-
Topological Woodward-Hoffmann classification for cycloadditions in polycyclic aromatic azomethine ylides
Authors:
Juan Li,
Amir Mirzanejad,
Wen-Han Dong,
Kun Liu,
Marcus Richter,
Xiao-Ye Wang,
Reinhard Berger,
Shixuan Du,
Willi Auwärter,
Johannes V. Barth,
Ji Ma,
Klaus Müllen,
Xinliang Feng,
Jia-Tao Sun,
Lukas Muechler,
Carlos-Andres Palma
Abstract:
The study of cycloaddition mechanisms is central to the fabrication of extended sp2 carbon nanostructures. Reaction modeling in this context has focused mostly on putative, energetically preferred, exothermic products with limited consideration for symmetry allowed or forbidden mechanistic effects. Here, we introduce a scheme for classifying symmetry-forbidden reaction coordinates in Woodward-Hoff…
▽ More
The study of cycloaddition mechanisms is central to the fabrication of extended sp2 carbon nanostructures. Reaction modeling in this context has focused mostly on putative, energetically preferred, exothermic products with limited consideration for symmetry allowed or forbidden mechanistic effects. Here, we introduce a scheme for classifying symmetry-forbidden reaction coordinates in Woodward-Hoffmann correlation diagrams. Topological classifiers grant access to the study of reaction pathways and correlation diagrams in the same footing, for the purpose of elucidating mechanisms and products of polycyclic aromatic azomethine ylide (PAMY) cycloadditions with pentacene-yielding polycyclic aromatic hydrocarbons with an isoindole core in the solid-state and on surfaces as characterized by mass spectrometry and scanning tunneling microscopy, respectively. By means of a tight-binding reaction model and density functional theory (DFT) we find topologically-allowed pathways if a product is endothermic, and topologically-forbidden if a product is exothermic. Our work unveils topological classification as a crucial element for reaction modeling for nanographene engineering, and highlights its fundamental role in the design of cycloadditions in on-surface and solid-state chemical reactions, while underscoring that exothermic pathways can be topologically-forbidden.
△ Less
Submitted 1 August, 2024; v1 submitted 31 July, 2024;
originally announced July 2024.
-
Optimizing the Ullmann coupling reaction efficiency on an oxide surface by metal atom addition
Authors:
Mikel Abadia,
Ignacio Piquero-Zulaica,
Jens Brede,
Alberto Verdini,
Luca Floreano,
Johannes V. Barth,
Jorge Lobo-Checa,
Martina Corso,
Celia Rogero
Abstract:
The bottom-up synthesis of carbon based nanomaterials directly on semiconductor surfaces allows to decouple their electronic and magnetic properties from the substrates. However, the lack of reactivity on these non-metallic surfaces hinders or reduces significantly the yield of these reactions. Such hurdles practically precludes transferring bottom-up synthesis strategies onto semiconducting and i…
▽ More
The bottom-up synthesis of carbon based nanomaterials directly on semiconductor surfaces allows to decouple their electronic and magnetic properties from the substrates. However, the lack of reactivity on these non-metallic surfaces hinders or reduces significantly the yield of these reactions. Such hurdles practically precludes transferring bottom-up synthesis strategies onto semiconducting and insulating surfaces. Here, we achieve a high polymerization yield of terphenyl molecules on the semiconductor TiO$_2$(110) surface by incorporating cobalt atoms as catalysts in the Ullmann coupling reaction. Cobalt atoms trigger the debromination of 4,4-dibromo-p-terphenyl (DBTP) molecules on TiO$_2$(110) and the formation of an intermediate organometallic phase already at room-temperature (RT). As the debromination temperature is drastically reduced, the homo-coupling temperature is also significantly lowered, preventing the desorption of DBTP molecules from the TiO$_2$(110) surface and leading to a radical improvement on the poly-para-phenylene (PPP) polymerization yield. The universality of this mechanism is demonstrated with an iodinated terphenyl derivative (DITP), which shows analogous dehalogenation and polymerization temperatures with a very similar reaction yield. Consequently, we propose to use minute amounts of metal catalyst to drive forward generic bottom-up synthesis strategies on non-metallic surfaces.
△ Less
Submitted 20 June, 2023;
originally announced June 2023.
