利用同步輻射光電子發射研究金屬/8-羥基喹啉鋁(Alq3)界面

A synchrotron radiation photoemission study of metal-doped tris(8-hydroxyquinoline) aluminum (Alq3) interface

李欣翰(Hsin-Han Lee)

指導教授 ： 黃振昌 ； 皮敦文

國立清華大學/工學院/材料科學工程學系/博士(2009年)

https://doi.org/10.6843/NTHU.2009.00788

摘要

A series of electronic structures of the metal doped Alq3 interfaces have been characterized in-situ by using synchrotron radiation photoemission techniques. The benefit of the synchrotron radiation photoemission techniques are surface sensitivity that can be tuned by adjusting the photon energy provided by different monochromators in different beamlines at NSRRC.
Alkali metals, alkaline earth metals and Ag transition metal are chosen as the metals to dope into the Alq3 layers under ultrahigh vacuum in order to investigate the interaction between these metals and Alq3 molecules in details. The interaction may provide fundamental evidences regarding the possible chemical reaction occurred at the Alq3/cathode interface in the organic light emitting diodes (OLEDs). The major findings are the surface reaction near the metal/Alq3 interface that depends on the types of metal and the critical doping concentration.
At the Cs/Alq3 interface, a critical deposition time (220 s) exists, longer than which bond scission of Alq3 by Cs occurs. An Alq3 molecule may be disassembled into Csq and Alq2 by a formation of Csq through a bond scission mechanism. Subsequent formations of Alq and Al are also possible by bond scission of Alq2 and Alq by Cs.
The bond scission phenomenon also occurs at the K/Alq3 interface. A critical K concentration (x=2.4) exists above which the Al−O−C bonds next to the phenoxide ring are bond-scission. An Alq3 molecule may be disassembled into Kq and Alq2 by bond-scission and bondformation. The Alq2 is likely to be further dissociated into Alq or even Al through subsequent formations of Kq.
At the Ca/Alq3 interface, a critical Ca deposition time (4 min) exists. At deposition time longer than 4 min, the Al−O−C bonds next to the phenoxide ring are broken and reformed. An Alq3 molecule may be disassembled into Caq2 and Alq2 by bond-scission and bond-formation. In contrast, the strained C=N−C bonds in the pyridyl ring in Alq3 remain intact.
At the Ag/Alq3 interface, no chemical interaction between Ag and Alq3 occurs inferred from the same Al 2p, Ag 3d, N 1s and O 1s spectra at different deposition time. The Ag doping generates strained environments near the Al-O-C bonds next to the phenoxide ring and near C=N−C bonds in the pyridyl ring in Alq3.

關鍵字

同步輻射 ； 光電子

並列摘要

本篇論文利用同步輻射光電子技術量測金屬/Alq3界面的電子結構，同步輻射光電子技術的優點是，藉由不同的光束線的分光儀選取不同的光能量，提高表面靈敏度。 將鹼金屬、鹼土族金屬或銀，蒸鍍到Alq3表面，量測在超高真空環境下這些金屬與Alq3介面的反應，探討有機發光二極體（OLEDs）的Alq3/陰極可能發生的反應。論文最主要的發現是一些金屬會在金屬/Alq3界面，大於鍵切臨界蒸鍍量時，會發生鍵切現象（bond-scission）。 在Cs/Alq3界面，存在一個臨界蒸鍍時間（220秒）。當蒸鍍時間大於220秒，Alq3分子鍵會被Cs原子切掉而分解，產生Alq2和Csq，Alq2 和Alq分子會更近一步地被Cs原子切掉，形成Alq和Al。 在K/Alq3界面，存在一個臨界濃度（x=2.4）。當掺入濃度大於臨界濃度時，鄰近phenoxide環的Al−O−C鍵會K原子切掉，重新形成新鍵結。Alq3分子鍵會被K原子切掉而分解，產生Alq2和Kq。同樣地，Alq2會因為Kq的形成而分解成Alq甚至Al。 在Ca/Alq3界面，存在一個臨界蒸鍍時間（4分鐘）。當蒸鍍時間大於4分鐘時，鄰近phenoxide環的Al−O−C鍵會Ca原子切掉，重新形成新鍵結。Alq3分子會被Ca原子切掉而分解，產生Alq2和Caq2。相對地，在pyridyl環產生應變的C=N−C鍵沒有被切斷。 在Ag/Alq3界面，根據Al 2p、 Ag 3d、N 1s和O 1s能譜顯示，在Ag和Alq3之間不會產生化學反應，銀的摻入只會在鄰近phenoxide環的Al−O−C鍵與鄰近pyridyl環的C=N−C鍵，產生一個應變的環境。

並列關鍵字

Synchrotron ； Photoemission ； Alq3

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