arXiv subjects

Zhenchao Dong

Publications and source records attributed to Zhenchao Dong.

4 recordsLinked to original sources

arXiv2019

Self-decoupled tetrapodal perylene molecules for luminescence studies of isolated emitters on Au(111)

Self-decoupled tetrapodal perylene molecules were designed, synthesized, and deposited on the Au(111) surface through the electrosprayionization technique. Photoluminescence and lifetime measurements show that the chromophore groups of the designed molecules are welldecoupled from the gold substrate. Preliminary scanning tunneling microscopy induced luminescence measurements indicate theobservation of molecule-specific emissions from isolated single tetrapodal perylene molecules adsorbed directly on Au(111). The emergenceof significant emission when the tip is positioned at the molecular center suggests that there is a considerable vertical component of the transitiondipole of the designed molecule along the tip axial direction. Our results may open up a route for the realization of nanolight sourcesand plasmonic devices based on organic molecules.

physics.optics↗

arXiv2019

Magnetically-Sensitive Valley Polarization Reversal and Revival of Defect-Localized Excitons in WSe2-WS2

Manipulating and reserving the valley pseudospin of excitons is one core aim in the two-dimensional transition metal dichalcogenides (TMDs). However, due to the strong electron-hole exchange and spin-orbit coupling interactions, the exciton recombination lifetime is subject to picosecond timescale intrinsically, and the valley polarization is hardly modulated by a moderate magnetic field. It is fortunate that interlayer and defect-localized excitons promise to overcome these difficulties by suppressing the above interactions. Here we clearly reveal that the valley polarization can be reversed and revived in the defect-localized excitons with a microsecond lifetime in AB-stacked WSe2-WS2 heterobilayer. Specifically, for the interlayer defect-localized exciton, the valley polarization is reversed and can be efficiently enhanced by a weak out-of-plane magnetic field (<0.4 T). In sharp contrast, the valley polarization of the intralayer defect-localized exciton can revive after a fast decay process and follows the direction of the moderate out-of-plane magnetic field (<3 T). We explain the reversed valley polarization with highly magnetic sensitivity by the delocalization of defect-localized holes under a weak magnetic field and the revival of valley polarization by the valley Zeeman effect under a moderate magnetic field. Our results demonstrate that the valley pseudospin of defect-localized excitons can be efficiently modulated by the external magnetic field and enrich both the understanding and the technical approaches on manipulating the valley dynamics in TMDs and their heterostructure.

cond-mat.mtrl-sci↗

arXiv2018

Single-molecule Electroluminescence and Beyond

A scanning tunneling microscope (STM) can do more than atomic imaging and manipulation. Its tunneling current can also be used for the excitation of light, converting electron energy to photon energy. STM based single-molecule electroluminescence can be realized by adopting a combined strategy of both efficient electronic decoupling and nanocavity plasmonic enhancement. The emission intensity, upon optimized material combination for the molecule, spacer, tip, and substrate, can be strong and stable enough for performing second-order photon correlation measurements. The observation of an evident photon antibunching effect demonstrates clearly the nature of single-photon emission for single-molecule electroluminescence. Strikingly, the spectral peak of a monomer is found to split when a molecular dimer is artificially constructed through STM manipulation, which suggests that the excitation energy from tunneling electrons is likely to rapidly delocalize over the whole molecular dimer. The spatial distribution of the excitonic coupling for different energy states in a dimer can be visualized in real space through sub-nanometer resolved electroluminescence imaging technique, which correlates very well with the local optical responses predicted in terms of coherent intermolecular dipole-dipole coupling. Furthermore, a single molecule can also couple coherently with a plasmonic nanocavity, resulting in the occurrence of interference-induced Fano resonance. These findings open up new avenues to fabricate electrically driven quantum light sources as well as to study intermolecular energy transfer, field-matter interaction, and molecular optoelectronics, all at the single-molecule level.

physics.optics↗

arXiv2015

Raman Images of a Single Molecule in a Highly Confined Plasmonic Field

Under the local plasmonic excitation, the Raman images of a single molecule can now reach sub-nanometer resolution. We report here a theoretical description of the interaction between a molecule and a highly confined plasmonic field. It is shown that when the spatial distribution of the plasmonic field is comparable with the size of the molecule, the optical transition matrix of the molecule becomes to be dependent on the position and the spatial distribution of the plasmonic field, resulting in spatially resolved Raman image of a molecule. It is found that the resonant Raman image reflects the electronic transition density of the molecule. In combination with the first principles calculations, the simulated Raman image of a porphyrin derivative adsorbed on the silver surface nicely reproduces its experimental counterpart. The present theory provides the basic framework for describing linear and nonlinear responses of molecules under the highly confined plasmonic field.

cond-mat.mes-hall↗