arXiv subjects

Emanuel Lörtscher

Publications and source records attributed to Emanuel Lörtscher.

3 recordsLinked to original sources

arXiv2024

Light Emission and Conductance Fluctuations in Electrically Driven and Plasmonically Enhanced Molecular Junctions

Electrically connected and plasmonically enhanced molecular junctions combine the optical functionalities of high field confinement and enhancement (cavity function), and of high radiative efficiency (antenna function) with the electrical functionalities of molecular transport. Such combined optical and electrical probes have proven useful for the fundamental understanding of metal-molecule contacts and contribute to the development of nanoscale optoelectronic devices including ultrafast electronics and nanosensors. Here, we employ a self-assembled metal-molecule-metal junction with a nanoparticle bridge to investigate correlated fluctuations in conductance and tunneling-induced light emission at room temperature. Despite the presence of hundreds of molecules in the junction, the electrical conductance and light emission are both highly sensitive to atomic-scale fluctuations -- a phenomenology reminiscent of picocavities observed in Raman scattering and of luminescence blinking from photo-excited plasmonic junctions. Discrete steps in conductance associated with fluctuating emission intensities through the multiple plasmonic modes of the junction are consistent with a finite number of randomly localized, point-like sources dominating the optoelectronic response. Contrasting with these microscopic fluctuations, the overall plasmonic and electronic functionalities of our devices feature long-term survival at room temperature and under an electrical bias of a few volts, allowing for measurements over several months.

cond-mat.mes-hall↗

arXiv2022

Thermal Simulation and Experimental Analysis of Optically Pumped InP-on-Si Micro- and Nanocavity Lasers

There is a general trend of downscaling laser cavities, but with high integration and energy densities of nanocavity lasers, signifi-cant thermal issues affect their operation. The complexity of geometrical parameters and the various materials involved hinder the extraction of clear design guidelines and operation strategies. Here, we present a systematic thermal analysis of InP-on-Si micro- and nanocavity lasers based on steady-state and transient thermal simulations and experimental analysis. In particular, we investi-gated the use of metal cavities for improving the thermal properties of InP-on-Si micro- and nanocavity lasers. Heating of lasers is studied by using Raman thermometry and the results agree well with simulation results, both reveal a temperature reduction of hundreds of kelvins for the metal-clad cavity. Transient simulations are carried out to improve our understanding of the dynamic temperature variation under pulsed and continuous-wave pumping conditions. The results show that the presence of a metal clad-ding not only increases the overall efficiency in heat dissipation, but also causes a much faster temperature response. Together with optical experimental results under pulsed pumping, we conclude that a pulse width of 10 ns and repetition rate of 100 kHz is the optimal pumping condition for a 2 micrometer wide square cavity.

physics.optics↗

arXiv2015

High-Conductive Organometallic Molecular Wires with Delocalized Electron Systems Strongly Coupled to Metal Electrodes

Besides active, functional molecular building blocks such as diodes or switches, passive components as, e.g., molecular wires, are required to realize molecular-scale electronics. Incorporating metal centers in the molecular backbone enables the molecular energy levels to be tuned in respect to the Fermi energy of the electrodes. Furthermore, by using more than one metal center and sp-bridging ligands, a strongly delocalized electron system is formed between these metallic "dopants", facilitating transport along the molecular backbone. Here, we study the influence of molecule--metal coupling on charge transport of dinuclear X(PP)$_2$FeC$_4$Fe(PP)$_2$X molecular wires (PP = Et$_2$PCH$_2$CH$_2$PEt$_2$); X = CN (1), NCS (2), NCSe (3), C$_4$SnMe$_3$ (4) and C$_2$SnMe$_3$ (5)) under ultra-high vacuum and variable temperature conditions. In contrast to 1 which showed unstable junctions at very low conductance ($8.1\cdot10^{-7}$ G$_0$), 4 formed a Au-C$_4$FeC$_4$FeC$_4$-Au junction 4' after SnMe$_3$ extrusion which revealed a conductance of $8.9\cdot10^{-3}$ G$_0$, three orders of magnitude higher than for 2 ($7.9\cdot10^{-6}$ G$_0$) and two orders of magnitude higher than for 3 ($3.8\cdot10^{-4}$ G$_0$). Density functional theory (DFT) confirmed the experimental trend in the conductance for the various anchoring motifs. The strong hybridization of molecular and metal states found in the C--Au coupling case enables the delocalized electronic system of the organometallic Fe$_2$ backbone to be extended over the molecule-metal interfaces to the metal electrodes to establish high-conductive molecular wires.

cond-mat.mes-hall↗