Journal of Applied Spectroscopy, Vol. 82, No. 1, March, 2014 (Russian Original Vol. 82, No. 1, January–February, 2015) FORMATION AND OPTICAL PROPERTIES OF CdI 2 NANOSTRUCTURES I. M. Bolesta, a I. N. Rovetskii, a I. D. Karbovnik, a UDC 620.3;535.375.5 S. V. Rykhlyuk, a* M. V. Partyka, a and N. V. Gloskovskaya b 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. Keywords: atomic-force microscopy, nanopores, nanoclusters, nanowires, van-der-Waals surface. 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 [1–4]. 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 [5–8]. 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 [9–13]. 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 purified beforehand by zone refinement. Simultaneously, thin single- crystalline CdI 2 plates precipitated from the gas phase onto the walls of the upper part of the ampul during growth of the single crystal. Fresh chips of crystals grown from the melt were obtained by removing their upper layers using adhesive tape. The surfaces of CdI 2 grown from the gas phase were not mechanically treated. The vdW-surface morphology of single crystals was studied by contact and semicontact AFM using a Solver P47-PRO atomic-force microscope. The radius of the probe point was ≤10 nm. The instrument height resolution was 1 Å. Luminescence a Ivan Franko National University of Lviv, Lviv, Ukraine; e-mail: rykhlyuk@gmail.com; b N. N. Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine, Kyiv, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 82, No. 1, pp. 89–95, January–February, 2015. Original article submitted June 10, 2014. _____________________ * To whom correspondence should be addressed. 84 0021-9037/15/8201-0084 ©2015 Springer Science+Business Media New York DOI 10.1007/s10812-015-0068-1