🕑 15:40

KEYNOTE
Subnanometer resolved single-molecule optical spectroscopy

Zhen-Chao DONG
University of Science and Technology of China, Hefei, China

Aspirations for reaching atomic resolution with light have been a major force in shaping nano-optics, whereby a central challenge is to achieve highly localized optical fields. Recent progresses on two STM-based optical phenomena to this end will be presented. One is single-molecule Raman spectromicroscopy down to single-bond resolution, allowing to track the bond breaking and forming in surface reactions as well as the local heating effect of a non-equilibrium single molecule. The other is single-molecule electro-phosphorescence with the discovery of a new optomagnetic channel to activate the emission from triplet-to-singlet transition. Unlike the common electric-dipole induced emission via the electric channel, the optical-frequency magnetic field is found to be significantly enhanced in a confined plasmonic picocavity, leading to a new observation of optomagnetism induced molecular phosphorescence via the magnetic channel that goes beyond the conventional spin-orbit coupling mechanism. Our results provide new routes to optical imaging, spectroscopy and engineering of light–matter interactions at the sub-nanometer scale.

🕑 09:00

INVITED
Optics of single molecules explored with sub-nm precision

Anna ROSŁAWSKA
Max Planck Institute for Solid State Research, Stuttgart, Germany

The fundamental origin of light-matter interaction lies at the sub-nm scale where single photons are absorbed, scattered, or emitted by single atoms and molecules. Reaching that precision in optics is now possible thanks to the combination of optical spectroscopy approaches with scanning probe microscopy. In my talk, I will briefly discuss how mapping optical properties of single molecules with nearly atomic precision is enabled by the extreme field enhancement provided by the tip and show its application to induce and probe electroluminescence, photoluminescence, resonant energy transfer, and photochemical reactions with sub-nm precision.

🕑 09:40

Light emission of single VOPc molecules in up and down orientations

Lukas GERHARD
Karlsruhe Institute of Technology (KIT), Germany

Scanning tunneling microscopy (STM) induced luminescence is best suited to study two dimensional molecules that absorb in a planar configuration on thin insulating layers on metallic substrates. Typically, these molecules are essentially mirror symmetric with respect to the surface. This means that there is only one possible adsorption configuration with respect to the electric field of the STM junction which is oriented perpendicular to the substrate. Here we show electroluminescence of single Vanadyl-phthalocyanine (VOPc) molecules deposited on NaCl on Au(111). The VO breaks the mirror symmetry and allows for different up or down configurations [1]. As this is expected to have direct consequences on the coupling of the molecular orbitals to the underlying metals, it allows to explain the observed differences in the light emission pattern in terms of charge state, excited state lifetime and efficiency.

[1] K. Kaiser et al, ACS Nano 2019, 13 (6).

🕑 10:00

Atomic-Scale Engineering of Optical Properties of Graphene Nanoribbons

Song JIANG
IPCMS, CNRS

Song Jiang, Jian-Cheng Wong, Eve Ammerman, Fabrice SCHEURER, Alex Boeglin, Roman Fasel , Sschuler Bruno, Tomáš Neuman, Guillaume Schull

Graphene nanoribbons (GNRs) have emerged as promising candidates for the next generation of nanoelectronic and optoelectronic devices due to their tunable energy band structures. We developed a strategy to investigate the excitonic emissions from atomically precise GNRs using scanning tunneling microscopy.In this presentation, I will focus on the “atomic-scale engineering” of the optical properties of GNRs, with the aim of precisely controlling and enhancing their luminescence characteristics.

🕑 10:20

Single-Molecule Time-Resolved Spectroscopy in a Tunable STM Nanocavity

Jiri DOLEZAL
Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences

Spontaneous fluorescence rates of single-molecule emitters are typically on the order of nanoseconds. However, coupling them with plasmonic nanostructures can substantially increase their fluorescence yields. The confinement between a tip and sample in an STM creates a tunable nanocavity, an ideal platform for exploring the yields and excitation decay rates of single-molecule emitters, depending on their coupling strength to the nanocavity. With such a setup, we determine the excitation lifetimes from the direct time-resolved measurements of phthalocyanine fluorescence decays, decoupled from the metal substrates by ultrathin NaCl layers. We find that when the tip is approached to single molecules, their lifetimes are reduced to the picosecond range due to the effect of coupling with the tip-sample nanocavity. On the other hand, molecules measured without the nanocavity manifest nanosecond-range lifetimes.

🕑 11:20

INVITED
Atomic-scale terahertz time-domain spectroscopy

Tyler COCKER
Michigan State University

The terahertz range of the electromagnetic spectrum hosts material excitations that are particularly important for nanotechnology, such as the collective motion of charges, spins, and ions. These excitations are often studied on macroscopic length scales with terahertz time-domain spectroscopy, which directly measures the oscillating electric field of a terahertz light pulse and relates it to key material processes through the light-matter interaction. Here, we show that lightwave-driven microscopy, which uses the field of a terahertz pulse to coherently control tunneling across a scanning tunneling microscope junction, can also be used as a platform for atomic-scale terahertz time-domain spectroscopy. We apply our new technique to silicon-vacancy centers at the surface of GaAs and discover a single-atom resonator with features reminiscent of the technologically important DX centers.

🕑 12:00

Subcycle optical microscopy with atomic-scale resolution

Valentin BERGBAUER
University of Regensburg and Regensburg Center for Ultrafast Nanoscopy

Pushing scanning near-field optical microscopy to ultra-high vacuum, cryogenic temperatures, and sub-nm tip tapping amplitudes, we discover an unprecedented non-classical response that is strictly confined to atomic dimensions. This ultrafast signal is characterized by an optical phase delay of ~π/2 and facilitates direct monitoring of tunnelling dynamics. We demonstrate that it results when lightwave-driven alternating tunneling currents in the tip-sample junction emit light, according to Maxwell’s equations. We showcase the power of this novel near-field optical tunneling emission (NOTE) microscope by imaging nanometre-sized defects hidden to atomic force microscopy and by subcycle sampling of current transients on a semiconducting van der Waals material. NOTE enables a radically new access to quantum light-matter interaction and electronic dynamics at ultimately short spatio-temporal scales in both conductive and insulating quantum materials.

