Fig. 1: Mechanism of nitric oxide doping in monolayer WSe2.
From: Uncovering the doping mechanism of nitric oxide in high-performance P-type WSe2 transistors
a Local density of states (LDOS) as a function of the electron energy (E) relative to the Fermi level (EF) of pristine monolayer WSe2. Inset: atomic structure of monolayer WSe2 (gray, tungsten atoms; green, selenium atoms). b LDOS of monolayer WSe2 with a single nitric oxide (NO) molecule. The presence of nitric oxide dopants introduces an acceptor doping band near the mid-gap region. Insets show the corresponding atomic structures obtained from density functional theory (DFT) calculations. c Schematic density of states (DOS) plots of the doping impact as extracted from a and b. EC and EV denote the conduction band minimum and valence band maximum, respectively. The blue shaded regions represent the filled valence bands, while the red shaded region represents filled conduction bands for pristine WSe2 and the doping-induced acceptor band introduced by NO in WSe2. X-ray photoelectron spectroscopy (XPS) spectra of d W (4 f) peak; e Se (3 d) peak; and f Raman spectra of monolayer WSe2 before and after NO treatment at various temperatures. The black lines represent the spectra of the undoped monolayer WSe2, while the red, blue, and green lines indicate the spectra after NO treatment at temperatures of 100 °C, 150 °C, and 200 °C for 2 h, respectively.
