Hello,
I have prepared carbon coated metal nanoparticles. In raman specta I found intensity ration of D and G band (Id/Ig) ratio to decrease from 0.91 to 0.95 with increase in heat treatment temperature (Id was smaller than Ig at both the temperatures, also the intensity of both the band decreased with temperature).
The peak position for D band was 1360 cm-1 at both temperature, while G band was 1576 cm-1 at low temperature which shifted to 1607 cm-1 at higher temperature.
What can be concluded from it ?
Can we say that with increase in temperature the graphitization increases or decreases? Please explain in terms of sp2 and sp3 terms.
Raman spectroscopy is a very effective method to characterize the detailed bonding structure of carbon nanomaterials. The method is the most widely used to distinguish the bonding type, domain size, and internal stress in amorphous and nanocrystalline carbon material .Peak at ˜1350 cm−1(D) associated with nanocrystalline carbon while peak at ˜1575 cm-1(G) associates with amorphous carbon materials (that still sp2 bonded). The peak positions and the ratio of the peak intensities vary from carbon material to another.
Also, the ratio of intensity of D/G peaks is a measure of the defects present on carbon nanomaterials structure. The D peak is present in defective carbon materials. Both D and G peaks are the result of vibrations of sp2-bonded carbon atoms. The G peak is a result of in-plane vibrations of SP2 bonded carbon atoms whereas the D peak is due to out of plane vibrations attributed to the presence of structural defects .D/G ratio is relates to sp3/sp2 carbon ratio. If carbon material is fully oxidized, i.e., all carbons are sp3. If D peak is higher, it means that the sp2 bonds are broken which in turn means that there are more sp3 bonds and more transition from sp2 to sp3 material, and there will be a maximum D/G ratio. If ID/IG ratio is higher than pristine material, it means that there are defects on carbon material.
As the ID/IG ratio of your carbon material was decreased, this mean that graphitization is domain
Raman spectroscopy is a very effective method to characterize the detailed bonding structure of carbon nanomaterials. The method is the most widely used to distinguish the bonding type, domain size, and internal stress in amorphous and nanocrystalline carbon material .Peak at ˜1350 cm−1(D) associated with nanocrystalline carbon while peak at ˜1575 cm-1(G) associates with amorphous carbon materials (that still sp2 bonded). The peak positions and the ratio of the peak intensities vary from carbon material to another.
Also, the ratio of intensity of D/G peaks is a measure of the defects present on carbon nanomaterials structure. The D peak is present in defective carbon materials. Both D and G peaks are the result of vibrations of sp2-bonded carbon atoms. The G peak is a result of in-plane vibrations of SP2 bonded carbon atoms whereas the D peak is due to out of plane vibrations attributed to the presence of structural defects .D/G ratio is relates to sp3/sp2 carbon ratio. If carbon material is fully oxidized, i.e., all carbons are sp3. If D peak is higher, it means that the sp2 bonds are broken which in turn means that there are more sp3 bonds and more transition from sp2 to sp3 material, and there will be a maximum D/G ratio. If ID/IG ratio is higher than pristine material, it means that there are defects on carbon material.
As the ID/IG ratio of your carbon material was decreased, this mean that graphitization is domain
it is not that simple. As shown by Rouzaud et al. (see attached paper, especially Fig. 2) and as I could observe myself, the changes of D/G intensity ratio are not only related to graphitisation but also to the pyrolysis state.
There are in fact 2 regimes: first, pyrolysis, during which D/G ratio increases with temperature, followed by graphitisation, during which D/G ratio decreases with temperature. In other words, the D bands first increases with temperature, then decreases if the temperature keeps increasing. So, depending on your material (graphitisable or not), and depending on the temperature of treatment, a same D/G intensity ratio may have different meanings. Few people are aware of this.
Alain
In addition to what I wrote, you can have a look at Fig. 5 of the other paper attached here, showing the transition between the 2 regimes mentioned in my previous post.
If you have an amorphous carbon, the D/G intensity ratio increases as the square of the crystallite size, whereas it decreases as the inverse of the crystallite size in the graphitisation regime. This is totally different !
So, as I said, a same D/G intensity ratio may have 2 different meanings, and you have to know in which regime your material is. It is therefore recommended to treat it at different temperatures and see how the ratio changes (increases or decreases with temperature).
Alain
I agree with Dr. Celzard. The interpretation of increase of ID/IG cannot be directly concluded as disordering of sp2 clusters. As pointed out above, ID/IG does increase with increase in pyrolysis temperature (initial carbonization phase) where heteroatoms in the precursor are released. As temperature is increased to graphitization regime, ID/IG decreases suggesting increase in ordering of sp2 bonded graphitic domains.
Dr. Alain Celzard has explained well. Ratio of the intensity of D- Raman peak and G- Raman peak (ID/IG) is often used for characterization of diamond-like carbon films, for example to estimate the number and size of the sp2 clusters existing in the carbon structures. in addition, the intensity ratio of the D and G bands i.e (ID/IG ratio) helps to estimate the defects of carbon based materials.
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