T. Siday et al., Nature 629, 329 (2024)

🕑 12:20

Ultrafast Luminescence in a Scanning Tunneling Microscope

Kurt LICHTENBERG
University of Stuttgart

Many processes in nature and technology rely on the ultrafast interaction between light and matter on nanometer-length scales. Yet, experimental probes capable of reaching this spatial regime and simultaneously achieving ultrafast time resolution are lacking. Scanning Tunneling Luminescence (STL) probes light emission with sub-molecular resolution. We combine STL with the sub-picosecond time resolution of THz-Scanning Tunneling Microscopy (THz-STM), to achieve atomic-scale spatial resolution and ultrafast time resolution simultaneously. In initial experiments with this new method, we detect THz-induced plasmonic luminescence on a bare silver surface. The THz-induced voltage transients ignite luminescence in time windows considerably smaller than the width of the center THz pulse, enabling us to sample one THz pulse with a second one. Beyond exciting surface plasmons, this method can now be applied to probe THz-induced luminescence, e.g. from single molecules.

🕑 12:40

Tip-enhanced femtosecond spectroscopy at the atomic scale

Yang LUO
Max Planck Institute for Solid State Research

Many fundamental physical and chemical processes occur on extremely fast time scales (femtoseconds to picoseconds) and at very small length scales (picometers to nanometers), such as energy and charge transfer processes in molecules and nanostructures. The precise characterization and manipulation of these processes at their intrinsic time and length scales are crucial for understanding microscopic mechanisms and developing novel nanomaterials. To achieve this, we have combined femtosecond time-resolved spectroscopic techniques with scanning tunneling microscopy (STM), which allow us to probe and control nanoscale dynamics with high spatial, temporal, and energy resolutions. Specifically, we investigate hot electron dynamics in the plasmonic junction and track atomic motions within single graphene nanoribbons via anti-Stokes emission. Our approach offers new perspectives for exploring ultrafast light-mater interactions at the atomic scale.

🕑 14:40

INVITED
Optomechanical interaction of plasmons and single molecule vibrations in tunneling junctions

Javier AIZPURUA
Donostia International Physics Center (DIPC)

Plasmonic resonances supported in tunneling junctions can be used to localize and enhance light at optical frequencies, dramatically increasing the signal in a variety of molecular spectroscopies, as in surface-enhance fluorescence or in surface-enhanced Raman scattering (SERS), the latter constituting an example of an optomechanical interaction analogous to that existing between cavity photons and mechanical vibrations. In this context, SERS in tunneling junctions can bring cavity optomechanics down to the molecular scale giving access to larger vibrational frequencies of molecular motion. We will introduce the molecular optomechanics description of SERS and address novel molecular dynamics regimes of fundamental and practical interest in extreme plasmonic picocavities. Non-linear Raman signals, collective phenomena involving many molecules, as well as the modification of the width and energy of molecular vibrations due to plasmon−vibration interaction will be described in the case of a single C60 molecule attached to a tip of a tunneling junction.

🕑 15:20

Electronically-probed strong coupling of hybrid nanostructures

Antonio FERNANDEZ-DOMINGUEZ
Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Center (IFIMAC)

In this talk, we will analyse two different scenarios in which electrons are used as a probe of light-matter strong coupling. Firstly, we will show how modulated electron wavepackets provide access to quantum effects in the exciton-plasmon interaction taking place between a metallic nanocavity and a nearby single quantum emitter. Secondly, we will present results on the use of electroluminescence to probe polariton formation in hybrid structures consisting of a nanoscale plasmonic tunnel junction and a two-dimensional transition-metal dichalcogenide.

🕑 15:40

Theoretical Study of Electronic and Optical Properties in Edge-Modified Graphene Nanoribbons

Jian Cheng WONG
Institute of Physics (FZU) of the Czech Academy of Sciences

Jian Cheng Wong, Song Jiang, Sofia Canola, Alex Boeglin, Guilaume Schull, Tomáš Neuman

The edge structure of graphene nanoribbons (GNRs) influences its optoelectronic properties. Previous scanning tunneling microscopy-induced luminescence (STML) studies [1] reveal localized excitations with interesting optical properties at the GNR end states. A comprehensive description of these optical excitations in GNRs with edge modifications, and its interplay with the end states, remains to be explored theoretically. Thus, we construct a many-body model of the GNR states to describe the mechanisms of excitonic emission under STML using ab initio electronic structure methods. We will show electroluminescence maps obtained from theory and compare them to experimental results.

🕑 16:00

Tailored strategies for fine-tuning the (opto)electronic properties of covalent organic frameworks

Jose Ignacio MARTINEZ
Institute of Material Science of Madrid (ICMM-CSIC). C/Sor Juana Inés de la Cruz 3, 28049 Madrid

Covalent organic frameworks are a class of crystalline macromolecular materials constructed from monomers with specific symmetries/functionalities. Their structural versatility offers avenues for tailoring their (opto)electronic properties through various strategies. One approach involves the in silico predesign of the chemical structure of building blocks, allowing for slight modifications of precursor conformations to achieve desired functionalities. Alternatively, a mixed linker strategy can be adopted, wherein fluorescent molecules are incorporated into COF structures allowing for controlled doping to achieve specific optical behaviors. Furthermore, the inclusion of interpore ligands with enhanced optical properties leads to a global enhancement of the COF performance, since systems with low conjugation retain the (opto)electronic properties of the building blocks. Lastly, on this basis, novel COF materials hold potential for evaluation as ion sensors through fluorescence emission.

🕑 16:20

Cooperative electron-vibron interactions in Surface-Enhanced Raman Scattering (SERS)

Diego MARTÍN CANO
Dept. Theoretical Condensed Matter Physics and IFIMAC, Universidad Autónoma de Madrid

In this work we identify cooperative electron-vibron interactions occurring between both near-resonant and non-resonant electronic levels in SERS [1]. By developing an open-system quantum model based on fundamental molecular interaction principles, we illustrate how Raman interference, involving both resonant and non-resonant components, can lead to several orders of magnitude modifications in SERS peaks compared to the former established optomechanical models. This cooperative optomechanical mechanism gives rise to the generation of enhanced nonclassical correlations between Stokes and anti-Stokes photons, detectable through photon-counting measurements. Our findings reveal coherent Raman enhancements and suppressions that significantly impact the conventional assessments of the optomechanical contribution in SERS spectra and their quantum mechanical observable effects.

[1] M.Á. Martínez-García & D. Martín-Cano, Physical Review Letters 132, 093601 (2024)

🕑 17:20

INVITED
Tip-Enhanced Raman Spectroscopy in STM picocavities

Takashi KUMAGAI
Institute for Molecular Science, Okazaki, Japan

Tip-enhanced Raman spectroscopy (TERS) has been established as an atomic-scale chemical characterization method [1, 2], enabling the examination of atomic-scale light–matter interactions. It has been revealed that remarkable enhancement of Raman scattering occurs in a sub-nanometer scale cavity, called “picocavity” [3], and further enhancement is facilitated by formation of a point contact between the tip apex and the molecule. The enhancement originates from extreme confinement of the plasmonic field and charge transfer within the hybridized metal–molecule states. However, a full description of Raman scattering in picocavities remains to be elucidated, requiring detailed understanding of the atomic-scale confinement of the plasmonic field and electronic transition within the hybrid systems. In the talk, I will discuss our recent experiments on TERS in several STM picocavities including a single adatom [4], a single molecule on a semiconductor surface [5], and a physisorbed molecule [6].

