Laser-Controlled Charge Transfer in a Two-Dimensional Organic/Inorganic Optical Coherent Nanojunction

Abstract

Understanding the fundamental mechanisms ruling laser-induced coherent charge transfer in hybrid organic/inorganic interfaces is of paramount importance to exploit these systems in next-generation optoelectronic applications. In a first-principles work based on real-time time-dependent density-functional theory, we investigate the ultrafast charge-carrier dynamics of a prototypical two-dimensional vertical nanojunction formed by a MoSe2 monolayer with adsorbed pyrene molecules. The response of the system to the incident pulse, set in resonance with the frequency of the lowest-energy transition in the physisorbed moieties, is clearly nonlinear. Under weak pulses, charge transfer occurs from the molecules to the monolayer, while for intensities higher than 1000 GW/cm2, the direction of charge transfer is reverted, with electrons being transferred from MoSe2 to pyrene. This finding is explained by Pauli blocking: laser-induced (de)­population of (valence) conduction states saturates for intensities beyond 200 GW/cm2. Evidence of multiphoton absorption is also provided by our results. A thorough analysis of electronic current density, excitation energy, and number of excited electrons supports the proposed rationale and suggests the possibility to create an inorganic/organic coherent optical nanojunction for ultrafast electronics.

Magnification of Plasmon Resonances in Monolayer MoS2 via Conjugated Molecular Adsorbates

“…Tetracene is a member of the oligoacene family and is characterized by an anisotropic geometry. Pyrene, in contrast, is more isotropic and is often used in first-principles studies [37][38][39]45 as a prototype for larger conjugated compounds such as (functionalized) rylenes that favorably adsorb on TMDCs. 22,27,52,53 These compounds exhibit a weak coupling with MoS 2 as extensively discussed in previous work specifically dedicated to this aspect.…”

“…38 In particular, the band structure and the density of states of the TMDC are negligibly affected by the presence of the physisorbed molecule, and apart from hybridization effects that are ruled by specific conditions, 37 the electronic structure of the interface is essentially a superposition of the features of its constituents. [37][38][39]45,54 For this reason, in optical absorption, specific transitions within the molecular frontier orbitals can be targeted, e.g., by a laser pulse. 39 In order to explore the impact of the molecular orientation on the loss function of the corresponding interfaces with MoS 2 , we consider the four different configurations shown in Figure 1.…”

“…In the past few years, molecular functionalization has emerged as a viable way to modulate the electronic and optical properties of TMDCs. − The deposition of organic layers on top of these materials gives rise to hybrid interfaces with tunable level alignment, − work functions, , and spectral responses , depending on the choice of the constituents. While organic dopants lead to strong electronic interactions with the substrate, , thus dramatically altering their intrinsic features already in the ground state, nonpolar carbon-conjugated molecules influence the characteristics of the underlying TMDCs with respect to the interaction with electromagnetic fields. − First-principles studies on this class of hybrid materials have contributed to a better understanding of their fundamental properties. − For example, the possibility to computationally explore the effects of a large variety of molecules adsorbed on TMDCs has provided the community not only with a catalog of electronic-structure data but also with a rationale for predictions. ,,,− Likewise, the study of the optical absorption properties of such hybrid interfaces, including excitons, − has contributed to a deeper understanding of these materials and opened new avenues to tuning the exceptional optical properties of TMDCs. On the other hand, the electron energy loss of such systems is still largely unexplored.…”

The Exact Exchange-Correlation Potential in Time-Dependent Density Functional Theory: Choreographing Electrons with Steps and Peaks

“…XC [n(t)](r) which can be a useful analysis tool in cases where the exact groundstate xc potential can be computed (usually model 1D systems). Due to the lack of memory, the adiabatic approximation leads to large errors in some applications, sometimes failing completely [52][53][54][55][56][57][58][59][60], but in other cases it has been found to yield good predictions [5][6][7][8][9][10][11][12][13][14][15][16][17][18], even when the system is far from a ground-state. It is not completely understood why: possible reasons include, that the adiabatic approximation satisfies a number of exact conditions that are important in the time-dependent case [2], that in some applications a strong external field dominates over xc effects in driving the dynamics and that partial compensation of selfinteraction in the Hartree potential, even at the groundstate level, is enough, especially when the observables involve averaging over the details of the density distribution.…”

“…While perturbations around the ground-state yields a formalism for excited states, their couplings, and response, it is particularly the generality and practical efficiency of the real-time formulation that has led to the possibility of applications on large systems which could not be done otherwise, e.g. [5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”