Nano And Mesoscale Morphology Evolution Of Metal Films On Weakly Interacting Surfaces
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Nano- and mesoscale morphology evolution of metal films on weakly-interacting surfaces by Bo Lü Pdf
Thin films are structures consisting of one or several nanoscale atomic layers of material that are used to either functionalize a surface or constitute components in more complex devices. Many properties of a film are closely related to its microstructure, which allows films to be tailored to meet specific technological requirements. Atom-by-atom film growth from the vapor phase involves a multitude of atomic processes that may not be easily studied experimentally in real-time because they occur in small length- (? Å) and timescales (? ns). Therefore, different types of computer simulation methods have been developed in order to test theoretical models of thin film growth and unravel what experiments cannot show. In order to compare simulated and experimental results, the simulations must be able to model events on experimental time-scales, i.e. on the order of microseconds to seconds. This is achievable with the kinetic Monte Carlo (kMC) method. In this work, the initial growth stages of metal deposition on weakly-interacting substrates is studied using both kMC simulations as well as experiments whereby growth was monitored using in situ probes. Such film/substrate material combinations are widely encountered in technological applications including low-emissivity window coatings to parts of microelectronics components. In the first part of this work, a kMC algorithm was developed to model the growth processes of island nucleation, growth and coalescence when these are functions of deposition parameters such as the vapor deposition rate and substrate temperature. The dynamic interplay between these growth processes was studied in terms of the scaling behavior of the film thickness at the elongation transition, for both continuous and pulsed deposition fluxes, and revealed in both cases two distinct growth regimes in which coalescence is either active or frozen out during deposition. These growth regimes were subsequently confirmed in growth experiments of Ag on SiO2, again for both pulsed and continuous deposition, by measuring the percolation thickness as well as the continuous film formation thickness. However, quantitative agreement with regards to scaling exponents in the two growth regimes was not found between simulations and experiments, and this prompted the development of a method to determine the elongation transition thickness experimentally. Using this method, the elongation transition of Ag on SiO2 was measured, with scaling exponents found in much better agreement with the simulation results. Further, these measurement data also allowed the calculation of surface properties such as the terrace diffusion barrier of Ag on SiO2 and the average island coalescence rate. In the second part of this thesis, pioneering work is done to develop a fully atomistic, on-lattice model which describes the growth of Ag on weakly-interacting substrates. Simulations performed using this model revealed several key atomic-scale processes occurring at the film/substrate interface and on islands which govern island shape evolution, thereby contributing to a better understanding of how 3D island growth occurs at the atomic scale for a wide class of materials. The latter provides insights into the directed growth of metal nanostructures with controlled shapes on weakly-interacting substrates, including twodimensional crystals for use in catalytic and nano-electronic applications.
Thin metal films on weakly-interacting substrates by Andreas Jamnig Pdf
Vapor-based growth of thin metal films with controlled morphology on weakly-interacting substrates (WIS), including oxides and van der Waals materials, is essential for the fabrication of multifunctional metal contacts in a wide array of optoelectronic devices. Achieving this entails a great challenge, since weak film/substrate interactions yield a pronounced and uncontrolled 3D morphology. Moreover, the far-from-equilibrium nature of vapor-based film growth often leads to generation of mechanical stress, which may further compromise device reliability and functionality. The objectives of this thesis are related to metal film growth on WIS and seek to: (i) contribute to the understanding of atomic-scale processes that control film morphological evolution; (ii) elucidate the dynamic competition between nanoscale processes that govern film stress generation and evolution; and (iii) develop methodologies for manipulating and controlling nanoscale film morphology between 2D and 3D. Investigations focus on magnetron sputter-deposited Ag and Cu films on SiO2 and amorphous carbon (a-C) substrates. Research is conducted by strategically combining of in situ and real-time film growth monitoring, ex situ chemical and (micro)-structural analysis, optical modelling, and deterministic growth simulations. In the first part, the scaling behavior of characteristic morphological transition thicknesses (i.e., percolation and continuous film formation thickness) during growth of Ag and Cu films on a-C are established as function of deposition rate and temperature. These data are interpreted using a theoretical framework based on the droplet growth theory and the kinetic freezing model for island coalescence, from which the diffusion rates of film forming species during Ag and Cu growth are estimated. By combining experimental data with ab initio molecular dynamics simulations, diffusion of multiatomic clusters, rather than monomers, is identified as the rate-limiting structure-forming process. In the second part, the effect of minority metallic or gaseous species (Cu, N2, O2) on Ag film morphological evolution on SiO2 is studied. By employing in situ spectroscopic ellipsometry, it is found that addition of minority species at the film growth front