Semiconducting properties of oxide films formed onto an Nb electrode in NaOH solutions

In this paper, the results of the potentiostatic formation of homogeneous and heterogeneous, nano-crystalline passive films of Nb2O5 onto an Nb electrode in NaOH solutions of different concentrations at potentials lower than 3.0 V vs. SCE are presented. The semiconducting properties of such films were investigated by EIS measurements. After fitting the EIS results by appropriate equivalent circuits, the space charge capacitance (Csc) and space charge resistance (Rsc) of these films were determined. The donor density (Nsc), flat band potential (Efb) and thickness of the space charge layer (dsc) for such oxide films were determined from the corresponding Mott-Schottky (M-S) plots. It is shown that all oxide films were n-type semiconductors in a certain potential range. U ovom radu prikazani su rezultati potenciostatskog formiranja homogenih i heterogenih, nano-kristalnih, pasivnih filmova Nb2O5 na elektrodi od niobijuma u rastvorima NaOH razlicitih koncentracija i na potencijalima manjim od 3,0 V prema ZKE. Poluprovodnicka svojstva ovakvih filmova ispitivana su EIS metodom. Nakon fitovanja EIS rezultata odgovarajucim ekvivalentnim kolom odredjivane su vrednosti "space charge" kapaciteta (Csc) i "space charge" otpora (Rsc). Gustina nosilaca naelektrisanja (Nsc), "flat band" potencijal (Efb) i debljina "space charge" sloja (dsc) ovih oksidnih filmova odredjena su iz odgovarajucih Mott-Schottky zavisnosti. Pokazano je da se u 5,00 M NaOH formira heterogeni oksidni film sa otvorenim porama (pukotinama) na povrsini, dok se pri nizim koncentracijama NaOH formira kompaktan i homogen oksidni film. Mott-Schottky zavisnosti sa pozitivnim nagibom, registrovane za sve dobijene filmove, potvrdjuju da su iz svih rastvora dobijeni poluprovodnicki filmovi n-tipa.