Visualizing and identifying single atoms using electron energy-loss spectroscopy with low accelerating voltage

Abstract

Visualizing atoms and discriminating between those of different elements is a goal in many analytical techniques. The use of electron energy-loss spectroscopy (EELS) in such single-atom analyses is hampered by an inherent difficulty related to the damage caused to specimens by incident electrons. Here, we demonstrate the successful EELS single-atom spectroscopy of various metallofullerene-doped single-wall nanotubes (known as peapods) without massive structural destruction. This is achieved by using an incident electron probe with a low accelerating voltage (60 kV). Single calcium atoms inside the peapods were unambiguously identified for the first time using EELS. Elemental analyses of lanthanum, cerium and erbium atoms were also demonstrated, which shows that single atoms with adjacent atomic numbers can be successfully discriminated with this technique.

Atomic-scale effects behind structural instabilities in Si lamellae during ion beam thinning

“…11 So far, predominantly low-dimensional materials such as graphene, 5,8,10 hexagonal boron nitride, 6 and carbon nanotubes 7 have been studied at low electron beam voltages by HRTEM. In the future, however, there will be a demand to extend these low-voltage studies to conventional materials, which similarly suffer from knock-on damage at higher voltages.…”

“…The current development in AC-HRTEM is to lower the voltage from the usual 200-300 kV to well below 100 kV, [5][6][7][8][9][10] in order to minimize displacement damage in fragile samples. 11 So far, predominantly low-dimensional materials such as graphene, 5,8,10 hexagonal boron nitride, 6 and carbon nanotubes 7 have been studied at low electron beam voltages by HRTEM.…”

Chromatic Aberration Correction by Combination Concave Lens

“…By development of spherical aberration correctors, geometrical limitation of resolution has been overcome. The correctors operated at acceleration voltage of 60-300 kV in electron microscopes have been widely used and allow us to perform high-resolution structural and analytical studies [3][4][5][6]. The performances at these middle acceleration voltages had been improve enough to resolve an atomic position in a specimen.…”

“…Operation at low acceleration voltage has an advantage for observation of soft matter made of light elements, due to small electron-related irradiation damage and high contrast on account of the larger scattering cross-section [6]. It is an interesting challenge to maintain the resolution at the atomic level by using a Cc corrector for low-voltage electron microscopy.…”

Low voltage electron diffractive imaging of atomic structure in single-wall carbon nanotubes

“…Although, electron microscopes with spherical aberration correctors are widely used in the atomic scale analysis, 1,2 to apply them at low-voltage, especially below few tens of kilovolts, it is required to correct some additional aberrations such as chromatic and higher-order aberrations. 3,4 Moreover, even if an aberration corrector is used, the increasing of numerical aperture of imaging ͑or probe forming͒ lens decreases the depth of focus, which makes three-dimensional ͑3D͒ structure observation difficult. Electron-diffractive imaging [5][6][7][8][9][10][11][12] with iterative phase retrieval ͑iteration procedures͒ [13][14][15] has reconstructed atomic-level specimen structures and has a capability of imaging 3D structures.…”