The crystal structure of LnFeAsO 1- y (Ln = La, Nd) has been studied by the powder neutron diffraction technique. superconducting phase diagram NdFeAsO is established as a function oxygen content which determined Rietveld refinement. small As–Fe bond length suggests that As and Fe atoms are connected covalently. FeAs 4 -tetrahedrons transform toward regular shape with increasing deficiency. Superconducting transition temperatures seem to attain maximum values for -tetrahedrons.

The growth of Shockley type stacking faults in p-i-n diodes fabricated on the C-face 4H-SiC during forward current operation was investigated using Berg-Barrett X-ray topography and photoluminescence imaging. After experiment, were generated from very short portions basal plane dislocations lower than conversion points to threading edge epitaxial layer. behavior discussed. Growth substrates not observed.

The crystal structure of the double-layered ${\mathrm{Ca}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ has been studied by convergent beam electron diffraction and powder neutron diffraction. temperature dependence pattern reveals that all lattice constants jump at first-order metal-nonmetal transition $48\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ without a change space group symmetry $Bb{2}_{1}m$. In experiment, an additional magnetic reflection emerges below N\'eel temperature,...

A systematic study of exciton dynamics is presented in quantum boxes formed naturally along the axis a V-shaped wire, by means time and spatially resolved resonant photoluminescence. The dependence radiative lifetimes relaxation mechanisms excitons determined versus size boxes. recombination rate varies linearly with length box, showing that has coherence volume equal to box. In low excitation regime, emission from excited states not been observed, which would be consequence bottleneck, but...

Structural properties of GaN films grown on vicinal sapphire (0001) substrates with various angles by plasma-assisted molecular beam epitaxy are investigated. High-resolution x-ray diffraction (HRXRD) results reveal the dramatic improvement both tilting and twisting grain features when angle is larger than 0.5° formation multilayer macro-steps surface. The threading dislocation density reduces over an order magnitude estimated from HRXRD results. Cross-sectional transmission electron...

Flow rate modulation epitaxy (FME) is applied to the low-temperature growth of AlGaAs/GaAs quantum wires (QWRs) on nonplanar substrates. The selectivity found be enhanced greatly by use FME, as compared with conventional metalorganic chemical vapor deposition due migration Ga species. An QWR a central thickness about 9 nm and lateral width 28 grown at 600 °C V-grooved substrate. Good photoluminescence properties are observed from QWR, peak energy being in good agreement calculated level...

While the effectiveness of surfactants in Si/Ge heteroepitaxial growth has recently been reported, their disadvantages self-incorporation and poor surface morphology restrict practical application. We propose Bi as a surfactant which overcomes these disadvantages. demonstrate by means reflection high-energy electron diffraction secondary ion mass spectrometry (SIMS) that is an effective for heteroepitaxy preventing both 3D islanding segregation Ge, while amount incorporated epitaxial layer...

Time-dependent dielectric breakdown (TDDB) measurement of MOS capacitors on an n-type 4 ° off-axis 4H-SiC(0001) wafer free from step-bunching showed specific in the Weibull distribution plots. By observing as-grown SiC-epi surface, two kinds epitaxial surface defect, Trapezoid-shape and Bar-shape defects, were confirmed with confocal microscope. Charge to (Qbd) including upstream line these defects is almost same value as that a Wear-out region. On other hand, gate oxide occurred at...

X-ray and electron diffraction measurements on the metal-insulator (M-I) transition compound PrRu$_4$P$_{12}$ have revealed emergence of a periodic ordering charge density around Pr atoms. It is found that associated with onset low temperature insulator phase. These conclusions are supported by facts space group crystal structure transforms from Im$\bar{3}$ to Pm$\bar{3}$ below M-I also dependence superlattice peaks in phase follows squared BCS function. The could be originated perfect...

We have proposed a T c vs n relationship for multilayered high- superconductors from the analysis of HgBa 2 Ca -1 Cu O y grain-aligned samples containing =6 to 16 phases. The sample showed large and sharp superconducting transition at 105 K in its susceptibility temperature curve. This means that can maintain high least up ≈16, otherwise many transitions would been observed. It is generally believed highest decreases with ≥4–5 superconductors. conclude almost constant above about =5 if...

