I am using Terahertz time domain system to measure the thickness of a thin film on a substrate. I am able to calculate the thickness of substrate(~100um) alone. But what signs should I see for if there is a thin film ( ~100nm) on this substrate. I am not willing to do the fft ! Can time domain signal alone determines the thickness of film. The resolution is 33fs.
Üst tabakada zamana bağlı değişkenler alt tabakaya da bağlı olur. Fakat alt tabaka daha hassas olduğu için gözlemler daha hassas olması gerekiyor.
This essay aims at determining the thickness of a thin layer on a reflective substrate. Methods to obtain the refractive index and layer thickness based on.
Dear Dr. Dayakrishn Purohit,
When the terahertz pulse reflects off the top surface of the thin film and the bottom surface of the substrate, interference patterns can occur in the time-domain signal. These interference fringes are related to the film's thickness and the refractive indices of both the film and substrate.
In transmission mode, there are echo pulses and through this i am able to calculate the thickness and refractive index of substrate (~200um), but with thin film on the substrate, it's difficult to find the echo pulses for film. Does it have to do with the resolution of the instrument ? Or there could be some different way other than the numerical approaches suggested in various literature.
Yes, the instrument's resolution seems to be an issue in those geometries.
I don't think it's possible to use such a system to measure ~100 nm film. in transmission mode, the THz reflected from film back surface will eventually reflecting in the front surface and captured by detector. it would create a time flight gap between the main beam. however for ordinary material index in terahertz wave it could be hard to disdinguish as the strong overlap happens in time domian signal.
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