We recently used the 3 omega method to detect the thermal conductivity of a film with about 100nm thickness on a STO substrate with thickness about 500um. In the detection, we strangely found the calculated substrate temperature enhancement is higher than that of the heater line, leading to a negative film temperature enhancement so a negative thermal conductivity. It is unreasonable in our opinion. We have checked the calcualtion process carefully several times. Can anyone give some suggestions?
There seems to be an issue with the 3 Omega method in certain circumstances, where it may be that there are contributions of additional frequencies, not just 3 Omega. If these contributions can not be neglected, than the calculation results in weird numbers that are not physical relevant. People from the project "Green Silicon" http://greensilicon.eu also have found weird results in superlattices, you should contact them and discuss your issues.
Thank you very much！ your information would be quite important for me！
I am curious. More elaboration to your research will be good for others.
Yes, it is very interesting. However, i believe the thermal conducitivity of a material could not be negative accroding to the defination of k. The negative results should be a reasult of measurement method, i.e the 3 Omega method maybe is not applicable in our system.
Yes I agree with your thinking. You can try with other measurement methods so that this result would be compared and you could get more idea about negative thermal conductivity
Prof. Douglas J. Paul, the co-ordinator of the project Green Silicon, has replied me that the 3 Omega method maybe not applicable to a nanostructured materials such as superlattices according to their experimental results and theoretical checking in the simplification condition for geting the 3 Omega method formulas.
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