Light-matter interaction at the atomic scale rules fundamental phenomena such as photoemission and lasing, while enabling basic everyday technologies, including photovoltaics and optical communications. In this context, plasmons -the collective electron oscillations in conducting materials-are important because they allow manipulating optical fields at the nanoscale. The advent of graphene and other two-dimensional crystals has pushed plasmons down to genuinely atomic dimensions, displaying appealing properties such as a large electrical tunability. However, plasmons in these materials are either too broad or lying at low frequencies, well below the technologically relevant nearinfrared regime. Here we demonstrate sharp near-infrared plasmons in lithographically-patterned wafer-scale atomically-thin silver crystalline films. Our measured optical spectra reveal narrow plasmons (quality factor ∼ 4), further supported by a low sheet resistance comparable to bulk metal in few-atomic-layer silver films down to seven Ag(111) monolayers. Good crystal quality and plasmon narrowness are obtained despite the addition of a thin passivating dielectric, which renders our samples resilient to ambient conditions. The observation of spectrally sharp and strongly confined plasmons in atomically thin silver holds great potential for electro-optical modulation and optical sensing applications. * These two authors contributed equally to the work. † Electronic address: enrique.ortega@ehu.es ‡ Electronic address: javier.garciadeabajo@icfo.es arXiv:1901.07739v2 [cond-mat.mes-hall]

A new class of nanostructured templates is obtained by submitting Au111 films to high-temperature vapor deposition of Gd in ultrahigh vacuum. In a low coverage regime, Gd atoms are embedded in the topmost Au layer, inducing a structural transformation of the herringbone reconstruction to create a network of trigons. At higher dose, the reactive deposition of Gd leads to the formation of an atomically perfect GdAu2 surface compound characterized by a long-range periodic Moire pattern. Both the trigon and Moire lattices are highly ordered nanostructures, which turned out to be robust templates to grow metal nanodots. As a test example, Co was deposited at room temperature, forming uniform dots that faithfully arrange by following the underlying trigons or Moire periodicity. For the latter, one can achieve nanodot arrays that exhibit record areal density.

The evolution of titanyl-phthalocyanine (TiOPc) thin films on Ag(111) has been investigated using IRAS, SPA-LEED and STM. In the (sub)monolayer regime various phases are observed that can be assigned to a 2D gas, a commensurate and a point-on-line phase. In all three phases the non-planar TiOPc molecule is adsorbed on Ag(111) in an oxygen-up configuration with the molecular -conjugated backbone oriented parallel to the surface. The commensurate phase reveals a high packing density, containing two molecules at inequivalent adsorption sites within the unit cell.Both molecules assume different azimuthal orientations which is ascribed to preferred sites and azimuthal orientations with respect to the Ag(111) substrate and, to a lesser extent, to a minimization of repulsive Pauli interactions between adjacent molecules at short distances. At full saturation of the monolayer the latter interaction becomes dominant and the commensurate long range order is lost. DFT calculations have been used to study different adsorption geometries of TiOPc on Ag(111). The most stable configurations among those with pointing up oxygen atoms (bridge + , bridge x , top x ) seem to correspond to those identified experimentally. The calculated dependence of the electronic structure and molecular dipole on the adsorption site and configuration is found to be rather small. 2

Materials that exhibit ferromagnetism, interfacial stability, and tunability are highly desired for the realization of emerging magnetoelectronic phenomena in heterostructures. Here we present the GdAg2 monolayer alloy, which possesses all such qualities. By combining X-ray absorption, Kerr effect, and angle-resolved photoemission with ab initio calculations, we have investigated the ferromagnetic nature of this class of Gd-based alloys. The Curie temperature can increase from 19 K in GdAu2 to a remarkably high 85 K in GdAg2. We find that the exchange coupling between Gd atoms is barely affected by their full coordination with noble metal atoms, and instead, magnetic coupling is effectively mediated by noble metal-Gd hybrid s,p-d bands. The direct comparison between isostructural GdAu2 and GdAg2 monolayers explains how the higher degree of surface confinement and electron occupation of such hybrid s,p-d bands promote the high Curie temperature in the latter. Finally, the chemical composition and structural robustness of the GdAg2 alloy has been demonstrated by interfacing them with organic semiconductors or magnetic nanodots. These results encourage systematic investigations of rare-earth/noble metal surface alloys and interfaces, in order to exploit them in magnetoelectronic applications.