Tip-enhanced nano-imaging of 2D alloy with gradual concentration profile

Systematic optical studies of 2D MoxW1-xS2 alloys, with 0.05≤x≤0.45 grown by chemical vapor deposition (CVD) on Si/SiO2 were carried out using Raman and photoluminescence (PL) spectroscopy using 532 nm laser. Atomic force microscopy (AFM) imaging showed the correlation with the optical images. We demonstrate nano-optical imaging using tip-enhanced photoluminescence (TEPL) as a function of the composition x for obtaining the higher spatial resolution beyond the diffraction limit. Quantum plasmonic quenching of the TEPL signals was observed for larger x revealing the tunneling electron injection. In order to overcome the problem of excitation efficiency we used a 405 nm laser for TEPL which showed efficient excitation of different x components. Tip-enhanced Raman spectroscopy (TERS) confirms the alloy composition at the nanoscale.