Effects of temperature on the ion-induced bending of germanium and silicon nanowires

Abstract

Nanowires can be manipulated using an ion beam via a phenomenon known as ion-induced bending (IIB). While the mechanisms behind IIB are still the subject of debate, accumulation of point defects or amorphisation are often cited as possible driving mechanisms. Previous results in the literature on IIB of Ge and Si nanowires have shown that after irradiation the aligned nanowires are fully amorphous. Experiments were recently reported in which crystalline seeds were preserved in otherwise-amorphous ion-beam-bent Si nanowires which then facilitated solid-phase epitaxial growth (SPEG) during subsequent annealing. However, the ion-induced alignment of the nanowires was lost during the SPEG. In this work, in situ ion irradiations in a transmission electron microscope at 400°C and 500°C were performed on Ge and Si nanowires, respectively, to supress amorphisation and the build-up of point defects.Both the Ge and Si nanowires were found to bend during irradiation thus drawing into question the role of mechanisms based on damage accumulation under such conditions. These experiments demonstrate for the first time a simple way of realigning single-crystal Ge and Si nanowires via IIB whilst preserving their crystal structure.

Shape Modification of Germanium Nanowires during Ion Irradiation and Subsequent Solid‐Phase Epitaxial Growth

“…Furthermore, it was found that the straightening of the nanowires during annealing can be driven to a sufficient degree for complete recovery of the original straight shape observed prior to irradiation. As discussed in this work and previously, [19], [23]- [25] bending away from the ion beam could be caused by density changes of the ion-beam-facing side of the nanowire due to displacement damage (i.e. point defect accumulation and/or amorphisation).…”

“…[5], [6], [11], [12], [14] For instance, different SPEG recrystallisation activation energies and/or altered damage profiles have been reported. [12], [15] The phenomenon of ion-induced bending (IIB) has been observed where nanostructures such as cantilevers, [16], [17] nanotubes [18] or nanowires [19]- [25] suffer plastic deformation under irradiation.…”

“…[27]- [29] As IIB can be induced using either dopant or inert-gas ion beams, the bending can therefore occur in the processing of nanostructured semiconductors during both the pre-amorphisation step and the subsequent doping . [20], [25] As well as showing potential for future transistor technologies, IIB has also been used by Yoshida et al [30] to create waveguides by bending silicon wires using self-ion irradiation. [30] Furthermore, as straining of germanium nanowires is being investigated as a way of optically activating germanium, IIB might modify the optoelectronics properties of germanium as residual strain is expected to be present in bent nanowires .…”

“…Whilst our former work gave valuable insights into the mechanisms behind IIB, [25] the exact irradiation conditions which induce either bending direction at room temperature need to be determined if IIB is to be used as a predictable tool. Additionally, as damage accumulates during irradiation, semiconductors are routinely subject to an annealing step.…”

On the fabrication of micro- and nano-sized objects: the role of interstitial clusters

“…A rather recent application, which is the topic of this contribution, is the bending of free-standing thin structures such as films, nanotubes and nanowires [5][6][7][8][9][10][11]. The mechanisms controlling this phenomenon are not sufficiently clear in a quantitative way, and different ideas have been proposed but rather qualitatively [11][12][13].…”