Diffraction Microscopy using 20-kV Electron Beam for Multi-Wall Carbon Nanotubes
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1026-C07-06
Diffraction Microscopy using 20-kV Electron Beam for Multi-Wall Carbon Nanotubes Osamu Kamimura1, Kota Kawahara2, Takahisa Doi1, Takashi Dobashi1, Takashi Abe2, and Kazutoshi Gohara2 1 Central Research Laboratory, Hitachi, Ltd., 1-280, Higashi-koigakubo, Kokubunji-shi, Tokyo, Japan 2 Department of Applied Physics, Hokkaido University, Sapporo, Japan ABSTRACT Diffraction microscopy (or diffractive imaging) with iterative phase retrieval was performed using a low-energy (20-keV) electron beam to verify the possibility of high-resolution imaging with low specimen damage. Diffraction patterns of fine and uniform multi-wall carbon nanotubes (MWCNTs) were recorded without a post-specimen lens. One- and two-dimensional phase retrievals were processed from the diffraction pattern alone. The reconstructed object images reflected the characteristic structure of the MWCNT. These results show the possibility of high-resolution imaging with a low-energy electron beam.
INTRODUCTION High-resolution imaging that produces low damage is required in various fields, especially biology and carbon material development. Diffraction microscopy (or diffractive imaging) with iterative phase retrieval is one of the most promising candidates for highresolution imaging, which can reconstruct an object’s structure from a diffraction pattern, avoiding lens aberrations. This method is based on the original works of D. Sayer in 1952 [1], R. W. Gershberg and W. O. Saxton in 1971 [2], and J. Fienup in 1982 [3]. Through these prominent works, many experimental results using X-rays were reported [4-6, and references there in]. However, in the electron beam field, only two groups verified the method [7,8]. In 2002, Weierstall et al examined a two-empty-hole imaging using a 40-kV electron beam [7], and Zuo et al reported the reconstruction of a double-wall carbon nanotube image at 200 kV with the resolution of 0.1 nm [8] in 2003. In the present study, we applied diffraction microscopy to a low-energy electron beam with an acceleration voltage of 20 kV to verify the possibility of high-resolution imaging with low specimen damage.
EXPERIMENT A schematic diagram of our system is shown in Fig. 1. An electron beam emitted from a thermal-field-emission gun is focused on a specimen by a magnetic lens. The convergence angle of the illumination beam was geometrically determined to be 0.05 mrad (half angle) by a radius of an aperture in the magnetic lens and a distance between the aperture and the specimen. A measurement of the angular intensity distribution of the illumination beam is shown in Fig. 2.
From Gaussian fitting of the measured distribution, a practical convergence angle was determined to be 0.078 mrad. TFE electron gun: Acc. voltage 20 kV Magnetic lens + aperture Geometrical convergence angle: 0.05 mrad Specimen Camera length: 570 mm
Imaging plate (Diffraction pattern)
Figure 1. Schematic diagram of our system. 14 12 ) it 10 n u . b r a ( y ti s n e t n I
Beam intensity Gaussian func.
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