  To understand the chemical composition of planets, it is important to know
the chemical composition of the region where they form in protoplanetary disks.
Due to its fundamental role in chemical and biological processes, carbon is a
key element to trace. We aim to identify the carriers and processes behind the
extended NIR flux observed around several Herbig stars. We compare the extended
NIR flux from objects in the PIONIER Herbig Ae/Be survey with their flux in the
PAH features. HD 100453 is used as a benchmark case to investigate the
influence of quantum heated particles, like PAHs or very small carbonaceous
grains, in more detail. We use the Monte Carlo radiative transfer code MCMax to
do a parameter study of the QHP size and scale- height and examine the
influence of quantum heating on the amount of extended flux in the NIR
visibilities. There is a correlation between the PAH feature flux of a disk and
the amount of its extended NIR flux. We find that very small carbonaceous
grains create the observed extended NIR flux around HD 100453 and still lead to
a realistic SED. These results can not be achieved without using quantum
heating effects, e.g. only with scattered light and grains in thermal
equilibrium. It is possible to explain the extended NIR emission around Herbig
stars with the presence of carbonaceous, quantum heated particles.
Interferometric observations can be used to constrain the spatial distribution
and typical size of carbonaceous material in the terrestrial planet forming
region.
