Oxidized-driven and strain-tunable anisotropic effects in crystalline graphene oxides

The study of anisotropic effects in two-dimensional (2D) materials has fundamental scientific interest and application benefits. Herein, we reveal that highly anisotropic semiconductors and strongly tilted Dirac cones are discovered in a family of crystalline graphene oxide named cGO-nz. Specifically, cGO-2z is a direct band gap (1.24 eV) semiconductor having highly anisotropic electrons but almost isotropic holes. cGO-4z is a narrow direct band gap (0.4 eV) semiconductor with both highly anisotropic electrons and holes. Moreover, cGO-4z can be strain-tailored to a metal and its preferred hole conducting direction can be rotated by 90° under external strain. cGO-nz (n ≥ 6) are strongly tilted Dirac semimetals and their tilted strength are strain-tunable. Besides, all of the mechanical, thermal transport and optical properties in cGO-nz exhibit obvious anisotropic behaviors. With the help of tight-binding analysis, we elucidate these anisotropic electronic behaviors in cGO-nz can be ascribed to the competitive mechanism of on-site energies between carbon's p z orbitals and oxygen's p y orbitals together with the high-order terms from oxygen(p y )-to-oxygen(p y ) and carbon(p z )-to-carbon(p z ) interactions. Such many appealing physical properties, especially the conspicuous anisotropic aspects, uncovered in cGO-nz endow them are promising candidates for investigating basic physical laws and also for exploiting prospective angular-dependent devices.