[1] J. Lee et al. Nature 568, 78 (2019).
[2] Y. Zhang et al. Natl. Sci. Rev. 6, 1169 (2019).
[3] F. Benz et al. Science 354, 726 (2016).
[4] S. Liu et al. ACS Nano 17, 10172 (2023).
[5] B. Cirera et al. under revision.
[6] Shiotari et al. submitted.

🕑 18:00

Tuning the plasmonic response of optical pico-cavities by STM.

Roberto OTERO
Universidad Autónoma de Madrid, IMDEA Nanoscience

The optical properties of metallic nano-systems are dominated by their interesting plasmonic excitations. The gap between the tip and the sample in an STM constitutes an optical pico-resonator which can be tuned by repositioning the tip at different locations with respect to atomic-scale defects. The raw electroluminescence spectra, however, depends not only on the optical properties, but also on the different electronic structure at these different locations. The purely optical contribution can be obtained by a simultaneous determination of the electronic structure and the optical properties [1]. In this contribution we exploit this method to investigate the plasmonic modes of the tip-surface resonator in the presence of atomic step edges and adsorbed molecules, leading to anisotropic emission and spectral changes. Thus, STM can be considered as a unique tool, enabling the atomic-scale design of pico-cavities and the investigation of their optical properties.

[1] Nat Commun 11, 1021

🕑 18:20

Plasmon-magnon hybridation in two-dimensional Ag/NiO heterostructures

Carmen DEL PINO BATLLES
Instituto de Cerámica y Vidrio, CSIC

Antiferromagnetic materials (AFM) have recently attracted attention due to their potential application as an active element for spintronic applications. For that, the control of their magnetic domains is a challenge, being light irradiation one possible route.
In this work we propose to activate and control spin waves (i.e., magnons) of AFM by the excitation of localized surface plasmons (LSPs) of metallic nanoparticles (NPs). For this purpose, a hybrid system based on NiO films and Ag NPs is fabricated controlling the morphological and structural properties. The interaction between the LSPs and the spin waves is identified by micro-Raman spectroscopy and evaluated according to the plasmonic response, which is tailored with the type of substrate and the annealing temperature for the Ag nanostructuration.

🕑 18:40

Combined STM and optical microscopy for the study of excitons in monolayer transition metal dichalcogenides

Eric LE MOAL
CNRS, Université Paris-Saclay, Institut des Sciences Moléculaires d'Orsay

The luminescence of two-dimensional (2D) semiconductors is electrically activated in a nanoscale tunnel junction using a scanning tunneling microscope (STM) operating in air. The emitted light is spatially, angularly, and spectrally resolved using an optical microscope and spectrometer, in order to investigate the emission processes and identify the involved excitonic species. The STM-induced generation of neutral and charged excitons in monolayer transition metal dichalcogenides is demonstrated [1,2]. In addition, the tip and tunneling current of an STM is used to control the quantum yields of photoluminescence in 2D semiconductors [3].

[1] Pommier et al, Phys. Rev. Lett. 123, 027402 (2019)
[2] Peña Román et al, Phys. Rev. B 106, 085419 (2022)
[3] Peña Román et al, Nano Lett. 22, 9244 (2022)

🕑 19:00

No Helium No problem

Hrag KARAKACHIAN
Omicron GmbH

This contribution is a commercial presentation of one of the sponsors of the conference

🕑 09:00

INVITED
Probing photoinduced dynamics in the local density of states of quantum materials

Melanie MÜLLER
Fritz Haber Institute of the Max Planck Society, Berlin, Germany

Recent advances in the coupling of broadband optical and terahertz (THz) radiation with low-temperature scanning tunneling microscopes (STM) have greatly expanded the possibilities for studying ultrafast dynamics on surfaces at the atomic scale [1]. In particular, THz-lightwave-driven STM (THz-STM) has enabled ultrafast imaging with simultaneous angstrom spatial and femtosecond temporal resolution [2]. In this talk, I will discuss the prospects of THz-STM for studying ultrafast dynamics of single quantum states in quantum materials. As a first step in this direction, we probe the photoinduced dynamics of the charge density wave (CDW) insulator 1T-TaS2 in its low-temperature commensurate CDW phase, where 1T-TaS2 is assumed to be a Mott insulator. Upon photoexcitation, we observe a periodic modulation of the tunneling current at a frequency of 2.4 THz, resulting from a coherent modulation of the Mott-Hubbard bands by the CDW amplitude mode [3]. In addition, the photoinduced collapse of the insulating gap causes a transient metallization on THz sub-cycle time scales, resulting in a strong modulation of the rectified tunneling current. Finally, I will briefly outline the future prospects of THz-STM for the atomic-scale imaging of light-induced processes in quantum materials.

[1] M. Müller, Prog. Surf. Sci. 99, 1 (2024)
[2] T. Cocker, Nature 539, 263–267 (2016)
[3] L. Parra Lopéz et al., in preparation

🕑 09:40

Ultrafast nanoscopy of single-grain structure, composition, and carrier dynamics in metal halide perovskites

Svenja NERRETER
Department of Physics and Regensburg Center for Ultrafast Nanoscopy (RUN), University of Regensburg

The skyrocketing efficiencies of metal halide perovskite solar cells have been attributed to effective carrier diffusion. Still, the characteristic nanocrystalline structure and competing crystal phases of perovskite films have impeded a detailed understanding of the vertical transport. Here, we promote ultrafast terahertz nanoscopy to deep subcycle time scales to simultaneously access the nanoscale chemical composition, structural phase and ultrafast vertical dynamics in FA0.83Cs0.17Pb(I1−xClx)3 films. Using phonon fingerprinting, we discern domains of 𝛼- and 𝛿-phases as well as PbI2 nano-islands. Tracing subcycle shifts of the scattered near-field after photoexcitation, we access local vertical carrier diffusion, which is found to be surprisingly homogeneous on the nanoscale, while variations occur between mesoscopic regions. Our approach, connecting nano-morphology with carrier dynamics, may benefit a broad variety of future optoelectronic devices using nanocrystalline materials.

