59,495 research outputs found
Resonant tunnelling features in the transport spectroscopy of quantum dots
We present a review of features due to resonant tunnelling in transport
spectroscopy experiments on quantum dots and single donors. The review covers
features attributable to intrinsic properties of the dot as well as extrinsic
effects, with a focus on the most common operating conditions. We describe
several phenomena that can lead to apparently identical signatures in a bias
spectroscopy measurement, with the aim of providing experimental methods to
distinguish between their different physical origins. The correct
classification of the resonant tunnelling features is an essential requirement
to understand the details of the confining potential or predict the performance
of the dot for quantum information processing.Comment: 18 pages, 7 figures. Short review article submitted to
Nanotechnology, special issue on 'Quantum Science and Technology at the
Nanoscale
A non-destructive analytic tool for nanostructured materials : Raman and photoluminescence spectroscopy
Modern materials science requires efficient processing and characterization
techniques for low dimensional systems. Raman spectroscopy is an important
non-destructive tool, which provides enormous information on these materials.
This understanding is not only interesting in its own right from a physicist's
point of view, but can also be of considerable importance in optoelectronics
and device applications of these materials in nanotechnology. The commercial
Raman spectrometers are quite expensive. In this article, we have presented a
relatively less expensive set-up with home-built collection optics attachment.
The details of the instrumentation have been described. Studies on four classes
of nanostructures - Ge nanoparticles, porous silicon (nanowire), carbon
nanotubes and 2D InGaAs quantum layers, demonstrate that this unit can be of
use in teaching and research on nanomaterials.Comment: 32 pages, 13 figure
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
Quantum photonic networks in diamond
Advances in nanotechnology have enabled the opportunity to fabricate nanoscale optical devices
and chip-scale systems in diamond that can generate, manipulate, and store optical signals
at the single-photon level. In particular, nanophotonics has emerged as a powerful interface
between optical elements such as optical fibers and lenses, and solid-state quantum objects
such as luminescent color centers in diamond that can be used effectively to manipulate
quantum information. While quantum science and technology has been the main driving
force behind recent interest in diamond nanophotonics, such a platform would have many
applications that go well beyond the quantum realm. For example, diamond’s transparency
over a wide wavelength range, large third-order nonlinearity, and excellent thermal properties
are of great interest for the implementation of frequency combs and integrated Raman lasers.
Diamond is also an inert material that makes it well suited for biological applications and for
devices that must operate in harsh environments
MRI: Acquisition of a SQUID Magnetometer for Analysis of Advanced Materials
Technical Summary: Superconducting quantum interference device (SQUID) magnetometry is a non-destructive technique that reveals detailed information about the electron spin interactions in many types of materials. This project will involve a state-of-the-art SQUID magnetometer and Magnetic Property Measurement System (MPMS), which is a critical tool for characterizing several types of materials currently being investigated by researchers within the Laboratory for Surface Science & Technology (LASST) and other University of Maine (UMaine) laboratories. Specific measurement capabilities include DC and AC magnetic susceptibility, magnetoresistivity, van der Paaw conductivity, and Hall mobility. State-of-the-art MPMS capabilities will be especially valuable to several research programs at UMaine pertaining to (i) surface magnetism in nanoparticles, (ii) magnetic anisotropies in sedimentary rocks, (iii) electrical transport in physical and chemical sensing devices, (iv) optical properties of nanostructures in high magnetic fields, and (v) magnetic nanoparticle based biosensors. The MPMS will serve as a focal point for training undergraduates, graduate students, postdocs, and visiting scientists in magnetic materials, nanotechnology, biophysics, and materials science. This instrument is a critical tool for expanding the capacity of UMaine research into magnetic aspects of nanotechnology, biophysics, sensor technology, and materials science. As no SQUID magnetometer currently exists in the State of Maine, the instrumentation will provide access for research projects from interested parties throughout the state, including non-Ph.D. granting institutions and small Maine businesses. The instrument is relatively easy to operate and provides direct information on electron spin interactions, and thus it will be a powerful tool to teach physics and nanotechnology concepts to several different constituents participating in UMaine outreach activities, including K-12 students and teachers, the general public, under-represented groups, and industry partners.Layman Summary: Superconducting quantum interference device (SQUID) magnetometry is a non-destructive technique that reveals detailed information about the electron spin interactions in many types of materials. Knowledge of electron interactions in materials is extremely important in building the next generation of computers, electronics, and contrast agents in biological magnetic screening techniques (i.e. MRI). To gain the necessary information, a system with control over both the magnetic field strength and temperature is critical. To this end, a SQUID/Magnetic Property Measurement System (MPMS) is ideal for these measurements. This project will purchase a state-of-the-art MPMS system and will be especially valuable to several research programs at UMaine pertaining to surface magnetism in nanoparticles, magnetic anisotropies in sedimentary rocks, electrical transport in physical and chemical sensing devices, and magnetic nanoparticle based biosensors. The proposed MPMS will serve as a focal point for training undergraduates, graduate students, postdocs, and visiting scientists in magnetic materials, nanotechnology, biophysics, and materials science. As no SQUID magnetometer currently exists in the State of Maine, the instrumentation will provide access for research projects from interested parties throughout the state, including non-Ph.D. granting institutions and small Maine businesses. The instrument is relatively easy to operate and provides direct information on electron spin interactions, and thus it will be a powerful tool to teach physics and nanotechnology concepts to several different constituents participating in UMaine outreach activities, including K-12 students and teachers, the general public, under-represented groups, and industry partners
In situ interface engineering for probing the limit of quantum dot photovoltaic devices.
Quantum dot (QD) photovoltaic devices are attractive for their low-cost synthesis, tunable band gap and potentially high power conversion efficiency (PCE). However, the experimentally achieved efficiency to date remains far from ideal. Here, we report an in-situ fabrication and investigation of single TiO2-nanowire/CdSe-QD heterojunction solar cell (QDHSC) using a custom-designed photoelectric transmission electron microscope (TEM) holder. A mobile counter electrode is used to precisely tune the interface area for in situ photoelectrical measurements, which reveals a strong interface area dependent PCE. Theoretical simulations show that the simplified single nanowire solar cell structure can minimize the interface area and associated charge scattering to enable an efficient charge collection. Additionally, the optical antenna effect of nanowire-based QDHSCs can further enhance the absorption and boost the PCE. This study establishes a robust 'nanolab' platform in a TEM for in situ photoelectrical studies and provides valuable insight into the interfacial effects in nanoscale solar cells
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