A study has been made of space-charge-limited hole flow in germanium by investigating the current-voltage-temperature characteristics of selected p-n-p transistors used as diodes with the base open-circuited. These transistors were selected so as to minimize the effect of avalanche multiplication. These diodes pass hole current through the base after a voltage designated as the punchthrough voltage has been applied to deplete the n type base of electrons. The resulting space-charge-limited current above punchthrough has been closely studied and also its temperature dependence. To explain the form of these characteristics, published data have been used for the relationship between electric field and carrier drift velocity for holes in germanium in order to consider the hole flow through the high field region of the base. It was further found necessary to consider the variation of effective emitting area as the applied voltage is increased past punchthrough. For high applied voltages and hence high applied fields in the base, a constant differential resistance is obtained of magnitude about equal to that expected theoretically for a constant drift velocity of holes in the base. The temperature dependence of this current can be satisfactorily explained by the temperature variation of the base-generated current and of the punchthrough voltage itself. A satisfactory model of the latter variation has been made by considering the temperature variation of the potential barrier at the emitter junction. If the observed characteristics are corrected for these variations, there is found to be negligible variation of the space-charge-limited hole -flow. Capacitance measurements were made on both junctions for these diodes. From these measurements the assumption of a step junction and of uniform impurity distribution in the base were justified. No abrupt change of capacitance was observed as the voltage was increased through the punchthrough voltage contrary to the findings of Barker. The original theories of Shockley-Prim-Dacey were extended to include the effects of (i) mobility variation over a wide range of-fields (ii) non-planar geometry and (iii) the potential distribution near the emitter junction. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

PNP structures have been investigated and the various effects encountered described in terms of fundamental aspects of carrier flow. The capacitance of a reverse biased junction in a pnp structure is found to rise abruptly with increase of its reverse bias past the punch-through voltage. This effect arises from the addition of the capacitance of the second junction by the low resistance connection of the space charge column across the n region. An unusual phenomenon called "induced breakdown" is found to occur in certain grown junction transistors. Here the punch-through effect of the space-charge spreading from one junction causes the other junction to suffer avalanche breakdown. Negative resistance is observed in some pnp diodes. This is shown to be a result of the current dependence of the hole transmission process occuring in the n-type transmission region combined with the multiplication effect in the high field region at the collector junction. Current flow in the thin base diode is of a space-charge limited nature in the n region. It is shown that the field over most of the n region is large enough to cause the hole mobility to decrease many fold from its low field value. The slope resistance of a typical diode tends asymptotically to a constant value which is approximately consistent with the model based on a saturated drift velocity for holes in the n region. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Previous work on the reverse current-voltage characteristics of Ge point contact diodes has shown the presence of a voltage maximum ("turnover"). The present investigation is an attempt to explain the fact that the power dissipated at this voltage maximum decreases with increasing ambient temperature. Using diodes which were given rigorous tests to ensure stability of operation, accurate reverse characteristics were obtained at carefully controlled ambient temperatures. On the basis of a model involving surface leakage currents as well as the main bulk flow, a current characteristic involving two activation energies was proposed. It was shown that this model was capable of giving the observed behavior of the turnover power. Using parameters obtained from the static constant-voltage plots, the theoretical dependence of the turnover power on ambient temperature was obtained and was very closely the same form as that found experimentally by Benzer over a very wide range of temperature. By adjusting one parameter (the dissipation constant) excellent agreement was obtained between the theoretical turnover power and that measured in the present experiments. A series of pulse measurements established the fact that the thermal relaxation time of the diode was less than 1 μsec. The experimental and theoretical study presented here shows that a completely consistent model for the turnover phenomenon can be constructed in terms of a reverse current composed of two components with different activation energies; physically there is evidence that these components correspond to bulk and surface current flow. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Germanium(ll)phthalocyanine forms crystals belonging to space group P2/c with a=27.11, sigma=0.012 Å, b=10.39, sigma=0.020 Å, c=21.96, sigma=0.014 Å, beta=107.86, sigma-0.0680. There are eight molecules per unit cell.Patterson maps show that the molecule is planar, that the molecular axis is inclined 500 to the b axis, and that molecules are located parallel to each other along the b axis with an interplanar distance of 3.9 Å.

