Atomic-Scale Electron-Beam Sculpting of Defect-Free Graphene Nanostructures

Abstract

First isolated in 2004,1 graphene has received tremendous scientific attention due to its unique electronic properties.2 Graphene also features edge dynamics 3 and mechanical properties, 4 opening up even more opportunities such as its use to sequence genomic DNA using nanopores. 5 In order to harvest the many promising properties of graphene in applications, a technique is required to cut, shape or sculpt the material on a nanoscale without damage to its atomic structure, as this drastically influences the electronic properties of the nanostructure. Here, we reveal a temperature-dependent self-repair mechanism allowing damage-free atomic-scale sculpting of graphene using a focused electron beam. Our technique allows reproducible fabrication and simultaneous imaging of singlecrystalline free-standing nanoribbons, nanotubes, nanopores, and single carbon chains.Temperature has a remarkable effect on the changes induced by 300 keV electrons (Figure 1). At room temperature (RT), a rapid amorphisation occurs, which prevents detailed high-resolution electron microscopy (HREM). At temperatures of 200 °C, we observe that electron beam irradiation leads to amorphisation with only short range order (Figure 1a). At 500 °C, the electron beam results in the formation of polycrystalline monolayers. The single crystalline graphene transforms into polycrystalline graphene with clear straight but short grain boundaries. At 700 °C, remarkably, graphene conserves its full crystallinity even under a very intense electron beam, as shown in Figure 1c. Figure 2 shows various graphene nanostructures made at 600°C~700°C. Carbon nanotubes can be made using elongated electron beams with a shape similar to the holes made (Figure 2a, inset).

Stone-Wales-type transformations in carbon nanostructures driven by electron irradiation

“…More abundant, however, are changes in the atomic configuration through bond rotations in the reconstructed vacancy defects, as recent experiments indicate [14,15]. In presence of a (multi-)vacancy, the atomic configuration of a defect can be transformed between different metastable structures via bond rotations.…”

“…Moreover, SW transformations play an important role in the response of graphene to electron irradiation [14,15], leading to changes in the morphology of vacancy-type defects [16] and to their migration. Such changes are equally surprising, because the barrier for bond rotation is about 5 eV [6,17], which should exclude thermal activation as a cause for SW transformation at room temperature during experimentally relevant time scales.…”

Raman spectroscopy and transmission electron microscopy of long linear atomic carbon chains generated by field electron emission accompanied with electrical discharge of carbon nanotube films

“…The organic synthesis technique yielded an acetylenic carbon chain consisting of 44 atoms [20]. In addition, transmission electron microscopy has also identified short free-standing carbon chains directly forming from carbon nanotubes [21][22][23][24][25] and graphene [26][27][28][29][30][31][32][33][34][35][36] under electron-beam irradiation and application of electrical current. Furthermore, the electric current passing through carbon chains [25,30,32,35] and their tensile force at fracture [23] were measured in situ.…”

Nanobubble dynamics studied with transmission electron microscopy

“…It was also confirmed from the analysis that the graphene liquid cell has multiple layers at some points. The sharp G-peaks indicate the presence of multiple layers of graphene [46]. The peak broadening shows the deformation in the crystal structure due to strain [47].…”

“…with the bubbles being nucleated through a solvent exchange process [30,[42][43][44][45], a change in liquid temperature [45,46], or by the electrolytic production of hydrogen [47].…”