Experimental and Atomistic Theoretical Study of Degree of Polarization from Multi-layer InAs/GaAs Quantum Dots

Recent experimental measurements, without any theoretical guidance, showed that isotropic polarization response can be achieved by increasing the number of QD layers in a QD stack. Here we analyse the polarization response of multi-layer quantum dot stacks containing up to nine quantum dot layers by linearly polarized PL measurements and by carrying out a systematic set of multi-million atom simulations. The atomistic modeling and simulations allow us to include correct symmetry properties in the calculations of the optical spectra: a factor critical to explain the experimental evidence. The values of the degree of polarization (DOP) calculated from our model follows the trends of the experimental data. We also present detailed physical insight by examining strain profiles, band edges diagrams and wave function plots. Multi-directional PL measurements and calculations of the DOP reveal a unique property of InAs quantum dot stacks that the TE response is anisotropic in the plane of the stacks. Therefore a single value of the DOP is not sufficient to fully characterize the polarization response. We explain this anisotropy of the TE-modes by orientation of hole wave functions along the [-110] direction. Our results provide a new insight that isotropic polarization response measured in the experimental PL spectra is due to two factors: (i) TM[001]-mode contributions increase due to enhanced intermixing of HH and LH bands, and (ii) TE[110]-mode contributions reduce significantly due to hole wave function alignment along the [-110] direction. We also present optical spectra for various geometry configurations of quantum dot stacks to provide a guide to experimentalists for the design of multi-layer QD stacks for optical devices. Our results predict that the QD stacks with identical layers will exhibit lower values of the DOP than the stacks with non-identical layers.Comment: 10 pages, 7 figures, and 1 tabl

Location Selection Study For Building Fish Landing Place In Districts Bukit Batubengkalisdistrict Riauprovince

The survey was conducted in July 2015, in the village Bukitbatu, Api-api andTenggayun, Bukitbatu district in Riau Province.The purpose of this study was to find thebest location suitable for fish landing building. The method used is the method review /revise the field. Can be seen from the survey data in the technical aspects, fisheries, socioeconomicand infrastructural purpose of the examination of the three villages.The location in the village Tenggayun have advantages, including the opportunity forfishing based on factors such as the number of fishing gear, fishing, the fishing fleet and thenumber of population, which is more than Bukitbatu villages and Api-api. Waters in thevillage Tenggayun fishery potential confounding factors and population factors get thehighest score compared to two other villages, with 55 points and 30 points. The final score ofthe third evaluation village consists of 187 points for Bukitbatu village, 173 points for thevillage burning and 195 points for Tenggayun village. The results of the research using thescoring method showed that the location in the village Tenggayun is the best place to build afish landing site

Location Selection Study For Building Fish Landing Place In Districts Bukit Batubengkalisdistrict Riauprovince

The survey was conducted in July 2015, in the village Bukitbatu, Api-api andTenggayun, Bukitbatu district in Riau Province.The purpose of this study was to find thebest location suitable for fish landing building. The method used is the method review /revise the field. Can be seen from the survey data in the technical aspects, fisheries, socioeconomicand infrastructural purpose of the examination of the three villages.The location in the village Tenggayun have advantages, including the opportunity forfishing based on factors such as the number of fishing gear, fishing, the fishing fleet and thenumber of population, which is more than Bukitbatu villages and Api-api. Waters in thevillage Tenggayun fishery potential confounding factors and population factors get thehighest score compared to two other villages, with 55 points and 30 points. The final score ofthe third evaluation village consists of 187 points for Bukitbatu village, 173 points for thevillage burning and 195 points for Tenggayun village. The results of the research using thescoring method showed that the location in the village Tenggayun is the best place to build afish landing site

Towards visualisation of central-cell-effects in scanning-tunnelling-microscope images of subsurface dopant qubits in silicon

Atomic-scale understanding of phosphorous donor wave functions underpins the design and optimisation of silicon based quantum devices. The accuracy of large-scale theoretical methods to compute donor wave functions is dependent on descriptions of central-cell-corrections, which are empirically fitted to match experimental binding energies, or other quantities associated with the global properties of the wave function. Direct approaches to understanding such effects in donor wave functions are of great interest. Here, we apply a comprehensive atomistic theoretical framework to compute scanning tunnelling microscopy (STM) images of subsurface donor wave functions with two central-cell-correction formalisms previously employed in the literature. The comparison between central-cell models based on real-space image features and the Fourier transform profiles indicate that the central-cell effects are visible in the simulated STM images up to ten monolayers below the silicon surface. Our study motivates a future experimental investigation of the central-cell effects via STM imaging technique with potential of fine tuning theoretical models, which could play a vital role in the design of donor-based quantum systems in scalable quantum computer architectures.Comment: Nanoscale 201

