Advantage of Low-kV Aberration-corrected Scanning/ Transmission
Electron Microscopy
T. Sasaki1,2, H. Sawada1,2, F. Hosokawa1, T. Kaneyama1,2, Y. Kondo1, K. Kimoto2,3, K. Suenaga2,4
1
EM Business Unit, JEOL Ltd., Tokyo 196-8558, Japan
CREST Triple C Project, Japan Science and Technology Agency, Tokyo 102-0075, Japan
3
National Institute for Materials Science (NIMS), Ibaraki 305-0044, Japan
4
National Institute of Advanced Industrial Science and Technology (AIST), Ibaraki 305-8565, Japan
2
We have been developing 30-60 kV high-resolution transmission electron
microscopes (STEM/TEM) equipped with cold field emission gun (CFEG) and
aberration correctors in probe and image forming systems to observe carbon-based
materials at atomic resolution with less knock-on damage. The first machine, Triple C
#1 (30-60 kV), equipped delta-type Cs correctors enables atomic resolution high-angle
annular dark field (HAADF)-STEM imaging. Figure 1 shows HAADF images of
Si[110] taken at (a) 30 kV and (b) 60 kV. Si-Si dumbbells were clearly resolved in these
images. In the corresponding power spectrum of Fourier transforms, spots for 111 pm
and 96 pm were clearly seen for 30 kV and 60 kV, respectively [1]. The calculations of
probe shapes under the conditions of these images were performed with the incoherent
superposition method [2], which takes chromatic and geometrical aberrations of the
microscope into account. As shown in Fig. 1(c), the resulted probe diameters in D59 and
FWHM were 154.0 pm and 127.8 pm at 30 kV, and 99.2 pm and 92.8 pm at 60 kV [3].
The multislice image simulation of using the probe shapes successfully reproduced the
dip depth of Si-Si dumbbells of the experimental images.
The second machine, Triple C #2 (30 kV), is equipped with a delta-type Cs
corrector and a Cc corrector that utilizes a combination concave effect for image
forming system [4,5]. The Cc and Cs correctors are arranged in tandem. The Cs and Cc
correction were successfully accomplished. The system showed that the transferred
information reached after and before the corrections were 0.14 nm and 0.28 nm at 30
kV [6]. Figures 2(a) and (b) show a Cc and Cs-corrected TEM image of multi layered
h-BN[0001] film at 30 kV and its power spectrum of Fourier transform. Hexagonal
structure is clearly seen in the image, and spots corresponding to (108 pm)-1 is clearly
visible in the Fourier transform. Figure 3 shows a Cc and Cs-corrected TEM image of
metallofullerenes ((La, Ce, Er)@C82) encapsulated inside single-walled carbon
nanotubes (SWCNT) taken with an exposure time of 2 s (four 0.5 s-images are
overlaid.). The lattice fringes of 0.21 nm are observed at the wall of the SWCNTs. The
C82 fullerenes are regularly-arranged in the SWCNT and a single metal atom in a
fullerene appears as a dark dot (indicated by arrows). Some metal atoms are clearly
imaged, while some are unclear. This is due to motion of the metal atoms in the
fullerenes under the electron dose (4.3×104 e-/nm2/s). At 30 kV, fullerenes did not
coalesce with the other fullerenes. The coalescence is frequent under the high energy
electrons. We can conclude that the high resolution imaging at 30 kV with less knock-on
damage is definitely the benefit of Cc and Cs-corrected TEM.
References
[1] T. Sasaki et al., J. Electron Microsc. 59 (2010) S7.
[2] M. Haider et al., Ultramicrosc. 81 (2000) 163.
[3] T. Sasaki et al., Micron 43 (2012) 551.
[4] H. Sawada et al., Advances in Imaging and Electron Physics 168 (2011) 297.
[5] F. Hosokawa, et al., submitted.
[6] T. Sasaki et al., Conference Proceedings of APMC 10 (2012) 385.
(a) 30kV
(b) 30kV
(c)
0.5 nm
(b) 60kV
Intensity [a.u.]
30 kV
60 kV
FWHM = 92.8 pm @ 60 kV
FWHM = 99.2 pm @ 30 kV
D59 = 127.8 pm
@ 60 kV
D59 = 154.0 pm
@ 30 kV
0.5 nm
-200
-150
-100
-50
0
50
Distance [pm]
100
150
200
FIG. 1. Cs-corrected HAADF-STEM images of Si[110] taken at (a) 30 kV and (b) 60 kV. (c)
Calculated probe shapes on experimental conditions for images in (a) and (b). The intensity
of the beam tail at 30 kV is larger than that at 60 kV due to the larger chromatic aberration,
resulting in a larger D59 diameter at 30 kV than at 60 kV.
(a)
1nm
(b)
0.21 nm
(108 pm)-1
(125 pm)-1
FIG. 2. (a) Cc and Cs-corrected TEM
image of multi-layered h-BN[0001]
film at 30 kV. (b) its power spectrum
of Fourier transform.
FIG. 3 Cc/Cs-corrected TEM image of metallofullerenes
-(Metal@C82) encapsulated with SWCNT at 30 kV.