Efficacy of single and double SiNx interlayers on defect reduction in GaN overlayers grown by organometallic vapor-phase epitaxy

We report on the growth of and evolution of defects in GaN epilayers having single- and double-layer SiNx nanoporous insertion layers. The SiNx was formed in situ in the growth chamber of an organometallic vapor-phase epitaxy system by simultaneous flow of diluted silane and ammonia. The GaN epilayers and SiNx interlayers were grown on 6H-SiC substrates using three different nucleation layers, namely, low-temperature GaN, high-temperature GaN, and high-temperature AlN nucleation layers. X-ray-diffraction rocking curves and cross-sectional and plan-view transmission electron microscope analyses indicated that a nanoporous SiNx layer can reduce the dislocations density in the GaN overgrown layer to ∼3×108cm−2 range; below this level the defect blocking effect of SiNx would saturate. Therefore the insertion of a second SiNx layer becomes much less effective in reducing dislocations, although it continues to reduce the point defects, as suggested by time-resolved photoluminescence measurements. The insertion of SiNx interlayers was found to improve significantly the mechanical strength of the GaN epilayers resulting in a much lower crack line density

Prior dengue virus exposure shapes T Cell immunity to Zika Virus in humans

While progress has been made in characterizing humoral immunity to Zika virus (ZIKV) in humans, little is known regarding the corresponding T cell responses to ZIKV. Here we investigate the kinetics and viral epitopes targeted by T cells responding to ZIKV and address the critical question of whether pre-existing dengue virus (DENV) T cell immunity modulates these responses. We find that memory T cell responses elicited by prior infection with DENV or vaccination with Tetravalent Dengue Attenuated Vaccines (TDLAV) recognize ZIKV-derived peptides. This cross-reactivity is explained by the sequence similarity of the two viruses, as the ZIKV peptides recognized by DENV-elicited memory T cells are identical or highly conserved in DENV and ZIKV. DENV exposure prior to ZIKV infection also influences the timing and magnitude of the T cell response. ZIKV-reactive T cells in the acute phase of infection are detected earlier and in greater magnitude in DENV-immune patients. Conversely, the frequency of ZIKV-reactive T cells continues to rise in the convalescent phase in DENV-naive donors, but declines in DENV pre-exposed donors, compatible with more efficient control of ZIKV replication and/or clearance of ZIKV antigen. The quality of responses is also influenced by previous DENV exposure, and ZIKV-specific CD8 T cells form DENV pre-exposed donors selectively up-regulated granzyme B and PD1, as compared to DENV-naïve donors. Finally, we discovered that ZIKV structural proteins (E, prM and C) are major targets of both the CD4 and CD8 T cell responses, whereas DENV T cell epitopes are found primarily in nonstructural proteins

Materials to Microsystems:Heterogeneous Integration Technologies

Microsystems technology is increasingly comprised of multi-function devices and materials. Heterogeneous integration technologies are being developed to enable the flexible integration of high-performance devices, materials,and circuits.In our approach,the processing required for integration,such as substrate removal and bonding,is coupled with pre-and post-processing to enable new device and materials configurations not achieved in standard fabrication sequences.Materials and device processes and designs must be considered differently in the context of integration.Herein,we examine these issues specifically for InAs-,InP-and GaN-based heterojunction electronic and optoelectronic device integration processes

New methodology for mechanical characterisation of solders for IC packaging

Advances in Electronic Packaging1551-55

Comparative reactivity studies of dppf-containing CpRuII and (C6Me6)RuII complexes towards different donor ligands (dppf=1,1′-bis(diphenylphosphino)ferrocene)

10.1016/j.jorganchem.2004.03.022Journal of Organometallic Chemistry689111978-1990JORC