Th. doct.-ing.--Grenoble, I.N.P., 1985.

Rice is a staple food for more than half of the world's population, and is therefore one of the most important crops directly involved in global food security. Rice accumulates high concentrations of silicon (Si), up to 10% of its dry mass. Silicon has been shown to be involved in plant growth, high yield and mitigating biotic and abiotic stresses. Importantly, inorganic arsenic (As) is taken up by rice through Si transporters. The aims of this project were: 1) To identify natural variation for shoot silicon concentration in rice 2) To determine if germanium is a suitable analogue of silicon for determining natural variation of silicon concentration in rice 3) To identify the underlying putative genes for shoot silicon/germanium concentration in rice. Initially the concentration of silicon in 50 accessions grown in the field was assessed. There was a significant difference of shoot Si concentration observed in these rice accessions. This indicated that there is genetic regulation of natural variation of shoot Si concentration in rice. Germanium (Ge) is an analogue of silicon which produces brown lesion in shoot and leaves. Ge has previously been used to screen a large population of mutant rice plants to identify Si transporters Lsi1 and Lsi2 and the homologue of these two genes Lsi6 and Lsi3 respectively. In this study a Ge screen was developed to identify natural genetic variation for shoot Ge lesions in rice. To identify the Ge tolerant loci in the rice genome, a phenotypic method for Ge screening was developed and performed on two different genetic mapping populations. An experiment with 19 cultivars from RDP1 where Ge uptake was measured found a positive relationship between shoot Ge lesions and shoot Ge concentration in rice. A genetic mapping study of the Bala × Azucena F6 population with 15 µM of GeO2 had a broad sense heritability of 75.8% - 86.1% and identified 15 significant quantitative trait loci (QTLs) and 7 putative QTLs for Ge lesions. A number of QTLs co-localised with previously detected Si and As QTLs. A genome-wide association (GWA) study was also conducted for Ge lesion with 341 rice accessions from the Rice Diversity Panel 1. Statistical analysis indicated genotype v explained 66.10%, 63.70% and 57.60% of the phenotypic variation on days 4, 5 and 6 respectively. Rice subpopulation structure explained 16.50%, 14.70% and 15.90% of the phenotypic variation on days 4 and 5 and 6 respectively. A total of 17 significant SNPs (P < 0.0001; MAF > 0.05) were detected in GWA mapping of Ge tolerant loci for all accessions and a further 54 significant SNPs were detected when performing the analysis with individual rice subpopulations. A number of associations co-localised with previously detected Ge, Si and As QTLs. From the QTL mapping of Bala × Azucena F6 population a QTL was identified on top of chromosome 1 on multiple days where LOC_Os01g02190 is located. LOC_Os01g02190 is 86.71% and 83.57% homologous with Lsi6 and Lsi1 respectively. The GWA mapping of Ge tolerant loci in RDP1 identified a significant SNP near to LOC_Os10g31040 which is 53.60% and 55.46% homologous with Lsi2 and Lsi3 respectively. This high-throughput, cost effective and time saving method can be used for the identification of Si transporters in any other crop as well as to screen a bigger population in rice that may help for the identification of Si/As transporters.

