Probing graphene grain boundaries with optical microscopy

Abstract

Grain boundaries in graphene are formed by the joining of islands during the initial growth stage, and these boundaries govern transport properties and related device performance. Although information on the atomic rearrangement at graphene grain boundaries can be obtained using transmission electron microscopy and scanning tunnelling microscopy, large-scale information regarding the distribution of graphene grain boundaries is not easily accessible. Here we use optical microscopy to observe the grain boundaries of large-area graphene (grown on copper foil) directly, without transfer of the graphene. This imaging technique was realized by selectively oxidizing the underlying copper foil through graphene grain boundaries functionalized with O and OH radicals generated by ultraviolet irradiation under moisture-rich ambient conditions: selective diffusion of oxygen radicals through OH-functionalized defect sites was demonstrated by density functional calculations. The sheet resistance of large-area graphene decreased as the graphene grain sizes increased, but no strong correlation with the grain size of the copper was revealed, in contrast to a previous report. Furthermore, the influence of graphene grain boundaries on crack propagation (initialized by bending) and termination was clearly visualized using our technique. Our approach can be used as a simple protocol for evaluating the grain boundaries of other two-dimensional layered structures, such as boron nitride and exfoliated clays.

A facile method for the selective decoration of graphene defects based on a galvanic displacement reaction

“…Defect sites present on the SLG layer, including GBs and intrinsic topological defects, act as electronically favorable sites for Pd deposition because of their chemical instability. 25,26 Therefore, graphene imperfections effectively function as nucleation sites, as observed when Pd NPs were formed on both graphene GBs and graphene regions over Cu fatigue cracks. Defect sites that act as nucleation sites for Pd can be generated during the galvanic displacement reaction.…”

Structure of graphene and its disorders: a review

“…Furthermore, STEM can provide histograms of gain sizes and relative grain rotation angles for better understanding of the GBs [209,210]. It is also possible to visualize GBs by optical birefringence of graphene surface covered with nematic liquid crystal [211], by spectroscopic Raman imaging of the defect-activated D mode [78,212], and by infrared nanoimaging technique [213]. …”

What are grain boundary structures in graphene?

“…[4][5][6][7][8][9] In practice, however, graphene is always grown with different defects, among which grain boundary (GB) is one of the most frequently formed defects. [10][11][12] GBs provide numerous novel possibilities in modifying graphene such as tuning the charge distribution 12 and transport property 13 . Therefore, GBs in graphene have been the focus of numerous researches due to their great significance in science and application.…”

“…Therefore, GBs in graphene have been the focus of numerous researches due to their great significance in science and application. [10][11][12][13][14][15] Intensive works have been done to study the broad properties of GBs. [13][14][15][16][17][18][19][20][21][22][23][24][25] By analyzing the symmetry between the Brillouin zones of two sides, a theory was developed to predict the electronic transport property through GBs, 13 indicating symmetric GBs have zero transport gap, but the asymmetric GBs have finite gaps.…”