A model for dynamical solvent control of molecular junction electronic properties

Experimental measurements of electron transport properties of molecular junctions are often performed in solvents. Solvent-molecule coupling and physical properties of the solvent can be used as the external stimulus to control electric current through a molecule. In this paper, we propose a model, which includes dynamical effects of solvent-molecule interaction in the non-equilibrium Green's function calculations of electric current. The solvent is considered as a macroscopic dipole moment that reorients stochastically and interacts with the electrons tunnelling through the molecular junction. The Keldysh-Kadanoff-Baym equations for electronic Green's functions are solved in time-domain with subsequent averaging over random realisations of rotational variables using Furutsu-Novikov method for exact closure of infinite hierarchy of stochastic correlation functions. The developed theory requires the use of wide-band approximation as well as classical treatment of solvent degrees of freedom. The theory is applied to a model molecular junction. It is demonstrated that not only electrostatic interaction between molecular junction and solvent but also solvent viscosity can be used to control electrical properties of the junction. Aligning of the rotating dipole moment breaks particle-hole symmetry of the transmission favouring either hole or electron transport channels depending upon the aligning potential

Signature of adsorbed solvents for molecular electronics revealed via scanning tunneling microscopy

After evaporation of the organic solvents, benzene, toluene, and cyclohexane on gold substrates, Scanning Tunneling Microscope (STM) shows the presence of a remaining adsorbed layer. The different solvent molecules were individually observed at ambient conditions, and their electronic transport properties characterized through the STM in the Break Junction approach. The combination of both techniques reveals, on one hand, that solvents are not fully evaporated over the gold electrode and, secondly, characterize the electronic transport of the solvents in molecular electronics.This work was supported by the Spanish Government (MAT2016-78625-C2 and PID2019-109539 GB-C41) and the Generalitat Valenciana through PROMETEO/2017/139 and program CDEIGENT/2018/028

Imaging intramolecular hydrogen migration with time- and momentum-resolved photoelectron diffraction

Imaging ultrafast hydrogen migration with few- or sub-femtosecond time resolution is a challenge for ultrafast spectroscopy due to the lightness and small scattering cross-section of the moving hydrogen atom. Here we propose time- and momentum-resolved photoelectron diffraction (TMR-PED) as a way to overcome limitations of existing methodologies and illustrate its performance in the ethanol molecule. By combining different theoretical methods, namely molecular dynamics and electron scattering methods, we show that TMR-PED, along with a judicious choice of the reference frame for multi-coincidence detection, allows for direct imaging of single and double hydrogen migration in doubly-charged ethanol with both few-fs and Å resolutions, all the way from its birth to the very end. It also provides hints of proton extraction following H2 roaming. The signature of hydrogen dynamics shows up in polarization-averaged molecular-frame photoelectron angular distributions (PA-MFPADs) as moving features that allow for a straightforward visualization in spaceThis work was performed under the European COST Action CA18222 AttoChem and Cooperative Research Program of ‘‘Network Joint Research Center for Materials and Devices.’’ K. H. acknowledges funding by JSPS KAKENHI under Grant No. 18K05027 and 17K04980. This work was partially funded by the Spanish Ministry of Science and Innovation – Ministerio Español de Ciencia e Innovación MICINN – projects PID2019-105458RB-I00 and PID2019-110091GB-I00, the Severo Ochoa Programme for Centres of Excellence in R & D (SEV-2016-0686) and the María de Maeztu Programme for Units of Excellence in R & D (CEX2018-000805-M

CMInject:Python framework for the numerical simulation of nanoparticle injection pipelines

