No abstract

The enhancement of deuterium retention was investigated for tungsten in the presence of both 2.8 MeV self-ion induced cascade damage and fuel hydrogen isotope plasma. Vacancy clustering in cascade damaged polycrystalline tungsten occurred due to deuterium irradiation and was observed near the grain boundary by using all-step transmission electron microscopy analysis. Analysis of the highest desorption temperature peak using thermal desorption spectroscopy supports reasonable evidence of defect clustering in the damaged polycrystalline tungsten. The defect clustering was neither observed on the damaged polycrystalline tungsten without deuterium irradiation nor on the damaged single-crystalline tungsten with deuterium irradiation. This result implies the synergetic role of deuterium and grain boundary on defect clustering. This study proposes a path for the defect transform from point defect to defect cluster, by the agglomeration between irradiated deuterium and cascade damage-induced defect. This agglomeration may induce more severe damage on the tungsten divertor at which the high fuel hydrogen ions, fast neutrons, and self-ions are irradiated simultaneously and it would increase the in-vessel tritium inventory.

Spatiotemporal dynamic simulations are carried out for the carrier-field interactions of photonic quantum ring lasers of three dimensional (3D) whispering cave modes (WCMs). We observe quantum wires-like carrier re-distributions naturally formed in the Rayleigh band region of the active quantum well plane. Apart from the regular two dimensional (2D) whispering gallery mode (WGM), the 3D WCM's major polarization state favors a strong carrier-photon coupling for the carriers in the Rayleigh band, such that the powerful transient coupling generates photonic quantum rings (PQRs), or concentric quantum rings with a half-wavelength pitch of imminently recombinant carriers, i.e., a photonic quantum corral effect. This feature is responsible for the low threshold currents and thermally stable spectra, which opens the way for easy optical mega-pixel ('Omega') chip fabrications.

InGaN/GaN multi-quantum well (MQW) is the leading structure for the next generation of lighting systems. Even though silicon and silicon carbide are used as substrates to grow GaN thin films, majority of the GaN are being grown onto sapphire substrates, whose techniques were well exercised for the past decades and had wide variation to reduce the strain induced by the lattice mismatch. Dislocations are unavoidable because of the large lattice mismatch between GaN and substrate, regardless of the substrates being used. Dislocations formed in InGaN/GaN MQW have different lattice periodicity and should deliver different emission characteristics compared to the perfect periodic lattice. Dislocations can be seen using transmission electron microscopy (TEM) and in order to link the emission characteristics with the dislocations, cathodoluminescence capability in TEM. Cathodoluminescence in transmission electron microscopy (CL-TEM) delivers superior performance to the CL-SEM because of its higher spatial resolution with short diffusion length and the capability of one-to-one mapping of the interested microstructural area with point-luminescence and the internal microstructure. In this study, luminescence characteristics were investigated using CL-TEM to identify the shift of the emission wavelength with different types of dislocations. Dislocations revealed short wavelength shift in the region with QW and threading dislocations. No emission was observed with the edge dislocations, but the screw dislocations either close to the surface or close to the substrate delivered shift of wavelength toward the higher energy side. Plane-view TEM revealed the fluctuations of the wavelengths, which gave low and high band gap area and local minima might be the contribution of the high efficiency of InGaN/GaN light emitting system.

This work has investigated the microstructure characteristics of high-quality alpha-Ga2O3 thin film grown on the Al2O3 single crystal substrate membrane. Hetero-epitaxial alpha Ga2O3 crystals reveal the formation of a three-fold symmetry at the initial stage of the growth by the oxygen template provided by the Al2O3. Inversion domains are found, and they have a 180° inverted configuration from the surroundings. These IDs lead to extra diffraction spots when observed along [110] and [010].