### Abstract

Aluminum oxide layer dissolution was studied between 700 and 1200 K in the substrate areas of W〈111〉, Mo〈111〉, and on W{110} by means of FEM. Varying the electric field strength, F, between +45 and +105 MV cm, two types of dissolution could be observed: dissolution by surface diffusion (low F's) and dissolution by ion desorption (high F's). It is assumed that aluminum suboxides - preferentially AlO - are involved in the dissolution processes. The preexponential factors, A_{F}, of an Arrhenius-Frenkel type equation were measured as a function of F. The field dependence of A_{F} is determined by the dissolution mechanism: (a) dissolution by diffusion: log A^{0}_{F} = log A^{0}_{0} - ΔμF 2.3k^{*}T (μ molecular dipole moment, ^{*}T ≡ isokinetic for W〈111〉, log A^{0}_{0} = - 6.0 and ^{*}T = 940 K; for Mo〈111〉, log A^{0}_{0} = - 3.1 and ^{*}T = 860K; and (b) dissolution by ion desorption: log A^{+}_{F} = log A^{+}_{0} + n^{ 3 2}e^{ 3 2}F^{ 1 2} 2.3k^{*}T; for A^{+}_{0} = - 22 and ^{*}T = 1200 K; for W〈111〉, log A^{+}_{0} = - 21 and ^{*}T = 1200 K. Using earlier proposed safeguards, isokinetic relationships (compensation effects) could be established for each of the two dissolution processes. The coordinates of the isokinetic points have the following average values: log^{ *}A^{0}_{0} = 2.5 and ^{*}T = 920K for diffusion; log^{*}A^{+}_{0} = - 1 and ^{*}T = 1240K for ion desorption. The entropy changes (at T = ^{*}T, zero field strength, and unit pressure) for the phase changes: solid layer → diffusion layer and solid layer → ion gas, are of the order of 30 cal K · mol and 90cal K · mol, respectively. The two dissolution mechanisms can be described by the following Arrhenius-Frenkel type equations: τ^{0}_{F} = ^{*}A^{0}_{0} exp[ - (E^{0}_{0} + ΔμF) k^{*}T] exp[( E^{0}_{0} + ΔμF) kT] for diffusion and τ^{+}_{F} = ^{*}A^{+}_{0} exp[ - (E^{+}_{0} - n^{ 3 2}e^{ 3 2}F^{ 1 2}) k^{*}T] exp[( E^{+}_{0} - n^{ 3 2}e^{ 3 2}F^{ 1 2}) kT] for ion desorption.

Original language | English |
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Pages (from-to) | 123-136 |

Number of pages | 14 |

Journal | Surface Science |

Volume | 140 |

Issue number | 1 |

DOIs | |

Publication status | Published - 1 May 1984 |

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### ASJC Scopus subject areas

- Condensed Matter Physics
- Surfaces and Interfaces
- Surfaces, Coatings and Films
- Materials Chemistry

### Cite this

*Surface Science*,

*140*(1), 123-136. https://doi.org/10.1016/0039-6028(84)90386-8