Les polluants organiques persistants (POPs) sont des substances toxiques ayant la capacité de se bioaccumuler le long de la chaîne alimentaire. Une fois émis dans l'atmosphère, ils sont dispersés par le vent puis se déposent au sol. Du fait de leur persistance, ils peuvent être réémis depuis le sol vers l'atmosphère et parcourir ainsi de longues distances. Ce processus est couramment appelé « effet saut de sauterelle ». On peut donc retrouver les POPs très loin de leurs sources d'émissions. Pour pouvoir prendre des décisions visant à réduire leur impact environnemental, il est nécessaire de comprendre leur comportement dans l'atmosphère mais également dans les autres milieux, tels que le sol, la végétation ou l'eau. De nombreux modèles numériques de complexité variable ont été développés dans le but de prédire le devenir des POPs dans l'environnement. La plupart d'entre eux considèrent le sol comme un compartiment homogène, pouvant ainsi mener à une sous-estimation des réémissions du sol vers l'atmosphère. Or, du fait de la mise en place de réglementations visant à réduire les émissions anthropiques des POPs, la concentration dans l'atmosphère tend à diminuer et le sol, qui semblait jusqu'alors être seulement un réservoir, devient une source potentielle de POPs pour l'atmosphère. Il apparaît donc nécessaire de coupler les modèles de dispersion atmosphérique à un modèle de sol réaliste. Mes recherches ont permis d'étudier l'impact des interactions entre le sol et l'atmosphère sur la concentration dans les différents milieux. Pour cela, nous avons développé un modèle de sol multi-couches permettant de mieux estimer le profil de concentration dans le sol et les échanges entre ces deux milieux. Une analyse de sensibilité a été effectuée afin d'identifier les paramètres clés dans la détermination des réémissions. Puis ce modèle a été couplé à un modèle 3D de chimie-transport atmosphérique. Une étude de cas à l'échelle européenne a alors été réalisée afin d'évaluer ce modèle et d'estimer l'impact des réémissions sur les concentrations de POPs dans l'environnement / Persitent Organic Pollutants (POPs) are toxic substances that bioaccumulate in the food chain. Once emitted in the atmosphere, they are transported by the wind and deposited on soil. Since they are persistent, they can be reemited from soil to atmosphere by volatilization and travel over very long distances. This process is called grasshopper effect. Thus, POPs may be found at significant levels far from their emission source. It is necessary to understand the transport and fate of these pollutants in order to support the decision making process and reduce human exposure to POPs. Regulations over the last decades lead to a decrease of anthropogenic emissions and subsequent decrease of atmospheric concentration. In this context, the soil is no longer a sink of POPs but can be a source to the atmosphere. Many numeric models aim to study the behavior of POPs in the environment. Most of them consider soil compartment as a homogeneous box, leading to an underestimation of reemissions. Then, it appears of great importance to develop more realistic soil models. The objective of my thesis was to develop such a model, with vertical transport within the soil. This model was evaluated against measured concentration soil profile. We also conducted a sensitivity analysis to identify the key parameters involved in the process of reemissions. Then, the soil model was coupled with an atmospheric transport model. A case study was finally undertaken to estimate the impacts of reemissions on global-mass balance of POPs at European scale

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Agricultural producers are invested in managing the impacts of crop damage on their yields and profit. When damage occurs early enough in an agricultural growing season, farmers have the option to replant their corn stand in an effort to recoup some of the lost profits. In this thesis two different types of naturally occurring damage, wildlife depredation and persistent weed or insect patches, were simulated on two representative regions of Mississippi. These data were then used to assess the financial viability of a range of damage mitigation methods, including partial replanting, enrollment into a government conservation buffer, and no action. Replanting was demonstrated to be generally the most economically viable method of management across all simulation scenarios. This analysis showed a lower return on conservation enrollment than expected, indicating that an increase in financial benefits for some conservation programs may be warranted.

