No abstract

Up to now, the analysis of organic or biological samples was mainly investigated using static SIMS, while dynamic SIMS was generally limited to the analysis of inorganic samples. The increasing sophistication of organic optoelectronic devices (e.g. organic light emitting diodes and organic photovoltaic cells, etc.) requires molecular-level dimensional control in the fabrication of multilayered structures with specifically engineered interfaces. However, analytical tools for monitoring such fabrication precision are scarce. In a current project, we address this challenge by advancing the development of low-energy Secondary Ion Mass Spectrometry (LE-SIMS) for the analysis of organic-based optoelectronic materials systems.In the present work, we investigate the fragmentation as well as the ionization mechanisms for several molecules used in such devices: fullerene, copper phthalocyanine and tris(8-hydroxyquinolinato) aluminium have been deposited onto silicon wafers. The study has been carried out on a Cameca SC-Ultra instrument under Cs + bombardment for various impact energies in the M − mode. Constant M − secondary ion intensities have been observed throughout the organic layers for some characteristic fragments of the organic molecules.

aThe increasing sophistication of optoelectronic devices requires molecular-level dimensional control in the fabrication of multilayered structures with specifically engineered interfaces. However, the effectiveness of growth and doping strategies devised to achieve the desired device structures often remains unverified due to the lack of adequate characterization techniques. This is particularly true for devices based on conjugated organic compounds, which find increasing use in energy applications (e.g. organic light emitting diodes and organic photovoltaic cells, etc.). The buried interfaces are simply inaccessible or suffer damage when using conventional characterization techniques. In a current project, we address this challenge by advancing the development of low-energy (LE) SIMS for the analysis of organic-based optoelectronic materials systems.In the present study, multilayered organic thin films have been analyzed, varying experimental conditions such as the impact energies for Cs + bombardment in the MCs x + and M − mode on a Cameca Sc-Ultra instrument to investigate the ionization mechanisms as well as the atomic mixing at the interfaces between layers, and the degradation of the organic information. Low-energy dynamic SIMS proved to be a reliable tool for the characterization of organic multilayered optoelectronic devices: MCs x + secondary ions provide information about the distribution of elements within the samples, while negative fragments that are characteristic for the different molecules give information about the structure.

The development of organic optoelectronic devices relies on controlling interfaces during thin-film deposition and requires an accurate characterization of the film composition at these interfaces. Dynamic secondary ion mass spectrometry (SIMS) is widely used to investigate multilayer thin-film structures. Routine analysis protocols are well established for classical semiconductor samples, but for organic or mixed metallic−organic samples the limitations of the technique are less well established. In the current work, low-energy dynamic SIMS is used on metal−organic multilayered model structures similar to those in organic optoelectronic devices to study the origin of diffusion of metal into the organic layer (e.g., irradiation-induced diffusion during SIMS analysis or during the deposition process). Samples contain silver and organic compounds sequentially deposited by thermal evaporation in vacuum onto a Si substrate. They are analyzed using a 250 eV to 1 keV Cs + primary ion beam. It is found that the mixing of silver into the organic layer depends on the impact energy and the conditions for sample preparation. This irradiation effect can be minimized by a back-side depth profiling approach, which was developed in this work. By applying this method, it is shown that some silver is likely to diffuse into the organic layers during the deposition process.