Graphene nanoribbons

Graphene nanoribbons (GNRs) - strips of graphene few tens of nanometers wide - are good candidates for next-generation graphene based electronics. At the Istituto Nanoscienze of CNR (CnrNano) a research focus is dedicated to the study of structural, electronic, optical and vibrational properties of graphene nanoribbons with theoretical approaches that are developed in collaboration with leading experimental research groups.

One of the recent results achieved in the field, is the first systematic analysis of the Raman spectrum of different types of nanoribbons, which showed that GNR width, edge geometry, and functionalization all influence their Raman spectra. The study, published on NanoLetters, in collaboration with German and British colleagues, provides new insights into how electronic and vibrational properties of nanostructures change with their dimensionality and shows that Raman spectroscopy is a powerful GNRs characterization tool. By combining Raman spectroscopy and ab-initio simulations researchers show that the characteristic low-energy peak is particularly sensitive to edge morphology. They also observed a characteristic dispersion of the so-called 'D peak' which can be used to uniquely fingerprint the presence of GNRs and differentiates them from other carbon-based systems such as graphene or carbon nanotubes.

Another recent study demonstrates that GNRs are potentially useful for optoelectronic applications to generate, detect and control light as well as to absorb and convert light into energy - a promising use, for example in photovoltaics. The research, carried out by Deborah Prezzi and Elisa Molinari from CnrNano in collaboration Ifn-Cnr, Politecnico di Milano, University of Modena and Reggio Emilia and Max Planck Institute in Mainz, is published on Nature Communications. Scientists used atomically precise GNR less than five nanometers wide. Due to their one-dimensional structure such GNRs display a 'band gap' similar to that of a semiconductor and yet retains many features of the semi-metallic material. Measuring the GNRs' ultrafast processes following optical excitation, observed the formation of bound states called excitons as well as biexcitons. An exciton is formed when an electron and a hole are attracted to each other instead of moving freely inside the material. Moreover, excitons can form so-called biexcitons, another bound state that can serve as an additional channel to store energy. Also stimulated emission was demonstrated arising from strongly bound biexcitons and having a great efficiency. These results could pave the way for the use of Graphene nanoribbons as active materials in lasers, photodetectors and new generations of ultrafast optoelectronic devices.

Raman fingerprints of atomically precise graphene nanoribbons - Nano Letters DOI: 10.1021/acs.nanolett.5b04183 - February, 2016

Exciton-exciton annihilation and biexciton stimulated emission in graphene nanoribbons - Nature Communications 7 (A.n.110109), DOI:10.1038/ncomms11010 - March, 2016