Evaluation of Dislocation Mobility in Wurtzite Semiconductors

ABSTRACTThe indentation hardness and yield strength of various wurtzite-structured semiconductors, such as AlN, GaN, InN, and ZnO, were summarized together with those of 6H-SiC. From analysis of the data, the activation energy for motion of an individual dislocation was deduced to be 2–2.7 and 0.7–1.2 eV in GaN and ZnO, respectively, and the evaluated activation energy for dislocation motion showed a dependence on the dislocation energy in the minimum length. The results were evaluated in terms of homology and the basic mechanism of the dislocation process. Dislocation motion is thought to be primarily controlled by the atomic bonding character of the semiconductors.

ENHANCED TENSILE DUCTILITY IN AN ELECTRODEPOSITED CU WITH NANO-SIZED GROWTH TWINS

A fully dense electrodeposited microcrystalline copper with nano-scale twins was synthesized by electrodeposition. The microstructure of this copper was analyzed X-ray diffractometer (XRD) and by transmission electron microscopy (TEM). The grains of mean size about 2mm were divided by high density of growth twins with mean lamellar thickness of about 90 nm. Tensile tests at different strain rates and room temperature showed that the strength increased from 379 MPa to 458 MPa with strain rate increasing from 10-5 s-1 to 0.1 s-1. The elongations to fracture were in the range of 13.6~15.5%. So this Cu has good combination of strength and ductility. The strengths are much higher than that determined by Hall-Petch relation with the same grain size, which means that twin boundaries are effective in blocking dislocation motion. The strain rate sensitivity and activation volume estimated from the flow stress versus strain curves was 0.016 and 84 b3~69b3, respectively. Such a large activation volume indicates that the deformation of this copper was controlled by dislocation process.

SEL1L, the homologue of yeast Hrd3p, is involved in protein dislocation from the mammalian ER

Protein quality control in the endoplasmic reticulum (ER) involves recognition of misfolded proteins and dislocation from the ER lumen into the cytosol, followed by proteasomal degradation. Viruses have co-opted this pathway to destroy proteins that are crucial for host defense. Examination of dislocation of class I major histocompatibility complex (MHC) heavy chains (HCs) catalyzed by the human cytomegalovirus (HCMV) immunoevasin US11 uncovered a conserved complex of the mammalian dislocation machinery. We analyze the contributions of a novel complex member, SEL1L, mammalian homologue of yHrd3p, to the dislocation process. Perturbation of SEL1L function discriminates between the dislocation pathways used by US11 and US2, which is a second HCMV protein that catalyzes dislocation of class I MHC HCs. Furthermore, reduction of the level of SEL1L by small hairpin RNA (shRNA) inhibits the degradation of a misfolded ribophorin fragment (RI332) independently of the presence of viral accessories. These results allow us to place SEL1L in the broader context of glycoprotein degradation, and imply the existence of multiple independent modes of extraction of misfolded substrates from the mammalian ER.