Resonant enhancement of the 2G Raman band in twisted bilayer graphene

Ana Carolina Ferreira de Brito, Samuel Marques de Sousa, Helane Lucia Oliveira de Morais, Pedro Henrique Mendes da Costa, Nathanael Vieira Medrado, Mariana Castro de Prado, Ingrid David Barcelos, Érika Costa de Alvarenga, Bernardo Ruegger Almeida Neves, Ana Paula Moreira Barboza, and Taíse Matte Manhabosco. 2024. “Cutting-edge collagen biocomposite reinforced with 2D nano-talc for bone tissue engineering.” Nanomedicine: Nanotechnology, Biology and Medicine, Pp. 102756. Publisher's Version Abstract

The advancement of nanobiocomposites reinforced with 2D nano-materials plays a pivotal role in enhancing bone tissue engineering. In this study, we introduce a nanobiocomposite that reinforces bovine collagen with 2D nano-talc, a recently exfoliated nano-mineral. These nanobiocomposites were prepared by blending collagen with varying concentrations of 2D nano-talc, encompassing mono- and few-layers talc from soapstone nanomaterial. Extensive characterization techniques including AFM, XPS, nano-FTIR, s-SNOM nanoimaging, Force Spectroscopy, and PeakForce QNM® were employed. The incorporation of 2D nano-talc significantly enhanced the mechanical properties of the nanobiocomposites, resulting in increased stiffness compared to pristine collagen. In vitro studies supported the growth and proliferation of osteoblasts onto 2D nano-talc-reinforced nanobiocomposites, as well as showed the highest mineralization potential. These findings highlight the substantial potential of the developed nanobiocomposite as a scaffold material for bone tissue engineering applications.

Frederico B. Sousa, Rafael Nadas, Rafael Martins, Ana P. M. Barboza, Jaqueline S. Soares, Bernardo R. A. Neves, Ive Silvestre, Ado Jorio, and Leandro M. Malard. 2024. “Disentangling doping and strain effects at defects of grown MoS2 monolayers with nano-optical spectroscopy.” Nanoscale, Pp. -. Publisher's Version Abstract

The role of defects in two-dimensional semiconductors and how they affect the intrinsic properties of these materials have been a widely researched topic over the past few decades. Optical characterization techniques such as photoluminescence and Raman spectroscopies are important tools to probe the physical properties of semiconductors and the impact of defects. However, confocal optical techniques present a spatial resolution limitation lying in a μm-scale, which can be overcome by the use of near-field optical measurements. Here, we use tip-enhanced photoluminescence and Raman spectroscopies to unveil the nanoscale optical properties of grown MoS2 monolayers, revealing that the impact of doping and strain can be disentangled by the combination of both techniques. A noticeable enhancement of the exciton peak intensity corresponding to trion emission quenching is observed at narrow regions down to a width of 47 nm at grain boundaries related to doping effects. Besides, localized strain fields inside the sample lead to non-uniformities in the intensity and energy position of photoluminescence peaks. Finally, two distinct MoS2 samples present different nano-optical responses at their edges associated with opposite strains. The edge of the first sample shows a photoluminescence intensity enhancement and energy blueshift corresponding to a frequency blueshift for E2g and 2LA Raman modes. In contrast, the other sample displays a photoluminescence energy redshift and frequency red shifts for E2g and 2LA Raman modes at their edges. Our work highlights the potential of combining tip-enhanced photoluminescence and Raman spectroscopies to probe localized strain fields and doping effects related to defects in two-dimensional materials.

Tamara Teixeira, Gabriel H. Ribeiro, Guilherme R. Gonçalves, João Honorato, Katia M. Oliveira, and Rodrigo S. Correa. 2024. “Selective Ru(II)/benzoate complexes against triple-negative breast tumor cells and their interactions with DNA and BSA.” Inorganica Chimica Acta, Pp. 122078. Publisher's Version Abstract

New ruthenium(II) complexes bearing benzoate (AB) ligand with the general formula [Ru(AB)(bipy)(PP)]PF6, where 2,2′-bipyridine (bipy) and different diphosphine ligands, (PP) = 1,2′-bis(diphenylphosphine)ethane (dppe, 1), 1,3′-bis(diphenylphosphine)propane (dppp, 2) and 1,2′-bis(diphenylphosphine)ferrocene (dppf, 3), were synthesized. The compounds were characterized by molar conductivity, elemental analysis, cyclic voltammetry, infrared and UV–Vis spectroscopies, NMR, and by single-crystal X-ray diffraction for complexes 1 and 2. The complexes showed a weak interaction to CT-DNA through DNA minor groove, with Kb values at around 103-104 M−1. CT-DNA interaction assays by viscosity and circular dichroism (CD) suggested that the compounds do not significantly alter the secondary DNA structure. The complexes are cytotoxic against MDA-MB-231, MCF-7 (breast) and A549 (lung) tumor cell lines, with IC50 values in the range of 1 to 17 µM, presenting high selectivity against triple-negative breast tumor cells. Remarkably, complexes 1 and 3 show greater cytotoxic activity against cells than cisplatin, being promising agents for tumor treatment.

