shifting (add or subtract) to Psi and Del values to minimize error to model and x-axis shifting to compensate for AOI measurement errors.