奈米碳管光磁性研究與探討

Abstract

有鑑於三聯吡啶釕錯合物（Tris(2,2'-bipyridine) ruthenium(Ⅱ)，簡稱[Ru(bpy)3]2+）是一具電化學發光特性的光敏劑，可在可見光照射下進行metal-to-ligand charge transfer（簡稱MLCT），具光電應用潛力，本實驗遂製備[Ru(bpy)3]2+的5-胺基菲羅啉（5-amino-1,10- phenanthroline，簡稱NH2-phen）衍生物：Bis(2,2'-bipyridine)-5-amino- 1,10-phenanthroline ruthenium(Ⅱ)（簡稱[Ru(bpy)2(NH2-phen)]2+），再利用化學偶氮修飾法將之修飾在多層奈米碳管表面，得到含釕錯合物奈米碳管，簡稱為Ru@CNT，以進行光磁轉換探討。 實驗結果顯示：在合成條件為13.5 mg [Ru(bpy)2(NH2-phen)]2+、5 mg CNT、0.8 mg NaNO2、20 mg AA與10 mL的0.1 M HCl，反應溫度為80℃，反應時間24 h，能合成出表面修飾較為均勻的Ru@CNT。若以VSM、AC susceptibility分析法、磁性模組與導電模組AFM進行分析，我們發現Ru@CNT受到藍光雷射（ex: 473 nm）照射時，表面上的釕吸附微粒會產生電荷分離，電子組態會由單重態轉變成參重態，而在室溫下產生磁性。若進一步分析其電子躍遷能位，我們推論Ru@CNT受光激發時，電子轉移障礙約為0.5 eV。由於此時MFM所測得的相位差明顯增加，間接證實其光磁性來自電荷分離與電荷轉移，顯示Ru@CNT具有光電與光磁轉換應用潛力。

Bis(2,2'-bipyridine)-5-amino-1,10-phenanthroline ruthenium(II) (Ru(bpy)2(NH2-phen)2+) is an MLCT complex, possessing a long-lived triplet state in water and a structure analogous to Ru(bpy)32+. When Ru(bpy)2(NH2-phen)2+ was subjected to diazotization in the presence of carbon nanotubes (CNTs), it formed nanodots on the CNTs, rendering the resulting tubes (Ru@CNT) capable of transducing photo stimuli (473 nm) into electricity and magnetism at ambient conditions. The increased functionality was highly reproducible, confirmed by the conductive-mode AFM, vibrating sample magnetometry (VSM), and AC susceptibility analysis. Local magnetism probing of the Ru@CNT with the magnetic-mode AFM techniques (MFM) indicated that the magnetism was originating from the photoexcited nanodots. The resulting phase shift behaved as a function of the luminous power and the voltage (Vb) of the electrical bias applied to the Ru@CNT. The Vb dependence deviated from the expected quadratic correlation, suggesting that the formation of the triplet state at the nanodots could be a limiting factor for the photomagnetism. Nevertheless, the Ru@CNT tubes showed mobility toward an external magnet when exposed to visible light on water. The Ru@CNT is thus shown as a multifunctional material that might be useful in spintronics.