Chemical characterization of extra layers at the interfaces in MOCVD InGaP/GaAs junctions by electron beam methods

Electron beam methods, such as cathodoluminescence (CL) that is based on an electron-probe microanalyser, and (200) dark field and high angle annular dark field (HAADF) in a scanning transmission electron microscope, are used to study the deterioration of interfaces in InGaP/GaAs system with the GaAs QW on top of InGaP. A CL emission peak different from that of the QW was detected. By using HAADF, it is found that the GaAs QW does not exist any longer, being replaced by extra interlayer(s) that are different from GaAs and InGaP because of atomic rearrangements at the interface. The nature and composition of the interlayer(s) are determined by HAADF. Such changes of the nominal GaAs QW can account for the emission observed by CL

Utilizing Miscanthus stalks as raw material for particleboards

Miscanthus x giganteus stalks were studied as a possible replacement for wood in particleboards. Produced particles from Miscanthus contained 38% of cellulose, and 17% of lignin, while spruce had 45% cellulose, and 28% lignin. The amount of hemicelluloses was the same for both, spruce and Miscanthus (21%). Miscanthus-made particleboards were produced at two levels of methylene diphenyl diioscyanate resination, i.e. 4% and 6%. Modulus of rupture (MOR), modulus of elasticity (MOE), internal bonding strength (IB), thickness swelling and water absorption were measured. Mechanical properties of the Miscanthus-made particleboards were overall reduced: compared to spruce, MOR and MOE were down by 30%, while IB was lowered by 60%. Microscopic analysis of fracture surfaces of the Miscanthus-made particleboards after IB testing showed collapsed cells regions in the soft parenchyma, with no obvious adhesive failures. In contrast, spruce-made particleboards revealed much smoother fracture surfaces with structural failures running through cell walls and possibly also through gluelines. The collapsed parenchyma cell regions suggest a direct link to the reduced mechanical properties. Further, compared to spruce the Miscanthus-made particleboards have shown higher thickness swelling, but lower water absorption. For Miscanthus, no effects of higher MDI adhesive dosages on MOE, MOR and IB were observed. To further improve properties of Miscanthus-made particleboards, at sorting-out of parenchyma tissue components to the highest degree possible is recommended, prior to hot-pressing

Seed Transmission of Como and Potyviruses in Fababean and Vetch Cultivars Introduced into Slovakia

Two each of como (broad bean stain, BBSV; broad bean true mosaic, BBTMV) and potyviruses (bean yellow mosaic, BYMV; pea seed-bome mosaic, PSbMV) were seed transmitted by test fababean and vetch cultivars. Number of cultivars supporting seed transmission of BBSV (100%) were highest compared to those of BBTMV, BYMV and PSbMV (86%). Seed transmission levels of BBSV (3-20%) and BBTMV (0-28%) were higher than those of BYMV (0-17%) and PSbMV (0-11%) in these cultivars. Common bean cultivars were infected by BBSV (36%) and BYMV (9%) but not by BBTMV or PSbMV. In reactions of test common bean cultivars, the BYMV-fababean isolate was more similar to pea mosaic (PMV) than to other BYMV strains

Aluminum oxide as passivation and gate insulator in GaAs-based field-effect transistors prepared in situ by metal-organic vapor deposition

Application of GaAs-based metal-oxide-semiconductor (MOS) structures, as a "high carrier mobility" alternative to conventional Si MOS transistors, is still hindered due to difficulties in their preparation with low surface/interface defect states. Here, aluminum oxide as a passivation and gate insulator was formed by room temperature oxidation of a thin Al layer prepared in situ by metal-organic chemical vapor deposition. The GaAs-based MOS structures yielded two-times higher sheet charge density and saturation drain current, i.e., up to 4 x 10 12 cm(-2) and 480 mA/mm, respectively, than the counterparts without an oxide surface layer. The highest electron mobility in transistor channel was found to be 6050 cm(2)/V s. Capacitance measurements, performed in the range from 1 kHz to 1 MHz, showed their negligible frequency dispersion. All these results indicate an efficient suppression of the defect states by in situ preparation of the semiconductor structure and aluminum oxide used as a passivation and gate insulator. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3701584

Individual vortex nucleation/annihilation in ferromagnetic nanodots with broken symmetry observed by micro-Hall magnetometry

We studied vortex nucleation/annihilation process and its temperature dependence in micromagnetic objects with lowered symmetry using micro-Hall magnetometry. Magnetization reversal curves were obtained for the Pacman-like nanodots placed directly on Hall probes. Lowered symmetry of the object leads to good control of its chirality. Vortex nucleation and annihilation fields strongly depend on the angle of the external in-plane magnetic field with respect on the nanodot symmetry. The micromagnetic simulations support the experimental results - the vortex nucleation fields are controlled by local magnetization configurations present in the object (C-, S-, and double S-states) for field just above vortex nucleation field. The experiments also confirm that the vortex nucleation proceeds via thermal activation over an energy barrier

Vortex Dynamics in Ferromagnetic Nanoelements Observed by Micro-Hall Probes

In this work we measure the nucleation and annihilation of magnetic vortices in Pacman-like (PL) micromagnets prepared from Permalloy ($Ni_{81}Fe_{19}$, Py) at 77 K. Lateral dimensions of explored objects are ≤1 μm with thickness of about 40 nm. The micromagnets are located directly on the high-sensitive micro-Hall probe based on GaAs/AlGaAs heterostructure by lift-off process. Experiments show good agreement of the magnetization reversal with the micromagnetic simulation. Other shapes of micromagnets are also considered to obtain more precise picture of the vortex dynamics