Atomically precise bottom-up fabrication of graphene nanoribbons. Graphene nanoribbons-narrow and straight-edged stripes of graphene, or single-layer graphite-are predicted to exhibit electronic properties that make them attractive for the fabrication of nanoscale electronic devices. In particular, although the two-dimensional parent material graphene exhibits semimetallic behavior, quantum confinement and edge effects should render all graphene nanoribbons with widths smaller than 10 nm semiconducting.
But exploring the potential of graphene nanoribbons is hampered by their limited availability: although they were made using chem. Here the authors report a simple method for the prodn. The topol. The authors expect that the authors' bottom-up approach to the atomically precise fabrication of graphene nanoribbons will finally enable detailed exptl. It should even provide a route to graphene nanoribbon structures with engineered chem.
Fullerenes from aromatic precursors by surface-catalysed cyclodehydrogenation. Here the formation of C60 and the triazafullerene C57N3 from arom. It was found that after deposition onto a platinum surface and heating to K, the precursors are transformed into the corresponding fullerene and triazafullerene mols. This approach is expected to allow the prodn. Also, if the process is carried out in an atm. Nano-architectures by covalent assembly of molecular building blocks.
The construction of electronic devices from single mol. A key challenge is the controlled assembly of mols. However, no mol. Here, such covalently bound mol. The authors' results represent a versatile route for future bottom-up construction of sophisticated electronic circuits and devices, based on individual functionalized mols. Insight into organometallic intermediate and its evolution to covalent bonding in surface-confined Ullmann polymerization.
Surface-catalyzed dehalogenative polymn. On-surface light-induced generation of higher acenes and elucidation of their open-shell character. Nature communications , 10 1 , ISSN:. Acenes are an important class of polycyclic aromatic hydrocarbons which have recently gained exceptional attention due to their potential as functional organic semiconductors. Fundamentally, they are important systems to study the convergence of physico-chemical properties of all-carbon sp 2 -frameworks in the one-dimensional limit; and by virtue of having a zigzag edge topology they also provide a fertile playground to explore magnetism in graphenic nanostructures.
The study of larger acenes is thus imperative from both a fundamental and applied perspective, but their synthesis via traditional solution-chemistry route is hindered by their poor solubility and high reactivity. On-surface synthesis of heptacene and its interaction with a metal surface. Royal Society of Chemistry. The surface-assisted formation of heptacene occurs around K. Both the heptacene and the precursor mols. The interaction with the Ag substrate is not laterally uniform, but appears to be strongest on the central part of the mol.
In the STM images, heptacene shows a dumbbell shape, which may correspond to the substantial out-of-plane deformations of heptacene on Ag As revealed by DFT, the center of the mol. Heptacene acts as an acceptor and receives a neg. Decacene: On-surface generation. Acenes are intriguing mols. The difficulties in their prepn. Only unsubstituted acenes up to heptacene have been isolated in bulk, with nonacene being the largest acene detected to date.
The authors use on-surface assisted redn. Higher acenes by on-surface dehydrogenation: From heptacene to undecacene. A unified approach to the synthesis of higher acenes up to previously unreported undecacene were developed through the on-surface dehydrogenation of partially satd.
The structure of the generated acenes was visualized by high-resoln. Nonacene generated by on-surface dehydrogenation. The on-surface synthesis of nonacene has been accomplished by dehydrogenation of an air-stable partially satd. This transformation allowed the in-detail anal. The spatial mapping of MOs was corroborated by d. Furthermore, the thermally induced dehydrogenation uncovered the isomerization of intermediate dihydrononacene species, which allowed for their in-depth structural and electronic characterization.
On-surface synthesis of heptacene on Ag from brominated and non-brominated tetrahydroheptacene precursors. Colazzo, Luciano; Mohammed, Mohammed S. Achieving the Ag -supported synthesis of heptacene from 2 related reactants reveals the effect of the presence of Br atoms on the reaction process. The properties of reactants, intermediates and end-products are further characterized by scanning tunneling microscopy and spectroscopy.
