arXiv subjects

Pablo Merino

Publications and source records attributed to Pablo Merino.

23 records · Page 2Linked to original sources

arXiv2019

Single Photon Emission from a Plasmonic Light Source Driven by a Local Field-Induced Coulomb Blockade

A hallmark of quantum control is the ability to manipulate quantum emission at the nanoscale. Through scanning tunneling microscopy induced luminescence (STML) we are able to generate plasmonic light originating from inelastic tunneling processes that occur in a few-nanometer thick molecular film of C$_{60}$ deposited on Ag(111). Single photon emission, not of excitonic origin, occurs with a 1/$e$ lifetime of a tenth of a nanosecond or less, as shown through Hanbury Brown and Twiss photon intensity interferometry. We have performed tight-binding calculations of the electronic structure for the combined Ag-C$_{60}$-tip system and obtained good agreement with experiment. The tunneling happens through electric field induced split-off states below the C$_{60}$ LUMO band, which leads to a Coulomb blockade effect and single photon emission. The use of split-off states is shown to be a general technique that has special relevance for narrowband materials with a large bandgap.

cond-mat.mes-hall↗

arXiv2019

Charge carrier injection electroluminescence with CO functionalized tips on single molecular emitters

We investigate electroluminescence of single molecular emitters on NaCl on Ag(111) and Au(111) with submolecular resolution in a low-temperature scanning probe microscope with tunneling current, atomic force and light detection capabilities. Role of the tip state is studied in the photon maps of a prototypical emitter, zinc phthalocyanine (ZnPc), using metal and CO-metal tips. CO-functionalization is found to have a dramatic impact on the resolution and contrast of the photon maps due to the localized overlap of the p-orbitals on the tip with the molecular orbitals of the emitter. The possibility of using the same CO-functionalized tip for tip-enhanced photon detection and high resolution atomic force is demonstrated. We study the electroluminescence of ZnPc, induced by charge carrier injection at sufficiently high bias voltages. We propose that the distinct level alignment of the ZnPc frontier orbital with the Au(111) and Ag(111) Fermi levels governs the primary excitation mechanisms as the injection of electrons and holes from the tip into the molecule, respectively. These findings put forward the importance of the tip status in the photon maps and contribute to a better understanding of the photophysics of organic molecules on surfaces.

cond-mat.mes-hall↗

arXiv2018

A single hydrogen molecule as an intensity chopper in an electrically-driven plasmonic nanocavity

Photon statistics is a powerful tool for characterizing the emission dynamics of nanoscopic systems and their photophysics. Recent advances that combine correlation spectroscopy with scanning tunneling microscopy-induced luminescence (STML) have allowed measuring the emission dynamics from individual molecules and defects demonstrating their nature as single photon emitters. The application of correlation spectroscopy to the analysis of the dynamics of a well-characterized adsorbate system in ultrahigh vacuum remained to be shown. Here we combine single photon time correlations with STML to measure the dynamics of individual $H_2$ molecules between a gold tip and a Au(111) surface. An adsorbed $H_2$ molecule performs recurrent excursions below the tip apex. We use the fact that the presence of the $H_2$ molecule in the junction modifies plasmon emission to study the adsorbate dynamics. Using the $H_2$ molecule as a chopper for STM-induced optical emission intensity we demonstrate bunching in the plasmonic photon train in a single measurement over six orders of magnitude in the time domain (from microseconds to seconds) that takes only a few seconds. Our findings illustrate the power of using photon statistics to measure the diffusion dynamics of adsorbates with STML.

cond-mat.mes-hall↗

arXiv2018

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$_{60}$ 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.

cond-mat.mes-hall↗

arXiv2014

Silicene vs. ordered 2D silicide: the atomic and electronic structure of the Si-$(\sqrt{19}\times\sqrt{19})R23.4^{\circ}$/Pt(111) surface reconstruction

We discuss the possibility of a 2D ordered structure formed upon deposition of Si on metal surfaces. We investigate the atomic and electronic structure of the Si-$(\sqrt{19}\times\sqrt{19})R23.4^{\circ}$/Pt(111) surface reconstruction by means of a set of experimental surface-science techniques supported by theoretical calculations. The theory achieves a very good agreement with the experimental results and corroborate beyond any doubt that this phase is a surface alloy consisting of Si$_3$Pt tetramers that resembles a twisted Kagome lattice. These findings render unlikely any formation of silicene or germanene on Pt(111) and other transition metal surfaces.

cond-mat.mtrl-sci↗