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 28SiH4, 29SiH4, and 30SiH4 with purity better than 99.9%. More specifically, isotopically mixed nanowires 28Six30Si1-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 29Si 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 28Si and 30Si 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 28Six30Si1-x nanowires behave remarkably differently from those in 29Si nanowires suggesting a reduced thermal conductivity induced by mass disorder. Using Raman nanothermometry, we found that the thermal conductivity of isotopically mixed 28Six30Si1-x nanowires is ∼30% lower than that of isotopically pure 29Si nanowires in agreement with theoretical predictions. (Figure Presented).
ASJC Scopus subject areas
- 化学 (全般)