CMInject simulates nanoparticle injection experiments of particles with diameters in the micrometer to nanometer-regime, e.g., for single-particle-imaging experiments. Particle-particle interactions and particle-induced changes in the surrounding fields are disregarded, due to low nanoparticle concentration in these experiments. CMInject's focus lies on the correct modeling of different forces on such particles, such as fluid-dynamics or light-induced interactions, to allow for simulations that further the scientific development of nanoparticle injection pipelines. To provide a usable basis for this framework and allow for a variety of experiments to be simulated, we implemented first specific force models: fluid drag forces, Brownian motion, and photophoretic forces. For verification, we benchmarked a drag-force-based simulation against a nanoparticle focusing experiment. We envision its use and further development by experimentalists, theorists, and software developers. Program summary: Program Title: CMInject CPC Library link to program files: https://doi.org/10.17632/rbpgn4fk3z.1 Developer's repository link: https://github.com/cfel-cmi/cminject Code Ocean capsule: https://codeocean.com/capsule/5146104 Licensing provisions: GPLv3 Programming language: Python 3 Supplementary material: Code to reproduce and analyze simulation results, example input and output data, video files of trajectory movies Nature of problem: Well-defined, reproducible, and interchangeable simulation setups of experimental injection pipelines for biological and artificial nanoparticles, in particular such pipelines that aim to advance the field of single-particle imaging. Solution method: The definition and implementation of an extensible Python 3 framework to model and execute such simulation setups based on object-oriented software design, making use of parallelization facilities and modern numerical integration routines. Additional comments including restrictions and unusual features: Supplementary executable scripts for quantitative and visual analyses of result data are also part of the framework

Cosmic-Ray Anisotropies in Right Ascension Measured by the Pierre Auger Observatory

We present measurements of the large-scale cosmic-ray (CR) anisotropies in R.A., using data collected by the surface detector array of the Pierre Auger Observatory over more than 14 yr. We determine the equatorial dipole component, through a Fourier analysis in R.A. that includes weights for each event so as to account for the main detector-induced systematic effects. For the energies at which the trigger efficiency of the array is small, the east-west method is employed. Besides using the data from the array with detectors separated by 1500 m, we also include data from the smaller but denser subarray of detectors with 750 m separation, which allows us to extend the analysis down to ∼0.03 EeV. The most significant equatorial dipole amplitude obtained is that in the cumulative bin above 8 EeV, %, which is inconsistent with isotropy at the 6σ level. In the bins below 8 EeV, we obtain 99% CL upper bounds on d ⊥ at the level of 1%-3%. At energies below 1 EeV, even though the amplitudes are not significant, the phases determined in most of the bins are not far from the R.A. of the Galactic center, at GC =-94°, suggesting a predominantly Galactic origin for anisotropies at these energies. The reconstructed dipole phases in the energy bins above 4 EeV point instead to R.A. that are almost opposite to the Galactic center one, indicative of an extragalactic CR origin

Uno studio sulla massima deflessione degli ultra-high-energy cosmic rays da parte dei campi magnetici primordiali

Gli Ultra-High-Energy Cosmic Rays sono dei raggi cosmici-dotati di energia estremamente elevata-che raggiungono la Terra con un bassissimo rateo e dei quali abbiamo pochi dati a riguardo; le incertezze riguardano la loro composizione, la loro sorgente, i metodi di accelerazione e le caratteristiche dei campi magnetici che li deviano durante il loro cammino. L’obiettivo di questo studio è determinare quali modelli di campo magnetico possano descrivere correttamente la propagazione degli UHECRs, andando a fare un confronto con i dati sperimentali a disposizione; infatti, quello che osserviamo è una distribuzione isotropa nel cielo e, di conseguenza, i modelli teorici di propagazione, per poter essere accettati, devono rispecchiare tale comportamento. Sono stati testati nove modelli di campo magnetico tratti da simulazioni cosmologiche, andando a considerare due diverse composizione per i CRs (simil-ferro e simil-protone) e il risultato ha dato delle risposte positive solo per tre di essi. Tali modelli, per cui troviamo accordo, sono caratterizzati da una scala di inomegeneità più ampia rispetto a quella dei modelli scartati, infatti, analizzando il loro spettro di potenza, il maggior contributo è dato da fluttuazioni di campo magnetico su scale di 10 Mpc. Ciò naturalmente, viste anche le poche informazioni riguardo ai campi magnetici intergalattici, ci porta a pensare che campi di questo tipo siano favoriti. Inoltre, per tali modelli, gli esiti sono risultati particolarmente in accordo con i dati sperimentali, considerando CRs con composizione simile al ferro: ciò fa pensare che tale composizione possa essere quella effettiva

