Elastic properties of porous silicon studied by acoustic transmission spectroscopy

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Porous silicon bulk acoustic wave resonator with integrated transducer

We report that porous silicon acoustic Bragg reflectors and AlN-based transducers can be successfully combined and processed in a commercial solidly mounted resonator production line. The resulting device takes advantage of the unique acoustic properties of porous silicon in order to form a monolithically integrated bulk acoustic wave resonator

Dem eigenen Anspruch auf der Spur : Autoethnographische Einblicke zu studierendenzentrierter Lehre

Der Beitrag geht der Frage nach, welchen Herausforderungen Lehrende durch die digitale Lehre im ersten Corona-Semester 2020 begegnet sind und welche Strategien sie für deren Bewältigung gewählt haben. Als Datengrundlage dienendazu sechs autoethnographische Stories, entstanden im Projekt AEDiL. Diese haben sich als wertvolles Material erwiesen, um unmittelbare Einblicke in das Lehrhandeln und die -planung zu erhalten und die weiterführende Analyse zu ermöglichen. Dabei offenbarte sich der gemeinsame Anspruch der studierenden-zentrierten Lehre als wiederkehrendes Muster. Die mehrstufige Analyse legt offen, wie Lehrpersonen mit den Themen Beziehungsaufbau, Schaffung eines (digitalen) Raums sowie Sicherheit für Studierende umgehen und sich daraus Handlungsmuster entwickeln

The personal experience of parenting a child with Juvenile Huntington’s Disease: perceptions across Europe

The study reported here presents a detailed description of what it is like to parent a child with juvenile Huntington’s disease in families across four European countries. Its primary aim was to develop and extend findings from a previous UK study. The study recruited parents from four European countries: Holland, Italy, Poland and Sweden,. A secondary aim was to see the extent to which the findings from the UK study were repeated across Europe and the degree of commonality or divergence across the different countries. Fourteen parents who were the primary caregiver took part in a semistructured interview. These were analyzed using an established qualitative methodology, interpretative phenomenological analysis. Five analytic themes were derived from the analysis: the early signs of something wrong; parental understanding of juvenile Huntington’s disease; living with the disease; other people’s knowledge and understanding; and need for support. These are discussed in light of the considerable convergence between the experiences of families in the United Kingdom and elsewhere in Europe

Porous silicon bulk acoustic wave resonator with integrated transducer

We report that porous silicon acoustic Bragg reflectors and AlN-based transducers can be successfully combined and processed in a commercial solidly mounted resonator production line. The resulting device takes advantage of the unique acoustic properties of porous silicon in order to form a monolithically integrated bulk acoustic wave resonator

Quasi-periodic Fibonacci and periodic one-dimensional hypersonic phononic crystals of porous silicon:Experiment and simulation

A one-dimensional Fibonacci phononic crystal and a distributed Bragg reflector were constructed from porous silicon. The structures had the same number of layers and similar acoustic impedance mismatch, and were electrochemically etched in highly boron doped silicon wafers. The thickness of the individual layers in the stacks was approximately 2 μm. Both types of hypersonic band gap structure were studied by direct measurement of the transmittance of longitudinal acoustic waves in the 0.1-2.6 GHz range. Acoustic band gaps deeper than 50 dB were detected in both structures. The experimental results were compared with model calculations employing the transfer matrix method. The acoustic properties of periodic and quasi-periodic structures in which half-wave retarding bi-layers do not consist of two quarter-wave retarding layers are discussed. The strong correlation between width and depth of gaps in the transmission spectra is demonstrated. The dominant mechanisms of acoustic losses in porous multilayer structures are discussed. The elastic constants remain proportional over our range of porosity, and hence, the Grüneisen parameter is constant. This simplifies the expression for the porosity dependence of the Akhiezer damping.</p

Reactive nano silicon: mediated processes

In this thesis basic methods for the fabrication and characterisation of several nano-silicon containing systems are presented. Due to their morphology, these systems are highly reactive. Silicon wafers were used to prepare layers of porous silicon via electrochemically etching and micro– and nano– sized silicon powders were chemically etched in order to yield silicon nanoparticles. Dependent on the fabrication, particle size of the nanocrystals and porosity of the assemblies can be tailored over a wide range: mean particle sizes can be between 3 to 20 nm and porosities can be varied from 10 to 90 %. A huge surface area of up to 500m2/g which is in addition, due to the fabrication process, hydrogen terminated, entail the outstanding chemical and photo-chemical properties of nanocrystalline silicon. Both, chemical and photo-chemical properties of silicon nanocrystal structures are investigated. The emphasis lies on optical spectroscopy. The indirect band gap structure of silicon in combination with quantum confinement effects are the origin of the interesting luminescence properties of nano-silicon. The energy transfer process from photo-excited excitons confined in silicon nanocrystals to molecules present in the surrounding ambient, like oxygen or a variety of organic substances, has been studied. Measurements demonstrated that long-living excitons very efficiently transfer their energy to surrounding molecules. The low probability of creating excitons which can persist for a long time, from μs to ms, by a photon and structural properties of porous silicon, or rather its reactive surface, however, seem to be the reason for a low total quantum yield of sensitised excited singlet state oxygen.EThOS - Electronic Theses Online ServiceGBUnited Kingdo