The Ti-Al-N system has been shown to include two phases in the nanolaminated MAX family. The Ti4AlN3 phase has hitherto only been synthesized in bulk form [1], however successful growth of epitaxial single crystal thin films of the Ti2AlN phase has been reported.[2-4] The reported growth temperatures have been 690 -1050 °C and lower temperatures are desirable, hence, a possible route towards synthesis of Ti-Al-N MAX phase films is to deposit multilayer structures of Ti and AlN at lower temperatures. By applying an annealing process to the film, MAX phase formation by a solid phase epitaxial reaction has been shown to occur.[5] Outstanding questions for this process include reaction steps with nucleation sites and diffusing species.
In this study, we have performed an in situ transmission electron microscope (TEM) annealing up to 900 °C of as prepared cross sectional samples from the Ti/ AlN multilayers. By increasing the annealing temperature in steps of 50 °C every 60 min. we are able to follow the phase transformation to Ti2AlN as it occurred at 700 °C. Structural information on the phase change was obtained from TEM images and electron diffraction patterns, while information concerning the diffusing elements was revealed by a combination of scanning TEM and simultaneous EELS and EDX.
1. M.W. Barsoum, L. Farber, I. Levin, A.T. Procopio, T. El-Raghy, A. Berner, J. Am. Chem. Soc. 82, 2545 (1999).
2. T. Joelsson, A. Hörling, J. Birch, L. Hultman. Appl. Phys. Lett. 86 111913 (2005).
3. M. Beckers, N. Schell, R.M.S. Martins, A. Mücklich, W. Möller, L. Hultman Appl. Phys. Lett. 89 074101 (2006).
4. P. O.Å. Persson, S. Kodambaka, I. Petrov, L. Hultman, Acta. Mater. Submitted.
5. C. Höglund, M. Beckers, N. Schell, J. Birch, J.v Borany, L. Hultman. Submitted.
|