This work concerns the microstructure of CSS-grown CdTe layers used for CdTe/CdS solar cells. Particular attention is given to how the development of microstructure on annealing with CdCl(_2) may correlate with increases in efficiency. By annealing pressed pellets of bulk CdTe powder, it is shown that microstructural change does occur on heating the material, enhanced by the inclusion of CdCl(_2) flux. However, the temperature required to cause significant effects is demonstrated to be higher than that at which heavy oxidation takes place. The dynamics of this oxidation are also examined. To investigate microstructural evolution in thin-films of CdTe, bi-layers of CdTe and CdS are examined by bevelling, thus revealing the microstructure to within ~1 µm of the interface. This allows optical microscopy and subsequent image analysis of grain structure. The work shows that the grain- size, which is well described by the Rayleigh distribution, varies linearly throughout the layer, but is invariant under CdCl(_2) treatment. Electrical measurements on these bi-layers, however, showed increased efficiency, as is widely reported. This demonstrates that the efficiency of these devices is not dictated by the bulk microstructure. Further, the region within 1 µm of the interface, of similar bi-layers to above, is examined by plan-view TEM. This reveals five-fold grain-growth on CdCl(_2) treatment. Moreover, these grains show a considerably smaller grain size than expected from extrapolating the linear trend in the bulk. These observations are explained in terms of the pinning of the CdTe grain size to the underlying CdS, and the small grain size this causes. A simple model was proposed for a link between the grain-growth to the efficiency improvement. The study also examines the behaviour of defects within grains upon CdCl(_2) treatment provided the first direct evidence of recovery on CdCl(_2) treatment in this system. Finally, a computer model is presented to describe the evolution of microstructure during growth. This is shown to be capable of reproducing the observed variation in grain size, but its strict physical accuracy is questioned.

Im Rahmen der Dissertation wurde untersucht, wie die Wasserdurchlässigkeit von ToB unter Baustellenbedingungen geprüft werden kann und welcher Zusammenhang zwischen Verformungsmodul und Wasserdurchlässigkeit besteht und ob diese Eigenschaften baustofftech-nisch oder bautechnologisch beeinflussbar sind. Dazu wurden bei einer Vielzahl von Baumaßnahmen beim Ausbau des Autobahnnetzes in den neuen Bundesländern baubegleitende Messungen auf Tragschichten durchgeführt. Außerdem wurden auf verschiedenen ToB-Versuchsfeldern in einem Lysimeter Vergleichsuntersuchungen mit den Prüfgeräten Tropf-, Doppelring- und Standrohr-Infiltrometer durchgeführt. Außerdem fanden Untersuchungen auf zwei Versuchs-Baustraßen in Schotterwerken statt. Untersucht wurde zunächst, wie sich die Variation der Parameter Korngrößenverteilung, Kornform und Sandtyp sowie Verdich-tungswassergehalt und Verdichtungsgrad auf die Eigenschaften der ToB im Neuzustand auswirken. Es wurde außerdem Untersucht, inwieweit sich ein Zusammenhang darstellen lässt zwischen dem Anstieg der Tragfähigkeit (Ev2-Wert) über eine bestimmte Schichtdicke der ToB und ihrer Wasserdurchlässigkeit.

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No description available.

