From RF-Microsystem Technology to RF-Nanotechnology

The RF microsystem technology is believed to introduce a paradigm switch in the wireless revolution. Although only few companies are to date doing successful business with RF-MEMS, and on a case-by-case basis, important issues need yet to be addressed in order to maximize yield and performance stability and hence, outperform alternative competitive technologies (e.g. ferroelectric, SoS, SOI,…). Namely the behavior instability associated to: 1) internal stresses of the free standing thin layers (metal and/or dielectric) and 2) the mechanical contact degradation, be it ohmic or capacitive, which may occur due to low forces, on small areas, and while handling severe current densities.The investigation and understanding of these complex scenario, has been the core of theoretical and experimental investigations carried out in the framework of the research activity that will be presented here. The reported results encompass activities which go from coupled physics (multiphysics) modeling, to the development of experimental platforms intended to tackles the underlying physics of failure. Several original findings on RF-MEMS reliability in particular with respect to the major failure mechanisms such as dielectric charging, metal contact degradation and thermal induced phenomena have been obtained. The original use of advanced experimental setup (surface scanning microscopy, light interferometer profilometry) has allowed the definition of innovative methodology capable to isolate and separately tackle the different degradation phenomena under arbitrary working conditions. This has finally permitted on the one hand to shed some light on possible optimization (e.g. packaging) conditions, and on the other to explore the limits of microsystem technology down to the nanoscale. At nanoscale indeed many phenomena take place and can be exploited to either enhance conventional functionalities and performances (e.g. miniaturization, speed or frequency) or introduce new ones (e.g. ballistic transport). At nanoscale, moreover, many phenomena exhibit their most interesting properties in the RF spectrum (e.g. micromechanical resonances). Owing to the fact that today’s minimum manufacturable features have sizes comparable with the fundamental technological limits (e.g. surface roughness, metal grain size, …), the next generation of smart systems requires a switching paradigm on how new miniaturized components are conceived and fabricated. In fact endowed by superior electrical and mechanical performances, novel nanostructured materials (e.g. carbon based, as carbon nanotube (CNT) and graphene) may provide an answer to this endeavor. Extensively studied in the DC and in the optical range, the studies engaged in LAAS have been among the first to target microwave and millimiterwave transport properties in carbon-based material paving the way toward RF nanodevices. Preliminary modeling study performed on original test structures have highlighted the possibility to implement novel functionalities such as the coupling between the electromagnetic (RF) and microelectromechanical energy in vibrating CNT (toward the nanoradio) or the high speed detection based on ballistic transport in graphene three-terminal junction (TTJ). At the same time these study have contributed to identify the several challenges still laying ahead such as the development of adequate design and modeling tools (ballistic/diffusive, multiphysics and large scale factor) and practical implementation issues such as the effects of material quality and graphene-metal contact on the electrical transport. These subjects are the focus of presently on-going and future research activities and may represent a cornerstone of future wireless applications from microwave up to the THz range

Modelling and Characterization of Guiding Micro-structured Devices for Integrated Optics

In this thesis we show several modelling tools which are used to study nonlinear photonic band-gap structures and microcavities. First of all a nonlinear CMT and BPM were implemented to test the propagation of spatial solitons in a periodic device, composed by an array of parallel straight waveguides. In addition to noteworthy theoretical considerations, active functionalities are possible by exploiting these nonlinear regimes. Another algorithm was developed for the three-dimensional modelling of photonic cavities with cylindrical symmetry, such as microdisks. This method is validated by comparison with FDTD. We also show the opportunity to confine a field in a region of low refractive index lying in the centre of a silicon microdisk. High Q-factor and small mode volumes are achieved. Finally the characterization of microdisks in SOI with Q-factor larger than 50000 is presente

