Electronic structures, field effect transistor and bipolar field-effect spin filtering behaviors of functionalized hexagonal graphene nanoflakes

We report first-principles calculations on the electronic properties, spin magnetism, and potential applications of the functionalized hexagonal armchair graphene nanoflakes (GNFs). It is found that the gap of the GNF changes in an obvious oscillating manner with the size of its hexagonal defect (antidot), and when the antidot is large enough, it will lead to a prominent splitting of the α-spin and β-spin orbitals and the intriguing property of bipolar magnetic semiconductors for the GNF. And also shown is that the electronic structures of the GNF can be tuned from semiconducting to metallic properties by different edge modifications. More importantly, based on the suitable hexagonal defective GNFs, we design a field effect transistor (FET) and a bipolar field-effect spin-filtering (BFESF) device, and find that they all exhibit extremely high performances. For this FET, its ON/OFF ratio reaches ∼105, subthreshold swing ∼90 meV per decade, and the transconductance ∼103 S/m, and for this BFESF device, the spin polarization nearly reaches 100% with different spin directions only by altering signs of gate voltages.