苝四甲酸二酐有機自旋閥系統中介面特性對磁電容效應的影響

Abstract

我們成功地經由磁控濺鍍和熱蒸鍍的技術製備出苝四甲酸二酐(3,4,9,10-perylene-teracarboxylic dianhydride)有機自旋閥，且透過直流四點量測與交流兩點量測的分析技術對樣品做一系列的特性分析，並討論室溫之下樣品磁性與電性的性質。從 2奈米中間層厚度的有機自旋閥中得到具有14.6%磁電阻率以及-1.93%磁電容率的行為表現，並找出與以氧化鋁作為中間層的磁性穿隧元件截然不同的介面行為，也就是負數介面電容。我們推測這樣的行為表現來自於介面能階的電荷累積，而這種電荷累積是由金屬與有機介面偶極層和有機層內靠近介面邊緣處因能帶彎曲造成的擴散層所貢獻。此外，藉由分析磁阻抗頻譜以及介面電容的特性，討論有機自旋閥中不同中間層厚度的影響，並發現截止頻率會隨著有機自旋閥中中間層厚度增厚而變小，磁電容率的大小也與磁電阻率一樣會隨著厚度增厚而減少以及觀察出介面電容具有厚度依賴性的電荷累積情形。簡單地說，透過磁電容的量測分析技術，我們展示了介面電容與中間層特性及厚度的關係並提供了許多關於有機自旋閥系統中電容以及介面特性的相關資訊。

Organic spin valves (OSVs) with a thin organic semiconductor (OSC) spacer of 3,4,9,10-perylene-teracarboxylic dianhydride (PTCDA) were fabricated using magneto-sputtering and thermal evaporating technique, and characterized by DC four-probe sensing, AC two-terminal measuring analysis technique to discuss the magnetic and electric properties at room temperature. The magnetoresistance ratio of 14.6% and the magnetocapacitance of -1.93% were demonstrated in the OSV with 2nm-PTCDA spacer at room temperature. To figure out the negative interfacial capacitances, we speculate that the behavior is attributed to the charge accumulation at the metal-organic interfacial dipole layer and the diffusion layer induced by band bending. The capacitive property is different to the Al2O3-based magnetic tunnelling junction. Furthermore, the influence of spacer thickness to magnetoimpedance and interfacial capacitance in OSVs with three different thickness spacers are investigated. Working out that the cut-off frequency is got smaller as the OSV spacer became thicker in magnetoimpedance spectrum. The influence of spacer thickness to magnetocapacitance performance is decay with the same to magnetoresistance, and that charge accumulation at the interface states can be affected by the thickness of the PTCDA-spacer. Briefly, the interfacial capacitance related to the spacer thickness and characteristic using the analysis technique of magnetocapacitance is demonstrated, which provide the information about the capacitive and interfacial properties in PTCDA-OSV system.