有機雙穩態材料AIDCN(2-amino-4,5-imidazoledicarbonitrile)
為2004年發表的第一個有機雙穩態元件的材料，其工作原理仍然存在許多爭議。有機雙穩態元件的工作表現與電極有很大的關聯，目前研究顯示AIDCN以銀替代鋁為電極使得電流-電壓特性曲線在NDR(negative differential resistance)區域較穩定，論文所使用
的有機材料為AIDCN。
我們在新竹的國家同步輻射研究中心的 BL-08A 實驗站成功的在矽(111)上製備有機分子材料AIDCN蒸鍍於銀和鋁的表面，藉由同步輻射光電子能譜(synchrotron-radiation photoemission spectroscopy)研究其介面變化。實驗中所取得能譜的能量範圍為136電子伏特。根據價帶能譜，我們發現AIDCN/Ag在低薄膜厚度時AIDCN可以均勻平躺的成長在銀表面上，在高薄膜厚度時分子排列與低薄膜時的分子排列不同，在價帶能譜所顯示低厚度與高厚度之間最高已填滿軌域的能量差為0.5電子伏特，電洞注射位能障約0.2電子伏特。然而AIDCN/Al在低薄膜厚度時沒有可觀察到的最高已填滿軌域，原因可能是因為ADICN分子是凌亂的生長在鋁表面。因為這個原因使得靠近費米能階0.7電子伏特的部份有額外的電子態出現，即電洞注射位能障在相同厚度時相對於銀較小。

The electronic structures of interface between an organic bistable material 2-amino-4,5-imidazoledicarbonitrile (AIDCN) and electrode metal surfaces (Ag and Al) were investigated by ultraviolet photoemission spectroscopy. The electrical bistability strongly depends on metal electrodes, and the working mechanism is still controversial. The photoemission spectra of the highest occupied molecular orbital (HOMO) of AIDCN on Ag and Al substrate and the corresponding vacuum level (VL) shift are investigated in this thesis. The thickness dependence of VL shift shows a dip in both systems. In AIDCN/Ag system, the HOMO peak shows two-component line shape, which can be divided into the contributions from the monolayer state and mutilayer state. In AIDCN/Al system, a diffuse tailing structure was observed below Fermi edge (~1 eV), and attributed to random molecular orientation. The tailing structure causes lower hole injection barrier than Ag surface (~2 eV). Angle dependence photoemission data also infer different growth mechanism for AIDCN/Ag and AIDCN/Al interfaces.
For AIDCN/Ag, the intensity of HOMO peak increases with increasing incident angle for monolayer coverage, indicating that the pi bonds are normal to Ag surface according to the symmetry selection rule. In multilayer region, the AIDCN dipole moment orients at a certain angle with respect to surface normal on top of monolayer AIDCN. For AIDCN/Al, of the HOMO peak (and also the other peaks) is absent for 2.99 nm-thick AIDCN film on Al. As increasing AIDCN thickness, angular dependence of the HOMO peak gradually generated and it finally became similar to the bulk-like behavior, where the HOMO intensity shows a local maximum representing formation of the bulk phase. We also examined the AIDCN/Al2O3 system by dosing 11000 L oxygen on clean Al surface. The HOMO peak of AIDCN thin film is observed at lower coverage than that for AIDCN/Al. The hole injection barriers from Ag and Al to AIDCN were estimated to be 1.6 and 0.7 eV,
respectively.

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