Modeling nanoplasmonics from an atomistic point of view: from theory to applications

The theoretical modeling of plasmonics is challenging due to the complex interplay&nbsp;between electromagnetic waves, the electronic properties of the material, and the&nbsp;geometrical arrangement of the substrate. In the last decades, the comprehension of&nbsp;plasmons related phenomena arising in noble metal nanostructures and in graphene&nbsp;has benefited from the development of several theoretical methods, which can be divided into two main categories: continuum and&nbsp;ab initio&nbsp;methods respectively. The&nbsp;first are based on classical electrodynamics principles and are limited to the study&nbsp;of systems with a simple shape only, because otherwise the resolution of Maxwell&rsquo;s&nbsp;equation would be impossible.In addition, they may fail when quantum effects&nbsp;have a predominant role on the optical properties of the system, such as in the&nbsp;case of complex-shape structures and nanojunctions.On the contrary,&nbsp;ab initio&nbsp;methods are able to overcome such limitations and return a precise description of&nbsp;plasmonic substrates. However, due to their high computational cost, such methods&nbsp;are constrained to systems of a few thousand of atoms. In this context, classical, yet&nbsp;atomistic models can predict results close to&nbsp;ab initio&nbsp;methods, while being computationally efficient such as continuum models. In this thesis, the optical properties of&nbsp;plasmonic nanostructures are investigated by using a classic, atomistic model called&nbsp;&omega;FQ, which has been developed by the research group I joined during my Ph.D.&nbsp;internship. In&nbsp;&omega;FQ, the charge interaction between the atoms of the nanostructure&nbsp;is modeled in terms of electric conduction between nearest neighbors via a simple&nbsp;Drude mechanism, which is modulated by a Fermi-like step function that mimics&nbsp;quantum tunneling effects. In this way,&nbsp;&omega;FQ is able to take into account quantum&nbsp;effects and returns results in agreement with&nbsp;ab initio&nbsp;references. In particular, the&nbsp;Thesis discusses the developments performed during my Ph.D. research activity to&nbsp;the initial formulation of the&nbsp;&omega;FQ model. Attention is firstly paid to the extension&nbsp;of&nbsp;&omega;FQ to model the optical properties of noble metal NPs which are characterized&nbsp;by interband effects. Then, the coupling between a molecular system, treated at the&nbsp;quantum mechanical level, and a plasmonic substrate, described by means of the&nbsp;&omega;FQ model, is presented and analysed. In this way, the modeling of the enhanced&nbsp;Raman spectrum of target molecules adsorbed on a plasmonic substrate becomes&nbsp;possible.<br /

QM/Classical Modeling of Surface Enhanced Raman Scattering Based on Atomistic Electromagnetic Models

We present quantum mechanics (QM)/frequency dependent fluctuating charge (QM/ωFQ) and fluctuating dipoles (QM/ωFQFμ) multiscale approaches to model surface-enhanced Raman scattering spectra of molecular systems adsorbed on plasmonic nanostructures. The methods are based on a QM/classical partitioning of the system, where the plasmonic substrate is treated by means of the atomistic electromagnetic models ωFQ and ωFQFμ, which are able to describe in a unique fashion and at the same level of accuracy the plasmonic properties of noble metal nanostructures and graphene-based materials. Such methods are based on classical physics, i.e. Drude conduction theory, classical electrodynamics, and atomistic polarizability to account for interband transitions, by also including an ad-hoc phenomenological correction to describe quantum tunneling. QM/ωFQ and QM/ωFQFμ are thus applied to selected test cases, for which computed results are compared with available experiments, showing the robustness and reliability of both approaches

Graphene Plasmonics: a Novel Fully Atomistic Approach for Realistic Structures

We demonstrate that the plasmonic properties of realistic graphene and graphene-based materials can effectively and accurately be modeled by a novel, fully atomistic, yet classical, approach, named $\omega$FQ. Such model is able to reproduce all plasmonic features of these materials, and their dependence on shape, dimension and fundamental physical parameters (Fermi energy, relaxation time and two-dimensional electron density). Remarkably, $\omega$FQ is able to accurately reproduce experimental data for realistic structures of hundreds of nanometers ($\sim$ 370.000 atoms), which cannot be afforded by any \emph{ab-initio} method. Also, the atomistic nature of $\omega$FQ permits the investigation of complex shapes, which can hardly be dealt with by exploiting widespread continuum approaches.Comment: 20 pages, 4 figure

Lake Afrera, a structural depression in the Northern Afar Rift (Red Sea)

