Disentangling phonon channels in nanoscale heat transport

Phonon surface scattering has been at the core of heat transport engineering in nanoscale devices. Herein, we demonstrate that this phonon pathway can be the sole mechanism only below a critical, size-dependent temperature. Above this temperature, the lattice phonon scattering coexists along with surface effects. By tailoring the mass disorder at the atomic level, the lattice dynamics in nanowires was artificially controlled without affecting morphology, crystallinity, chemical composition, or electronic properties, thus allowing the mapping of the temperature-thermal conductivity-diameter triple parameter space. This led to the identification of the critical temperature below which the effects of lattice mass disorder are suppressed to an extent that phonon transport becomes governed entirely by the surface. This behavior is discussed based on a modified Landauer-Datta-Lundstrom near-equilibrium transport model. Besides disentangling the main phonon scattering mechanisms, the established framework also provides the necessary input to further advance the design and modeling of heat transport in semiconductor nanoscale systems

Spatially Resolved Correlation of Active and Total Doping Concentrations in VLS Grown Nanowires

Controlling axial and radial dopant profiles in nanowires is of utmost importance for NW-based devices, as the formation of tightly controlled electrical junctions is crucial for optimization of device performance. Recently, inhomogeneous dopant profiles have been observed in vapor–liquid–solid grown nanowires, but the underlying mechanisms that produce these inhomogeneities have not been completely characterized. In this work, P-doping profiles of axially modulation-doped Si nanowires were studied using nanoprobe scanning Auger microscopy and Kelvin probe force microscopy in order to distinguish between vapor–liquid–solid doping and the vapor–solid doping. We find that both mechanisms result in radially inhomogeneous doping, specifically, a lightly doped core surrounded by a heavily doped shell structure. Careful design of dopant modulation enables the contributions of the two mechanisms to be distinguished, revealing a surprisingly strong reservoir effect that significantly broadens the axial doping junctions