Probing the nanoscale origin of strain and doping in graphene-hBN heterostructures

Abstract

We use confocal Raman microscopy and modified vector analysis methods to investigate the nanoscale origin of strain and carrier concentration in exfoliated graphene-hexagonal boron nitride (hBN) heterostructures on silicon dioxide (SiO2). Two types of heterostructures are studied: graphene on SiO2 partially coved by hBN, and graphene fully encapsulated between two hBN flakes. We extend the vector analysis methods to produce spatial maps of the strain and doping variation across the heterostructures. This allows us to visualise and directly quantify the much-speculated effect of the environment on carrier concentration as well as strain in graphene. Moreover, we demonstrate that variations in strain and carrier concentration in graphene arise from nanoscale features of the heterostructures such as fractures, folds and bubbles trapped between layers. For bubbles in hBN-encapsulated graphene, hydrostatic strain is shown to be greatest at bubble centres, whereas the maximum of carrier concentration is localised at bubble edges. Raman spectroscopy is shown to be a non-invasive tool for probing strain and doping in graphene, which could prove useful for engineering of two-dimensional devices.

Application of Molecular Vapour Deposited Al2O3 for Graphene-Based Biosensor Passivation and Improvements in Graphene Device Homogeneity

“…It is known that graphene on SiO 2 dielectric is heavily p-doped [ 72 ] and the presence of the trace photoresist, after graphene device fabrication, adds additional strain on the graphene, seen by the shift in its Raman spectrum. With the presence of the Al 2 O 3 on the graphene surface, this stress is relieved and an inherent n-doping effect takes place, causing a redshift in the Raman peaks ( Figure 6 d) [ 71 , 73 , 74 , 75 , 76 ].…”

A Facile Method for the Non-Covalent Amine Functionalization of Carbon-Based Surfaces for Use in Biosensor Development

“…Raman spectra were obtained, centered at 1600 cm −1 and 2600 cm −1 , in a grid pattern. Peak analysis based on previous reports [ 36 , 38 , 39 ] was performed using custom scripts. Graphene on SiO 2 is typically p-doped [ 40 ], under ambient conditions, this is in contrast to high vacuum, where the graphene (on SiO 2 ) might be intrinsic or n-doped [ 41 ].…”

Graphene Bioelectronic Nose for the Detection of Odorants with Human Olfactory Receptor 2AG1

“…Using a custom script, the Raman peak positions of the G-peaks and 2D-peaks were obtained after each functionalization stage and were placed into a scatter plot (Figure 5b). The shifts in the G-peak positions, with respect to the shifts in the 2D-peak position, after each functionalization stage could be used to analyse the changes in stress or strain in the graphene crystalline structure and alterations in the charge carrier doping [38]. The application of DAN resulted in electron donation between the DAN and the graphene surface, introducing an n-doping effect on the graphene, shown by the blue-shifting of the Raman peaks [34,35,39].…”

“…However, once the glutaraldehyde and OR2AG1 receptor proteins were attached, the Raman peaks shifted again in the opposite direction, indicating that a p-doping effect was taking place. This p-doping effect took place due to the charge transfer occurring between the glutaraldehyde/protein layers and the graphene buried underneath [35,[38][39][40][41]. After the final functionalization step, the doping level of the graphene was shown to be p-doped overall, resulting in the graphene being further away from the charge neutrality point.…”