arXiv subjects

Rodrigo G. Lacerda

Publications and source records attributed to Rodrigo G. Lacerda.

7 recordsLinked to original sources

arXiv2025

Graphene-based magnetoelastic biosensor for COVID-19 serodiagnosis

This work presents an innovative magnetoelastic (ME) biosensor using graphene functionalized with the SARS-CoV-2 N protein for antibody detection via magnetoelastic resonance. Graphene was chosen for its biocompatibility and high surface area, enabling efficient antigen adsorption, validated by techniques such as energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), and micro-Raman spectroscopy. Changes in Raman bands (a $\sim 10~\mathrm{cm}^{-1}$ shift in the 2D band and an increase in the $I_D/I_G$ ratio from 0.03 to 0.60) confirmed non-covalent interactions and enhanced surface coverage with ~100 $μ$g of N protein. Tests using human plasma (10 RT-PCR-positive and 10 negative samples) demonstrated a clear distinction between groups using graphene sensors functionalized with ~100 $μ$g of N protein. Enzyme-linked immunosorbent assay (ELISA) validation corroborated the results. Optimization of protein concentration and biofunctionalization time highlighted the importance of homogeneous surface coverage for reproducibility of the graphene-based ME biosensor. The platform combines graphene's advantages with the wireless, real-time detection capabilities of ME sensors, offering low cost, high sensitivity, and potential for automation, with applications in point-of-care diagnostics.

physics.bio-ph↗

arXiv2020

Gate-tunable non-volatile photomemory effect in MoS$_2$ transistors

Non-volatile memory devices have been limited to flash architectures that are complex devices. Here, we present a unique photomemory effect in MoS$_2$ transistors. The photomemory is based on a photodoping effect - a controlled way of manipulating the density of free charges in monolayer MoS$_2$ using a combination of laser exposure and gate voltage application. The photodoping promotes changes on the conductance of MoS$_2$ leading to photomemory states with high memory on/off ratio. Such memory states are non-volatile with an expectation of retaining up to 50 % of the information for tens of years. Furthermore, we show that the photodoping is gate-tunable, enabling control of the recorded memory states. Finally, we propose a model to explain the photodoping, and we provide experimental evidence supporting such a phenomenon. In summary, our work includes the MoS$_2$ phototransistors in the non-volatile memory devices and expands the possibilities of memory application beyond conventional memory architectures.

physics.app-ph↗

arXiv2020

Local photodoping in monolayer MoS2

Inducing electrostatic doping in 2D materials by laser exposure (photodoping effect) is an exciting route to tune optoelectronic phenomena. However, there is a lack of investigation concerning in what respect the action of photodoping in optoelectronic devices is local. Here, we employ scanning photocurrent microscopy (SPCM) techniques to investigate how a permanent photodoping modulates the photocurrent generation in MoS2 transistors locally. We claim that the photodoping fills the electronic states in MoS2 conduction band, preventing the photon-absorption and the photocurrent generation by the MoS2 sheet. Moreover, by comparing the persistent photocurrent (PPC) generation of MoS2 on top of different substrates, we elucidate that the interface between the material used for the gate and the insulator (gate-insulator interface) is essential for the photodoping generation. Our work gives a step forward to the understanding of the photodoping effect in MoS2 transistors and the implementation of such an effect in integrated devices.

physics.app-ph↗

arXiv2020

Probing the Electronic Properties of Monolayer MoS$_2$ via Interaction with Molecular Hydrogen

This work presents a detailed experimental investigation of the interaction between molecular hydrogen (H$_2$) and monolayer MoS$_2$ field effect transistors (MoS$_2$ FET), aiming for sensing application. The MoS$_2$ FET exhibits a response to H$_2$ that covers a broad range of concentration (0.1 - 90%) at a relatively low operating temperature range (300-473 K). Most important, H$_2$ sensors based on MoS$_2$ FETs show desirable properties such as full reversibility and absence of catalytic metal dopants (Pt or Pd). The experimental results indicate that the conductivity of MoS$_2$ monotonically increases as a function of the H$_2$ concentration due to a reversible charge transferring process. It is proposed that such process involves dissociative H$_2$ adsorption driven by interaction with sulfur vacancies in the MoS$_2$ surface (VS). This description is in agreement with related density functional theory studies about H$_2$ adsorption on MoS$_2$. Finally, measurements on partially defect-passivated MoS$_2$ FETs using atomic layer deposited aluminum oxide consist of an experimental indication that the VS plays an important role in the H$_2$ interaction with the MoS$_2$. These findings provide insights for futures applications in catalytic process between monolayer MoS$_2$ and H$_2$ and also introduce MoS$_2$ FETs as promising H$_2$ sensors.

physics.app-ph↗

arXiv2017

Tuning the pn junction at a metal-graphene interface via H2 exposure

Combining experiment and theory, we investigate how the naturally created heterojunction at a graphene and metallic contact is modulated via interaction with molecular hydrogen (H2). Due to electrostatic interaction, a Cr/Au electrode induces a pn junction in graphene, leading to an asymmetrical resistance between the charge carriers (electron and hole). This asymmetry is well modeled by considering the preferential charge scattering at the pn junction, and we show that it can be modulated in a reversible, selective and asymmetrical manner by exposing H2 to the metal-graphene interface. Our results are valuable for understanding the nature of the metal-graphene interfaces and demonstrate a novel route towards hydrogen sensor application. KEYWORDS: graphene, contact resistance,

cond-mat.mes-hall↗

arXiv2014

Observation of strain-free rolled-up CVD graphene single layers: towards unstrained heterostructures

Single layer graphene foils produced by Chemical Vapor Deposition (CVD) are rolled with self-positioned layers of InGaAs/Cr forming compact multi-turn tubular structures that consist on successive graphene/metal/semiconductor heterojunctions on a radial superlattice. Using elasticity theory and Raman spectroscopy we show that it is possible to produce homogeneously curved graphene with curvature radius on the 600nm-1200nm range. Additionally, the study of tubular structures also allows the extraction of values for the elastic constants of graphene that are in excellent agreement with elastic constants found in the literature. However, our process has the advantage of leading to a well-defined and nonlocal curvature. Since our curvature radius lie in a range between the large radius studied using mechanical bending and the reduced radius induced by Atomic Force Microscopy experiments we can figure out whether bending effects can be a majoritary driving force for modifications in graphene electronic status. From the results described in this work one can assume that curvature effects solely do not modify the Raman signature of graphene and that strain phenomena observed previously can be ascribed to stretching due to the formation of local atomic bonds. This implies that the interactions of graphene with additional materials on heterostructures must be investigated in detail prior to the development of applications and devices.

cond-mat.mtrl-sci↗

arXiv2013

ZnO UV photodetector with controllable quality factor and photosensitivity

ZnO nanowires have an enormous potential for applications as ultra-violet (UV) photodetectors. Their mechanism of photocurrent generation is intimately related with the presence of surface states where considerable efforts, such as surface chemical modifications, have been pursued to improve their photodetection capabilities. In this work, we report a step further in this direction demonstrating that the photosensitivity and quality factor (Q factor) of the photodetector are entirely tunable by an applied gate voltage. This mechanism enables UV photodetection selectivity ranging from wavelengths from tens of nanometers (full width at half maximum - FWHM) down to a narrow detection of 3 nm. Such control paves the way for novel applications, especially related to the detection of elements that have very sharp luminescence.

cond-mat.mes-hall↗