A TOF-SIMS and XPS correlative protocol to minimise analysis-induced damage on organic light-emitting diode layers
Résumé
The understanding of the degradation mechanisms due to aging is essential to improve the lifetime of organic light-emitting diodes (OLEDs) [1]. To identify the electro- and photo-chemical reactions occurring in the thin multilayers (~100 nm) during aging, a high depth-resolution technique capable of probing small chemical changes is required. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) are suitable characterization instruments for such analysis. Both techniques have already been used to investigate degradation mechanisms [2, 3]. However, few studies correlate the complementary results from the two techniques.
Here, we present a correlative protocol using a bevel crater to obtain precise chemical characterization of OLED layers and insight on the degradation mechanisms. This wedge crater is formed by varying the fluence of argon cluster ions over the surface of the sample. Measurements on the same bevel crater enable an easy correlation of the information of the two techniques. In TOF-SIMS, molecular information is collected by scanning the surface of the bevel crater, allowing the reconstruction of a profile with good depth resolution. Then, the sample is transferred to the XPS chamber using a transfer vessel under N2 atmosphere. A linescan along the crater enables the localization of the different layers where high-resolution core-level spectra will be acquired to obtain information on the chemical environment of each elements. As well as the easy correlation of the techniques, a reduction of the damage from the analysis and sputtering beams is also achieved with this protocol.
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