Adatom doping-enriched geometric and electronic properties of pristine graphene: a method to modify the band gap

Unusual features of nitrogen substitutions in silicene

The quasiparticle properties resulting from charge and spin are clearly identified in nitrogen-substituted silicenes, for which a theoretical framework is successfully developed from first-principles calculations. Such systems create extremely non-uniform chemical and physical environments through the distribution of the guest atoms. They present unusual geometric, electronic, and magnetic properties, which can be identified from the optimal honeycomb lattices, the atom- and spin-dominated energy spectra, the spatial charge density distributions, and the atom-, orbital- and spin-projected van Hove singularities [the net magnetic moments]. The complicated relations between the highly hybridized sp²-N-Si bonds and the ferromagnetic/non-magnetic configurations are responsible for the p-type or semiconducting behavior, the significant modifications to the Dirac cone structures, the difficulty in identifying the π and σ bands, and the vanishing or finite magnetic moments. The theoretical predictions could be verified by high-resolution experimental measurements.

Interfacial engineering in graphene bandgap

Graphene exhibits superior mechanical strength, high thermal conductivity, strong light-matter interactions, and, in particular, exceptional electronic properties. These merits make graphene an outstanding material for numerous potential applications. However, a graphene-based high-performance transistor, which is the most appealing application, has not yet been produced, which is mainly due to the absence of an intrinsic electronic bandgap in this material. Therefore, bandgap opening in graphene is urgently needed, and great efforts have been made regarding this topic over the past decade. In this review article, we summarise recent theoretical and experimental advances in interfacial engineering to achieve bandgap opening. These developments are divided into two categories: chemical engineering and physical engineering. Chemical engineering is usually destructive to the pristine graphene lattice via chemical functionalization, the introduction of defects, doping, chemical bonds with substrates, and quantum confinement; the latter largely maintains the atomic structure of graphene intact and includes the application of an external field, interactions with substrates, physical adsorption, strain, electron many-body effects and spin-orbit coupling. Although these pioneering works have not met all the requirements for electronic applications of graphene at once, they hold great promise in this direction and may eventually lead to future applications of graphene in semiconductor electronics and beyond.