  Here we present deep (16 mumJy), very high (40 mas) angular resolution 1.14
mm, polarimetric, Atacama Large Millimeter/submillimeter Array (ALMA)
observations towards the massive protostar driving the HH 80-81 radio jet. The
observations clearly resolve the disk oriented perpendicular to the radio jet,
with a radius of ~0.171 arcsec (~291 au at 1.7 kpc distance). The continuum
brightness temperature, the intensity profile, and the polarization properties
clearly indicate that the disk is optically thick for a radius of R<170 au. The
linear polarization of the dust emission is detected almost all along the disk
and its properties suggest that dust polarization is produced mainly by
self-scattering. However, the polarization pattern presents a clear
differentiation between the inner (optically thick) part of the disk and the
outer (optically thin) region of the disk, with a sharp transition that occurs
at a radius of 0.1 arcsec (~170 au). The polarization characteristics of the
inner disk suggest that dust settling has not occurred yet with a maximum dust
grain size between 50 and 500 mum. The outer part of the disk has a clear
azimuthal pattern but with a significantly higher polarization fraction
compared to the inner disk. This pattern is broadly consistent with
self-scattering of a radiation field that is beamed radially outward, as
expected in the optically thin outer region, although contribution from
non-spherical grains aligned with respect to the radiative flux cannot be
excluded.
