High speed imaging detectors with diamond dynode materials
thesisposted on 18.03.2014, 10:11 by Virgil Taillandier
The primary focus of this thesis has been to experimentally study the secondary electron emission of diamond films; to identify materials and process parameters producing a high performance dynode for novel fast imaging photomultiplier designs. Material investigations and performance measurements were made to measure the effect of film thickness, substrate, surface termination, dopant concentration and crystallinity; in order to identify the optimum parameters for dynode manufacture and performance. In addition, a novel gain structure for two dimensional imaging using a diamond-coated image charge dynode in combination with a transparent mesh, was investigated by simulation and experimentally. Experimental work involved 65 CVD (Chemical Vapour Deposition) diamond samples on silicon, molybdenum, niobium substrates or free standing, micro- nano- crystalline and hydrogen or cesium terminated. The secondary electron (SE) yield was found to be far lower than the results found in the literature. Several hypotheses regarding the sample’s low SE yield measured have been considered, for example charge mobility could be reduced due to grain boundaries, high amounts of boron impurities, surface contamination and/or low electron affinity. The main cause identified, after bad quality films was the negative electron affinity of the surface produced when hydrogen terminated. Measurements have indicated that the majority of samples were not fully hydrogen terminated and thus could not produce the potentially high SE yield. The hydrogen termination has also shown to desorb under beam irradiation causing a problem of repeatability of the measurements. However, despite the poor results an interesting phenomenon has been measured: three time domains were observed on the SE yields during beam irradiation. These three processes correspond to different phases of trapping holes, electrons and hydrogen desorption. They have helped to better understand what happens during the process of secondary electron emission of diamond and could be used to determine the initial yield independent of the termination lost when modelling.