Colour and Colorimetry Multidisciplinary Contributions Vol. XIb

It is well known that the subject of colour has an impact on a range of disciplines. Colour has been studied in depth for many centuries, and as well as contributing to theoretical and scientific knowledge, there have been significant developments in applied colour research, which has many implications for the wider socio-economic community. At the 7th Convention of Colorimetry in Parma, on the 1st October 2004, as an evolution of the previous SIOF Group of Colorimetry and Reflectoscopy founded in 1995, the "Gruppo del Colore" was established. The objective was to encourage multi and interdisciplinary collaboration and networking between people in Italy that addresses problems and issues on colour and illumination from a professional, cultural and scientific point of view. On the 16th of September 2011 in Rome, in occasion of the VII Color Conference, the members assembly decided to vote for the autonomy of the group. The autonomy of the Association has been achieved in early 2012. These are the proceedings of the English sessions of the XI Conferenza del Colore

6th International Probabilistic Workshop - 32. Darmstädter Massivbauseminar: 26-27 November 2008 ; Darmstadt, Germany 2008 ; Technische Universität Darmstadt

These are the proceedings of the 6th International Probabilistic Workshop, formerly known as Dresden Probabilistic Symposium or International Probabilistic Symposium. The workshop was held twice in Dresden, then it moved to Vienna, Berlin, Ghent and finally to Darmstadt in 2008. All of the conference cities feature some specialities. However, Darmstadt features a very special property: The element number 110 was named Darmstadtium after Darmstadt: There are only very few cities worldwide after which a chemical element is named. The high element number 110 of Darmstadtium indicates, that much research is still required and carried out. This is also true for the issue of probabilistic safety concepts in engineering. Although the history of probabilistic safety concepts can be traced back nearly 90 years, for the practical applications a long way to go still remains. This is not a disadvantage. Just as research chemists strive to discover new element properties, with the application of new probabilistic techniques we may advance the properties of structures substantially. (Auszug aus Vorwort

CISBAT 2009: International Scientific Conference - Renewables in a changing climate - From Nano to Urban Scale

Centred on research and development in solar energy applications to the built environment, the international conference CISBAT 2009 highlighted a large number of interesting technological innovations. The discoveries and developments presented by scientists from five continents are all part of the effort to mitigate greenhouse gas emissions generated by buildings. Renewables are expected to play a very important role against the global threat of a changing climate, even more so as 2009 will hopefully see a new “Post-Kyoto” era in their favour to be initiated at the COP15 United National Climate Change Conference to be held in Copenhagen (Denmark).“Anti-crisis” programmes, which have been launched by several countries in favour of job creation within the framework of a “Green New Deal” will also contribute to sustain the solar momentum.The organisers of the CISBAT Conference, financially supported by the Swiss Federal Office of Energy (SFOE), therefore had no problem convincing their academic partners - Cambridge University (CU) and the Massachusetts Institute of Technology (MIT) - to collaborate in the organisation of this event on the EPFL campus. More than 200 participants from 30 different countries were present during the two conference days and we are confident that they will be even more numerous at the next edition, as feedback from attendees encourages the organisers to increase the size and the duration of the CISBAT conference

Elektronenspektroskopische Untersuchung Rb-induzierter, elektronischer und morphologischer Modifkationen der Oberfläche von WSe2

