Nanovoid formation through the annealing of amorphous Al2O3 and WO3 films

Enhancement of nanovoid formation in annealed amorphous Al2O3 including W

“…At 1073 K, crystallized regions appear in the amorphous matrix of EB-Al 2 O 3 , as has been reported by the authors. 4 The mean diameter of the nanovoids in the BFI of the crystallized region shown in Fig. 2(c) was estimated to be 2.6 nm.…”

“…2 It has been reported that nanovoid formation in the crystallization process of amorphous Al 2 O 3 , which is approximately 20% less dense than c-Al 2 O 3 , is most likely due to the accumulation of the large amount of free volume. 4 This is true of amorphous RH-Al 2 O 3 with about 10 at. % W, because the formation and growth of nanovoids occur during the structural change toward c-Al 2 O 3 as it does in the case of EB-Al 2 O 3 without W. However, there are clear differences in the crystallization and void formation behavior between EB-Al 2 O 3 and RH-Al 2 O 3 .…”

“…According to extensive studies on the atomic configuration of amorphous Al 2 O 3 , it is commonly accepted that amorphous Al 2 O 3 is composed of a majority of AlO 4 and AlO 5 basic units, and some AlO 6 units. 5,6,22 nearest neighbor atomic distances.…”

“…4 and 5) and WO 3 (Ref. 4) were found to become nanoporous structures as a result of annealing in air. The evolution of nanovoids can be explained by the accumulation of the free volume in amorphous Al 2 O 3 and WO 3 , both of which have 20-30% lower density than their crystalline phases.…”

“…The evolution of nanovoids can be explained by the accumulation of the free volume in amorphous Al 2 O 3 and WO 3 , both of which have 20-30% lower density than their crystalline phases. [6][7][8] As explained in earlier papers, 4,5 void formation takes place in the amorphous states before crystallization. The experimental and theoretical analyses carried out by Tane et al 5 indicated that as-deposited amorphous Al 2 O 3 consists of lower-and higher-density regions containing lower and higher fractions of AlO 6 basic units, respectively, and that local density growth in the unstable lower-density regions during annealing leads to nanovoid formation before crystallization.…”