Many important energy-transfer and optical processes, in both biological and artificial systems, depend crucially on excitonic coupling that spans several chromophores. Such coupling can in principle be described in a straightforward manner by considering the coherent intermolecular dipole-dipole interactions involved. However, in practice, it is challenging to directly observe in real space the coherent dipole coupling and the related exciton delocalizations, owing to the diffraction limit in conventional optics. Here we demonstrate that the highly localized excitations that are produced by electrons tunnelling from the tip of a scanning tunnelling microscope, in conjunction with imaging of the resultant luminescence, can be used to map the spatial distribution of the excitonic coupling in well-defined arrangements of a few zinc-phthalocyanine molecules. The luminescence patterns obtained for excitons in a dimer, which are recorded for different energy states and found to resemble σ and π molecular orbitals, reveal the local optical response of the system and the dependence of the local optical response on the relative orientation and phase of the transition dipoles of the individual molecules in the dimer. We generate an in-line arrangement up to four zinc-phthalocyanine molecules, with a larger total transition dipole, and show that this results in enhanced 'single-molecule' superradiance from the oligomer upon site-selective excitation. These findings demonstrate that our experimental approach provides detailed spatial information about coherent dipole-dipole coupling in molecular systems, which should enable a greater understanding and rational engineering of light-harvesting structures and quantum light sources.

The coherent interaction between quantum emitters and photonic modes in cavities underlies many of the current strategies aiming at generating and controlling photonic quantum states. A plasmonic nanocavity provides a powerful solution for reducing the effective mode volumes down to nanometre scale, but spatial control at the atomic scale of the coupling with a single molecular emitter is challenging. Here we demonstrate sub-nanometre spatial control over the coherent coupling between a single molecule and a plasmonic nanocavity in close proximity by monitoring the evolution of Fano lineshapes and photonic Lamb shifts in tunnelling electron-induced luminescence spectra. The evolution of the Fano dips allows the determination of the effective interaction distance of ∼1 nm, coupling strengths reaching ∼15 meV and a giant self-interaction induced photonic Lamb shift of up to ∼3 meV. These results open new pathways to control quantum interference and field–matter interaction at the nanoscale.

A self-decoupled porphyrin with a tripodal anchor has been synthesized and deposited on Au(111) using different wet-chemistry methods. Nanoscale electroluminescence from single porphyrin molecules or aggregates on Au(111) has been realized by tunneling electron excitation. The molecular origin of the luminescence is established by the vibrationally resolved fluorescence spectra observed. The rigid tripodal anchor not only acts as a decoupling spacer but also controls the orientation of the molecule. Intense molecular electroluminescence can be obtained from the emission enhancement provided by a good coupling between the molecular transition dipole and the axial nanocavity plasmon. The unipolar performance of the electroluminescence from the designed tripodal molecule suggests that the porphyrin molecule is likely to be excited by the injection of hot electrons, and then the excited state decays radiatively through Franck-Condon π*-π transitions. These results open up a new route to generating electrically driven nanoscale light sources.

We describe a reliable fabrication procedure of silver tips for scanning tunneling microscope (STM) induced luminescence experiments. The tip was first etched electrochemically to yield a sharp cone shape using selected electrolyte solutions and then sputter cleaned in ultrahigh vacuum to remove surface oxidation. The tip status, in particular the tip induced plasmon mode and its emission intensity, can be further tuned through field emission and voltage pulse. The quality of silver tips thus fabricated not only offers atomically resolved STM imaging, but more importantly, also allows us to perform challenging "color" photon mapping with emission spectra taken at each pixel simultaneously during the STM scan under relatively small tunnel currents and relatively short exposure time.

The confinement of light into nanometer-sized metallic nanogaps can lead to an extremely high field enhancement, resulting in dramatically enhanced absorption, emission, and surface-enhanced Raman scattering (SERS) of molecules embedded in nanogaps. However, low-cost, high-throughput, and reliable fabrication of ultra-high-dense nanogap arrays with precise control of the gap size still remains a challenge. Here, by combining colloidal lithography and atomic layer deposition technique, a reproducible method for fabricating ultra-high-dense arrays of hexagonal close-packed annular nanogaps over large areas is demonstrated. The annular nanogap arrays with a minimum diameter smaller than 100 nm and sub-1 nm gap width have been produced, showing excellent SERS performance with a typical enhancement factor up to 3.1 × 10 and a detection limit of 10 M. Moreover, it can also work as a high-quality field enhancement substrate for studying two-dimensional materials, such as MoSe. Our method provides an attractive approach to produce controllable nanogaps for enhanced light-matter interaction at the nanoscale.

The limited ability to fabricate nanostructures on nonplanar rugged surfaces has severely hampered the applicability of many emerging technologies. Here we report a resist stencil lithography based approach for in situ fabrication of multidimensional nanostructures on both planar and uneven substrates. By using the resist film as a flexible stencil to form a suspending membrane with predesigned patterns, a variety of nanostructures have been fabricated on curved or uneven substrates of diverse morphologies on demand. The ability to realize 4 in. wafer scale fabrication of nanostructures as well as line width resolution of sub-20 nm is also demonstrated. Its extraordinary capacity is highlighted by the fabrication of three-dimensional wavy nanostructures with diversified cell morphologies on substrates of different curvatures. A robust general scheme is also developed to construct various complex 3D nanostructures. The use of conventional resists and processing ensures the versatility of the method. Such an in situ lithography technique has offered exciting possibilities to construct nanostructures with high dimensionalities that can otherwise not be achieved with existing nanofabrication methods.

We investigate molecular electroluminescence from individual tubular porphyrin J-aggregates on Au(111) by tunneling electron excitations in an ultrahigh-vacuum scanning tunneling microscope (STM). High-resolution STM images suggest a spiral tubular structure for the porphyrin J-aggregate with highly ordered “brickwork”-like arrangements. Such aggregated nanotube is found to behave like a self-decoupled molecular architecture and shows red-shifted electroluminescence characteristics of J-aggregates originated from the delocalized excitons. The positions of the emission peaks are found to shift slightly depending on the excitation sites, which, together with the changes in the observed spectral profiles with vibronic progressions, suggest a limited exciton coherence number within several molecules. The J-aggregate electroluminescence is also found unipolar, occurring only at negative sample voltages, which is presumably related to the junction asymmetry in the context of molecular excitations via the carrier injection mechanism.

Metamaterials have gained much attention thanks to their extraordinary and intriguing optical properties beyond natural materials. However, universal high‐resolution fabrications of 3D micro/nanometastructures with high‐resolution remain a challenge. Here, a novel approach to fabricate sophisticated 3D micro/nanostructures with excellent robustness and precise controllability is demonstrated by simultaneously modulating of flexible resist stencils and basal molds. This method allows arbitrary manipulations of morphology, size, and orientation, as well as contact angles of the objects. Combined with a new alignment strategy of high‐resolution, previously inaccessible architectures are fabricated with ultrahigh precision, leading to an excellent spectra response from the fabricated metastructures. This method provides a new possibility to realize true 3D metamaterial fabrications featuring high‐resolution and direct‐compatibility with broad planar lithography platforms.