Dodecacene generated on surface: Reopening of the energy gap. Here, the authors present the on-surface generation of the longest acene obtained so far: dodecacene. Scanning tunneling spectroscopy gives access to the energy position and spatial distribution of its electronic states on the Au surface.
Considering the acene series as an exemplary general case, the evolution with length of the single tunneling resonances in comparison with ionization energy, electronic affinity, and optical gap are discussed. Larger acenes, such as hexacene, are increasingly considered as promising materials for applications in optoelectronic devices. We studied electronic interface properties and the mol.
Interactions between hexacene and the substrate are weak. The detailed investigation of the orientation greatly benefits from a combination of polarization-dependent XAS and angle-resolved photoemission. The angular dependence of valence band features indicates that the mols. Electronic structure of hexacene and interface properties on Au Although hexacene was first synthesized in , the thin film properties, which are interesting for future applications and fundamental research, have never been investigated.
Therefore, we synthesized hexacene by redn. This allowed us to study the electronic properties and mol. Valence band spectra of a multilayer hexacene film are compared to those of electronic states obtained from d. C 1s core-level spectra show typical satellite structures of the extended arom.
XAS shows that anisotropy rises with decreasing film thickness and indicates that hexacene is almost flat lying on the Au substrate. The different peak shapes of XAS spectra as a function of the film thickness, as well as changes in valence band spectra and C 1s satellite structures, indicate a strong electronic coupling of the mol.
Heptacene: Characterization in solution, in the solid state, and in films. Acenes comprise an important class of org. As graphene nanoribbons of ultimate width, they are valuable atom-precise model systems for studying the properties of this form of nanoscale carbon materials. Heptacene is the smallest member of the acene series that could only be studied under matrix isolation conditions.
Its existence in bulk had never been pos. We report that the redn. The diheptacenes undergo thermal cleavage to heptacene at high temps. Monitoring this cycloreversion by solid state 13C cross-polarized magic angle spinning NMR reveals that solid heptacene has a half-life time of several weeks at room temp. The diheptacenes are valuable precursors for generating films of heptacene by vapor phase deposition that can be studied below or at room temp.
Molecular template growth and its applications in organic electronics and optoelectronics. The review provides an overview of the growth behavior of org. Also described are template growth methods and their applications in org. Multiphenyland multithiophene-based MTG; perylene-deriv. MTG are described. Orbital tomography: Molecular band maps, momentum maps and the imaging of real space orbitals of adsorbed molecules.
Electron Spectrosc. The frontier orbitals of mols. Arguably, the most direct method of addressing the filled frontier orbitals is ultra-violet photoemission spectroscopy UPS. Although UPS is a mature technique from the early s on, the angular distribution of the photoemitted electrons was thought to be too complex to be analyzed quant.
The approach, based on the assumption of a plane wave final state is becoming known as orbital tomog. Here we will demonstrate, with selected examples of pentacene 5A and sexiphenyl 6P , the potential of orbital tomog. First it will be shown how the full angular distribution of the photocurrent momentum map from a specific orbital is related to the real space orbital by a Fourier transform.
Examples of the reconstruction of 5A orbitals will be given and the procedure for recovering the lost phase information will be outlined. We then move to examples of sexiphenyl where we interrogate the original band maps of thick sexiphenyl in the light of our understanding of orbital tomog. With comparison to theor. New results for the sexiphenyl monolayer on Al 1 1 0 will then be presented.
From the band maps it will be concluded that the mol. Finally the momentum maps down to HOMO will be analyzed and real space orbitals reconstructed. Exploring three-dimensional orbital imaging with energy-dependent photoemission tomography. Weiss, S. Recently, it has been shown that exptl. Here, we extend this orbital tomog. The overall dependence of the photocurrent on the photon energy can be well accounted for by assuming a plane wave for the final state.
However, the exptl. Nevertheless, as these effects beyond a plane wave final state are comparably small, we are able, with extrapolations beyond the attainable photon energy range, to reconstruct three-dimensional images for both orbitals in agreement with calcns. American Association for the Advancement of Science.
