Navegando por Autor "Neme, Natália Paz"

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Electromechanical modulations in transition metal dichalcogenide nanosheets : implications for environmental sensors.
(2021) Bessa, Maurício Vasconcelos; Freitas, Wellington Damaceno de; Neme, Natália Paz; Martins, Luiz Gustavo Pimenta; Barboza, Ana Paula Moreira; Matos, Matheus Josué de Souza; Mazzoni, Mário Sérgio de Carvalho; Neves, Bernardo Ruegger Almeida
Transition metal dichalcogenides (TMDs) are key players in the two-dimensional materials nanoarena due to their exquisite optoelectronic properties under a standard environment (room temperature and atmospheric pressure). Nevertheless, as reported in the literature, they may also portray interesting physical properties under different environments. Here, we show two distinct and significant electromechanical modulations in TMD nanosheets which are tuned by the environmental conditions (applied pressure and adsorbents). Using scanning probe microscopy techniques, we modify the environmental conditions and observe steplike rises in the electrical response of all studied TMDs (MoS2, WS2, MoSe2, and WSe2monolayers and few layers). Ab initio calculations enable full understanding of specific mechanisms behind these electromechanical modulations, which may find important applications in the design of TMD-based environmental sensors.
Electronic band tuning and multivalley raman scattering in monolayer transition metal dichalcogenides at high pressures.
(2022) Martins, Luiz Gustavo Pimenta; Carvalho, Bruno Ricardo de; Occhialini, Connor A.; Neme, Natália Paz; Park, Ji-Hoon; Song, Qian; Venezuela, Pedro Paulo de Mello; Mazzoni, Mário Sérgio de Carvalho; Kong, Jing; Comin, Riccardo
Transition metal dichalcogenides (TMDs) possess spin-valley locking and spin-split K/K′ valleys, which have led to many fascinating physical phenomena. However, the electronic structure of TMDs also exhibits other conduction band minima with similar properties, the Q/Q′ valleys. The intervalley K−Q scattering enables interesting physical phenomena, including multivalley superconductivity, but those effects are typically hindered in monolayer TMDs due to the large K−Q energy difference (ΔEKQ). To unlock elusive multivalley phenomena in monolayer TMDs, it is desirable to reduce ΔEKQ, while being able to sensitively probe the valley shifts and the multivalley scattering processes. Here, we use high pressure to tune the electronic properties of monolayer MoS2 and WSe2 and probe K−Q crossing and multivalley scattering via double-resonance Raman (DRR) scattering. In both systems, we observed a pressure-induced enhancement of the double-resonance LA and 2LA Raman bands, which can be attributed to a band gap opening and ΔEKQ decrease. First-principles calculations and photoluminescence measurements corroborate this scenario. In our analysis, we also addressed the multivalley nature of the DRR bands for WSe2. Our work establishes the DRR 2LA and LA bands as sensitive probes of strain-induced modifications to the electronic structure of TMDs. Conversely, their intensity could potentially be used to monitor the presence of compressive or tensile strain in TMDs. Furthermore, the ability to probe K−K′ and K−Q scattering as a function of strain shall advance our understanding of different multivalley phenomena in TMDs such as superconductivity, valley coherence, and valley transport.
Estudo das propriedades de filmes finos de hidróxido ftalocianina de alumínio e de dissulfeto de molibdênio hidrogenado por primeiros princípios.
(2020) Neme, Natália Paz; Mazzoni, Mário Sérgio de Carvalho; Matos, Matheus Josué de Souza; mazzoni@fisica.ufmg.br; matheusmatos@ufop.edu.br; Mazzoni, Mário Sérgio de Carvalho; Ribeiro, Guilherme de Almeida Silva; Barboza, Ana Paula Moreira
Neste trabalho investigamos, por meio de cálculos de primeiros princípios baseados na Teoria do Funcional da Densidade, dois problemas independentes: a formação de filmes finos de Hidróxido Ftalocianina de Alumínio (AlOHPc) e a hidrogenação parcial de monocamadas de Dissulfeto de Molibdênio MoS2. O primeiro trabalho teve como principal motivação explicar os resultados experimentais que mostraram um comportamento diferente do esperado para os filmes finos de AlOHPc depositados a partir da técnica de spin-coating. Os resultados mostraram um deslocamento hipsocrômico no espectro de absorção do filme e a difração de Raios X mostrou que ocorre uma distância interplanares no filme fino. Inicialmente caracterizamos a molécula monomérica e, em seguida, calculamos o espectro de absorção, orbitais moleculares e estados excitados da molécula. Posteriormente, foram feitos diversos cálculos para diferentes dimerizações com o objetivo de encontrar a possível agregação dos filmes experimentais. Os espectros de absorção para o monômero e dímeros foram comparados como equivalentes aos espectros da solução e filme fino, respectivamente. Resultados mostraram que o monômero possui uma maior contribuição eletrônica HOMO para LUMO, com uma alta intensidade no espectro de absorção. Para os diferentes tipos de agregados foi calculado um blue shift no espectro de absorção, concordando com os resultados experimentais. Por fim, foram feitas simulações de diferentes configurações cristalinas assim como cálculo da difração de Raios X dessas cristalizações. O segundo trabalho também teve como motivação resultados experimentais nos quais mono- e multi-camadas de MoS2 são submetidas a pressões em meios ricos em moléculas de H2O. Isso acontece, por exemplo, em experimentos de Microscopia de Força Atômica (AFM) - nesse caso, um campo elétrico também pode ser aplicado e o comportamento eletrônico da amostra monitorado via medidas de injeção de carga. Na etapa inicial de aplicação de força, grupos -H podem ser gerados próximos à superfície do material podendo assim interagir com a superfície do MoS2 . Procuramos, mais especificamente, por transições no comportamento eletrônico que possam ser detetadas na caracterização da amostra por Microscopia de Força Elétrica. Nossos resultados mostram uma transição semicondutor-metal reversível que é compatível com os resultados experimentais obtidos.
