arXiv subjects

Fernando Aguilar-Galindo

Publications and source records attributed to Fernando Aguilar-Galindo.

5 recordsLinked to original sources

arXiv2026

Adsorption-Driven Symmetry Lowering in Single Molecules Revealed by Ångstrom-scale Tip-Enhanced Raman Imaging

The vibrational landscape of adsorbed molecules is central to understanding surface interactions at the atomic scale, influencing phenomena from catalysis to molecular electronics. Recent advances in atomic-scale tip-enhanced Raman spectroscopy (TERS) have enabled vibrational mapping of single molecules with sub-nanometer spatial resolution, providing unprecedented insights into molecule-surface interactions by confining light in plasmonic picocavities. Here, we exploit TERS in a cryogenic scanning tunneling microscope junction to perform Raman hyperspectral mapping of single iron phthalocyanine (FePc) molecules in three non-equivalent adsorption configurations on Ag surfaces. We explore the changes in the vibrational modes of FePc molecules adsorbed on two distinct silver crystal terminations with differing symmetry, Ag(111) and Ag(110), revealing how subtle variations in the adsorption geometry due to substrate anisotropy can strongly influence molecular vibrations, lifting the degeneracy of individual normal modes. Our findings not only demonstrate the first use of sub-nanometer TERS mapping across different symmetry configurations but also provide a deeper understanding of how site-specific vibrational properties are intimately linked to local atomic environments. This capability paves the way for precisely tailoring surface interactions and controlling chemical reactions at the atomic scale.

cond-mat.mes-hall↗

arXiv2024

Uncovering low-frequency vibrations in surface-enhanced Raman of organic molecules

Accessing the terahertz (THz) spectral domain through surface-enhanced Raman spectroscopy (SERS) is challenging and opens up the study of low-frequency molecular and electronic excitations. Compared to direct THz probing of heterogenous ensembles, the extreme plasmonic confinement of visible light to deep sub-wavelength scales allows the study of hundreds or even single molecules. We show that self-assembled molecular monolayers of a set of simple aromatic thiols confined inside single-particle plasmonic nanocavities can be distinguished by their low-wavenumber spectral peaks below 200 cm-1, after removal of a bosonic inelastic contribution and an exponential background from the spectrum Developing environment-dependent density-functional-theory simulations of the metal-molecule configuration enables the assignment and classification of their THz vibrations as well as the identification of intermolecular coupling effects and of the influence of the gold surface configuration Furthermore, we show dramatically narrower THz SERS spectra from individual molecules at picocavities, which indicates the possibility to study intrinsic vibrational properties beyond inhomogeneous broadening further supporting the key role of local environment.

physics.optics↗

arXiv2023

Emergence of π-Magnetism in Fused Aza-Triangulenes: Symmetry and Charge Transfer Effects

On-surface synthesis has paved the way towards the fabrication and characterization of conjugated carbon-based molecular materials that exhibit π-magnetism such as triangulenes. Aza-triangulene, a nitrogen-substituted derivative, was recently shown to display rich on-surface chemistry, offering an ideal platform to investigate structure-property relations regarding spin-selective charge transfer and magnetic fingerprints. Herein, we study electronic changes upon fusing single molecules into larger dimeric derivatives. We show that the closed-shell structure of aza-triangulene on Ag(111) leads to closed-shell dimers covalently coupled through sterically accessible carbon atoms. Meanwhile, its open-shell structure on Au(111) leads to coupling via atoms displaying high spin density, resulting in symmetric or asymmetric dimer products. Interestingly, whereas all fused products on Au(111) exhibit similar charge transfer properties, only asymmetric dimers show magnetic fingerprints. We rationalize this in terms of molecular bonding structure and π-conjugation: in contrast to the symmetric and highly conjugated dimer, asymmetric dimers display more localized orbitals, which result in a larger Coulomb repulsion and thus promote single electron occupancies with associated spin density and π-magnetism. These results expose a clear relationship between molecular symmetry, charge transfer, and spin states in π-conjugated carbon-based nanostructures.

cond-mat.mtrl-sci↗

arXiv2021

Order from a mess: the growth of 5-armchair graphene nanoribbons

The advent of on-surface chemistry under vacuum has vastly increased our capabilities to synthesize carbon-nanomaterials with atomic precision. Among the types of target structures that have been synthesized by these means, graphene nanoribbons (GNRs) have probably attracted the most attention. In this context, the vast majority of GNRs have been synthesized from the same chemical reaction: Ullmann coupling followed by cyclodehydrogenation. Here, we provide a detailed study of the growth process of 5-atom-wide armchair GNRs starting from dibromoperylene. Combining scanning probe microscopy with temperature-dependent XPS measurements and theoretical calculations, we show that the GNR growth departs from the conventional reaction scenario. Instead, precursor molecules couple by means of a concerted mechanism whereby two covalent bonds are formed simultaneously, along with a concomitant dehydrogenation. Indeed, this novel reaction path is responsible for the straight GNR growth, something remarkable considering the initial mixture of reactant isomers with irregular metal-organic intermediates that we find. The provided insight will not only help understanding the reaction mechanisms of other reactants, but also serve as a guide for the design of new precursor molecules.

cond-mat.mtrl-sci↗

arXiv2016

Mechanical Isolation of Highly Stable Antimonene under Ambient Conditions

Using mechanical exfoliation combined with a controlled double step transfer procedure we demonstrate that single layers of antimony can be readily produced. These flakes are not significantly contaminated upon exposure to ambient conditions and they do not react with water. DFT calculations confirm our experimental observations and predict a band gap of 1.2-1.3 eV (ambient conditions) for single layer antimonene, which is smaller than that calculated under vacuum conditions at 0 K. Our work confirms antimonene as a highly stable 2D material with promising relevant applications in optoelectronics.

cond-mat.mtrl-sci↗