Photoemission spectroscopy is commonly applied to study the band structure of solids by measuring the kinetic energy vs. Here, the authors apply this exptl. By measuring the photoemission intensity from a const. The real-space electron distribution of MOs in both a cryst. The results are in good agreement with d. Identifying surface reaction intermediates with photoemission tomography.
The determination of reaction pathways and the identification of reaction intermediates are key issues in chemistry. Surface reactions are particularly challenging, since many methods of analytical chemistry are inapplicable at surfaces. Recently, atomic force microscopy has been employed to identify surface reaction intermediates. While providing an excellent insight into the molecular backbone structure, atomic force microscopy is less conclusive about the molecular periphery, where adsorbates tend to react with the substrate.
Here we show that photoemission tomography is extremely sensitive to the character of the frontier orbitals. Specifically, hydrogen abstraction at the molecular periphery is easily detected, and the precise nature of the reaction intermediates can be determined. This is illustrated with the thermally induced reaction of dibromo-bianthracene to graphene which is shown to proceed via a fully hydrogenated bisanthene intermediate. We anticipate that photoemission tomography will become a powerful companion to other techniques in the study of surface reaction pathways.
Kekulene: On-surface synthesis, orbital structure, and aromatic stabilization. We revisit the question of kekulene's aromaticity by focusing on the electronic structure of its frontier orbitals as determined by angle-resolved photoemission spectroscopy. To this end, we have developed a specially designed precursor, 1,4,7 2,7 -triphenanthrenacyclononaphane-2,5,8-triene, which allows us to prepare sufficient quantities of kekulene of high purity directly on a Cu surface, as confirmed by scanning tunneling microscopy.
Supported by density functional calculations, we determine the orbital structure of kekulene's highest occupied molecular orbital by photoemission tomography. First results from a second generation toroidal electron spectrometer. Broekman, L. A second generation toroidal electron spectrometer is briefly described and results presented that demonstrate its capabilities.
Band structure measurements obtained from graphitized SiC and x-ray photoelectron diffraction results from Cu and graphite are presented. Ab initio molecular dynamics for liquid metals. The authors present ab initio quantum-mech. This is possible using conjugate-gradient techniques for energy minimization, and predicting the wave functions for new ionic positions using sub-space alignment.
This approach avoids the instabilities inherent in quantum-mech. This method gives perfect control of the adiabaticity and allows one to perform simulations over several picoseconds. From ultrasoft pseudopotentials to the projector augmented-wave method. American Physical Society. The formal relationship between ultrasoft US Vanderbilt-type pseudopotentials and Blochl's projector augmented wave PAW method is derived.
The total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out.
These tests include small mols. Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni. Generalized gradient approximation made simple vol 77, pg , A consistent and accurate ab initio parametrization of density functional dispersion correction DFT-D for the 94 elements H-Pu. The method of dispersion correction as an add-on to std. Kohn-Sham d.
The main new ingredients are atom-pairwise specific dispersion coeffs. The coeffs. System geometry dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination nos.
They are used to interpolate between dispersion coeffs. The method only requires adjustment of two global parameters for each d. Three-body nonadditivity terms are considered. The method has been assessed on std. The mean abs. Spectacular improvements are found for a tripeptide-folding model and all tested metallic systems. The rectification of the long-range behavior and the use of more accurate C6 coeffs.
We propose the revised DFT-D method as a general tool for the computation of the dispersion energy in mols. Projector augmented-wave method. Physical review. Products and mechanism of acene dimerization.
A computational study. A Computational Study. Zade, Sanjio S. The high reactivity of acenes can reduce their potential applications in the field of mol. Although pentacene is an important material for use in org. In this study, several reaction pathways for the thermal dimerization of acenes were considered computationally.
The formation of acene dimers via a central benzene ring and the formation of acene-based polymers were found to be the preferred pathways, depending on the length of the monomer. Interestingly, starting from hexacene, acene dimers are thermodynamically disfavored products, and the reaction pathway is predicted to proceed instead via a double cycloaddn.
