10 research outputs found
Photon super-bunching from a generic tunnel junction
Generating correlated photon pairs at the nanoscale is a prerequisite to
creating highly integrated optoelectronic circuits that perform quantum
computing tasks based on heralded single-photons. Here we demonstrate
fulfilling this requirement with a generic tip-surface metal junction. When the
junction is luminescing under DC bias, inelastic tunneling events of single
electrons produce a photon stream in the visible spectrum whose super-bunching
index is 17 when measured with a 53 picosecond instrumental resolution limit.
These photon bunches contain true photon pairs of plasmonic origin, distinct
from accidental photon coincidences. The effect is electrically rather than
optically driven - completely absent are pulsed lasers, down-conversions, and
four-wave mixing schemes. This discovery has immediate and profound
implications for quantum optics and cryptography, notwithstanding its
fundamental importance to basic science and its ushering in of heralded photon
experiments on the nanometer scale
Single charge and exciton dynamics probed by molecular-scale-induced electroluminescence
Excitons and their constituent charge carriers play the central role in
electroluminescence mechanisms determining the ultimate performance of organic
optoelectronic devices. The involved processes and their dynamics are often
studied with time-resolved techniques limited by spatial averaging that
obscures the properties of individual electron-hole pairs. Here we overcome
this limit and characterize single charge and exciton dynamics at the nanoscale
by using time-resolved scanning tunnelling microscopy-induced luminescence
(TR-STML) stimulated with nanosecond voltage pulses. We use isolated defects in
C thin films as a model system into which we inject single charges and
investigate the formation dynamics of a single exciton. Tuneable hole and
electron injection rates are obtained from a kinetic model that reproduces the
measured electroluminescent transients. These findings demonstrate that TR-STML
can track dynamics at the quantum limit of single charge injection and can be
extended to other systems and materials important for nanophotonic devices
Tip-induced excitonic luminescence nanoscopy of an atomically-resolved van der Waals heterostructure
Low-temperature scanning tunneling microscopy is used to probe, with
atomic-scale spatial resolution, the intrinsic luminescence of a van der Waals
heterostructure, made of a transition metal dichalcogenide monolayer stacked
onto a few-layer graphene flake supported by an Au(111) substrate. Sharp
emission lines arising from neutral, charged and localised excitons are
reported. Their intensities and emission energies vary as a function of the
nanoscale environment of the van der Waals heterostructure, explaining the
variability of the emission properties observed with diffraction-limited
approaches. Our work paves the way towards understanding and control of
optoelectronic phenomena in moir\'e superlattices with atomic-scale resolution.Comment: 14 pages, 4 figures, 3 supplementary figure
Internal Stark effect of single-molecule fluorescence
International audienceThe optical properties of chromophores can be efficiently tuned by electrostatic fields generated in their close environment, a phenomenon that plays a central role for the optimization of complex functions within living organisms where it is known as internal Stark effect (ISE). Here, we realised an ISE experiment at the lowest possible scale, by monitoring the Stark shift generated by charges confined within a single chromophore on its emission energy. To this end, a scanning tunneling microscope (STM) functioning at cryogenic temperatures is used to sequentially remove the two central protons of a free-base phthalocyanine chromophore deposited on a NaCl-covered Ag(111) surface. STM-induced fluorescence measurements reveal spectral shifts that are associated to the electrostatic field generated by the internal charges remaining in the chromophores upon deprotonation
Mapping Lamb, Stark, and Purcell Effects at a Chromophore-Picocavity Junction with Hyper-Resolved Fluorescence Microscopy
International audienceThe interactions of the excited states of a single chromophore with static and dynamic electric fields spatially varying at the atomic scale are investigated in a joint experimental and theoretical effort. In this configuration, the spatial extension of the fields confined at the apex of a scanning tunneling microscope tip is smaller than that of the molecular exciton, a property used to generate fluorescence maps of the chromophore with intramolecular resolution. Theoretical simulations of the electrostatic and electrodynamic interactions occurring at the picocavity junction formed by the chromophore, the tip, and the substrate reveal the key role played by subtle variations of Purcell, Lamb, and Stark effects. They also demonstrate that hyper-resolved fluorescence maps of the line shift and linewidth of the excitonic emission can be understood as images of the static charge redistribution upon electronic excitation of the molecule and as the distribution of the dynamical charge oscillation associated with the molecular exciton, respectively
Energy funnelling within multichromophore architectures monitored with subnanometre resolution
International audienc
Light-matter interaction at the single-molecule level probed with STM
International audienceLight-matter interaction plays a crucial role in the quantum properties of light emission from single molecules. They are usually probed using optical methods, which are, however, spatially limited by diffraction to a few hundred nanometers. On the other hand, scanning tunneling microscopy (STM) routinely reaches picometre spatial scale. Recent works have shown that the tunneling current of an STM can be used to excite the intrinsic luminescence of individual molecules enabling light-matter interaction investigations with unprecedented resolution. Processes that can be addressed involve charging, dipole-dipole interactions or energy transfer between individual chromophores. Here, we study STM-induced luminescence from phthalocyanine molecules adsorbed on a few-monolayer NaCl film epitaxially grown on Ag(111) substrate. We show how the atomically-confined electromagnetic field at the STM tip apex acts as a “picocavity” for localized plasmons and both enables optical studies with atomic-scale precision and interacts with the emitter [1]. Profiting from that resolution, we investigate a critical mechanism in the photosynthesis process – resonant energy transfer in multichromophoric architectures. We use individual phthalocyanines as ancillary, passive or blocking elements to promote and direct resonant energy transfer between distant donor and acceptor units. Such an approach constitutes a powerful model to study the role of the relative dipole orientation, distance and chemical nature of the chromophores on the efficiency of the energy transfer [2]
Single Charge and Exciton Dynamics Probed by Molecular-Scale-Induced Electroluminescence
Excitons and their
constituent charge carriers play the central
role in electroluminescence mechanisms determining the ultimate performance
of organic optoelectronic devices. The involved processes and their
dynamics are often studied with time-resolved techniques limited by
spatial averaging that obscures the properties of individual electron–hole
pairs. Here, we overcome this limit and characterize single charge
and exciton dynamics at the nanoscale by using time-resolved scanning
tunneling microscopy-induced luminescence (TR-STML) stimulated with
nanosecond voltage pulses. We use isolated defects in C<sub>60</sub> thin films as a model system into which we inject single charges
and investigate the formation dynamics of a single exciton. Tunable
hole and electron injection rates are obtained from a kinetic model
that reproduces the measured electroluminescent transients. These
findings demonstrate that TR-STML can track dynamics at the quantum
limit of single charge injection and can be extended to other systems
and materials important for nanophotonic devices