Understanding surface fine features, such as topological and compositional information, is essential for controlling synthesis conditions of these materials and for designing novel materials and utilizing their functions. The materials are becoming complicated composites composed of Nano crystals in order to have functions with better performance. Therefore, higher spatial resolution, sensitivity and capability are required for characterization techniques are required now. The recent developments in compound type objective lens, electron beam deceleration method, high solid angle multi EDS system and Soft X-ray Emission Spectrometry (SXES) of high-resolution scanning electron microscopy (HR-SEM) show great advances for the study of structures, chemical information, and electron state of Nano structured materials (1). Here, we will discuss newly developed spectroscopy approaches in EDS and SXES, and show some of their examples using low voltage (LV) HR-SEM.
The electron beam deceleration method brings a lot benefits. Because it is improving size of electron beam diameter due to smaller aberration even at LV condition, high probe current condition and long working distance (2). Fig. 1 shows high spatial resolution EDS map from Au@TiO2 Yolk-shell type sample where a gold nanoparticle with 15 nm in diameter is encapsulated in a TiO2 hollow sphere. The gold nanoparticles are well resolved within 3 min even at low electron landing-energy (see observation conditions in the Fig caption).
The low energy SXES spectra obtained from Al-B nano composites are shown in Fig. 2. SXES technique requires high probe current to acquire enough X-ray signals as it is based on wavelength dispersive spectrometry (WDS). The spectra from small area of aluminum alloy (a) and aluminum boride (b) show different peak top energy and shape for aluminum L-line at around 70 eV. In addition, the boron peak was also detected at around 67 eV. The spectra at this energy range, which corresponds to K-line from light elements including Lithium, was hard to observe by EDS and WDS before. So the SXES detector has high-energy resolution and can also detect extremely low energy X-ray.
The electron beam deceleration method has advantages in SXES analysis. We demonstrated SXES line profiles in between metal Aluminum and Aluminum boride in Fig. 3. Actually, there is deference between with beam deceleration method or not even at 5 keV with 30 nA. Compares to Line (b) and (c), Electron beam deceleration method of line (c) shows better sharpness and details of spectrum than line (b). Probably it is due to smaller probe size was created by electron beam deceleration method. Here we have also tired low voltage condition that is 1 keV with -5 keV sample bias in line (a). The line (a) shows much higher spatial resolution line profile due to smaller interaction volume in sold than 5 keV.
Reference
1) M. Terauchi, H. Yamamoto and M. tanaka, Journal of Electron Microscopy, 50, 101, (2001)
2) S. Asahina, M. Suga, H. Takahashi, H. Y. Jeong, C. Galeano, F. Schuth, and O. Terasaki,. APL Materials 2, 113317 (2014); doi:
Figures:
Figure 1. High resolution EDS map collected within 3 min using electron-beam-deceleration method
Figure 2. Low voltage SXES spectra
Figure 3. Comparison of SXES line profiles
To cite this abstract:
ASAHINA Shunsuke, TAKAHASHI Hideyuki, TAKAKURA Masaru, FERDI Schüth, TERASAKI Osamu; Great advantages of using low voltage HR-SEM in spatial resolution and sensitivity for low energy X-ray analyses. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/great-advantages-of-using-low-voltage-hr-sem-in-spatial-resolution-and-sensitivity-for-low-energy-x-ray-analyses/. Accessed: December 2, 2023« Back to The 16th European Microscopy Congress 2016
EMC Abstracts - https://emc-proceedings.com/abstract/great-advantages-of-using-low-voltage-hr-sem-in-spatial-resolution-and-sensitivity-for-low-energy-x-ray-analyses/