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The m alpha,beta x-ray emission spectra of some of the heavy rare earths were measured using a high resolution x-ray spectrometer. The x-ray spectrometer was designed to allow the preparation of pure samples in ultra-high vacuum conditions so that accurate spectra could be measured. Due to the large number of measurements necessary, the spectrometer was automatically controlled by a microprocessor based system. From the high resolution data obtained, it has been possible to produce an explanation of the gross structures seen in the rare earth m alpha,beta x-ray emission spectra. It has been shown that the spectra are made up from several competing processes but that the main features can be explained in terms of resonant excitation of a 3d electron to the 4f shell followed by 4f - 3d emission and by normal 4f - 3d emission after ionisation of a 3d electron. Modifications to the spectra caused by excited final state transitions have also been observed. The dramatic effects on the malpha spectra of ytterbium due to chemical combination have also been explained in terms of the reduction of the 4f occupancy from 4f14 to 4f13. It has been shown that much of the published data for the m alpha,beta rare earth emission spectra is incorrect. The distorting effects of self absorption and sample contamination have been shown to be particularly severe for the rare earths.

<p> Mechanical softness and deformability underpin most of the advantages offered by semiconducting polymers. A detailed understanding of the mechanical properties of these materials is crucial for the design and manufacturing of robust, thin-film devices such as solar cells, displays, and sensors. The mechanical behavior of polymers is a complex function of many interrelated factors that span multiple scales, ranging from molecular structure, to microstructural morphology, and device geometry. This thesis builds a comprehensive understanding of the thermomechanical properties of polymeric semiconductors through the development and experimental-validation of computational methods for mechanical simulation. A predictive computational methodology is designed and encapsulated into open-sourced software for automating molecular dynamics simulations on modern supercomputing hardware. These simulations are used to explore the role of molecular structure/weight and processing conditions on solid-state morphology and thermomechanical behavior. Experimental characterization is employed to test these predictions&mdash;including the development of simple, new techniques for rigorously characterizing thermal transitions and fracture mechanics of thin films.</p><p>

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An experiment has been carried out to compare directly the frequencies of the 1S_1/2-2S_1/2 and 2S_1/2-4P_1/2 transitions in atomic hydrogen and hence obtain a value for the 1S_1/2 Lamb shift. It is the first of a new generation of 1S_1/2 Lamb shift experiments which are much less dependent on external frequency standards than earlier work [1,2] because no absolute measurement of the 1S_1/2-2S_1/2 frequency is required. This pilot experiment gave a result of 8167(10) MHz for the 1S_1/2 Lamb shift. The 1S_1/2-2S_1/2 transition was excited by two-photon Doppler-free spectroscopy. The necessary radiation at 243 nm was generated by intra-cavity frequency doubling with a crystal of β-barium borate (BBO) placed inside a ring dye laser operating at 486 nm. For the first time, the 1S_1/2-2S_1/2 transition was excited in an atomic beam, thereby removing the uncertainties inherent in cell experiments and generating an optically-excited beam of metastable (2S_1/2) hydrogen atoms. The single-photon 2S_1/2-4P_1/2 transition was excited by radiation at 486 nm from a second ring dye laser, incident transversely on the optically excited metastable beam. The small frequency difference (~ 4.7 GHz) between the fundamental output of the doubled laser and that of the second laser when both were on resonance was directly measured using a stabilised optical cavity. From this measured frequency interval, the value quoted above for the 1S_1/2 Lamb shift was obtained. The result is in agreement with theory and is considerably more precise than that obtained from earlier direct comparisons of 1S_1/2-2S_1/2 and Balmer-β [3]. The error on the result was largely due to the limited amount of data available. However, the aim of the experiment was to demonstrate the feasibility of the method. This has been achieved and considerable improvements in precision should be possible in the future.