🕑 10:00

Li intercalation into graphene through LiCl photodissociation

Jon AZPEITIA
Instituto de Ciencia de Materiales de Madrid, CSIC

Lithium-ion chemistry on graphene (Gr) has gained importance due to its applicability to lithium-ion batteries. However, the most important contributions are based on wet chemistry approaches. Here, we explore an alternative route, where lithium intercalates into graphene by photon irradiation. We expose LiCl thin films grown on Gr/Ir(111) to soft X-ray radiation, leading to the photodissociation of LiCl. We observe fast chlorine desorption while Li follows a complex intercalation process: it first intercalates, forming an amorphous structure between Gr and Ir(111). While irradiation time increases, it forms the Li(1x1) reconstruction. This structure evolves and, for sufficiently long exposure times, Li promotes within the metal substrate. Finally, we recover the pristine Gr/I(111) by thermal annealing, where Li desorbs. We follow in real time the structural evolution by utilizing LEED, the chemical evolution employing XPS, and changes in the electronic band structure with µ-ARPES.

🕑 10:20

Anhydride Photolysis on a Semiconductor Surface

Ana SÁNCHEZ GRANDE
Institute of Physics, Czech Academy of Sciences

Only in recent years the field of photochemistry on surfaces has been developed. So far, very few examples of light-driven chemical reactions on semiconductors or insulating surfaces have been reported, representing a unique bottom-up approach strategy toward the synthesis of carbon-based nanomaterials directly on technologically relevant substrates. Here, we present a new on-surface reaction employing anhydride-functionalized molecules as precursors on a SnSe surface. Our studies reveal how we can tailor the photoactivity of different anhydride-functionalized molecules by modulating the π-conjugation of the molecular core. The experimental results were corroborated by quantum chemical calculations that confirm the impact of the π-conjugation in the ordering of the excited state. Theoretical investigations of alternative anhydride-based precursors demonstrate that their photochemical activity relies on the presence of a n→π* first excited state with strong dissociative character.

🕑 10:40

Optical Manipulation of the Charge Density Wave state in RbV3Sb5

Seokjin BAE
University of Illinois at Urbana-Champaign

Broken time-reversal symmetry in the absence of spin order indicates the presence of unusual phases such as orbital magnetism and loop currents. The recently discovered kagome superconductors AV3Sb5 (A = K, Rb, or Cs), hosting an exotic charge-density wave (CDW) state, have emerged as strong candidates for this phase. The idea that the CDW breaks time-reversal symmetry is however being intensely debated due to conflicting experimental data. In this work we use laser-coupled scanning tunneling microscopy (STM) to study RbV3Sb5. By applying linearly polarized light along high-symmetry directions, we show that the relative intensities of the CDW peaks can be reversibly switched, implying a substantial electro-striction response, indicative of strong non-linear electron-phonon coupling. A similar CDW intensity switching is observed with perpendicular magnetic fields, which implies an unusual piezo-magnetic response that, in turn, requires time-reversal symmetry-breaking. We show that the simplest CDW that satisfies these constraints is an out-of-phase combination of bond charge order and loop currents that we dub congruent CDW flux phase. Our laser-STM data opens the door to the possibility of dynamic optical control of complex quantum phenomenon in correlated materials.

🕑 11:40

INVITED
Theory of photon emission characteristics from current-driven single-molecule junctions

Thomas FREDERIKSEN
Donostia International Physics Center (DIPC)

In this talk I will describe our theoretical efforts to understand various properties of photon emission driven by an electronic current across single-molecule junctions. We focus on simple yet effective models with one or two molecular levels interacting with a cavity mode, embedded in an environment of electronic leads and propagating electromagnetic modes. Using a quantum master equation approach, we study the current-driven photon emission characteristics, computing both the emission spectrum and the second-order photon correlation function across different parameter regimes. Our findings contribute to a deeper understanding of light-matter interactions at the molecular level, which is essential for the development of efficient quantum light sources and supporting experimental investigations.

[1] Q. Schaeverbeke et al. Phys. Rev. Lett. 123, 246601 (2019)
[2] R. Avriller et al. Phys. Rev. B 104, L241403 (2021)
[3] A. Bejarano et al, manuscript in preparation.

🕑 12:20

Effective computational methods for photophysics in complex environments

Javier CEREZO
Universidad Autónoma de Madrid

Light-matter interaction provides a unique route to extract detailed information about molecular systems, unveiling the potential complexity of the environment. It is also involved in many technological applications or key biological processes. Advances in these fields thus require detailed knowledge of such processes, and computational methods stand as a valuable tool, giving access to fine details of the system that can enormously help interpret experimental outcomes and guide new experimental setups.
While photophysical simulation involving semirigid molecules is customary, complex environments and the molecule's flexibility represent a current challenge. In this talk, we will offer a general review of the mixed quantum-classical methods recently developed by our group. These methods provide an effective route towards the full ab initio simulation of photophysics in complex environments. We shall focus on some essential pieces to apply this strategy and show promising applications.

🕑 12:40

Synthesis of 2D Polymers via Light Irradiation: Enhanced Mechanical Properties

Jesús MENDIETA-MORENO
Institute of Material Science of Madrid (ICMM-CSIC).

Sustainable synthetic routes are essential for the implementation of 2D materials. Among these, photo-induced reactions leading to two-dimensional polymers pose experimental challenges. In this work, we demonstrate the synthesis of 2D polymeric layers from their constituent monomers, activated by visible light, directly on the surface where they were drop-casted. We report the efficient growth of a molecular bilayer of (3-TBTT) molecules via [2+2] cycloaddition, as revealed by a combination of AFM and theoretical simulations. These reactions are facilitated by the specific interactions of 3-TBTT molecules with mica surface, allowing the system to maintain a structure conducive to reaction, as shown by molecular dynamics calculations. The resulting polymers expand the thickness by approximately 30% and exhibit enhanced mechanical stability and robustness. The increase in thickness and the enhanced robustness has been rationalized through classical MD and QM/MM simulations through the fo

🕑 13:00

Vibrational spectroscopy from first-principles: Normal mode analysis to assign Raman and IR spectra

Carlos ROMERO-MUÑIZ
Universidad de Sevilla

Vibrational spectroscopy is currently an essential tool to characterize either organic or inorganic materials. Unfortunately, a systematic assignment of vibrational spectra is difficult to carried out solely from the experiments. In this contribution, We show how it is possible to obtain an accurate description of the vibrational properties of different materials by means of first-principles calculations based on standard density functional theory. Our approach leads to the construction of theoretical vibrational spectra that can be directly compared to the experimental ones, usually achieving a good agreement even in complex systems. For instance, solid-state benzylic amide [2]catenane, a mechanically interlocked molecular architecture, the adsorption and functionalization of metal-organic frameworks or the influence of point defects in transparent conducting oxides.

