Ion beam irradiation is a promising approach to fabricate nanoporous graphene for various applications, including DNA sequencing, water desalination, and phase separation. Further advancement of this approach and rational design of experiments all require improved mechanistic understanding of the physical drilling process. Here, we demonstrate that, by using oblique ion beam irradiation, the nanopore family is significantly expanded to include more types of nanopores of tunable geometries. With the hopping, sweeping, and shoving mechanisms, ions sputter carbon atoms even outside the ion impact zone, leading to extended damage particularly at smaller incident angles. Moreover, with lower energies, ions may be absorbed to form complex ion-carbon structures, making the graphene warped or curly at pore edges. Considering both efficiency and quality, the optimal ion energy is identified to be 1000 eV at an incident angle of 30° with respect to the graphene sheet and 400-500 eV at higher incident angles. All of these results suggest the use of oblique ion beam and moderate energy levels to efficiently fabricate high-quality nanopores of tunable geometries in graphene for a wide range of applications.

Ion bombardment is a key physical process in the ion implantation and irradiation of graphene, with important implications for tuning graphene’s electronic properties and for understanding the material’s behavior in irradiative environment. Using molecular dynamics with a reactive force field, this work systematically investigates the influence of the incident angle on the generation of defects and vacancies during the bombardment process. It is found that larger incident angles (between the incident line and the surface of graphene) ranging from 70° to 90° are desired for substitution and single vacancy, whereas smaller incident angles ranging from 30° to 50° are favored for forming double vacancies, multiple vacancies, and in-plane disorder. Oxygen ions with the incident angle of 70° produce the highest probability of ion substitution, and the ions at 40–60 eV and 70° yield the highest quality of doping with minimum other defects. These results demonstrate that bombarding graphene along oblique directions may be a promising approach to effectively and efficiently modify graphene for wide applications in nanoelectronics. The angle/energy-damage relationships developed by this study are expected to guide future efforts in ion implantation and to improve the understanding of various irradiation processes.

Interchain hydrogen bonds enhance thermal conduction in crystalline polymer nanofibers by confining torsional motion of polymer chains and by increasing the group velocity of phonons.

the exceptional thermal properties of graphene and nanotubes, thereby reducing the overall conductivities of the nanocomposites.To improve the interfacial thermal conduction, interfaces between dissimilar materials need to be engineered for reduced phonon scattering. Current approaches include, but are not limited to, controlling interfacial adhesion, [16][17][18] improving interfacial stiffness, [ 19,20 ] strengthening interfacial interactions, [ 21,22 ] and manipulating phonon modes. [23][24][25] For graphene/polymer nanocomposites, in particular, the interfacial thermal transport can be improved by changing the orientation of few-layer graphene, [ 8 ] grafting graphene with polymer chains, [ 26 ] and functionalizing graphene for tailored phonon modes. [ 27 ] In the fi rst approach, the improvement results from the high thermal conductivity of graphene/graphite in the basal plane along with the enhanced interfacial coupling. [ 28,29 ] In the other two, the polymer chains and functional groups serve as thermal bridges to couple the vibrational modes of graphene with those of the polymeric matrix, thereby minimizing phonon scattering and improving thermal transport.Despite the progress, little attention has been drawn to the manipulation of bonding strength at the graphene/polymer interfaces for improved heat transfer. In most nanocomposites, [ 26,27 ] molecular interactions at material interfaces are dominated by van der Waals forces. It is hypothesized that, interfacial heat transfer can be signifi cantly improved by enabling hydrogen bonds at the interfaces. The hypothesis is made based on three reasons. First, the strength of hydrogen bonds ranges from 10 to 190 kJ mol -1 , 1-2 orders of magnitude higher than that of the van der Waals interactions. [ 30,31 ] Second, recent advances in surface treatment [ 32 ] have made it relatively simple to anchor hydrogen-bond-capable chemical groups to the graphene surfaces to enable hydrogen bonds with many polymers. Third, hydrogen-bond-facilitated thermal conduction has been recently demonstrated in several other material systems including crystalline polymer nanofi bers, [ 33 ] amorphous polymer blends, [ 34 ] along with silk β-sheets [ 35,36 ] and α-helices. [ 37,38 ] However, the use of hydrogen bonds to improve the interfacial thermal transport at graphene/polymer interfaces has not yet been reported.Here, using reverse nonequilibrium molecular dynamics along with various vibrational mode and structural analysis tools, we demonstrate that the presence of hydrogen bonds Ineffective heat transfer between dissimilar materials of drastically different properties is a challenge for many areas including nanoelectronics and nanocomposites. Here, using atomistic simulations, it is demonstrated that the thermal conductance across the interfaces between graphene and poly(methyl methacrylate) (PMMA) can be improved by 273% by introducing hydrogen-bond-capable hydroxyl groups to the interfaces. Stronger than van der Waals interactions, the hydrogen bonds are found to improve t...