  The interface of two solids in contact introduces a thermal boundary
resistance (TBR), which is challenging to measure from experiments. Besides, if
the interface is reactive, it can form an intermediate recrystallized or
amorphous region, and extra influencing phenomena are introduced. Reactive
force field Molecular Dynamics (ReaxFF MD) is used to study these interfacial
phenomena at the (non-)reactive interface. The non-reactive interfaces are
compared using a phenomenological theory (PT), predicting the temperature
discontinuity at the interface. By connecting ReaxFF MD and PT we confirm a
continuous temperature profile for the homogeneous non-reactive interface and a
temperature jump in case of the heterogeneous non-reactive interface. ReaxFF MD
is further used to understand the effect of chemical activity of two solids in
contact. The selected Si/SiO$_2$ materials showed that the TBR of the reacted
interface is two times larger than the non-reactive, going from $1.65\times
10^{-9}$ to $3.38\times 10^{-9}$ m$^2$K/W. This is linked to the formation of
an intermediate amorphous layer induced by heating, which remains stable when
the system is cooled again. This provides the possibility to design
multi-layered structures with a desired TBR.
