Semiconductor-to-Metal Transition in the Bulk of WSe2 upon Potassium Intercalation

We present electron energy-loss spectroscopic measurements of potassium (K) intercalated tungsten diselenide (WSe2). After exposure of pristine WSe2 films to potassium, we observe a charge carrier plasmon excitation at about 0.97 eV, which indicates a semiconductor to metal transition. Our data signal the formation of one particular doped K-WSe2 phase. A Kramers-Kronig analysis (KKA) allows the determination of the dielectric function and to estimate the composition of about K0.6WSe2. Momentum dependent measurements reveal a substantial plasmon dispersion to higher energies.