-
Engineering interfacial quantum states and electronic landscapes by molecular nanoarchitectures
Authors:
Ignacio Piquero-Zulaica,
Jorge Lobo-Checa,
Zakaria M. Abd El-Fattah,
J. Enrique Ortega,
Florian Klappenberger,
Willi Auwärter,
Johannes V. Barth
Abstract:
Surfaces are at the frontier of every known solid. They provide versatile supports for functional nanostructures and mediate essential physicochemical processes. Being intimately related with 2D materials, interfaces and atomically thin films often feature distinct electronic states with respect to the bulk, which are key for many relevant properties, such as catalytic activity, interfacial charge…
▽ More
Surfaces are at the frontier of every known solid. They provide versatile supports for functional nanostructures and mediate essential physicochemical processes. Being intimately related with 2D materials, interfaces and atomically thin films often feature distinct electronic states with respect to the bulk, which are key for many relevant properties, such as catalytic activity, interfacial charge-transfer, or crystal growth mechanisms. Of particular interest is reducing the surface electrons' dimensionality and spread with atomic precision, to induce novel quantum properties via lateral scattering and confinement. Both atomic manipulation and supramolecular principles provide access to custom-designed molecular superlattices, which tailor the surface electronic landscape and influence fundamental chemical and physical properties at the nanoscale. Herein, we review the confinement of surface state electrons focusing on their interaction with molecule-based scaffolds created by molecular manipulation and self-assembly protocols under ultrahigh vacuum conditions. Starting from the quasi-free 2D electron gas present at the (111)-terminated surface planes of noble metals, we illustrate the enhanced molecule-based structural complexity and versatility compared to simple atoms. We survey low-dimensional confining structures in the form of artificial lattices, molecular nanogratings or quantum dot arrays, which are constructed upon appropriate choice of their building constituents. Whenever the realized (metal-)organic networks exhibit long-range order, modified surface band structures with characteristic features emerge, revealing intriguing physical properties, such as discretization, quantum coupling or energy and effective mass renormalization. Such collective electronic states can be additionally modified by positioning guest species at the voids of open nanoarchitectures [...].
△ Less
Submitted 21 July, 2021;
originally announced July 2021.
-
Cyano-functionalized Ag-bis-acetylide wires on Ag(110)
Authors:
Raphael Hellwig,
Martin Uphoff,
Yiqi Zhang,
Mateusz Paszkiewicz,
Liding Zhang,
Ping Du,
Mario Ruben,
Florian Klappenberger,
Johannes V. Barth
Abstract:
Organometallic nanostructures are promising candidates for applications in optoelectronics, magnetism and catalysis. Our bottom-up approach employs a cyano-functionalized terminal alkyne species (CN-DETP) on the Ag(110) surface to fabricate 2D domains of regularly stacked Ag-acetylide nanowires. We unravel their adsorption properties and give evidence to their organometallic character with the aid…
▽ More
Organometallic nanostructures are promising candidates for applications in optoelectronics, magnetism and catalysis. Our bottom-up approach employs a cyano-functionalized terminal alkyne species (CN-DETP) on the Ag(110) surface to fabricate 2D domains of regularly stacked Ag-acetylide nanowires. We unravel their adsorption properties and give evidence to their organometallic character with the aid of complementary surface-sensitive techniques, i.e. scanning tunneling microscopy, X-ray photoelectron spectroscopy and near-edge X-ray absorption fine-structure spectroscopy. Guided by the anisotropic (110) surface, highly oriented nanowires form in two enantiomorphic domains of regularly stacked trans isomers, whereby the bifunctional design of CN-DETP gives rise to orthogonal bonding motifs. Based on STM imaging, we find high thermal stability of the Ag-bis-acetylide wires, without conversion into graphdiyne chains. Our approach based on orthogonal bifunctionalization and selective functional group recognition extends the toolbox of creating alkyne-based nanostructures at interfaces.
△ Less
Submitted 13 July, 2019;
originally announced July 2019.
