We have investigated the interfaces of aluminum on tris-(8-hydroxyquinoline) aluminum (Alq3) and aluminum on LiF/Alq3, using x-ray and ultraviolet photoemission spectroscopy (UPS). Aluminum appears to react destructively with Alq3 causing significant modification of the oxygen, nitrogen, and aluminum spectra. The well-defined UPS spectrum of Alq3 is quickly destroyed by very low coverages of aluminum. With only a 5 Å layer of LiF on the Alq3, the reaction with aluminum is significantly suppressed. The Alq3 molecular orbital features in the UPS shift to higher binding energy but remain easily recognizable. In addition, a well-defined gap-state forms which is significantly different from that produced without LiF. Both the core-level spectra and the gap-state suggest that the Alq3 anion is formed in the presence of aluminum and LiF.
Wet-only removal of post-etch (meth-)acrylate based photoresist on porous low-k dielectrics applied in either resist or metal hard mask based patterning is investigated. Characterization of photoresist degradation by etch is applied to support the selection of wet cleaning chemistries and/or cleaning processes. FTIR and 1H-NMR analysis results indicate a common degradation mechanism for both patterning schemes with formation of double carbon bonds in a cross-linked crust that is insoluble in organic solvents. Even though a common degradation method is observed, resist cleanability in metal hard mask applications is by far more difficult due to a higher degree of resist cross-linking. Cleaning approaches by dissolution in solvents in combination with physical forces, for both patterning schemes, are discussed in detail.
Stability is an essential issue in the application of organic light-emitting devices (OLEDs). We have investigated the indium tin oxide (ITO) surface for operated and unoperated OLEDs using x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques. The device structure consists of ITO/phenyl-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq3)/Mg:Ag with NPB thickness varied from 0 to 300 Å. The ITO surface was exposed by removing the organic and metal layers with dichloromethane, an organic solvent in which NPB and Alq3 are highly soluble. Electroluminescence characterization demonstrates that the NPB layer substantially enhanced the stability. XPS analysis shows that for the device made without NPB and after 90 h of operation, there exists an insoluble organic material on the ITO surface. This organic material is not observed on the ITO of unoperated devices. Lateral force AFM also shows a striking difference between the ITO surface of devices with and without NPB after operation. The XPS and AFM results suggest that the organic residue is the degradation product of Alq3 that acts as quenching sites at the ITO/Alq3 interface, which contribute to the early failure of the single-layer devices.
The formation of the interface between a thin film of a ladder-type poly(para-phenylene) m-LPPP and aluminum was investigated with x-ray and ultraviolet photoemission spectroscopy. The physical properties of this interface are of actual interest as m-LPPP is successfully applied as active material in organic light emitting devices (LED). Almost no changes in the core-level and valence electronic structure of the polymer upon increasing coverage with aluminum (in situ) are found. This gives indication for a weak interaction of Al with m-LPPP, ruling out the formation of chemical bonds between the two materials. The rapid occurrence of metallic aluminum at rather low coverage in the presented experiment is an important finding for the understanding of charge injection and the interfacial electronic structure in organic LEDs.
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