JOURNAL OF MATERIALS SCIENCE 39 (2 0 0 4 ) 6183 – 6190 ‘Smart’ Raman/Rayleigh imaging of nanosized SiC materials using the spatial correlation model M. HAVEL Nanophases and Heterogeneous Solids Group, LADIR-UMR7075 Centre National de la Recherche Scientifique & Universit ´ e Pierre et Marie Curie, 2 rue Henry Dunant, 94320 Thiais, France; D ´ epartement des Mat ´ eriaux et Syst ` emes Composites, Office National d’Etudes et de Recherches A ´ erospatiales, 29 Ave de la Division Leclerc, 92320 Chatillon, France D. BARON, Ph. COLOMBAN ∗ Nanophases and Heterogeneous Solids Group, LADIR-UMR7075 Centre National de la Recherche Scientifique & Universit ´ e Pierre et Marie Curie, 2 rue Henry Dunant, 94320 Thiais, France E-mail: colomban@glvt-cnrs.fr Non-destructive Raman and Rayleigh microspectrometries were used to map nanostructural and topological variations across the diameter of the SCS-6 TM Textron SiC fibre. It is shown for the first time that Rayleigh imaging offers a competitive alternative to AFM measurements for materials containing carbon as a second phase. The Spatial Correlation Model has been used to decompose the SiC Raman spectra into amorphous and crystalline components. ‘Smart’ Raman images, which contain the calculated structural parameters revealed the nanostructure distribution. A good agreement has been obtained at the nanoscale between these smart images and transmission electron microscopy (TEM) data. A major asset of Raman ‘smart’ images is to give a non destructive and global view on the crystal quality, grain size and residual stress. The potential and the limitations of the procedure are discussed. C  2004 Kluwer Academic Publishers 1. Introduction Nanophased materials received considerable attention in the last few years but their characterisation is not easy. The challenge for the nanotechnologies, which is to achieve perfect control on nanoscale related prop- erties, requires to correlate the production conditions with the resulting nanostructure. Nanocrystalline sil- icon carbide materials are interesting because of their remarkable properties such as high thermal stability, ex- treme hardness and good dielectric properties. They are expected to have applications in wide-gap semiconduc- tors, air and spacecraft thermostructural composites, etc. SiC crystallises in a large number of polymorphs made of Si/C bilayers with various stacking combina- tions called polytypes [1]. Each one has its own band gap energy and electrical properties. Recent develop- ment in crystal growth technology such as molecular beam epitaxy or pulsed laser deposition [2] for SiC crystals requires the polytypes structure identification to optimise the material properties. Raman microspec- troscopy is a powerful technique for the characterisa- tion of SiC since it is a low-cost (non vacuum) and non-destructive method with a high efficiency because of the strong covalency of Si C bonds [3]. This method provides information even on heterogeneous materials (e.g., composites), such as the phases nature, distribu- ∗ Author to whom all correspondence should be addressed. tion, residual stress, etc. [4]. The main advantage com- pared to infrared spectroscopy is that the laser in Raman equipment can be focused down to ∼1 µm, allowing for imaging specific areas [5, 6]. In the case of resonant materials, Raman scattering becomes a surface analy- sis technique in the range of ∼20 to 100 nm in-depth penetration [7]. The purpose of this paper is to show how Raman and Rayleigh microspectrometries can image structural and topological information from heterogeneous mate- rials. As an example, we analysed the SCS-6 TM Textron SiC fibre (φ = 140 µm), which is prepared by chem- ical vapour deposition (CVD) of a SiC/C mixture on a C fibre. This fibre finds applications in metal-matrix composites, as reported previously [8–10]. Compari- son is made with available data from transmission elec- tron microscopy (TEM). The objective is to image the nanophases physical properties distribution based on an accurate modelling of Raman spectra. 2. Experimental procedure 2.1. Samples Silicon carbide fibres produced by the chemical vapour deposition (CVD) process are composites in themselves and present structural changes linked to the production 0022–2461 C  2004 Kluwer Academic Publishers 6183