Chlorine-doped tungsten disulfide monolayer (1L-WS2) with tunable charge carrier concentration has been realized by pulsed laser irradiation of the atomically thin lattice in a precursor gas atmosphere. This process gives rise to a systematic shift of the neutral exciton peak towards lower energies, indicating reduction of the crystal's electron density. The capability to progressively tune the carrier density upon variation of the exposure time is demonstrated; this implicates that the Fermi level shift is directly correlated to the respective electron density modulation due to the chlorine species. Notably, this electron withdrawing process enabled the determination of the trion binding energy of the intrinsic crystal, found to be as low as 20 meV, in accordance to theoretical predictions. At the same time, it is found that the effect can be reversed upon continuous wave laser scanning of the monolayer in air. Scanning Auger Microscopy and X-ray photoelectron spectroscopy are used to link the actual charge carrier doping to the different chlorine configurations in the monolayer lattice. The spectroscopic analyses, complemented by density functional theory calculations, reveal that chlorine physisorption is responsible for the carrier density modulation induced by the pulsed laser photochemical reaction process. Such bidirectional control of the Fermi level, coupled with the capability offered by lasers to process at pre-selected locations, can be advantageously used for spatially resolved doping modulation in 1L-WS2 with micrometric resolution. This method can also be extended for the controllable doping of other TMD monolayers. Monolayer (1L) transition metal dichalcogenides (TMDs) are promising materials for future 2D nanoelectronics due to their unique electrical, 1 optical 2,3 and mechanical properties. 4 Indeed, TMDs have been demonstrated to be ideal candidates for field-effect transistors, photovoltaic cells, lightemitting diodes, single-atom storage, molecule sensing, quantum-state metamaterials and electrocatalytic water splitting applications. 5-7 Carrier modulation is an important parameter in the study of the electronic properties of semiconductors and at the heart of many applications in microelectronics. Tuning the charge carrier density, i.e. doping, can be realized chemically, via bonding of foreign atoms to the crystal structure, 8-10 or electrostatically, by inducing a charge accumulation. 11-13 Electrical doping
A simple and low temperature post-glass quenching encapsulation method for the formation of highly luminescent and ultrastable perovskite patterns within phosphate glass.
Degenerate minima in momentum space—valleys—provide an additional degree of freedom that can be used for information transport and storage. Notably, such minima naturally exist in the band structure of transition metal dichalcogenides (TMDs). When these atomically thin crystals interact with intense laser light, the second harmonic generated (SHG) field inherits special characteristics that reflect not only the broken inversion symmetry in real space but also the valley anisotropy in reciprocal space. The latter is present whenever there exists a valley population imbalance (VPI) between the two valleys and affects the polarization state of the detected SHG. In this work, it is shown that the temperature-induced change of the SHG intensity dependence on the excitation field polarization is a fingerprint of VPI in TMDs. In particular, pixel-by-pixel VPI mapping based on polarization-resolved raster-scanning imaging microscopy was performed inside a cryostat to generate the SHG contrast in the presence of VPI from every point of a TMD flake. The generated contrast is marked by rotation of the SHG intensity polar diagrams at low temperatures and is attributed to the VPI-induced SHG.
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