碳六十多晶薄膜於不同溫度下之光電特性

Variation of photoelectronic properties of C60 polycrystalline films with temperature

王聖欣(Sheng-Shin Wang)

指導教授 ： 邱寬城

中原大學/理學院/應用物理研究所/碩士(2009年)

https://doi.org/10.6840/cycu200901088

摘要

本文利用物理汽相沉積 (Physical vapor deposition, PVD) 法，固定基板端溫度Tsub = 370 ± 5℃，並藉由改變粉末端溫度Tsou (400 ~ 500℃) 與成長時間τg (0.5 ~ 3 h)，以製備覆蓋性及結晶大小均勻之不同厚度C60多晶薄膜。在物性量測方面，首先，利用光穿透量測，可得出一系列隨厚度變化之光穿透頻譜，並觀察到 10 根不隨溫度變化的吸收峰。這些吸收峰的成因可用分子之間的凡得瓦爾力作用造成 Davydov 分裂與 Herzberg - Teller (HT) 能階偶合所建構出一個符合 C60 分子固體能項架構模型來解釋。其中，特徵能量峰值E = 2.016 eV 對應 S0 至 S1 能階之躍遷，以及 E = 1.688 eV為 S0 至 T1 能階躍遷所致。然後藉由光電導率頻譜 (PC) 與光激螢光光譜 (PL) 之結果，與光穿透量測 (PT) 結果互相比較，這三者間有一致性的峰值對應關係，並吻合上述之分子能項架構。另外，根據光激螢光光譜與時間響應頻譜 (TRPL) 量測，於變溫條件 20 ~ 300 K 下，觀察其中四根主要之 PL 峰值之光譜衰減時間為 ns 等級，証明其放出的光為螢光。再由光電導率頻譜所得之結果，取對光反應最明顯的特徵電流峰值能量 1.824 eV，做 30 ~ 120 K 持續性光電導率 (PPC) 的變溫量測，探討 C60 多晶薄膜上缺陷捕捉中心之性質。最後，根據抽氣時間越長，C60 多晶薄膜之暗電流值越大的性質，可用來探討氧分子在 C60 分子固體中的影響，包括活化壁障的大小與對 256 K 有序 - 無序相轉變溫度附近之電流變化，並利用 Arrehinius plot 擬合暗電流隨溫度倒數的變化。

關鍵字

捕捉中心 ； 光學能階 ； 物理汽相沉積法

並列摘要

In this study, C60 polycrystalline films of various thicknesses are prepared in a physical vapor deposition system with fixed substrate temperature Tsub (= 370℃) but with changing source temperature Tsou (400 to 500℃) and growth time (0.5 to 3 h). From temperature dependent photo-transmittance (PT) spectra, 10 absorption peaks are clearly observed and their energy positions are temperature independent. These peaks are explained in terms of an energy-terms diagram due to the Davydov splitting and Herzberg-Teller coupling for C60 molecular solid to account for the interplay between the intramolecular and intermolecular interactions. Among these peaks, the peak with E = 2.016 eV is proposed to be corresponding to the transition from S0 - state derived band to S1 - state derived band; while the one with E = 1.688 eV corresponding to the transition from S0 - state to T1 - state. Then, photoconductivity (PC) and photoluminescence (PL) spectra are measured and compared with PT spectra, and a well correspondence among PT, PC and PL is observed and it agrees with the proposed energy - terms diagram. Furthermore, according to the time-resolved PL spectra, the decay-time constants for the major four peaks (with E = 1.521, 1.608, 1.653, and 1.696 eV) are observed to be in the nano-sec order, and therefore the fluorescence characteristic is again confirmed. In addition, the decay of persistent PC with incident photon energy of 1.824 eV is measured to study the properties of trapping centers in these polycrystalline C60 molecular solid. Finally, under a dynamic vacuum system, a time dependent dark current profile for an O2 - exposed sample is taken for the investigation of the effects from O2 molecules. As the stay-period of the sample in the dynamic vacuum system goes longer, the dark current increases and the dark current variation near the structural - phase transition temperature of 256 K becomes more complicate.

並列關鍵字

trapping center ； optical band gap ； physical vapor deposition

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