多孔性氧化鋁薄膜之發光性質研究及其在光學上應用

Abstract

本研究的目的是以純鋁的陽極處理法製備多孔性氧化鋁薄膜，並且研究其光激發光特性，更進ㄧ步利用氧化鋁薄膜為基板，製造奈米光學材料—硫化鉛奈米晶體，作為其光學應用的延伸。此研究內容分為下列兩部份: 首先採用三種不同陽極處理溶液所製備出的氧化鋁模板其孔徑分別為20、80及200奈米，進行光激發光實驗後發現，只有利用草酸溶液製備的氧化鋁薄膜才能產生高效能的藍光特性，其發光強度隨著氧化鋁薄膜厚度增加而增強，針對其放射光譜分析，發現此一高效能的藍光是由兩種發光中心所貢獻，短波長部份(443 奈米)來源為氧缺陷，而較長波長部分(470奈米)為草酸溶液中解離出來的陰離子所造成。此外藉由掃描式電子顯微鏡觀察與放射光譜分析可以得知草酸雜質於氧化鋁薄膜中概略的分布情形。 另一方面, 將氧化鋁薄膜應用於製造奈米的光學材料硫化鉛奈米晶體前，需要先利用真空鑄造法製備出鉛的奈米線陣列，由穿透式電子顯微鏡以及凝固行為的理論計算顯示利用此製程可製得不同線徑的單晶奈米線。使用此奈米線陣列與硫化氫氣體進行反應，控制不同的反應溫度及時間，可以得到邊長約為8奈米的硫化鉛正方晶體，由光激發光實驗得知，此硫化鉛奈米晶體具有橘紅光的放光特性，相較於硫化鉛塊材(發光特性為紅外光)顯現出強烈的量子限制效應，且隨著反應時間增加，晶體成長過程中所形成的晶體缺陷對於奈米晶體的發光強度有著顯著的影響。

The objective of this research is to investigate the photoluminescence properties of porous alumina membranes prepared by anodization method. Furthermore, it is an application of porous alumina membranes to work as a template fabricating an optical nanomaterial, PbS nanocrystals. The research results can be divided into two parts. Porous alumina membranes were produced by anodization method in three kinds of electrolytes in this study. As indicated by the PL emission spectra, the alumina membrane prepared only in oxalic acid solution has a strong blue emission band and the intensity of PL band increases with increasing thickness of alumina membranes. According to the deconvolution of the PL spectra by Gaussian functions, both centers contribute greatly to the PL emission band, one at 443 nm is correlated with the oxygen vacancies and the other at 470 nm is originated from the oxalic impurities. Finally, a distribution of oxalic impurities in the porous alumina wall can be found by the results of SEM and PL experiments. Before the production of PbS nanocrystals in porous alumina membrane, we have to fabricate Pb nanowires in alumina membranes by the pressure casting process firstly. According to the theoretical calculation and TEM analyses, the nanowires prepared by the pressure casting process are single crystal structure regardless of the diameter. Then, the PbS nanocrystals can be produced by the reaction between Pb nanowires and H2S gas. According to the PL spectra, there is a broad orange-red emission band in PbS nanocrystals and the existence of the defects would induce the nonradiative transition and substantially decline the intensity of the emission band. In this study, it can be found that a significant quantum confinement effect makes the energy gap of PbS nanocrystals produce a blue shift from 0.41eV to 1.89 eV.