Invited Talks, Lectures, Seminars, MSc. Students, Ph.D Students, Books, Articles, Submitted Papers.
Overview of my research topics:
The study of surface phonon dispersion curves is motivated by the quest for a detailed understanding of the forces between the atoms at the surface and in the bulk. In the case of graphene (Gr), additional motivation comes from the fact that thermal conductivity is dominated by contributions from acoustic phonons, while optical phonon properties are essential to understand Raman spectra. Phonon dispersion curves are extremely sensitive to interatomic forces of adsorbed layers, including the interaction between adlayer and substrate atoms. The system formed by Gr on metal surfaces provides a good example of how small changes in the strength of the Gr-substrate interaction modify the corresponding phonon dispersion curves. Thus, phonon spectra may provide valuable information on the bonding of Gr with the substrate as well as on the electron–phonon coupling. The phonon spectrum allows to quantify subtle properties like the Gr-metal bond strength, the bending rigidity and Kohn anomalies, which are especially difficult to get for weakly interacting systems like the ones formed by Gr on Cu(1 1 1), Ir(1 1 1) and Pt(1 1 1). Moreover, phonon dispersion curves provide an excellent scenario to test the performance of current state-of-the-art calculations. As far as we know, a full theoretical description of the phonon spectra for Gr bounded to a metal substrate is still lacking.
The dissociative chemisorption of hydrogen at metal surfaces is the first step in the surface chemistry of heterogeneous catalysis. Up to now, most of our understanding of this process has been obtained from sticking probability measurements. Recent experiments have shown that more detailed information on the potential energy surface (PES) governing the dissociative chemisorption of hydrogen can be obtained by employing a different technique, namely diffraction of monochromatic beams of molecular hydrogen and deuterium. In this paper, we review recent progress made by using this technique to characterize the corresponding PES for hydrogen dissociative chemisorption at metal surfaces. Elastic and rotationally inelastic diffraction (RID) peaks were observed in experiments performed on different single-crystal metal surfaces, ranging from nonreactive to very reactive ones, at incident energies between 20 and 200 meV. Extrapolation of data points by using the Debye–Waller attenuation model makes comparison with theory possible. It is shown that an analysis of both H2 diffraction and RID intensities as a function of incident energy provides a very sensitive way to test the quality of ab initio determined six-dimensional PESs. In addition, we have recently shown that coherent quantum scattering from a metal surface can be obtained using CH4 beams.
Because of the low energies employed (100meV), neutral He atoms probe the topmost surface layer of any material in an inert, completely nondestructive manner. They can be equally used to investigate insulating or conducting materials as well as fragile samples, which are difficult to examine by other methods because of sample charging or electron excitation effects. Using light particles at low energies the scattering is predominantly elastic and, as the de Broglie wavelengths are of the order of 1 Angstroem, diffraction effects dominate. In these experiments, the positions of the different diffraction peaks provide detailed information on the surface structure, while the relative intensities of the diffraction peaks contain information on the corrugation of the particle–surface potential energy surface (PES). In the case of He–diffraction, this very often provides direct pictures of the geometrical arrangement of the surface atoms.
Este libro está dirigido a todos aquellos curiosos sin formación científica que deseen conocer cuál es la visión moderna del mundo que nos ofrecen la relatividad y la mecánica cuántica. Va dirigido a estudiantes de secundaria o de carreras de humanidades que deseen acercarse por primera vez a estas dos grandes teorías de la ciencia de una forma amena y accesible. Va dirigido a aquellos que piensan que la relatividad nos dice que todo es relativo, a aquellos que creen que la cuántica solo nos habla de gatos que pueden estar vivos y muertos a la vez, y a quienes piensan que la relatividad y la cuántica no tienen ninguna aplicación práctica. Se puede comprar en este enlace
Associate Professor, Condensed Matter Physics Departmen, Universidad Autónoma de Madrid, Spain. E-mail: daniel.farias@uam.es