Capsulate structure effect on SWNTs doping in RbxAg1-xI@SWNT composites

The paper reports the relationship between single-walled carbon nanotube (SWNT) doping and capsulate crystal structure in RbxAg1−xI@SWNT composites. The structures of one dimensional (1D) RbI, AgI and RbAg4I5 crystals inside single-walled carbon nanotubes were established by high-resolution transmission electron microscopy (HRTEM) and high-resolution scanning transmission electron microscopy (HAADF HRSTEM), and confirmed by image simulation. Opposite to one-dimensional RbI and AgI, inheriting the structure of bulk analogues, 1D RbAg4I5 forms a new phase within a confined space of the SWNT channel, which differs from the bulk RbAg4I5 structure and can be described by a deformed cubic 1D lattice. X-ray absorption, XPS, optical absorption and Raman spectroscopies were used for comprehensive study of the composites' electronic structures. The study reveals the donor behavior of RbI capsulate and the acceptor behavior of RbAg4I5 and AgI. Quantification of doping levels indicated the prevalence of the effect of the chemical composition of the capsulate on the overall doping efficiency, while a structural effect is mostly prominent in potential distribution on nanotube walls and partial charges on SWNT atoms.This work was supported by the Helmholtz Zentrum Berlin für Materialien und Energie within a bilateral Russian-German Laboratory program. The authors express gratitude to Orekhov A. S. for help with the STEM image simulation. This work was performed using the equipment of the Shared Research Centre FSRC “Crystallography and Photonics” RAS and was supported by the Russian Ministry of Education and Science.Peer Reviewe

Study of One-Dimensional Crystal@Single Wall Carbon Nanotube Nanocomposites Using Atomic Resolution Scanning Transmission Electron Microscopy

1DCuI@SWCNT nanocomposites have been studied by scanning transmission electron microscopy (STEM) using the registration modes of large-angle scattered electrons and bright-field images in combination with the spectroscopy of electron energy losses. A new structure of a 1DCuI@SWCNT nanocomposite has been found. The results of the studies indicate that by using STEM modes it is necessary to obtain simultaneously both the images in a bright field and in high-angle annular dark field (HAADF) imaging. Using the spectroscopy of electron energy losses, the formation of a chemical bond between Cu3d and C2pz states of an intercalated nanocrystal and nanotube with the corresponding transfer of the electron density similar to 0.09 e/carbon atom has been shown

The structure and continuous stoichiometry change of 1DTbBr(x)@SWCNTs

HRTEM and HAADF STEM of 1DTbBr(x)@SWCNT meta-nanotubes reveal three structural modifications of 1D nanocrystals within single wall carbon nanotube channels attributed to a different stoichiometry of the guest crystal. For SWCNTs with diameters D-m > 1.4 nm a most complete tetragonal unit cell is observed. When crystallization occurs inside SWCNT with D-m < 1.4 nm 1D TbBrx crystal deforms a nanotube to elliptical shape in cross section. In this case the 1D crystal unit cell becomes monoclinic, with possible loss of a part of bromine atoms. Two modifications of a monoclinic unit cell appear. One of them is characterized by single or pair vacancies in the structure of the 1D crystal. Another structure is explained by peripheral and central bromine atoms loss. An appearance of such modifications can be stimulated by electron irradiation. The loss of bromine atoms is in agreement with chemical analysis data. Electronic properties of obtained meta-nanotubes are investigated using optical absorption and Raman spectroscopy. It is shown that intercalation of terbium bromide into SWCNTs leads to acceptor doping of SWCNTs. According to local EDX analysis and elemental mapping this doping can arise from significant stoichiometry change in 1D nanocrystal indicating an average Tb:Br atomic ratio of 1:2.8 0.1

The structure and continuous stoichiometry change of 1DTbBr x

HRTEM and HAADF STEM of 1DTbBr(x)@SWCNT meta-nanotubes reveal three structural modifications of 1D nanocrystals within single wall carbon nanotube channels attributed to a different stoichiometry of the guest crystal. For SWCNTs with diameters D-m > 1.4 nm a most complete tetragonal unit cell is observed. When crystallization occurs inside SWCNT with D-m < 1.4 nm 1D TbBrx crystal deforms a nanotube to elliptical shape in cross section. In this case the 1D crystal unit cell becomes monoclinic, with possible loss of a part of bromine atoms. Two modifications of a monoclinic unit cell appear. One of them is characterized by single or pair vacancies in the structure of the 1D crystal. Another structure is explained by peripheral and central bromine atoms loss. An appearance of such modifications can be stimulated by electron irradiation. The loss of bromine atoms is in agreement with chemical analysis data. Electronic properties of obtained meta-nanotubes are investigated using optical absorption and Raman spectroscopy. It is shown that intercalation of terbium bromide into SWCNTs leads to acceptor doping of SWCNTs. According to local EDX analysis and elemental mapping this doping can arise from significant stoichiometry change in 1D nanocrystal indicating an average Tb:Br atomic ratio of 1:2.8 0.1

Mass Transport through Defects in Graphene Layers

The paper reports an experimental study of ZnTe and CuI transport through graphene wall of SWNTs by high resolution transmission electron microscopy. It is shown that encapsulated material evacuates the tube through the defects in the nanotube walls, while in-tube diffusion appears high enough to provide matter intake from the nanotube volume. Diffusion kinetics was studied by “atoms count” resulting in ZnTe and CuI diffusivities of 7.67 × 10^–21 and 1.99 × 10^–20 m²/s through single defects in SWNT wall. Semiempirical and DFT modeling of potential energy profiles for different types of defects was utilized to propose minimal structural disturbances in a graphene layer to make possible cross-plane transport of matter. The comparison of experimentally observed diffusivities with calculated activation barrier heights was carried out taking into account an effective temperature of substance under electron beam. Neither of the defects including framework disturbance with 5–7 defects or sp³-bound carbon atomic pairs give rise to valuable mass-transport efficiencies through graphene layer. Reasonable conformity of the results is only achieved with carbon vacancy pairs in sp²-carbon layer, thus, indicating effective transport of matter occurring through the “holes” in graphene

Size-Dependent Structure Relations between Nanotubes and Encapsulated Nanocrystals

The structural organization of compounds in a confined space of nanometer-scale cavities is of fundamental importance for understanding the basic principles for atomic structure design at the nanolevel. Here, we explore size-dependent structure relations between one-dimensional PbTe nanocrystals and carbon nanotube containers in the diameter range of 2.0–1.25 nm using high-resolution transmission electron microscopy and ab initio calculations. Upon decrease of the confining volume, one-dimensional crystals reveal gradual thinning, with the structure being cut from the bulk in either a <110> or a <100> growth direction until a certain limit of ∼1.3 nm. This corresponds to the situation when a stoichiometric (uncharged) crystal does not fit into the cavity dimensions. As a result of the in-tube charge compensation, one-dimensional superstructures with nanometer-scale atomic density modulations are formed by a periodic addition of peripheral extra atoms to the main motif. Structural changes in the crystallographic configuration of the composites entail the redistribution of charge density on single-walled carbon nanotube walls and the possible appearance of the electron density wave. The variation of the potential attains 0.4 eV, corresponding to charge density fluctuations of 0.14 e/atom