promotes 2D morphology, but also yields an increased continuous-layer resistivity. Ex situ analyses show that 2D morphology is favored because minority species hinder the rate of coalescence completion. Hence, a novel growth manipulation strategy is compiled in which minority species are deployed with high temporal precision to selectively target specific film growth stages and achieve 2D morphology, while retaining opto-electronic properties of pure Ag films. In the third part, the evolution of stress during Ag and Cu film growth on a-C and its dependence on growth kinetics (as determined by deposition rate, substrate temperature) is systematically investigated. A general trend toward smaller compressive stress magnitudes with increasing temperature/deposition rate is found, related to increasing grain size/decreasing adatom diffusion length. Exception to this trend is found for Cu films, in which oxygen incorporation from the residual growth atmosphere at low deposition rates inhibits adatom diffusivity and decreases the magnitude of compressive stress. The effect of N2 on stress type and magnitude in Ag films is also studied. While Ag grown in N2-free atmosphere exhibits a typical compressive-tensile-compressive stress evolution as function of thickness, addition of a few percent of N2 yields to a stress turnaround from compressive to tensile stress after film continuity which is attributed to giant grain growth and film roughening. The overall results of the thesis provide the foundation to: (i) determine diffusion rates over a wide range of WIS film/substrates systems; (ii) design non-invasive strategies for multifunctional contacts in optoelectronic devices; (iii) complete important missing pieces in the fundamental understanding of stress, which can be used to expand theoretical descriptions for predicting and tuning stress magnitude. La morphologie de films minces métalliques polycristallins élaborés par condensation d’une phase vapeur sur des substrats à faible interaction (SFI) possède un caractère 3D intrinsèque. De plus, la nature hors équilibre de la croissance du film depuis une phase vapeur conduit souvent à la génération de contraintes mécaniques, ce qui peut compromettre davantage la fiabilité et la fonctionnalité des dispositifs optoélectroniques. Les objectifs de cette thèse sont liés à la croissance de films métalliques sur SFI et visent à: (i) contribuer à une meilleure compréhension des processus à l'échelle atomique qui contrôlent l'évolution morphologique des films; (ii) élucider les processus dynamiques qui régissent la génération et l'évolution des contraintes en cours de croissance; et (iii) développer des méthodologies pour manipuler et contrôler la morphologie des films à l'échelle nanométrique. L’originalité de l’approche mise en œuvre consiste à suivre la croissance des films in situ et en temps réel par couplage de plusieurs diagnostics, complété par des analyses microstructurales ex situ. Les grandeurs mesurées sont confrontées à des modèles optiques et des simulations atomistiques. La première partie est consacrée à une étude de comportement d’échelonnement des épaisseurs de transition morphologiques caractéristiques, à savoir la percolation et la continuité du film, lors de la croissance de films polycristallins d'Ag et de Cu sur carbone amorphe (a-C). Ces grandeurs sont examinées de façon systématique en fonction de la vitesse de dépôt et de la température du substrat, et interprétées dans le cadre de la théorie de la croissance de gouttelettes suivant un modèle cinétique décrivant la coalescence d’îlots, à partir duquel les coefficients de diffusion des espèces métalliques sont estimés. En confrontant les données expérimentales à des simulations par dynamique moléculaire ab initio, la diffusion de clusters multiatomiques est identifiée comme l’étape limitante le processus de croissance. Dans la seconde partie, l’incorporation, et l’impact sur la morphologie, d’espèces métalliques ou gazeuses minoritaires (Cu, N2, O2) lors de la croissance de film Ag sur SiO2 est étudié. A partir de mesures ellipsométriques in situ, on constate que l'addition d'espèces minoritaires favorise une morphologie 2D, entravant le taux d'achèvement de la coalescence, mais donne également une résistivité accrue de la couche continue. Par conséquent, une stratégie de manipulation de la croissance est proposée dans laquelle des espèces minoritaires sont déployées avec une grande précision temporelle pour cibler sélectivement des stades de croissance de film spécifiques et obtenir une morphologie 2D, tout en conservant les propriétés optoélectroniques des films d’Ag pur. Dans la troisième partie, l'évolution des contraintes résiduelles lors de la croissance des films d'Ag et de Cu sur a-C et leur dépendance à la cinétique de croissance est systématiquement étudiée. On observe une tendance générale vers des amplitudes de contrainte de compression plus faibles avec une augmentation de la température/vitesse de dépôt, liée à l'augmentation de la taille des grains/à la diminution de la longueur de diffusion des adatomes. Également, l’ajout dans le plasma de N2 sur le type et l'amplitude des contraintes dans les films d'Ag est étudié. L'ajout de quelques pourcents de N2 en phase gaz donne lieu à un renversement de la contrainte de compression et une évolution en tension au-delà de la continuité du film. Cet effet est attribué à une croissance anormale des grains géants et le développement de rugosité de surface. L’ensemble des résultats obtenus dans cette thèse fournissent les bases pour: (i) déterminer les coefficients de diffusion sur une large gamme de systèmes films/SFI; (ii) concevoir des stratégies non invasives pour les contacts multifonctionnels dans les dispositifs optoélectroniques; (iii) apporter des éléments de compréhension à l’origine du développement de contrainte, qui permettent de prédire et contrôler le niveau de contrainte intrinsèque à la croissance de films minces polycristallins.
