Facile Fabrication of Subnanopores in Graphene under Ion Irradiation: Molecular Dynamics Simulations

Abstract

Two-dimensional (2D) nanoporous membranes have attracted great interest in water desalination, energy conversion, electrode, and gas separation. The performances of these membranes are mainly determined by the nanopores, and only with satisfactory subnanometer pores can applications such as high-precision ion separation be realized. Therefore, to efficiently create subnanopores in 2D materials is of great importance. Here, using molecular dynamics simulations, we demonstrate that the direct irradiation of energetic ion is capable of introducing subnanopores in monolayer graphene. By changing the energy of the incident Au ion, the averaged pore diameter can be adjusted from 4.2 to 5.6 Å, and pore diameter distributions are narrow. In the formation processes of the subnanopores, the cascade collisions caused by the primary knock-on atom (PKA) predominates, and pores can only be created in ion impact positions close to the PKA, especially for the incident ion with high energy. Our results show the promise of ion irradiation as a facile method to fabricate subnanopores in 2D materials. As hydrated ions, gases, and small organic molecules have diameters of several angstroms, close to the pore sizes, the created nanoporous membranes can be used to separate those matter, which is conducive to accelerating related applications.

Multifunctional graphene heterogeneous nanochannel with voltage-tunable ion selectivity

“…Aberration-corrected scanning transmission electron microscope (STEM) was used to characterize the graphene subnanopores created under the ion irradiation, and the pores had the average diameter of ∼0.5 nm and density of ∼5.47 × 10 11 cm −2 (Supplementary Fig. 3 ), which are consistent with the results of our recent molecular dynamics simulations 44 . Figure 1 c shows four representative subnanopores with the corresponding atomic structures, and the observed pores (see all of them in Supplementary Fig.…”

Defect-Dependent Corrugation in Graphene

“…Graphene’s remarkable properties strongly depend on its morphology with many physical phenomena arising as a consequence of its intrinsic ripples and corrugation − or by the presence of defects. − For instance, introducing eight-membered-ring defects can enhance graphene’s ion permeability. − This makes graphene an ideal candidate for nanoengineering where material properties are tuned by modifying the atomic morphology. , To this end, a plethora of experimental techniques has emerged ranging from the atomically precise insertion of defects via electron beam − or ion bombardment ,− to chemical etching with KOH , and the regulation of rippling patterns by inducing strain . More recent approaches like laser-assisted chemical vapor deposition or high-temperature quenching go one step further by incorporating the desired morphology a priori in the growth process.…”

Long-Term Evolution of Vacancies in Large-Area Graphene

“…The above simulation results show the stability of vacancy distributions after the long-term vacancy evolution in monolayer graphene, which is also confirmed by our previous theoretical and experimental works on subnanopores fabricated using the irradiation of energetic ions in monolayer graphene. 43 , 44 In the classical MD simulations, the irradiation of ions can directly generate subnanopores due to the cascade collisions, and most of the pores, which are essentially vacancies, are with several atoms removed. 43 Such theoretical predictions agreed with the pores observed in experiments using a scanning transmission electron microscope, where most subnanopores with several atoms missed were found.…”

“…44 Besides, the averaged pore diameter predicted in the MD simulations is 5 Å for Au ions with an energy of 500 keV, which is also consistent with our experimental result. 43,44 It is worth noting that in the MD simulations, vacancies (pores) fabricated under the ion irradiation have not undergone further thermodynamical evolution (migration, coalescence, and dissociation), which are similar to the initial vacancies in this work. The experimentally observed subnanopores were actually the results after the vacancy evolution because there is a long period of time (at least several hours) between the fabrication and observation of the pores, which is enough for the finishing of the evolution.…”