Making graphene nanoribbons photoluminescent

We demonstrate the alignment-preserving transfer of parallel graphene nanoribbons (GNRs) onto insulating substrates. The photophysics of such samples is characterized by polarized Raman and photoluminescence (PL) spectroscopies. The Raman scattered light and the PL are polarized along the GNR axis. The Raman cross section as a function of excitation energy has distinct excitonic peaks associated with transitions between the one-dimensional parabolic subbands. We find that the PL of GNRs is intrinsically low but can be strongly enhanced by blue laser irradiation in ambient conditions or hydrogenation in ultrahigh vacuum. These functionalization routes cause the formation of sp3 defects in GNRs. We demonstrate the laser writing of luminescent patterns in GNR films for maskless lithography by the controlled generation of defects. Our findings set the stage for further exploration of the optical properties of GNRs on insulating substrates and in device geometries

Coupling to zone center optical phonons in VSe2 enhanced by charge density waves

We investigate electron phonon coupling EPC in the charge density wave CDW phase of VSe2 by Raman spectroscopy, angle resolved photoemission spectroscopy ARPES , and ab initio calculations. Zone folding induced by the 4 4 in plane CDW phase promotes the appearance of a Raman peak at amp; 8764;170cm amp; 8722;1. The suppression of ARPES intensity in parts of the Fermi surface is also a result of CDW induced zone folding and anticrossing of the electron energy bands. The appearance of the new Raman peak is in line with the ARPES observation of a kink feature in the spectral function at the same energy. A self energy analysis yields an EPC constant of amp; 955; 0.3. Our calculations of the EPC are in excellent agreement and reveal that the kink is caused by several optical phonon branches close in energy. Our paper highlights the CDW phase as a means of inducing EPC pathways to optical phonons that directly affect its Raman spectru