Acid resistance of palm oil fuel ash and metakaolin ternary blend cement mortar

This paper examines the effects of blend of Palm Oil fuel ash (POFA) and Metakaolin (MK) on the resistance of cement mortar to sulphuric acid (H2SO4) attack. Tests were conducted on POFA and MK ternary blended cement mortar immersed in a 3% H2SO4 solution for up 180 d. Binaries of POFA/cement and MK/cement as well as plain ordinary Portland cement (OPC) mortar was also tested for comparison. The parameters measured include residual compressive strength and residual mass. Additionally, the microstructures of the specimens were analysed using the X-ray diffraction and Fourier transformed infrared techniques. The residual compressive strengths of the mortar specimens for plain OPC, binary blend of POFA and cement, binary blend of MK and cement, and ternary blend of POFA, MK and cement after 180 d of immersion in the acid solution were 25, 30, 33, and 32%, respectively. Moreover, the corresponding residual masses of the specimens were 39, 52, 58, and 54%. Accordingly, the ternary blended mortar performed better in resisting H2SO4 attack than the plain OPC and binary blend of POFA/cement mortars

Polarization Response in InAs Quantum Dots: Theoretical Correlation between Composition and Electronic Properties

III-V growth and surface conditions strongly influence the physical structure and resulting optical properties of self-assembled quantum dots (QDs). Beyond the design of a desired active optical wavelength, the polarization response of QDs is of particular interest for optical communications and quantum information science. Previous theoretical studies based on a pure InAs QD model failed to reproduce experimentally observed polarization properties. In this work, multi-million atom simulations are performed to understand the correlation between chemical composition and polarization properties of QDs. A systematic analysis of QD structural parameters leads us to propose a two layer composition model, mimicking In segregation and In-Ga intermixing effects. This model, consistent with mostly accepted compositional findings, allows to accurately fit the experimental PL spectra. The detailed study of QD morphology parameters presented here serves as a tool for using growth dynamics to engineer the strain field inside and around the QD structures, allowing tuning of the polarization response.Comment: 8 pages, 6 figures; accepted for publication in IOP Nanotechnology journa

Valley filtering and spatial maps of coupling between silicon donors and quantum dots

Exchange coupling is a key ingredient for spin-based quantum technologies since it can be used to entangle spin qubits and create logical spin qubits. However, the influence of the electronic valley degree of freedom in silicon on exchange interactions is presently the subject of important open questions. Here we investigate the influence of valleys on exchange in a coupled donor/quantum dot system, a basic building block of recently proposed schemes for robust quantum information processing. Using a scanning tunneling microscope tip to position the quantum dot with sub-nm precision, we find a near monotonic exchange characteristic where lattice-aperiodic modulations associated with valley degrees of freedom comprise less than 2~\% of exchange. From this we conclude that intravalley tunneling processes that preserve the donor's $\pm x$ and $\pm y$ valley index are filtered out of the interaction with the $\pm z$ valley quantum dot, and that the $\pm x$ and $\pm y$ intervalley processes where the electron valley index changes are weak. Complemented by tight-binding calculations of exchange versus donor depth, the demonstrated electrostatic tunability of donor/QD exchange can be used to compensate the remaining intravalley $\pm z$ oscillations to realise uniform interactions in an array of highly coherent donor spins.Comment: 6 pages, 4 figures, 6 pages Supplemental Materia

Comparative Study of the Compressive Strength of Cement Laterite Brick Produced with Rice Husk Ash and Wood Ash as Partial Replacement Of Cement

The paper presents an outcome of experimental comparative study on the compressive strength of laterite brick made with rice husk ash and wood ash as partial replacement of cement. First, Rice Husk Ash (RHA) and Wood Ash (WA) were prepared and subjected to the following tests: specific gravity, density and bulk density. This was followed by the production of three types of bricks viz cement laterite-bricks(control), cement-laterite bricks produced using RHA as partial replacement of cement and another brick made with WA as partial replacement of cement. Replacement levels range from 0 - 30% at 10% intervals. The samples were cured by water sprinkling, before testing them for compressive strength at 7, 14, 21 and 28 curing days. Result of the tests showed that the specific gravity of RHA and WA are 2.20 and 2.13 respectively. The Absorption capacity of all the samples is in the range of 4.5 – 9.1%which is within the allowable value of 25% set by the Nigerian Industrial Standard. Compressive strength for 10 % replacements range from 0.75N/mm2 for 7days to 3.7N/mm2 for 28 days for RHA, as against 2.6 N/mm2 for 7days to 5.3N/mm2 for 28days curing for WA. This shows that bricks produced using WA are relatively higher in strength than those made with RHA. Though it is concluded that RHA and WA, can be used as partial replacements of cement in the production of laterite brick. Also, laterite brick produced with 20% and 30% partial replacements of cement with RHA and WA, respectively,, have, satisfied the minimum requirement as contained in BS 6073, and are recommendable.Keywords: Cement, compressive strength, rice husk ash, laterite brick, partial replacement levels, wood ash