It is important to study the distribution of host and guest molecules in organic electroluminescence materials because their distribution dramatically affects the functionalities of these materials. In order to understand this distribution, a new analysis method should be developed to obtain sub-nanometer scale information. In this regard, we used Atom Probe Tomography (APT). APT is a three-dimensional analysis technique with sub-nanometer scale resolution and is frequently used in material science and engineering. There are many reports on the analysis of inorganic materials using APT analysis, however only a few studies report the analysis of organic materials because of difficulties in the sample preparation, measurements, and the three-dimensional reconstruction of organic materials. In this study, we focused on developing a new sample preparation method and suggested the new sample preparation method for the analysis of organic materials. This new preparation method needs only a small amount of organic materials for analysis. Moreover, it is very simple and combines electrolytic polishing with the dipping method.
The present reconstruction method of Atom Probe Tomography (APT) has the problem that the parameter, in particular the shank angle which represents the region the signal of APT is detectable, is adjusted according to the internal length reference of the sample. The reliable APT reconstruction image could not be obtained in the sample without the reference. We propose the method to calculate the value of the shank angle from the shape of sample and the geometric position relationship between the sample and the detector. We compared the APT reconstruction image in this method to the image in the conventional method with the sample of Si isotope superlattice. The result is that APT 3D image by the new method was reconstructed equivalently to the image by the conventional method.
Atom probe tomography (APT) is a three-dimensional (3D) analysis technique with atomic resolution in materials science and engineering. The ionized atoms are sequentially released from the surface of the sample with needle shape by applying high voltage and are detected by the position-sensitive detector. The original arrangement is reconstructed using reconstruction parameters such as the image compression factor and the field factor from recorded data during measurement. It is crucial to the integrity of the reconstruction to estimate the reconstruction parameters as accurately as possible. However, it is difficult to determine the reconstruction parameters accurately due to sequential change of the shape of the sample during measurement. In this study, by using FEM we propose a new reconstruction method that the reconstruction parameters can be determined even during the measurement.
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