Simultaneous Data Collection and Utilization of DPC/OBF STEM, EDS and EELS

The use of a segmented detector has become standard for various STEM observations, particularly for Differential Phase Contrast (DPC) STEM and Optimum Bright Field (OBF) STEM. DPC STEM can visualize weak electromagnetic fields such as p-n junction interfaces and magnetic skyrmions. In low-dose experiments with beam-sensitive materials, like zeolites and metal-organic frameworks (MOFs), OBF STEM method achieves noticeably better contrast during live imaging. Direct imaging using a segmented detector extends across various material fields and extremely contributes to research and developments. As an example of the application, this research shows a combined analysis of these advanced imaging techniques with elemental analysis methods, EDS and EELS, simultaneously acquired in our new FEMTUS™ platform.<br/>The sample was a semiconductor memory. The experiment was performed using JEM-F200, equipped with SAAF-Quad detector (an annular four-segmented detector), Dual SDD detector for EDS, CEOS Energy Filtering and Imaging Device (CEFID) with Dectris ELA hybrid-pixel electron detector, and integrated analysis platform FEMTUS™ developed by JEOL. In the FEMTUS™ platform, all detectors and cameras can be synchronized and simultaneous acquisition becomes possible with easy operation. For all experiments we chose an accelerating voltage of 200 kV, STEM mapping was performed with a dwell time of 10ms, convergence semi-angle of 6.6 mrad, and EELS collection semi-angle of 2.2 mrad limited by the central hole of SAAF-Quad detector. All DPC STEM and EDS/EELS elemental mapping data were acquired simultaneously in a single scan.<br/>The result of simultaneous acquisition is described below. EDS mapping detected heavy elements such as tungsten and titanium, which are difficult to access using the phase imaging method (DPC or OBF STEM) and EELS. EELS mapping clearly showed the contrast for light elements (oxygen, nitrogen, and silicon) with the higher S/N ratio compared to EDS. The information from EDS and EELS was used to analyze the origin of DPC STEM contrast. The DPC STEM method has better sensitivity for differences in projected potential, originating from both electromagnetic field and/or local chemical composition. We compared intensity profiles of the same area of the center of mass (COM) DPC STEM and EELS data and revealed the peaks of COM intensity correspond to the increase of oxygen component, whereas the amount of nitrogen decreases in the interface region. This result shows the composition difference between SiOx film and SiNx bulk region. Such combined information is very helpful to investigate the origin of phase contrast images.<br/>In summary, we acquired DPC STEM, EDS, and EELS data of semiconductor samples simultaneously and revealed that the origin of DPC STEM signals was due to changes in the local chemical composition. Without the additional information from EDS and EELS, it was difficult to clarify whether the obtained phase contrast represents chemical composition, electromagnetic field, or just a difference in local thickness. Such simultaneous acquisition of DPC, EDS, and EELS enables us to directly understand the origin of the observed phase image contrast more easily. Furthermore, since compared to EDS and EELS mappings, DPC STEM is very sensitive to changes in the projected potential, it will be possible to clarify compositional differences by integrating the EDS and EELS signals of regions where phase contrast differences could be observed, even under low-dose conditions. This should also be useful for the composition analysis of electron beam-sensitive materials whose structures are destroyed with just a few scans. On the day of the presentation, we will show the details of the experimental results and additional instances of simultaneous data acquisition including OBF STEM.