Background

CVD

The group for Microscopy and Microanalysis at the Department of Applied Physics at Chalmers University of Technology has worked on CVD related projects for more than 20 years. This has resulted in five Ph. D. theses, three licentiate reports and a number of publications in international journals, see publications page. 

One of the most interesting CVD coating materials is alumina, which can be produced as three crystallographic modifications, a-Al2O3, g-Al2O3 and k-Al2O3, all which can be useful for wear-resistant purposes. Control of the deposition of the alumina polymorphs can be obtained by applying special intermediate layers prior to the alumina deposition. This technique can be used to deposit both single and multilayer coatings.

The details of the microstructure, such as crystal structures, surface morphologies, twinning, dislocation density, porosity, orientation relationships, grain size and chemical compositions of both single- and multilayer coatings containing a-Al2O3, g-Al2O3 and k-Al2O3 have been examined and provided the basis for a model describing the preferential nucleation of a particular alumina polymorph on a particular bonding or modification layer. In addition, in multilayer coatings epitaxy was frequently found and the orientation relationships could be determined using electron diffraction in TEM. The reason for and the general form of these relationships could be described using crystallographic information from the TEM investigations.

CVD alumina multilayer coating