There are many situations where workers are required to wear personal protective clothing (PPC), to protect against a primary hazard, such as heat or chemicals. But the PPC can also create ergonomic problems and there are important side effects which typically increase with rising protection requirements. The most extensively studied side effect is that of increased heat strain due to reduced heat and vapour transfer from the skin. Less studied is the extra weight, bulk and stiffness of PPC garments which is likely to increase the energy requirements of the worker, reduce the range of movement and lead to impaired performance. Current heat and cold stress standards assume workers are wearing light, vapour permeable clothing. By failing to consider the metabolic effects of actual PPC garments, the standards will underestimate heat production and therefore current standards cannot be accurately applied to workers wearing PPC. Information on the effect of the clothing on the wearer and the interactions between PPC, wearer and environment is limited. Data was collected to quantify the effect of PPC on metabolic load based on the properties of the PPC for the EU THERMPROTECT project (GERD-CT-2002-00846). The main objective of the project was to provide data to allow heat and cold stress assessment standards to be updated so that they need no longer exclude specialised protective clothing. The aim of this thesis was to investigate the effect of PPC and its properties on energy consumption during work. For this purpose, the effects of a range of PPC garments (Chapter 3), weight (Chapter 4), number of layers and material friction (Chapter 5) and wet layers (Chapter 6) on energy consumption whilst walking, stepping and completing an obstacle course were studied. The impact of PPC on range of movement in the lower limbs was also investigated (Chapter 7). The main findings were; a) Increased metabolic cost of 2.4 - 20.9% when walking, stepping and completing an obstacle course in PPC compared to a control condition. b) An average metabolic rate increase of 2.7% per kg increase in clothing weight, with greater increases with clothing that is heavier on the limbs and in work requiring greater ranges of movement. c) 4.5 to 7.9% increase in metabolic cost of walking and completing an obstacle course wearing 4 layers compared to a single layer control condition of the same weight. d) Changes in range of movement in PPC due to individual behavioural adaptations. e) Garment torso bulk is the strongest correlate of an increased metabolic rate when working in PPC (r=0.828, p<0.001). f) Garment leg bulk (r=0.615), lower sleeve weight (r=0.655) and weight of the garment around the crotch (r=0.638) are also all positively correlated with an increased metabolic rate. Total clothing weight and clothing insulation had r values of 0.5 and 0.35 respectively. This thesis has confirmed the major effect of clothing on metabolic rate, and the importance of including this effect in standards and models.

This thesis contains primarily a study of CdTe/CdS heterojunction solar cells^ chiefly using photoluminescence spectroscopy. These solar cells show a good potential for commercial power generation in the near Aiture and are of interest to several major companies. A vital but little understood step in the manufacturing process is: annealing the cells in the presence of chlorine prior to back contact application. Studies are performed on a selection of thin film CdTe/CdS cells subjected to CdCl(_2) anneals of different duration. A chemical bevel etch was used to study the spectra at different depths into the sample and laser intensity arid sarhple temperature variations to identify the mechanisms behind the observed photoluminescence peaks. Evidence was found for the CdCl(_2) anneal promoting sulphur diffusion and subsequent grain boundary passivation in the CdTe, leading to increased minority carrier lifetimes and device efficiencies Attempts to obtain electroluminescence from the CdTe/CdS solar cells were madei By using current pulses electroluminescence was obtained in the 780-850nm range with discernible spectral features. Photoluminescence (PL) studies were also performed on a single crystal of CdTe grown to an unprecedented size of approx. 5 cm diameter at Durham university by a multi-tube seeded vapour method of crystal growth. Much higher resolution spectra were: obtained for this than for the solar cells. Several peaks were identified arid the mechanisms responsible were theorised. By taking slices of the crystal boule the PL spectra at different points-throughout the bulk of the crystal were determined. A series of high quality ion-implanted CdTe crystals were also studied! by intensity and temperature dependent PL in order to obtain a better understanding of the effects of known concentrations of known impurities on the PL spectra of CdTe. Specific PL features associated with certain dopants were observed.

The IceCube Neutrino Telescope is designed to detect high energy neutrinos with a large array of photomultiplier tubes placed deep within the Antarctic ice. The way that light propagates through the ice needs to be modelled accurately to enable the paths of charged particles to be reconstructed from the distribution of their Cerenkov radiation. Light travelling through even the purest of ice will undergo scattering and absorption processes, however the ice in which IceCube is embedded has optical properties that vary significantly with depth which need to be accurately modelled. Currently, simulation of the muon background using the current ice model is unable to fully replicate experimental data. In this thesis we investigate a potential method of improving on the current generation of ice models. We introduce thin, highly absorbing layers into the current description of the detection medium and investigate the effect on the simulation of muon tracks in IceCube. We find that better agreement between simulation and data can be seen in the occupancy of optical modules, through the introduction of such absorptive layers into the existing ice layers.

Thesis (Ph.D.); Submitted to the Department of Physics and Astronomy, Rice University, Houston, TX (US); 1 Sep 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "LA-14149-T" J. Koller. US DOE (US) 09/01/2004. Report is also available in paper and microfiche from NTIS.

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