The rubidium-covered surface of the semiconducting transition metal dichalcogenide tungsten diselenide (WSe2) is examined using photoelectron spectroscopy (PES) and photoemission electron microscopy (PEEM). Adsorbed Rb is known to induce a variety of effects in this system concerning electronic, structural, and mechanical properties. In this work, the surface potential created by charge transfer upon Rb deposition is examined in thermal equilibrium (band bending) and stationary non-equilibrium (surface photovoltage (SPV) effect), which is induced by the absorption of light. It will be shown that combined measurements and numerical simulations of the SPV effect as a function of the photon flux can be exploited for the estimation of many material parameters of the system, especially of the unoccupied adsorbate state. Issues of extending a conventional photoelectron spectrometer setup by a secondary light source will be discussed in the context of simulations and calibration measurements. The customization of an existing theoretical model of the SPV effect for the WSe2 : Rb system is introduced and a comprehensive validation of the obtained predictions will be given in the context of experimental data. In addition, the self-organized formation of Rb domains at room temperature was examined by application of spatially resolved XPS spectroscopy using the PEEM setup at the end station of beamline UE49/PGMa at the BESSY II synchrotron facility. From the obtained results, the arrangement of Rb in surface lattices can be concluded. Furthermore, an X-Ray absorption study of self-organized nanostructure networks, aiming at the chemical characterization, is presented. Based on the interpretation of the examined structures as tension-induced cracks, a statistical approach to analyzing large-scale features was pursued. First accordance with the predictions made by a primitive, mechanical model of crack creation developed here gives gives some evidence for the validity of the proposed structure creation mechanism. A detailed analysis of technical aspects of processing spatially resolved photoemission data was carried out during this work. Several novel methods were developed as compensation for well-known technical limitations of the experimental setup. As will be shown, specific perturbations of PEEM data can be eliminated efficiently hereby, so comparability of all data channels in a detector image is granted. Extensive tests with actual experimental data prove the great applicability of the approaches made here. Though usually having low individual quality, the large number of data channels allows for novel approaches to the classification of spectroscopic data. A concept originating from the field of data mining was ported to work with photoemission spectra and is applied here as an aid to the recognition of spatial structures from spectral features.Inhalt der vorliegenden Arbeit sind Untersuchungen der rubidiumbedeckten Oberfläche des halbleitenden Übergangsmetalldichalkogenids Wolframdiselenid (WSe2) durch Photoelektronenspektroskopie (PES) und Photoemissionselektronenmikroskopie (PEEM). Vielfältige, Rb-induzierte Effekte mit Auswirkungen auf elektronische, strukturelle und mechanische Eigenschaften sind von diesem System bekannt. Diese Arbeit ist der Untersuchung des Oberflächenpotentials als Folge des Ladungstransfers bei der Adsorption von Rb gewidmet. Wie gezeigt werden wird, können durch ein theoretisches Modell unterstützte Messungen des Potentials im thermischen Gleichgewicht ('Bandverbiegung') und im lichtinduzierten, stationären Nichtgleichgewicht ('surface photovoltage'(SPV)-Effekt) in Abhängigkeit von der Lichtintensität zur Bestimmung einer Reihe von Materialkonstanten, insbesondere des unbesetzten Oberflächenzustands, herangezogen werden. Die Wirksamkeit spezieller Maßnahmen zur Integration einer Sekundärlichtquelle in einen konventionellen PES-Aufbau wird anhand von Simulationsrechnungen und Kalibrierungsmessungen belegt. Umfassende Anpassungen eines bestehenden Modells des SPV-Effekts an das untersuchte System werden diskutiert. Anhand von experimentellen Daten wird die Gültigkeit des Modells demonstriert. Das selbstorganisierte Wachstum von Rubidiumdomänen bei Raumtemperatur konnte mit Hilfe von ortsaufgelöster XPS-Spektroskopie am PEEM-Experiment an der Beamline UE49/PGMa an der Synchrotronstrahlungsquelle BESSY II beobachtet werden. Die hier vorgestellten Daten lassen auf die Existenz von Rb-Oberflächengittern schließen. Neben den beobachteten, relativ großen Domänen auf der Mikrometerskala wurden ausgedehnte Netzwerke linearer Nanostrukturen spektroskopisch vermessen. Ein Ansatz zur chemischen Charakterisierung dieser Strukturen mittels Röntgenabsorptionsspektroskopie wird hier präsentiert. Ausgehend von der Annahme, dass die beobachteten Strukturen Spannungsrisse der Oberfläche repräsentieren, wurde eine statistische Analyse geometrischer Eigenschaften durchgeführt und mit den Voraussagen eines zu diesem Zweck entwickelten, stark vereinfachten Modells der Rissverteilung verglichen. Eine erste Übereinstimmung der daraus abgeleiteten Aussagen mit den experimentellen Daten gibt Hinweise auf die Gültigkeit der hierfür gemachten Annahmen. Besondere Aufmerksamkeit wurde technischen Aspekten der Datenverarbeitung von PEEM-Daten gewidmet. Einige neue Ansätze wurden entwickelt, um den Einfluss wohlbekannter Störungen in den Daten zu quantifizieren und zu entfernen. Wie anhand zahlreicher Beispiele unter realistischen Bedingungen gezeigt wird, gelingt dies mit einer derartigen Effizienz, dass die Vergleichbarkeit aller parallel gemessenen Spektren im Detektorbild sichergestellt ist. Obwohl die Information eines einzelnen Datenkanals fürgewöhnlich eine relativ schlechte Qualität aufweist, ermöglicht die große Zahl parallel gemessener Spektren neue Ansätze zur Klassifizierung der erworbenen Daten. Hier wird ein Konzept aus dem Gebiet des 'Data Mining' auf spektroskopische Daten übertragen und unter anderem zur Strukturerkennung anhand von spektraler Information eingesetzt

