Correlation between supersaturation and phase for the heterogeneous nucleation and coalescence of HgI2 onto amorphous substrates

Abstract

HgI2 99 % was purified by four evaporations at 300 ºC and with an initial pressure of 10-3 Pa. Theheterogeneous nucleation of HgI2 onto glass was studied by the physical vapor deposition (PVD) method,with and without argon atmosphere. Glass substrates 2”x2” in area, with and without palladium coating,were used for nucleation and coalescence. Nucleation conditions, specially supersaturation, stronglydetermined nuclei population and size but also determined the HgI2 nucleation phase. A range ofnucleation temperature between 30 ºC and 60 ºC for the substrate and the same temperature of the sourcefor each set, and a range of initial Ar pressure between 1.3–2.6 x 104 Pa were found as appropriate fornucleation of the a (red) phase of HgI2. Other nucleation condition, as a temperature gradient between thesource and the substrate or an argon pressure higher than 4 x 104 Pa, determine nucleation of the b (yellowHgI2) metastable phase.Nucleation took place by the Volmer Weber mechanism, with islands 1-5 mm in size, for both, a and b phase. Coalescence was performed annealing the substrate at a temperature between 30 and 60 ºC andfrom 5 minutes to 24 hours, at an initial argon pressure of 104 Pa. Nuclei coalesce to form larger islands,which, in the case of b phase nuclei also transform to the a stable phase. From the experimentalnucleation and coalescence conditions, correlations between supersaturation conditions and nuclei phasewere established; theoretical considerations about the surface adhesion energy (ghkl) were made. Futureefforts will be conducted to improve nucleation uniformity, to better study nuclei properties and to searchfor coalescence and further growth better conditions.