Real-time observation of nanoscale topological transitions in epitaxial PbTe/CdTe heterostructures

• Published in: APL materials Vol. 2; no. 1; pp. 012105 - 012105-8
• Main Authors: Groiss, H., Daruka, I., Koike, K., Yano, M., Hesser, G., Springholz, G., Zakharov, N., Werner, P., Schäffler, F.
• Format: Journal Article
• Language: English
• Published: United States AIP Publishing LLC 01.01.2014
• Subjects: CADMIUM TELLURIDES; EPITAXY; LEAD TELLURIDES; MATERIALS SCIENCE; NUMERICAL SOLUTION; QUANTUM DOTS; SOLIDS; TRANSMISSION ELECTRON MICROSCOPY
• ISSN: 2166-532X; 2166-532X
• DOI: 10.1063/1.4859775

The almost completely immiscible PbTe/CdTe heterostructure has recently become a prototype system for self-organized quantum dot formation based on solid-state phase separation. Here, we study by real-time transmission electron microscopy the topological transformations of two-dimensional PbTe-epilayers into, first, a quasi-one-dimensional percolation network and subsequently into zero-dimensional quantum dots. Finally, the dot size distribution coarsens by Ostwald ripening. The whole transformation sequence occurs during all stages in the fully coherent solid state by bulk diffusion. A model based on the numerical solution of the Cahn-Hilliard equation reproduces all relevant morphological and dynamic aspects of the experiments, demonstrating that this standard continuum approach applies to coherent solids down to nanometer dimensions. As the Cahn-Hilliard equation does not depend on atomistic details, the observed morphological transformations are general features of the model. To confirm the topological nature of the observed shape transitions, we developed a parameter-free geometric model. This, together with the Cahn-Hilliard approach, is in qualitative agreement with the experiments.