Surface reactions of low-energy carbon ions with boron nitride thin films
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Surface reactions of low-energy carbon ions with boron nitride thin films I. Monteroa) and L. Gal´an Instituto de Ciencia de Materiales, CSIC and Departamento de F´ısica Aplicada, C-XII, Universidad Aut´onoma de Madrid, Cantoblanco, 28049-Madrid, Spain (Received 10 September 1996; accepted 2 February 1997)
The chemical reactions between hyperthermal species from a methane plasma and the boron nitride surface have been studied. In this work we report an x-ray photoemission study of the boron nitride with varying degrees of carburization. The carbon ions react, forming C –B and C–N bonds; for surface carbon concentration, smaller than ,0.30, C–B bonds are formed, while for higher surface carbon concentrations C–N bonds are also observed. In addition, the binding energy difference between the N1s and B1s core levels increases with increasing carbon content of the film. These chemical shifts are interpreted in terms of the decrease of the ionicity of the material as a consequence of the increase in the number of C–B and C–N bonds. For surface carbon concentration higher than 0.30, amorphous carbon is also formed that grows and finally forms a surface layer. The valence band spectra of the BNC compounds show that the density of states filling the gap at about 15 eV between the two characteristic peaks of the valence band of BN, marking the nitrogen 2s orbitals and the boron and nitrogen 2p electrons and the orbital hybridization between the 2s of boron and 2p states, increases with increasing carbon fluence as a consequence of the hybridization with carbon orbitals.
I. INTRODUCTION
Considerable attention has been paid recently to the synthesis and properties of new materials such as C3 N4 , BN, and BCN ternary compounds for different applications: optical coatings, waveguides, intermetallic dielectrics in integrated circuits, hard coatings, etc.1–6 Generally, carbon-boron nitride materials have been prepared by chemical vapor deposition,7–9 and the codeposited films were two-phase BN–C mixtures; also, the formation of B–C–N solid solutions has been reported.10 In this work, a low-energy ion beam technique was used to study the carbon reactions with boron nitride surfaces. Previously, plasma enhanced chemical vapor deposition (PECVD) was used to obtain BN films on Si substrates. Low-energy ion implantation and ion-assisted growth processes are a common trend in materials technology.11,12 Depending on the nature and energy of the incident ions and the properties of the substrate, the extent of penetration, damage, and back-sputtering of the target material may vary. It is also well known that the bombardment of a surface by low-energy ions may induce chemical reactions between the active ions and the lattice atoms.13,14 In fact, low energy ion bombardment favors the formation of high-energy bonds a)
Address correspondence to this author at Instituto de Ciencia de Materiales, Consejo Superior de Investigaciones Cient´ıficas, CSIC, Campus de la Universidad Aut´onoma de Madrid
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