First-principle calculation of electrons charge density in the diamond–structure semiconductor crystals

A computational study of the total electrons charge density in the diamond-structure semiconductor crystals has been performed. In a typical modern electronic structure calculation, the charge density is obtained from a certain density functional, however, the charge density in this work was obtained from first principles. It is assumed that the one-electron Bloch functions for the crystals will not very seriously differ from the wave functions in the atomic systems, therefore, they are represented by the well known normalized Slater atomic orbital for multi-electron atoms and ions. Since the spherical harmonics are expressed in the spherical coordinate system, all the calculations are done in this system. The wave functions and the total electron charge densities are calculated along the [l00], [010], and [00l] directions for the state k=0. The atomic system of units is used throughout the calculations. i.e. distances are expresPsed in unit of the Bohr radius, and charges in unit of the electronic charge. It has been found that in each crystal, the total electrons charge density along the [100] and [010] directions are equal, however, the charge densities at a given distance from the center of the cell along [001] and [100] directions are not exactly equal; the density along [100] been always higher. This shows that the potentials arising from the electrons are not spherically symmetric. The results are presented and discusse

Design and construction of a 12kV D.C. power supply

An experimental work on a modified version of the so-called Cockroft-Walton type voltage multiplying rectifier was carried out. This involved the study of the factors governing the output voltage of the Cockroft-Walton multiplier, designing a multiplier based on these factors that can yield the targeted output voltage of over 10 kV, and the construction of a 12-kV d.c voltage generator. Essentially, the constructed generator is a modified 32-stage Cockroft-Walton type voltage multiplying rectifier. It is suitable as a power supply for the nitrogen laser. It can also be used in particle acceleration. The results of the study of the factors governing the output of the Cockroft-Walton multiplier, the components type and specification, and the construction and performance of the generator are presented and discussed Keywords: Design, Power, Construction, Cockrof

The Effect of the Shape of Atomic Potential on the Diffraction Pattern of one Dimensional Quasicrystal Material

We have simulated the diffraction patterns of both periodic and quasiperiodic monatomic chains using the code Laue (written by Silsbee and Drager) and investigated the effects of the shape of the atomic potential. Three fundamental differences between the diffraction patterns of periodic and quasiperiodic monatomic chain were observed. The width and modulated shape of the diffraction pattern formed by the quasiperiodic chain was found to depend on the shape of the atomic potential. For guassian and exponential atomic shapes, the width decreases as the lattice constant is increased. It also decreases as the size of the atom is increased. For a pseudoatomic shape, the width varies with lattice constant and size of atom in an un-orderly manner.Keywords: Quasicrystal, Pseudo, Gaussian and Exponential Atomic Potential

Comparitive study of electrical properties of carbon nano tube (CNT) and silicon nanowire (SNW) MOSFET devices

Metal oxide semiconductor field effect transistor (MOSFET) is a semiconductor device used in many electronic devices for amplification and switching electrical signals. MOSFET downscaling has been the driving force towards the technological advancement, but continuous scaling down of MOSFET causes problem of high power dissipation, high leakage current, Short Channel Effects (SCEs), excessive process variation and reliability issues. In this work, comparative study of electrical properties of carbon nanotube (CNT) and silicon nanowire (SWN) were carried out using CNT and SNW as channel materials, silicon dioxide as the gate dielectric, silicon substrate as base material. The analysis is carried out using FETTOY simulating software for oxide thickness (0.3,0.5,0.7,0.9 and 1.2nm). The results show that carbon nanotube channel material have highest transconductance (gm) of 1.00 x 10-4S, highest conductance (g4) of 4.00 x 10-6S, highest carrier injection velocity (vinj)of 5.43 x 10 5m/s, highest on current (Ion) of 59.79uA, at oxide thickness of 0.3nm when used as MOSFET device and improved short channel effects with subthreshold swing (S) of 67.79 mV/dec and drain induced barrier lowering (DIBL) of 39.67. More results such as drain current (Id) versus gate voltage ( Vg) , quantum capacitance (QC) versus gate voltage (Vg) , and average velocity of mobile electron versus gate voltage (Vg) for all devices are also investigated. Various results obtained indicate that CNT has the higher performance of decreasing gate capacitance with decrease in oxide thickness ( TOx) in deep nanometer regime. This decrease in gate capacitance is observed at a gate voltage of 0.5V and above which leads to the reduction of propagation delay, lower leakage current, low power dissipation, short channel effects (SCEs) as compared to silicon nanowire MOSFET device.KEYWORDS: Ballistic nanoscale MOSFET, Channel materials, FETTOY simulating software, Short channel effects (SCEs), Drain Induces Barrier Lowering (DIBL

Dry Matter Accumulation in Maize as Influenced by Row Arrangement, Nitrogen and Phosphorus Levels in Maize (Zea Mays L)/ Castor (Ricinus Commumis L.) Mixture