Etude de la variabilité de la vapeur d'eau dans la haute troposphère-basse stratosphère tropicale et du monoxyde de carbone troposphérique à partir d'observations spatiales

La tropopause tropicale est une région de l'atmosphère où l'abondance de vapeur d'eau (H2O) affecte le climat. Cette thèse examine le rôle de la convection profonde sur la variabilité de H2O dans cette région. En se basant sur les observations de l'instrument spatial Microwave Limb Sounder (MLS), je montre que la convection continentale impacte le cycle diurne de H2O par injection de cristaux de glace hydratant après sublimation cette région de l'atmosphère. Dans le cadre du projet TRO-pico, je présente aussi un cas d'étude en se focalisant sur le Sud du Brésil. J'analyse également la variabilité du monoxyde de carbone (CO) troposphérique grâce à l'Atmospheric InfraRed Sounder (AIRS). Cette étude est complétée par l'évaluation de la version 6 des inversions de AIRS et de la fusion de données combinant les observations de AIRS à celles du Tropospheric Emission Spectrometer (TES) et MLS. Je démontre ainsi la valeur ajoutée de ces produits pour des études liées à la qualité de l'air, la dynamique et le transport dans la haute troposphère-basse stratosphère.The Tropical Tropopause Layer (TTL) is a key region of the atmosphere where abundance of water vapor (H2O) can affect the climate. In this thesis, I address the question of the impact of deep convection on the H2O variability in the TTL. Based on the space-borne Microwave Limb Sounder (MLS) observations, I show that the continental convection drives the H2O diurnal variability in the TTL where the sublimation of ice crystals injected by overshoots has a moistening effect. As part of the TRO-pico project, I also emphasize the results obtained in southern Brazil. I also analyze the tropospheric carbon monoxide (CO) variability derived from the Atmospheric InfraRed Sounder (AIRS) measurements. This study is completed by the validation of the AIRS CO operational product version 6, and that of the data fusion combining observations from AIRS with the Tropospheric Emission Spectrometer (TES) and MLS, providing valuable information for air quality, upper troposphere-lower stratosphere dynamics and transport studies

Proceedings of the 10th international conference on disability, virtual reality and associated technologies (ICDVRAT 2014)

The proceedings of the conferenc

Strategies to support South African smallholders as a contribution to government’s second economy strategy. Volume 2: Case studies

This second volume of Strategies to support South African smallholders as a contribution to government’s second economy strategy contains sixteen case studies that comprise the main data for the analysis detailed in Volume 1. This collection of case studies provides a useful resource on its own, providing a rich and diverse repository of narratives depicting various types of smallholders in diverse circumstances and environments. As researchers were given the latitude to deviate from a standardised approach, this volume reveals the authors’ different styles, different emphases, and indeed different disciplinary strengths. The ‘unit of analysis’ also differs across case studies: some are studies of single individuals, others focus on particular schemes or projects, and still others involve a comparative analysis of individuals or projects. Due to the complexity of categorising the case studies they have been simply grouped by province, and are ordered, roughly, from southwest to northeast