Navegando por Autor "Guimarães, Luciano de Moura"

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Effects of post-lithography cleaning on the yield and performance of CVD graphene-based devices
(Beilstein Journal of Nanotechnology, 2019) Araujo, Eduardo Nery Duarte de; Sousa, Thiago Alonso Stephan Lacerda de; Guimarães, Luciano de Moura; Plentz, Flavio
The large-scale production of high-quality and clean graphene devices, aiming at technological applications, has been a great challenge over the last decade. This is due to the high affinity of graphene with polymers that are usually applied in standard lithography processes and that, inevitably, modify the electrical proprieties of graphene. By Raman spectroscopy and electrical-transport investigations, we correlate the room-temperature carrier mobility of graphene devices with the size of well-ordered domains in graphene. In addition, we show that the size of these well-ordered domains is highly influenced by post-photolithography cleaning processes. Finally, we show that by using poly(dimethylglutarimide) (PMGI) as a protection layer, the production yield of CVD graphene devices is enhanced. Conversely, their electrical properties are deteriorated as compared with devices fabricated by conventional production methods.
Eletrodeposição galvanostática de telureto de cádmio sobre silício monocristalino (111)
(Universidade Federal de Viçosa, 2006-12-21) Guimarães, Luciano de Moura; Albuquerque, José Eduardo de; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4760294Y0; Carvalho, Regina Simplício; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4786013T2; Carvalho, Alexandre Tadeu Gomes; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4787153D2; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4770245H6; Reis, Efraim Lázaro; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4788214H7; Ladeira, Luiz Orlando; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4787115T0
No presente trabalho, estudamos filmes finos de CdTe eletrodepositados galvanostaticamente em meio aquoso ácido (pH<1) sobre silício monocristalino, tipo-n, (111). A densidade de corrente de 0,3 mA/cm2 permitiu a obtenção de filmes de melhor qualidade. Os filmes foram caracterizados por microscopia eletrônica de varredura (SEM), difração de raios-X (XRD) e espectroscopia fotoacústica (PAS). Obtivemos depósitos que cobriram efetivamente o substrato tanto a temperatura ambiente quanto a 85 ºC. Os filmes depositados são cinza escuros e a tonalidade varia com a temperatura de deposição e a densidade de corrente. A SEM revelou nos filmes uma estrutura granular, sem indicações de faces que pudessem evidenciar algum arranjo cristalino. A XRD dos filmes depositados a 85 ºC mostrou picos associados à fase cúbica do CdTe e também picos correspondendo à fase hexagonal do telúrio e do cádmio livres. Porém a XRD dos filmes depositados a temperatura ambiente não mostrou picos que pudessem ser associados ao CdTe. Os filmes foram submetidos a tratamento térmico a 420 e 450 ºC, em atmosfera de nitrogênio, depois de umedecidos com solução saturada de CdCl2. A XRD dos filmes depois do tratamento térmico mostrou picos intensos associados à fase cúbica do CdTe, com orientação preferencial dos grãos na direção (111), tanto nos filmes depositados a temperatura ambiente quanto a 85 ºC. Os resultados mostraram também uma redução na concentração do Te e Cd livres. Micrografias SEM mostraram recristalização da superfície do filme devido ao tratamento térmico. As medidas de absorção óptica por PAS, efetuadas em filmes tratados termicamente, revelaram uma banda de absorção em torno do valor esperado do gap óptico do CdTe. Nossos experimentos mostraram também que os filmes de CdTe aderem melhor em substratos de silício não polidos.
Experimental and theoretical studies on the characterization of monocrotaline by infrared and Raman spectroscopies
(Journal of Molecular Structure, 2017-05-05) Oliveira, Ramon Prata; Demuner, Antonio Jacinto; Alvarenga, Elson Santiago; Parma, Monica Cropo; Barbosa, Luiz Claudio Almeida; Guimarães, Luciano de Moura; Aguiar, Alex Ramos
The use of plants in folk medicine has a long and ancient history in the treatment of various diseases. Currently, a large proportion of commercial drugs are based on natural products or are synthetic compounds inspired on such natural substances. Therefore, in this communication to aid that research, structural and spectroscopic analysis of the natural pyrrolizidine alkaloid called monocrotaline was carried out. Pyrrolizidine alkaloids that are commonly found in the Boraginaceae and Asteraceae families are among the great diversity of secondary metabolites which are produced by plants to act as a defense mechanism against herbivores and microbes. In the present study, the natural product, monocrotaline, an alkaloid isolated from the leaves of Crotalaria paulina, with potential application in medicine, was characterized by infrared (IR) and Raman spectroscopy with the support of Density Functional Theory (DFT) calculations. IR and Raman spectra of monocrotaline were recorded at room temperature ranging from 4000 to 400 cm 1 . DFT calculations with the hybrid functional B3LYP and the basis set 6-31 þ G(d,p) were performed with the purpose of obtaining information on the structural and vibrational properties of this structure. A perfect fit between the experimentally measured frequencies of the IR and Raman spectra and the calculated values were observed, and we have performed the complete identification of monocrotaline by these techniques.
Insights on physicochemical aspects of chitosan dispersion in aqueous solutions of acetic, glycolic, propionic or lactic acid
(International Journal of Biological Macromolecules, 2019-05-01) Soares, Lucas de Souza; Perim, Rayza Badiani; Alvarenga, Elson Santiago de; Guimarães, Luciano de Moura; Teixeira, Alvaro Vianna Novaes de Carvalho; Coimbra, Jane Sélia dos Reis; Oliveira, Eduardo Basílio de
Chitosan is a polysaccharide well-known for its applicability as a biocompatible, biodegradable, and non-toxic material to produce drugs excipients and food coatings. Acidic media are required to disperse chitosan, and aqueous solutions of acetic acid have been typically used for this purpose. However, this acid has several sensory drawbacks. In this study, chitosan was dispersed [0.1 g·(100 mL)−1] in aqueous media containing acetic (AA), glycolic (GA), propionic (PA), or lactic (LA) acid, at 10, 20, 30, 40, or 50 mmol·L−1. The increase of acid concentration reduced pH and viscosity of the dispersions, and |ζ potential| of dispersed particles. Conversely, it increased electrical conductivity and density of the dispersions, and hydrodynamic diameter of dispersed particles. At a given concentration, these effects were slightly more pronounced for dispersions formed with GA or LA, compared to AA or PA. FT-IR data suggested more intense attractive interactions of chitosan chains with glycolate and lactate anions, than with acetate and propionate. Chitosan chains interacted more strongly with hydroxylated acids counter-anions than with their non-hydroxylated counterparts, leading to slight quantitative changes of physicochemical properties of these systems. Then, in physicochemical terms, GA, LA or PA are suitable to replace AA when preparing aqueous chitosan dispersions for technological applications.