by Lau Chui-fong. / Title also in Chinese characters. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references. / Acknowledgements --- p.ii / Abstract --- p.iii / Table of Contents --- p.v / Chapter Chapter 1 : --- Nucleation --- p.1-1 / Chapter 1.1 --- Introduction --- p.1-1 / Chapter 1.1.1 --- Homogeneous Nucleation --- p.1-1 / Chapter 1.1.2 --- Heterogeneous Nucleation --- p.1-4 / Chapter 1.2 --- Experiments to Achieve High Undercooling --- p.1-6 / Chapter 1.2.1 --- General Reviews --- p.1-6 / Chapter 1.2.2 --- Experimental Details to Obtain Undercooled Ge --- p.1-8 / Chapter 1.2.2.1 --- Effects and Limitations of B2O3 --- p.1-8 / Chapter 1.2.2.2 --- Preparation of B2O3 --- p.1-9 / Chapter 1.2.2.3 --- Preparation of Highly Undercooled Ge --- p.1-10 / Table --- p.1-12 / Figures --- p.1-13 / References --- p.1-15 / Chapter Chapter 2 : --- Growth --- p.2-1 / Chapter 2.1 --- Introduction --- p.2-1 / Chapter 2.1.1 --- Morphologies of Solid´ؤliquid Interface --- p.2-1 / Chapter 2.1.2 --- Edgewise & Normal Growth Mechanism --- p.2-2 / Chapter 2.1.3 --- Formation of Dendrites --- p.2-4 / Chapter 2.2. --- Dendritic Growth of Ge --- p.2-5 / Chapter 2.2.1 --- Edgewise Dendritic Growth by Twin Planes --- p.2-5 / Chapter 2.2.2 --- Normal Growth of Ge at High Undercoolings --- p.2-7 / Figures --- p.2-8 / References --- p.2-15 / Chapter Chapter 3 : --- Polishing and Etching --- p.3-1 / Chapter 3.1. --- Introduction --- p.3-1 / Chapter 3.1.1 --- Surface Preparation --- p.3-1 / Chapter 3.1.2 --- Chemical Etching Experiments --- p.3-3 / Chapter 3.1.3 --- Morphology of Etch Pits --- p.3-5 / Chapter 3.2. --- Polishing and Etching of Ge <110> Dendrite --- p.3-7 / Chapter 3.2.1 --- Finding Twin Planes of <110> Dendrite --- p.3-7 / Chapter 3.2.2 --- Finding Twin Plane Orientation of <110> Dendrite --- p.3-9 / Figures --- p.3-11 / References --- p.3-15 / Chapter Chaptert 4 : --- Sound Emission During Crystallization of Undercooled Liquid Germanium --- p.4-1 / Abstract --- p.4-2 / Introduction --- p.4-3 / Experimental --- p.4-3 / Results --- p.4-4 / Discussion --- p.4-7 / Table --- p.4-10 / Figures --- p.4-11 / References --- p.4-14 / Chapter Chapter 5 : --- Microstructures of Undercooled Germanium --- p.5-1 / Abstract --- p.5-2 / Introduction --- p.5-3 / Experimental --- p.5-4 / Results --- p.5-5 / Discussion --- p.5-10 / Table --- p.5-14 / Figures --- p.5-15 / References --- p.5-25 / Chapter Chapter 6 : --- On the Dendrites and Dendritic Transitions in Undercooled Germanium --- p.6-1 / Abstract --- p.6-1 / Introduction --- p.6-2 / Experimental --- p.6-5 / Results --- p.6-9 / Discussion --- p.6-15 / Table --- p.6-17 / Figures --- p.6-18 / References --- p.6-32 / Chapter Chapter 7 : --- On the Growth of <110> Twin Dendritein / Undercooled Ge --- p.7-1 / Abstract --- p.7-1 / Introduction --- p.7-2 / Experimental --- p.7-3 / Results --- p.7-5 / Discussion --- p.7-8 / Figures --- p.7-13 / References --- p.7-24

Reproduction de : Thèse de doctorat : Génie physique : Metz : 1985. / Titre provenant de l'écran-titre. Notes bibliogr.

No description available.

Thesis (M.S.)--Virginia Polytechnic Institute, 1955. / Vita. Includes bibliographical references (leaves 80-99). Also available via the Internet.