1,719 research outputs found
Electronic and spintronic devices using two-dimensional materials
179 p.
El contenido del capítulo 8 está sujeto a confidencialidadEver since in 2004 atomically-thin two-dimensional van der Waals materials became available to the scientific community, at the reach of manual microexfoliation techniques, their implementation in novel device structures and concepts promised disruptive new applications and motivated research in a vast range of fields.Confined to the thinnest possible thickness, electrons in these materials exhibit a plethora of electronic properties, from semiconducting MoS2, to superconductor NbSe2, dielectric BN, and, jack-of-all trades, graphene.In this thesis, we explore fundamental and applied aspects of chemical vapor deposition (CVD) graphene, MoS2, and WSe2 using electronic device structures that use them as transporting channel, namely field-effect transistors (FETs), Hall bars, and diodes.MoS2 is a n-type semiconducting 2D vdW that complements one of the weak aspects of graphene-based transistors, which is the small ratio between the maximum current output and of the minimum current output of the transistors. Using MoS2 we identify an electron doping constraint for performing stable magnetotransport measurements, and we investigate the origins of the strong current fluctuations of the FETs. We study the low-frequency noise (LFN) of the current output of devices made with different layer thicknesses, and use the strong light-matter interactions of MoS2 to employ photodoping techniques together with the electrostatic gating to dope the channel. By converging all these conditions, we are able to discern the mechanism behind the different types of LFN noise reported in literature for MoS2, while at the same time identifying a LFN crossover driven by photodoping.With p-type semiconducting WSe2 we optimize the electron and hole transport properties of ambipolar FETs by considering BN as a top and bottom interface substrate and encapsulation layer, respectively. By doing so, we areable to address to some extent the strong hysteretic effects that adversely affect the operation of WSe2 FETs on oxide substrates, and improve the overall device performance.The versatility of CVD graphene allows us to do both applied and fundamental studies, both related to spintronics and electronics.The unique properties of graphene make it a core material in the search of full-electrical approaches to generate, transport, and detect spin currents without the use of magnetic elements. Using a Hall-bar shaped sample, non-local signals in graphene have been demonstrated to be associated with spin transport. In our case, we use the large area availability of CVD graphene to study non-local effects in an unlikely scenario for the transport of spins. We study the non-local signals of millimeter sized Hall-bars of CVD graphene, and by doing a systematic study as a function of device scale, from macro-to-microscale we identify a mechanism that cannot be connected with spin diffusion that also leads to large signals. By evaluating the microscopic details of the samples, and the different effects observed, we propose a mechanism mediated by grain boundaries to drive such effects.In a more applied manner, we use CVD graphene for two other types of devices. First, we study the use of graphene as an electrode material for lateral and vertical field-effect transistors that operate using organic channels, and determine that the low density of states of graphene allows for unscreened electric fields to reach the organic layer and enable the transistor operation in the vertical geometry.The second applied study is the large-scale fabrication of diodes using CVD graphene. Benefiting from the ultra-thin cross section of graphene, and using a lateral geometry we demonstrate the reliable fabrication of lateral metal/insulator/graphene diodes. The time constants determined from the direct-current analysis place the operation of the fabricated devices in the THz range. Additionally, the material combination considered enabled large current densities based on field-emission processes.CICnanoGUNE : nanoscience cooperative research cente
Electronic and spintronic devices using two-dimensional materials
179 p.
