Atomistic quantum transport modeling of metal-graphene nanoribbon heterojunctions

We calculate quantum transport for metal-graphene nanoribbon heterojunctions within the atomistic self-consistent Schr\"odinger/Poisson scheme. Attention is paid on both the chemical aspects of the interface bonding as well the one-dimensional electrostatics along the ribbon length. Band-bending and doping effects strongly influence the transport properties, giving rise to conductance asymmetries and a selective suppression of the subband formation. Junction electrostatics and p-type characteristics drive the conduction mechanism in the case of high work function Au, Pd and Pt electrodes, while contact resistance becomes dominant in the case of Al.Comment: 4 pages, 5 figure

An Ensemble of Adaptive Classifiers for Improving Faulty and Drifting Sensor Performance

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Low temperature deactivation of Ge heavily n-type doped by ion implantation and laser thermal annealing

International audienceHeavy doping of Ge is crucial for several advanced micro-and optoelectronic applications, but, at the same time, it still remains extremely challenging. Ge heavily n-type doped at a concentration of 1 X 10(20) cm(-3) by As ion implantation and melting laser thermal annealing (LTA) is shown here to be highly metastable. Upon post-LTA conventional thermal annealing As electrically deactivates already at 350 degrees C reaching an active concentration of similar to 4 x 10(19) cm(-3). No significant As diffusion is detected up to 450 degrees C, where the As activation decreases further to similar to 3 x 10(19) cm(-3). The reason for the observed detrimental deactivation was investigated by Atom Probe Tomography and in situ High Resolution X-Ray Diffraction measurements. In general, the thermal stability of heavily doped Ge layers needs to be carefully evaluated because, as shown here, deactivation might occur at very low temperatures, close to those required for low resistivity Ohmic contacting of n-type Ge

Temperature- and quantum phonon effects on Holstein-Hubbard bipolarons

The one-dimensional Holstein-Hubbard model with two electrons of opposite spin is studied using an extension of a recently developed quantum Monte Carlo method, and a very simple yet rewarding variational approach, both based on a canonically transformed Hamiltonian. The quantum Monte Carlo method yields very accurate results in the regime of small but finite phonon frequencies, characteristic of many strongly correlated materials such as, e.g., the cuprates and the manganites. The influence of electron-electron repulsion, phonon frequency and temperature on the bipolaron state is investigated. Thermal dissociation of the intersite bipolaron is observed at high temperatures, and its relation to an existing theory of the manganites is discussed.Comment: 12 pages, 7 figures; final version, accepted for publication in Phys. Rev.

Room Temperature CO Detection by Hybrid Porphyrin-ZnO Nanoparticles

AbstractPorphyrins are the natural candidates to the detection of carbon monoxide however the physical properties of solid-state layers of porphyrins limit their use as gas sensors mainly with mass and optical transducers. Recently we shown that the photonic properties of porphyrins, brilliantly exploited in organic solar cells, can lead to a new class of photo-activated sensors made by porphyrins coated metal oxides. Here we investigate the sensitivity to carbon monoxide of resistive sensors made by zinc oxide nanoparticles coated by a porphyrin layer. Sensors were prepared following two different routes and tested, at room temperature and in various light conditions, to CO and few volatile compounds. Results show a significant sensitivity and selectivity to CO

Indicators Blends Extend the Receptive Field of Colorimetric Chemical Sensors

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Chiral recognition with broad selective sensor arrays

The detection and discrimination of chiral analytes has always been a topical theme in food and pharmaceutical industries and environmental monitoring, especially when dealing with chiral drugs and pesticides, whose enantiomeric nature assessment is of crucial importance. The typical approach matches novel chiral receptors designed ad hoc for the discrimination of a target enantiomer with emerging nanotechnologies. The massive synthetic efforts requested and the difficulty of analyzing complex matrices warrant the ever-growing exploitation of sensor array as an alternative route, using a limited number of chiral or both chiral and achiral sensors for the stereoselective identification and dosing of chiral compounds. This review aims to illustrate a little-explored winning strategy in chiral sensing based on sensor arrays. This strategy mimics the functioning of natural olfactory systems that perceive some couples of enantiomeric compounds as distinctive odors (i.e., using an array of a considerable number of broad selective receptors). Thus, fundamental concepts related to the working principle of sensor arrays and the role of data analysis techniques and models have been briefly presented. After the discussion of existing examples in the literature using arrays for discriminating enantiomers and, in some cases, determining the enantiomeric excess, the remaining challenges and future directions are outlined for researchers interested in chiral sensing applications

The vanadium isotope composition of Mars: Implications for planetary differentiation in the early solar system

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nielsen, S. G., Bekaert, D., V., Magna, T., Mezger, K., & Auro, M. The vanadium isotope composition of Mars: Implications for planetary differentiation in the early solar system. Geochemical Perspectives Letters, 15, (2020): 35-39, doi:10.7185/geochemlet.2032.The V isotope composition of martian meteorites reveals that Bulk Silicate Mars (BSM) is characterised by δ51V = −1.026 ± 0.029 ‰ (2 s.e.) and is thus ∼0.06 ‰ heavier than chondrites and ∼0.17 ‰ lighter than Bulk Silicate Earth (BSE). Based on the invariant V isotope compositions of all chondrite groups, the heavier V isotope compositions of BSE and BSM relative to chondrites are unlikely to originate from mass independent isotope effects or evaporation/condensation processes in the early Solar System. These differences are best accounted for by mass dependent fractionation during core formation. Assuming that bulk Earth and Mars both have a chondritic V isotopic compostion, mass balance considerations reveal V isotope fractionation factors Δ51Vcore-mantle as substantial as −0.6 ‰ for both planets. This suggests that V isotope systematics in terrestrial and extraterrestrial rocks potentially constitutes a powerful new tracer of planetary differentiation processes accross the Solar System.This work was funded by NASA Emerging Worlds grant NNX16AD36G to SGN. Samples were acquired with funds from the Helmholtz Association through the research alliance HA 203 “Planetary Evolution and Life” to KM. TM contributed through the Strategic Research Plan of the Czech Geological Survey (DKRVO/ČGS 2018-2022). KM acknowledges support through NCCR PlanetS supported by the Swiss National Science Foundation. We thank Jurek Blusztajn for support in the WHOI Plasma Facility

Drift Correction in a Porphyrin-coated ZnO Nanorods Gas Sensor

AbstractPhotoconductivity and gas sensitivity cooperate in porphyrins coated ZnO nanostructures. However, in organic coated semiconductors the former is regulated by a number of mechanisms, involving the charge transfer in the organic layer. Since organic layers are poor conductors these processes are quite slow and the sensor may exhibits a long time drift before to be operative as gas sensor. In this paper we show that under light modulation, the carrier frequency component of the signal is free of drift and it can readily indicate the interaction with volatile compounds