W. D. Freitas, M. S. C. Mazzoni, M. J. S. Matos, and B.R.L. Galvão. 2024. “Predicting molecular crystals of polynitrogen (N6) structures with cage-like geometries using ab initio evolutionary algorithm.” Chemical Physics Letters, 844, Pp. 141262. Publisher's Version Abstract

In this work, we employed Density Functional Theory calculations combined with search techniques based on evolutionary algorithms to predict and characterize crystalline structures composed of nitrogen (N6) cage-like molecules. We found stable molecular crystals and a rich phenomenology associated with their behavior under pressure, including atomic rebonding and semiconductor-metal transitions. This investigation resides in the context of high-energy-density materials, since molecular species containing only nitrogen atoms tend to dissociate into N2 molecules, releasing large amounts of energy.

Alex Milton Albergaria Campos, Amauri Leal, Sinésio Salles, and Paulo Santos Assis. 2024. “Biomass and energy connected with iron and steelmaking.” Tecnologia em Metalurgia, Materiais e Mineração, 21, Pp. 0–0.

Rafael N. Gontijo, Marcus V. O. Moutinho, Ariete Righi, Po-Wen Chiu, Pedro Venezuela, and Marcos A. Pimenta. 2024. “Resonant enhancement of the 2G Raman band in twisted bilayer graphene.” Materials Chemistry and Physics, Pp. 129279. Publisher's Version Abstract

Raman spectroscopy is an extremely useful tool to characterize graphene systems. The strongest Raman features are the first-order G band and the second-order 2D and 2D′ bands, which are the overtones of the double resonance D and D’ bands. However, the 2G band, which is the overtone of the G band, is not usually observed in the spectra of monolayer graphene and of crystalline graphite. In this work, we present an experimental and theoretical investigation of the resonance Raman spectra in twisted bilayer graphene (TBG) with different twisting angles and using several laser excitation energies in the NIR and visible ranges. We observed that the 2G band is enhanced when the incident photons are in resonance with the transition between the van Hove singularities in the density of states of the TBG. We show that the 2G band has three contributions (2G1, 2G2 and 2G3), that are not dispersive by changing the laser excitation energy. We also present theoretical calculations showing that the 2G1 and 2G2 bands are related to combinations of the in-phase (IP) and out-of-phase (OP) vibrations of the atoms in the different layers. The Raman excitation profiles (REPs) of the 2G peaks are upshifted in comparison with the REP of the G band. This behavior was confirmed theoretically using a graphene tight binding model. We conclude that the different resonance behavior comes from the fact that the G band is a first-order process whereas the 2G band is second-order processes giving rise to overall different resonance conditions.

Camila Cavalini, Cesar Rabahi, Caique S. de Brito, Eunji Lee, José R. Toledo, Felipe F. Cazetta, Raphael B. Fernandes de Oliveira, Marcelo B. Andrade, Mohamed Henini, Yuhao Zhang, Jeongyong Kim, Ingrid D. Barcelos, and Yara Galvão Gobato. 2024. “Revealing localized excitons in WSe2/β-Ga2O3.” Applied Physics Letters, 124, 14, Pp. 142104. Publisher's Version Abstract

We have investigated the optical and magneto-optical properties of monolayer (ML) WSe2 on flakes of β-Ga2O3 under high magnetic fields. Remarkably, sharp emission peaks were observed and associated with localized excitons related to point defects. A detailed study of low-temperature photoluminescence (PL) and magneto-PL under high perpendicular magnetic field up to 9 T was carried out. Several sharp emission peaks have shown valley g-factors values close to −4, which is an unusual result for localized excitons in WSe2. Furthermore, some PL peaks have shown higher g-factor values of ≈−7 and ≈−12, which were associated with the hybridization of strain localized dark excitons and defects. The reported results suggest that β-Ga2O3 is, indeed, a promising dielectric substrate for ML WSe2 and also to explore fundamental physics in view of possible applications in quantum information technology.

Marília I. F. Barbosa Javier Ellena Alzir A. Batista André V. Alves, Rafael G. Silveira and Rodrigo S. Corrêa. 2024. “cis and trans isomers of Ru(III)-based complexes with lapachol: X-ray diffractions and DFT theoretical insights.” Molecular Crystals and Liquid Crystals, 768, 5, Pp. 168-179. Publisher's Version

Gabriel H. A. Jorge, Filipe A. Couto, Juliana M. P. Almeida, Victor A. S. Marques, Marcelo B. Andrade, and Cleber R. Mendonça. 2024. “Active Optical Tuning of Azopolymeric Whispering Gallery Mode Microresonators for Filter Applications.” Photonics, 11, 2. Publisher's Version Abstract

Light confinement provided by whispering gallery mode (WGM) microresonators is especially useful for integrated photonic circuits. In particular, the tunability of such devices has gained increased attention for active filtering and lasering applications. Traditional lithographic approaches for fabricating such devices, especially Si-based ones, often restrict the device’s tuning due to the material’s inherent properties. Two-photon polymerization (2PP) has emerged as an alternative fabrication technique of sub-diffraction resolution 3D structures, in which compounds can be incorporated to further expand their applications, such as enabling active devices. Here, we exploited the advantageous characteristics of polymer-based devices and produced, via 2PP, acrylic-based WGM hollow microcylinders incorporated with the azoaromatic chromophore Disperse Red 13 (DR13). Within telecommunication range, we demonstrated the tuning of the microresonator’s modes by external irradiation within the dye’s absorption peak (at 514 nm), actively inducing a blueshift at a rate of 1.2 nm/(Wcm−2). Its thermo-optical properties were also investigated through direct heating, and the compatibility of both natural phenomena was also confirmed by finite element simulations. Such results further expand the applicability of polymeric microresonators in optical and photonic devices since optically active filtering was exhibited.

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Resonant enhancement of the 2G Raman band in twisted bilayer graphene

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