Crystal orientation dynamics of collective Zn/ZnO dot coherently grown on Si(111) before preferential nucleation
Chun-Chu Liu1, Jun-Han Huang2, Ching-Shun Ku3, Shang-Jui Chiu3, Jay Ghatak3, Sanjaya Brahma1, Chung-Wei Liu1, Chuan-Pu Liu2, Kuang-Yao Lo1*
1Physics, National Cheng Kung University, Tainan, Taiwan
2Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan
3National Synchrotron Radiation Research Center, Hsinchu, Taiwan
* presenting author:Kuang Yao Lo,
In the context of current growth technology, almost all thin films are grown under kinetic conditions or conditions far away from thermal equilibrium with the detailed nucleation and growth mechanisms hardly investigated. This is mainly due to the limited availability of analytical methods that allow assessing complex evolution of film growth at small volumes directly, especially during nucleation period. Therefore, we develop a simple and non-destructive analytic method based on signals from reflective second harmonic generation (RSHG), allowing to probe the orientation distribution of surface islands over a large area. The island nucleation in the context of heterogeneous thin film growth is often complicated by the growth kinetics involved in the subsequent thermodynamics. We show how the evolution of sputtered Zn island nucleation on Si(111) by magnetron sputtering in a large area can be completely understood as a model system by combining RSHG, a 2D pole figure with synchrotron X-ray diffraction. Zn dots are then oxidized on the surfaces when exposed to the atmosphere as Zn/ZnO dots. Derived from the RSHG patterns of Zn dots at different growth times, the Zn dots grow following a unique transition from kinetic to thermodynamic control. Under kinetic-favoring growth, tiny Zn dots prefer arranging themselves with a tilted c-axis to the Si(111) substrate toward any of the sixfold in-plane Si<110> directions. Upon growth, the Zn dots subsequently evolve themselves to a metastable state with a smaller tilting angle toward selective <110> directions. As the Zn dots grow over a critical size, they become most thermodynamically stable with the c-axis vertical to the Si(111) substrate. For a system with large lattice mismatch, small volume dots take kinetic pathways with insignificant deviations in energy barriers.

Keywords: nucleation, Zn, second harmonic generation, pole figure, metastable state