Search

Copyright of Revista Facultad de Ingeniería Universidad de Antioquia is the property of Universidad de Antioquia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The quantum Hall (QH) effect in two-dimensional electron systems (2DESs) is conventionally observed at liquid-helium temperatures, where lattice vibrations are strongly suppressed and bulk carrier scattering is dominated by disorder. However, due to large Landau level (LL) separation (~2000 K at B = 30 T), graphene can support the QH effect up to room temperature (RT), concomitant with a non-negligible population of acoustic phonons with a wave-vector commensurate to the inverse electronic magnetic length. Here, we demonstrate that graphene encapsulated in hexagonal boron nitride (hBN) realizes a novel transport regime, where dissipation in the QH phase is governed predominantly by electron-phonon scattering. Investigating thermally-activated transport at filling factor 2 up to RT in an ensemble of back-gated devices, we show that the high B-field behaviour correlates with their zero B-field transport mobility. By this means, we extend the well-accepted notion of phonon-limited resistivity in ultra-clean graphene to a hitherto unexplored high-field realm., (© 2023. The Author(s).)

Two-dimensional transition metal dichalcogenides (2D-TMDs) are among the most promising materials for exploring and exploiting exciton transitions. Excitons in 2D-TMDs present remarkably long lifetimes, even at room temperature. The spectral response of exciton transitions in 2D-TMDs has been thoroughly characterized over the past decade by means of photoluminescence spectroscopy, transmittance spectroscopy, and related techniques; however, the spectral dependence of their electronic response is still not fully characterized. In this work, we investigate the electronic response of exciton transitions in monolayer MoSe 2 via low-temperature photocurrent spectroscopy. We identify the spectral features associated with the main exciton and trion transitions, with spectral bandwidths down to 15 meV. We also investigate the effect of the Fermi level on the position and intensity of excitonic spectral features, observing a very strong modulation of the photocurrent, which even undergoes a change in sign when the Fermi level crosses the charge neutrality point. Our results demonstrate the unexploited potential of low-temperature photocurrent spectroscopy for studying excitons in low-dimensional materials, and provide new insight into excitonic transitions in 1L-MoSe 2 .

Ionic-liquid gating (ILG) is able to enhance carrier densities well above the achievable values in traditional field-effect transistors (FETs), revealing it to be a promising technique for exploring the electronic phases of materials in extreme doping regimes. Due to their chemical stability, transition metal dichalcogenides (TMDs) are ideal candidates to produce ionic-liquid-gated FETs. Furthermore, as recently discovered, ILG can be used to obtain the band gap of two-dimensional semiconductors directly from the simple transfer characteristics. In this work, we present an overview of the operation principles of ionic liquid gating in TMD-based transistors, establishing the importance of the reference voltage to obtain hysteresis-free transfer characteristics, and hence, precisely determine the band gap. We produced ILG-based bilayer WSe 2 FETs and demonstrated their ambipolar behavior. We estimated the band gap directly from the transfer characteristics, demonstrating the potential of ILG as a spectroscopy technique.

Two-dimensional transition metal dichalcogenide (TMD) phototransistors have been the object of intensive research during the last years due to their potential for photodetection. Photoresponse in these devices is typically caused by a combination of two physical mechanisms: the photoconductive effect (PCE) and photogating effect (PGE). In earlier literature for monolayer (1L) MoS 2 phototransistors, PGE is generally attributed to charge trapping by polar molecules adsorbed to the semiconductor channel, giving rise to a very slow photoresponse. Thus, the photoresponse of 1L-MoS 2 phototransistors at high-frequency light modulation is assigned to PCE alone. Here we investigate the photoresponse of a fully h-BN encapsulated monolayer (1L) MoS 2 phototransistor. In contrast with previous understanding, we identify a rapidly-responding PGE mechanism that becomes the dominant contribution to photoresponse under high-frequency light modulation. Using a Hornbeck-Haynes model for the photocarrier dynamics, we fit the illumination power dependence of this PGE and estimate the energy level of the involved traps. The resulting energies are compatible with shallow traps in MoS 2 caused by the presence of sulfur vacancies.

We report on the enhancement of responsivity by more than one order of magnitude of a silicon-based sub-terahertz detector when a mesoscopic dielectric particle was used to localize incident radiation to a sub-wavelength volume and focus it directly onto the detector. A strained-silicon modulation field-effect transistor was used as a direct detector on an incident terahertz beam at 0.3 THz. A systematic study in which Teflon cubes were placed in front of the detector to focus the terahertz beam was performed. In this study, cubes with different sizes were investigated, and an enhancement of the responsivity up to 11 dB was observed for a cube with an edge length of 3.45 mm (or 3.45 λ ). Electromagnetic simulation results were in good agreement with the experimental ones and demonstrated that the size of the mesoscopic particle plays an important role in focalizing the electric field within an area below the diffraction limit. This approach provides an efficient, uncostly, and easy to implement method to substantially improve the responsivity and noise equivalent power of sub-terahertz detectors.

Introduction: The influence of age and gender in the electrical charge delivered in a given population was analysed using an electroconvulsive therapy (ECT) clinical database., Material and Method: An observational, prospective, longitudinal study with descriptive analysis was performed using data from a database that included total bilateral frontotemporal ECT carried out with a Mecta spECTrum 5000Q ® in our hospital over 6 years. From 2006 to 2012, a total of 4,337 ECT were performed on 187 patients. Linear regression using mixed effects analysis was weighted by the inverse of the number of ECT performed on each patient per year of treatment., Results: The results indicate that age is related with changes in the required charge (P=.031), as such that the older the age a higher charge is needed. Gender is also associated with changes in charge (P=.014), with women requiring less charge than men, a mean of 87.3mC less. When the effects of age and gender are included in the same model, both are significant (P=.0080 and P=.0041). Thus, for the same age, women require 99.0mC less charge than men, and in both genders the charge increases by 2.3mC per year., Conclusions: From our study, it is concluded that the effect of age on the dosage of the electrical charge is even more significant when related to gender. It would be of interest to promote the systematic collection of data for a better understanding and application of the technique., (Copyright © 2015 SEP y SEPB. Publicado por Elsevier España, S.L.U. All rights reserved.)

Background: Health professionals who care for patients with imported diseases often lack enough training. The aim of the study is to assess the knowledge of Chagas disease among doctors and nurses attending at-risk pregnant women in our province., Method: descriptive study through a performed anonymous and voluntary knowledge questionnaire for 278 physicians and nurses working at maternity and children's health services in the three hospitals in the province. In Poniente Hospital was established in 2007 a program of screening for the disease in pregnant women. For statistical analysis, quantitative variables were described using the mean and standard deviation. For comparison of qualitative variables we used the chi-square test or Fisher exact test as appropriate. Differences in age and years of experience depending on the hospital were measured by Brown-Forsy the robust test., Results: 116 (41.7%) professionals agreed to participate in the study. 80 (69%) were women and 36 (31%) men, mean age 36.78 years. By professional categories, physicians have a mean of 73.9% correct responses, the nurses 50.7%. Poniente Hospital had the highest percentage of correct answers on aspects of the geographical distribution of the disease (73.7%), the mechanisms of transmission (86%) and diagnosis (82.5%)., Conclusions: The Poniente Hospital professionals generally have a better Knowledge about Chagas disease compared with two other professionals hospitals, which probably is related to the existence of the screening program for the disease.