77 research outputs found
Heating Rate Effects in Rapid Thermal Annealing of Arsenic Implanted Silicon
No full textABSTRACTCross section TEM and channeling analysis show that the heating rate (HR) of a rapid thermal annealing (RTA) cycle affects the residual defect distribution in Si implanted with As+ to a heavy dose (≈ 1016 cm−2). Two defect bands are observed after solid phase epitaxial growth (SPEG): the first one centered at a depth corresponding to the projected range of the As (band I), and the second one located at depth corresponding to the original amorphous crystalline (a-c) interface (band II). The density of defects in band I is found to increase with the As dose, and with the annealing temperature (550 - 650°C, furnace annealing). However, for RTA (800 - 1000°C) both the density and depth distribution of these defects are dependent on HR. We propose that Si self-interstitials (SiI) are created at the a-c interface when As becomes substitutional during SPEG. The SPEG velocity determines whether the SiI are accommodated in the amorphous Si layer (low velocities) or are captured by the regrowing c-Si (high velocities)</jats:p
Full waveform inversion of the African crust and mantle: strategies for accelerating model convergence
No full textMaster of Science in Applied Geophysics at Delft University of Technology, ETH Zürich and RWTH Aachen University. - The continent of Africa is one of the most geophysically interesting regions on the planet. More specifically, Africa contains the Afar Depression, which is the only place on Earth where incipient sea-floor spreading is sub-aerially exposed, along with other anomalous features such as the unexplained topography in the south. Despite its geophysical significance, relatively few tomographic images exist of Africa. This stems mainly from the sparse distribution of seismic monitoring stations on the continent, which itself is a result of the political instability and general geographical remoteness. As a result, the debate on the geophysical origins of Africa's anomalies is rich and ongoing. In this project a tomographic image is produced using the technique of elastic Full Waveform Inversion (FWI). To our knowledge this is the first attempt at performing a continental-scale FWI of the region. Data recorded from 100 earthquakes has been used as input for the inversion. The adjoint method was used to iteratively update the initial model, which was extracted from the Collaborative Seismic Earth Model. Forward and adjoint modelling were performed in the regional version of SPECFEM3D GLOBE, a global wave propagation solver based on the spectral element method. Over the course of ten iterations, the time-frequency phase misfit decreased satisfactorily, and additional details were added to the starting model. The final model was validated by evaluating the change in misfit for ten earthquakes not previously used in the inversion. All of these events showed a decrease in misfit.Civil Engineering and GeosciencesGeoscience & EngineeringIDEA League Joint Master's in Applied Geophysic
Microstructure and He Bubble Effects on Al-Cu Thin Films
No full textABSTRACTThe effects of film morphology (mosaic- or bamboo-like grain structures) and of He bubbles on the redistribution of Cu, as well as on the formation of Al-Cu precipitates in 200 nm thick Al/SiO2 films similar to microelectronic device interconnects, are investigated using Rutherford backscattering spectrometry, elastic recoil detection analysis and transmission electron microscopy. As-deposited and pre-annealed Al films were implanted with Cu and/or He ions forming concentration profiles located 100 nm below the surface and with peak concentrations of about 3 at.%. It is shown that grain boundaries and/or He bubbles can affect the vacancy fluxes inside the grains and reduce or even inhibit the Cu redistribution as well as the nucleation and growth of θ and θ′ Al-Cu precipitates during post-implantation annealings at temperatures from 473 to 553 K. It is also shown that mosaic-like grain structures allow the control of grain size distribution within the 25 to 1500 nm size range, thus providing an additional microstructure engineering tool to improve device reliability against electromigration failures.</jats:p
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