Here we report the experimental observation of circular dichroism in the second-harmonic field (800–400 nm conversion) generated by self-organized gold nanowire arrays with subwavelength periodicity (160 nm). Such circular dichroism, raised by a nonlinear optical extrinsic chirality, is the evident signature of the sample morphology. It arises from the curvature of the self-assembled wires, producing a lack of symmetry at oblique incidence. The results were compared, both in the optical linear and nonlinear regime, with a reference sample composed of straight wires. Despite the weak extrinsic optical chirality of our samples (not observable by our optical linear measurements), high visibility (more than 50%) was obtained in the second-harmonic generated field.

Large-scale integration of MoS ₂ in electronic devices requires the development of reliable and cost-effective deposition processes, leading to uniform MoS ₂ layers on a wafer scale. Here we report on the detailed study of the heterogeneous vapor–solid reaction between a pre-deposited molybdenum solid film and sulfur vapor, thus resulting in a controlled growth of MoS ₂ films onto SiO ₂ /Si substrates with a tunable thickness and cm ² -scale uniformity. Based on Raman spectroscopy and photoluminescence, we show that the degree of crystallinity in the MoS ₂ layers is dictated by the deposition temperature and thickness. In particular, the MoS ₂ structural disorder observed at low temperature (<750 °C) and low thickness (two layers) evolves to a more ordered crystalline structure at high temperature (1000 °C) and high thickness (four layers). From an atomic force microscopy investigation prior to and after sulfurization, this parametrical dependence is associated with the inherent granularity of the MoS ₂ nanosheet that is inherited by the pristine morphology of the pre-deposited Mo film. This work paves the way to a closer control of the synthesis of wafer-scale and atomically thin MoS ₂ , potentially extendable to other transition metal dichalcogenides and hence targeting massive and high-volume production for electronic device manufacturing.