Synchronous Growth of High‐Quality Bilayer Bernal Graphene: From Hexagonal Single‐Crystal Domains to Wafer‐Scale Homogeneous Films

Abstract

The precise control of the domain structure, layer thickness, and stacking order of graphene has attracted intense interest because of its great potential for nanoelectronics applications. Much effort has been devoted to synthesize semiconducting Bernal (AB)-stacked bilayer graphene because of its tunable band structure and electronic properties that are unavailable to single-layer graphene. However, fast growth of large-scale bilayer graphene sheets with a high AB-stacking ratio and high mobility on copper poses a tremendous challenge, which has to overcome the self-limiting effect. This study reports a low-cost but facile method to rapidly synthesize bilayer Bernal graphene by atmospheric pressure chemical vapor deposition using polystyrene as the feedstock. The bilayer graphene grains and continuous film obtained are of high quality and exhibit field-effect hole mobilities as high as 5700 and 2200 cm 2 V −1 s −1 at room temperature, respectively. In addition, a synchronous growth mechanism of bilayer graphene is revealed by monitoring the growth process, resulting in a high surface coverage of nearly 100% for a near-perfect AB-stacking order. This new synthesis route is significant for industrial application of bilayer graphene and investigation of the growth mechanism of graphene by the chemical vapor deposition process.

Controlling the Three‐Phase Boundary in Na–Oxygen Batteries: The Synergy of Carbon Nanofibers and Ionic Liquid

“…For fundamental studies, Lutz et al [22,23] applied a current density of 0.025 mA cm À2 when studying glyme-based electrolytes using ag as diffusion layer air electrode with capacities ranging from 0.2 to 7mAh cm À2 .H igher rates have been appliedi ns tudies focused on the cyclability of the Na-O 2 battery.B ender et al [24] investigated carbon nanotube (CNT)based electrodes (CNT/carbon fiber,C NT/carbon black, pure CNT) at 0.2 mA cm À2 ,w here pure CNT achieved the highest dischargec apacity (4.2 mAh cm À2 ). [25][26][27] Other air electrodes investigated include carbon spheres [28] and catalysts such as CaMnO 3 [29] and NiCo 2 O 4 . [25][26][27] Other air electrodes investigated include carbon spheres [28] and catalysts such as CaMnO 3 [29] and NiCo 2 O 4 .…”

“…Yadegari et al [4] have also reported an air electrode composed of vertically grown nitrogen-doped carbon nanotubes on carbon paper at currentd ensities of 0.1, 0.2 and 0.5 mA cm À2 with ac apacity of 11,9and 6mAh cm À2 ,r espectively.I na ddition, graphene-based materials have also been studied at much lower applied currents than in this work, leadingt ol ow specific capacity (e.g.,0 .05-0.2 mAh cm À2 ). [25][26][27] Other air electrodes investigated include carbon spheres [28] and catalysts such as CaMnO 3 [29] and NiCo 2 O 4 . [30] Therefore, the discharge rate applied in this study is the highest amongN a-O 2 battery studies, which might be related to the unique combination and synergy of the CNF electrode and the ionic liquid electrolyte.…”

Controlled Nucleation of Graphene Domains on Copper With an Oxide Layer by Atmospheric Pressure Chemical Vapor Deposition

“…(Figures 5b-h) The layer number was further confirmed by the intensity of the diffraction spots along the line. In region C and D, marked in Figure 5a, the intensity of spots of the outer hexagon is twice or more than that of the inner hexagon, indicating the bilayer (Wu et al, 2017a) or multilayer (Hernandez et al, 2008) stacking of graphene (Figures 5d,e). It was observed that the 6folded symmetrical SAED patterns of other regions were almost the same, with the intensity ratio of spots in the outer hexagon to the inner hexagon >1, revealing the single-crystal nature of the detected areas (point A,B,E,F,G) (Hernandez et al, 2008).…”

“…The oxide layer possibly also contributed to the accumulation of impurities such as residual metals (Huet and Raskin, 2018). During the growth process, the first single-crystal graphene layer was attributed to the adsorbed carbon atoms on the surface (Gan and Luo, 2013;Hao et al, 2013;Guo et al, 2018), while the multilayer graphene branches formed by active C species passing through the edge of up-layer graphene domains due to the catalytic activity of accumulated residual metal impurities (Zhang et al, 2014;Wu et al, 2017a), or by the diffusion of carbon atoms through the Cu bulk (Hao et al, 2016;Sun et al, 2016). The growth of the single-crystal graphene domains and the multilayer graphene branches was almost synchronous.…”

Growth of Ordered Graphene Ribbons by Sublimation Epitaxy

“…Due to its unique properties, such as the unusual half-integer quantum Hall effect [1,2] and mass-less Dirac fermion behavior [3,4], graphene has many potential applications in the fields of novel physics, chemistry, optics, and mechanics [5,6], and as realistic technology transfer in the fields of membrane technology [7], energy [8], photodetection [9], and plasmonics [10]. Since the successful preparation of the first stable graphene flake at room temperature by peeling highly oriented pyrolytic graphite (HOPG) [11], people have developed many methods to prepare graphene, including monolayer [12,13], bilayer [14,15], and few-layer graphene [16,17], in the form of powder [18], flake [19], and film [20]. Although intrinsic monolayer graphene is a semimetal without a bandgap, we can open a specific bandgap by patterning graphene into nano-ribbons or coupling graphene with certain substrates [21,22]; bilayer graphene can be operated to have a high on/off ratio, and a bandgap up to hundreds of millielectronvolts controlled by an electronic field, which paves the way for its applications in high performance electronics [23].…”