Ellipsometric investigation of anodic hafnium oxide films

M. J. ESPLANDIÚ; E. M. PATRITO; V. MACAGNO

ELECTROCHIMICA ACTA

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 1997 vol. 42 p. 1315 - 1324

0013-4686

The galvanostatic oxidation of hafnium in different electrolytes was investigated by means of i/l-G/l, ellipsometry in the range O-150 V corresponding to oxides thicknesses in the range O-350 nm. The oxide surfaces were characterized by scanning electron microscopy (SEM) examination. Single and double-layer models were used to interpret the experimental results and it was observed that the nature of the electrocatalytic affects mainly the properties of the external thin layer close to the solution. The bulk oxide grown in H2SO,. NaOH and H3PO4,, has a refractive index of 2.0662.07 and an absorption coefticient of 0.02 0.03. The A/C profiles recorded during the oxidation in HNOi reveal different stages of oxide corrosion. The tilms formed in this electrolyte have the lowest refractive indices as a consequence of their porous nature. An electric ticld strength increase with thickness was observed which could be associated to changes from amorphous to crystalline oxide structure. This fact could produce internal stresses during the oxide growth resulting III an anodic fracture. The ellipsometric results of the present work confirm previous impedance investigation\