Metal film growth on weakly-interacting substrates by Víctor Gervilla Palomar Pdf
Thin films are nanoscale layers of material, with exotic properties useful in diverse areas, ranging from biomedicine to nanoelectronics and surface protection. Film properties are not only determined by their chemical composition, but also by their microstructure and roughness, features that depend crucially on the growth process due to the inherent out-of equilibrium nature of the film deposition techniques. This fact suggest that it is possible to control film growth, and in turn film properties, in a knowledge-based manner by tuning the deposition conditions. This requires a good understanding of the elementary film-forming processes, and the way by which they are affected by atomic-scale kinetics. The kinetic Monte Carlo (kMC) method is a simulation tool that can model film evolution over extended time scales, of the order of microseconds, and beyond, and thus constitutes a powerful complement to experimental research aiming to obtain an universal understanding of thin film formation and morphological evolution. In this work, kMC simulations, coupled with analytical modelling, are used to investigate the early stages of formation of metal films and nanostructures supported on weakly-interacting substrates. This starts with the formation and growth of faceted 3D islands, that relies first on facile adatom ascent at single-layer island steps and subsequently on facile adatom upward diffusion from the base to the top of the island across its facets. Interlayer mass transport is limited by the rate at which adatoms cross from the sidewall facets to the island top, a process that determines the final height of the islands and leads non-trivial growth dynamics, as increasing temperatures favour 3D growth as a result of the upward transport. These findings explain the high roughness observed experimentally in metallic films grown on weakly-interacting substrates at high temperatures. The second part of the study focus on the next logical step of film formation, when 3D islands come into contact and fuse into a single one, or coalesce. The research reveals that the faceted island structure governs the macroscopic process of coalescence as well as its dynamics, and that morphological changes depend on 2D nucleation on the II facets. In addition, deposition during coalescence is found to accelerate the process and modify its dynamics, by contributing to the nucleation of new facets. This study provides useful knowledge concerning metal growth on weakly-interacting substrates, and, in particular, identifies the key atomistic processes controlling the early stages of formation of thin films, which can be used to tailor deposition conditions in order to achieve films with unique properties and applications.
