  Tin sulfide promises very interesting properties such as a high optical
absorption coefficient and a small band gap, while being less toxic compared to
other metal chalcogenides. However, the limitations in growing atomically thin
structures of tin sulfide hinder the experimental realization of these
properties. Due to the flexibility of the colloidal synthesis, it is possible
to synthesize very thin and at the same time large nanosheets. Electrical
transport measurements show that these nanosheets can function as field-effect
transistors with high on/off ratio and p-type behavior. The temperature
dependency of the charge transport reveals that defects in the crystal are
responsible for the formation of holes as majority carriers. During
illumination with circularly polarized light, these crystals generate a
helicity dependent photocurrent at zero-volt bias, since their symmetry is
broken by asymmetric interfaces (substrate and vacuum). Further, the observed
circular photogalvanic effect shows a pronounced in-plane anisotropy, with a
higher photocurrent along the armchair direction, originating from the higher
absorption coefficient in this direction. Our new insights show the potential
of tin sulfide for new functionalities in electronics and optoelectronics, for
instance as polarization sensors.
