Search results for "Planar"
showing 10 items of 412 documents
Design of a 1 kW output power Folded Waveguide TWT operating in ka-band
2019
A Ka-band Serpentine Folded Waveguide Travelling Wave Tube (TWT) has been designed. The imposed design parameters values in terms of high power, high load, wide bandwidth, low weight, along with a structure manufactured with planar technique or by means of a micro milling process, have been obtained. Small signal simulations have been carried out with an in-house software for interaction impedance evaluation. The commercial electromagnetic simulation code CST Suite has been used for dispersion diagram prediction. An optimization of the one-dimensional software, normally used for large-signal simulation in coupled cavity TWTs (“Computer Program for Analysis of Coupled-cavity Travelling-wave-…
Evidence for Graphene Edges Beyond Zigzag and Armchair
2009
The edges of nanoscopic objects determine most of their properties. For this reason the edges of honeycomb carbon--always considered either zigzag- or armchair-like--need special attention. In this report we provide experimental evidence confirming a previous unexpected prediction: zigzag is a metastable edge, as its planar reconstruction lowers energy and forms the most stable graphene edge. Our evidence is based on re-analyzing a recent experiment. Since the reconstructed edge, along with other unconventional edges we discuss, has distinct chemical properties, this discovery urges for care in experiments and theory--we must enter the realm beyond zigzag and armchair.
Boosting inverted perovskite solar cell performance by using 9,9-bis(4-diphenylaminophenyl)fluorene functionalized with triphenylamine as a dopant-fr…
2019
In this study, two newly developed small molecules based on 9,9-bis(4-diphenylaminophenyl)fluorene functionalized with triphenylamine moieties, namely TPA-2,7-FLTPA-TPA and TPA-3,6-FLTPA-TPA, are designed, synthesized and characterized. The electrochemical, optical and thermal properties of both materials are investigated using various techniques. Afterwards, these materials are employed as dopant-free hole transporting materials (HTMs) in planar inverted perovskite solar cell devices with the aim of determining the device performance and studying their stability in comparison with reference N4,N4,N4′′,N4′′-tetra([1,10-biphenyl]-4-yl)-[1,1′:4′,1′′-terphenyl]-4,4′′-diamine (TaTm)-based devic…
Dense ionic fluids confined in planar capacitors: in- and out-of-plane structure from classical density functional theory
2016
The ongoing scientific interest in the properties and structure of electric double layers (EDLs) stems from their pivotal role in (super)capacitive energy storage, energy harvesting, and water treatment technologies. Classical density functional theory (DFT) is a promising framework for the study of the in- and out-of-plane structural properties of double layers. Supported by molecular dynamics simulations, we demonstrate the adequate performance of DFT for analyzing charge layering in the EDL perpendicular to the electrodes. We discuss charge storage and capacitance of the EDL and the impact of screening due to dielectric solvents. We further calculate, for the first time, the in-plane str…
Fabrication and characterization of small tunnel junctions through a thin dielectric membrane
1998
We show that a small tapered hole through a thin silicon nitride membrane provides a mask for tunnel junction structures. Our experiments imply, unlike in the conventional planar electron beam lithography, that tunnel junctions are well voltage biased in this structure with vanishingly small on-chip impedance. Our technique allows fabrication of double junctions, and even multijunction linear arrays, with small metallic islands in between.
Planar Array Technology for the Fabrication of Germanium X-Ray Microcalorimeters
2008
Several technologies are presently competing for measuring the temperature increase in cryogenic micro-calorimeters used as high resolution energy-dispersive X-ray detectors. Doped germanium, whose resistivity depends on temperature, is a promising material for this purpose, because of its comparatively low specific heat and the possibility of making wafers with high doping uniformity by neutron transmutation. Presently, Ge-based microcalorimeters are still micro-machined and manually assembled. Here we present a planar approach to the fabrication of 2-D arrays of microcalorimeters and show the preliminary technological results.
Planar Technology for NDT-Ge X-Ray Microcalorimeters: Absorber Fabrication
2009
We have investigated the electroplating process to deposit thick uniform films of tin on a Ge wafer coated with Spin‐On Glass, in order to fabricate the absorbers for Ge microcalorimeter arrays. Here we discuss some technological details and propose two alternative metal bilayer to be used as seed for the electroplating.
Electroplated bismuth absorbers for planar NTD-Ge sensor arrays applied to hard x-ray detection in astrophysics
2018
Single sensors or small arrays of manually assembled neutron transmutation doped germanium (NTD-Ge) based microcalorimeters have been widely used as high energy-resolution detectors from infrared to hard X-rays. Several planar technological processes were developed in the last years aimed at the fabrication of NTD-Ge arrays, specifically designed to produce soft X-ray detectors. One of these processes consists in the fabrication of the absorbers. In order to absorb efficiently hard X-ray photons, the absorber has to be properly designed and a suitable material has to be employed. Bismuth offers interesting properties in terms of absorbing capability, of low heat capacity (needed to obtain h…
Mode expansion for the density profiles of crystal–fluid interfaces: hard spheres as a test case
2012
We present a technique for analyzing the full three-dimensional density profiles of a planar crystal-fluid interface in terms of density modes. These density modes can also be related to crystallinity order parameter profiles which are used in coarse-grained, phase field type models of the statics and dynamics of crystal-fluid interfaces and are an alternative to crystallinity order parameters extracted from simulations using local crystallinity criteria. We illustrate our results for the hard sphere system using finely-resolved, three-dimensional density profiles from density functional theory of fundamental measure type.
Energy leaks through the optical barrier created by H+ implantation in BaTiO3 and LiNbO3 planar waveguides
1998
Abstract The energy leaks through the index barrier created by the proton implantation process are put in evidence in planar optical waveguides made in BaTiO 3 and LiNbO 3 substrates. The selective detection of the light emerging from the guiding region permits to measure the optical attenuation of the guided wave. The results obtained on mono or twice implanted LiNbO 3 and BaTiO 3 waveguides are presented and discussed. It is shown that the light confinement is better in BaTiO 3 than in LiNbO 3 .