Electronic Structure Investigation of MAX-Phases by Soft X-ray Emission Spectroscopy
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1023-JJ09-01
Electronic Structure Investigation of MAX-Phases by Soft X-ray Emission Spectroscopy Martin Magnuson Department of Physics, Uppsala University, P. O. Box 530, Uppsala, S-75121, Sweden ABSTRACT The electronic structure of nanolaminate Ti2AlC and Ti2AlN thin films, so-called MAX-phases, were investigated by soft X-ray emission spectroscopy. These nanolaminated carbide and nitride compounds represent a class of layered materials with a combination of properties from both metals and ceramics. The bulk-sensitive soft X-ray emission technique is particularly useful for detecting detailed electronic structure information about internal monolayers and interfaces. The Ti-Al bonding is manifested by a pronounced peak in the Ti L-emission of Ti2AlC and Ti2AlN that is not present in the binary TiC system. The spectral shape of Al L-emission in the MAXphase is strongly modified in comparison to metallic Al. By replacing or partly exchanging C with N, a change of the electron population can be achieved causing a change of covalent bonding between the laminated layers, which enables control of the material properties.
INTRODUCTION The important family of ternary carbide and nitride compounds, so-called Mn+1AXnphases is the subject of intense research [1]. Three different kinds of crystal structures (stoichiometries) are classified as 211 (n=1), 312 (n=2) and 413 (n=3) phases [2-4]. Here, the letter M denotes an early transition metal, A is an element in the groups III-V and X is either carbon or nitrogen. The MAX-phases exhibit a technologically important combination of metallic and ceramic properties, including high strength and toughness at high temperature, resistance to oxidation and thermal shock, exhibit high electrical and thermal conductivity [1], is environmentally friendly and relatively cheap to produce. The unique materials properties of the MAX-phases are related to the internal nanolaminated crystal structure, the choice of the three constituent elements, as well as the electronic structure and the chemical bonding between the intercalated atomic layers. For the 211 type of crystal structure, there are about 50 different ternary carbides and nitrides, among which Ti2AlC and Ti2AlN can be anticipated to be technologically useful. Sintered bulk MAX-compounds are useful in many technological hightemperature applications such as heating elements in ovens and construction parts of combustion engines. In other applications where tribological properties e.g., low-friction and wear resistance are important such as electrical switches, high quality thin film single-crystalline coatings of MAX-phases can be utilized.
In this paper, soft x-ray emission (SXE) spectroscopy was applied to probe the internal electronic structures of Ti2AlC and Ti2AlN in comparison to the binary compounds TiC and TiN. The photon-in-photon-out SXE spectroscopic technique is element selective and more bulk sensitive than electron-based techniques such as x-ray absorption and x-ray photoemission spectroscopy [5-7]. This makes it possib
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