Abnormal nonlinear optical properties of hybrid graphene-TiO2 nanostructures.

The nonlinear optical (NLO) properties of graphene-TiO2 nanoparticle (GNP) composite and graphene-TiO2 nanowire composite (GNW) are investigated by spatial self-phase modulation (SSPM) and Z-scan. The SSPM results of the GNP and GNW show that they possess strong self-diffraction effects at 1100 nm and no signal at 700 nm, which is different from all previous reports of other two-dimensional materials. A possible mechanism is that NLO behaviors are dominated by TiO2 at the visible wavelength, while by graphene at a near-infrared wavelength. The Z-scan results of the GNP and GNW show reverse saturable absorption (RSA) at 700 nm, but saturable absorption (SA) at 1100 nm. Our results demonstrate that, by choosing appropriate coupling, we could design two-dimensional materials that have specific NLO properties at particular wavelengths.