190 research outputs found
Analog MIMO Radio-over-Copper: Prototype and Preliminary Experimental Results
Analog Multiple-Input Multiple-Output Radio-over-Copper (A-MIMO-RoC) is an
effective all-analog FrontHaul (FH) architecture that exploits any pre-existing
Local Area Network (LAN) cabling infrastructure of buildings to distribute
Radio-Frequency (RF) signals indoors. A-MIMO-RoC, by leveraging a fully analog
implementation, completely avoids any dedicated digital interface by using a
transparent end-to-end system, with consequent latency, bandwidth and cost
benefits. Usually, LAN cables are exploited mainly in the low-frequency
spectrum portion, mostly due to the moderate cable attenuation and crosstalk
among twisted-pairs. Unlike current systems based on LAN cables, the key
feature of the proposed platform is to exploit more efficiently the huge
bandwidth capability offered by LAN cables, that contain 4 twisted-pairs
reaching up to 500 MHz bandwidth/pair when the length is below 100 m. Several
works proposed numerical simulations that assert the feasibility of employing
LAN cables for indoor FH applications up to several hundreds of MHz, but an
A-MIMO-RoC experimental evaluation is still missing. Here, we present some
preliminary results obtained with an A-MIMO-RoC prototype made by low-cost
all-analog/all-passive devices along the signal path. This setup demonstrates
experimentally the feasibility of the proposed analog relaying of MIMO RF
signals over LAN cables up to 400 MHz, thus enabling an efficient exploitation
of the LAN cables transport capabilities for 5G indoor applications.Comment: Part of this work has been accepted as a conference publication to
ISWCS 201
Improving image contrast in fluorescence microscopy with nanostructured substrates
Metallic and dielectric nanostructures can show sharp contrastedresonances, sensitive to the environment, and high field enhancement insub-wavelength volumes. For this reason, these structures are commonlyused as molecular sensors. Only few works have focused on theirapplication in optical microscopy, in particular in superresolution. In thiswork we have designed, fabricated and optically tested a nanostructuredTiO2 substrate, fabricated by direct embossing of TiO2 derived film, as asubstrate for fluorescence microscopy. Moreover, using numericalsimulations, we have compared the signal to background noise with respectto other metallo-dielectric structures. We show that the TiO2 structure is agood candidate for reducing the thickness of the fluorescence excitationdown to ~100 nm. Therefore, this substrate can be used to obtain TotalInternal Reflection (TIRF) axial resolution without a TIRF-Microscopysystem.Fil: Brunstein, Maia. Centre National de la Recherche Scientifique; Francia. Université Paris-Saclay; FranciaFil: Cattoni, Andrea. Centre National de la Recherche Scientifique; Francia. Université Paris-Saclay; FranciaFil: Estrada, Laura Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Yacomotti, Alejandro M.. Centre National de la Recherche Scientifique; Francia. Université Paris-Saclay; Franci
Quantitative Assessment of Carrier Density by Cathodoluminescence (2): GaAs nanowires
Precise control of doping in single nanowires (NWs) is essential for the
development of NW-based devices. Here, we investigate a series of MBE-grown
GaAs NWs with Be (p-type) and Si (n-type) doping using high-resolution
cathodoluminescence (CL) mapping at low- and room-temperature. CL spectra are
analyzed selectively in different regions of the NWs. Room-temperature
luminescence is fitted with the generalized Planck's law and an absorption
model, and the bandgap and band tail width are extracted. For Be-doped GaAs
NWs, the bandgap narrowing provides a quantitative determination of the hole
concentration ranging from about to
cm, in good agreement with the targeted doping levels. For Si-doped GaAs
NWs, the electron Fermi level and the full-width at half maximum of
low-temperature CL spectra are used to assess the electron concentration to
approximately to cm. These findings
confirm the difficulty to reach highly-doped n-type GaAs NWs, may be due to
doping compensation. Notably, signatures of high concentration (5-9 cm) at the very top of NWs are unveiled
Quantitative Assessment of Carrier Density by Cathodoluminescence (1): GaAs thin films and modeling
Doping is a fundamental property of semiconductors and constitutes the basis
of modern microelectronic and optoelectronic devices. Their miniaturization
requires contactless characterization of doping with nanometer scale
resolution. Here, we use low- and room-temperature cathodoluminescence (CL)
measurements to analyze p-type and n-type GaAs thin films over a wide range of
carrier densities ( to cm). The
spectral shift and broadening of CL spectra induced by shallow dopant states
and band filling are the signature doping. We fit the whole spectral lineshapes
with the generalized Planck's law and refined absorption models to extract the
bandgap narrowing (BGN) and the band tail for both doping types, and the
electron Fermi level for n doping. This work provides a rigorous method for the
quantitative assessment of p-type and n-type carrier density using CL. Taking
advantage of the high spatial resolution of CL, it can be used to map the
doping in GaAs nanostructures, and it could be extended to other semiconductor
materials.Comment: Supplemental Materia
Replacing Metals with Oxides in Metal-Assisted Chemical Etching Enables Direct Fabrication of Silicon Nanowires by Solution Processing
Metal-assisted chemical etching (MACE) has emerged as an effective method to fabricate high aspect ratio nanostructures. This method requires a catalytic mask that is generally composed of a metal. Here, we challenge the general view that the catalyst needs to be a metal by introducing oxide-assisted chemical etching (OACE). We perform etching with metal oxides such as RuO2 and IrO2 by transposing materials used in electrocatalysis to nanofabrication. These oxides can be solution-processed as polymers exhibiting similar capabilities of metals for MACE. Nanopatterned oxides can be obtained by direct nanoimprint lithography or block-copolymer lithography from chemical solution on a large scale. High aspect ratio silicon nanostructures were obtained at the sub-20 nm scale exclusively by cost-effective solution processing by halving the number of fabrication steps compared to MACE. In general, OACE is expected to stimulate new fundamental research on chemical etching assisted by other materials, providing new possibilities for device fabrication
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