Results of the comprehensive morphological study of CdI 2 -BiI 3 layered crystals are presented. Direct AFM observations of micro-and nanostructures formed in the volume of the crystals confirm the predictions made on the basis of positron annihilation spectroscopy studies. The model explaining the possible pores formation mechanism is proposed and validated by the results of luminescence measurements at 8 K.

Atomic force microscopy studies of the dynamics of the nanostructure formation on a van der Waals surface of CdI2 crystals during aging in air environment under near-equilibrium thermodynamic conditions have been carried out. The nanostructure growth process is found to consist of three stages. At the first stage, there appear nano-sized pores due to the lattice dissolution at the outcrops of screw dislocations or other structural defects. At the second stage, the cone-shaped nanoclusters arise and grow in those nano-sized pores. At the third stage, the nanoclusters coagulate. The growth kinetics of cone-shaped nanoclusters is described by a diffusion model based on the interdiffusion approximation for the components. The growth rate of nanoclusters is shown to depend on the time evolution of the concentration gradient of Cd 2+ ions in the near-reaction zone. K e y w o r d s: atomic force microscopy, van der Waals surface, nanopores, nanoclusters, diffusion.

Nano-sized structures (nanopores, nanoclusters, nanowires) that formed on van-der-Waals surfaces of CdI 2 during their curing in air under near-equilibrium thermodynamic conditions were found using atomic-force microscopy. A mechanism of nanocluster formation was proposed. They nucleated and grew in nano-sized pores. Aggregation of the nanoclusters gave rise to the formation of nanowires. Photoluminescence and Raman spectroscopy showed that the nanoclusters contained cadmium hydroxide [Cd(OH) 2 )] and oxide (CdO). A formation mechanism of these nanophases was proposed. Introduction.Research on nanostructures that is aimed at discovering materials with new functional properties that enable them to be used in modern devices and micro-and nanoelectronics is a critical area of modern semiconductor and dielectric physics. In this respect, layered crystals, the surfaces of which are characterized by elongated atomically smooth portions with a low density of dangling bonds [van-der-Waals (vdW) surfaces], are promising. This feature is responsible for their use as substrates for forming molecular, organic, and metallic nanostructures for preparing heterostructures by incoherent vdW-epitaxy as natural nanorelief standards in the metrology of nano-sized objects [1][2][3][4].At present, the formation and properties of nano-sized structures in narrow-bandgap layered A III B V crystals (GaSe, InSe) and alloys In x Se 1-x are under intense scrutiny [5][6][7][8]. Analogous investigations of wide-bandgap layered MX 2 halides are practically unknown. The surfaces of layered CdI 2 crystals grown from aqueous solutions were studied by microscopy [9][10][11][12][13]. Optical and tunneling (TEM) and scanning (SEM) electron microscopy revealed new spiral growth regions that were formed on the basal surfaces (0001) of CdI 2 , namely, steps of a height equal to the structure period c and multiples of c. The horizontal distance between steps was a multiple of lattice constant a [9-11]. Also, a detected mismatch between the height of the growth spiral and lattice period c was explained by the interaction of dangling bonds in the broken I-Cd-I layers (steps) with the crystal surface. This decreased the thickness of the structural bilayer unit I-Cd-I from 0.343 to 0.310 nm. The surface morphology of CdI 2 crystals grown from aqueous solution was investigated by atomic-force microscopy (AFM) and exhibited linear steps (terraces), depressions, and islets. The CdI 2 surface between these features was atomically smooth with relief non-uniformity of 10.2 and 4.7 Å [13].The goal of the present work was to establish the formation mechanism and the phase composition of nanostructures formed on vdW surfaces of CdI 2 crystals after storage in air under normal thermodynamic conditions (290 K, relative humidity 80%).Experimental. CdI 2 crystals were grown from the melt and the gas phase. Single crystals of CdI 2 were grown by the Bridgman-Stockbarger method from a melt that was purifi ed beforehand by zone refi nement. Simultaneously, thin singlecryst...

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The morphology of nanostructures formed in non-stoichiometric CdI2 crystals has been studied, by using the atomic force microscopy methods. Morphological changes are observed, when the concentration of cadmium atoms approaches a non-stoichiometric threshold value of 0.1 mol%. The features in the phase composition of nanostructures are analyzed with the help of Raman and infrared absorption spectroscopies. The influence of the researched nanostructures on the optical characteristics of non-stoichiometric CdI2 crystals is analyzed.