why the intensity of Raman shift reduced for thin-film coated on glass substrate? and huge noise generated? Please suggest a suitable method to perform Raman spectroscopy for thin films.
That depends on several things to improve the intensity of detected Raman: the materials of the film and its thickness, equipment including the laser wavelength, the objectives you are using if your device has applied a focused laser beam, etc..
@Muhammad Usman Following Dr Wu's comments, your films should coat on a silicon substrates rather transparent glass substrates. In this way, you can collect a strong signal via reflection from the sample.
Since the glass substrate does not affect the structural properties of the thin films, it may be the obstacle in diagnosing the sample with Raman Spectroscopy. I suggest you separate this film after preparing it from the glass and then grinding it and making it as a homogeneous powder for increse the intensity of Raman and reduced noise generated.
Shouldn't be a problem to investigate the films on the substrate, either glass or silicon wafer.
To separate the film from the substrate would 1st probably change its structures as it is destructive and 2nd, grinding could also change its physical properties. Hence, the data you have obtained cold be absolutely different from that of the film on the substrate as it is.
I had similar problem when doing Raman for Graphene film on a glass substrate. You can do multiple scans to increase the intensity of the peaks. However, this will also increase the intensity of the noise. Although the ratio between the peaks and noise should be the same, the magnitude difference should increase, which will facilitate extracting the peaks when you subtract the noise signal from the measurement.
without knowledge about th equipment used, i would say ingeneral to change the configuration of your measurement, such as exposure time and aquisation number, lenses if your are using, laser power/wavelength, etc. all of them could change your data for beteer signals or raman peaks. for instance, normally shorter exposure time with larger aquisation numbers can get better s/n than longer exposure time with smaller aquisation number.