Figure 1

(a) A nanopipe that is $\sim 45\mathrm{n}\mathrm{m}$ in diameter in MOCVD grown GaN. This open core screw dislocation is empty in the middle (dark area). (b) Higher magnification image of one portion of one side of the nanopipe. The image has been marked with five positions where the probe was placed for EELS analysis. (c) The EELS spectra from the five positions show that as the probe is placed closer to the edge of the nanopipe, the nitrogen signal decreases while the oxygen signal increases, extending $\sim 20$ monolayers away from the edge.Reuse & Permissions

Figure 2

(a) Image of a filled nanopipe, or filled core, that is $\sim 90\AA$ in diameter. The positions for the EELS analysis are marked on the image. (b) The spectra from position 1 do not show a quantifiable oxygen signal above the noise, but the signal from positions 2 and 3 do show an oxygen edge, indicating that oxygen is still bonded at the edges of the nanopipe. (c) A closer look at the background subtracted and smoothed oxygen $K$ edge shows the differences in oxygen concentration from the three areas. Position 1 has no oxygen, as can be seen from the fluctuation of signal about the zero line (dotted line). Position 2 shows oxygen is present although the peak is not well defined, and finally position 3 has the highest concentration. The difference in intensity is caused by spectrum 2 sampling a face of the pinhole and spectrum 3 sampling purely an edge. (d) The fine structure of the N $K$ edge shows that position 1 has the signature of a screw dislocation, while position 2 appears to be bulklike. However, the fine structure at position 3 seems not to be bulklike, and a prepeak has appeared, both as a result of oxygen at this position. The prepeak indicates that oxygen is responsible for the formation of localized states in the band gap.Reuse & Permissions

Figure 3

(a) $Z$-contrast image of a full core screw dislocation. (b) Inverse Fourier transform of the $Z$-contrast image to see the strain at the center of the core (brighter region). (c) EELS spectra were acquired from this central bright position and are shown plotted against a simulation. The inset shows that there is no oxygen present in this closed core.Reuse & Permissions