Nanostructured system based on hydroxyapatite and curcumin : a promising candidate for osteosarcoma therapy.
(2023) Marinho, Jéssica Pauline Nunes; Neme, Natália Paz; Matos, Matheus Josué de Souza; Batista, Ronaldo Junio Campos; Macedo, Waldemar Augusto de Almeida; Gastelois, Pedro Lana; Gomes, Dawidson Assis; Rodrigues, Michele Angela; Cipreste, Marcelo Fernandes; Sousa, Edésia Martins Barros de
Osteosarcoma is the most common type of bone cancer. Despite therapeutic progress, survival rates for meta- static cases or that do not respond well to chemotherapy remain in the 30% range. In this sense, the use of nanotechnology to develop targeted and more effective therapies is a promising tool in the fight against cancer. Nanostructured hydroxyapatite, due to its biocompatibility and the wide possibility of functionalization, is an interesting material to design nanoplatforms for targeted drug delivery. These platforms have the potential to enable the use of natural substances in the fight against cancer, such as curcumin. Curcumin is a polyphenol with promising properties in treating various types of cancer, including osteosarcoma. In this work, hydroxyapatite (n- HA) nanorods synthesized by the hydrothermal method were investigated as a carrier for curcumin. For this, first-principle calculations based on the Density Functional Theory (DFT) were performed, in which the modi- fication of curcumin (CM) with the coupling agent (3-aminopropyl) triethoxysilane (APTES) was theoretically evaluated. Curcumin was incorporated in n-HA and the drug loading stability was evaluated by leaching test. Samples were characterized by a multi-techniques approach, including Fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy (UV–Vis), X-ray diffraction (XRD), X-ray fluorescence spectrometry (FRX), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), zeta potential analysis (ζ), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results show that n-HAs with a 90 nm average size were obtained and successful incorporation of curcumin in the nanostructure was achieved. Cell viability and the number of osteosarcoma cells were decreased by CMAP-HA treatment. Furthermore, the stability test suggests that hydroxyapatite nanoparticles present great potential for the trans- portation of curcumin in the bloodstream, crediting this system for biological performance evaluations aiming at the treatment of osteosarcomas. Keywords: nanostructures, curcumin, hydroxyapatite, osteosarcoma.
Synthesis, photophysical and electrochemical properties of novel and highly fluorescent difluoroboron flavanone β-diketonate complexes.
(2020) Ariza Paez, Elida Betania; Curcio, Sergio Fernando; Neme, Natália Paz; Matos, Matheus J. S.; Correa, Rodrigo de Souza; Pereira, Fabio Junio; Hilário, Flaviane Francisco; Cazati, Thiago; Taylor, Jason Guy
Difluoroboron β-diketonates complexes are highly luminescent with extensive properties such as their fluorescence both in solution and in solid state and their high molar extinction coefficients. Due to their rich optical properties, these compounds have been studied for their applications in organic electronics such as in self-assembly and applications in biosensors, bio-imaging and optoelectronic devices. The easy and fast synthesis of difluoroboron β-diketonate (BF2dbm) complexes makes their applications even more attractive. Although many different types of difluoroboron β-diketonates complexes have been studied, the cyclic flavanone analogues of these compounds have never been reported in the literature. Therefore, the present work aims to synthesize difluouroboron flavanone β-diketonate complexes, study their photophysical and electrochemical properties and assess their suitability for applications in optoelectronic devices. The synthesis was based on a Baker–Venkataraman reaction which initially provided substituted diketones, which were subsequently reacted with aldehydes to afford the proposed flavanones. The complexation was achieved by reacting flavanones and BF3. Et2O and in total 9 novel compounds were obtained. A representative difluoroboron flavanone complex was subjected to single crystal X-ray diffraction to unequivocally confirm the chemical structure. A stability study indicated only partial degradation of these compounds over a few days in a protic solvent at elevated temperatures. Photophysical studies revealed that the substituent groups and the solvent media significantly influence the electrochemical and photophysical properties of the final compounds, especially the molar absorption coefficient, fluorescence quantum yields, and the band gap. Moreover, the compounds exhibited a single excitedstate lifetime in all studied solvent. Computational studies were employed to evaluate ground and excited states properties and carry out DFT and TDDFT level analysis. These studies clarify the role of each state in the experimental absorption spectra as well as the effect of the solvent.