Dislocations that cause a reverse leakage current in vertical p-n diodes on a GaN free-standing substrate were investigated. Under a high reverse bias, dot-like leakage spots were observed using an emission microscope. Subsequent cathodoluminescence (CL) observations revealed that the leakage spots coincided with part of the CL dark spots, indicating that some types of dislocation cause reverse leakage. When etch pits were formed on the dislocations by KOH etching, three sizes of etch pits were obtained (large, medium, and small). Among these etch pits, only the medium pits coincided with leakage spots. Additionally, transmission electron microscopy observations revealed that pure screw dislocations are present under the leakage spots. The results revealed that 1c pure screw dislocations are related to the reverse leakage in vertical p-n diodes.

Mutations in isocitrate dehydrogenase (IDH), a key enzyme in the tricarboxylic acid cycle, have recently been found in ~75% glioma and ~20% acute myeloid leukemia. Different from the wild-type enzyme, mutant IDH1 catalyzes the reduction of α-ketoglutaric acid to D-2-hydroxyglutaric acid. Strong evidence has shown mutant IDH1 represents a novel target for this type of cancer. We found two 1-hydroxypyridin-2-one compounds that are potent inhibitors of R132H and R132C IDH1 mutants with Ki values as low as 120 nM. These compounds exhibit >60-fold selectivity against wild-type IDH1 and can inhibit the production of D-2-hydroxyglutaric acid in IDH1 mutated cells, representing novel chemical probes for cancer biology studies. We also report the first inhibitor-bound crystal structures of IDH1(R132H), showing these inhibitors have H-bond, electrostatic and hydrophobic interactions with the mutant enzyme. Comparison with the substrate-bound IDH1 structures revealed the structural basis for the high enzyme selectivity of these compounds.

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The expansion behavior of a single Shockley stacking fault (SSSF) originating from a basal plane dislocation in a 4H-SiC epitaxial layer on the (112¯0) a-plane under electron beam (EB) (//[112¯0]) irradiation was observed. The width of the SSSF was proportional to the EB current. EB irradiation at a fixed spot outside an SSSF can expand the SSSF as effectively as direct SSSF irradiation. It was found that the selective excitation of an SSSF and/or a Si-core partial dislocation (PD) is possible by appropriately setting the EB irradiation position because the cathodoluminescence spectrum varies with the irradiation position around an SSSF. The rate of SSSF expansion upon the indirect excitation of a Si-core PD is much larger than that upon direct SSSF excitation. However, the expansion rate under both indirect SSSF excitation and indirect Si-core PD excitation is smaller than that under indirect Si-core excitation. The C-core PD became mobile after supplying a threshold number of electron-hole pairs.

In considering a novel function in ferromagnetic tunnel junctions consisting of ferromagnet (FM)/barrier/FM junctions, we have theoretically investigated the multiple-valued (or multi-level) cell property, which is in principle realized by sensing the conductances of four states recorded with magnetization configurations of two FMs; that is, (up, up), (up, down), (down, up), (down, down). To obtain such 4-valued conductances, we propose FM1/spin-polarized barrier/FM2 junctions, where FM1 and FM2 are different ferromagnets, and the barrier has spin dependence. The proposed idea is applied to the case of the barrier having localized spins. Assuming that all the localized spins are pinned parallel to the magnetization axes of FM1 and FM2, 4-valued conductances are explicitly obtained for the case of many localized spins. Furthermore, objectives for an ideal spin-polarized barrier are discussed.

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Ion-conductive polymers having a well-defined phase-separated structure show the potential application of separating mono- and bivalent ion separation. In this work, three side-chain-type poly­(arylene ether sulfone)-based anion exchange membranes (AEMs) have been fabricated to investigate the effect of the stiffness of the polymer backbone within AEMs on the Cl–/NO3 – and Cl–/SO4 2– separation performance. Our investigations via small-angle X-ray scattering (SAXS), positron annihilation, and differential scanning calorimetry (DSC) demonstrate that the as-prepared AEM with a rigid benzimidazole structure in the backbone bears subnanometer ion channels resulting from the arrangement of the rigid polymer backbone. In particular, SAXS results demonstrate that the rigid benzimidazole-containing AEM in the wet state has an ion cluster size of 0.548 nm, which is smaller than that of an AEM with alkyl segments in the backbone (0.760 nm). Thus, in the electrodialysis (ED) process, the former exhibits a superior capacity of separating Cl–/SO4 2– ions relative to latter. Nevertheless, the benzimidazole-containing AEM shows an inability to separate the Cl–/NO3 – ions, which is possibly due to the similar ion size of the two. The higher rotational energy barrier (4.3 × 10–3 Hartree) of benzimidazole units and the smaller polymer matrix free-volume (0.636%) in the AEM significantly contribute to the construction of smaller ion channels. As a result, it is believed that the rigid benzimidazole structure of this kind is a benefit to the construction of stable subnanometer ion channels in the AEM that can selectively separate ions with different sizes.

Threading dislocations have been studied by means of etch pit method using molten KOH+Na 2 O 2 solution, cathodoluminescence and transmission electron microscopy. We focus on the geometrical features of etch pits and their correlation with the recombination behavior at the dislocations. Four types of etch pits can be recognized after etching according to their sizes and depths, among which the middle-sized etch pits correspond to dislocations with the strongest non-radiative recombination. TEM observation has confirmed that dislocation beneath the large-sized etch pit is a mixed-type dislocation having both c-and a-component.