Phonon Engineering in Isotopically Disordered Silicon Nanowires

Abstract

The introduction of stable isotopes in the fabrication of semiconductor nanowires provides an additional degree of freedom to manipulate their basic properties, design an entirely new class of devices, and highlight subtle but important nanoscale and quantum phenomena. With this perspective, we report on phonon engineering in metal-catalyzed silicon nanowires with tailor-made isotopic compositions grown using isotopically enriched silane precursors (28)SiH4, (29)SiH4, and (30)SiH4 with purity better than 99.9%. More specifically, isotopically mixed nanowires (28)Si(x)(30)Si(1-x) with a composition close to the highest mass disorder (x ∼ 0.5) were investigated. The effect of mass disorder on the phonon behavior was elucidated and compared to that in isotopically pure (29)Si nanowires having a similar reduced mass. We found that the disorder-induced enhancement in phonon scattering in isotopically mixed nanowires is unexpectedly much more significant than in bulk crystals of close isotopic compositions. This effect is explained by a nonuniform distribution of (28)Si and (30)Si isotopes in the grown isotopically mixed nanowires with local compositions ranging from x = ∼0.25 to 0.70. Moreover, we also observed that upon heating, phonons in (28)Si(x)(30)Si(1-x) nanowires behave remarkably differently from those in (29)Si nanowires suggesting a reduced thermal conductivity induced by mass disorder. Using Raman nanothermometry, we found that the thermal conductivity of isotopically mixed (28)Si(x)(30)Si(1-x) nanowires is ∼30% lower than that of isotopically pure (29)Si nanowires in agreement with theoretical predictions.

Tuning thermal transport in Si nanowires by isotope engineering

“…This is the same isotope blend used in recent experiments. 18 Similar to other molecular dynamics techniques, 25 a converged estimate of the thermal conductivity by means of the approach-to-equilibrium methodology employed here requires very large simulation cells, which are often beyond current computational capabilities. Not only these cells must be large enough to fit all the long wavelength phonons whose contribution to thermal transport is not negligible; they must also account properly for the anharmonic phonon-phonon scattering, i.e.…”

Measurement and analysis of thermal conductivity of isotopically controlled silicon layers by time‐resolved X‐ray scattering

“…A low thermal conductivity due to nanostructuring was reported by Venkatasubramanian et al for composite multilayered structures. Other nanostructures such as nanowires , nanopowders , or nanoparticles investigated in recent years confirm low thermal conductivities and thus highlight their advanced properties as thermoelectric materials.…”

Defining the Potential of Nanoscale Re‐Os Isotope Systematics Using Atom Probe Microscopy

“…, Mukherjee et al . , , Ironside et al . ), but only a few have attempted to demonstrate that these fractions are quantitative (i.e., Stadermann et al .…”

“…The mass resolving power of APM suggests that isotopic analysis of most materials is possible. Several papers have reported isotopic fractions using APM (i.e., Shimizu et al 2009, Thuvander et al 2011, Mukherjee et al 2015, 2016, Ironside et al 2017), but only a few have attempted to demonstrate that these fractions are quantitative (i.e., Stadermann et al 2011, Heck et al 2014, Valley et al 2014, Parman et al 2015, Peterman et al 2016. Constraints on the observable size of isotopic variability using APM have not yet been established.…”