Ordered CaSi 2 Microwall Arrays on Si Substrates Induced by the Kirkendall Effect

We have specified the synthetic conditions to obtain one‐directionally ordered CaSi 2 microwall arrays vertically grown on a Si substrate. Our basic concept is based on the utilization of the Kirkendall effect for reactive deposition epitaxy (RDE). We found for the first time that: 1) a much larger Ca vapor supply on the Si substrate than the conventional RDE, 2) the adoption of a two‐step heating process, and 3) the selection of the crystal axis of the Si surface are the keys to control the microstructures of CaSi 2 on the Si substrate. The CaSi phase was first formed on Si, then the CaSi 2 phase was formed at the CaSi/Si interface. Based on the Kirkendall effect, the interdiffusion of Ca and Si was enhanced in the vertical direction rather than in the parallel direction to the Si surface. CaSi 2 tends to grow along four equivalent Si{111} planes, however, the specific orientation of the Si surface resulted in CaSi 2 microwalls grown along its Si(11 1 ‾ ) plane, the only plane directing nearly vertical to the surface among the Si{111} planes. These results suggest that the Kirkendall effect under asymmetric growth of target materials would be a rational strategy to obtain their ordered microstructures.