JAST
2012 March;3(1):128-134.
Published online 2012 March 20.
doi:http://dx.doi.org/10.5355/JAST.2012.128
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| Copyright ⓒ 2010 Journal of Analytical Science & Technology |
| Application of FFT Data from HREM images to Electron crystallography |
| Sang-Gil Lee1, Youn-Joong Kim1,2, Seung-Jo Yoo1, Seok-Hoon Lee1, Jin-Gyu Kim1* |
1Division of Electron Microscopic Research, Korea Basic Science Institute, 169-148 Gwahangno, Yuseong-gu, Daejeon 305-806, Republic of Korea
2Graduate School of Analytical Science and Technology, Chungnam National University, 79 Daehangro, Yuseong-gu, Daejeon, 305-764, Republic of Korea |
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Corresponding Author:
Jin-Gyu Kim ,Tel: +82-42-865-3961, Fax: +82-42-865-3939, Email: jjintta@kbsi.re.kr |
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ABSTRACT |
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| We succesfully determined the 3D crystal structure of inorganic nano-crystalline material using fast fourier transform (FFT) data from high-resolution electron microscopy (HREM) images. For extracting the reliable structure information from nano-crystalline materials by HREM imaging, it is essential to minimize the dynamical scattering effects happend from interactions bewteen electrons and matters. To alleviate this restriction, we tried to solve the crystal structure by employing high voltage electron microscope (HVEM) which has excellent tilting capability, atomic resolution as well as higher penetration power. First, the allowed sample thickness for CaMoO4 crystal was evaluated by examining the existence of forbidden reflections in FFT data of HREM images obtained at various sample thickness. The kinematical scattering conditions were satisfied up to a sample thickness of about 28.2 nm. Next, we tried to extract the crystallographic data and determine the atomic structure of CaMoO4 crystal by FFT analysis of HREM images obtained from 15 different zone axes. Consequently, its cell parameters and space group were a = 5.24(3) Å, c = 11.50(8) Å and I41/a (#88), respectively. These values were coincided with X-ray crystallography results within 0.002 ~ 0.080 Å. Finally, the atomic structure could be determined with an accuracy of 0.16 Å. |
| Keywords: High voltage electron microscope, Fast fourier transform, Electron crystallography, High-resolution electron microscopy, CaMoO4 |
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FIGURES |
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Fig.1
TEM image of CaMoO4 crystal for thickness estimation (a) and their corresponding EELS spectrums (b). |
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Fig.2
HREM images of CaMoO4 crystal and their FFT data. |
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Fig.3
A tilt series of HREM images taken along the [110] zone axis and their FFT data. |
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Fig.4
The determining procedures of the cell parameters from tilt series of HREM image. (a) 2D indexing of FFT data, (b) Extracting of reflection data, (c) 3D reconstruction map of all FFT data in reciprocal space. |
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Fig.5
Extraction of reflection conditions from four major zone axes to determine the 3D symmetry. |
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Fig.6
The 3D potential map reconstructed with 92 reflections. (a) shows an structure drawing of CaMoO4 crystal with the atomic labeling scheme based on XRD analysis. (b)~(d) show 2D potential maps of [100], [010] and [001] direction, respectively. |
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TABLES |
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Table.1
The results of thickenss estimation from different sample positions. |
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Table.2
Cell parameters of CaMoO4 determined by FFT analysis of three tilt series HREM images. |
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Table.3
12 atomic positions extracted from 3D potential map. |
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Table.4
Comparison of atomic coordinates of CaMoO4 crystal structure determined by electron and X-ray crystallography. |
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