Photoluminescence studies of monolayer WSe₂ in proximity with BiFeO₃ thin films.

We have studied the photoluminescence (PL) properties of 1-layer WSe₂ in proximity with multiferroic BiFeO₃ (BFO) thin films. Using pulsed laser deposition, we have grown epitaxial single crystalline BFO films of 20 -80 nm thick on SrRuO₃ buffered (001) SrTiO₃ substrates. X -Ray and AFM characterizations show the films have high crystallinity and smooth surface. Piezo-response force microscopy studies show that the as-grown PZT films have uniform polarization pointing away from the substrate. We then transferred WSe₂ flakes onto 300 nm SiO₂ and BFO using elastic film assisted micro-mechanical exfoliation. Optical microscopy combined with Raman spectroscopy is used to identify and determine the layer number of WSe₂ flakes. Spatially-resolved PL spectroscopy measurements are performed using a scanning confocal microscope to investigate the valley excitonic properties of WSe₂ in proximity with BFO. When compared to SiO₂, we observed a quenching in PL signal for WSe₂ on BFO at 300 K. We have also studied the effect of temperature and magnetic fields on the valley polarization of monolayer WSe₂ in proximity with multiferroic BFO thin films.