Hi everyone
I need help in preparation samples for RAMAN spectroscopy, i am working in thin film field, spin coated on ITO or Si wafer. Can any one suggest RAMAN sample preparation method ? should i use powder ? or I can check in film form?
Thank you in advance
Ideally, you should measure both and compare them.
It is not guaranteed that a thin film will provide a good spectrum; that depends strongly on the material: Graphene in a confocal setup can be measured as a single monolayer, fullerenes require ca. 50 layers and weakly polarizable ceramics will give low signals even in millimeter thickness.
So, if you can get a signal from your film, measure film and powder, if only the powder gives sufficient signal, just show the powder spectrum and annotate that the film itself can't be measured.
Ideally, you should measure both and compare them.
It is not guaranteed that a thin film will provide a good spectrum; that depends strongly on the material: Graphene in a confocal setup can be measured as a single monolayer, fullerenes require ca. 50 layers and weakly polarizable ceramics will give low signals even in millimeter thickness.
So, if you can get a signal from your film, measure film and powder, if only the powder gives sufficient signal, just show the powder spectrum and annotate that the film itself can't be measured.
For a Si wafer, which is a comparably good reflector, you have to take into account the interference effect, which will greatly enhance your Raman signal at certain thicknesses and strongly decrease it at others. If you cannot vary your film thickness, think of using different excitation wavelengths.
You can use thin films, powder, liquid, pellet, nano material, single crystals etc to study Raman spectroscopy. Before starting the experiment, you should know the basic knowledge of position of frequencies of Raman modes of the sample under investigation, which are usually available in the literature. Initially start the measurement with low laser power to avoid the sample burning.
If you have issues with reflection or interferences, try tilting the sample so the major reflection does not reenter the spectrometer.
What Raman instrument are you using? Microscope coupled, measuring in backscattering geometry?
If you intend to use your material in thin film form, it is probably best to measure it in thin film form, but the signal you get will depend on the material, the thickness, the objective used, the wavelength.
Usually the best for a thin film is a high NA objective (x100).
Si wafer is usually used to Calibrate, wherein Silicon substrate has only one sharp peak around 515 or so. Therefore,if its on Silicon, no worry. And in Si, as it is highly Oriented in particular plane, whereas if other substrate used like glass or TCMs, its better either to find out where its peak appear or scan for the substrate and subtract afterwards as these substrates are polycrystalline. Actually, For thin film samples there is no need for any preparations.
In a Raman experiment the laser light is shone on the film and scattered light is analysed. Typically the film is too thin to prevent the light from penetrating into the substrate. As a consequence, the Raman spectra of both the film and the substrate are detected in the experiment. In majority of the situations only the spectrum of the film is of interest to a researcher. Hence it is necessary to separate the spectrum of the film from that of the substrate. A vast majority of the film’s low energy excitations is typically located below eight to nine hundred wavenumbers (
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