Probing the inter-layer exciton physics in a MoS2_2/MoSe2_2/MoS2_2 van der Waals heterostructure

Stacking atomic monolayers of semiconducting transition metal dichalcogenides (TMDs) has emerged as an effective way to engineer their properties. In principle, the staggered band alignment of TMD heterostructures should result in the formation of inter-layer excitons with long lifetimes and robust valley polarization. However, these features have been observed simultaneously only in MoSe$_2$/WSe$_2$ heterostructures. Here we report on the observation of long lived inter-layer exciton emission in a MoS$_2$/MoSe$_2$/MoS$_2$ trilayer van der Waals heterostructure. The inter-layer nature of the observed transition is confirmed by photoluminescence spectroscopy, as well as by analyzing the temporal, excitation power and temperature dependence of the inter-layer emission peak. The observed complex photoluminescence dynamics suggests the presence of quasi-degenerate momentum-direct and momentum-indirect bandgaps. We show that circularly polarized optical pumping results in long lived valley polarization of inter-layer exciton. Intriguingly, the inter-layer exciton photoluminescence has helicity opposite to the excitation. Our results show that through a careful choice of the TMDs forming the van der Waals heterostructure it is possible to control the circular polarization of the inter-layer exciton emission.Comment: 19 pages, 3 figures. Just accepted for publication in Nano Letters (http://pubs.acs.org/doi/10.1021/acs.nanolett.7b03184

Spectral Dependence of the Energy Transfer from Photosynthetic Complexes to Monolayer Graphene

Fluorescence excitation spectroscopy at cryogenic temperatures carried out on hybrid assemblies composed of photosynthetic complexes deposited on a monolayer graphene revealed that the efficiency of energy transfer to graphene strongly depended on the excitation wavelength. The efficiency of this energy transfer was greatly enhanced in the blue-green spectral region. We observed clear resonance-like behavior for both a simple light-harvesting antenna containing only two chlorophyll molecules (PCP) and a large photochemically active reaction center associated with the light-harvesting antenna (PSI–LHCI), which pointed towards the general character of this effect

to improvement in photocurrent generation

We report the fabrication of an oriented bioelectrode of photosystem I (PSI) on single-layer graphene (SLG). This bioelectrode demonstrates improved photocurrent generation, which can be directly attributed to the molecular conductive interface formed by cytochrome c(553) (cyt c(553)) promoting the uniform orientation of PSI with its donor side towards the electrode. The conductive interface between PSI-cyt c(553) and SLG is facilitated by a monolayer composed of pi-pi-stacked pyrene functionalized with the Ni-NTA moiety, which binds the His6-tagged cyt c(553). The surface uniformity of the PSI protein orientation in the electrode structure is evidenced by cross-sectional scanning electron microscopy and fluorescence microscopy, with the latter also proving the efficient electronic coupling between majority of the PSI complexes and graphene. With the uniform organization of the biological photoactive layer, photocurrents are generated at the open circuit potential, which can be further increased when a negative potential is applied. Indeed, at the highest applied negative potential (-0.3 V), over 5-fold increase in the cathodic photocurrent for the PSI complexes conjugated via cyt c(553) to the SLG substrate is observed compared with that obtained for the randomly oriented structure where PSI is physisorbed on graphene. These results indicate the key role of a strictly defined orientation of photoactive proteins on electrodes for proper electron transfer and substantial improvement in photocurrent generation in the present or similar bioelectrode architectures

Probing the Interlayer Exciton Physics in a MoS2/MoSe2/MoS2 van der Waals Heterostructure

International audienceStacking atomic monolayers of semiconducting transition metal dichalcogenides (TMDs) has emerged as an effective way to engineer their properties. In principle, the staggered band alignment of TMD heterostructures should result in the formation of interlayer excitons with long lifetimes and robust valley polarization. However, these features have been observed simultaneously only in MoSe2/WSe2 heterostructures. Here we report on the observation of long-lived interlayer exciton emission in a MoS2/MoSe2/MoS2 trilayer van der Waals heterostructure. The interlayer nature of the observed transition is confirmed by photoluminescence spectroscopy, as well as by analyzing the temporal, excitation power, and temperature dependence of the interlayer emission peak. The observed complex photoluminescence dynamics suggests the presence of quasi-degenerate momentum-direct and momentum-indirect bandgaps. We show that circularly polarized optical pumping results in long-lived valley polarization of interlayer exciton. Intriguingly, the interlayer exciton photoluminescence has helicity opposite to the excitation. Our results show that through a careful choice of the TMDs forming the van der Waals heterostructure it is possible to control the circular polarization of the interlayer exciton emission

Probing the Interlayer Exciton Physics in a MoS₂/MoSe₂/MoS₂ van der Waals Heterostructure

Stacking atomic monolayers of semiconducting transition metal dichalcogenides (TMDs) has emerged as an effective way to engineer their properties. In principle, the staggered band alignment of TMD heterostructures should result in the formation of interlayer excitons with long lifetimes and robust valley polarization. However, these features have been observed simultaneously only in MoSe₂/WSe₂ heterostructures. Here we report on the observation of long-lived interlayer exciton emission in a MoS₂/MoSe₂/MoS₂ trilayer van der Waals heterostructure. The interlayer nature of the observed transition is confirmed by photoluminescence spectroscopy, as well as by analyzing the temporal, excitation power, and temperature dependence of the interlayer emission peak. The observed complex photoluminescence dynamics suggests the presence of quasi-degenerate momentum-direct and momentum-indirect bandgaps. We show that circularly polarized optical pumping results in long-lived valley polarization of interlayer exciton. Intriguingly, the interlayer exciton photoluminescence has helicity opposite to the excitation. Our results show that through a careful choice of the TMDs forming the van der Waals heterostructure it is possible to control the circular polarization of the interlayer exciton emission