a first-order approximation a mean diffusion length can be calculated by 2, = [Aza2(T) -AZ,~]'/~, with Az,(T) and Az, denoting the measured Az at the same interface after and before heat treatment of the sample, respectively. An apparent diffusion coefficient can be estimated from D, = Za2/2t, with the annealing time t. Values for D, between 2.5 x lo-'' and 1.3 x lo-'' m2 s -l were determined between T = 470°C and T = 680 "C, which agree quite well with earlier measurements on rotating samplesg at 400°C and 500°C. This shows that the constancy of profiling parameters in each experimental set-up is more important than the optimum resolution achieved. On the other hand, a marked increase of D, was observed with increasing individual layer thickness. This can be explained only if other effects, such as primary recrystallization and grain boundary diffusion, contribute to the apparent diffusion coefficients. These influences have to be explored further, e.g. by transmission electron microscopy studies. In conclusion, the determination of depth resolution for multilayer structures of Cr/Ni with varying layer thickness have shown the influence of individual layer thickness on Az and its use for extracting diffusion parameters. REFERENCES 1. S. Hofmann, in Practical Surface Analysis with AES and XPS, ed. by D. Briggs and M . P. Seah, p. 141. Wiley, Chichester (1983). 2. J. Fine, P. A. Lindfors, M . E. Mitchell and G. P. Chambers, J.Carbon fibres for carbon/epoxy composite materials are generally surface-treated through an electrochemical process prior to their introduction in the epoxy matrix. The usual treatments lead to the formation of oxygen-containing groups at the fibre surface, which enhance the interfacial cohesion in a composite' and consequently improve most of the mechanical properties of the material. In addition, anodic processes that have been developed at ONERA for the last six offer a large range of modifications of fibre surfaces and fibre/ matrix interfaces, since they make it possible to graft electrochemically various kinds of amino groups at the fibre surface. Moreover, one of these treatments6.' leads to an enhancement of both interfacial cohesion and toughness of the composite material. Such an effect has never been obtained with classical oxidative processes and motivates further investigations of our amino treatments.As a guide for choosing adequate treatment conditions (electrolytes, amine to be grafted, potential, duration, etc.) and for characterization of the process, a physicochemical description of the surface of treated fibres is needed. Namely, using x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS), our aim is to determine the efficiency of the treatment (i.e. abundance of deposited nitrogen), the chemical environment of carbon and nitrogen at the fibre surface and the thickness of the deposit.The treatments are carried out in an electrochemical cell under the following conditions :4 (1) the anode is a row of carbon fibres to be treated;(2) the solution i...