Nanoscale structure forming processes by Viktor Elofsson Pdf
Thin film growth from the vapor phase has for a long time intrigued researchers endeavouring to unravel and understand atomistic surface processes that govern film formation. Their motivation has not been purely scientific, but also driven by numerous applications where this understanding is paramount to knowledge-based design of novel film materials with tailored properties. Within the above framework, this thesis investigates growth of metal films on weakly bonding substrates, a combination of great relevance for applications concerning e.g., catalysis, graphene metallization and architectural glazing. When metal vapor condenses on weakly bonding substrates three dimensional islands nucleate, grow and coalesce prior to forming a continuous film. The combined effect of these initial growth stages on film formation and morphology evolution is studied using pulsed vapor fluxes for the model system Ag/SiO2. It is shown that the competition between island growth and coalescence completion determines structure evolution. The effect of the initial growth stages on film formation is also examined for the tilted columnar microstructure obtained when vapor arrives at an angle that deviates from the substrate surface normal. This is done using two metals with distinctly different nucleation behaviour, and the findings suggest that the column tilt angle is set by nucleation conditions in conjunction with shadowing of the vapor flux by adjacent islands. Vapor arriving at an angle can in addition result in films that exhibit preferred crystallographic orientations, both out-of-plane and in-plane. Their emergence is commonly described by an evolutionary growth model, which for some materials predict a double in-plane alignment that has not been observed experimentally. Here, an experiment is designed to replicate the model’s growth conditions, confirming the existence of double in-plane alignment. New and added film functionalities can further be unlocked by alloying. Properties are then largely set by chemistry and atomic arrangement, where the latter can be affected by thermodynamics, kinetics and vapor flux modulation. Their combined effect on atomic arrangement is here unravelled by presenting a research methodology that encompasses high resolution vapor flux modulation, nanoscale structure v vi probes and growth simulations. The methodology is deployed to study the immiscible Ag-Cu and miscible Ag-Au model systems, for which it is shown that capping of Cu by Ag atoms via near surface diffusion processes and rough morphology of the Ag-Au growth front are the decisive structure forming processes in each respective system. The results generated in this thesis are of relevance for tuning structure of metal films grown on weakly bonding substrates. They also indicate that improved growth models are required to accurately describe structure evolution and emergence of a preferred in-plane orientation in films where vapor arrives at an angle that deviates from the substrate surface normal. In addition, this thesis presents a methodology that can be used to identify and understand structure forming processes in multicomponent films, which may enable tailoring of atomic arrangement and related properties in technologically relevant material systems.
Nanocasting by An-Hui Lu,Dongyuan Zhao,Ying Wan Pdf
Nanostructured materials with tailored properties are regarded as a fundamental element in the development of future science and technology. Research is still ongoing into the nanosized construction elements required to create functional solids. The recently developed technique, nanocasting, has great advantage over others in terms of the synthesis of special nanostructured materials by the careful choice of suitable elements and nanoengineering steps. This new book summarizes the recent developments in nanocasting, including the principles of nanocasting, syntheses of novel nanostructured materials, characterization methods, detailed synthetic recipes and further possible development in this area. The book focuses on the synthesis of porous solids from the viewpoint of methodology and introduces the science of nanocasting from fundamental principles to their use in synthesis of various materials. It starts by outlining the principles of nanocasting, requirements to the templates and precursors and the tools needed to probe matter at the nanoscale level. It describes how to synthesize nano structured porous solids with defined characteristics and finally discusses the functionalization and application of porous solids. Special attention is given to new developments in this field and future perspectives. A useful appendix covering the detailed synthetic recipes of various templates including porous silica, porous carbon and colloidal spheres is included which will be invaluable to researchers wanting to follow and reproduce nanocast materials. Topics covered in the book include: * inorganic chemistry * organic chemistry * solution chemistry * sol-gel and interface science * acid-base equilibria * electrochemistry * biochemistry * confined synthesis The book gives readers not only an overview of nanocasting technology, but also sufficient information and knowledge for those wanting to prepare various nanostructured materials without needing to search the available literature.
Surface Science Techniques by Gianangelo Bracco,Bodil Holst Pdf
The book describes the experimental techniques employed to study surfaces and interfaces. The emphasis is on the experimental method. Therefore all chapters start with an introduction of the scientific problem, the theory necessary to understand how the technique works and how to understand the results. Descriptions of real experimental setups, experimental results at different systems are given to show both the strength and the limits of the technique. In a final part the new developments and possible extensions of the techniques are presented. The included techniques provide microscopic as well as macroscopic information. They cover most of the techniques used in surface science.