Field experiment was conducted at the Institute for Agricultural Research farm Samaru, Zaria in the Northern Guinea Savanna zone of Nigeria during the 2007, 2008 and 2009 rainy seasons to evaluate the effect of row arrangements, nitrogen and phosphorus levels on maize dry matter  accumulation. The treatments consisted of factorial combinations of three alternate row arrangements of maize: castor in 1:1, 1:2 and 2:1, four levels of nitrogen (0, 40, 80 and 120 kg N ha-1) and three levels of phosphorus (13, 26 and 39 kg P ha-1), laid out in a split plot design and replicated three times.  Nitrogen and phosphorus fertilizer were assigned to the main plots while row arrangements were assigned to the sub-plots. The result showed that row arrangement significantly increased plant height and LAI only at 10 WAS in 2007and 2008. Where 1:2 recorded higher measured parameters than the other patterns. Increase in nitrogen up to 120 kg N ha-1 resulted in significantly taller plants and higher LAI in 2007 and at 10 WAS in 2009. TDM was also observed to increase throughout the years of study except at 10 WAS. The response was observed up to 120 kg N ha-1 for most of the parameters. Application of phosphorus significantly increased plant height only in 2009, LAI in 2007 and 2009, and TDM at 6 WAS in 2007 only. These parameters showed no response beyond applied 26 kg P ha-1. Based on the finding of this study, maize can be intercropped with castor with 1:2 planting pattern with application of 80 kg N ha –l plus 26 kg P ha –l. Key words; nitrogen, phosphorus, leaf area index, total dry matte

Dynamics of a Perturbed Linear Chain of Atoms

Since approximately 1950 an increasing portion of experimental solid state physics research has been concerned with studying defects in crystals. This work uses the code BORN written by Silsbee and Drager to simulate the dynamics of a perturbed linear chain of atoms. Specifically, the dispersion curves for pure and impure monatomic crystal has been obtain. Also the power law dependence of the impurity mode investigated. It has been found that the impurity atom does not alter the shape of the dispersion curve. The effect of the impurity occurs at higher wave vectors, that is, in the lower wavelength limit. As the ratio of the atomic mass of the impurity to the host mass decreases, the maximum angular frequency increases. Also, the power law dependence has been confirmed.Kaywords: Lattice vibration, Dispersion relation, Impurity mode, DefectJournal of the Nigerian Association of Mathematical Physics, Volume 20 (March, 2012), pp 267 – 27

Simulation of the diffraction pattern of one dimensional quasicrystal

The effects of the variation of atomic spacing ratio of a one dimensional quasicrystal material are investigated. The work involves the use of the solid state simulation code, Laue written by Silsbee and Drager. We are able to observe the general features of the diffraction pattern by a quasicrystal. In addition, it has been found that each golden mean produces a unique diffraction pattern and that the lower the golden mean the better the diffraction pattern resembles that of a periodic chain. Also the intensity of the central peak was found to decrease as the golden mean increases. However the value of golden mean has no effect on the spacing between the Bragg planes.Keywords: QuasicrystalJournal of the Nigerian Association of Mathematical Physics, Volume 20 (March, 2012), pp 285 – 29

Simulation of the diffraction pattern of one dimensional quasicrystal

The effects of the variation of atomic spacing ratio of a one dimensional quasicrystal material are investigated. The work involves the use of the solid state simulation code, Laue written by Silsbee and Drager. We are able to observe the general features of the diffraction pattern by a quasicrystal. In addition, it has been found that each golden mean produces a unique diffraction pattern and that the lower the golden mean the better the diffraction pattern resembles that of a periodic chain. Also the intensity of the central peak was found to decrease as the golden mean increases. However the value of golden mean has no effect on the spacing between the Bragg planes.Keywords: Quasicrysta

Geometry optimization, cohesive energy and harmonic vibration of Al9Cu41 Cu12Fe And Al13Fe icosahedral metallic alloys

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First-Principle Study on Lead-Free Perovskite for Optoelectrical Applications

The research into new types of light harvesters for solar cells is driven by the need to increase their efficiency and make them more reliable. One promising material for replacing the dye-molecule light harvesters is the Organometallic perovskite; the most popular among them is methyl ammonium lead iodide, CH3NH3PbI3. Although methyl ammonium lead iodide, (CH3NH3PbI3) has proven to be an effective photovoltaic material, there remains a huge concern about the toxicity of lead.  An investigation into the possible replacement of lead (Pb) with Germanium (Ge), Silicon (Si), and Tin (Sn) in CH3NH3PbI3 was carried out. Before this investigation, structure building, parameter optimization, determination of the best exchange functional, k-grid convergence test, and determination of equilibrium lattice constant and geometry relaxation were carried out for the first set of materials. Visualization for Electronic and Structural Analysis (VESTA) and Avogadro software were used for the structure building while FHI-aims code was used to simulate these Perovskites materials. The BLYP (a parameterization of GGA) exchange functional gave the minimum single-point energy at a minimum run time for all the structures. The lattice constants obtained using Phonopy (with zero-point energy) are 5.894, 5.907, 6.248, 5.950, and 6.049 ? for CH3NH3GeBr3, CH3NH3GeI3, CH3NH3PbI3, CH3NH3SiI3, and CH3NH3SnI3 respectively. The energy band gap calculated for the second set of materials: CH3NH3GeI3, CH3NH3PbI3, CH3NH3SiI3, CH3NH3SnI3, and CH3NH3GeBr3 at their respective equilibrium lattice constants are 1.606, 1.513, 1.804, 1.051 and 1.925 eV respectively. These calculated band gap values were compared with reported theoretical and experimental values. There is a close agreement in calculated lattice constants and bandgaps with reported theoretical and experimental values. Dielectric constants, refractive index extinction coefficient, absorption coefficient, reflectivity, and optical conductivity of these materials were also determined. The optical properties obtained show that Sn and Ge are a good choice for the replacement of Pb; also, the optical properties obtained indicate that these materials have other possible applications in areas other than photovoltaic technology