  Phonon surface scattering has been at the core of heat transport engineering
in nanoscale structures and devices. Herein, we demonstrate that this phonon
pathway can be the sole mechanism only below a characteristic, size-dependent
temperature. Above this temperature, the lattice phonon scattering co-exist
along with surface effects. By artificially controlling mass disorder and
lattice dynamics at the atomic-level in nanowires without affecting morphology,
crystallinity, chemical composition, and electronic properties, the
temperature-thermal conductivity-diameter triple parameter space is mapped, and
the main phonon scattering mechanisms are disentangled. This led to the
identification of the critical temperature at which the effect of lattice
mass-disorder on thermal conductivity is suppressed to an extent that phonon
transport becomes governed entirely by the surface. This behavior is discussed
based on Landauer-Dutta-Lundstrom near-equilibrium transport model. The
established framework provides the necessary input to further advance the
design and modelling of phonon and heat transport in semiconductor nanoscale
systems.