The boundary between the African and Arabian plates in the Southern Red Sea region is displaced inland in the northern Afar rift, where it is marked by the Red Sea-parallel Erta Ale, Alaita, and Tat Ali volcanic ridges. The Erta Ale is offset by about 20 and 40 km from the two en echelon ridges to the south. The offset area is highly seismic and marked by a depression filled by lake Afrera, a saline body of water fed by hydrothermal springs. Acoustic bathymetric profiles show ≈80 m deep canyons parallel to the NNW shore of the lake, part of a system of extensional normal faults striking parallel to the Red Sea. This system is intersected by oblique structures, some with strike-slip earthquakes, in what might evolve into a transform boundary. Given that the lake’s surface lies today about 112 m below sea level, the depressed (minus ≈190 m below sea level) lake’s bottom area may be considered the equivalent of the “nodal deep” in slow-slip oceanic transforms. The chemistry of the lake is compatible with the water having originated from hydrothermal liquids that had reacted with evaporites and basalts, rather than residual from evaporation of sea water. Bottom sediments include calcitic grains, halite and gypsum, as well as ostracod and diatom tests. The lake’s level appears to have dropped by over 10 m during the last ≈50 years, continuing a drying up trend of the last few thousand years, after a “wet” stage 9,800 and 7,800 years before present when according to Gasse (1973) Lake Afrera covered an area several times larger than at present. This “wet” stage corresponds to an early Holocene warm-humid climate that prevailed in Saharan and Sub Saharan Africa. Lake Abhé, located roughly 250 km south of Afrera, shows similar climate-driven oscillations of its level

Fully Atomistic Modeling of Plasmonic Bimetallic Nanoparticles: Nanoalloys and Core-Shell Systems

The recently developed ωFQFμ model (ACS Photonics, 9, 3,025–3,034) is extended to bimetallic nanoparticles, such as nanoalloys and core-shell systems. The method finds its grounds in basic physical concepts, such as Drude conduction theory, electrostatics, interband transitions, and quantum tunneling. The approach, which is parametrized on ab initio simulations of Ag-Au nanoalloys, is challenged against complex Ag-Au nanostructures (spheres, nanorods, and core-shell nanoparticles). Remarkable agreement with available experimental data is found, thus demonstrating the reliability of the newly developed approach

Mechanisms of Weak Governance in Grasslands and Wetlands of South America

Weak governance is a major threat to sustainable development, especially in rural contexts and within ecosystems of great social and economic value. To understand and compare its arrangement in the grasslands and wetlands of the Colombian Llanos and the Paraguayan Pantanal, we build upon the Institutional and Development Framework (IAD) as we explore the role of political, economic, and social institutions and combine components of the theory of common-pool resources (CPR) and new institutional economics (NIE). This hybrid conceptualization provides a synthesis of how top-down hierarchical and market-based systems of community-based and natural resource management negatively affect sustainable development in both study areas. Our findings suggest three underlying mechanisms causing a situation of weak governance: centralized (economic and political) power, the role of central and local governments, and social exclusion. Understanding these multidimensional contextual mechanisms improves the understanding that institutional structures supporting arrangements that handle grasslands and wetlands in a sustainable way are needed to protect the ecosystem’s social and economic values, especially in rural and marginalized contexts.Peer Reviewe

Community-Based Governance and Sustainability in the Paraguayan Pantanal

Themegadiverse biome of the Paraguayan Pantanal is in danger due to the expansion of cattle ranching and agricultural frontiers that threaten not only the fragile equilibrium of natural resources, but also that of local governance and cultural identities. As a consequence,weak governance stresses the relations between natural resource-dependent communities, generating socio-environmental conflicts. This perception study seeks to find community-based governance models for sustainability in the context of Paraguayanwetlands. According to the organizational principles of community-based natural resource management (CBNRM), we applied qualitative approaches with the use of the Governance Analytical Framework (GAF) to identify problems and social norms. Our findings suggest that the Yshiro indigenous self-organized group (Unión de las Comunidades Indígenas de la Nación Yshiro (UCINY)) can be considered as a model for community-based governance. Besides, we discovered that this specific governancemodel is highly threatened by the impact of the national neo-extractive economy.Peer Reviewe

Collective Perception of Anthropic and Extractive Interventions in the Colombian Llanos

