Formation of 0D and 1D Graphene-based Nanostructures by [2+2] Cycloaddition of Ortho-dihalogen Aromatics

Trabajo presentado en la conferencia Fuerzas y Túnel (FyT2016), celebrada en Girona del 5 al 7 de septiembre de 2016.During the last decade, on-surface chemistry has experienced a significant development driven by the necessity of finding novel tools for the fabrication of new (macro)molecular structures with novel properties. Several synthetic reactions commonly used in traditional solution-based chemistry have recently been applied to on-surface chemistry [1-3]. This approach has allowed for the fabrication of novel structures with fascinating properties such as metal-organic frameworks, covalent organic frameworks (COF) or graphene nanoribbons, to name only some of them. However, there is still a wide variety of coupling reactions that are well-known in solution-based chemistry but which have not yet been explored with respect to on-surface chemistry. This is the case, for example, of the [2+2] cycloaddition for the controlled formation of carbon tetragons. In this talk, we will present the on-surface synthesis of 0D and 1D graphene-based nanostructures via [2+2] cycloaddition of halogen-functionalized precursor monomers. For this purpose, we have used aromatic precursors which have been functionalized at orthopositions, a novel approach in on-surface reactions. We will show, by means of highresolution scanning tunnelling microscopy and non-contact atomic force microscopy, that these precursor monomers afford the formation of carbon tetragons. Furthermore, we show that the functionalization pattern of the precursor monomers allows for the selective formation of either 0D or 1D nanostructures.N

Transverse momentum spectra of charged particles in proton-proton collisions at s=900\sqrt{s} = 900 GeV with ALICE at the LHC

The inclusive charged particle transverse momentum distribution is measured in proton-proton collisions at $\sqrt{s} = 900$ GeV at the LHC using the ALICE detector. The measurement is performed in the central pseudorapidity region $(|\eta|<0.8)$ over the transverse momentum range $0.15<p_{\rm T}<10$ GeV/$c$. The correlation between transverse momentum and particle multiplicity is also studied. Results are presented for inelastic (INEL) and non-single-diffractive (NSD) events. The average transverse momentum for $|\eta|<0.8$ is $\left<p_{\rm T}\right>_{\rm INEL}=0.483\pm0.001$ (stat.) $\pm0.007$ (syst.) GeV/$c$ and \left_{\rm NSD}=0.489\pm0.001 (stat.) $\pm0.007$ (syst.) GeV/$c$, respectively. The data exhibit a slightly larger $\left<p_{\rm T}\right>$ than measurements in wider pseudorapidity intervals. The results are compared to simulations with the Monte Carlo event generators PYTHIA and PHOJET.Comment: 20 pages, 8 figures, 2 tables, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/390

On-surface synthesis and atomic-scale characterization of porphyrin-based nanostructures

Resumen del póster presentado a la XXXVIII Reunión Bienal de la Real Sociedad Española de Química, celebrada en el Palacio de Congresos de Granada, del 27 de junio al 30 de junio de 2022.Porphyrins (Pors) are tetrapyrrolic macrocycles that offer a palette of highly attractive features for applications in materials science. In particular, π-extended Pors have gained considerable attention in the field of organic semiconductors and molecular electronics due to their low HOMO-LUMO gaps. Furthermore, Pors can chelate transition metal ions in their inner cavity, which allows the construction of magnetically-active nanostructures, such as organic spin filters. However, the synthesis of such π-extended Pors typically suffers severe limitations, arising from lengthy synthetic schemes, low yields, poor solubility and significant stability issues. In this context, on-surface synthesis under ultra-high vacuum (UHV) conditions has emerged as an appealing alternative for the fabrication of such poorly soluble and inherently unstable structures. In addition to the synthetic benefits, the resulting on-surface synthesized nanostructures can directly be accessed by local-probe techniques such as scanning probe microscopy, allowing for an “in situ” structural and electronic characterization with sub-molecular resolution. In this communication, we present our recent progress in the on-surface preparation of Por-based nanostructures. A special focus will be laid on the electronic effects of the π-extension of the Por core, either with graphene nanoribbon (GNR) fragments or with open-shell polyaromatic hydrocarbons (PAHs), which in some cases leads to the appearance of an open-shell character as well as new and exciting reactive sites. Furthermore, the inherent open-shell structure of some of these structures can be combined with magnetically active transition metal ions, which opens the path towards complex and intriguing nanostructures.Peer reviewe

Semiconductor-metal transition of the single-domain K/Si(100)-(2×1) interface by Fermi-surface determination

