Formation of Three-Dimensional Silicon Mounds on the Si(111) 7 ×7 Surface Using the Tip of a Scanning Tunneling Microscope

Truncated triangular silicon pyramids are fabricated one by one on the Si(111) 7 ×7 surface in the temperature range from 400°C to 500°C. Two types of three-dimensional (3D) silicon mounds are fabricated with a mirror symmetry against the [101] direction. One type consists of normal stacking mounds with {311} and {221} on the side facets and a (111) on the top surface. The other type consists of silicon mounds with a stacking fault at the interface between the silicon mounds and the substrate surface, which have {311} facets, {331} facets and a (111) facet. Normal stacking mounds are produced with a probability of 75%. Silicon mounds with a stacking fault are produced with a probability of 25%. The difference in the formation energy between normal stacking mounds and silicon mounds with a stacking fault is about 0.07 eV per 1 ×1 unit cell at 500°C. Silicon mounds are fabricated with large tunneling currents and sample bias voltages near 0 V. During the production of silicon mounds, the scanning tunneling microscope (STM) tip moves away from the substrate surface by about 26 nm. The production rates of silicon mounds are 120 ±10 s-1 at 440°C, 220 ±20 s-1 at 465°C and 570 ±80 s-1 at 485°C. The activation energy required for the production of silicon mounds is 1.3 ±0.1 eV and the pre-exponential factor is 4 ×1011±1 s-1.