Radio Measurements of Cosmic Rays at the South Pole

Die ultrahochenergetische kosmische Strahlung, die in der Erdatmosphäre massive Teilchenkaskaden (ausgedehnt Luftschauer) auslöst, kann am Erdboden mit Hilfe von Detektorfeldern gemessen werden. Unter den verschiedenen Detektoren, die zum Einsatz kommen, haben Radioantennen im letzten Jahrzehnt an Bedeutung gewonnen, da sie eine einzigartige Möglichkeit bieten diese Luftschauer zu untersuchen. Die Radioemission, die während der Entwicklung des Luftschauers hauptsächlich durch die Ablenkung der Elektronen und Positronen in der Teilchenkaskade durch das Erdmagnetfeld entsteht, enthält Informationen über die Art der Teilchen, die den Schauer ausgelöst haben. Insbesondere können Radioantennen zusammen mit Fluoreszenzteleskopen die Position des Maximums der Entwicklung des Luftschauers $X_\mathrm{max}$ rekonstruieren. Dieser rekonstruierte Parameter ist abhängig von der Art des primären Atomkerns der kosmischen Strahlung, die den Luftschauer ausgelöst hat. Die Kenntnis des Typs der kosmischen Strahlung wiederum trägt zu einem besseren Verständnis der Beschleunigungsprozesse astrophysikalischer Quellen in unserem Universum bei. Das IceCube Neutrino Observatorium am geografischen Südpol ist ein Mehrzweckdetektor, der sowohl astrophysikalische Neutrinos, als auch Luftschauer nachweisen kann, insbesondere mit seinem Oberflächendetektor, IceTop. Um IceTop als Detektor für kosmische Strahlung zu verbessern und die Auswirkungen der Schneeansammlung abzuschwächen, soll in den kommenden Jahren ein hybrider Dektector aus anhebbaren Szintillationsplatten und Radioantennen installiert werden. Dieser Sub-Detektor wird aus 32 Stationen bestehen, die jeweils 8 Szintillationspaneele und 3 Antennen umfassen und eine Fläche von 1 km$^2$ abdecken. Die Radioantennen nutzen mit 70 bis 350 MHz statt 30 bis 80 MHz ein höheres Frequenzband als bisher üblich. Der erste vollständige Prototyp einer Hybridstation wurde im Januar 2020 in Betrieb genommen. Diese Arbeit behandelt die Hardware der Prototyp-Station und der zukünftigen geplanten Stationen, die Inbetriebnahme der Daten der Prototyp-Station sowie eine Methode zur Energie- und $X_\text{max}$-Rekonstruktion, die auf der Grundlage gemessener Ereignisse und Monte-Carlo-Simulationen entwickelt wurde. Insbesondere wurde eine Struktur zum Anheben der Antennen über dem Schnee entworfen, gebaut, im Feld getestet und produziert, zusammen mit einer Radio-Frontend-Platine für die analoge Vorverarbeitung des von den Antennen empfangenen Signals. Die Kalibrierung der anderen Radiosignalkomponenten bei verschiedenen Temperaturen erreicht eine Amplitudenunsicherheit von nur 3,9%, was deutlich unter der geforderten Unsicherheit von 10% für die Radio-Signalkette liegt. Die Funktionsweise der Detektoren wurde durch die Analyse des Radio-Untergrunds unter Verwendung der entwickelten Radio-Datenanalysekette bestätigt. Es wurden insgesamt 121 Luftschauer nachgewiesen, von denen 5 auch durch die anderen Detektoren nachgewiesen wurden. Sechszehn Luftschauer wurden verwendet, um die erste Energie- und $X_\text{max}$-Rekonstruktionsmethode für die Radiokomponente der Detektorerweiterung zu entwickeln. Diese Rekonstruktionsmethode basiert auf dem neuesten Stand der Technik für Radio-Detektoren. Es wurde eine Analyse des Einflusses des Radio-Untergrundes auf das Signal durchgeführt. Anschließend wird die üblicherweise verwendete Methode der $\chi^2$-Minimierung durch eine Log-Likelihood-Minimierung mit einer Parametrisierung des Rauschens ersetzt, und es wird gezeigt, dass diese Technik mit den gemessenen Daten funktioniert. Darüber hinaus zeigt sich, dass bei denselben rekonstruierten Ereignissen das Hochfrequenzband mit den nur drei Antennen der Prototypstation eine deutlich bessere Genauigkeit als das traditionelle Niedrigfrequenzband aufweist. Sobald der gesamte Detektor fertiggestellt ist, wird die erwartete Rekonstruktionsgenauigkeit auf 15 g/cm$^2$ für $X_\text{max}$ und besser als 10% für die Energie geschätzt