Amorphous-to-Crystalline Transition of Anodic Niobia

H. Habazaki, T. Ogasawara, H. Konno, K. Shimizu, K. Asami, S. Nagata, P. Skeldon, G. E. Thompson

Research output: Chapter in Book/Report/Conference proceedingChapter

1 Citation (Scopus)


This chapter presents a study in which an amorphous-to crystalline transition of anodic niobia is examined by using magnetron-sputtered niobium and its alloy substrates, with particular attentions paid to the preexisting surface oxide layer as a nucleation site of crystalline oxide and incorporation of foreign species hindering its nucleation. Niobium and Nb-N films were prepared by magnetron sputtering on to glass, silicon and aluminum substrates. Aluminum substrates were electropolished and subsequently anodized in 0.1 mol dm-3 ammonium pentaborate electrolyte to 200 V to provide flat surfaces. The niobium and niobium alloy films prepared were anodized at a constant current density of generally 50 A m-2 to selected voltages with and without current decay in stirred 0.1 mol dm-3 ammonium pentaborate and 0.1 mol dm-3 phosphoric acid electrolytes at 60. o C. Platinum sheet was used as a counter electrode. Amorphous-to-crystalline transition of anodic niobia formed on the sputter-deposited niobium films, which are free from preferable sites, such as inclusions and surface roughness, of the transition, initiated at approximately outer 30% of the film thickness where air-formed oxide is located. The growth of the crystalline oxide to the metal/film interface is rapid and the phosphorus species incorporated from the phosphoric acid electrolyte suppress effectively the amorphous-to-crystalline transition. Similarly, the foreign species incorporated from the substrate, such as nitrogen, silicon, and tungsten species suppress the crystalline oxide formation.

Original languageEnglish
Title of host publicationPassivation of Metals and Semiconductors, and Properties of Thin Oxide Layers
Number of pages6
ISBN (Print)9780444522245
Publication statusPublished - 2006

ASJC Scopus subject areas

  • Chemical Engineering(all)


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