1,721,056 research outputs found
An Exploration of Bank Erosion Dynamics in a Hypertidal Estuarine System
No full textHypertidal estuaries are very dynamic environments characterised by severe tidal ranges (>6 m) that can experience rapid rates of bankline retreat. Indeed, bank erosion is a well-recognised factor that can substantially influence channel hydraulics and sedimentary processes, while also impacting socio-ecological and economic elements in both riverine and tide-dominated settings. Whilst a large body of work on the processes, rates, patterns and factors driving bank erosion
has been undertaken in fluvial environments, bank erosion processes in estuarine (especially hypertidal estuaries) settings is not well documented. In particular, the mutual role of stabilising and destabilising elements that affect the stability of estuarine banks with respect to mass failure have not been explored in detail before. In this study, the processes and trends leading to bank
failure and consequent retreat in hypertidal estuaries is treated within the context of the Severn Estuary (UK) by employing a combination of numerical models and field-based observations. The nature and distribution of the erosive processes in hypertidal estuaries is explored and compared with their fluvial counterparts, helping to inform on the principal elements able to affect severe bank erosion in such environments
Electron-microscopy study of Fe-implanted InP
No full textInP implanted with 200 keV Fe ions to a dose of 1 x 10(14) atoms/cm(2) has been investigated by Transmission Electron Microscopy (TEM). The as-implanted sample exhibits an amorphous surface region. At the annealing temperature of 650 degrees C, nearly complete solid-phase epitaxial regrowth is achieved only for annealing times greater than 1.5 h. For annealing times up to 2 h. however, the samples still contain extended defects such as stacking-fault tetrahedra of vacancy-type and dislocation loops of interstitial-type, mostly concentrated in a band which corresponds to the region of transition between amorphous top layer and crystalline substrate, as was detected in the as-implanted sample. Stacking-fault tetrahedra and loops have also been observed above and below this band, respectively. The origin of these defects is discussed
Stabilizing effects of n-type doping on Fe and Mn acceptors in III-V compounds
No full textAn n-type doping significantly increases the number of active, Fe atoms substituting In (FeIn) in Fe-implanted InP. A previous theoretical study has shown that donor-acceptor pairs have direct stabilizing effects on Fe_In related to charge rearrangements strongly localized at the Fe site and involving d orbitals. Here, we extend that study to Fe and Mn acceptors in InP and GaAs. Present results show that the theoretical model proposed for FeIn in InP generally holds for Fe and Mn acceptors in III-V semiconductors
Correlation among structural, electrical, and deep-level properties of Fe centers implanted in InP
No full textThe Fe-related properties in high-temperature Fe implanted and annealed InP were studied by means of PIXE-RBS-channeling and correlated with the results of electrical (current-voltage) measurements. It is found that the point defect mobility, the concentration of substitutional Fe, and the resistivity of the implanted layer, all follow a similar temperature behavior. For annealing temperatures higher than 500degreesC semi-insulating behavior controlled by the Fe2+ deep levels is observed
Influence of Channeling Effects On Ion Distribution and Damage Profiles During High-energy Ion-implantation In Si
No full textNitrogen implantation has been performed in silicon [001] crystals in carefully controlled alignment conditions. The channeling effects are clearly evident when implanting in [001] and [011] directions at energies ranging from 0.6 to 1.4 MeV. Both ion distribution and damage profiles are strongly influenced by channeling effects during ion implantation. The angular region around the [001] direction has been also investigated by implanting at small angles with respect to the axis. The same kind of study has been performed by implanting at different angles with respect to the planar (01 1) direction. The ion distributions (investigated by SIMS) show a strong dependence upon the alignment conditions. Moreover in high energy ion implantation, the lattice damage is located deep inside the crystal, leaving the surface layer almost unperturbed. The channeling effects on the damage production have been investigated by double crystal diffraction (DCD) in the low-dose regime and by RBS-channeling experiments (after implantation at doses greater than 1 x 10(15) cm-2) and for different ion alignment conditions. A big increase in the ion ranges and a strong reduction in the lattice damage is evident when implanting along major crystal axes. No saturation of the lattice damage and of the channelled component of the beam has been detected if the implantation is performed parallel to the [011] axis. The combined use of SIMS, RBS-channeling and double crystal X-ray diffraction allow a rather complete description of the ion-crystal interaction
Deep-level electroluminescence at 3.5 Âμm from semi-insulating InP layers ion implanted with Fe
No full textIon beam characterization of Fe implanted GaN
No full textFe ion implantation in GaN has been investigated by means of ion beam analysis techniques. Implantations at an energy of 150 keV and fluences ranging from 2 x 10^15 to 1 x 10^16 cm^-2 were done, both at room temperature and at 623 K. Secondary Ions Mass Spectrometry was used to determine the Fe implantation profiles, whereas Rutherford Backscattering in channeling conditions with a 2.2 MeV 4He^+ beam allowed us to follow the damage evolution. Particle Induced X-ray Emission in channeling conditions with a 2 MeV H+ beam was employed to study the lattice location of Fe atoms after implantation. The results show that a high fraction of Fe-implanted atoms are located in high symmetry sites in low fluence implanted samples, where the damage level is lower, whereas the fraction of randomly located Fe atoms increases by increasing the fluence and the resulting damage. Moreover, dynamical annealing present in high temperature implantation has been shown to favor the incorporation of Fe atoms in high symmetry sites
On the contribution of secondary fluorescence to the Fe signal in proton-induced X-ray emission channeling measurements of Fe-doped GaN
No full textWe present an experimental investigation of the contribution of secondary fluorescence to the iron signal in proton-induced X-ray emission (PIXE) channeling measurements of Fe-doped GaN layers. A method for the analysis of the PIXE angular scans has been developed, which is necessary for the correct quantification of the lattice site occupation of the Fe atoms in the GaN matrix. This approach should be taken into account any time the lattice location of small amounts of substitutional impurities has to be measured by PIXE channeling in analogous experimental conditions
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