Focused ion beam preparation and EFTEM/EELS studies on vanadium nitride thin films

A two-beam focused ion beam (FIB) instrument was used to prepare transmission electron microscopy (TEM) specimens of vanadium nitride layers produced by rapid thermal processing in a NH3 or N-2 atmosphere. For the FIB preparation method an in-situ liftout technique was used, which was found to be highly efficient regarding specimen transfer yield but also very convenient as the final milling steps were carried out with the TEM specimen already fixed to the TEM grid. Electron energy-loss spectroscopy (EELS) and energy-filtering TEM (EFTEM) was applied to characterize the films morphologically and chemically. EFTEM investigations provided chemical information over the whole film thickness and revealed that the vanadium nitride layers consisted partly of two different nitride phases. By interpreting the EELS near edge structure of the nitrogen K-edge and comparing them to high-resolution spectra recorded on a monochromator TEM at an energy resolution of similar to 0.25 eV, the nitride layers could be unambiguously identified.