Controlled photoemission from graphene using laser pulses

Fernando AGUILAR-GALINDO
Universidad Autónoma de Madrid

The control of electrons at the atomic scale has attracted the attention of multiple scientists in different fields such as Physics, Chemistry or Material Science due to the wide applications where it could be applied: from improved photovoltaic devices, selective chemical reactivity or nanodevices.Among the techniques to control these dynamics, the use of laser pulses stands as one of the most powerful, since the use (ultra)short pulses allows for a control and monitoring of the processes at the atto-scale. In this communication, we present a theoretical study, where we apply our approach to solve the TDSE [1], to follow the electron dynamics in graphene, including excitation and/or photoionization, under the effect of strong IR pulses. The influence of several factors, such as the carrier envelope phase or the position in the Brillouin zone are discussed, as well as the transition from the multiphoton to the strong field regime.

[1] J.Chem.Theory Comput.,17,639(2021)

Tip-enhanced Raman spectroscopy for nanometre-scale characterisation of hydrogenated graphene on Pt(111)

Daniel ARRIBAS MERCADO
Material Science Institute of Madrid (ICMM), CSIC

Hydrogen atoms chemisorb to graphene locally breaking the sp2 hybridization. In the final configuration, the hydrogen is located on top of a sp3-hybridised carbon atom with the C-H bond perpendicular to the graphene plane. The stability of the chemisorbed H atoms improves when other H atoms are adsorbed in the proximities, which results in the formation of hydrogen dimers and clusters. In addition, moiré superstructures, induced from the mismatch between the graphene and its substrate lattices can present a corrugation that favours H chemisorption on the more protruding areas. If graphene is grown on a metal with a plasmon resonance, tip-enhanced Raman spectroscopy experiments allow to characterise the resulting C-H stretching modes. In this work, we propose a Raman characterisation at the nanometre scale of the hydrogenated moiré superstructures appearing on a graphene layer grown on a Pt(111) surface.

Fluorescence of single molecules in STM picocavities: beyond the point-dipole approximation

Xabier ARRIETA ARISTI
Materials Physics Center, CSIC-UPV/EHU, Donostia-San Sebastián, Spain.

X. Arrieta, N. Friedrich, A. Rosławska, K. Kaiser, M. Romeo, E. Le Moal, F. Scheurer, A. G. Borisov, G. Schull, R. Esteban, J. Aizpurua, T. Neuman

Scanning tunnelling microscope (STM) configurations are able to measure fluorescence maps of single organic molecules with subnanometric resolution due to the extreme field confinement produced in the picocavity formed between the atomic protrusion at the metallic tip and the metallic substrate. The field gradients in the picocavity are huge, so that the commonly used point-dipole approximation is no longer valid to model the interaction between the picocavity and the organic molecule. In this work, we explain how to describe the interaction beyond this approximation by considering the spatial dependence of the transition density of the molecule. We illustrate the importance of this description by considering an experimental setup involving a PTCDA molecule inside a STM picocavity and calculating the Purcell factor (see Figure).

Light emission from current-driven plasmonic nanocavities

Andrés BEJARANO
Donostia International Physics Center

In recent years, the scientific community has shown growing interest in the study of light emission in molecules. The Scanning Tunneling Microscope (STM), in particular, stands out for its remarkable ability to inject electrons with atomic precision. This precision enables the probing of various internal molecular transitions, shedding light on the intricate mechanisms behind molecular light emission. In fact, it has been reported that when the STM tip is positioned close to the molecule, a distinct sharp resonance appears in the emission spectrum. This phenomenon, known as the Purcell effect, arises from the weak interaction between the confined electric field and the molecule, enhancing the emission efficiency [1, 2, 3]. Additionally, several research groups have investigated the statistical behavior of the emitted photons and observed antibunching. This phenomenon indicates that it is unlikely to detect two photons in close temporal proximity, providing further insights into the quantum nature of the light emission process [4, 5, 6]. We propose a microscopic model based on the quantum master equation to accurately describe the emission spectrum and photon statistics. Our model, through different levels of approximation, enables precise predictions of the various lifetimes of the involved excitations. This approach offers insights into the underlying mechanisms of light emission.Light emission from current-driven plasmonic nanocavities In recent years, the scientific community has shown growing interest in the study of light emission in molecules. The Scanning Tunneling Microscope (STM), in particular, stands out for its remarkable ability to inject electrons with atomic precision. This precision enables the probing of various internal molecular transitions, shedding light on the intricate mechanisms behind molecular light emission.

[1] B. Doppagne et al., PRL 118, 127401 (2017)
[2] G. Chen et al., PRL 122, 177401 (2019)
[3] S. Jiang et al., PRL. 130, 126202 (2023)
[4] P. Merino et al., Nat. Commun. 6, 8461 (2015)
[5] L. Zhang et al., Nat. Commun. 8, 580 (2017)
[6] A. Rosławska, ACS Nano, 14, 6366 (2020)

Avoiding fluorescence quenching in NiPc single molecules via resonant energy transfer and plasmonic excitation

Roel BURGWAL
Radboud University Nijmegen, The Netherlands

Metal phtalocyanines (MPcs) are optically active molecules with a core metal atom that have potential applications in optoelectronics and photovoltaics. While several MPcs show fluorescence, NiPc is an example where it is quenched, caused by fast non-radiative relaxation channels involving metal-centered d-orbital states. Recently, we have shown that NiPc emission can be restored by using resonant energy transfer from a nearby MPc (M=Pt,Pd,Zn). This can be explained assuming a small activation barrier between the S1 and the metal-centered states, which would typically be overcome except when exciting NiPc within a precise energy window. The barrier height can so far only be roughly estimated. Here, we present a possible strategy that allows us to quantify this barrier, based on experiments where NiPc gets indirectly excited via nanocavity plasmons in the tip-sample junction of a scanning tunneling microscope. We discuss the feasibility of this approach and show first results.

Photon-SPM a new ALBA line for in situ experiments

Emigdio CHAVEZ ANGEL
Catalan Institute of Nanoscience and Nanotechnology (ICN2)

A new photon-SPM facility will soon be available at ALBA for correlative measurements with various beamlines. It will operate in controlled atmospheres and in-operando conditions, including electrochemical environments. Several AFM/STM modes and VIS optical spectroscopies will be accesible. Noteworthy features include the study of low energy Raman modes (<10 cm-1) and high wavelength resolution (<0.2 cm-1), enabling precise Raman maps, determination of elastic constants in 2D materials, and tracking subtle perturbations related to chemical interactions, doping, strain, and beyond. This line will also include 3 excitation lasers operated at 532, 633 and 785 nm, with entries for others external laser. The optics include the automatization of polarization dependence and enough space to bring your own external optical set-up for custom made experiments. It is expected that the equipment will be fully operational by mid 2025, and first tests will be carried out in Nov of 2024.

