Using STM equipment, we can get the LDOS(local density of states) on the surface of a sample. I want to know whether the LDOS within the sample(not surface) can be detected by STM. what is the limitation of the depth?
On the other hand, a thin film is grown on a substrate, and one want to use STM to detect the DOS of the film. How thick should the film be to make the DOS of substrate be negligible for STM studies?