Plasmons in one and two dimensions

Plasmons in low-dimensional systems respresent an important tool for coupling energy into nanostructures and the localization of energy on the scale of only a few nanometers. Contrary to ordinary surface plasmons of metallic bulk materials, their dispersion goes to zero in the long wavelength limit, thus covering a broad range of energies from terahertz to near infrared, and from mesoscopic wavelengths down to just a few nanometers. Using specific and most characteristic examples, we review first the properties of plasmons in two-dimensional (2D) metallic layers from an experimental point of view. As demonstrated, tuning of their dispersion is possible by changes of charge carrier concentration in the partially filled 2D conduction bands, but for the relativistic electron gas like in graphene only in the long wavelength limit. For short wavelengths, on the other hand, the dispersion turns out to be independent of the position of the Fermi level with respect to the Dirac point. A linear dispersion, seen under the latter conditions in graphene, can also be obtained in non-relativistic electron gases by coupling between 2D and 3D electronic systems. As a well investigated example, the acoustic surface plasmons in Shockley surface states, coupled with the bulk electronic system, are discussed. Also the introduction of anisotropy, e.g. by regular arrays of steps, seems to result in linearization (and to partial localization of the plasmons normal to the steps, depending on wavelengths). In quasi-one dimensional (1D) systems, such as arrays of gold chains on regularly stepped Si surfaces, only the dispersion is 1D, whereas shape and slope of the dispersion curves depend on the 2D distribution of charge within each terrace and on coupling between wires on different terraces

Geomorphological evolution of the western piedmont of Cumbres Calchaquíes (Tucumán Province, NW Argentina)

The aim of this paper is to present a detailed geomorphological map of the western piedmont of Cumbres Calchaquíes (Tucumán Province, NW Argentina) bounded by the Amaicha River to the south and the administrative border with Salta Province to the north. It contains information about geomorphological units, their relative ages, and morphogenetic processes. The main map shows the presence of seven aggradation stages separated by incision phases. The first three stages (St1, St2, and St3) were modeled on a thick accumulation located in the upper piedmont from the Late Pliocene and Early Pleistocene. Intermediate stages (St4 and St5) are alluvial fans and pediments with less thickness and gradient. They cover the Early Pleistocene (St4) and the Late Pleistocene-Middle Holocene (St5). Finally, stages St6 and St7 are from the Upper Holocene

Influence of growing conditions on the reactivity of Ni supported graphene towards CO

Free standing graphene is chemically inert but, as recently demonstrated, CO chemisorption occurs at low crystal temperature on the single layer grown by ethene dehydrogenation on Ni(111). Such layer is inhomogeneous since different phases coexist, the relative abundance of which depends on the growth conditions. Here we show by X ray photoemission and high resolution electron energy loss spectroscopies that the attained CO coverage depends strongly on the relative weight of the different phases as well as on the concentration of carbon in the Ni subsurface region. Our data show that the chemical reactivity is hampered by the carbon content in the substrate. The correlation between the amount of adsorbed CO and the weight of the different graphene phases indicates that the top-fcc configuration is the most reactive

HREELS study of 0, molecular chemisorption on Ag( 001)

Abstract O2 adsorption on Ag(OO1) at 100 K has been investigated by HREELS. Contrary to previous reports we could resolve 4 oxygen related peaks, 3 of which are due to the internal stretching vibration as confirmed by isotope labelling. The lowest frequency mode at 63 meV is assigned to molecular oxygen chemisorbed at defect sites. The further two features are very close to each other in frequency, at 79 and 84 meV. We assign them to molecules chemisorbed in a peroxidic state in two different adsorption sites. Initially both sites are Mled simultaneously while at higher coverage adsorption in the higher frequency site is favoured

Paleotsunami evidence in the Bahía Inglesa coast (Atacama, Chile) based on a multi-approach analysis

The Atacama coast is located in an area with a current high risk of tsunami, and the sedimentary deposits found in the Bahía Inglesa area, in the Morro sector, clearly indicate that this was also the case in the past. This investigation analyzes a paleotsunami sedimentary deposit consisting of a block field associated with three sand lobes oriented towards land on top of a marine terrace at an altitude of 70–75 m, which originated from a tsunamigenic event occurred between interglacial periods MIS 7 (ca. 210 ± 10 ky) and MIS5e (ca. 125 ± 5 ky). The deposits have been studied using a multiple approach combining geomorphological, sedimentological, biological, and geochemical criteria. The first type of criteria clearly indicate that the energy required to move the blocks and form the sand lobes could only have been generated by a tsunami. Sedimentological criteria constitute direct evidences of a marine origin due to the presence of siliceous remains from diatom species and spicules from strictly marine sponges, while geochemical criteria, such as the stable isotope signature and chemical composition, constitute evidence of a marine intrusion. © 2022, The Author(s)

Holocene alluvial sequence in the val de zaragoza (Los Monegros) in the palaeoenvironmental context of the ebro basin (Ne Spain)

