  Strongly confined NaVO$^+$ segregation and its thermo-responsive
functionality at the interface between simple sputter-deposited amorphous
vanadium oxide thin films and soda-lime glass was substantiated in the present
study by in-situ temperature-controlled Time of Flight Secondary Ion Mass
Spectrometry (ToF-SIMS). The obtained ToF-SIMS depth profiles provided
unambiguous evidence for a reversible transformation that caused systematic
switching of the NaVO$^+$/ Na$^+$ and Na$^+$/ VO$^+$ intensities upon cycling
the temperature between 25 $^\circ$C and 340 $^\circ$C. Subsequently, NaVO
complexes were found to be reversibly formed (at 300 $^\circ$C) in vanadium
oxide diffused glass, leading to thermo-responsive electrical behaviour of the
thin film glass system. This new segregation -- and diffusion-dependent
multifunctionality of NaVO$^+$ -- points towards applications as an advanced
material for thermo-optical switches, in smart windows or in thermal sensors.