Home-made optimization of a variable temperature photon-STM

Borja CIRERA
ICMM-CSIC

Variable temperature scanning probe microscopy (VT-SPM) offers a versatile platform for probing material properties with high spatial resolution under controlled thermal conditions in a wide range of temperatures (10-400 K). Integrating VT-SPM with an optical setup allows to illuminate and/or collect light emitted from the junction, facilitating the exploration of the intricate interplay between thermal, electronic, and optical properties at the nanoscale. Here we present a home-built technical upgrade to position a retractable lens (f=12 mm) at the focal distance of the tunnelling junction of a commercial Scientia Omicron VT-SPM©. The implementation of a UHV-compatible printable structure allows to perform electro-, photoluminescence and Raman spectroscopy, making this technique accessible to a larger number of SPM groups (more than 500 VT-SPM systems worldwide). This integrated approach will contribute to the fundamental understanding of light-matter interactions at the nanoscale, advancing future investigations in atomic-scale photo physics and photo chemistry.

Resonant Raman of functionalized chiral graphene nanoribbons

Martina CORSO
Centro de Física de Materiales

Graphene nanoribbons (GNRs) grown with atomic precision are emergent materials for advanced electronic devices. They possess a bandgap tunable by different strategies. Among different types of GNRs grown by on-surface chemistry, only those exhibiting armchair type edges have been implemented into nanodevices. This work explores an avenue for enhancing the applicability of also chiral GNRs by strategically functionalizing them with nitrile chemical groups at their edges. The functionalization tunes the GNRs bandgap and enables their periodic coordination with metal atoms.
We use Raman spectroscopy in UHV to determine the structural and chemical stability of pristine, functionalized and metal coordinated GNRs upon air exposure and transfer to non-conductive substrates. This works demonstrates that chemical functionalization is a robust strategy for the implementation of reactive GNRs in electronics and sensing technologies.

Field driven crossover of bonding and antibonding states in excitonic aggregates

Rodrigo Cezar DE CAMPOS FERREIRA
Institute of Physics - CAS

In the study presented here, we investigate the effect of the electric field confined in an optical nanocavity and how it influences the excitonic states of PTCDA aggregate complexes. The experiment was performed in a low temperature scanning tunneling microscope (LT-STM) within an optical setup designed for near-field spectroscopies. Here, the molecules are assembled on top of a thin decoupling layer of NaCl on Ag(111) crystal surface and probed by tip-enhanced photoluminescence (TEPL). We observe a field-driven crossover in the spectra between bonding and antibonding excitonic sites of dimer, trimer and tetramer aggregates. Results reveal that the antibonding states experience a reversible and more pronounced energy shift compared to bonding states, which underscore a potential for quantum control of excitonic states in nanoscale systems, paving the way for advancements in optoelectronics.

Coupling single-cycle THz pulses into a scanning tunneling microscope: Characterization of pulse shape and amplitude

Florian FAABER
FU Berlin: Fachbereich Physik

The coupling of THz pulses into a scanning tunneling microscope (THz-STM) has emerged as a unique technique to achieve picosecond time resolution while maintaining sub nanometer spatial resolution [1]. For THz-STM, a stable generation of THz outside the STM as well as a method to reliably determine the pulse shape in the STM junction are of high importance. In this work, we show that the use of retroreflectors can increase the pointing stability of the exciting laser hence improving the stability of the pump-probe experiment. Furthermore, to determine the THz pulse shape in the STM junction, we use photoemission sampling on different dielectric materials [2,3]. Finally, we estimate the THz amplitude on a semiconductor which is essential to determine the nature of the probed excitation.

[1] Cocker, et al. Nature Photonics 7, 620–625 (2013)
[2] Yoshida et al. ACS Photonics, 6, 6, 1356–1364 (2019)
[3] Müller et al. ACS Photonics, 7, 8, 2046–2055 (2020)

Theoretical investigations of single molecule light emission

Moritz FRANKERL
Donostia International Physics Center (DIPC)

We study the electrofluorescence of single molecules in scanning tunneling microscopy (STM) nanocavities.
We employ a generalized master equation approach for the reduced density matrix of the central system, i.e. the molecule. We include the coupling to the metallic leads, the coupling to the cavity formed by the STM as well as electron-phonon coupling on the molecule and explain their respective effect on the light emission spectrum.

Low-temperature photon-SPM a new ALBA line for in-situ experiments

Marc G CUXART
Catalan Institute of Nanoscience and Nanotechnology

This poster will present a new low-temperature photon-SPM open to the community at ALBA Synchrotron. It will combine the powerful imaging capabilities of SPM with optical spectroscopies to provide insight into light-matter interactions with atom-scale and picosecond resolution. The instrument will count with an optical setup consisting on pulsed and narrow linewidth CW lasers, RF signal generators (<18GHz) and up-to-date spectrograph covering the VIS-NIR spectral range. Besides STM/STS/nc-AFM modes, the instrument will allow STML, TEPL (<1meV), trans-STML, trans-TEPL, HBT interferometry (<30ps) and TERS (<5cm-1) measurements, also at variable temperature and under variable magnetic field (<1T). The photon-SPM will integrate in InCAEM facility, aiming at performing in-situ correlative measurements with BOREAS, LOREA and CIRCE beamlines. This will be possible thanks to the use compatible sample holders and transfer system, fiducial markers system, and nanofabrication facilities at ICN2.

Neutral Exciton-Libron Coupling via Resonant Energy Transfer in Single Molecules

Thiago GONZALEZ-LLANA BRITO
Max Planck Institute for Solid State Research

The optical properties of single molecules can vary depending on their environment. In some surroundings, vibrations due to frustrated rotations (librations) may occur if the molecules feature some rotational freedom[1]. In this study, we provide evidence of coupling between neutral excitons and libration modes (librons). We observed this coupling through light emission resulting from resonant energy transfer (RET)[2,3]. We measured neutral and charged exciton emissions in isolated zinc phthalocyanine (ZnPc) and ZnPc-platinum phthalocyanine (PtPc) assemblies deposited on NaCl/Ag(111) using scanning tunneling microscopy induced luminescence. For isolated ZnPc, we observed a broad peak from the neutral exciton and exciton-libron coupling for the charged exciton. In contrast, in ZnPc-PtPc structures, we found libronic signatures in the neutral emission of ZnPc when excited via RET from PtPc. This study is providing deeper insights into exciton-libron dynamics in single molecules.

[1] Doležal, J. et al. Nat. Commun. 13, 6008 (2022)
[2] Cao, S. et al. Nat. Chem. 13, 766–770 (2021)
[3] Kong, F.-F. et al. Nat. Nanotechnol. 17, 729–736 (2022)

Studying Ba nanostructuctures by Low-energy Electron Miscrocopy and Photoemission Microscopy

Clara GUTIÉRREZ CUESTA
Instituto de Química Física Blas Cabrera (IQF-CSIC)

Clara Gutiérrez Cuesta, José Emilio Prieto, Juan de la Figuera, Ángel Guirao Elías.

