13,635 research outputs found
InSb charge coupled infrared imaging device: The 20 element linear imager
The design and fabrication of the 8585 InSb charge coupled infrared imaging device (CCIRID) chip are reported. The InSb material characteristics are described along with mask and process modifications. Test results for the 2- and 20-element CCIRID's are discussed, including gate oxide characteristics, charge transfer efficiency, optical mode of operation, and development of the surface potential diagram
Row-switched states in two-dimensional underdamped Josephson junction arrays
When magnetic flux moves across layered or granular superconductor
structures, the passage of vortices can take place along channels which develop
finite voltage, while the rest of the material remains in the zero-voltage
state. We present analytical studies of an example of such mixed dynamics: the
row-switched (RS) states in underdamped two-dimensional Josephson arrays,
driven by a uniform DC current under external magnetic field but neglecting
self-fields. The governing equations are cast into a compact
differential-algebraic system which describes the dynamics of an assembly of
Josephson oscillators coupled through the mesh current. We carry out a formal
perturbation expansion, and obtain the DC and AC spatial distributions of the
junction phases and induced circulating currents. We also estimate the interval
of the driving current in which a given RS state is stable. All these
analytical predictions compare well with our numerics. We then combine these
results to deduce the parameter region (in the damping coefficient versus
magnetic field plane) where RS states can exist.Comment: latex, 48 pages, 15 figs using psfi
High Conductance Ratio in Molecular Optical Switching of Functionalized Nanoparticle Self-Assembled Nanodevices
Self-assembled functionalized nano particles are at the focus of a number of
potential applications, in particular for molecular scale electronics devices.
Here we perform experiments of self-assembly of 10 nm Au nano particles (NPs),
functionalized by a dense layer of azobenzene-bithiophene (AzBT) molecules,
with the aim of building a light-switchable device with memristive properties.
We fabricate planar nanodevices consisting of NP self-assembled network
(NPSANs) contacted by nanoelectrodes separated by interelectrode gaps ranging
from 30 to 100 nm. We demonstrate the light-induced reversible switching of the
electrical conductance in these AzBT NPSANs with a record on/off conductance
ratio up to 620, an average value of ca. 30 and with 85% of the devices having
a ratio above 10. Molecular dynamics simulation of the structure and dynamics
of the interface between molecular monolayers chemisorbed on the nano particle
surface are performed and compared to the experimental findings. The properties
of the contact interface are shown to be strongly correlated to the molecular
conformation which in the case of AzBT molecules, can reversibly switched
between a cis and a trans form by means of light irradiations of well-defined
wavelength. Molecular dynamics simulations provide a microscopic explanation
for the experimental observation of the reduction of the on/off current ratio
between the two isomers, compared to experiments performed on flat
self-assembled monolayers contacted by a conducting cAFM tip.Comment: pdf files : publication and supporting informatio
Power Amplification and Coherent Combination Techniques for Terahertz Quantum Cascade Lasers
Power amplification and coherent combination are important ways to improve the output power and beam quality of singleâmode terahertz quantum cascade lasers (THz QCLs). Up to date, the tapered waveguide is the most convenient way to amplify the power of THz QCLs. The selfâfocusing effect in tapered THz QCLs induces nonâmonotonic behaviours of the peak power and farâfield beam divergence, which lead to the existence of optimal structural parameters. The surface and lateral grating techniques have also been employed in tapered THz QCLs to further improve the spectral purity. For coherent combinations, the progress of facetâemitting phaseâlocked arrays of THz QCLs is still limited due to both the lack of the understanding of dynamics of coupled QCLs and the difficulties in designing highâperformance coupled waveguides. We will briefly review the developments of coherent arrays of THz QCLs and present a design of monolithic QCL arrays with common coupled cavity to achieve the optical mutual injection, which may provide a new way for coherent combination of THz QCLs
Solcore: A multi-scale, python-based library for modelling solar cells and semiconductor materials
Computational models can provide significant insight into the operation
mechanisms and deficiencies of photovoltaic solar cells. Solcore is a modular
set of computational tools, written in Python 3, for the design and simulation
of photovoltaic solar cells. Calculations can be performed on ideal,
thermodynamic limiting behaviour, through to fitting experimentally accessible
parameters such as dark and light IV curves and luminescence. Uniquely, it
combines a complete semiconductor solver capable of modelling the optical and
electrical properties of a wide range of solar cells, from quantum well devices
to multi-junction solar cells. The model is a multi-scale simulation accounting
for nanoscale phenomena such as the quantum confinement effects of
semiconductor nanostructures, to micron level propagation of light through to
the overall performance of solar arrays, including the modelling of the
spectral irradiance based on atmospheric conditions. In this article we
summarize the capabilities in addition to providing the physical insight and
mathematical formulation behind the software with the purpose of serving as
both a research and teaching tool.Comment: 25 pages, 18 figures, Journal of Computational Electronics (2018
Confinement Effects on the Crystalline Features of Poly(9,9-dioctylfluorene)
Typical device architectures in polymer-based optoelectronic devices, such as
field effect transistors organic light emitting diodes and photovoltaic cells
include sub-100 nm semiconducting polymer thin-film active layers, whose
microstructure is likely to be subject to finite-size effects. The aim of this
study was to investigate effect of the two-dimensional spatial confinement on
the internal structure of the semiconducting polymer poly(9,9-dioctylfluorene)
(PFO). PFO melts were confined inside the cylindrical nanopores of anodic
aluminium oxide (AAO) templates and crystallized via two crystallization
strategies, namely, in the presence or in the absence of a surface bulk
reservoir located at the template surface. We show that highly textured
semiconducting nanowires with tuneable crystal orientation can be thus
produced. Moreover, our results indicate that employing the appropriate
crystallization conditions extended-chain crystals can be formed in
confinement. The results presented here demonstrate the simple fabrication and
crystal engineering of ordered arrays of PFO nanowires; a system with potential
applications in devices where anisotropic optical properties are required, such
as polarized electroluminescence, waveguiding, optical switching, lasing, etc
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