Structural transformations in graphene studied with high spatial and temporal resolution

Abstract

Graphene has remarkable electronic properties, such as ballistic transport and quantum Hall effects, and has also been used as a support for samples in high-resolution transmission electron microscopy and as a transparent electrode in photovoltaic devices. There is now a demand for techniques that can manipulate the structural and physical properties of graphene, in conjunction with the facility to monitor the changes in situ with atomic precision. Here, we show that irradiation with an 80 kV electron beam can selectively remove monolayers in few-layer graphene sheets by means of electron-beam-induced sputtering. Aberration-corrected, low-voltage, high-resolution transmission electron microscopy with sub-ångström resolution is used to examine the structural reconstruction occurring at the single atomic level. We find preferential termination for graphene layers along the zigzag orientation for large hole sizes. The temporal resolution can also be reduced to 80 ms, enabling real-time observation of the reconstruction of carbon atoms during the sputtering process. We also report electron-beam-induced rapid displacement of monolayers, fast elastic distortions and flexible bending at the edges of graphene sheets. These results reveal how energy transfer from the electron beam to few-layer graphene sheets leads to unique structural transformations.

The electronic states of a double carbon vacancy defect in pyrene: a model study for graphene

“…These defects arise in graphene or in graphitic nanostructures during defective growth and can also be created artificially by means of ion irradiation. [7][8][9][10][11][12][13][14] Their structural details can be directly observed by means of several experimental techniques such as transmission electron microscopy (TEM) [15][16][17][18][19] and scanning tunneling microscopy (STM). 20,21 Because of the occurrence of dangling bonds the defect structure will be associated with a high polyradical character with a multitude of closely spaced locally excited electronic states possessing different spin multiplicities which make their theoretical description very challenging.…”

Spatial control of defect creation in graphene at the nanoscale

“…Electron and ion beam irradiation have been successful in generating defects in carbon nanostructures, such as fullerenes, nanotubes, peapods, and recently graphene [12][13][14][15][16][17][18][19][20][21][22][23] . For ion beam irradiation, defects are sporadically formed over a wide area of graphene with lack of nanoscale spatial control and in situ monitoring at the atomic level.…”

“…Electron beam irradiation of graphene well above its knock-on damage (KOD) threshold of ~86 keV within an AC-TEM generates defects that can be subsequently imaged, with the electron beam accelerating voltage reduced to below the KOD threshold after defect creation to minimize further beam damage [19][20][21][22][23] . However, this approach exposes a large amount of the graphene to electrons with energy above the KOD threshold, and limiting defect creation to one specific location is nearly impossible.…”

Hydrogen-free graphene edges

“…Despite the progress made in scanning probe microscopy (STM and atomic force microscopy) and aberration-corrected transmission electron microscopy (AC-TEM) [26][27][28][29][30] , detecting bond length changes at the edges of graphene has been extremely difficult due to the need to fully resolve individual carbon atoms. Recent advances in monochromation of the electron source have enabled AC-TEM with B80 pm spatial resolution at the low accelerating voltage of 80 kV (refs 26,31).…”