Flat-bottomed valleys formed by Holocene fills are the most characteristic landforms in the center of the Ebro basin. This paper analyzes, within a regional framework, a small fluvial basin located in the north of the Alcubierre Range. Three Holocene morphosedimentary units (H1-H3) and a sub-functional level (H4) are identified. These units are representative of the regional geomorphological evolutionary process in the Ebro basin. New chronological insights on climate and landscape management are provided by a study of the Bastarás weir, a construction made for water flow management during the Little Ice Age (LIA). The integration of Val de Zaragoza radiocarbon datings into the regional framework enables the authors to identify the main formation stages, as well as the influence of climatic and human factors on its evolution. The intensification of human pressure in the territory is reflected in a progressive increase in sediment accumulation rates in the valleys, peaking during Roman times and the Little Ice Age. Los valles de fondo plano formados por rellenos holocenos constituyen los paisajes más característicos del sector central de la cuenca del Ebro. En este trabajo se analiza una pequeña cuenca fluvial localizada en el norte de la Sierra de Alcubierre, en la que se han identificado tres unidades morfosedimentarias holocenas (H1-H3) y un nivel subfuncional (H4), que son representativos de la evolución geomorfológica regional de la Cuenca del Ebro. Uno de los aspectos más relevantes del valle lo constituye el azud de Bastarás, construcción realizada durante la Pequeña Edad del Hielo para el aprovechamiento del agua, que aporta nuevos datos cronológicos sobre dicha época y acerca de la gestión del territorio. La integración de las dataciones radiocarbónicas obtenidas en la Val de Zaragoza en un marco regional ha permitido precisar las principales etapas de formación de los valles de fondo plano, así como la importancia de los factores climáticos y humanos en su evolución. La intensificación de la presión humana sobre el territorio queda reflejada en un progresivo aumento en las tasas de acumulación de sedimentos en los valles, alcanzando sus picos máximos en Época Romana y en la Pequeña Edad del Hielo

Upper Pliocene to Lower Pleistocene volcanic complexes and Upper Neogene deformation in the south-central Andes (36°30′-38°S)

The Agrio (37º51´S-70º26´W), Vilú Mallín (37º28´S-70º45´W), Trohunco (37º18´S-71º01´W), Domuyo (36º38´S-70º26´W) and Los Cardos-Centinela (37º06´S-70º52´W) volcanic complexes in Argentina are the principal Upper Pliocene to Lower Pleistocene volcanic complexes that occur in the Main Andean Cordillera east of the modern volcanic front in Chile, in the Southern Volcanic zone.Volcanic rocks from these centers along with their stratigraphic relations with nearby Neogene volcanic units provide constraints on the age and style of Neogene deformation in the modern backarc of the Southern Volcanic Zone between 36°30´ and 38°S. New and published radiometric ages and stratigraphic and structural relations show that the region was affected by a latest Miocene compressional deformation that took place between 9 and 6.8 Ma.A heterogeneous picture emerges for the younger deformation of the region which lies along the Quaternary orogenic front.The most important structures include a NNW-trending fault system that joins the Trohunco and Los Cardos-Centinela complexes and is characterized by compressive deformation, and a NE-trending extensional fault system along which the Agrio caldera, Vilú Mallín and Domuyo volcanic complexes are aligned. Overall, the backarc in this region was affected by compressional deformation in the late Miocene and subjected to tectonic collapse and transpressional deformation during the late Pliocene to Quaternary.Fil: Miranda, Fernando. Secretaría de Industria y Minería. Servicio Geológico Minero Argentino; ArgentinaFil: Folguera Telichevsky, Andres. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología. Laboratorio de Tectónica Andina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Leal, Pablo Rodrigo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Naranjo, José Antonio. Servicio Nacional de Geología y Minería; ChileFil: Pesce, Abel. Secretaría de Industria y Minería. Servicio Geológico Minero Argentino; Argentin

Caracterización geofísica de técnicas de explotación de nódulos de sílex en el yacimiento de la Leandra (La Muela, Zaragoza).

En el yacimiento de La Leandra (La Muela, Zaragoza) afloran unidades miocenas lacustres que incluyen habituales niveles de especial concentración de nódulos de sílex. Éstos han sido explotados durante varios periodos y, dadas las características climáticas y demográficas, conservan en ocasiones la topografía original desde su explotación. Con el objetivo de evaluar desde el punto de vista geofísico la estructura de una zona explotada del yacimiento, se realizó prospección geofísica por magnetometría, medidas de susceptibilidad magnética de los materiales y prospección geofísica por georradar que fueron integrados en la información obtenida de un vuelo de dron en la zona. La integración de datos obtenida permite identificar una dinámica de explotación a través de pozos verticales, continuidad lateral de las zonas de explotación generando explanadas horizontales cuando existían niveles de interés, o el abandono y posterior relleno de los huecos de explotación generados en el avance de la explotación. El caso analizado permite inferir a partir de los cambios geométricos y estructurales la progresión de las explotaciones de época previsiblemente neolítica y la identificación de una rutina de explotación a modo de minería de transferencia. In La Leandra archaeological site (La Muela, Zaragoza) Miocene lacustrine deposits outcrop and usually present levels with high concentration of silex nodules. These nodules have been exploited during several periods, and due to the weather and demographic characteristics, original topographical features related to their exploitation usually persists. With the aim of evaluating the site exploitation from a geophysical point of view magnetometry, magnetic susceptibility survey and ground penetrating radar were integrated with the obtained information from a drone flight. This analysis permits to identify an exploitation progression from vertical pits, lateral continuity of the excavation when profitable levels were found through horizontal platforms and the later filling of the excavated pits during the excavation progression. The studied case permits to infer from geometrical and structural changes the mining progression from an expected Neolithic quarry and the identification of an exploitation routine through transfer mining