Early stages of oxidation of aluminum nitride
- PDF / 286,812 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 58 Downloads / 230 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Early stages of oxidation of aluminum nitride Yongjun Geng and M. Grant Nortona) School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington 99164 (Received 8 February 1999; accepted 7 April 1999)
The early stages of oxidation of aluminum nitride have been studied by transmission electron microscopy and electron diffraction. It has been found that the oxide layer grows by the Stranki–Krastonow mechanism, where an initial uniform layer is followed by island formation. The onset of oxidation occurs at 800 °C and the initial oxide phase that forms is ␥–Al2O3, one of the transition aluminas. The orientation relationship between the oxide layer and the underlying nitride is (440)␥㛳(1120)AlN and [112]␥㛳[0110]AlN.
The oxidation of metals has been studied widely since the classical work of Tammann1 and has been reviewed extensively, most notably by Cabrera and Mott2 and Lawless.3 The mechanisms for oriented oxide layer formation are often described in terms of those used for growth in heteroepitaxial systems from solution or the vapor phase. The oxide growth may proceed in a layerby-layer fashion as described originally by Frank and van der Merwe4–6 and observed, for example, during the formation of ZnO on the basal planes of Zn by Finch and Quarrell.7,8 In this case, the oxide was pseudomorphic with the underlying metal (i.e., the oxide was strained elastically to match the lattice parameter of the metal). Oxide formation has also been observed to occur by nucleation and growth of three-dimensional islands, known as the Volmer–Weber mechanism.9 This type of oriented overgrowth has been observed to occur, for example, when Cu is oxidized to Cu2O.10–12 The third type of growth mode that has been identified in heteroepitaxial systems is known as the Stranski– Krastanow mode13 in which initially layer-by-layer growth occurs followed, typically after one to five monolayers, by islanding. This type of growth mode has been observed in a range of heteroepitaxial systems,14,15 but it has not been previously reported as a mechanism for oxide formation. Although the early stages of growth via the Stranski–Krastanow mode are not well understood the transition between layer-by-layer growth and island formation is often the result of a large strain energy in the film due to a mismatch in the lattice spacings of the two crystals.16 In oxidation of metals, the first part of the oxidation process involves adsorption of the oxygen on the metal
a)
Address all correspondence to this author. e-mail: [email protected]
2708
http://journals.cambridge.org
J. Mater. Res., Vol. 14, No. 7, Jul 1999 Downloaded: 31 Jan 2015
surface. For many metals (e.g., Cu, Ni, W, Fe) ordered surface adsorption structures occur.3 These structures may involve significant rearrangement of the surface metal atoms.17 However, there appears to be no evidence for formation of true oxide structures at this stage of the oxidation process.10,18 Island formation can then occur either on
Data Loading...