Low energy electron microscopy is a technique that used a beam of low-energy electrons to image a surface with nanometric resolution. The technique is well suited to exploring surface dynamics and growth processes by molecular beam epitaxy in real time.
The addition of a light source allows to directly observe the spatial (and angular) distribution of photoemitted electrons, in photoemission electron microscopy. In our case, we have added a violet laser (405nm) and an ultraviolet laser (261nm) as illumination sources.
We will present our first results in the characterization of barium oxides on W(110) by the combined low-energy electron microscopy and photoemission microscopy. Barium oxides are crucial to lower the work function in electron sources. We have been growing those oxides by oxygen-assisted molecular beam epitaxy under observation in low-energy electron microscopy.

Directional picoantenna behavior of tunnel junctions in the presence of atomic-scale defects

David MATEOS
Instituto IMDEA Nanociencia, Madrid,

Plasmonic nanoantennas have attracted much attention lately as they make the control of the directionality and temporal characteristics of light emitted by fluorophores possible [1]. Nanoantennas exploit light-matter interactions mediated by Localized Surface Plasmon Resonances and, so far, have been demonstrated using metallic nanoparticles or other metallic nanostructures [2]. Plasmonic picocavities could act as antennas to mediate light-matter interaction even more efficiently than their nanoscale counterparts due to their extreme field confinement, but the directionality of their emission is difficult to control. In this work, we show that the plasmonic picocavity formed between the tip of an STM and a metal surface with a monoatomic step shows directional emission profiles and, thus, can be considered as a realization of a picoantenna. Comparison with electromagnetic calculations demonstrates that the observed directionality arises from light emission tilting of the picocavity plasmons. Our results, thus, pave the way to exploiting picoantennas as an efficient way to control light-matter interaction at the nanoscale.

[1] C. Carnegie, et al. J Phys Chem Lett 9, 7146–7151 (2018).
[2] T. Coenen, et al. Nat Commun 5, 3250 (2014)

Observing correlated electron dynamics in the local density of states of 1T-TaS2 by THz-STM

Luis Enrique PARRA LOPEZ
Fritz Haber Institute of the Max Planck Society

THz scanning tunneling microscopy (THz-STM) has emerged as a promising technique for imaging surfaces with femtosecond (fs) temporal and atomic spatial resolution. We apply THz-STM to study the fascinating quantum material 1T-TaS2, where the formation of a commensurate charge density wave (C-CDW) phase is accompanied by the opening of a Mott gap at low temperatures.Fs -optical excitation leads to a transient collapse of the Mott gap and launches coherent amplitude mode (AM) motion of the CDW.Here we discuss the mechanisms by which the ultrafast gap collapse and coherent AM oscillations can modulate the THz-induced current.By using a simple 1D-tunneling model to reproduce the observed dynamics, we gain insight into the dynamics of the LDOS and the insulating gap in 1T-TaS2. Our results are an important step towards the future investigation of ultrafast dynamics in complex quantum materials at the atomic scale.

Light-induced generation of one-dimensional Stone-Wales-based polymers on surfaces

Elena PÉREZ ELVIRA
IMDEA Nanociencia

On-surface synthesis has become a promising approach to engineer low dimensional polymers that are unattainable through traditional solution chemistry and hold great scientific value for research fields like organic electronics [1]. The achievement of this polymers is typically initiated through a thermal annealing process, exploiting the catalytic properties of the metal substrate underneath [2].
Here, instead of using temperature as the driving force behind polymerization, we use a visible light source. 1D Stone-Wales-based polymers presenting a different termination than the ones observed after an annealing process are observed after exposing the precursor to a LED light source of 470 nm.
Scanning tunneling microscopy (STM) and spectroscopy (STS) reveal the electronic properties and tailor the topology of such nanomaterials.

[1] Facchetti, A. Chem. Mater. 2011, 23, 733–758.
[2] Cirera, B. et al. Nat. Nanotechnol. 2020, 15, 437–443.

Time-Resolved Measurements with THz-STM on Semiconducting MoTe2

Vibhuti RAI
Freie Universität Berlin, Department of Physics, Arnimallee 14,14195 Berlin, Germany

Dynamics of elementary excitations on surfaces are on the scale of nano- to pico-seconds. Hence, probing them requires an ultrafast measurement technique such as pump-probe scheme employing ultrashort laser pulses. Combining this with scanning tunnelling microscopy (STM) not only yields the required time resolution but also provides spatial resolution on a sub-nanometer scale [1]. In this work, we utilize our home-built THz-STM setup at 5K in ultra-high vacuum to study the charge dynamics of the bulk 2H-MoTe2. Through THz pump-probe measurements, we observe a temporally decaying oscillatory signal, suggesting the presence of coherent excitations [2]. The energies associated with these excitations imply coherent lattice vibrations or phonons. We also observe the influence of the local defects, as some of the excitations are only detected upon probing specific defect states.

[1] Cocker, et al. Nature Photonics 7, 620–625 (2013).
[3] Liu et al. Sci. Adv. 8, eabq5682 (2022).

Strong influence of plasmonic Au nanoparticles on two-magnon scattering of α-Fe2O3 nanostructures

Aida SERRANO
Instituto de Cerámica y Vidrio, CSIC

In this work we report an enhancement of two-magnon (i.e., spin waves) mode in α-Fe2O3 nanostructures through the localized surface plasmon excitation of Au nanoparticles deposited on top. The effect is observed and investigated by micro-Raman spectroscopy on Au/α-Fe2O3 heterostructures obtained from solid state dewetting of Fe and Au thin films in a process of two-steps. Varying the initial Fe thickness, we notice changes in the physical properties of samples: optical extinction signal of metallic nanoparticles is tuned and with that, their interaction with the α-Fe2O3 nanostructures. Under specific growth conditions, a coupling of spins of d-orbital electrons with the strongly localized electromagnetic field is locally observed at nanometer scale between Au and α-Fe2O3 nanostructures in contact and accompanied by a structural modification of the antiferromagnet material. This influence is a breakthrough for spintronics and magnonics without applying external magnetic fields.

Studying a single-molecule optoelectronic converter model

Martin ŠVEC
Institute of Physics CAS

Measuring photon-induced current over a single chromophore absorber with submolecular resolution provides information needed to identify the internal energy conversion pathways that lead to a net current. Understanding well such processes in molecules can lead to generally better organic-based optoelectronic devices. We investigate a single-molecule model in light-SPM under illumination using a differential photoconductance method in combination with the differential tunneling current spectroscopy. Spatial bias-dependent mapping reveals orbital-like patterns associated with particular internal energy conversion pathways, involving charge transfer and excitation/deexcitation mechanisms.

