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We investigate the effects of dielectric environments on the transition levels of Re and Nb dopants in monolayer MoS2 through density functional theory calculations. The inherently weakly screened Coulomb interaction in free-standing monolayer MoS2 makes the dopant electrons and holes strongly bound, and the Re and Nb impurities are found to produce deep levels. It is shown that when the monolayer MoS2 is placed near high permittivity dielectrics the screened Coulomb interaction induces carrier derealization with generating shallow levels. [ABSTRACT FROM AUTHOR]

The atomic and electronic structures and stability of native defects in a single-layer MoS2 are investigated, based on density-functional theory calculations. Native defects such as a S vacancy (Vs), a S interstitial (Si), a Mo vacancy (VMo)> and a Mo interstitial (Moi) are considered. The Si is found to have S-adatom configuration on top of a host S atom, and the Moi has Mo-Moi split interstitial configuration along the c direction. The formation energies of the native defects in neutral and charged states are calculated. For the charged states, the artificial electrostatic interactions between image charges in supercells are eliminated by a supercell size scaling scheme and a correction scheme that uses a Gaussian model charge. It is found that the Vs has a low formation energy of 1.3-1.5 eV in the Mo-rich limit condition, and the Si has 1.0 eV in the S-rich limit condition. The Vs is found to be a deep single acceptor with the (0/-) transition level at 1.7 eV above the valence-band maximum (VBM). The Si is found to be an electrically neutral defect. The Mo-related native defects of VMo and Moi are found to be high in formation energy above 4 eV. The VMo is a deep single acceptor and the Moi is a deep single donor, of which the (0/-) acceptor and (+/0) donor transition levels are found at 1.1 and 0.3 eV above the VBM, respectively. [ABSTRACT FROM AUTHOR]

Using a Green function method based on an atomic vibration model, herein we report the results from our investigation of phonon transport through multiple Si/PtSi layered structures. In contrast with values predicted using elastic wave theory and an impedance mismatch method, we find that a detailed atomic-vibration approach exhibits significantly suppressed phonon transport and leads to a 30-times reduction of the thermal conductance, compared to that of Si bulk. We attribute the origin of the suppression to the lack of PtSi phonon modes in the energy range of 20-30 meV, and to the effects of interface scattering between Si and PtSi layers. [ABSTRACT FROM AUTHOR]

Recent studies on a quasi-one-dimensional (quasi-1D) charge-density-wave (CDW) system, In atomic wires on Si(111), have brought intriguing issues on topological solitons in quasi-1D systems: the existence of few-atom-sized solitons, chirality of solitons, and the realization of logic exploiting the chirality switching. Using scanning tunneling microscopy and first-principles calculations, we show that the previously reported "short" phase-flip defects are In adatoms and thus have nonsolitonic nature, resolving the controversy over the existence of highly localized solitons. The observed "long" phase-flip and phase-slip defects are genuine solitons with and without chirality, respectively. While achiral solitons (phase-slip defects) can exist on the pristine CDW (8×2) surface, chiral solitons (phase-flip defects) cannot due to their breakage of 8×2 ordering. The chiral solitons can exist only when they are trapped by In adatoms and constitute a part of a closed-loop domain wall. The intertwinement of chiral solitons and In adatoms implies the limitations of the previously proposed logic utilizing soliton chirality, but it provides an opportunity to realize this by controlling the In-adatom defect. [ABSTRACT FROM AUTHOR]

Impurities interact with a charge density wave (CDW) and affect the phase transitions in low-dimensional systems. By using scanning tunneling microscopy, we visualize the interaction between oxygen impurities and the CDW in indium atomic wires on Si(111), a prototypical one-dimensional electronic system, and unveil the microscopic mechanism of the intriguing O-induced increase of the transition temperature (Tc). Driven by the fluctuating CDW, the O atoms adopt an asymmetric structure. By adjusting the asymmetry, a pair of O impurities in close distance can pin the one-dimensional CDW, which develops into the two-dimensional domains. First-principles calculations showed that the asymmetric interstitially-incorporated O defects induce shear strains, which assists the formation of hexagon structure of the CDW phase. The cooperative interplay between the O impurities and the CDW is responsible for the enhancement of the CDW condensation and the consequent increase in Tc. [ABSTRACT FROM AUTHOR]