Enhancement of nanovoid formation in annealed amorphous Al2O3 including W

Abstract

The effect of W on the nanovoid formation in annealed amorphous Al 2 O 3 was studied by transmission electron microscopy and molecular dynamics simulations. A comparison of the void formation behavior in electron-beam deposited Al 2 O 3 (without W) and resistance-heating deposited Al 2 O 3 (with 10 at. % W) revealed that W enhances the formation and growth of nanovoids. An analysis of the pair distribution function (PDF) in both types of amorphous Al 2 O 3 showed that the introduction of W into amorphous Al 2 O 3 brings about a significant change in the amorphous structure. Furthermore, it was found by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) that sub-nm sized W clusters exist in as-deposited Al 2 O 3 prepared by resistance-heating and then dissolve in the amorphous matrix with annealing. The combination of PDF analysis and HAADF-STEM observation provides evidence that the enhancement of void formation originates in the heterogeneous short-range atomic configurations induced by the addition of W.

Formation of highly oriented nanopores via crystallization of amorphous Nb2O5 and Ta2O5

“…11 It seems that the difference in the effect of W on the amorphous structure of these oxides arises from the conformity of ionic properties in the matrices. In Al 2 O 3 , the introduction of W must disorder the state of coordination and bond-length in amorphous Al 2 The fully crystallized samples contain partly the grains with spherical, non-oriented pores.…”

“…One of the possible routes for the purpose must be to introduce additive elements. In a previous work, 11 we examined the effect of a third element, tungsten, on the pore formation in aAl 2 O 3 . The addition of tungsten into a-Al 2 O 3 is effective for inducing larger and denser pores than in a-Al 2 O 3 without tungsten.…”

“…In evaporating a grain of the oxides on a tungsten coil as a heating source, tungsten is inevitably introduced into the deposited oxide films. 11 A cleavage NaCl crystal was used as the substrate. The NaCl on which the 15-30 nm thick oxide thin film was deposited was put into distilled water, and then the floating thin film was mounted onto a platinum grid.…”

Behavior of Sn atoms in GeSn thin films during thermal annealing: Ex-situ and in-situ observations

“…Based on the density functional theory, it has been reported that vacancies are preferentially trapped with Sn atoms in Ge. [20][21][22][23] In general, amorphous materials contain free volumes, [24][25][26] which presumably causes the Sn-vacancy pairs. As a consequence, substitutional Sn atoms, with a concentration that is much higher than the solubility limit, are stabilized in the crystalline Ge matrix.…”

Effect of iron doping on the properties of nanopowders and coatings on the basis of Al2O3 produced by pulsed electron beam evaporation

“…It is known that, at the ini tial stage of heating γ phase Al 2 O 3 , its specific surface increases as a result of the formation of the nanosize pores (2-3 nm) [35]. In particular, it was shown in [36] [21]. We note that, in the literature, the problem about the reversibil ity of the phase transformations of the metastable phases of Al 2 O 3 is treated rather poorly; in particular, the absence of the reversible transformations with decreasing temperature was underlined in [21].…”