Nanoalloys: From Fundamentals to Emergent Applications presents and discusses the major topics related to nanoalloys at a time when the literature on the subject remains scarce. Particular attention is paid to experimental and theoretical aspects under the form of broad reviews covering the most recent developments. The book is organized into 11 chapters covering the most fundamental aspects of nanoalloys related to their synthesis and characterization, as well as their theoretical study. Aspects related to their thermodynamics and kinetics are covered as well. The coverage then moves to more specific topics, including optics, magnetism and catalysis, and finally to biomedical applications and the technologically relevant issue of self-assembly. With no current single reference source on the subject, the work is invaluable for researchers as the nanoscience field moves swiftly to full monetization. Encapsulates physical science of structure, properties, size, composition and ordering at nanoscale, aiding synthesis of experimentation and modelling Multi-expert and interdisciplinary perspectives on growth, synthesis and characterization of bimetallic clusters and particulates supports expansion of your current research activity into applications Synthesizes concepts and draws links between fundamental metallurgy and cutting edge nanoscience, aiding interdisciplinary research activity
Cluster Beam Deposition of Functional Nanomaterials and Devices by Paolo Milani,Mukhles Sowwan Pdf
Cluster Beam Deposition of Functional Nanomaterials and Devices, Volume 15, provides up-to-date information on the CBD of novel nanomaterials and devices. The book offers an overview of gas phase synthesis in a range of nanoparticles, along with discussions on the development of several devices and applications. Applications include, but are not limited to catalysis, smart nanocomposites, nanoprobes, electronic devices, gas sensors and biosensors. This is an important reference source for materials scientists and engineers who want to learn more about this sustainable, innovative manufacturing technology. Explores the use of CBD for the fabrication of functionalized nanomaterials and devices Shows how CBD is used for both sensing and biomedical applications Discusses how this emerging technology is being commercialized for use on a large-scale
Thin Films of Soft Matter by S. Kalliadasis,Uwe Thiele Pdf
This book provides a detailed overview and comprehensive analysis of the main theoretical and experimental advances on free surface thin film and jet flows of soft matter. The book outlines the basic equations and boundary conditions and the derivation of low-dimensional models for the evolution of the free surface. At the experimental front, a variety of recent experimental developments is outlined and the link between theory and experiments is illustrated.
Two Dimensional Transition Metal Dichalcogenides by Narayanasamy Sabari Arul,Vellalapalayam Devaraj Nithya Pdf
This book presents advanced synthesis techniques adopted to fabricate two-dimensional (2D) transition metal dichalcogenides (TMDs) materials with its enhanced properties towards their utilization in various applications such as, energy storage devices, photovoltaics, electrocatalysis, electronic devices, photocatalysts, sensing and biomedical applications. It provides detailed coverage on everything from the synthesis and properties to the applications and future prospects of research in 2D TMD nanomaterials.
Non-Noble Metal Fuel Cell Catalysts by Zhongwei Chen,Jean-Pol Dodelet,Jiujun Zhang Pdf
Written and edited by top fuel cell catalyst scientists and engineers from both industry and academia, this is the first book to provide a complete overview of this hot topic. It covers the synthesis, characterization, activity validation and modeling of different non-noble metal electrocatalysts, as well as their integration into fuel cells and their performance validation, while also discussing those factors that will drive fuel cell commercialization. With its well-structured approach, this is a must-have for researchers working on the topic, and an equally valuable companion for newcomers to the field.
This book is an overview of replication technology for micro- and nanostructures, focusing on the techniques and technology of hot embossing, a scaleable and multi-purpose technology for the manufacture of devices such as BioMEMS and microfluidic devices which are expected to revolutionize a wide range of medical and industrial processes over the coming decade. The hot embossing process for replicating microstructures was developed by the Forschungszentrum Karlsruhe (Karlsruhe Institute of Technology) where the author is head of the Nanoreplication Group. Worgull fills a gap in existing information by fully detailing the technology and techniques of hot embossing. He also covers nanoimprinting, a process related to hot embossing, with examples of actual research topics and new applications in nanoreplication. *A practical and theoretical guide to selecting the materials, machinery and processes involved in microreplication using hot embossing techniques. *Compares different replication processes such as: micro injection molding, micro thermoforming, micro hot embossing, and nanoimprinting *Details commercially available hot embossing machinery and components like tools and mold inserts
Gas-Phase Synthesis of Nanoparticles by Yves Huttel Pdf
The first overview of this topic begins with some historical aspects and a survey of the principles of the gas aggregation method. The second part covers modifications of this method resulting in different specialized techniques, while the third discusses the post-growth treatment that can be applied to the nanoparticles. The whole is rounded off by a review of future perspectives and the challenges facing the scientific and industrial communities. An excellent resource for anyone working with the synthesis of nanoparticles, both in academia and industry.
Serving as the only systematic and comprehensive treatment on the topic of nanoparticle-based materials, this book covers synthesis, characterization, assembly, shaping and sintering of all types of nanoparticles including metals, ceramics, and semiconductors. A single-authored work, it is suitable as a graduate-level text in nanomaterials courses.