Size dependent magnetic and optical properties in diamond shaped graphene quantum dots: A DFT study

The magnetic and optical properties of diamond shaped graphene quantum dots (DSGQDs) have been investigated by varying their sizes with the help of density functional theory (DFT). The study of density of states (DOS) has revealed that the Fermi energy decreases with increase in sizes (number of carbon atoms). The intermediate structure with 30 carbon atoms shows the highest magnetic moment (8 mu(B), mu(B) being the Bohr magneton). The shifting of optical transitions to higher energy in smallest DSGQD (16 carbon atoms) bears the signature of stronger quantum confinement. However, for the largest structure (48 carbon atoms) multiple broad peaks appear in case of parallel polarization and in this case electron energy loss spectra (EELS) peak (in the energy range 0-5 eV) is sharp in nature (compared to high energy peak). This may be attributed to pi plasmon and the broad peak (in the range 10-16 eV) corresponds to pi + sigma plasmon. A detail calculation of the Raman spectra has indicated some prominent mode of vibrations which can be used to characterize these structures (with hydrogen terminated dangling bonds). We think that these theoretical observations can be utilized for novel device designs involving DSGQDs. (C) 2016 Elsevier Ltd. All rights reserved.