The dissociation of (a+c) misfit dislocations at the InGaN/GaN interface.

In hexagonal materials, (a+c) dislocations are typically observed to dissociate into partial dislocations. Edge (a+c) dislocations are introduced into (0001) nitride semiconductor layers by the process of plastic relaxation. As there is an increasing interest in obtaining relaxed InGaN buffer layers for the deposition of high In content structures, the study of the dissociation mechanism of misfit (a+c) dislocations laying at the InGaN/GaN interface is then crucial for understanding their nucleation and glide mechanisms. In the case of the presented plastically relaxed InGaN layers deposited on GaN substrates, we observe a trigonal network of (a+c) dislocations extending at the interface with a rotation of 3° from <1 1 ¯ $\bar 1$ 00> directions. High-resolution microscopy studies show that these dislocations are dissociated into two Frank-Shockley 1/6<2 2 ¯ $\bar 2$ 03> partial dislocations with the I1 BSF spreading between them. Atomistic simulations of a dissociated edge (a+c) dislocation revealed a 3/5-atom ring structure for the cores of both partial dislocations. The observed separation between two partial dislocations must result from the climb of at least one of the dislocations during the dissociation process, possibly induced by the mismatch stress in the InGaN layer.

Tuning heterogeneous ion-radiation damage by composition in NixFe1-x binary single crystals.

Radiation-induced heterogeneous damage is the single largest source of failures seen in structural components in nuclear power reactors. Single crystal materials without grain boundaries, show considerable promise for overcoming this problem. In this work, such heterogeneous damage was further overcome in NixFe1-x single crystal alloys via a simple strategy of fine-tuning the composition. [001] NixFe1-x (x = 0, 0.38 and 0.62 at%) single crystals prepared using the Bridgman method were irradiated over a wide fluence range (4 × 1013 to 4 × 1015 ions per cm2). The irradiation-induced defect evolution was studied using Rutherford backscattering/channeling spectrometry, Monte Carlo simulations, transmission electron microscopy and nanoindentation. The results indicate an increased radiation tolerance of Ni0.38Fe0.62 compared to pure Ni and Ni0.62Fe0.38. The structural analysis performed by transmission electron microscopy revealed that defects tend to agglomerate at one place in Ni and Ni0.62Fe0.38, while in Ni0.38Fe0.62 no defect accumulation zone (characteristic damage peak) has been captured either at low or high fluence. Moreover, we found that the hardness change with the increase of Fe content is due to different arrangements of Fe atoms in the crystal structure, which influences the obtained mechanical properties of NixFe1-x in the pristine state and after ion implantation.