Optimized Substrates and Measurement Approaches for Raman Spectroscopy of Graphene Nanoribbons

Abstract

The on‐surface synthesis of graphene nanoribbons (GNRs) allows for the fabrication of atomically precise narrow GNRs. Despite their exceptional properties which can be tuned by ribbon width and edge structure, significant challenges remain for GNR processing and characterization. Herein, Raman spectroscopy is used to characterize different types of GNRs on their growth substrate and track their quality upon substrate transfer. A Raman‐optimized (RO) device substrate and an optimized mapping approach are presented that allow for the acquisition of high‐resolution Raman spectra, achieving enhancement factors as high as 120 with respect to signals measured on standard SiO2/Si substrates. This approach is well suited to routinely monitor the geometry‐dependent low‐frequency modes of GNRs. In particular, the radial breathing‐like mode (RBLM) and the shear‐like mode (SLM) for 5‐, 7‐, and 9‐atom‐wide armchair GNRs (AGNRs) are tracked and their frequencies are compared with first‐principles calculations.

Optical Imaging and Spectroscopy of Atomically Precise Armchair Graphene Nanoribbons

“…In order to improve signal to noise ratio Raman maps (10x10um) were obtained for GNRs on Au and on fused silica under vacuum (1x 10 -2 mbar). 40…”

Massive Dirac Fermion Behavior in a Low Bandgap Graphene Nanoribbon Near a Topological Phase Boundary

“…We also observe well‐defined edge‐related modes in the spectral region labeled CH. These modes are characteristic fingerprints of the particular width and edge structure of this ribbon, and their presence after exposure to air strongly suggests the ribbons are stable under ambient conditions 18–20. The observed wavelength dependence (Figure S11, Supporting Information) points towards an optical resonance in the infrared, in accordance with the low bandgap of the pGNR.…”

“…Raman spectra were acquired with a WITec confocal Raman microscope (WITec Alpha 300R) equipped with a home‐built vacuum chamber at pressures below 10 −2 mbar. Imaging conditions were optimized independently for each laser wavelength and substrate to yield optimum signal‐to‐noise ratio, while avoiding laser‐induced changes to the GNRs (see Table T1/Figure S10, Supporting Information) 19. Signatures of cosmic rays and a polynomial background were subtracted from the spectra.…”

“…Electronic device fabrication requires the transfer of GNRs to suitable substrates with pre‐patterned electrodes 19,20. We monitor this transfer process by Raman spectroscopy to verify the ribbon integrity.…”

In situ laser annealing as pathway for the metal free synthesis of tailored nanographenes

“…At the same time, the absence of signal from the decomposition products points to a non-uniform synthesis and to their fast transition into amorphous carbon due to the high irradiance used during laser annealing. 41 A quantitative study of the spectrum's decay can be made af- Intensity decay of the peak at 1326cm −1 . Two distinct regimes can be identified: during the first, the decay is governed by evaporation, during the second by molecular decomposition into graphitized amorphous carbon.…”