Subscriber access provided by - Access paid by the | UCSB Libraries
Article
Mass Transport Through Defects in Graphene Layers Andrei A. Eliseev, Andrey S Kumskov, Nikolay S Falaleev, Victoria G. Zhigalina, Artem A. Eliseev, Artem A. Mitrofanov, Dmitrii I. Petukhov, Alexander L. Vasiliev, and Nikolay A. Kiselev J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b06100 • Publication Date (Web): 05 Sep 2017 Downloaded from http://pubs.acs.org on September 7, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 22
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
The Journal of Physical Chemistry
Mass Transport through Defects in Graphene Layers Andrei A. Eliseev1,2,*, A.S. Kumskov3,4,5, N.S Falaleev1, V.G. Zhigalina3,4,5, Artem A. Eliseev1,2, A.A. Mitrofanov1,2, D.I. Petukhov1,2, A.L. Vasiliev3,4, N.A.Kiselev3 1. Department of Materials Science, Moscow State University, 119992, Moscow, Russia 2. Department of Chemistry, Moscow State University, 119992, Moscow, Russia 3. FSRC “Crystallography and Photonics” RAS, 119333, Moscow, Russia 4. NRC "Kurchatov Institute", 123182, Moscow, Russia 5. Scientific-Research Center for Studying Surface and Vacuum Properties, Moscow, 119421 Russia Corresponded author: Andrei A. Eliseev, e-mail:
[email protected] Abstract 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. Semi-empirical 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.
Introduction Mass transport through atomically-thin graphene layers is now receiving an increasing attention from different science and technology areas including membrane technology1, energy storage2, inclusion chemistry3,4, nanofabrication5, etc. Despite numerous theoretical predictions presented in literature6,7, experimental evidences for mass transport though graphene are rather scarce. In most the cases experimental studies are limited to transport of water or gas molecules1 or ionic transport in solutions9 with no insured tight sealing of free-standing monoatomic-film. The experimental results on transport of gas molecules or different ionic species across defects in 1 ACS Paragon Plus Environment
The Journal of Physical Chemistry
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 22
nanoporous graphene are reviewed in Ref. 8. Another example of transport through graphene emerges as intercalation of metals10 or semiconductors11,12 under monolayer graphene. In both the cases mass transport through graphene was accounted to atomic diffusion through defects or grain boundaries in a layer9,13,14. However, the proposed mechanism was not confirmed yet experimentally and matter diffusivity has not been quantified for different defects types15. As soon as direct mass transport observations through plane graphene layers is hardly realized experimentally, we have chosen encapsulated SWNTs as a simples test object for the study. Single walled nanotubes are known as a perfect container for growing inorganic one-dimensional crystals16,17, polymer chains18, nanoribbons19,20 and even carbyne molecules21, as illustrated by multiple state-of-art microscopy works20,22. Moreover chemical reactions and transformations within carbon nanotube volume have been reported for both organic and inorganic materials23,24. Those are not limited to intratube reactions but also involve an exchange with an exterior medium25. Besides appropriate main reactions, several authors have noticed matter evacuation from the intratube volume during electron microscopy observations24,26. This process was studied in detail in the present paper to quantify the diffusivity of capsulate species through graphene layers.
Experimental Section CuI@SWNT and ZnTe@SWNT composites having isoelectronic structure were used as the test objects. These composites have a well-resolved structure of one-dimensional crystals, allowing accurate determination of the capsulate atomic quantity25,27. Moreover they represent a family of one-dimensional narrow-gap semiconductors, exciting for studying quantum size effects. To achieve filling of SWNTs internal channels, purified nanotubes with diameters of 1.2-1.6 nm (>90%, Carbon-ChG, Russia), obtained by catalytic arc discharge method, were loaded by ZnTe and CuI salts by capillary filling at high temperatures
28
. The tubes were pre-opened by heat
treatment at 500ºС in dry air for 0.5 hour. The filling process was performed by thermal treatment of vacuum-sealed (10-5 mbar) SWNT-salt mixture (with mass ratio 1: 10) at the temperature of 700 °C (in case of CuI) or 1200 °C (in case of ZnTe) for 10 h, with subsequent slow cooling (0.02K/min) to induce crystallization of encapsulated materials. Direct high-resolution transmission electron microscopy (HRTEM) observations were engaged in the study as an ultimate method, enabling atoms count at sub-nanometer resolution. HRTEM was performed on an FEI Titan 80-300 (80 keV), ARM 200F (80 keV) and Zeiss Libra 200 (200 keV) electron microscopes with spherical/chromatic aberration correction. The samples were dispersed onto lacey carbon-coated grids (SPI). 2 ACS Paragon Plus Environment
Page 3 of 22
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
The Journal of Physical Chemistry
