i want analyze thin film of organic material on metal substrate such as Au, Ti with FTIR. substrate is rigid. is it possible??
Dear Meherad Noemi,
Many FTIR spectrometers include reflectance mode as an option. If it is not included in the basic configuration of your spectrometer, some firms provide accessories for reflection measurements. Once you have this option available, you can use it to take spectra of your thin film deposited on metal substrate, provided the metal substrate surface is mirror like.
The reference spectrum must be taken on the clean metal substrate.
Through the spectral range were your thin film is weakly absorbing, the normalized reflection spectrum should be the same as the transmission spectrum of a thin film with double thickness (as the IR beam crosses your film twice). In the spectral range through which your thin film is strongly absorbing (polar modes), the normalized spectrum would yield the reflectivity of your sample (obviously, only if your sample also has a mirror-like surface).
Best regards
Dear Mehrdad Naemi , most FTIR spectrometers work in transmission mode, so it is necessary that your sample allows the transmission of light. You described your metalic substrates as rigid, so we can imagine they are thick and probably opaque to light and therefore they wouldn´t be useful for transmission FTIR.
Fortunately, many FTIR spectrometers have an ATR device you can set up in the optical path of the spectrometer. ATR stands for Attenuated Total Reflectance, and this device allows you to do FTIR measurements by reflectance, so your sample can be transparent or opaque. The ATR device holds a triangular prism, with one face acting as the surface where you place your sample, to improve the contact between the sample and the prism an arm with a screw let you press the sample. Light from the excitation laser hits another prism´s face and send the light towards your sample, where it excites the IR modes, and the signal is directed towards the other prism´s face and from there to the detector.
To obtain the spectrum of your sample, of course the side of your sample where the organic material is, must be placed in contact with the prism.
Often this prism is tiny, and it is often protected with a metallic stage, so it is possible to do measures in small samples, even powder or little bits of your sample.
After each sample you must clean the prism with an appropriate solvent (ethanol, isopropanol, water... )
Hope it helps.
Mehrdad Naemi FTIR measurement is done on transmittance mode for which you have to choose substrate through which IR can be transmitted i.e. Si substrate. But IR is fully absorbed by the rigid metal substrate which will restrict the FTIR measurement.
Dear all, you can deposit your organic thin film on glass, KBr pastille, or any other substrate that doesn't absorb in the IR domaine and allow beam transmitance. My Regards
It has a limitation/restriction for metal substrate and what is important is thickness the sample. It is better to test an alternative spectroscopy.
Dear Meherad Noemi,
Many FTIR spectrometers include reflectance mode as an option. If it is not included in the basic configuration of your spectrometer, some firms provide accessories for reflection measurements. Once you have this option available, you can use it to take spectra of your thin film deposited on metal substrate, provided the metal substrate surface is mirror like.
The reference spectrum must be taken on the clean metal substrate.
Through the spectral range were your thin film is weakly absorbing, the normalized reflection spectrum should be the same as the transmission spectrum of a thin film with double thickness (as the IR beam crosses your film twice). In the spectral range through which your thin film is strongly absorbing (polar modes), the normalized spectrum would yield the reflectivity of your sample (obviously, only if your sample also has a mirror-like surface).
Best regards
Dovbeshko, G. I., V. I. Chegel, N. Ya Gridina, O. P. Repnytska, Y. M. Shirshov, V. P. Tryndiak, I. M. Todor, and G. I. Solyanik. "Surface enhanced IR absorption of nucleic acids from tumor cells: FTIR reflectance study." Biopolymers: Original Research on Biomolecules 67, no. 6 (2002): 470-486.
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