The support of multimedia traffic over IEEE 802.11 wireless local area networks (WLANs) has recently received considerable attention. This dissertation has proposed a new framework that provides efficient channel access, service differentiation and statistical QoS guarantees in the enhanced distributed channel access (EDCA) protocol of IEEE 802.11e. In the first part of the dissertation, the new framework to provide QoS support in IEEE 802.11e is presented. The framework uses three independent components, namely, a core MAC layer, a scheduler, and an admission control. The core MAC layer concentrates on the channel access mechanism to improve the overall system efficiency. The scheduler provides service differentiation according to the weights assigned to each Access Category (AC). The admission control provides statistical QoS guarantees. The core MAC layer developed in this dissertation employs a P-Persistent based MAC protocol. A weight-based fair scheduler to obtain throughput service differentiation at each node has been used. In wireless LANs (WLANs), the MAC protocol is the main element that determines the efficiency of sharing the limited communication bandwidth of the wireless channel. In the second part of the dissertation, analytical Markov chain models for the P-Persistent 802.11 MAC protocol under unsaturated load conditions with heterogeneous loads are developed. The Markov models provide closed-form formulas for calculating the packet service time, the packet end-to-end delay, and the channel capacity in the unsaturated load conditions. The accuracy of the models has been validated by extensive NS2 simulation tests and the models are shown to give accurate results. In the final part of the dissertation, the admission control mechanism is developed and evaluated. The analytical model for P-Persistent 802.11 is used to develop a measurement-assisted model-based admission control. The proposed admission control mechanism uses delay as an admission criterion. Both distributed and centralized admission control schemes are developed and the performance results show that both schemes perform very efficiently in providing the QoS guarantees. Since the distributed admission scheme control does not have a complete state information of the WLAN, its performance is generally inferior to the centralized admission control scheme. The detailed performance results using the NS2 simulator have demonstrated the effectiveness of the proposed framework. Compared to 802.11e EDCA, the scheduler consistently achieved the desired throughput differentiation and easy tuning. The core MAC layer achieved better delays in terms of channel access, average packet service time and end-to-end delay. It also achieved higher system throughput than EDCA for any given service differentiation ratio. The admission control provided the desired statistical QoS guarantees.

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Im ersten Teil der vorliegenden Arbeit wird der Einfluss der Abscheideparamter von In2S3 Dünnfilmen, die mittels thermischem Verdampfen hergestellt wurden, auf ihre physikalischen Eigenschaften untersucht. Es zeigte sich, dass die Abscheideparameter einen starken Einfluss auf die Oberflächenmorphologie und die strukturellen Eigenschaften haben. Durch eine Optimierung der Herstellungsparameter konnten β-In2S3 Dünnfilme in (103) Orientierung hergestellt werden. Epitaktisches Wachstum von In2S3 Schichten mit jeweils zwei bzw. vier Rotationsdomainen wurden auf c- und a-Saphir erreicht. Die fundamentale optische Bandlücke wurde für alle Dünnfilme zu 2.1 eV bestimmt. Eine starke persistente Photoleitung, welche auf tiefe Defekte innerhalb der Bandlücke zurückgeführt werden konnte, wurde unabhängig von den Abscheideparametern und dem gewählten Substrat beobachtet. Prototypen für Solarzellen wurden aus n-In2S3 und p-Zinkkobaltoxid (ZCO) hergestellt und zeigen ein hohes Sperrverhältniss und photovoltaische Aktivität, welche jedoch durch Absorption im ZCO limitiert wird. Im zweiten Teil der Arbeit wurden In2S3:V Dünnfilme ohne bzw. mit Saat- und Pufferschichten hergestellt, um deren physikalische Eigenschaften zu untersuchen bzw. um Zwischenbandsolarzellen herzustellen. Ein großer Dotierbereich von bis zu 11.4 at-% V, wurde durch einen kombinatorischer Ansatz erziehlt. Für Dünnfilme ohne Saatschicht wurde die Löslichkeitsgrenze von Vanadium in In2S3 zu 3.2 at-% V (auf Saphirsubstraten) bzw. 5.4 at-% V (auf Glassubstraten) bestimmt. Durch die Verwendung einer Saatschicht konnte die In2S3 β-Phase stabilisiert und darüber hinaus die Ausbildung von Fremdphasen unterdrückt werden. In2S3:V Dünnfilme mit über 5.8 at-% V auf Saphirsubstraten zeigten bei Raumtemperatur p-Typ Leitfähigkeit. Für Temperaturen unterhalb einer kritischen Temperatur ergab sich ein Wechsel von p- zu n-Leitung. Darüber hinaus sank die Mobilität dieser Schichten unterhalb der kritischen Temperatur signifikant ab. Die Ladungsträgerdichte blieb jedoch über den gesamte Temperaturbereich hinweg konstant und war mit Werten im Bereich von 1022 cm−3 zudem sehr hoch. Diese elektrischen Eigenschaften sind sehr untypisch für einen gewöhnlichen Halbleiter. Sie konnten jedoch im Rahmen dieser Arbeit durch das Modell der Zwischenbandsolarzelle beschieben werden. Als Schlussfolgerung dessen, wurde die Vanadiumkonzentration, bei der sich das Zwischenband ausbildet zu 3.2 at-% V bestimmt. Da sich herausstellte, das In2S3:V bei Raumtemperatur p-Typ ist, konnten keine Zwischenbandsolarzellen mit p-ZCO hergestellt werden.:1 Introduction 1 2 Theoretical background 3 2.1 Indium sulfide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2 The physics of solar cells . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.3 The concept of intermediate band solar cells . . . . . . . . . . . . . . . 8 2.4 Indium sulfide as intermediate band material . . . . . . . . . . . . . . . 11 2.5 Charge transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.6 Electronic defect states . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3 Methods 17 3.1 Growth and structuring techniques . . . . . . . . . . . . . . . . . . . . 17 3.1.1 Thermal evaporation . . . . . . . . . . . . . . . . . . . . . . . . 17 3.1.2 Pulsed laser deposition . . . . . . . . . . . . . . . . . . . . . . . 19 3.1.3 Sputter deposition . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.1.4 Photolithography . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2 characterization techniques . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.2.1 X-ray diffraction measurement . . . . . . . . . . . . . . . . . . . 22 3.2.2 Hall effect measurement . . . . . . . . . . . . . . . . . . . . . . 23 3.2.3 Current-voltage measurement . . . . . . . . . . . . . . . . . . . 25 3.2.4 Temperature-dependent current-voltage measurement . . . . . . 26 3.2.5 Resistance measurement . . . . . . . . . . . . . . . . . . . . . . 26 3.2.6 Spectroscopic ellipsometry . . . . . . . . . . . . . . . . . . . . . 26 3.2.7 Energy dispersive X-ray spectroscopy . . . . . . . . . . . . . . . 27 3.2.8 Transmittance and reflection spectroscopy . . . . . . . . . . . . 27 4 Physical properties of undoped In2S3 . . . . . . . . . .29 4.1 Impact of the growth parameters on the composition . . . . . . . . . . 31 4.2 Desorption mechanisms and their influence on the growth rates . . . . . 33 4.3 Surface morphological properties . . . . . . . . . . . . . . . . . . . . . 35 4.4 Structural properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.5 Optical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4.5.1 Dielectric function and absorption coefficient of In2S3 . . . . . . 43 4.5.2 Impact of the growth parameter . . . . . . . . . . . . . . . . . . 48 4.5.3 Impact of the composition . . . . . . . . . . . . . . . . . . . . . 49 4.5.4 Impact of the substrate crystallinity . . . . . . . . . . . . . . . . 51 4.6 Electrical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 4.6.1 Persistent photoconductivity . . . . . . . . . . . . . . . . . . . . 52 4.6.2 Temperature dependent resistivity and Hall effect measurements 63 4.7 Device characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 4.7.1 Impact of the growth parameter . . . . . . . . . . . . . . . . . . 70 4.7.2 Impact of the substrate crystallinity . . . . . . . . . . . . . . . . 79 4.8 Solar cell performance . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 4.8.1 Impact of the growth parameter . . . . . . . . . . . . . . . . . . 83 4.8.2 Impact of the substrate crystallinity . . . . . . . . . . . . . . . . 88 5 Physical properties of vanadium-doped In2S3. . . . . . . . . .91 5.1 Vanadium incorporation into the In2S3 thin films . . . . . . . . . . . . 93 5.2 Surface morphological properties . . . . . . . . . . . . . . . . . . . . . 95 5.3 Structural properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 5.4 Optical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 5.5 Electrical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.6 Device characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 6 Summary and Outlook . . . . . . . . . .125 List of Abbreviations. . . . . . . . . . 131 List of Symbols. . . . . . . . . . 133 Bibliography . . . . . . . . . .137 List of Own and Contributed Articles . . . . . . . . . .149 Appendix . . . . . . . . . .151 Publikationsliste nach Promotionsordnung § 11(3). . . . . . . . . . 161 Zusammenfassung nach Promotionsordnung § 11(4) . . . . . . . . . .163 / In the first part of the presented work the influence of the growth parameter of In2S3 thin films, grown by physical vapor deposition, on their physical properties is investigated. The deposition parameters were found to have a strong influence on the surface morphology and the structural properties. By choosing appropriate deposition parameters β-phase In2S3 with a pure (103) orientation was achieved. Epitaxial growth with 2 and 4 rotational domains could be induced using c- and a-plane sapphire, respectively. The fundamental optical bandgap was determined to be direct with an energy of 2.1 eV for all In2S3 thin films. A strong persistent photoconductivity, which was attributed to deep defects within the bandgap, was observed for all In2S3 thin films independent of the preparation conditions and independent of the kind of substrate. Solar cells of n-In2S3/p-zinc-cobalt-oxide (ZCO) exhibit high current rectifications and photovoltaic activity but suffer from absorption in the ZCO layer. To study the physical properties of In2S3:V thin films and to implement intermediate