-
Local adsorption structure and bonding of porphine on Cu(111) before and after self-metalation
Authors:
D. A. Duncan,
P. Casado Aguilar,
M. Paszkiewicz,
K. Diller,
F. Bondino,
E. Magnano,
F. Klappenberger,
I. Píš,
A. Rubio,
J. V. Barth,
A. Pérez Paz,
F. Allegretti
Abstract:
We have experimentally determined the lateral registry and geometric structure of free-base porphine (2H-P) and copper-metalated porphine (Cu-P) adsorbed on Cu(111), by means of energy-scanned photoelectron diffraction (PhD), and compared the experimental results to density functional theory (DFT) calculations that included van der Waals corrections within the Tkatchenko-Scheffler approach. Both 2…
▽ More
We have experimentally determined the lateral registry and geometric structure of free-base porphine (2H-P) and copper-metalated porphine (Cu-P) adsorbed on Cu(111), by means of energy-scanned photoelectron diffraction (PhD), and compared the experimental results to density functional theory (DFT) calculations that included van der Waals corrections within the Tkatchenko-Scheffler approach. Both 2H-P and Cu-P adsorb with their center above a surface bridge site. Consistency is obtained between the experimental and DFT-predicted structural models, with a characteristic change in the corrugation of the four N atoms of the molecule's macrocycle following metalation. Interestingly, comparison with previously published data for cobalt porphine adsorbed on the same surface evidences a distinct increase in the average height of the N atoms above the surface through the series 2H-P, Cu-P, cobalt porphine. Such an increase strikingly anti-correlates the DFT-predicted adsorption strength, with 2H-P having the smallest adsorption height despite the weakest calculated adsorption energy. In addition, our findings suggest that for these macrocyclic compounds, substrate-to-molecule charge transfer and adsorption strength may not be univocally correlated.
△ Less
Submitted 6 May, 2019;
originally announced May 2019.
-
Letter of Intent: A New QCD facility at the M2 beam line of the CERN SPS (COMPASS++/AMBER)
Authors:
B. Adams,
C. A. Aidala,
R. Akhunzyanov,
G. D. Alexeev,
M. G. Alexeev,
A. Amoroso,
V. Andrieux,
N. V. Anfimov,
V. Anosov,
A. Antoshkin,
K. Augsten,
W. Augustyniak,
C. D. R. Azevedo,
A. Azhibekov,
B. Badelek,
F. Balestra,
M. Ball,
J. Barth,
R. Beck,
Y. Bedfer,
J. Berenguer Antequera,
J. C. Bernauer,
J. Bernhard,
M. Bodlak,
P. Bordalo
, et al. (242 additional authors not shown)
Abstract:
A New QCD facility at the M2 beam line of the CERN SPS
COMPASS++/AMBER
A New QCD facility at the M2 beam line of the CERN SPS
COMPASS++/AMBER
△ Less
Submitted 25 January, 2019; v1 submitted 2 August, 2018;
originally announced August 2018.
-
A high-resolution carbon balance in a temperate catchment: insights from the Schwabach River, Germany
Authors:
Kern Y. Lee,
Robert van Geldern,
Johannes A. C. Barth
Abstract:
This study examines stable carbon isotope (d13C) and concentration dynamics of DIC, DOC, and POC over an entire year, using a high resolution dataset. This research was performed in the catchment of the Schwabach River, a small, karstic headwater stream in Germany. The DIC data indicated the dominance of mineral weathering as a DIC source, with a dilution effect during high flow periods. A weakly…
▽ More
This study examines stable carbon isotope (d13C) and concentration dynamics of DIC, DOC, and POC over an entire year, using a high resolution dataset. This research was performed in the catchment of the Schwabach River, a small, karstic headwater stream in Germany. The DIC data indicated the dominance of mineral weathering as a DIC source, with a dilution effect during high flow periods. A weakly negative relationship between discharge and d13CDIC indicates an increase in plant-derived organic matter during floods, transported to river waters via overland runoff and intermediate flow. DOC inputs were enhanced during periods of high discharge, indicating a greater importance of overland runoff as a DOC source. POC concentrations seem unaffected by discharge, but a slight negative correlation between d13CPOC and discharge may be derived from increased C4 plant material inputs. CO2 concentrations exceeded ambient atmospheric values throughout the year, confirming that the river surface waters are a net CO2 source. The total riverine carbon flux was dominated by DIC (70%), followed by CO2 efflux (21%), DOC (7%), and POC (2%). While a bi-monthly sampling scheme yielded a similar carbon flux estimate to that utilizing the entire dataset, the use of a monthly sampling interval differed by up to 19%. This discrepancy is due to the inability of a monthly sampling scheme to capture sudden and large variations in river discharge and associated dissolved/particulate carbon concentration changes, such as those observed during flooding. Bi-monthly sampling may be the minimum timeframe required for an acceptable degree of accuracy in carbon flux calculations. The application of high sampling frequencies and comprehensive DIC, DOC, and POC studies in future research would reduce uncertainties in riverine carbon budgets, and clarify the role of small streams in the global carbon cycle.
