Optical Excitations and Field Enhancement in Short Graphene Nanoribbons.
The optical excitations of elongated graphene nanoflakes of finite length are investigated theoretically through quantum chemistry semiempirical approaches. The spectra and the resulting dipole fields are analyzed, accounting in full atomistic details for quantum confinement effects, which are crucial in the nanoscale regime. We find that the optical spectra of these nanostructures are dominated at low energy by excitations with strong intensity, comprised of characteristic coherent combinations of a few single-particle transitions with comparable weight. They give rise to stationary collective oscillations of the photoexcited carrier density extending throughout the flake and to a strong dipole and field enhancement. This behavior is robust with respect to width and length variations, thus ensuring tunability in a large frequency range. The implications for nanoantennas and other nanoplasmonic applications are discussed for realistic geometries.
†Centro S3, CNR-Istituto Nanoscienze, I-41125 Modena, Italy.|‡Dipartimento di Fisica, Università di Modena e Reggio Emilia, I-41125 Modena, Italy.
Caterina
C
Cocchi
†Centro S3, CNR-Istituto Nanoscienze, I-41125 Modena, Italy.
Deborah
D
Prezzi
†Centro S3, CNR-Istituto Nanoscienze, I-41125 Modena, Italy.|‡Dipartimento di Fisica, Università di Modena e Reggio Emilia, I-41125 Modena, Italy.
Alice
A
Ruini
†Centro S3, CNR-Istituto Nanoscienze, I-41125 Modena, Italy.
Enrico
E
Benassi
¶Instituto de Física, Universidade de São Paulo, 05508-900 São Paulo, SP, Brazil.
Marilia J
MJ
Caldas
†Centro S3, CNR-Istituto Nanoscienze, I-41125 Modena, Italy.
Stefano
S
Corni
†Centro S3, CNR-Istituto Nanoscienze, I-41125 Modena, Italy.|‡Dipartimento di Fisica, Università di Modena e Reggio Emilia, I-41125 Modena, Italy.
Elisa
E
Molinari
UV−vis spectrum; ZINDO; carbon nanostructures; nanoplasmonics; transition density