Novel Heterostructured Ge Nanowires Based on Polytype Transformation

Abstract

We report on a strain-induced phase transformation in Ge nanowires under external shear stresses. The resulted polytype heterostructure may have great potential for photonics and thermoelectric applications. ⟨111⟩-oriented Ge nanowires with standard diamond structure (3C) undergo a phase transformation toward the hexagonal diamond phase referred as the 2H-allotrope. The phase transformation occurs heterogeneously on shear bands along the length of the nanowire. The structure meets the common phenomenological criteria of a martensitic phase transformation. This point is discussed to initiate an on going debate on the transformation mechanisms. The process results in unprecedented quasiperiodic heterostructures 3C/2H along the Ge nanowire. The thermal stability of those 2H domains is also studied under annealing up to 650 °C by in situ TEM.

Phonon transmission at Si/Ge and polytypic Ge interfaces using full-band mismatch based models

“…Among the novel nanostructures promising for thermal engineering, polytype nanowires that can be fabricated in both Silicon [12] and Germanium [13] are appealing as they are compatible with mature technology developed for decades in microelectronic industry. Indeed, in these structures, nano-clusters crystallized in the 2H phase, a phase that cannot be stabilized in a bulk form under normal conditions, can be embedded in a standard 3C phase background.…”

“…Hence, such polytype interfaces should be a promising option to reduce the thermal conductance, in particular in systems with many interfaces as the nanowires shown in Ref. [13], with a good potential for thermoelectric applications.…”

Comprehensive analysis of nanodiamond evidence relating to the Younger Dryas Impact Hypothesis

“…While such lamellae should not be considered a 2H hexagonal phase, there is sufficient evidence that well‐ordered … ( A b )( B a )… stacking of tetrahedral planes (Figs and ) occurs at scales up to, at least, tens of nanometers for C (e.g. see Chen et al , ; Daulton et al , ; Lifshitz et al , ; Kulnitskiy et al , ; Kraus et al , ), Si (Dahmen et al , ; Cerva, ; Algra et al , ; Hauge et al , ), Ge (Xiao and Pirouz, ; Vincent et al , ) and SiC (Daulton et al , ). Therefore, lonsdaleite, as well as other 2H hexagonal‐diamond isostructural phases, do exist on at least this spatial scale.…”

Neu zusammengesetzt: Gruppe‐14‐Elemente als Halbleiter

“…Eine martensitische Phasenumwandlung — also ein Verschieben entlang von Gleitebenen in einer Raumrichtung — wandelt kleine Teilbereiche in eine hexagonale Phase um. Diese hexagonalen Bereiche bleiben voneinander durch kubische Segmente getrennt 4,5. Es ergibt sich jedoch kein praktischer Nutzen aus dieser Phasenumwandlung, da sie auf kleine Bereiche der Nanodrähte begrenzt ist.…”