Characterization of organic thin films using transmission electron microscopy and Fourier Transform Infra Red spectroscopy

Abstract

Organic Light Emitting Diodes (OLEDs) have received much attention for use in display and solid-state lighting applications. Consequently, evaluating materials analyses techniques to better understand potential issues between the different films constituting the OLED device structure becomes important. In particular, film thickness monitoring and control is essential for reproducible and reliable OLED performance. Typically, Quartz Crystal Microbalances (QCMs) are used to monitor the thicknesses in-situ. While QCMs can provide thickness information, they do not provide information about the composition or quality of the deposited films. To overcome these issues, in this paper, we have used Fourier Transform InfraRed Spectroscopy (FT-IR) to measure film thicknesses and compositions in individual as well as stacked organic layers relevant to OLED structures and used cross-sectional Transmission Electron Microscopy imaging to correlate the physical thickness of the organic films to their IR (infrared) absorption peak intensities from FT-IR. We demonstrate that this technique can be used to precisely measure film thicknesses within 5% of the nominal thickness and provide information about film composition.