Composition and chemical width of ultrathin amorphous films at grain boundaries in silicon nitride
- PDF / 587,209 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 65 Downloads / 182 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Composition and chemical width of ultrathin amorphous films at grain boundaries in silicon nitride H. Gua) Japan Science and Technology Corporation, “Ceramics Superplasticity” project, JFCC 2F, 2-4-1 Mutsuno, Atusta, Nagoya 456, Japan and Max-Planck-Institut f¨ur Metallforschung, Seestraße 92, 70174, Stuttgart, Germany
R. M. Cannon Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
M. R¨uhle Max-Planck-Institut f¨ur Metallforschung, Seestraße 92, 70174, Stuttgart, Germany (Received 20 December 1996; accepted 6 April 1997)
Two different electron energy loss spectroscopy (EELS) quantitative analytical methods for obtaining complete compositions from interface regions are applied to ultrathin oxide-based amorphous grain boundary (GB) films of , 1 nm thickness in high-purity HIPed Si3 N4 ceramics. The first method, 1, is a quantification of the segregation excess at interfaces for all the elements, including the bulk constituents such as silicon and nitrogen; this yields a GB film composition of SiN0.4961.4 O1.0260.42 when combined with the average film thickness from high resolution electron microscopy (HREM). The second method, II, is based on an EELS near-edge structure (ELNES) analysis of the Si–L2,3 edge of thin GB films which permits a subtraction procedure that yields a complete EELS spectrum, e.g., that also includes the O–K and N–K edges, explicitly for the GB film. From analysis of these spectra, the film composition is directly obtained as SiN0.6360.19 O1.4460.33 , close to the one obtained by the first method but with much better statistical quality. The improved quality results from the fewer assumptions made in method II; while in method I uniform thickness and illumination condition have to be assumed, and correction of such effects yields an extra systematic error. Method II is convenient as it does not depend on the film thickness detected by HREM, nor suffer from material lost by preferential thinning at the GB. In addition, a chemical width for these films can be deduced as 1.33 6 0.25 nm, that depends on an estimation of film density based on its composition. Such a chemical width is in good agreement with the structural thickness determined by HREM, with a small difference that is probably due to the different way in which these techniques probe the GB film. The GB film compositions are both nonstoichiometric, but in an opposite sense, this discrepancy is probably due to different ways of treating the surface oxidation layers in both methods. I. INTRODUCTION
Grain boundaries (GB) are important microstructural elements in materials. They often play an essential role in materials processing or in controlling the properties that make the materials useful, such as in functional and structural ceramics. For high temperature structural ceramics based on Si3 N4 , GB’s are found to be covered with thin amorphous films.1 Fast diffusion that occurs in the intergranular films facilitates mass transport during the formation of den
Data Loading...
