In situ studies of growth

Fet us start this section with real-time measurements of the crystallization process of highly ordered thin films of the molecular organic radical / -NPNN grown from the vapour phase on glass substrates (Caro et al, 2000). These films exhibit 2D 

Video microscopy with crossed polarizers permits the direct and non-invasive observahon of the nucleahon and growth process for many substances, and thus the study of the hme evoluhon of the spherulite radius R t). When the growth is controlled by diffusion the radius of the spherulites increases as R t) a while when the growth is determined by a nucleation-controlled process (incorporahon of atoms or molecules to the surface of the crystalline part) the radius increases linearly with hme, R t) a t. 

The hme evoluhon of the formahon of the him during evaporation is shown in Fig. 5.8 as recorded with a CCD camera assembled to an optical microscope with crossed polarizers. The 2D spherulites are labelled by order of formahon. The in-plane spherulitic crystallization is completed 300 s after the observahon of the hrst spherulite, 1 in Fig. 5.8(a). From Fig. 5.8 we observe that the nucleation centres do not appear simultaneously and that the density of spherulites is rather low ( 1.6 mm ). This low density permits a detailed analysis of the time evoluhon of 

The mechanism of growth of the films may be modelled by considering that the vapour phase transported to the substrate initially condenses in an amorphous state 

The observed non-linear radial growth of the spherulites can be described in terms of a thickness-dependent growth law given by the expression  

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