(a) A cross-sectional BF TEM image of -irradiated GaN with an electron diffraction pattern shown in an inset. (b) A magnified BF TEM image showing dark contrast features in the amorphized GaN surface layer.
HRTEM images: (a) an area without dark contrast features showing an amorphous matrix containing some medium-range ordered structures (indicated by circles) and (b) an area with dark contrast features that are clearly characterized as nanocrystals.
NBEDS spectra from a dark contrast feature together with the adjacent area revealing that the dark contrast feature is a Ga nanocrystal.
[(a)–(c)] Typical NBED patterns obtained from several dark contrast features. Simulation results of electron diffractions: (d)  and (e)  for a Ga phase ( and space ) (f) , (g) , and (h)  for a Ga phase with the diamond structure ( and space ).
A cross-sectional BF TEM image of -irradiated GaN after thermal annealing at 973 K. Examples of dark contrast features associated with GaN nanocrystals are denoted by arrows.
Two HRTEM images from (a) an area without dark contrast features and (b) an area with dark contrast features, showing that recrystallization occurred during thermal annealing at 973 K.
Typical NBED patterns obtained from dark contrast areas in the annealed samples (a) and (b), together with the corresponding simulated electron diffraction patterns (c) and (d).
Low energy loss spectra obtained from the virgin, as-irradiated, and annealed samples using EELS, showing a volume expansion of 18.9% after Au-irradiation and 7.7% after subsequent annealing at 973 K.
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