Electrically and mechanically decoupled single-molecule chromophores by tripodal scaffolds on gold

Michal VALÁŠEK
Karlsruhe Institute of Technology

Control of the molecular arrangement and spatial orientation of light-emitting molecules on metallic surfaces is of crucial importance for the construction of artificial photonic devices such as organic light-emitting diodes or single photon sources for quantum optical technologies. Our approach to achieve both an efficient decoupling of molecular chromophore and the spatial arrangement of functional molecules on gold surfaces is based on rigid multipodal scaffolds [1]. Series of functional molecular tripods based on tetraphenylmethane foot-structures have been prepared in order to analyze their arrangement and to investigate the mechanical and/or chemical manipulation of the protruding chromophore. Our particular focus is set on tripodal naphthalene diimide (NDI) chromophores with the intention to tune their optical properties by NDI-core substitution at the positions 2,6 and maintain their electronic decoupling [2]. Structurally improved NDI-chromophores on extended tripodal scaffolds are standing exclusively upright on Au(111) and thus enables both, efficient electrical and mechanical decoupling of individual chromophores from metallic leads [3]. The single molecule junction has an impressive efficiency of 10-3 photons per electron and is robust enough to allow for detailed STML experiments, including photon maps of an individual molecule. Furthermore, the chromophore mounted on the extended tripodal scaffold is also mechanically decoupled, increasing the lifetime of vibrational excited states indicated by hot luminescence bands.

[1] Valášek M.; Mayor M. Chem. Eur. J. 23, 13538–13548 (2017).
[2] Balzer N.; Lukášek J.; Valášek M.; Rai V.; Sun Q.; Gerhard L.; Wulfhekel W.; Mayor M. Chem. Eur. J. 27, 12144-12155 (2021).
[3] Rai V.; Balzer N.; Derenbach, G.; Holzer C.; Mayor M.; Wulfhekel W.; Gerhard L.; Valášek M. Nature Commun. 14, 8253 (2023).

Interactions between plasmons and excitons in single molecules

Miguel VAREA
Instituto IMDEA Nanociencia, Madrid

The interaction of localized plasmons and excitons in quantum emitters results in plexcitons, hybrid light-matter states, offering unique prospects for controlling single photon states. Scanning Tunneling Luminescence (STM-L) proves crucial in characterizing exciton-plasmon interactions, providing control over cavity dimensions and knowledge of molecular geometry. However, the incomplete comprehension of electron-tunneling luminescence processes hinders its full exploitation. Specifically, the optical behavior of metal-interfacing molecules lacks explanation when no insulation separates the molecule from the substrate. This study addresses this gap by studying changes in plasmonic modes within the cavity induced by organic molecules adsorbed on the metal surface. Despite a substantial drop in luminescence intensity due to the molecules, our analysis primarily links this decline to differences in the electronic structures of the molecules and the metal surface. By isolating the strictly optical effects of molecule presence, luminescence spectra become comparable, though not entirely identical. This contribution underscores the molecule-specific and aggregation-dependent nature of these modifications, paving the way for using STM-L to explore plasmon-exciton coupling at the nanoscale.

Light-matter interaction of field emission resonances in a scanning tunneling microscope

Alberto MARTÍN JIMÉNEZ
Instituto IMDEA Nanociencia, Madrid

The combination of scanning tunneling microscopy (STM) with laser light offers the unique possibility to investigate and control light-matter interaction at the atomic scale, which is critical for the development of novel technologies from diverse branches, such as quantum computing, optoelectronics, sensing, or catalysis, to mention a few. In our work, we investigate the effect of continuous wave (CW) laser illumination on the field emission resonances (FER) formed between a gold tip and an Ag(111) sample by measuring the derivative of the tunneling current as a function of the bias voltage. It was previously reported that the effect of CW illumination was that the lowest energy FER downshifts by the photon energy, being the hallmark of plasmon-assisted resonant tunneling [1]. We have extended these investigations and made a thorough experimental characterization of the effects induced by the laser power, tunneling current, and polarization of the excitation laser on the FERs. Interestingly, several peaks in the FER spectra appear/disappear upon laser illumination when varying polarization, laser power, or tunneling current, whose positions and intensities follow a non-trivial dependence. Our observations cannot be described only assuming plasmon-assisted resonant tunneling, indicating that the strong field confinement of the laser fields due to the tip-sample nanocavity may be responsible for the observed effects.

[1] Liu, S., Wolf, M., & Kumagai, T. (2018). Plasmon-assisted resonant electron tunneling in a
scanning tunneling microscope junction. Physical Review Letters, 121(22), 226802

2D Photocycloaddition? A Photonic and Thermal Study of a Three-Fold Symmetry Molecule on Metallic and Semiconductor Surfaces

Víctor VILLALOBOS VILDA
Instituto de Ciencia de Materiales de Madrid

On-surface synthesis (OSS) has revolutionized the way we synthesize and characterize molecules and nanostructures that are inaccessible in solution. One of the challenges of OSS is to achieve chemical reactions on non-metallic substrates to improve the applicability of these systems in practical devices.
Thermal reactions often fail on these substrates due to their low reactivity. This study proposes the use of photoinduced reactions, taking advantage of the surface properties to confine molecules, enhancing their interaction, and serving as a 2D canvas for the synthesis of nanostructures.
We focus on the [2+2] photocycloaddition of an α,β-unsaturated molecule with three ester groups on Au(111) and β-SnSe/Au(111) metal surfaces, and semiconductors α-SnSe/Au(111). Using STM and XPS, we investigate whether photonic and monolayer activation can induce the chemical reaction or if, on the contrary, thermal and/or multilayer activation are still necessary.

STM-Induced Luminescence of Ultrathin ZnO Films on Ag(111)

Henrik WIEDENHAUPT
Fritz-Haber-Institute of MPG

STM-induced luminescence (STML) offers a unique opportunity to study nanoscale optical properties and even at sub-molecular resolution. In this work, we use STML to gain insight into the optical properties of ultrathin ZnO. The previous studies revealed that the optical resonance between the interface state (IS) and conduction band edge (CBE) in the ZnO plays a crucial role in chemical enhancement in tip-enhanced Raman spectroscopy (TERS) and for the study of coherent phonons using photocurrent STM. In STML, we observe a bias polarity-dependent plasmonic emission, where at negative sample bias the STML resembles the plasmon response on Ag(111), but a bias-independent quenching of photon energies exceeding the IS-CBE energy is observed at positive sample bias. Together with spatially resolved STML, our results show that efficient light-emitting states reside near the CBE, which after charge injection into the CB serve as new initial states in the plasmonic decay.