Formation of N2O gas bubbles in anodic films on NbNx alloys

H. Habazaki, T. Matsuo, H. Konno, K. Shimizu, S. Nagata, K. Takayama, Y. Oda, P. Skeldon, G. E. Thompson

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)

Abstract

Sputter-deposited niobium, and Nb90N10, Nb83N17 and Nb60N40 alloys, have been anodized at 50 A m-2 in 0.1 mol dm-3 ammonium pentaborate electrolyte at 293 K and resultant amorphous anodic films have been characterized by transmission electron microscopy, glow discharge optical emission spectroscopy, Rutherford backscattering spectrometry and Fourier-transform, infra-red spectroscopy. Except for the Nb60N40 alloy, which shows a breakdown at approximately 60 V, the deposited layers reveal a linear voltage increase to more than 150 V, with the rate decreasing with the niobium content. Additionally, anodic films, with flat and parallel metal/film and film/electrolyte interfaces, are formed on the specimens with the formation ratio decreasing with increasing nitrogen content in the deposited films. Nitrogen is incorporated into the inner ∼70-75% of the film thickness as N2O molecules, forming fine bubbles, with typical sizes up to 10 nm, in a Nb2O5-based matrix material. The remaining 25-30% of the film comprises a layer of Nb2O5 with the outer regions containing boron species derived from the electrolyte. Release of high pressure N2O gas is associated with the relatively low breakdown voltage for the Nb60N40 alloy of highest nitrogen content. The two-layered nature of the anodic films arises from the film growth mechanism that involves outward migration of niobium species and inward migration of oxygen species; in contrast nitrogen species are immobile due either to the relatively high energy of the N-O bond or to their presence in bubbles.

Original languageEnglish
Pages (from-to)159-166
Number of pages8
JournalThin Solid Films
Volume429
Issue number1-2
DOIs
Publication statusPublished - 2003 May 1

Keywords

  • Anodizing
  • Ionic transport
  • NO bubbles
  • NbN alloys

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Materials Chemistry

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