El contenido del capítulo 8 está sujeto a confidencialidadEver since in 2004 atomically-thin two-dimensional van der Waals materials became available to the scientific community, at the reach of manual microexfoliation techniques, their implementation in novel device structures and concepts promised disruptive new applications and motivated research in a vast range of fields.Confined to the thinnest possible thickness, electrons in these materials exhibit a plethora of electronic properties, from semiconducting MoS2, to superconductor NbSe2, dielectric BN, and, jack-of-all trades, graphene.In this thesis, we explore fundamental and applied aspects of chemical vapor deposition (CVD) graphene, MoS2, and WSe2 using electronic device structures that use them as transporting channel, namely field-effect transistors (FETs), Hall bars, and diodes.MoS2 is a n-type semiconducting 2D vdW that complements one of the weak aspects of graphene-based transistors, which is the small ratio between the maximum current output and of the minimum current output of the transistors. Using MoS2 we identify an electron doping constraint for performing stable magnetotransport measurements, and we investigate the origins of the strong current fluctuations of the FETs. We study the low-frequency noise (LFN) of the current output of devices made with different layer thicknesses, and use the strong light-matter interactions of MoS2 to employ photodoping techniques together with the electrostatic gating to dope the channel. By converging all these conditions, we are able to discern the mechanism behind the different types of LFN noise reported in literature for MoS2, while at the same time identifying a LFN crossover driven by photodoping.With p-type semiconducting WSe2 we optimize the electron and hole transport properties of ambipolar FETs by considering BN as a top and bottom interface substrate and encapsulation layer, respectively. By doing so, we areable to address to some extent the strong hysteretic effects that adversely affect the operation of WSe2 FETs on oxide substrates, and improve the overall device performance.The versatility of CVD graphene allows us to do both applied and fundamental studies, both related to spintronics and electronics.The unique properties of graphene make it a core material in the search of full-electrical approaches to generate, transport, and detect spin currents without the use of magnetic elements. Using a Hall-bar shaped sample, non-local signals in graphene have been demonstrated to be associated with spin transport. In our case, we use the large area availability of CVD graphene to study non-local effects in an unlikely scenario for the transport of spins. We study the non-local signals of millimeter sized Hall-bars of CVD graphene, and by doing a systematic study as a function of device scale, from macro-to-microscale we identify a mechanism that cannot be connected with spin diffusion that also leads to large signals. By evaluating the microscopic details of the samples, and the different effects observed, we propose a mechanism mediated by grain boundaries to drive such effects.In a more applied manner, we use CVD graphene for two other types of devices. First, we study the use of graphene as an electrode material for lateral and vertical field-effect transistors that operate using organic channels, and determine that the low density of states of graphene allows for unscreened electric fields to reach the organic layer and enable the transistor operation in the vertical geometry.The second applied study is the large-scale fabrication of diodes using CVD graphene. Benefiting from the ultra-thin cross section of graphene, and using a lateral geometry we demonstrate the reliable fabrication of lateral metal/insulator/graphene diodes. The time constants determined from the direct-current analysis place the operation of the fabricated devices in the THz range. Additionally, the material combination considered enabled large current densities based on field-emission processes.CICnanoGUNE : nanoscience cooperative research cente
Anti-viral effects of medicinal plants in the management of dengue: a systematic review
Background: Dengue is considered as an important arboviral disease. Safe, low-cost, and effective drugs that possess inhibitory activity against dengue virus (DENV) are mostly needed to try to combat the dengue infection worldwide. Medicinal plants have been considered as an important alternative to manage several diseases, such as dengue. As authors have demonstrated the antiviral effect of medicinal plants against DENV, the aim of this study was to review systematically the published research concerning the use of medicinal plants in the management of dengue using the PubMed database.Materials and Methods: Search and selection of publications were made using the PubMed database following the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA statement).Results: Six publications met the inclusion criteria and were included in the final selection after thorough analysis.Conclusion: It is suggested that medicinal plants’ products could be used as potential anti-DENV agents.Keywords: Dengue, arbovirus, medicinal plants, PubMe
Measurement of the cosmic ray spectrum above eV using inclined events detected with the Pierre Auger Observatory
A measurement of the cosmic-ray spectrum for energies exceeding
eV is presented, which is based on the analysis of showers
with zenith angles greater than detected with the Pierre Auger
Observatory between 1 January 2004 and 31 December 2013. The measured spectrum
confirms a flux suppression at the highest energies. Above
eV, the "ankle", the flux can be described by a power law with
index followed by
a smooth suppression region. For the energy () at which the
spectral flux has fallen to one-half of its extrapolated value in the absence
of suppression, we find
eV.Comment: Replaced with published version. Added journal reference and DO
Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory
The Auger Engineering Radio Array (AERA) is part of the Pierre Auger
Observatory and is used to detect the radio emission of cosmic-ray air showers.