△ Less
Submitted 11 June, 2018; v1 submitted 8 June, 2018;
originally announced June 2018.
-
Sub-cycle optical control of current in a semiconductor: from the multiphoton to the tunneling regime
Authors:
Tim Paasch-Colberg,
Stanislav Yu. Kruchinin,
Özge Sağlam,
Stefan Kapser,
Stefano Cabrini,
Sascha Muehlbrandt,
Joachim Reichert,
Johannes V. Barth,
Ralph Ernstorfer,
Reinhard Kienberger,
Vladislav S. Yakovlev,
Nicholas Karpowicz,
Agustin Schiffrin
Abstract:
Nonlinear interactions between ultrashort optical waveforms and solids can be used to induce and steer electric current on a femtosecond (fs) timescale, holding promise for electronic signal processing at PHz frequencies [Nature 493, 70 (2013)]. So far, this approach has been limited to insulators, requiring extremely strong peak electric fields and intensities. Here, we show all-optical generatio…
▽ More
Nonlinear interactions between ultrashort optical waveforms and solids can be used to induce and steer electric current on a femtosecond (fs) timescale, holding promise for electronic signal processing at PHz frequencies [Nature 493, 70 (2013)]. So far, this approach has been limited to insulators, requiring extremely strong peak electric fields and intensities. Here, we show all-optical generation and control of directly measurable electric current in a semiconductor relevant for high-speed and high-power (opto)electronics, gallium nitride (GaN), within an optical cycle and on a timescale shorter than 2 fs, at intensities at least an order of magnitude lower than those required for dielectrics. Our approach opens the door to PHz electronics and metrology, applicable to low-power (non-amplified) laser pulses, and may lead to future applications in semiconductor and photonic integrated circuit technologies.
△ Less
Submitted 2 November, 2016; v1 submitted 5 August, 2016;
originally announced August 2016.
-
The COMPASS Setup for Physics with Hadron Beams
Authors:
Ph. Abbon,
C. Adolph,
R. Akhunzyanov,
Yu. Alexandrov,
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
V. Anosov,
A. Austregesilo,
B. Badelek,
F. Balestra,
J. Barth,
G. Baum,
R. Beck,
Y. Bedfer,
A. Berlin,
J. Bernhard,
K. Bicker,
E. R. Bielert,
J. Bieling,
R. Birsa,
J. Bisplinghoff,
M. Bodlak,
M. Boer
, et al. (207 additional authors not shown)
Abstract:
The main characteristics of the COMPASS experimental setup for physics with hadron beams are described. This setup was designed to perform exclusive measurements of processes with several charged and/or neutral particles in the final state. Making use of a large part of the apparatus that was previously built for spin structure studies with a muon beam, it also features a new target system as well…
▽ More
The main characteristics of the COMPASS experimental setup for physics with hadron beams are described. This setup was designed to perform exclusive measurements of processes with several charged and/or neutral particles in the final state. Making use of a large part of the apparatus that was previously built for spin structure studies with a muon beam, it also features a new target system as well as new or upgraded detectors. The hadron setup is able to operate at the high incident hadron flux available at CERN. It is characterised by large angular and momentum coverages, large and nearly flat acceptances, and good two and three-particle mass resolutions. In 2008 and 2009 it was successfully used with positive and negative hadron beams and with liquid hydrogen and solid nuclear targets. This article describes the new and upgraded detectors and auxiliary equipment, outlines the reconstruction procedures used, and summarises the general performance of the setup.
△ Less
Submitted 7 October, 2014;
originally announced October 2014.
