pubs.acs.org/cm Published on Web 03/01/2010 r 2010 American Chemical Society Chem. Mater. 2010, 22, 1949–1951 1949 DOI:10.1021/cm9038472 Effect of Carbon Incorporation on the Microstructure of BC x N (x =0.25, 1, and 4) Ternary Solid Solutions Studied by Transmission Electron Microscopy I. Caretti,* R. Torres, R. Gago, A. R. Landa-C anovas, and I. Jim enez Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Campus de Cantoblanco, 28049 Madrid, Spain Received December 24, 2009 Revised Manuscript Received February 23, 2010 The family of boron-carbon-nitrogen (B-C-N) com- pounds is characterized by a rich compositional and struc- tural diversity. Accordingly, a great variety of compounds in elemental, binary, or ternary form with different physico- chemical properties coexist within the B-C-N composi- tional diagram (see Figure 1). In general, the most representative structural phases of the B-C-N system are: (i) hexagonal, found in graphite and h-BN; (ii) cubic, such as diamond or c-BN; (iii) icosahedral units, distinctive of B and B 4 C; and (iv) amorphous, with different sp 3 /sp 2 ratios (e.g., a-C and ta-C). Recently, the structural B-C-N map has been considerably expanded through the possibility of synthesizing a multiplicity of C, CN x , BN x , BC x , and BC x N y nanostructures (nanotubes, nanofibers, nanoparti- cles, fullerenes, nanoribbons, etc.). 1 In the last three decades, research on ternary boron carbonitride (BC x N y ) solid solutions has received consider- able attention, inspired by the promising combination of the excellent chemical, thermal and mechanical properties of the hexagonal and cubic allotropic forms of BN (h-BN, c-BN) and C (graphite, diamond). From the very beginning, special interest has been paid to the BC x N stoichiometry, under- stood as a substitution of BN atomic pairs by isoelectronic CC pairs that satisfies the charge neutrality condition ex- pected for a stable ternary compound. Since then, practically all the experimental works on the synthesis of boron carbo- nitride in bulk form have reported a ternary BC x N composi- tion, both for hexagonal crystalline powders prepared by chemical methods from different precursors 2 and for cubic phases obtained by high-temperature and high-pressure (HT/HP) techniques. 3 In contrast, the synthesis of BC x N y compounds in thin film form-usually by chemical or physical vapor deposition methods-often produces a broad range of compositions far from BC x N. 4-6 One of the main obstacles in the formation of a ternary BC x N layered com- pound is its strong sensitivity to the conditions of synthesis. Actually, several theoretical 7 and experimental 4,6,8,9 studies have pointed to the metastable character of BC x N y , a fact that is frequently translated into elemental and/or binary phase segregation. In the case of phase segregation at the nanometric scale, its detection becomes complicated, and it is necessary to resort to high-resolution techniques for the analysis of the structure. In this sense, there exist at present an abundant number of characterization techniques to study the composition and bonding structure of thin film materials. 11 Among them, the progress of highly spatially resolved imaging technologies as transmission electron microscopy (TEM) has signified a major improvement in the study of nanometric structures, especially when coupled to electron energy loss spectroscopy (EELS). In this way, the bonding structure and the spatial distribution of each element can be assessed simultaneously at a nanometric level. 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