Graphene nanoribbons (GNRs) are of enormous research interest as a promising active component in electronic devices, for example, field-effect transistors (FET). The recently developed "bottomup" on-surface synthesis provides an unprecedented approach for the generation of GNRs on metal surfaces with atomic precision. In order to fabricate well-defined GNRs on surfaces, numerous previous works have been focused on the delicate engineering of building blocks. Lateral fusion of polyphenylene chains into GNRs, as a more flexible method, now has received an increasing attention. However, the lateral fusion into GNRs reported to date is merely limited to the straight GNRs. The GNRs with other topologies potentially displaying distinctive electronic properties are rarely reported. In this work, we report the synthesis of armchair-edged graphene nanoribbons (AGNRs) with zigzag topology for the first time via a stepwise polymerization reaction starting from 4,4″-dibromo-m-terphenyl (DMTP) precursor on Au(111). Self-assembled unreacted monomers, covalent dimers, and zigzag polyphenylene chains are observed at different temperatures. Various GNRs with zigzag topology, including 6-AGNRs, 9-AGNRs, and nanoporous AGNRs are eventually produced through lateral fusion of polyphenylene chains. This study further diversifies the GNR family. Confining the zigzag polyphenylene chains in an ideal arrangement for subsequent lateral fusion can be explored in the future.

Achieving strong coupling between plasmonic oscillators can significantly modulate their intrinsic optical properties. Here, we report the direct observation of ultrafast plasmonic hot electron transfer from an Au grating array to an MoS2 monolayer in the strong coupling regime between localized surface plasmons (LSPs) and surface plasmon polaritons (SPPs). By means of femtosecond pump-probe spectroscopy, the measured hot electron transfer time is approximately 40 fs with a maximum external quantum yield of 1.65%. Our results suggest that strong coupling between LSPs and SPPs has synergetic effects on the generation of plasmonic hot carriers, where SPPs with a unique nonradiative feature can act as an ‘energy recycle bin’ to reuse the radiative energy of LSPs and contribute to hot carrier generation. Coherent energy exchange between plasmonic modes in the strong coupling regime can further enhance the vertical electric field and promote the transfer of hot electrons between the Au grating and the MoS2 monolayer. Our proposed plasmonic strong coupling configuration overcomes the challenge associated with utilizing hot carriers and is instructive in terms of improving the performance of plasmonic opto-electronic devices.

Transition metal dichalcogenides with intrinsic spin-valley degrees of freedom hold great potentials for applications in spintronic and valleytronic devices. MoS monolayer possesses two inequivalent valleys in the Brillouin zone, with each valley coupling selectively with circularly polarized photons. The degree of valley polarization (DVP) is a parameter to characterize the purity of valley-polarized photoluminescence (PL) of MoS monolayer. Usually, the detected values of DVP in MoS monolayer show achiral property under optical excitation of opposite helicities due to reciprocal phonon-assisted intervalley scattering process. Here, it is reported that valley-polarized PL of MoS can be tailored through near-field interaction with plasmonic chiral metasurface. The resonant field of the chiral metasurface couples with valley-polarized excitons, and tailors the measured PL spectra in the far-field, resulting in observation of chiral DVP of MoS -metasurface under opposite helicities excitations. Valley-contrast PL in the chiral heterostructure is also observed when illuminated by linearly polarized light. The manipulation of valley-polarized PL in 2D materials using chiral metasurface represents a viable route toward valley-polaritonic devices.