The absorbance efficiency was calculated from the EELS spectra. EELS spectra for initial SWNT and formed composites were acquired with Zeiss Libra 200 analytical electron microscope with electron energy spectral decomposition by Ω-filter in 0-600 eV range. The EELS spectrum was then extrapolated by logarithmic function to extract high-energy losses tail. Image simulations were performed with SimulaTEM29 software (microscope parameters: U = 80 keV, Cs = 0.001-0.01 mm) at defocus varied within ±30 nm limits. Composite wire with conspicuous defect in the nanotube wall were chosen as sites of interest. Typical framing rate of ~2 Hz (exposure time 0.5 s) was used with a total sampling duration to full crystal unload (typically below 180s). Energy profile calculation Potential energy profile calculations were performed using unrestricted Hartree-Fock method with semiempirical PM730 Hamiltonian in MOPAC201631. Only singlet and doublet states were taken into account for odd and even total number of electrons respectively. All profiles were built with 0.1 A step and geometry optimization on each step. Ab initio DFT calculation with B3LYP/def2-SVP (and def2-SVP effective core potential) in ORCA package
32
was applied for
verification of semiempirical binding energies for ZnTe and Te-graphene structures, and, proving the possibility of further semiempirical methods utilization. For curved nanotube surfaces the computations were made in three steps. At the first stage we used semiempirical method for defects conformational analysis with initial geometry obtained from HRTEM and correspondingly modified33. At the second step we refined defect geometry with DFT calculation, and finally calculated energy profiles as described above.
Results and Discussion Composite wires of ZnTe@SWNT and CuI@SWNT illustrate well defined crystal structure with very similar lattice parameters (fig. 1). The structure of crystals was proved by image simulations giving an adequate conformity to experimental projections (fig. 1).
3 ACS Paragon Plus Environment
The Journal of Physical Chemistry
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 22
Fig. 1. The micrographs of one- dimensional crystals in SWNT channel, corresponding image simulation and ball-and-stick models for (a) ZnTe@SWNT with periodicity 0.7 nm, (b) CuI@SWNT with periodicity 0.72 nm. Values of ∆f represent defocuses for simulated projections of atomic structures, giving best match to experimental images.
Series of HRTEM images for both composite types demonstrating gradual crystal escape are shown on the fig. 2. Evacuation of the material from the tube is well pronounced in case of CuI@SWNT forming a cluster outside SWNT. In case of ZnTe@SWNT both Zn and Te atoms are expected to evaporate from the external surface to microscope vacuum chamber due to high partial pressures at the experimental conditions. The number of atoms escaping through the defect in the tube was calculated directly from a residual visible length of 1D nanocrystal, assuming 1D crystal has the structures represented on fig.1. The overall length of encapsulated crystal has been measured at all visible parts within the tube. Additional points in case of CuI@SWNT (fig. 3) at high irradiation durations were gained from a size of a nanocrystal growing at a defect site outside SWNT (fig. 2), assuming that deintercalated copper iodide is fully decomposed to give solid elemental copper and gaseous iodine. The size of the crystal in the direction perpendicular to the beam was assumed to equal minimal of two visible directions. The experimental points for both calculation pathways were joined together giving identical slope values (fig 3b). Original data on atoms counting is provided in the supporting information, section S1.
4 ACS Paragon Plus Environment
Page 5 of 22
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
The Journal of Physical Chemistry
Fig. 2. Crystal escape image series for ZnTe@SWNT (a) and CuI@SWNT (b). Initial defect sites in SWNT wall are indicated by arrows. In case of ZnTe@SWNT escaping atom is well seen on the micrographs, providing additional contrast at a site of the defect (frames at 0, 6, 13 and 54 s). Corresponding TEM image simulation of a defect site with an optimized geometry is provided on the inset. The irradiation doses (e·Å-2) are given on each frame under time label. The length of the one-dimensional CuI crystal utilized for atomic count is designated on the first frame of the series. Copper crystal growing outside SWNT in CuI@SWNT is encircled on several images. The resulting kinetic curves for ZnTe@SWNT and CuI@SWNT are illustrated at fig. 3a,b. Both curves are well-fitted by a logistic function, with a maximum slope of 9.6 atoms/s for ZnTe and 25.2 atoms/s for CuI. To avoid uncertainties with atomic count only atoms counted inside SWNT were taken into account for maximal slope determination. Moreover to minimize the role of possible knock-on damage in SWNT walls on further evaluations the slope rate was extracted at 5 ACS Paragon Plus Environment
The Journal of Physical Chemistry
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 6 of 22
the earliest stages of the kinetics curves (
