For thicker homogeneous films, the optical reflectance and transmittance spectra show several interference patterns which can be used to obtain optical constant using Swanepoel and other related methods. If the optical data does not have any/many interference patterns to produce accurate values of the constants, what method can one use to get the optical constants and film thickness instead?
Kindly download this excel file and substitute only transmittance value. You will get the refractive index value. Also I have attached a related article :)
Have you tried PUMA software?
freely available here:
http://www.ime.usp.br/~egbirgin/puma/
Dear Albert!
I would advice You to apply to Brewster angle measurement that help to determine index refraction and its dispersion as angle function of minimum reflected power on p-polarized laser beam. To be succesfull in the measurement You need only an prosizional instrument for absolute angle measurement and collection of laser diodes on different lasing waves.
Interference from optically polished films in reflected light presents alwais as pattern on equal angles (plane parallel film) or equal thicknes for wedge like film. It means that You can eveluate thickness through interference in reflected light. If one or both sides of film discover low light scattering both methods work. But in the case of strong light scattering. from film the both methods will fail and You should return to polishing of your subject.
Some details of similar measurement You will discover in my RG- publication list among last year contributions
Dear Albert,
As you wrote if there are no interference fringes, the thickness value obtained may not be accurate. It will be better you try other technique for thickness estimation. X-ray reflectivity may be a better choice for determination of thickness and refractive index if your film thickness is less than 1 micron. For high thickness films you will not get any interference fringes in x-ray reflectivity also.
Ellipsometry on the reflected signal can give you a consistent set of optical constants and thickness.
Hi, Albert.
I also have some comments: if there is no interference for a relatively thick film, usually two cases can result in this, 1) the film is very rough on the surface also may be rough inside like voids; 2) the film is thick enough that there is no coherent propagation through the film. if it is the latter case, then it could be easy to calculate the optical constants.
You can deposit simultaneously your film on two types of substrates - transparent (for example optical glass) and opaque (silicon substrate) and measure T and R from glass and Rsi from Si. Than use the three measurements for simultaneous determination of n, k and d. If it is not possible to deposit the film on two different substrates you can calculate n, k and d from measuring transmittance and reflectance from front and back side of the transparent substrate (in the absorption region both reflectances are different). Also you can use dispersion models for n and k and nonlinear optimization for determination of model parameters and thickness of the film from T and/or R spectra. See the attached papers. Good luck!
Thank you all for the responses and references from Tsvetanka and Hamed.
Hamed, I have not tried that software because I didn't know about it before. I will try it.
Tsvetank, I will be reading your papers in the next few days to learn about your approach - it is new to me I guess.
Guanchao I know your group specializes in optical analysis of various films and solar cells. Thanks
If I have interference fringes in the reflectivity, can I use the same approach as Swanepoel as applied to transmittance spectra?
Kindly download this excel file and substitute only transmittance value. You will get the refractive index value. Also I have attached a related article :)
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Optics