Otimização do processo de deposição de filmes de óxido de cobalto usando magnetron sputtering reativo
Carregando...
Data
2018-09-24
Autores
Azevedo Neto, Nilton Francelosi
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
A motivação para este trabalho foi buscar uma melhor compreensão sobre o processo de crescimento dos filmes de óxido de cobalto pela técnica de DC magnetron sputtering reativo. Os filmes de interesse foram depositados sobre substratos de sílica amorfa (a -SiO2 ), aluminato de lantânio (LaAlO3 ) e safira - c (Al2O3- c) usando diferentes valores de potência de deposição e fluxo de oxigênio . As condições de crescimento dos filmes foram analisadas utilizando simulação computacional do processo de sputtering reativo baseada no modelo de Depla, medidas da emissão óptica das espécies presentes no plasma e monitor amento da taxa de crescimento através de uma microbalança de quartzo. Os resultados de difração de raios X mostraram que em baixa potência é obtida a fase Co3O4 espinélio, enquanto que em alta potência os filmes apresentaram a fase CoO cúbica . A s simulações computacionais do processo de sputtering reativo indicaram que , quando as potências de deposição são baixas, o processo de crescimento dos filmes ocorre com o alvo no regime “envenenado” . Em contraste, altas potencias favorece m o regime metálico do alvo. Medidas de emissão do plasma de deposição mostraram que em baixa potência de deposição a intensidade da linha de emissão do oxigênio é alta , porém com o aumento da potência sua intensidade diminui e a d a linha do cobalto aumenta. O s filmes de Co 3 O 4 depositados sobre substratos cristalinos apresentaram resultados promissores . Medidas de difração de raios X de alta resolução , utilizando radiação síncrotron , indicaram que a deposição do Co 3 O 4 sobre Al2O3 - c resultou em crescimento epitaxial na qual a direção [ 111] do cristal de Co 3 O 4 é perpendicular à superfície do substrato de safira - c (0001). Enquanto que a deposição sobre LaAlO 3 resultou em crescimento com forte textura de orientação, com as direções [220] e [400] perpendiculares à superfície dos substratos . Os espectros Raman dessas amostras apresentaram picos de vibração bem definidos e característicos da fase Co 3 O 4 e a análise do Raman polarizado do s filmes de Co 3 O 4 sobre Al 2 O 3 - c concorda m com as regras de seleção para a orientação [111] . Para os filmes c om fase Co 3 O 4 , medidas de transmitância na região do UV - Vis - NIR mostraram alta absorção na região do visível e bandas de absorção no infravermelho próximo relacionadas a transições eletrônicas dos íons de Co 2+ e Co 3+ . Para esse crescimento observou - se também resposta intensa de fotocondutividade com exc itação em 405 nm e 532 nm em 10 K. Testes preliminares de fotocatálise indicaram que os filmes de Co 3 O 4 produzidos possuem uma pequena atividade fotocatalítica para degradação do corante Rodamina B. Neste trabalho uma correlação direta entre as condições de crescimento e as mudança s de fase do s filmes foi obtida, demonstrando a versatilidade da técnica de sputtering para crescimento de filmes de óxido de cobalto para estudos científicos e aplicações tecnológicas.
