We use crystal-phase tuning during epitaxial growth of InAs nanowires to create quantum dots with very strong confinement. A set of gate electrodes are used to reproducibly split the quantum dots into even smaller pairs for which we can control the populations down to the last electron. The double quantum dots, which are parallel-coupled to source and drain, show clear and stable odd-even level pairing due to spin degeneracy and the strong confinement. The combination of hard-wall barriers to source and drain, shallow interdot tunnel barriers, and very high single-particle excitation energies allow an order of magnitude tuning of the strength for the first intramolecular bond. We show examples for nanowires with different facet orientations, and suggest possible mechanisms behind the reproducible double-dot formation.
The main objective of the European Spallation Source (ESS) is to perform consistently high impact neutron scattering science using the highest neutron flux of any facility in its class. This ambition is naturally accompanied by operational challenges related to the vertical integration of the instruments' hardware and software shared between collaborators from 13 European countries. The present work will detail integration tests performed at the V20 Test Instrument at Helmholtz-Zentrum Berlin in Germany. An ESS chopper prototype was successfully controlled through the ESS Chopper Integration Controller (CHIC) and Experimental Physics and Industrial Control System (EPICS). Neutron data were successfully collected and time stamped using neutron beam monitors, the ESS prototype detector readout electronics and the Data Management Software Center (DMSC) data acquisition (DAQ) software. Chopper rotation events were timestamped and the chopper disk showed excellent stability and neutron absorption characteristics. The test resulted in (i) the expected time-of-flight (TOF) response, (ii) collected data that compared well with instrument reference data and (iii) revealing the diagnostic power of the performed integration tests. The results of this integration test validate the ESS chopper and detector DAQ architecture choices.Introduction. -The European Spallation Source, a European Research Infrastructure Consortium (ERIC), is a multi-disciplinary research facility based on the world's most powerful neutron source with a vision to enable scientific breakthroughs in research related to materials, energy, health and the environment, and address some of the most important societal challenges of our time [1][2][3]. The ESS will reach higher flux and longer pulse length compared to other neutron research facilities. In order to meet the needs of the diverse scientific areas, 16 neutron scattering instruments are currently foreseen in the baseline instrument suite. It is expected that the instruments, spanning over 3 instrument halls, requiring in total
A prototype quasiparasitic thermal neutron beam monitor based on isotropic neutron scattering from a thin natural vanadium foil and standard 3 He proportional counters is conceptualized, designed, simulated, calibrated, and commissioned. The European Spallation Source designed to deliver the highest integrated neutron flux originating from a pulsed source is currently under construction in Lund, Sweden. The effort to investigate a vanadium-based neutron beam monitor was triggered by a list of requirements for beam monitors permanently placed in the ESS neutron beams in order to provide reliable monitoring at complex beam lines: low attenuation, linear response over a wide range of neutron fluxes, near to constant efficiency for neutron wavelengths in a range of 0.6-10 Å, calibration stability and the possibility to place the system in vacuum are all desirable characteristics. The scattering-based prototype, employing a natural vanadium foil and standard 3 He proportional counters, was investigated at the V17 and V20 neutron beam lines of the Helmholtz-Zentrum in Berlin, Germany, in several different geometrical configurations of the 3 He proportional counters around the foil. Response linearity is successfully demonstrated for foil thicknesses ranging from 0.04 mm to 3.15 mm. Attenuation lower than 1% for thermal neutrons is demonstrated for the 0.04 mm and 0.125 mm foils. The geometries used for the experiment were simulated allowing for absolute flux calibration and establishing the possible range of efficiencies for various designs of the prototype. The operational flux limits for the beam monitor prototype were established as a dependency of the background radiation and prototype geometry. The herein demonstrated prototype monitors can be employed for neutron intensities ranging from 10 3-10 10 n=s.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.