MICROSTRUCTURES OF UNDERCOOLED SI

Molten Si was allowed to solidify isothermally at initial bulk underco olings Delta T from 5.7 to 157 K. It was found that in addition to the [211] twin dendrites two novel dendrites were found: the [110] twin a nd the [100] twin free dendrite. The [110] twin dendrite has multiple twin planes, and the orientation of the twin plane is {111}. These dif ferent dendrites exist at different initial bulk undercoolings, and th e dendritic transition temperatures for [110] to [211] and [211] to [1 00] are Delta T=22 and 68 K, respectively. The dendritic transitions f or [110] to [211] and [211] to [100] are edgewise to edgewise and edge wise to continuous normal growth, respectively.