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Master's Dissertation
DOI
https://doi.org/10.11606/D.18.2020.tde-19062020-165157
Document
Author
Full name
Weverton Alison dos Santos Silva
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 2020
Supervisor
Committee
Mastelaro, Valmor Roberto (President)
Mazon, Talita
Volanti, Diogo Paschoalini
Title in Portuguese
Modificação da morfologia de filmes finos de ZnO através de ataque químico: estudo do efeito sobre as propriedades sensoras ao gás ozônio
Keywords in Portuguese
ataque químico
filmes finos
HCl
sputtering
ZnO
Abstract in Portuguese
O presente estudo teve como objetivo investigar a influência do ataque químico por ácido clorídrico (HCl) nas propriedades sensoras ao gás ozônio (O3) de filmes de óxido de zinco (ZnO). Filmes entre 20 a 1570 nm espessuras foram obtidos por RF-Magnetron Sputtering a partir de um alvo de zinco sendo em seguida submetidos a um tratamento térmico ex-situ em um forno com atmosfera ambiente. Medidas de difração de raios X (DRX) e espalhamento Raman mostraram que a fase hexagonal wurtizita do ZnO P63/mc foi obtida em filmes tratados a 500 °C por 1 hora. As morfologias dos filmes foram analisadas por microscopia eletrônica de varredura (MEV) antes e após a imersão em ácido, na qual observa-se superfícies mais compactas e tamanhos de grãos menores para filmes de menor espessura e uma superfície mais porosa e maiores tamanhos de grãos para filmes mais espessos. Em relação ao ataque ácido, há um aumento na área superficial para maiores tempos de ataque. A caracterização composicional por espectroscopia de fotoelétrons excitados por raios X (XPS) mostrou que a componente centrada em 533 cm-1 do espectro de alta resolução do oxigênio 1s aumenta para maiores tempos de ataque, sugerindo um aumento na densidade de defeitos superficiais nessas amostras. As medidas realizadas com gás O3 em função da espessura apresentaram um máximo de resposta para filmes com espessura de 80 nm provavelmente devido a uma melhor sinergia entre a contribuição do tamanho de grão e o grau de porosidade. Os resultados obtidos sugerem que esta metodologia de modificação da morfologia pode ser utilizada para melhorar a sensibilidade e tempo de resposta de filmes finos e espessos de ZnO assim como de outros materiais óxidos metálicos semicondutores aplicados como sensores de gases.
Title in English
Modification of the morphology of thin films of ZnO through chemical attack: study of the effect on ozone gas sensing properties
Keywords in English
chemical attack
HCl
sputtering
thin films
ZnO
Abstract in English
The present study aimed to investigate the influence of chemical attack by hydrochloric acid (HCl) on the sensing properties of zinc oxide (ZnO) thin films to ozone gas (O3). Films between 20 to 1570 thicknesses was obtained by RF-Magnetron Sputtering from a zinc target and then subjected to ex-situ heat treatment in an ambient atmosphere furnace. X-ray diffraction (XRD) and Raman scattering measurements showed that the ZnO P63/mc wurtizite hexagonal phase was obtained at films treated 500 °C for 1 hour. The morphologies of the films was analyzed by scanning electron microscopy (SEM) before and after acid immersion, in which more compact surfaces and smaller grains sizes were observed for thinner films and a more porous surface and larger grains size for thicker films. Concerning the acid attack, there is an increase in surface area for longer attack times. The compositional characterization by X-ray photoelectron spectroscopy (XPS) showed that the 533 cm-1 centered component of the oxygen 1s high-resolution spectrum increases for longer attack times, suggesting an increase in the density of surface defects in these samples. The measurements made with O3 gas as a function of thickness had the maximum response for films with an intermediate thickness of 80 nm due probably due to a better synergy balance between the contributions of grain particle size contribution and porosity level. As a result of the attack, the response for all thicknesses increased with a maximum sample response of 80 nm. However, the largest relative increase for the response was presented by the 500 nm sample. The results obtained suggests that this method of altering morphology can be used to improve the sensitivity and response time of ZnO thin and thick films as well as other semiconductor metal oxide materials applied as gas sensors.
 
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Publishing Date
2021-06-28
 
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