Effect of high-k dielectric and ionic liquid gate on nanolayer black-phosphorus field effect transistors

Nanolayer black phosphorus (BP) is a direct bandgap semiconducting two dimensional crystal, showing immense promise for future nanoelectronic devices. Here, we report the effect of high-k dielectric and ionic-liquid gate in BP field effect transistors (BP FET). An ambipolar behavior is observed in pristine BP FETs with current modulation of 104. With a high-k HfO2 encapsulation, we observed identical switching performance in the BP FETs, however, with noticeable enhancement in mobility at room temperature. In comparison to the pristine device, the HfO2 encapsulation showed a contrasting decrease in mobility at lower temperatures. BP FETs with electric double layer ionic liquid gate showed a drastic improvement in the subthreshold swing (SS) to 173mV/dec and operation voltages less than 0.5V in comparison to solid state SiO2 back gated devices. Our results elucidate the effect of different electrostatic conditions on BP transistor channels and open up ways for further exploration of their prospects for nanoelectronic devices and circuits

Enhanced Tunnel Spin Injection into Graphene using Chemical Vapor Deposited Hexagonal Boron Nitride

The van der Waals heterostructures of two-dimensional (2D) atomic crystals constitute a new paradigm in nanoscience. Hybrid devices of graphene with insulating 2D hexagonal boron nitride (h-BN) have emerged as promising nanoelectronic architectures through demonstrations of ultrahigh electron mobilities and charge-based tunnel transistors. Here, we expand the functional horizon of such 2D materials demonstrating the quantum tunneling of spin polarized electrons through atomic planes of CVD grown h-BN. We report excellent tunneling behavior of h-BN layers together with tunnel spin injection and transport in graphene using ferromagnet/h-BN contacts. Employing h-BN tunnel contacts, we observe enhancements in both spin signal amplitude and lifetime by an order of magnitude. We demonstrate spin transport and precession over micrometer-scale distances with spin lifetime up to 0.46 nanosecond. Our results and complementary magnetoresistance calculations illustrate that CVD h-BN tunnel barrier provides a reliable, reproducible and alternative approach to address the conductivity mismatch problem for spin injection into graphene

Magnetoconductance anisotropy of a polymer thin film at the onset of metallicity

Thin films of poly(2,5-bis(3-dodecyl-2-yl)-thieno[3,2-b] thiophene) (C12-PBTTT) polymer under electrolyte gating and doping are investigated as model systems for organic thin films devices approaching the metallic side of a metal-insulator (M-I) transition. For the most doped samples, with an estimated density reaching 8 x 10(20) cm(-3) holes and a conductivity exceeding 1000 S cm(-1), a positive high-field magnetoconductance is found in a limited temperature range window and only when the field is perpendicular to the sample plane. This signature of weak localization, combined with indications of finite zero-temperature conductivity, allows us to identify delocalized metallic-like transport in these thin films, even though the conductivity decreases when cooling down the samples

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Influence of fabrication steps on optical and electrical properties of InN thin films

This paper reports on a case study of the impact of fabrication steps on InN material properties. We discuss the influence of annealing time and sequence of device processing steps. Photoluminescence (PL), surface morphology and electrical transport (electrical resistivity and low frequency noise) properties have been studied as responses to the adopted fabrication steps. Surface morphology has a strong correlation with annealing times, while sequences of fabrication steps do not appear to be influential. In contrast, the optical and electrical properties demonstrate correlation with both etching and thermal annealing. For all the studied samples PL peaks were in the vicinity of 0.7 eV, but the intensity and full width at half maximum (FWHM) demonstrate a dependence on the technological steps followed. Sheet resistance and electrical resistivity seem to be lower in the case of high defect introduction due to both etching and thermal treatments. The same effect is revealed through 1/f noise level measurements. A reduction of electrical resistivity is connected to an increase in 1/f noise level

Design of an efficient convolutional buck-boost converter for hybrid bioinspired parameter tuning

