Fig. 5: Characterization of enhanced nonlinear processes from few-monolayer flakes on dielectric/gold heterostructures.
From: Boosting classical and quantum nonlinear processes in ultrathin van der Waals materials
a The schematic of NbOCl2 flake on SiO2/Au structure. b SHG intensities as a function of h-BN and SiO2 (on top of gold) thicknesses for h-BN flakes with an odd number of layers, deposited on a substrate made of a SiO2/Au/Si wafer structure. The dashed line corresponds to the calculation range for the solid line shown in (c). c Simulated SHG intensities for h-BN on the SiO2/Au/Si wafer structure, considering different h-BN and SiO2 thicknesses: 64 nm for odd-layered h-BN (solid), 180 nm for odd-layered h-BN (dashed). d Experimental results highlighting the SHG intensities for an 8 nm h-BN flake on SiO2/Au (red), gold (yellow), SiO2/Si (blue) substrate. e Enhancement factor of SHG intensity from h-BN flakes on 64 nm SiO2-Au compared to Si wafer \(\left(\frac{{I}_{S-A}^{{SH}}}{{I}_{{wafer}}^{{SH}}},{{{\rm{red}}}}\right)\) and enhancement factor of SHG intensity from h-BN flakes on 64 nm SiO2/Au compared to gold \(\left(\frac{{I}_{S-A}^{{SH}}}{{I}_{{gold}}^{{SH}}},{{{\rm{blue}}}}\right)\), both involving h-BN flakes with an odd number of layers. f Polarization dependent SHG measurement of 16 nm NbOCl2 flake on 64 nm SiO2/Au substrate (green) and SiO2/Si wafer (orange). The 16 nm NbOCl2 flake on SiO2/Au substrate shows an enhancement of SHG intensity by a factor 306. g SPDC coincidence counts rate on 16 nm NbOCl2 flake on 64 nm SiO2/Au under co-polarized configuration with an enhancement factor 100 (lower bound) in a 100-minute measurement.
