Whether we can Observe any Difference in Raman Spectra taken from a thin film and a bunch of nanostructures of the same material?
If I am taking Raman Spectra from a thin film and I am repeating the experiment with same conditions for the same material on a buch of nanostructures which is distributed like a thin layer ( with same thickness as the thin film).
Then, What kind of observations I can expect? Whether we can observe any significant difference in the spectra?
Or if I am taking a Raman spectra of thin film after making some nanogrooves on the sample. How it will differ from the original spectra?
If you material is conductive then yes you will see difference because at the boundaries of the cluster some plasmon will be induced and you will see some Raman peaks. But If you material is non conductive then there will be no difference.
Dear Talha Nisar ...Thanks for your answer ..
My sample is semiconducting..... and I am Introducing so much nanogrooves on the thin film...So I am thinking about the light matter in case of thin film and nanostructures ...will it be similar???
Dear A K Sivadasan,
Simple Raman measurements in semiconductors are very useful. They can help in the determination of composition (for example: SiGe), strain, and crystallinity.
If you are only adding features, like groves at the film surface, then if your samples have some strain, the grove could release some of that strain. Also depending of the method to add the features and there size and shape you could end up with a variation in crystallinity and less likely composition.
If your samples are amorphous and you use micro-Raman, then can happen a crystallisation at the laser spot.
Excitation wavelength use can also interfere with the results, short wavelength are going to have less penetration resulting in higher sensitivity to the features.
Dear Filipe Oliveira
thanks for your kind reply....and my interest also to understand the difference in light matter interaction for both the case...in that way I may be more interested on your statement..
"Excitation wavelength use can also interfere with the results, short wavelength are going to have less penetration resulting in higher sensitivity to the features."
if you don't mind, can you elaborate it..!
If I am using light having short wavelength (or high energy).. Whether it will show similar sensitive to thin films as well as nanostructures (or thin film with nanogrooves) ?? or it will be differ from each other ??
Micro-Raman spectroscopy based upon the inelastic scattering of photons from a surface being irradiated by monochromatic light, provides information on the spatial
distribution of physical properties of semiconductor wafers that are sensitive
to crystalline quality, microstructure, strain, alloy composition and free carrier
density.
Dear AK,
If you are thinking about difference Raman spectra of thin film and of a bunch of nanostructures which is distributed like a thin layer on the substrates and bulk material. Certainly it would show some additional peak or peaks for thin films as compared with the nanostructure and bulk. This peak or peaks are may be due to formation of dangling bonds which are absent in bulk and in pure nanostructured material. Since Raman is surface sensitive technique thus it would be expeted to reflect in it. Also it depends on the intensity / power of the laser used.
Dear A K Sivadasan,
In general the absorption increases for shorter wavelengths and consequently the laser penetration is smaller. Since the groves of your samples are at the surface, a shorter wavelength could be more indicated to enhance the Raman scattering close to the surface.
For example in silicon, the penetration of 325nm laser is of a few nm but with a 633nm laser is in the range of hundred nm.
You also need to have in consideration that short wavelengths like UV can also result in photoluminescence and potential overcome the Raman scattering.
There can be different effects:
- plasmonic SERS due to conductive boundaries (should not affect spectral shape, only intensities)
- strain/stress effects due to mechanical deformations after processing (slightly moving peak positions in micro-Raman and make peaks more broad for macro)
- strain/stress due to dangling bond, chemical adsorption on the dangling bonds (-O- bridges, OH groups, COOH groups,...) - new lines and large shifts of existing ones
- if the powder is nanosized, resonance Raman effects can greatly alter peak intensities, also formation of new bonds can alter density of electronic states in material
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