Type of presentation: Poster

MS-3-P-3394 Determining the Crystal Structure of Metastable cubic SiN at the TiN/SiN Interface

Fallqvist A.1, Hultman L. G.1, Persson P. O.1
1Linköping University, Sweden
perpe@ifm.liu.se

The TiN-SiNx system is subject to intense research, mainly as a model system for superhard nanocomposite (NC) materials.1 Although the elements are commonly deposited simultaneously as a thin film, the TiN-SiNx nanocomposite formation is a consequence of phase separation of the immiscible components, leaving sharp interfaces between the two phases. It has been reported that such nanocomposites exhibit high hardness, which is of use for wear-resistant coatings.1 As a consequence of these small dimensions, dislocation glide is prevented while also the thin matrix prevents grain boundary sliding due to its high cohesive strength.2 While the structure of the crystallites is well known, e.g. B1 (NaCl) TiN in the TiN-SiNx system, the structure of the TiN-SiNx interface and the thin intergranular SiNx matrix has been debated for some time. The spatially constrained dimensions makes it challenging to just “look at it and see”. To limit the complexity, but also to investigate the hardening mechanisms a number of studies have reported successful growth of transition metal nitride-SiNx (001)-oriented multilayers and that these ML also exhibited increased hardness for thin SiNx layers.3 Depending on thickness of the SiNx layer, the ML structure can be grown epitaxially, indicating a crystalline nature of the SiNx. Constituting an epitaxial nature, these multilayers are the key towards understanding the nanocomposite TiN to SiNx interface. With increasing SiNx thickness, the layer assumes an amorphous structure and the epitaxial nature of the ML is lost. Through the significance of the TiN-SiNx (001) interface, it’s structural nature has been subject to intense theoretical studies. In contrast, few results have been published by high resolution microscopy methods.

In this contribution, the structure of a SiNx layer, epitaxially stabilized on TiN(001), is determined by atomically resolved aberration corrected scanning transmission electron microscopy ((S)TEM), using parallel high angle annular dark field (HAADF-) and annular bright field (ABF)-(S)TEM in combination with STEM image simulations. Complementarily, spatially resolved electron energy loss spectroscopy (EELS) spectrum imaging (SI) of the nitrogen (N-K) near edge fine structure (ELNES) was applied to the SiNx and corroborated with full potential calculations of candidate structures. This work was carried out at the Linköping double corrected Titan3, equipped with a Gatan Tridiem ERS imaging filter.

The study localizes the N atomic position in the structure, identifying the SiN structure to exhibit a B1 (NaCl) - like structure.

L. Hultman, et.al., Phys. Rev. B 75, 155437 (2007).

J. Schiøtz, F.D. Di Tolla, K.W. Jacobsen, Nature, 391, 561 (1998).

H. Söderberg, et.al., J. Appl.Phys 97, 114327 (2005).

The authors wish to acknowledge funding from the Swedish Research Council, and from the Knut and Alice Wallenberg Foundation for the Electron Microscopy Laboratory in Linköping

Fig. 1: The figure shows a layer of cubic SiN (indicated by an arrow in the HAADF images) embedded between TiN layers. The same location was viewed from the two different orientations, and enable identification of the N position in the structure from the ABF images.