These observations are compared to the data of the surface detector stations of
the Observatory, which provide well-calibrated information on the cosmic-ray
energies and arrival directions. The response of the radio stations in the 30
to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of
the incoming electric field. For the latter, the energy deposit per area is
determined from the radio pulses at each observer position and is interpolated
using a two-dimensional function that takes into account signal asymmetries due
to interference between the geomagnetic and charge-excess emission components.
The spatial integral over the signal distribution gives a direct measurement of
the energy transferred from the primary cosmic ray into radio emission in the
AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air
shower arriving perpendicularly to the geomagnetic field. This radiation energy
-- corrected for geometrical effects -- is used as a cosmic-ray energy
estimator. Performing an absolute energy calibration against the
surface-detector information, we observe that this radio-energy estimator
scales quadratically with the cosmic-ray energy as expected for coherent
emission. We find an energy resolution of the radio reconstruction of 22% for
the data set and 17% for a high-quality subset containing only events with at
least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO
Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy
We measure the energy emitted by extensive air showers in the form of radio
emission in the frequency range from 30 to 80 MHz. Exploiting the accurate
energy scale of the Pierre Auger Observatory, we obtain a radiation energy of
15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV
arriving perpendicularly to a geomagnetic field of 0.24 G, scaling
quadratically with the cosmic-ray energy. A comparison with predictions from
state-of-the-art first-principle calculations shows agreement with our
measurement. The radiation energy provides direct access to the calorimetric
energy in the electromagnetic cascade of extensive air showers. Comparison with
our result thus allows the direct calibration of any cosmic-ray radio detector
against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI.
Supplemental material in the ancillary file
EFFECT OF MECHANICAL VIBRATION GENERATED IN OSCILLATING/VIBRATORY PLATFORM ON THE CONCENTRATION OF PLASMA BIOMARKERS AND ON THE WEIGHT IN RATS.
Background: Whole body vibration (WBV) exercise has been used in health sciences. Authors have reported that
changes on the concentration of plasma biomarkers could be associated with the WBV effects. The aim of this
investigation is to assess the consequences of exposition of 25 Hz mechanical vibration generated in
oscillating/vibratory platform (OVP) on the concentration of some plasma biomarkers and on the weight of rats.
Materials and Methods: Wistar rats were divided into two groups. The animals of the Experimental Group (EG) were
submitted to vibration (25 Hz) generated in an OVP with four bouts of 30 seconds with rest time of 60 seconds between
the bouts. This procedure was performed daily for 12 days. The animals of the control group (CG) were not exposed to
vibration.
Results: Our findings show that the WBV exercise at 25 Hz was not capable to alter significantly (
Pervasive gaps in Amazonian ecological research
Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear un derstanding of how ecological communities respond to environmental change across time and space.3,4
While the increasing availability of global databases on ecological communities has advanced our knowledge
of biodiversity sensitivity to environmental changes,5–7 vast areas of the tropics remain understudied.8–11 In
the American tropics, Amazonia stands out as the world’s most diverse rainforest and the primary source of
Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepre sented in biodiversity databases.13–15 To worsen this situation, human-induced modifications16,17 may elim inate pieces of the Amazon’s biodiversity puzzle before we can use them to understand how ecological com munities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus
crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced
environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple or ganism groups in a machine learning model framework to map the research probability across the Brazilian
Amazonia, while identifying the region’s vulnerability to environmental change. 15%–18% of the most ne glected areas in ecological research are expected to experience severe climate or land use changes by
2050. This means that unless we take immediate action, we will not be able to establish their current status,
much less monitor how it is changing and what is being lostinfo:eu-repo/semantics/publishedVersio
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