Ion beam-induced bending of TiO2 nanowires with bead-like and prismatic shapes.

Zhina Razaghi,Ming-Hui Lin,Guo-Zhen Zhu,Dong Yue Xie

doi:10.1039/d1ra09122k

Abstract

Ion beam irradiation is a promising method to manipulate the composition and shape of nanowires. It causes the formation of crystal defects like vacancies and dislocations, and consequently, a volume expansion within the irradiated region, giving rise to the nanowire bending. The bending effect has been extensively discussed within nanowires with different diameters under ion beams with varying energies and ion fluences. However, the behaviors of nanowires with complicated shapes, which may have non-uniform irradiated regions due to the changing angle of incidence and shadowing effect, have remained largely unknown. Herein, the structural changes and bending of TiO2 nanowires with both bead-like and prismatic shapes are investigated under a Ga+ ion beam. The multi-faceted morphology, and consequently, varying angles of incidence, result in inhomogeneous irradiation and volume expansion. As a result, significant bending is only observed in prismatic nanowires. Since irradiation is confined within the half of nanowires facing the ion beam, the bending of nanowires is reversible by changing the direction of the ion beam. In order to provide insights into the tailoring composition and morphology of nanowires, we anticipate that this finding can establish the beam analog at the nanoscale, the bending of which can be tuned by ion irradiation.

Highlights

We investigated the in uence of Ga+ ion beam irradiation on TiO2 nanowires with both bead-like and prismatic shapes
In order to investigate the behavior of TiO2 nanowires under ion beam irradiation, TEScan Focused Ion Beam (FIB)-SEM was applied to observe the morphology changes of nanowires under Ga+ ion irradiation at 30 keV
The ion beam results in an inhomogeneous deformation, agreeing the computed results from Monte Carlo simulation. Such ion irradiation causes the volume expansion, which can be released within bead-like nanowires

Summary

Introduction

Nanowires with one-dimensional structures and high surfaceto-volume ratios have gained much attention in electronic, catalytic, and sensing applications.[1,2] Semiconductor nanowires used in solar cells signi cantly reduce re ection, enhance light trapping, improve electron transport and raise device efficiency, thereby prevailing over their thin- lm and nanoparticle counterparts.[3,4] Originating from their electronic band positions, metal-oxide nanowires hold promise as the favorable base for photoconversion processes, among which rutile titanium oxide (TiO2) is a representative candidate for solar cells and lithium-ion batteries applications.[5,6]. The possible mechanism is that the formation and movement of structural defects such as vacancies and interstitials under ion beams cause local density and volume changes,[24] instead of amorphization in nanowires. Rajput et al.[25] have discussed that polycrystalline Si nanowires bend towards the incident direction of a 16 keV Ga+ ion beam They reported that compressive stress, induced in the irradiated side of the nanowire caused by sputtering, leads to the nanowire bending towards the ion beam. Ion beams with low energies can lead to changes in bending directions, which is determined by the irradiation depth regarding the diameter of the nanowire.[17,26] For instance, Borchel et al.[27] have investigated the bending behavior of GaAs nanowires under the S, Ar, and Xe ions with 20 keV and 100 keV energies. Our results provide insights in controlling the morphology of nanowires by ion irradiation and establish a nanoscale beam model for exploiting the bending behavior of nanoscale beams

Nanowire growth

Ion beam irradiation

Results and discussion

Conclusion