A concerted asynchronous reaction mechanism was found for benzene and naphthalene dimerization, while a stepwise biradical mechanism was predicted for the dimerization of anthracene, pentacene, and heptacene. The biradical mechanism for dimerization of anthracene and pentacene proceeds via syn or anti transition states and biradical min. The activation barriers for thermal dimerization decrease rapidly with increasing acene chain length and are calcd.
If activation energy is calcd. Dimerization is exothermic from anthracene onward, but it is endothermic at the terminal rings, even for heptacene. Ph substitution at the most reactive meso-carbon atoms of the central ring of acene blocks the reactivity of this ring but does not efficiently prevent dimerization through other rings.
Orbital tomography of hybridized and dispersing molecular overlayers. With angle-resolved photoemission expts. On Ag , the orbitals remain essentially isolated-mol. We show how the photoemission intensity of extended systems can be simulated and that it behaves essentially like that of the isolated mol. Coverage induced structural transformations of tetracene on Ag Self-assembly of tetracene on an anisotropic surface of Ag has been investigated using scanning tunneling microscopy and LEED.
Multistage structural transformations of the self-assembled tetracene on Ag were obsd. They were analyzed by a balance between multiple mol. Adsorbate-substrate and adsorbate-adsorbate interactions of Na and K adlayers on Al Total-energy, force, and electronic-structure calcns.
The calcns. Special points for Brillouin-zone integrations. Photoemission spectroscopy—Correspondence between quantum theory and experimental phenomenology. Correspondence between quantum theory and experimental phenomenology. The relation between the obsd. A Fermi's Golden-Rule formula is derived for the angle- and energy-resolved photocurrent from an independent electron solid. The approxns.
In terms of the Golden-Rule formula, account is made for the direct-transition band-structure regime generally obsd. An explanation is proposed of Feuerbacher et al. The criteria which det. Understanding the photoemission distribution of strongly interacting two-dimensional overlayers.
Photoemission tomog. PT , the anal. Here we present a simple method for extending PT, which until now has been based on the calcns. By including the substrate and a damped plane-wave final state, we are able to simulate the photoemission intensity distribution of two-dimensional mol. It is shown that the interaction and hybridization of the LUMO of PTCDA with substrate states leads to its occupation and the formation of a strongly dispersing intermol.
Coexisting charge states in a unary organic monolayer film on a metal. Stefan; Ramsey, Michael G. The electronic and geometric structures of tetracene films on Ag and Cu have been studied with photoemission tomog. Despite similar energy level alignment of the two oligoacenes on these surfaces revealed by conventional UPS, the momentum-space resolved photoemission tomog.
Particularly, the satd. Structural evolution of pentacene on a Ag surface. Wang, Y. Structural evolution of pentacene thin films on Ag crystal, during mol. The pentacene mols. The ordered monolayer structure on Ag has two domains mirrored at the crystal axis of the silver substrate. The calcn. Electronic band structure of pentacene: An experimental and theoretical study.
Berkebile, S. The intermol. The band structure perpendicular to the mols. Parallel to the mols. In these intramol. Unexpected interplay of bonding height and energy level alignment at heteromolecular hybrid interfaces. Stefan; Kumpf, Christian. Although geometric and electronic properties of any phys.
The coadsorption of the org. Our comprehensive exptl. This resolves the apparent paradox, and demonstrates with exceptional clarity how geometric and electronic bonding parameters are intertwined at metal-org. Orbital tomography for highly symmetric adsorbate systems. Stadtmueller, B. EPL , 2 , , 6 pp. IOP Publishing Ltd. More by Katharina Greulich. More by Reimer Karstens. More by Axel Belser. More by Ruslan Ovsyannikov. More by Erika Giangrisostomi. More by Holger F. More by David Batchelor.
More by Heiko Peisert. Cite this: J. C , , 45 , — Article Views Altmetric -. Citations 4. Supporting Information. Cited By. This article is cited by 4 publications. Marie S. Bocquet, Serguei Soubatch, F. Stefan Tautz, Holger F. Ramsey, Peter Puschnig, Georg Koller. The Journal of Physical Chemistry C , 5 ,
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