Power-electronic systems with voltage boosts use buck-boost converters. These converters suppress current and invert voltage to improve voltage swing. Power-electronic systems with voltage boosts use buck-boost converters that suppress current and invert voltage to improve voltage swings. Researchers propose many converter models, but their total harmonic distortion (THD) limits their scalability. Harmonics from additional current components increase THD. The model filters excessive currents using inductor-based storage, capacitive filters, and resistive circuits. However, these models are unstable, reducing their performance in large converter circuits. This text proposes a novel convolutional neural network (CNN) with a hybrid bioinspired model based on genetic algorithm (GA) and particle swarm optimization (PSO) to overcome this limitation. Estimating internal buck and boost parameters efficiently reduces reverse currents. These parameters include inductor current ripple, recommended inductance, internal switch current limit, and switching frequency. The model finds low-power, high-efficiency buck-boost configurations based on these values. Incremental learning operations tuned the GA model, which was applied to many buck-boost configurations. The proposed model had a 5.9% lower delay, 16.2% lower harmonics, and 4.6% better power efficiency than state-of-the-art buck-boost models

Nonlinear absorption of InN/InGaN multiple-quantum-well structures at optical telecommunication wavelengths

We report on the nonlinear optical absorption of InN/ InxGa 1-x N (x=0.8,0.9) multiple-quantum-well structures characterized at 1.55 μm by the Z-scan method in order to obtain the effective nonlinear absorption coefficient (α2) of the samples at high repetition rate. Saturable absorption is observed for the sample with x=0.9, with an effective α2 ∼-9× 103 cm/GW for the studied optical regime. For lower In content in the barrier, reverse saturable absorption is observed, which is attributed to two-photon absorption. © 2011 American Institute of Physics.Peer Reviewe

Evidence of charge carrier number fluctuations in InN thin films?

Due to its small band-gap and its high mobility, InN is a promising material for a large number of key applications like band-gap engineering for high efficiency solar cells, light emitting diodes, and high speed devices. Unfortunately, it has been reported that this material exhibits strong surface charge accumulation which may depend on the type of surface. Current investigations are conducted in order to explain the mechanisms which govern such a behavior and to look for ways of avoiding it and/or finding applications that may use such an effect. In this framework, low frequency noise measurements have been performed at different temperatures on patterned MBE grown InN layers. The evolution of the 1/f noise level with temperature in the 77 K-300 K range is consistent with carrier number fluctuations thus indicating surface mechanisms: the surface charge accumulation is confirmed by the noise measurements

Appropriation du lexique lors d’un séjour linguistique : une étude de cas quantitative et qualitative

Dans les études sur l’apprentissage des langues, on recourt principalement aux analyses qualitatives en tant que moyens de décrire l’état actuel ou en développement des compétences des apprenants de langues. Dans cet article nous nous proposons, premièrement, de traiter de cette problématique d’un point de vue spécifique, notamment, de celui du lexique à partir d’une étude développementale. Notre corpus est tiré des dissertations écrites avant et après un séjour linguistique dans un contexte semi-institutionnel. Deuxièmement, nous présentons les résultats des analyses quantitative et qualitative qui donnent, à notre avis, une image plus complète du phénomène en question. Finalement, nous traitons des possibilités et des limites de ce genre d’approche dans une recherche longitudinale sur le lexique d’apprenants de langues.Interlingual studies, as a means to describe the actual or developmental phase of a student’s language knowledge, are very often of a qualitative nature. The present article deals with this issue from a special point of view, that of vocabulary learning and/or acquisition during a stay abroad in a mixed linguistic environment, i.e., a (semi-) instructed and (semi-) naturalistic environment. The corpus consisted of dissertations gathered before and after the study abroad. Secondly, we present the results of the quantitative and qualitative analyses which, in our opinion, when combined, provide a more complete picture of the phenomenon under study. Finally, we discuss the possibilities and limitations of this kind of approach in order to describe the lexical development of some second language learners