Electron microscopy
 
Thermal-diffuse-scattering in In-Situ Heating HAADF-STEM
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It is well-known that HAADF-STEM technique can be applied to observe crystals in Z-contrast; however, this technique may also provide information on a local thermal vibration anomaly at atomic-scale since the high-angle scattering of incident electrons is dominated by phonon scattering [1], which is also called thermal diffuse scattering (TDS). The phonon scattering reflects the Debye-Waller (DW) factor sensitively. For instance, the local anomaly of the DW factor has been observed in Al72Ni20Co8 decagonal phases through in-situ HAADF-STEM as shown in Figure 1434. At the room temperature (300 K), the transition metal (TM: Ni and/or Co)) atoms are much brighter than Al atoms due to Z-contrast. When the sample is heated and held at ~1100 K, the relative contrasts between TM and Al atoms were dramatically changed since the contrast of Al atoms is significantly enhanced. However, when the sample was cooled down to 300 K from 1100 K, the anomalous contrast regions became darker again as marked by the red arrows. The local DW anomaly indicates significant anharmonicity at these Al sites.

HAADF-STEM images of Al72Ni20Co8 decagonal phases: (a) At 300 K and (b) At 1,100 K.

Figure 1434. HAADF-STEM images of Al72Ni20Co8 decagonal phases: (a) At 300 K and (b) At 1100 K. Adapted from [2]

 

 

 

 

 

 

[1] Eiji Abe, S. J. Pennycook, A. P. Tsai, Direct observation of a local thermal vibration anomaly in a quasicrystal, NATURE, 421(23), 347, 2003.
[2] Eiji Abe, Atomic-Scale Characterization of Nanostructured Metallic Materials by HAADF/Z-contrast STEM, Materials Transactions, 44(10), 2035-2041, (2003).

 

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