Crystallography at the nanoscale: planar defects in ZnO nanospikes.

Niklas Wolff,Rainer Adelung,Lorenz Kienle,Viktor Hrkac,Yogendra K Mishra,David C Johnson,Jeffrey J Ditto,Viola Duppel

doi:10.1107/s1600576719009415

Niklas Wolff, Rainer Adelung + Show 6 more

Open Access

https://doi.org/10.1107/s1600576719009415

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Abstract

The examination of anisotropic nanostructures, such as wires, platelets or spikes, inside a transmission electron microscope is normally performed only in plan view. However, intrinsic defects such as growth twin interfaces could occasionally be concealed from direct observation for geometric reasons, leading to superposition. This article presents the shadow-focused ion-beam technique to prepare multiple electron-beam-transparent cross-section specimens of ZnO nanospikes, via a procedure which could be readily extended to other anisotropic structures. In contrast with plan-view data of the same nanospikes, here the viewing direction allows the examination of defects without superposition. By this method, the coexistence of two twin configurations inside the wurtzite-type structure is observed, namely and , which were not identified during the plan-view observations owing to superposition of the domains. The defect arrangement could be the result of coalescence twinning of crystalline nuclei formed on the partially molten Zn substrate during the flame-transport synthesis. Three-dimensional defect models of the twin interface structures have been derived and are correlated with the plan-view investigations by simulation.

Highlights

Nanostructured zinc oxide (ZnO) semiconductors have attracted much research interest over recent decades owing to their diversity of chemical and physical properties (Ozgur et al, 2005; Meyer et al, 2004; Pearton, 2005; Yang et al, 2002; Djurisic & Leung, 2006; Li et al, 2008)
With a direct bandgap of 3.37 eV and an exciton binding energy of 60 meV at room temperature, ZnO nanostructures are promoted for applications in the fields of electronic materials (Jebril et al, 2010; Gupta, 1990), opto-electronics (Keis et al, 2002; Konenkamp et al, 2000), sensor devices (Liu et al, 2016; Chai et al, 2012; Lupan et al, 2008) and field emitters (Wang et al, 2005; Li et al, 2004), among other sensor systems based on piezotronics (Wang, 2007)
Many of these reports relied on anisotropic ZnO nanostructures, e.g. nanospikes, which can be synthesized by manifold approaches (Singh, 2010), one of which is by flame transport (Mishra et al, 2013)

Summary

Introduction

Nanostructured zinc oxide (ZnO) semiconductors have attracted much research interest over recent decades owing to their diversity of chemical and physical properties (Ozgur et al, 2005; Meyer et al, 2004; Pearton, 2005; Yang et al, 2002; Djurisic & Leung, 2006; Li et al, 2008). Site-specific sectioning along selective crystal orientations is critical for structure–property investigations of anisotropic nanostructures including buried defects (Hrkac et al, 2013), and strain and chemical integrity at interfaces (Abes et al, 2013; Hrkac et al, 2013; Huang et al, 2014) In preparing these sections, filler materials, such as epoxy resins (Muller & Krumeich, 2000; Lenrick et al, 2014), platinum (Giannuzzi & Stevie, 1999), carbon (Leer et al, 2009; Baram & Kaplan, 2008) or aluminium oxide (Stiegler et al, 2012), are often used as stabilizing matrix materials or protective coatings against ion bombardment. This enabled the direct observation and identification of two types of twin boundary in the ZnO nanospikes which were not observed during planview examination

Experimental

Specimen preparation

Real-structure analysis

Structure modelling

Simulation

Conclusions