The resolution of TERS is defined mostly by the radius of the used tip (best case below 1 nm) however the correlation is not linear. Although it depends on the laser light used, and the chemical composition, orientation of the sample's molecules as well, enhancement of five or six order of magnitude is easily possible, but the light intensification at the tip apex can damage the sample.

G

In which paper is this subnanometer resolution reported? Could you provide a link please?

Dear Xiao,

            you might have a look at our paper (10.1039/C6NR00093B) regarding the simulation of TERS resolution. TERS resolution depends crucially on the distance and the tip geometry (among other things Attila was stating already).

Best, Thomas

You can also have a look at our recent review specifically on this subject (http://pubs.rsc.org/en/content/articlelanding/2017/cs/c7cs00203c#!divAbstract). In short, using high vacuum ultra low T STM set ups, several groups have been able to provide convincing evidence for subnanometer resolution. There are also several reports of nanometer range resolution using AFM in ambient conditions. Overall, it is now believed that resolution has nothing to do with the tip diameter, but would rather originate from atomic scale defects or protrusions at the tip apex. However, purely experimental factors such as tip to sample distances do play a significant role.

Here is the Angstrom resolution at room T TERS

http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.6b03958