Abstract Contrasts of dislocations in the sub-surface region Si-face a 4H-SiC wafer were observed by monochromatic synchrotron X-ray topography grazing-incidence Bragg-case geometry. Basal-plane show very characteristic contrast depending on their Burgers vectors, running directions, and types dislocations, whether they are screw C-core edge or Si-core dislocations. The rules for contrasts basal-plane summarized. It is shown that observing those at fixed diffraction conditions, vectors...

AbstractShockley partial dislocations in 4H-SiC were observed using monochromatic synchrotron X-ray topography with a grazing-incidence Bragg-case geometry, that is, Berg–Barrett topography. The contrast of at the edges Shockley-type stacking faults is discussed terms whether they have C- or Si-core edge components, screw components. dissociated state basal-plane dislocation on basis sequence for basal-planes crystal structure. It expected results obtained this study will be useful...

A structural phase transition has been found using electron diffraction technique in PrRu4P12 accompanied by a metal - insulator (M I) (TMI = 60K). Weak superlattice spots appeared at (H, K, L) (H + K L 2n 1; n is an integer) position temperature of T 12 and 40 K. Above 70 the completely vanished. The space group low probably Pm3. This first observation symmetry other than Im3 skutterudite compounds.

Electrical properties of stacking faults and bounding partial dislocations in 4H-SiC Schottky diode were investigated by using electron-beam-induced current (EBIC) cathodoluminescence (CL) techniques. EBIC images show that basal plane dislocation is easily dissociated into two [Si(g) 30° C(g) partials], with a fault between them. The contrast always several percent higher than Si(g) partial. brighter the background, having negative contrast. CL spectrum shows new peak (417nm) appears at...

The surface morphology and lattice defect structures in the subsurface regions of 4H-SiC wafers introduced during chemo-mechanical polishing (CMP) were studied by scanning electron microscopy transmission microscopy. It is known that local damage consisting high-density defects current CMP, however, optical showed was very flat clean without any presence defects. Specifically, this study focused on detailed analysis such structures. locally consisted nano-scale scratches, basal-plane...

We report on microscopic photoluminescence of a single V-shaped AlGaAs/GaAs quantum wire. The experiments are performed at low temperature by selectively exciting 1 μm2 the sample. main line is split into sharp peaks width less than 0.5 meV and separated few meV. energy position intensity characteristic scanned First microphotoluminescence results suggest that localization phenomena predominant in They due to formation extended monolayer-step islands, larger exciton radius, as case...

The temperature dependence of photoluminescence (PL) properties AlGaAs/GaAs quantum wire (QWR) grown on V-grooved substrates by flow rate modulation epitaxy is investigated. PL from a 7.1 nm thick QWR easily observed even at room temperature. full width half-maximum (FWHM) the emission peak increases linearly with increasing low temperatures and becomes almost independent high temperatures, while that well layer (QWL) sample up to FWHM found be considerably narrower than QWL which expected...

We have characterized the ground state of Sr3Ir2O7 by performing measurements electrical resistivity, magnetic susceptibility, magnetization, specific heat and electron diffraction (ED). Polycrystalline samples been synthesized using a high-pressure technique. exhibits weak ferromagnetism with small ferromagnetic component (2 × 10−3 μB/Ir) below TC∼280 K. The temperature dependence resistivity ρ shows semiconducting-like behaviour; dρ/dT<0 an anomaly near TC. From result for heat, λ-type...

The authors fabricated pn diodes with Al+ implantation in p-type epitaxial layers, and investigated the influence of dose on reverse leakage currents. Only highest Al concentration 2x1020cm-3, more than 90% devices showed high currents above 10-4A at maximum electric field 3MV/cm. In such devices, almost all emissive spots corresponded to threading screw dislocations (TSDs) by analysis emission microscopy X-ray topography. These TSDs were defined as killer defects estimated density 500cm-2...

We report on the pinning of recombination-enhanced dislocation motion in 4H–SiC by implantation Cu. The Cu was found to be preferentially gettered at basal plane dislocations (BPDs). Both EH1 and Z1/2 center were detected cathodoluminescence. It noticed that has high luminescence intensity central part BPDs, while does not. complex is regarded cause for effect. possible reason discussed.

SiO2/4H-SiC interfaces are examined by high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field scanning (HAADF-STEM), and spatially resolved energy-loss spectroscopy (EELS). HRTEM HAADF-STEM images of reveal that abrupt formed irrespective the fabrication conditions. Transition regions around reported Zheleva et al. were not observed. Using EELS, profiles C/Si O/Si ratios across an interface measured. Our measurements did a C-rich region on SiC side interface,...