Graphene Nanoflakes: Thermal Stability, Infrared Signatures, and Potential Applications in the Field of Spintronics and Optical Nanodevices

Abstract

We investigate the structural, electronic, and vibrational properties of graphene nanoflakes (GNFs) with a small number of atoms (<250) and distinct shapes (triangular, rectangular, and hexagonal) through classical molecular dynamics (CMD) and density functional theory (DFT) calculations. We show that these graphene nanostructures are able to retain their planarity for simulated temperatures up to 1500 K, starting to degrade into amorphous nanocarbon for temperatures above 3000 K. The shapes and types of border of the GNFs have a strong influence on their electronic properties and spin. The HOMO−LUMO energy gap of the studied nanoflakes spans the full range of the visible spectrum, suggesting potential applications in the fabrication of optical emission nanodevices, which is confirmed by TDDFT calculations to obtain the UV−vis absorption spectra of triangular armchair GNFs. In particular, the UV−vis maximum absorption energies and intensities scale linearly with the linear size of the GNF. In the special case of zigzag-edged triangular nanoflakes, a nonzero net spin which increases linearly with the edge size was found, pointing toward possible spintronic applications by tuning the spin distribution. The DFT calculations of the infrared spectra allowed the identification of shape- and border-related fingerprints.