Physico-Chemical nanomaterials science

Formation of nanoparticle arrays by melting of continuous tin films on a carbon substrate 
Dukarov S.V., Petrushenko S.I., Churilov I.G., Bulgakova O.O., Sukhov V.N.
School of Physics V. N. Karazin Kharkiv National University. 
4 Svobody Sq., Kharkiv, Ukraine. 
E-mail: petrushenkokhnu@gmail.com

Thermal dispergation is a perspective method for the creation of various functional structures, which use the collective effects observed in structured arrays of nano-sized particles. Such arrays can be created by the virtue of thermal dispergation of vacuum condensates. This paper is devoted to the study of thermal de-wetting initially continuous tin films, deposited on an amorphous carbon substrate.
The components of the film system were condensed in a vacuum of 10–6 mm Hg. onto fresh cleavages of KCl single crystals. The experiment geometry made it possible to obtain a series of samples of different thickness within one vacuum cycle. After the condensation termination, the films were heated slightly above the melting point of tin. Also, the samples deposited on a heated substrate were studied. The deposition of them on the heated substrate provided their condensation by the vapor-liquid mechanism.
After thermal exposure termination, the films were cooled to the room temperature, were removed from the vacuum chamber and were examined by the SEM methods. It was established, that, after melting, the samples consisted of spherical islands with a normal size distribution. The value of the most probable radius of formed particles and the full width at half maximum of the distribution histograms linearly depend on the on the mass thickness of the condensate.
The coverage of the substrate with a film, in the case of enough thick samples, slightly increases with a thickness. At the same time, for the films, which are thinner than 500 nm, the size dependence of the coverage changes the sign, and it quickly increases from 0.13 (t = 500 nm) to 0.4 (t = 100 nm). It should be noted, that the same coefficient value (0.4) has a place in films obtained by the vapor-liquid condensation mechanism, regardless of their thickness.
According to the data of electron microscopic studies, the excess energy that releases during the film dispergation was estimated. It is 600 mJ/m2 for the films, that are 500 nm thicker and decreases to zero for the films of 50 nm thickness. This indicates that enough thin samples are already of the island type, respectively, heating does not cause their dispergation.