Substrate effect induced growth of various single-crystalline Zn and Zn/ZnO core-shell polyhedrons with tunable photoemission

Single-crystalline Zn and Zn/ZnO core-shell polyhedrons of various types were synthesized by chemical vapor deposition on Si(111) and Si(100) followed by different oxidation treatments. The core-shell polyhedrons started with the growth of single-crystalline Zn polyhedrons, nucleated on a Si substrate, and the ZnO layers were formed on the surface of the Zn polyhedrons upon the oxidation treatments. The thickness of the oxide layers could be controlled precisely by adjusting the temperature during the oxidizing process. High-resolution transmission electron microscopy and focus ion beam show various polyhedrons were grown with different crystallographic orientations vertical to the Si substrate and exhibit special mechanical properties in tolerating strain induced by the lattice mismatch between Zn and Si. The strain energy as well as the surface and interfacial energy determine the number ratio of different polyhedrons on Si(111) and Si(001), and a thermodynamic model was proposed to explain the mechanism. Room-temperature cathodoluminescence measurements show that the Zn/ZnO core-shell polyhedrons exhibit tunable ultraviolet emissions and controllable green emission with different oxidation conditions, which were ascribed to the surface and strain effect. The growth of various Zn polyhedrons on Si provides evidence for understanding strain induced substrate effects and distinguishing strain tolerance between metal and oxide nanostructures.