Increasingly, the developmental model of anthropic and extractive interventions is a global concern. Its impacts are challenging not only the precarious equilibrium of natural resources but also the one of local communities and identities. The case of the Colombian Llanos shows how the local culture of the Cultura Llanera (CL) is deep-rooted with natural resources, their use and their management. Throughout the use of a survey based on the Governance Analytical Framework (GAF), this paper presents and discusses shared problems and social norms. The collective perception of local groups shows that the CL, in particular traditional livestock practices in flooded savannahs, is a key element for the sustainable development of the region. Furthermore, it reveals that agricultural and extractive activities, primarily rice and oil, are considered the main threats to both the ecosystem and the protection of the CL.Peer Reviewe

Mediterranean megaturbidite triggered by the AD 365 Crete earthquake and tsunami

Historian Ammianus Marcellinus documented the devastating effects of a tsunami hitting Alexandria, Egypt, on July 21, AD 365. "The solidity of the earth was made to shake … and the sea was driven away. The waters returning when least expected killed many thousands by drowning. Huge ships… perched on the roofs of houses… hurled miles from the shore….”. Other settlements around the Mediterranean were hit at roughly the same time. This scenario is similar to that of the recent Sumatra and Tohoku tsunamis. Based on geophysical surveys and sediment cores from the Ionian Sea we show that the 20–25 m thick megaturbidite known in the literature as Homogenite/Augias was triggered not by the Santorini caldera collapse but by the 365 AD Cretan earthquake/tsunami. An older similar megaturbidite was deposited after 14.590 ± 80 yr BP, implying a large recurrence time of such extreme sedimentary events in the Mediterranean Sea

Friedensförderung in Zeiten von COVID-19: Risikoadaptierte Strategien von Kooperations- und Entwicklungsprojekten

National and international cooperation and development projects (CDP) are fundamental for peacebuilding. However, unforeseen global crises, like COVID-19, can endanger such projects, requiring rapid adaption. In Colombia, the coronavirus outbreak threatens to slow the implementation of peace-related projects, while simultaneously violence over control and ownership of land increases. Although the mid- to long-term consequences for peacebuilding are unknown, exploring risk-adapted strategies of national and international CDP can help identify crucial aspects for future processes and implementations. This study explores the key challenges and coping strategies of implementing agencies and stakeholders to COVID-19, thus helping to derive and improve risk-adapted strategies. After reviewing academic and grey literature, and implementing a semi-structured survey, peacebuilding risked-adapted strategies to COVID-19 are explored with respect to conflict-affected and vulnerable areas of Colombia. Findings show that increasing complexity rooted in top down governmental measures, the rise of new local power relations (e.g. armed groups, illicit activities), and social alienation are negatively affecting peacebuilding in Colombia. Future CDP risk adapted strategies should build on local interests and needs through public-private and environmental cooperation.Nationale und internationale Kooperations- und Entwicklungsprojekte (CDP) sind für die Friedensförderung von grundlegender Bedeutung. Unvorhergesehene globale Krisen, wie COVID-19, können solche Projekte jedoch gefährden und erfordern eine rasche Anpassung. In Kolumbien droht der Ausbruch des Coronavirus die Durchführung friedensbezogener Projekte zu verlangsamen, während gleichzeitig die Gewalt über die Kontrolle und den Besitz von Land zunimmt. Obwohl die mittel- bis langfristigen Folgen für die Friedenskonsolidierung unbekannt sind, kann die Untersuchung risikoangepasster Strategien des nationalen und internationalen CDP dazu beitragen, entscheidende Aspekte für künftige Prozesse und Implementierungen zu ermitteln. Diese Studie untersucht die Herausforderungen und Bewältigungsstrategien der Durchführungsorganisationen und Interessengruppen im Kontext von COVID-19, umso risikoangepasste Strategien abzuleiten und zu verbessern. Basierend auf Literaturrecherche und der Durchführung semi-strukturierter Interviews werden risikoangepasste Strategien der Friedensförderung für COVID-19 in unterschiedlichen Teilen Kolumbiens untersucht. Die Ergebnisse zeigen, dass die zunehmende Komplexität, die in den Maßnahmen der Regierung von oben nach unten, dem Entstehen neuer lokaler Machtverhältnisse (z. B. bewaffnete Gruppen, illegale Aktivitäten) und in zunehmend sozialer Entfremdung wurzelt, die Friedensförderung in Kolumbien negativ beeinflusst. Künftige risikoangepasste Strategien des CDP sollten auf lokalen Interessen und Bedürfnissen durch öffentlich-private und umweltpolitische Zusammenarbeit aufbauen.Leibniz-Zentrum für Agrarlandschaftsforschung (ZALF) e.V. (3493)Peer Reviewe