Theoretical Analysis of a 2D Metallic/Semiconducting Transition-Metal Dichalcogenide NbS2//WSe2 Hybrid Interface

A first-principles theoretical study of a monolayer-thick lateral heterostructure (LH) joining two different transition metal dichalcogenides, NbS2 and WSe2, is reported. The NbS2//WSe2 LH can be considered a prototypical example of a metal (NbS2)/semiconductor (WSe2) 2D hybrid heterojunction. First, realistic atomistic models of the NbS2//WSe2 LH are generated and validated, its band structure is derived, and it is subjected to a fragment decomposition and electrostatic potential analysis to extract a simple but quantitative model of this interfacial system. Stoichiometric fluctuations models are also investigated and found not to alter the qualitative picture. Then, electron transport simulations are conducted and they are analyzed via band alignment analysis. It is concluded that the NbS2//WSe2 LH appears as a robust seamless in-plane 2D modular junction for potential use in optoelectronic devices going beyond the present miniaturization technology

Photodynamics and time resolved fluorescence of azobenzene in solution: A mixed quantum-classical simulation

We have simulated the photodynamics of azobenzene by means of the Surface Hopping method. We have considered both the trans --> cis and the cis --> trans processes, caused by excitation in the n -> π* band (S1 state). To bring out the solvent effects on the excited state dynamics, we have run simulations in four different environments: in vacuo, in n-hexane, in methanol, and in ethylene glycol. Our simulations reproduce very well the measured quantum yields and the time dependence of the intensity and anisotropy of the transient fluorescence. Both the photoisomerization and the S1 f S0 internal conversion require the torsion of the N=N double bond, but the N—C bond rotations and the NNC bending vibrations also play a role. In the trans f cis photoconversion the N=N torsional motion and the excited state decay are delayed by increasing the solvent viscosity, while the cis f trans processes are less affected. The analysis of the simulation results allows the experimental observations to be explained in detail, and in particular the counterintuitive increase of the trans f cis quantum yield with viscosity, as well as the relationship between the excited state dynamics and the solvent effects on the fluorescence lifetimes and depolarization

Exact decoupling of two dipole-dipole interacting dimers

It is today possible to test many quantum mechanical predictions, even the most puzzling ones, setting up sophisticated experiments on exemplary "textbook" physical systems like a single atom or molecule or a single material quantum harmonic oscillator. It is therefore conceptually highly exciting to conceive simple but not trivial physical situations representable by exactly solvable hamiltonian models, in the grasp of the experimentalists. In this paper we study a physical system consisting of two coupled identical dimers. Each molecule possesses both fermionic and bosonic degrees of freedom and its internal non adiabatic dynamics is governed by a bilinear term conserving the total excitation number. The two molecules are assumed to interact by a dipole like term. Our main result is that the hamiltonian model representing such a composite system may be unitarily put in a form describing two fictitious uncoupled JC dimers provided the initial excitation number is less than two. The advantage of these canonical transformations is that it makes the restricted dynamical problem exactly tractable. In this way we may successfully study the time evolution of quantum correlation effects get established in the dimer-dimer system due to dipolar like coupling

Competition between inter- and intra-molecular energy exchanges in a simple quantum model of a dimer

We propose a fully quantum model to describe the dynamics of a possible radiationless energy transfer process between identical and nearly localized molecules or monomers coupled through a dipole–dipole term. The system is studied as an environmentally isolated dimeric pair and we find that its dynamics exhibits a competition between the process ruling out the transfer of energy among different degrees of freedom of a given monomer and the one steering the intermolecular passage of excitations from a monomer to the other one. Such a competition is quantitatively characterized investigating on the temporal behaviour of quantum covariances of some couples of appropriate observables having a clear physical meanin

High-Performance 2D p-Type Transistors Based on GaSe Layers: An Ab Initio Study

Ultrascaled GaSe field effect transistors are investigated through ab initio calculations. GaSe monolayers, 3 nm long, exhibit excellent performance with reduced short‐channel effects and considerably high ON‐current. Such device characteristics are due to the valence band edge shape, which leads to very heavy holes in the transport direction and eventually suppresses intraband tunneling, detrimental for correct operation in the OFF state