Two-Dimensional Hallmark of Highly Interconnected Three-Dimensional Nanoporous Graphene

Abstract

Scaling graphene from a two-dimensional (2D) ideal structure to a three-dimensional (3D) millimeter-sized architecture without compromising its remarkable electrical, optical, and thermal properties is currently a great challenge to overcome the limitations of integrating single graphene flakes into 3D devices. Herewith, highly connected and continuous nanoporous graphene (NPG) samples, with electronic and vibrational properties very similar to those of suspended graphene layers, are presented. We pinpoint the hallmarks of 2D ideal graphene scaled in these 3D porous architectures by combining the state-of-the-art spectromicroscopy and imaging techniques. The connected and bicontinuous topology, without frayed borders and edges and with low density of crystalline defects, has been unveiled via helium ion, Raman, and transmission electron microscopies down to the atomic scale. Most importantly, nanoscanning photoemission unravels a 3D NPG structure with preserved 2D electronic density of states (Dirac cone like) throughout the porous sample. Furthermore, the high spatial resolution brings to light the interrelationship between the topology and the morphology in the wrinkled and highly bent regions, where distorted sp 2 C bonds, associated with sp 3 -like hybridization state, induce small energy gaps. This highly connected graphene structure with a 3D skeleton overcomes the limitations of small-sized individual graphene sheets and opens a new route for a plethora of applications of the 2D graphene properties in 3D devices.

Deuterium Adsorption on Free-Standing Graphene

“…As we will discuss in the following, the Raman spectra acquired in our NPG samples show a very slight presence of defect/disorder related peaks, typical of a very high-quality and low-defect one-to-few layer continuous graphene sheet with a turbostratic stacking, thereby having only weak bonding between the sheets, as discussed in previous papers [ 27 , 28 ].…”

“…Aside from this main peak, the structure at about 285.3 eV BE in the clean NPG is associated with an sp -like distorted bond. For the clean sample, this structure originates from the highly bent or wrinkled regions of the nano-pores, as recently discussed in micro-spectroscopy experiments [ 27 , 28 ]. There is another broad component characteristic of the bonding in graphene at about 291.3 eV BE, thereby at 6.7 eV from the main peak, which is the plasmon associated with the collective excitations [ 31 , 65 , 66 , 67 ].…”

“…In the UHV-clean NPG we observe the typical electronic spectral density of graphene, characterised by (i) the linear behaviour towards the Fermi level (E ) reflecting the Dirac cone band dispersion, (ii) the peak at about 3 eV BE due to the -state and (iii) the broad features between 6 and 8.5 eV BE associated with the band [ 27 ], evidencing the high quality of this free-standing graphene sample. The D-saturated NPG after annealing at 330 C presents a quenching of the peak, a redistribution of the of states and the strong reduction of the spectral density of states below the Fermi level, with the top of the valence band at ∼3.8 eV from E , in good agreement with what observed for H-decorated graphene [ 21 ].…”

“…To overcome these drawbacks we propose to expose to deuterium high-quality, three-dimensional (3D), warped, free-standing graphene. Here, we study the effect of deuterium incorporation in nanoporous graphene samples: NPG is constituted by a compact, bi-continuous interconnected 3D arrangement of high-quality graphene veils, with 1000 m /g specific surface area, high transport properties and Dirac fermion [ 25 , 26 ], composed by one to a few layers, weakly interacting among each other [ 27 , 28 ]. The veils present a curved structure at the sub-m scale, with intrinsic local scale curvatures and rippling that favour H and D adsorption.…”

A universal graphitic interlayered centroid intercalation theory for intercalation chemistry

“…Thus, the small amount of graphic N (< 30% in considering of the co-presence of pyrrolic N; Fig. 1b(iii)) may imply that most of the N elements tend to be doped at edges or defects [22,26,27,[32][33][34][35][36][37][38][39]. This inference can be supported by the chemical mappings of electron energy-loss spectroscopy (EELS) reported previously [31], as well as the subsequent HR-TEM image of the basal plane of NGF showing only a few mono defects (Fig.…”