Figure 1

Experimental (top) and simulated (bottom) CBED patterns for 30-nm-thick a-NWs sample at 200 kV. The growth direction is represented by the white arrow.Reuse & Permissions

Figure 2

Argand diagram illustrating the breakdown of Friedel's law: a difference in the magnitude of the two total structure factor $\left|F\left(hkl\right)\right|$ and $|F\left(\overline{hkl}\right)|$ moduli (thus in the diffracted intensity) occurs for non-centrosymmetrical systems when the absorption term $F_{\mathrm{A}}^{\prime \prime }$ of the resonant dispersive corrections is involved. $F_{\mathrm{T}}$ is the structure factor that includes the Thomson scattering of all atoms and the anomalous scattering of all nonresonant atoms (i.e., $F_{\mathrm{T}}=F_{\mathrm{A}}+F_{\mathrm{N}}$ where $F_{\mathrm{A}}$ corresponds to the Thomson scattering of all resonant atoms, and $F_{\mathrm{N}}$ gathers both Thomson and anomalous contributions of nonresonant atoms (nitrogen atoms in this study). $F_{\mathrm{A}}^{\prime }\left(hkl\right)+i{F}_{\mathrm{A}}^{\prime \prime }\left(hkl\right)$ is the complex anomalous scattering of all resonant atoms (Ga atoms in the present study), $F_{\mathrm{A}}^{\prime }\left(hkl\right)$ and $F_{\mathrm{A}}^{\prime \prime }\left(hkl\right)$ are related to dispersion and absorption, respectively.Reuse & Permissions

Figure 3

Evolution of the intensity of the $\left(11\overline{2}2\right)$ and $\left(\overline{1}\overline{1}2\overline{2}\right)$ pair with the energy around the Ga K-edge. Because of the non-centrosymmetrical characteristic of the wurtzite GaN structure, a discrepancy in intensity is clearly observed. In this way, a-NWs and u-NWs are identified as N-polar and Ga-polar, respectively.Reuse & Permissions

Figure 4

Side-view scanning electron micrographs (SEM) of NWs on their original substrate (a, b, e, f) and SEM in transmission images of GaN NWs containing a thin AlN insertion near their top (c, d). The flat top surface of N-polar NWs grown on bare Si(111) (a, c) is etched into a pencil-like shape after being dipped for 10 minutes in a solution saturated with KOH (b, d). The Ga-polar side (i.e., the bottom of N-polar NWs) (c) remains flat after being plunged into the same bath (d). GaN NWs grown on a thin AlN buffer layer (e) are also etched by KOH (f), a signature of their N-polar character.Reuse & Permissions