  NV-diamonds have attracted keen interest for nanoscale sensing and spin
manipulation. In particular, the non-equilibrium electron spin polarization
after optical excitation of single NV centers has successfully been transferred
to nuclear spin baths in the surrounding of the defects. However, these
experiments need to be extended to NV-ensembles which have promising practical
applications in the hyperpolarization of bulk sample volumes for NMR signal
enhancement. Here, we use a dense, shallow ensemble of NV-centers to
demonstrate polarization transfer to nuclear spins in a well-defined composite
diamond sample system. This allows us to address three different types of
nuclear spins in different positions with respect to the NV polarization
source: from the close proximity of $^{13}$C inside the diamond lattice to the
self-assembled molecular system consisting of $^{1}$H and $^{19}$F spins
outside the diamond and over multiple interfaces. We show that ensemble NV
experiments face problems different from single NV experiments. In particular,
using spinlock pulses, the inhomogeneously broadened ESR line of the NV
ensemble limits the minimal resonance linewidth with which the transfer
protocol can occur. Furthermore, we compare the NV spin-polarization losses and
polarization transfer rates to the different nuclear baths and discuss the role
of spin-diffusion as detrimentally affecting the direct observation of nuclear
polarization build-up within the detection volume of nanoscale NV-NMR
experiments.
