In-situ monitoring of the growth stress evolution during galvanostatic anodising of aluminium thin films

作者: Quentin Van Overmeere , Jean-François Vanhumbeeck , Joris Proost

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摘要: An efficient and convenient way to improve the anticorrosion properties of aluminum its alloys is electrochemically oxidize surface. Most industrial anodizing processes use sulfuric acid as electrolyte, in which growth oxide layer known proceed two steps. The first one formation a dense layer, referred barrier followed by porous outer with nearly cylindrical pores, perpendicular Despite significant amount work published on anodizing, exact mechanism acidic electrolytes not yet fully understood. Recent studies have suggested that stresses profound influence [1]. However, up now, these only been roughly estimated, or extracted from non-conclusive, mostly ex-situ experimental studies. aim present paper determine magnitude more precisely means high resolution, in-situ curvature measurement technique. Our technique based continuously monitoring differential spacings between number parallel laser beams reflecting off sputtered thin film sample during [2]. stressthickness product σox⋅tox was then calculated substrate change well-known Stoney formula. Growth stress values were obtained for current densities ranging 1 8 mA/cm. A typical evolution both stress-thickness cell voltage function thickness shown Figure 1. Note such graph, given slope product. During initial growth, traditionally monitored constant continuous rise voltage, observed tensile remains well. Upon pore initiation, suddenly decreases because porosity allows relaxation. Finally, when turned off, an instantaneous “jump” occurs, due sudden absence electrostriction. These jumps corresponding electrostrictive allowed evaluation permittivity anodic films, found be at 8.4 ± 0.4 over entire density range considered. intrinsic measured total after subtracting extrinsic contribution. thus are presented 2 density. It can seen studied densities, their value increasing This dependence predicted simple model correlates rate vacancy creation annihilation. AKNOWLEDGMENTS Belgian National Science Foundation F.N.R.S. gratefully acknowledged funding this through F.R.I.A. doctoral scholarship.

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