探討金屬與有機混成系統之電子結構與磁性耦合

Abstract

金屬與有機分子混成的材料因其特殊的性質所以具有相當好的發展潛力。如自旋過濾器、有機自旋電子學及半金屬等，對於未來的應用都是相當有前途。然而，鐵原子與苝四甲酸二酐(3, 4, 9, 10-perylene-tetracarboxylic-dianhydride)有機分子在金(111)表面的自組裝結構是很有趣的。因為此系統結合了磁性材料與有機分子，不單是電子結構，自旋磁性也是相當的重要。藉由低溫掃描穿隧式顯微鏡，我們觀察其成長模式與電子結構。再進一步的利用密度泛涵理論計算探討細部的性質。然而，密度泛涵理論計算的結果可以與低溫掃描穿隧式顯微鏡的量測互相配合，對於此系統我們可以有更完整的解釋。 在超高真空的環境下，我們可以控制鐵原子與苝四甲酸二酐有機分子在金(111)表面上的成長模式。並且在低溫的量測環境下，我們低溫掃描穿隧式顯微鏡的測量有著更好的穩定性。基於低溫掃描穿隧式顯微鏡的量測結果，配合密度泛涵理論計算，我們對於這自組裝系統建立了一個可信度高的幾何結構。在電子結構方面，我們實驗上解釋了此系統的電荷轉移。並且在密度泛涵理論計算得到了相似的結果。對於此系統的鍵結機制，我們也有完整的解釋。在磁性方面，我們發現有機分子在不同的自旋組態下會有不同的磁化表現。當在鐵磁態時，有機分子可以達到很高的自旋極化率。而在不同的自旋組態下，我們發現有機分子中的自旋電荷有類似RKKY的磁矩振盪出現。 我們的結果展示了磁性金屬與有機分子結合材料的潛力。由於不同的自旋組態能量差異甚大，此系統有著長距離磁性排列的特性；對於未來有機自旋電子學的發展與應用提供了一個基礎的知識。

Metal-organic hybrid systems are promising materials because of their special properties and applications. Such as, spin filter, organic spintronics, half-metal and spin injection. A self-assembly structure which consists of iron (Fe) and 3, 4, 9, 10-perylene-tetracarboxylic-dianhydride (PTCDA) on Au(111) is an interesting material due to the coupling of the magnetic material and the organic molecule. Not only the electronic structure but also the magnetic properties are important. Base on the scanning tunneling microscopy (STM) measurements, the growth mode and electronic structures can be resolved. To understand the details of this system, density functional theory (DFT) has been performed. The calculation results are signi_cant to compare with the STM measurements. Under ultra-high vacuum condition, we controlled the growth mode of Fe-PTCDA self-assembly structures on the Au(111) substrate. Based on the STM and STS measurements, we set up a reliable geometry structure for DFT calculations. For electronic structure, we analyzed the bonding mechanism between Fe and PTCDA, which is due to the d-orbital hybridization. Otherwise, the charging limitation of PTCDA in self-assembly system can be observed not only in DFT but also in STS measurements. For magnetic properties, we calculated the spin configurations of this system. The PTCDA molecules present spin-polarized and RKKY-like oscillations in different spin configurations. Our results show that the combination of magnetic materials and organic molecules has potentials for spintronic devices. Due to the significant energy difference between spin configurations, it's possible to build up a long range magnetic transport device. Moreover, our results provide a different insight in magnetism for metal-organic hybrid system.