### 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 |
---|---|

Pages (from-to) | 123-136 |

Number of pages | 14 |

Journal | Surface Science |

Volume | 140 |

Issue number | 1 |

DOIs | |

Publication status | Published - 1 May 1984 |

Externally published | Yes |

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### ASJC Scopus subject areas

- Physical and Theoretical Chemistry
- Condensed Matter Physics
- Surfaces and Interfaces

### Cite this

*Surface Science*,

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

**Observation of compensation effects during the thermal dissolution of aluminum oxide layers on tungsten and molybdenum 〈111〉 and on tungsten {110} in the presence of electric fields.** / Vanselow, R.; Pederson, L. R.

Research output: Contribution to journal › Article

*Surface Science*, vol. 140, no. 1, pp. 123-136. https://doi.org/10.1016/0039-6028(84)90386-8

}

TY - JOUR

T1 - Observation of compensation effects during the thermal dissolution of aluminum oxide layers on tungsten and molybdenum 〈111〉 and on tungsten {110} in the presence of electric fields

AU - Vanselow, R.

AU - Pederson, L. R.

PY - 1984/5/1

Y1 - 1984/5/1

N2 - 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, AF, of an Arrhenius-Frenkel type equation were measured as a function of F. The field dependence of AF is determined by the dissolution mechanism: (a) dissolution by diffusion: log A0F = log A00 - ΔμF 2.3k*T (μ molecular dipole moment, *T ≡ isokinetic for W〈111〉, log A00 = - 6.0 and *T = 940 K; for Mo〈111〉, log A00 = - 3.1 and *T = 860K; and (b) dissolution by ion desorption: log A+F = log A+0 + n 3 2e 3 2F 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 *A00 = 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: τ0F = *A00 exp[ - (E00 + ΔμF) k*T] exp[( E00 + ΔμF) kT] for diffusion and τ+F = *A+0 exp[ - (E+0 - n 3 2e 3 2F 1 2) k*T] exp[( E+0 - n 3 2e 3 2F 1 2) kT] for ion desorption.

AB - 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, AF, of an Arrhenius-Frenkel type equation were measured as a function of F. The field dependence of AF is determined by the dissolution mechanism: (a) dissolution by diffusion: log A0F = log A00 - ΔμF 2.3k*T (μ molecular dipole moment, *T ≡ isokinetic for W〈111〉, log A00 = - 6.0 and *T = 940 K; for Mo〈111〉, log A00 = - 3.1 and *T = 860K; and (b) dissolution by ion desorption: log A+F = log A+0 + n 3 2e 3 2F 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 *A00 = 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: τ0F = *A00 exp[ - (E00 + ΔμF) k*T] exp[( E00 + ΔμF) kT] for diffusion and τ+F = *A+0 exp[ - (E+0 - n 3 2e 3 2F 1 2) k*T] exp[( E+0 - n 3 2e 3 2F 1 2) kT] for ion desorption.

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U2 - 10.1016/0039-6028(84)90386-8

DO - 10.1016/0039-6028(84)90386-8

M3 - Article

VL - 140

SP - 123

EP - 136

JO - Surface Science

JF - Surface Science

SN - 0039-6028

IS - 1

ER -