Nanocrystal growth in alkali halides observed by exciton spectroscopy

Abstract

We have developed a method to study the growth of CuCl and CuBr nanocrystals in alkali halides by in situ absorption spectroscopy. Exciton lines are used as a signature of crystallinity and a broad absorption peak measures the number of Cu ϩ ions. The mean radius R and the concentration x cr of nanocrystals are determined simultaneously, which in turn enables the determination of the particle density N of crystals as a function of time. Neither the size-distribution function nor R(t) follow the prediction of the classical growth theory. x cr (t) reveals two different growth mechanisms, one for high and one for low growth temperatures. N(t) demonstrates that the growth of big crystals at the expense of small crystals happens from the beginning of the growth process. This result contradicts the traditional view of Ostwald ripening as a final stage of precipitation and stresses the dynamical character of cluster growth. The experimental data are described by a set of empirical parameters that can be used as a guide for controlled growth of CuCl nanocrystals in NaCl. The smallest nanocrystals detected by exciton spectroscopy consist of 50 unit cells. The kinetic properties of KCl and NaBr crystals doped with CuCl and CuBr are very similar to those observed in NaCl doped with CuCl.

Nonisothermal nucleation in the CuCl solid solution in glass: Nucleation under continuous cooling of the solid solution

“…Experimental investigations of the kinetics of nucleation on model solutions were also performed at a fixed temperature [4][5][6][7][8][9] or with a temperature jump [10,11]. Under nonisothermal conditions, changes in the supersatu ration and critical radius are caused by both the nucle ation and variation in the temperature, which makes it possible to control the growth of a new phase and to obtain new data for the development of the nucleation theory.…”

Неизотермическая нуклеация в твердом растворе CuCl в стекле: концентрационный эффект при нагреве твердого раствора

“…Образование новой фазы в твердом растворе при изо-термическом отжиге теоретически и экспериментально достаточно хорошо изучено [1][2][3][4][5][6]. Процессы выделения новой фазы в твердых растворах на стадии их разогрева до температуры изотермического отжига представляют собой важную и недостаточно изученную проблему.…”

PbS nanoparticles in Langmuir–Blodgett films: kinetics of formation and growth

“…However, both techniques do not have the capability to follow the reaction of nanoparticle formation continuously from the nucleation to final growth stages. Unlike known structural techniques, the optical absorption method, worked out by Hasselhoff and Weber [9], allows us to analyze different states of precursors, in particular metal ions in matrix molecules and semiconductor nanocrystals. Moreover, this method permits us to determine the nanocrystal size changing during the growth process.…”