Transformation of CaSi overgrowth domains to the CaSi2 crystal phase via vacuum annealing

2021 ◽  
Author(s):  
Tetsu Ohsuna ◽  
Kenji Ito ◽  
Hideyuki Nakano
Keyword(s):  
Scanning Transmission Electron Microscopy ◽  
Silicon Oxide ◽  
Vacuum Annealing ◽  
Dark Field ◽  
Silicon Oxide Layer ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Vacuum Anneal ◽  
Passivated Silicon

Abstract The phase transformation of overgrown CaSi crystal on an (00l)-oriented epitaxial CaSi2 film was studied using high-angle annular dark-field scanning transmission electron microscopy. After annealing at 450°C under vacuum conditions, the CaSi domain transformed to the CaSi2 phase with thin Si layers. The transformed CaSi2 crystal formed epitaxially along the under-layer epitaxial CaSi2 film. The results suggest that Ca atoms in the overgrown CaSi domain diffused to the outermost passivated silicon oxide layer during the low-temperature vacuum anneal.

scholarly journals Ru Catalyst Encapsulated into the Pores of MIL-101 MOF: Direct Visualization by TEM

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4531
Author(s):  
Maria Meledina ◽  
Geert Watson ◽  
Alexander Meledin ◽  
Pascal Van Der Voort ◽  
Joachim Mayer ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Scanning Transmission Electron Microscopy ◽  
Dark Field ◽  
Catalyst Nanoparticles ◽  
Ru Catalyst ◽  
Ru Nanoparticles ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field

Ru catalyst nanoparticles were encapsulated into the pores of a Cr-based metal-organic framework (MOF)—MIL-101. The obtained material, as well as the non-loaded MIL-101, were investigated down to the atomic scale by annular dark-field scanning transmission electron microscopy using low dose conditions and fast image acquisition. The results directly show that the used wet chemistry loading approach is well-fitted for the accurate embedding of the individual catalyst nanoparticles into the cages of the MIL-101. The MIL-101 host material remains crystalline after the loading procedure, and the encapsulated Ru nanoparticles have a metallic nature. Annular dark field scanning transmission electron microscopy, combined with EDX mapping, is a perfect tool to directly characterize both the embedded nanoparticles and the loaded nanoscale MOFs. The resulting nanostructure of the material is promising because the Ru nanoparticles hosted in the MIL-101 pores are prevented from agglomeration—the stability and lifetime of the catalyst could be improved.

A further investigation of the complex M3 murataite structure using Hf substitution and STEM-EELS techniques

2019 ◽  
Vol 75 (3) ◽  
pp. 442-448
Author(s):  
Ryosuke S. S. Maki ◽  
Peter E. D. Morgan
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Radioactive Waste ◽  
Scanning Transmission Electron Microscopy ◽  
Dark Field ◽  
Site Preference ◽  
Scanning Transmission Electron ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field

Many members of the complex crystalline fluorite supercell structures (e.g. zirconolite, pyrochlore and murataite polytypes) have been considered/studied for possible long-term radioactive-waste immobilization. The eight-coordinated sites in these crystals are of particular importance because they are preferred for the accommodation of trivalent rare earths and actinides present in radioactive waste from fuel element processing. The fluorite-type supercell structures include the murataites, M3, M5, M7, M8, having those numbers of repeating fluorite sub-cell units. One simple technique, as shown here, namely the substitution of Hf into the Zr site, is very helpful for structural analysis in these very complex cases in order to further illuminate the site preference of the Zr ion. Three M3 murataite samples, Ca-Mn-Ti-Zr-Al-Fe-O (regular M3), Ca-Ti-Zr-Al-Fe-O (Mn-free M3) and Ca-Mn-Ti-Hf-Al-Fe-O (Hf-substituted M3) are investigated and, through techniques described for larger cells, show that the Zr is very likely not to be hosted in the [6] Ti site in the M3 murataite structure, as suggested by Pakhomova et al. [(2013), Z. Kristallogr. Cryst. Mater. 228, 151–156], but more likely replaces the [8] Ca1 site and less likely the [8] Ca2 site. This adjusted site preference for each cation from the powder X-ray diffraction (PXRD) and scanning transmission electron microscopy electron energy-loss spectroscopy (STEM-EELS) methods, agrees well with the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image.

scholarly journals Atomic structural catalogue of defects and vertical stacking in 2H/3R mixed polytype multilayer WS2 pyramids

Nanoscale ◽  
2019 ◽  
Vol 11 (22) ◽  
pp. 10859-10871
Author(s):  
Gyeong Hee Ryu ◽  
Jun Chen ◽  
Yi Wen ◽  
Si Zhou ◽  
Ren-Jie Chang ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Scanning Transmission Electron Microscopy ◽  
Vapour Deposition ◽  
Chemical Vapour ◽  
Dark Field ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Aberration Corrected

We examine the atomic structure of chemical vapour deposition grown multilayer WS2 pyramids using aberration corrected annular dark field scanning transmission electron microscopy coupled with an in situ heating holder.

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