-
Visualization and thermodynamic encoding of single-molecule partition functions
Authors:
Carlos-Andres Palma,
Jonas Björk,
Florian Klappenberger,
Emmanuel Arras,
Dirk Kühne,
Sven Stafström,
Johannes V. Barth
Abstract:
Ensemble averaging of molecular states is fundamental for the experimental determination of thermodynamic quantities. A special case occurs for single-molecule investigations under equilibrium conditions, for which free energy, entropy and enthalpy at finite-temperatures are challenging to determine with ensemble-averaging alone. Here, we provide a method to access single-molecule thermodynamics,…
▽ More
Ensemble averaging of molecular states is fundamental for the experimental determination of thermodynamic quantities. A special case occurs for single-molecule investigations under equilibrium conditions, for which free energy, entropy and enthalpy at finite-temperatures are challenging to determine with ensemble-averaging alone. Here, we provide a method to access single-molecule thermodynamics, by confining an individual molecule to a nanoscopic pore of a two-dimensional metal-organic nanomesh, where we directly record finite-temperature time-averaged statistical weights using temperature-controlled scanning tunneling microscopy. The obtained patterns represent a real space equilibrium probability distribution. We associate this distribution with a partition function projection to assess spatially resolved thermodynamic quantities, by means of computational modeling. The presented molecular dynamics based Boltzmann weighting model is able to reproduce experimentally observed molecular states with high accuracy. By an in-silico customized energy landscape we demonstrate that distinct probability distributions can be encrypted at different temperatures. Such modulation provides means to encode and decode information into position-temperature space or to realize nanoscopic thermal probes.
△ Less
Submitted 27 July, 2014;
originally announced July 2014.
-
Implementation of mean-timing and subsequent logic functions on an FPGA
Authors:
J. Bieling,
G. Ahluwalia,
J. Barth,
F. Klein,
J. Pretz,
H. Fischer,
F. Herrmann,
C. Schill,
S. Schopferer
Abstract:
This article describes the implementation of a mean-timer and coincidence logic on a Virtex-5 FPGA for trigger purposes in a particle physics experiment. The novel feature is that the mean-timing and the coincidence logic are not synchronized with a clock which allows for a higher resolution of approximately 400 ps, not limited by a clock frequency.
This article describes the implementation of a mean-timer and coincidence logic on a Virtex-5 FPGA for trigger purposes in a particle physics experiment. The novel feature is that the mean-timing and the coincidence logic are not synchronized with a clock which allows for a higher resolution of approximately 400 ps, not limited by a clock frequency.
△ Less
Submitted 18 January, 2012; v1 submitted 22 September, 2011;
originally announced September 2011.
-
The Mass of the Black Hole in Arp 151 from Bayesian Modeling of Reverberation Mapping Data
Authors:
Brendon J. Brewer,
Tommaso Treu,
Anna Pancoast,
Aaron J. Barth,
Vardha N. Bennert,
Misty C. Bentz,
Alexei V. Filippenko,
Jenny E. Greene,
Matthew A. Malkan,
Jong-Hak Woo
Abstract:
Supermassive black holes are believed to be ubiquitous at the centers of galaxies. Measuring their masses is extremely challenging yet essential for understanding their role in the formation and evolution of cosmic structure. We present a direct measurement of the mass of a black hole in an active galactic nucleus (Arp 151) based on the motion of the gas responsible for the broad emission lines. B…
▽ More
Supermassive black holes are believed to be ubiquitous at the centers of galaxies. Measuring their masses is extremely challenging yet essential for understanding their role in the formation and evolution of cosmic structure. We present a direct measurement of the mass of a black hole in an active galactic nucleus (Arp 151) based on the motion of the gas responsible for the broad emission lines. By analyzing and modeling spectroscopic and photometric time series, we find that the gas is well described by a disk or torus with an average radius of 3.99 +- 1.25 light days and an opening angle of 68.9 (+21.4, -17.2) degrees, viewed at an inclination angle of 67.8 +- 7.8 degrees (that is, closer to face-on than edge-on). The black hole mass is inferred to be 10^(6.51 +- 0.28) solar masses. The method is fully general and can be used to determine the masses of black holes at arbitrary distances, enabling studies of their evolution over cosmic time.
△ Less
Submitted 25 April, 2011;
originally announced April 2011.