Thin Film Thickness Measurement: Thickness of thin film can be measured by the multiple beam interferometric method developed by Tolansky. Interference fringe can be formed with the help of interferometer and then film thickness can be calculated easily from the equation:

t = (/2) (D/d)

Where, D is the fringe shift and d is the fringe width. When Parallel monochromatic light is allowed to fall normally, dark fringes with displacement or stepper can be observed. In this case sodium light ( = 5893 A) can be used for illumination purpose. It is to be noted that step junction must be made on glass substrate for making a step.

Evaluated such films bye help of interference pattern in transmission spectra. If you can specify your question, i may be in a position to help you.

Joshua,

Yes. I've used a custom-built interferometer to measure thin film thicknesses. What would you like to know?

(specifically, I vapour-deposited amino acid layers in vacuum on to a silicon substrate, and with little more than a pair of laser diodes/photodiodes obtained clear interference fringes that let me measure the film thickness with an accuracy of about 10 nm for a total film thickness of about .5 micron)

Manoj, James:

I am trying to measure the profiles of printed layers of an OLED that I am creating layer-by-layer through solution processing. I was wondering, though, since the materials I am using have absorption and photo-luminescent spectra, if this will detriment the process greatly.

Joshua,

If you know the absorption/luminescence spectra in advance, then you could simply choose laser diodes that avoid the troublesome areas.

In solution eh? Mmm.

I can vouch that in vacuum one can build a simple interferometer that works rather well.

(http://www.bipbip.info/jg/make4.html)

But I imagine that taking the devices from a wet environment to air, and then to a hard vacuum would alter the structures if it were done too rapidly.

I wonder if there's scope for doing all of the measurement in solution? Namely having a fixed stage holding the laser diode and photodiode pair, and having it all immersed in a neutral fluid - one could imagine performing measurements whilst the device is being 'constructed'. As long as the relative distances of the diode/photodiode/device are well-fixed, then an intervening liquid shouldn't interfere.

(no pun intended)

Well, the layers will be deposited using solution processing (inkjet) but the solvent will have evaporated by the time I do characterization. Sorry for the confusion. The tool that I have access to is this: http://www.creol.ucf.edu/research/nv6300-specifications.pdf

It is specced as a white-light interferometer. This is what has me a bit worried.

Also, I want to point out that I'm just getting into optics, so sorry if my questions seem amateurish. I appreciate your input. Do you have a link to a publication regarding your usage? I'm interested. I'll probably also look around the net for other related literature as well.

Joshua,

Nice bit of kit.

I see that the illumination is by LED - so there'll be three (or more) sharp lines in the spectrum illuminating the device. If the LEDs' emission falls in a window that you know the material is sensitive to, and If you don't mind invalidating the warranty (!) I bet that you could;

a) disable the undesired LEDs - just unsolder their power lines.

b) reroute the light path and plug in the light source of your choice.

But this all may not be necessary - it's the phase difference you're looking for in interferometry, and a little absorption won't alter that.

It seems that PEDOT:PSS might be slightly hygroscopic, so you may want to track humidity (or even control it with a dessicating dry nitrogen flow) as the films may swell with raised humidity - guessing here!

Otherwise, the NewView is worth trying.

I never did get around to writing up my $150 interferometer - mail me offline for gory details if desired - might make a nice 3rd year project for your supervisor/tutor!

[email address deleted]