The semiconductor-metal electronic transition of the K/Si(100)-(2×1) interface is studied by exploring the Fermi surface with photoemission spectroscopy. Once metallized at a critical coverage the surface remains metallic up to saturation. The experimentally determined Fermi surface consists of hole pockets centered around the Γ + ̄ points of the surface Brillouin zone. These results are fairly well reproduced by calculations based on a 2D Mott-Hubbard model. The metallization process is related to the overlap of Si-confined electron clouds surrounding the K atoms rather than to changes in the surface atomic structure. © 1998 The American Physical SocietyThis work was partially funded by the Spanish agency DGCYT under Grant No. PB94-0022-c02-01 and PB92- 0030 .Peer Reviewe

Bottom-up fabrication and atomic-scale characterization of porphyrin-based nanostructures

Resumen del trabajo presentado a la XXXVIII Reunión Bienal de la Real Sociedad Española de Química, celebrada en el Palacio de Congresos de Granada, del 27 de junio al 30 de junio de 2022.Peer reviewe

Hydrogen‐bonding fingerprints in electronic states of two‐dimensional supramolecular assemblies

Induced charge polarization: Different hydrogen‐bonding configurations have a distinct impact on the electronic structure of 2D assemblies, as shown by STS experiments. First‐principles DFT calculations reveal that an intramolecular charge polarization induced by anisotropic strong triple hydrogen bonds is at the origin of the observed frontier molecular orbital energy level shifts.N.G.‐L. and A.A thank the Basque Government, UPV/EHU (No. ITC‐366‐07) and MEC (No.FIS2007‐6671‐CO2‐01) for financial support. R.F. gratefully acknowledges financial support from the Swiss National Science Foundation and the NCCR “Nanoscale Science”.Peer reviewe

Charged-particle multiplicity measurement in proton-proton collisions at root s=7 TeV with ALICE at LHC

The pseudorapidity density and multiplicity distribution of charged particles produced in proton-proton collisions at the LHC, at a centre-of-mass energy root s = 7 TeV, were measured in the central pseudorapidity region vertical bar eta vertical bar < 1. Comparisons are made with previous measurements at root s = 0.9 TeV and 2.36 TeV. At root s = 7 TeV, for events with at least one charged particle in |eta vertical bar| < 1, we obtain dN(ch)/d eta = 6.01 +/- 0.01(stat.)(-0.12)(+0.20) (syst.). This corresponds to an increase of 57.6%+/-0.4%(stat.)(-1.8%)(+3.6) (syst.) relative to collisions at 0.9 TeV, significantly higher than calculations from commonly used models. The multiplicity distribution at 7 TeV is described fairly well by the negative binomial distribution

Transverse momentum spectra of charged particles in proton–proton collisions at √s=900 GeV with ALICE at the LHC

The inclusive charged particle transverse momentum distribution is measured in proton–proton collisions at s=900 GeV at the LHC using the ALICE detector. The measurement is performed in the central pseudorapidity region (|η|<0.8) over the transverse momentum range 0.15<pT<10 GeV/c. The correlation between transverse momentum and particle multiplicity is also studied. Results are presented for inelastic (INEL) and non-single-diffractive (NSD) events. The average transverse momentum for |η|<0.8 is 〈pT〉INEL=0.483±0.001 (stat.)±0.007 (syst.) GeV/c and 〈pT〉NSD=0.489±0.001 (stat.)±0.007 (syst.) GeV/c, respectively. The data exhibit a slightly larger 〈pT〉 than measurements in wider pseudorapidity intervals. The results are compared to simulations with the Monte Carlo event generators PYTHIA and PHOJET

First proton-proton collisions at the LHC as observed with the ALICE detector: Measurement of the charged-particle pseudorapidity density at √s = 900 GeV

On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), two counter-rotating proton bunches were circulated for the first time concurrently in the machine, at the LHC injection energy of 450 GeV per beam. Although the proton intensity was very low, with only one pilot bunch per beam, and no systematic attempt was made to optimize the collision optics, all LHC experiments reported a number of collision candidates. In the ALICE experiment, the collision region was centred very well in both the longitudinal and transverse directions and 284 events were recorded in coincidence with the two passing proton bunches. The events were immediately reconstructed and analyzed both online and offline. We have used these events to measure the pseudorapidity density of charged primary particles in the central region. In the range |η|<0.5, we obtain dNch/dη=3. 10±0. 13(stat.)±0. 22(syst.) for all inelastic interactions, and dNch/dη=3.51±0. 15(stat.)±0. 25(syst.) for non-single diffractive interactions. These results are consistent with previous measurements in proton-antiproton interactions at the same centre-of-mass energy at the CERN SppS̄ collider. They also illustrate the excellent functioning and rapid progress of the LHC accelerator, and of both the hardware and software of the ALICE experiment, in this early start-up phase