Dear Ma Hongchen,
regarding your first reply, I think that TestEm0 is working correctly: I checked it just now and it gives me 0 eV/cm as restricted and unrestricted dE/dx for CoulombScat, exactly as you said. However, I think this should be expected - the G4eSingleCoulombScattering process is an elastic scattering, meaning that no energy is transferred to the targets. Hence, no energy is lost in the process and dE/dx is zero. In fact, I would expect that a low-energy electron propagating through a thin film would lose energy mainly by other processes, such as ionization, eventually but not necessairly with the production of secondary particles. And in facts, if you run the TestEm0 example using gold as target and 1 keV e- as particle, you can see that the other processes have non-zero dE/dx (I found values ranging from 75 keV/cm up to 450 MeV/cm, depending on the process considered).
As for the rest: I think that the processes in which you are interested are all the ones which include production of secondary particles or local energy deposit. I’m not sure of which ones exactly, since I never dealt with this matter specifically. In another topic of this forum (here, for reference) they advise to check the Physics List available in the hadr06 example, for the hadronic part. In that case, the user was studying heavy ion fragmentation, which may be similar to your physics case, at least as a starting point. If you do that, pay attention to the cuts applied for the secondary particles production. For the e.m. part, instead, I would start from EM Opt3 and work my way from there, keeping as reference the results given by SRIM in very simple scenarios.
Hope this helps!
Best wishes,
Pietro