The motivation for this work was to obtain a better understanding of the growth process of cobalt oxides by the DC magnetron reactive sputtering technique. The films were dep osited on amorphous silica (a-SiO2), lanthanum aluminate (LaAlO3) and sapphire-c (c-Al2O3) substrates using different values of deposition power and oxygen flow. The conditions of growth of the films were analyzed using the optical analysis of the species present in the plasma and the monitoring of the growth rate through a quartz microbalance. The X-ray diffraction results showed that at lower powers the Co3O4 phase was obtained, while at high er power s the films presented the CoO cubic phase. The computational simulations of the reactive sputtering process indicated that, at low deposition power, the gro wth process of the films occurs with the target in the "poisoned" regime, while in high powers it favors the metallic regime of the target. Plasma emission measurements showed that at low deposition power the oxygen intensity is high while at high power it s intensity decreases and that of cobalt increases. The Co 3 O 4 films deposited on crystalline substrates showed promising results. High - resolution X-ray diffraction measurements using synchrotron radiation indicated that the deposition of Co3O4 on c-Al2O3 resulted in epitaxial growth , in which the direction [111] is perpendicular to the surface of the c - sapphire (0001) substrates. However, the deposition on LaAlO 3 resulted in growth with strong texture in the directions [220] and [400]. The Raman spectra of these samples showed well - defined vibration peaks characteristic of the Co3O4 phase . The polarized Raman analysis of Co 3 O 4 deposited on c-Al2O3 agrees with the selection rules for the [111] orientation, in agreement with the high resolution X-ray diffraction analysis . In the optical transmittance measurements , t he films with Co 3 O 4 phase displayed high absorption bands in the region of the visible and near - infrared . These bands are related to el ectronic transitions of the Co2+ and Co3+ ions. For these films , strong photoconductivity responses were observed for excitations at 405 nm and 532 nm at 10 K . Preliminary photocatalysis tests indicated that the Co3O4 films produced by sputtering have a small photocatalytic activity for Rhodamine B (RhB) dye degradation. Concluding , a direct correlation between the growth conditions and the phase changes of the films was obtained, demonstrating the versatility of the sputtering technique for the growth of cobalt oxide films for scientific studies and technological applications.
The motivation for this work was to obtain a better understanding of the growth process of cobalt oxides by the DC magnetron reactive sputtering technique. The films were dep osited on amorphous silica (a-SiO2), lanthanum aluminate (LaAlO3) and sapphire-c (c-Al2O3) substrates using different values of deposition power and oxygen flow. The conditions of growth of the films were analyzed using the optical analysis of the species present in the plasma and the monitoring of the growth rate through a quartz microbalance. The X-ray diffraction results showed that at lower powers the Co3O4 phase was obtained, while at high er power s the films presented the CoO cubic phase. The computational simulations of the reactive sputtering process indicated that, at low deposition power, the gro wth process of the films occurs with the target in the "poisoned" regime, while in high powers it favors the metallic regime of the target. Plasma emission measurements showed that at low deposition power the oxygen intensity is high while at high power it s intensity decreases and that of cobalt increases. The Co 3 O 4 films deposited on crystalline substrates showed promising results. High - resolution X-ray diffraction measurements using synchrotron radiation indicated that the deposition of Co3O4 on c-Al2O3 resulted in epitaxial growth , in which the direction [111] is perpendicular to the surface of the c - sapphire (0001) substrates. However, the deposition on LaAlO 3 resulted in growth with strong texture in the directions [220] and [400]. The Raman spectra of these samples showed well - defined vibration peaks characteristic of the Co3O4 phase . The polarized Raman analysis of Co 3 O 4 deposited on c-Al2O3 agrees with the selection rules for the [111] orientation, in agreement with the high resolution X-ray diffraction analysis . In the optical transmittance measurements , t he films with Co 3 O 4 phase displayed high absorption bands in the region of the visible and near - infrared . These bands are related to el ectronic transitions of the Co2+ and Co3+ ions. For these films , strong photoconductivity responses were observed for excitations at 405 nm and 532 nm at 10 K . Preliminary photocatalysis tests indicated that the Co3O4 films produced by sputtering have a small photocatalytic activity for Rhodamine B (RhB) dye degradation. Concluding , a direct correlation between the growth conditions and the phase changes of the films was obtained, demonstrating the versatility of the sputtering technique for the growth of cobalt oxide films for scientific studies and technological applications.
Descrição
Palavras-chave
Co3O4, CoO, Sputtering reativo, Crescimento de filmes, Estrutura, Reactive sputtering, Film growth, Structure