$Si$-capping of $Ge$ nanohuts on $Si(001)$ analyzed by scanning tunneling microscopy and the finite element method

$Ge$ hut nanocrystals were grown on an $Si(001)$ surface and $Si$-capped by gas-source molecular-beam epitaxy. Growth and capping at $430°C$ were observed in real time by scanning tunneling microscopy, and analyzed by the finite element method. Observations made here of three-dimensional $Si$-cap growth (in the shape of pyramids and huts) on $Ge$⁠, similar to the $Ge$ growth on $Si(001)$⁠, are consistent with energetic arguments based on finite elements in the framework of linear elasticity. These observations are in contrast with the higher-temperature behavior, where $Si$ preferentially sticks to the $Ge$ nanocrystal facets, causing them to develop large flat (001) tops and a reduced height-base ratio.