Two-Dimensional Diamond—Diamane: Current State and Further Prospects

Abstract

Two-dimensional diamond, or diamane, is an ultrathin film with unique physical properties that combine the record values of the bulk crystal with the exciting features caused by the nanoscale nature. At the current stage of research, the diamane properties are mostly studied theoretically, and the main experimental efforts are directed at its synthesis. The latter is the trickiest problem since traditional methods involving the application of high pressure are not fully suitable due to the influence of surface effects. For diamane research, this poses a number of challenges, whose description is the main purpose and scope of this review. The paper also discusses the progress made so far and outlines the prospects for this field, at the crossroads of the timeless diamond and decade-old graphene.

Progress in Diamanes and Diamanoids Nanosystems for Emerging Technologies

“…The uniqueness of these structures largely depends on the type of structural deformation, the amount of sp 3 carbon, the nature of hetero atoms, and the area of hydrogenated graphene. [56][57][58][59][60][61] Thus, the primary factor is to select proper functional groups in terms of their molecular or atomic states to form the desired structures in diamane. The selection of the fittest form of hydrogen in the crystal lattice of diamane is illustrated in Figure 3a.…”

“…The selection of the fittest form of hydrogen in the crystal lattice of diamane is illustrated in Figure 3a. [61][62][63] In this regard, it is observed that uniform adsorption of atomic hydrogen to bilayer graphene leads to a strong chemical bonding between the layers of graphene, which, in turn, greatly stabilizes the structure of diamane, owing to the removal of Van der Waal forces. [64] Molecular hydrogen could only be used to perform physisorption on the surface of graphene rather than forming conventional bonds as discussed previously.…”

“…This structure is very close to the symmetry and morphology of those reported recently by Li et al for the diamondization of a few layered and bi-layered graphene (Figure 3b,c). [56,61] Experimentally, it is proved that hexagonal and rhombohedral configurations are the most stable forms (thermodynamic stable) of diamane, owing to the hexagonal Bernal stacking and lower energy than other stacking patterns. These two configurations are very similar to those cases of Stone-Wales defect in graphene (Figure 3d,e), but not identical to other 2D systems.…”

“…The Stone-Wales defect in graphene and related systems are shown in the HRTEM image (Figure 3f), as described elsewhere. [40,56,61] The schematic structure of graphene, a key component of diamanes and diamanoids, is shown in Figure 3h, for comparison, even though all the three are entirely dissimilar in nature. [56][57][58][59][60][61]63] The rhombohedral sequential layer has also been reported in the case of conversion of multilayered graphene to ultra-thin diamond films via chemical functionalization.…”

“…[40,56,61] The schematic structure of graphene, a key component of diamanes and diamanoids, is shown in Figure 3h, for comparison, even though all the three are entirely dissimilar in nature. [56][57][58][59][60][61]63] The rhombohedral sequential layer has also been reported in the case of conversion of multilayered graphene to ultra-thin diamond films via chemical functionalization. [57][58][59][60][61] Similarly, cubic and hexagonal structures can be achieved when AB stacked and AA stacked diamanes are synthesized; whilst diamane with Moire's pattern (a set of straight or curved lines being superposed onto another set), that is similar to graphene (but not identical) (Figure 3g) from rotational stacking, can be achieved using pristine graphene with a smaller twist angle between layers.…”