band solar cells (IBSC) In2S3:V thin films without and with seed and buffer layers were fabricated, respectively. Using a combinatorial material synthesis approach doping concentrations of up to 11.4 at-% V were achieved. Thin films without seed layers exhibit a solubility limit of vanadium of 3.2 at-% V and 5.4 at-% V for thin films on sapphire and glass substrates, respectively. The In2S3:V β-phase could be stabilized and the formation of secondary phases suppresed by inserting a seed layer. A change of the type of the charge carriers from p-type at room temperature to n-type at low temperatures was observed for thin films with doping concentrations above 5.8 at-% V on sapphire substrates. Furthermore, the mobility decreases significantly below the critical temperature. Contrarily, a very high charge carrier concentration was observed independent of the temperature. This behavior, which is untypical for conventional semiconductors, could be described using the intermediate band (IB) model. According to the results of this work and the IB model, one can conclude, that above a vanadium concentration 3.2 at-% V an IB has formed. Due to the p-type conductivity of In2S3:V thin films at room temperature, rectifying IBSCs could not be implemented using p-type ZCO. Therefore, it should be replaced by an n-type material in future investigations.:1 Introduction 1 2 Theoretical background 3 2.1 Indium sulfide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2 The physics of solar cells . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.3 The concept of intermediate band solar cells . . . . . . . . . . . . . . . 8 2.4 Indium sulfide as intermediate band material . . . . . . . . . . . . . . . 11 2.5 Charge transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.6 Electronic defect states . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3 Methods 17 3.1 Growth and structuring techniques . . . . . . . . . . . . . . . . . . . . 17 3.1.1 Thermal evaporation . . . . . . . . . . . . . . . . . . . . . . . . 17 3.1.2 Pulsed laser deposition . . . . . . . . . . . . . . . . . . . . . . . 19 3.1.3 Sputter deposition . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.1.4 Photolithography . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2 characterization techniques . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.2.1 X-ray diffraction measurement . . . . . . . . . . . . . . . . . . . 22 3.2.2 Hall effect measurement . . . . . . . . . . . . . . . . . . . . . . 23 3.2.3 Current-voltage measurement . . . . . . . . . . . . . . . . . . . 25 3.2.4 Temperature-dependent current-voltage measurement . . . . . . 26 3.2.5 Resistance measurement . . . . . . . . . . . . . . . . . . . . . . 26 3.2.6 Spectroscopic ellipsometry . . . . . . . . . . . . . . . . . . . . . 26 3.2.7 Energy dispersive X-ray spectroscopy . . . . . . . . . . . . . . . 27 3.2.8 Transmittance and reflection spectroscopy . . . . . . . . . . . . 27 4 Physical properties of undoped In2S3 . . . . . . . . . .29 4.1 Impact of the growth parameters on the composition . . . . . . . . . . 31 4.2 Desorption mechanisms and their influence on the growth rates . . . . . 33 4.3 Surface morphological properties . . . . . . . . . . . . . . . . . . . . . 35 4.4 Structural properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.5 Optical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4.5.1 Dielectric function and absorption coefficient of In2S3 . . . . . . 43 4.5.2 Impact of the growth parameter . . . . . . . . . . . . . . . . . . 48 4.5.3 Impact of the composition . . . . . . . . . . . . . . . . . . . . . 49 4.5.4 Impact of the substrate crystallinity . . . . . . . . . . . . . . . . 51 4.6 Electrical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 4.6.1 Persistent photoconductivity . . . . . . . . . . . . . . . . . . . . 52 4.6.2 Temperature dependent resistivity and Hall effect measurements 63 4.7 Device characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 4.7.1 Impact of the growth parameter . . . . . . . . . . . . . . . . . . 70 4.7.2 Impact of the substrate crystallinity . . . . . . . . . . . . . . . . 79 4.8 Solar cell performance . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 4.8.1 Impact of the growth parameter . . . . . . . . . . . . . . . . . . 83 4.8.2 Impact of the substrate crystallinity . . . . . . . . . . . . . . . . 88 5 Physical properties of vanadium-doped In2S3. . . . . . . . . .91 5.1 Vanadium incorporation into the In2S3 thin films . . . . . . . . . . . . 93 5.2 Surface morphological properties . . . . . . . . . . . . . . . . . . . . . 95 5.3 Structural properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 5.4 Optical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 5.5 Electrical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.6 Device characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 6 Summary and Outlook . . . . . . . . . .125 List of Abbreviations. . . . . . . . . . 131 List of Symbols. . . . . . . . . . 133 Bibliography . . . . . . . . . .137 List of Own and Contributed Articles . . . . . . . . . .149 Appendix . . . . . . . . . .151 Publikationsliste nach Promotionsordnung § 11(3). . . . . . . . . . 161 Zusammenfassung nach Promotionsordnung § 11(4) . . . . . . . . . .163