Semiconductor nanowires grown by molecular beam epitaxy for electronics applications

One-dimensional nanostructures such as semiconductor nanowires are very attractive for application in next generation electronics. This work presents an experimental study of InAs-based and ZnO-based nanowires grown by molecular beam epitaxy for electronics applications. InAs, InAsP and InAsSb nanowires were grown self-catalytically on silicon. Phosphorus incorporation was studied by means of HRTEM, XRD, EDX and PL. The phosphorus incorporation rate was shown to be 10 times smaller than that of arsenic. InAs and InAsP nanowires exhibit the wurtzite structure with a high density of stacking faults and phase boundaries. Conversely, InAsSb nanowires exhibit the zincblende structure with the density of stacking faults decreasing as the antimony content increases. Antimony incorporation and reduction of the stacking fault density improves the nanowire mobility. ZnO and ZnMgO nanowires and ZnO/ZnMgO core-shell nanowire heterostructures were grown by plasma-assisted molecular beam epitaxy on various substrates with gold particles as a growth catalyst. Nanowire growth was shown to occur only at temperatures between 700 and 850 C and Zn pressures between 1 and 3 10 7 Torr. A two-step growth procedure on silicon was implemented to increase the yield of nanowire growth. Mg incorporation was shown to be 4 times smaller than that of Zn. At Mg content higher than 20 %, MgZnO rocksalt phase segregation is observed in the as-grown samples. Core-shell nanowires were fabricated by growing the shell at a lower temperature of 500 C. ZnO nanowire field effect transistors were fabricated and optimised. High- and low-temperature transport measurements allowed determination of the bulk nanowire and contact properties. Nanowires grown on sapphire and silicon were compared. Nanowires grown on sapphire exhibit an extra donor that determines their low temperature conductivity and give a wider photoluminescence band-edge emission peak. A novel technique to measure the spectrum of deep traps in nanowire field effect transistors was implemented to study ZnO nanowires

On the difference between proton and neutron spin-orbit splittings in nuclei

The latest experimental data on nuclei at $^{132}$Sn permit us for the first time to determine the spin-orbit splittings of neutrons and protons in identical orbits in this neutron-rich doubly-magic region and compare the case to that of $^{208}$Pb. Using the new results, which are now consistent for the two neutron-rich doubly magic regions, a theoretical analysis defines the isotopic dependence of the mean field spin-orbit potential and leads to a simple explicit expression for the difference between the spin-orbit splittings of neutrons and protons. The isotopic dependence is explained in the framework of different theoretical approaches.Comment: 8 pages, revte

On the isospin dependence of the mean spin-orbit field in nuclei

By the use of the latest experimental data on the spectra of $^{133}$Sb and $^{131}$Sn and on the analysis of properties of other odd nuclei adjacent to doubly magic closed shells the isospin dependence of a mean spin-orbit potential is defined. Such a dependence received the explanation in the framework of different theoretical approaches.Comment: 52 pages, Revtex, no figure

Development of the algorithm for aircraft control at inaccurate measurement of the state vector and variable accuracy parameter

A parametric method of the synthesis of control in the closed circuit, taking into account explicitly generalized error of the inertial module, is presented. The law of control in the form of analytical formulas is typically assigned to the control program and does not change during flight of an unmanned aerial vehicle. This decreases the capabilities of the autonomous flight control system to overcome control errors, which occur for various reasons. To verify assumptions about a possibility of improving the accuracy of an aerial vehicle control by the data of the strapdown inertial navigation system on a certain time interval of autonomous operation, the calculation experiment was conducted with the use of the developed software complex, simulating operation of the automatic flight control system. Parametrization of the law of control is considered as the main contribution (the outcome). Introduction of the parameter made it possible to decrease a negative impact of measurement errors and other disturbing factors on accuracy of reaching by the point of flight destination. Through computer modeling, it was shown that it is possible to decrease the impact of a generalized measurement error on generation of values of control functions by changing the value of the parameter. Analytical expressions for the estimation of accuracy of automatic control at the known generalized error of the inertial module and limited disturbing influences were obtained. After analyzing the influence of these factors on accuracy of the object control, a set of recommendations on selection of a variable parameter of synthesis of control depending on precision level of the sensors, used in the inertial module of measuring sensors, was generated.Розглянуто розв’язання термінальної задачі управління та синтезований параметризований закон управління в аналітичному вигляді, який залежить від змінного параметра глибини прогнозу. Досліджено особливості впливу величини параметра управління на точність досягнення кінцевої точки, дані рекомендації з вибору параметра для нівелювання помилки інерційних вимірювань. Синтез управління здійснюється методом переслідування ведучої точки за інформацією, отриманою інтегруванням вимірювань фактичного прискорення і містить помилку, характерну для акселерометрів

Observation of coherent electron transport in self-catalysed InAs and InAs1–xSbx nanowires grown on silicon

We report the observation of phase coherent transport in catalyst-free InAs and InAs1–xSbx nanowires grown by molecular beam epitaxy on silicon (111) substrates. We investigate three different methods to gain information on the phase coherence length of the nanowires: first through the study of universal conductance fluctuations as a function of both magnetic field and gate voltage and then through localisation effects. The analysis of these different quantum effects gave consistent results and a phase-coherence length in the hundred nanometre range was extracted for all nanowires below 10 K. This demonstrates the potential of catalyst-free nanowires as building blocks for future quantum electronics devices directly integrated with silicon circuits