  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.
