1/5/2024 0 Comments Lighttable vs atom![]() 4a), in which 60 molecules align inside SWNTs, was obtained. In this process, a typical 60 peapod’ ( Fig. The commercially available (PF 6) −, which forms a rock salt type of ionic crystal, was used as the starting material 9. We first encapsulated the Li metallofullerenes inside single-walled CNT (SWNTs) through vapour phase doping. 2, we show another example of a CsF atomic chain in which the single F atoms ( Z=7) can be identified between Cs atoms ( Supplementary Note 2).įull size image Detection of single lithium atomsįigure 4 shows one of our attempts to capture single Li atoms ( Z=3). In a similar way, one can also detect much lighter halogen atoms. This demonstrates that even though the Cl atoms are not visible in the ADF image they are indeed captured between two Cs cations in the 1D space of the DWNT. On the other hand, the intensity maxima of the Cl L-edge appear between the Cs atoms with hardly visible ADF contrast ( Fig. Figure 3c shows the EELS chemical map of the Cs M-edge, which exactly corresponds to the higher contrast in the ADF image, confirming the positions of the Cs atoms. To confirm the presence of Cl atoms, one must perform an EELS chemical map using the Cl L-edge. In this case, the heavier Cs atoms ( Z=55) are clearly visible, while the Cl atoms are apparently missing in the ADF image ( Fig. Similar to the previous case, the CsCl atomic chain is also supposed to align in alternation in the DWNT ( Fig. Figure 3 shows an atomic chain of CsCl in a DWNT. Single halogen atoms such as F and Cl ( Z=9 and 17, respectively) are also detectable in a similar way. Note that there was a slight specimen drift during the EELS chemical map acquisition. The Na map is smoothed by a convolution of a 3 × 3 pixel matrix and overlapped with a simultaneously recorded ADF image, which reflects the positions of I atoms (blue spots in the upper panel of c). The EELS chemical map for the Na L-edge displays the positions of Na atoms (green spots in the upper panel of c) and proves that Na and I are alternatively aligned in the 1D configuration. The Na L-edge is clearly visible at 33 eV, even for a single atomic chain of NaI. A reference spectrum taken from the 3 × 3 NaI nanowire is also shown (black line in d). ( d) The EELS spectrum (red line in d) taken from the NaI atomic chain shown in c. ( c) An elemental map (upper panel) of a NaI atomic chain shown in a ADF image (bottom panel). In the ADF image, Na atoms are invisible while I atoms present as bright spots. ( a, b) A schematic model and an ADF image of a NaI atomic chain in a DWNT, respectively. ![]() To capture these light element atom, we have used the ‘peapod’ method to locate target atoms in a nanospace, in which a carbon cage such as fullerene or nanotube is used to encapsulate an isolated atom of the specific element 6, 7, 8. Also EELS is greatly advantageous for the light element detections because its contrast is not proportional to the atomic number Z but is related to the inelastic cross-section. EELS is a widely used technique in TEM/STEM for discerning the chemical composition of a sample, and its detection limit has been shown to be sensitive enough to capture a single atom 6. ![]() In this report, we have attempted to capture these light element atoms in EELS chemical map with atomic precision ( Fig. These invisible atoms in TEM often hinder the detailed study of energy storage devices or catalytic particles because one cannot identify the real atomic structures or the local chemical compositions involving those crucial elements. Even some other light elements such as fluorine (F, Z=9), sodium (Na, Z=11) or chlorine (Cl, Z=17), which are known to be unstable under the electron beam, are also extremely difficult to image as individual atoms, because of their radiation sensitivity 5. However this, the lighter element, such as Lithium (Li, Z=3), has only been imaged in a three-dimensional crystal as a projection of tens of the identical atoms in a row 3, 4 and never been imaged as single atom by means of TEM/scanning TEM (STEM) nor EELS. For those experiments, the materials are relatively resistive to the incident electron beam and the constituent atoms are scarcely kicked out during the observation as long as the acceleration voltage of incident electron beams is kept low. In solid state materials with covalent bonds, light elements such as B, C and N ( Z=5, 6 and 7) have been imaged as single atoms and their chemical assignment by means of electron energy loss spectroscopy (EELS) has been successfully demonstrated 1, 2. Imaging single atoms of light element by means of transmission electron microscopy (TEM) has two major difficulties compared with heavier elements: the smaller scattering power, which only produces very weak contrast in TEM, and the higher knock-on probability, which allows the atoms to be easily kicked out under the electron beam.
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