<p>This dissertation focuses on the development and calibration of reaction models for multilayered nanocomposites. The nanocomposites comprise sputter deposited alternating layers of distinct metallic elements. Specifically, we focus on the equimolar Ni-Al and Zr-Al multilayered systems. Computational models are developed to capture the transient reaction phenomena as well as understand the dependence of reaction properties on the microstructure, composition and geometry of the multilayers. Together with the available experimental data, simulations are used to calibrate the models and enhance the accuracy of their predictions.</p><p>Recent modeling efforts for the Ni-Al system have investigated the nature of self-propagating reactions in the multilayers. Model fidelity was enhanced by incorporating melting effects due to aluminum [Besnoin et al. (2002)]. Salloum and Knio formulated a reduced model to mitigate computational costs associated with multi-dimensional reaction simulations [Salloum and Knio (2010a)]. However, exist- ing formulations relied on a single Arrhenius correlation for diffusivity, estimated for the self-propagating reactions, and cannot be used to quantify mixing rates at lower temperatures within reasonable accuracy [Fritz (2011)]. We thus develop a thermal model for a multilayer stack comprising a reactive Ni-Al bilayer (nanocalorimeter) and exploit temperature evolution measurements to calibrate the diffusion parameters associated with solid state mixing (720 K - 860 K) in the bilayer.</p><p> </p><p>The equimolar Zr-Al multilayered system when reacted aerobically is shown to </p><p>exhibit slow aerobic oxidation of zirconium (in the intermetallic), sustained for about 2-10 seconds after completion of the formation reaction. In a collaborative effort, we aim to exploit the sustained heat release for bio-agent defeat application. A simplified computational model is developed to capture the extended reaction regime characterized by oxidation of Zr-Al multilayers. Simulations provide insight into the growth phenomenon for the zirconia layer during the oxidation process. It is observed that the growth of zirconia is predominantly governed by surface-reaction. However, once the layer thickens, the growth is controlled by the diffusion of oxygen in zirconia.</p><p>A computational model is developed for formation reactions in Zr-Al multilayers. We estimate Arrhenius diffusivity correlations for a low temperature mixing regime characterized by homogeneous ignition in the multilayers, and a high temperature mixing regime characterized by self-propagating reactions in the multilayers. Experimental measurements for temperature and reaction velocity are used for this purpose. Diffusivity estimates for the two regimes are first inferred using regression analysis and full posterior distributions are then estimated for the diffusion parameters using Bayesian statistical approaches. A tight bound on posteriors is observed in the ignition regime whereas estimates for the self-propagating regime exhibit large levels of uncertainty. We further discuss a framework for optimal design of experiments to assess and optimize the utility of a set of experimental measurements for application to reaction models.</p> / Dissertation

Neural probes are a promising tool in understanding the brain, alleviating symptoms of various diseases like Parkinson’s Disease and allowing for applications like controlling prosthetics directly using the mind. However, current probes suffer from deleterious glial tissue buildup, poor insulation and low electrode yield. In this work, to improve upon current probes, ultra-compliant probes are fabricated and integrated with biodissolvable needles. Mechanically compliant probes allow for reduction in the body’s immune response chronically whereas biodissolvable needles provide sufficient stiffness during insertion. To achieve this, contributions are made in the categories of probe design concepts, device level processes, and processes in support of final probe assembly. Major contributions include incorporation of interleaved atomic layer deposited ceramics to create hybrid materials that provide better insulation properties, reducing the distance between the electrode and the site-of-interest by developing a gray scale lithography based technique to fabricate protruding electrodes and creating probes that improve electrode yield by integrating liquid crystal polymers into the parylene-C probe structure, which allows the parylene-C probe to actuate. To allow for integration of the biodissolvable needle with the probe, a peel-based process is developed that controls the adhesion between parylene-C to Si using different HMDS conditions and a transfer based process is developed that enables hightemperature annealing. In addition, a generalized design of neural probes using meandering interconnect structures is developed, allowing for rapid mechanical design of probes. This is key for neural probes because of the application specific nature of neural probe design.

Friction and wear mitigation is typically accomplished by introducing a shear accommodating layer (e.g., a thin film of liquid) between surfaces in sliding and/or rolling contacts. When the operating conditions are beyond the liquid realm, attention turns to solid coatings. Solid lubricants have been widely used in governmental and industrial applications for mitigation of wear and friction (tribological properties). Conventional examples of solid lubricants are MoS2, WS2, h-BN, and graphite; however, these and some others mostly perform best only for a limited range of operating conditions, e.g. ambient air versus dry nitrogen and room temperature versus high temperatures. Conversely, lubricious oxides have been studied lately as good potential candidates for solid lubricants because they are thermodynamically stable and environmentally robust. Oxide surfaces are generally inert and typically do not form strong adhesive bonds like metals/alloys in tribological contacts. Typical of these oxides is ZnO. The interest in ZnO is due to its potential for utility in a variety of applications. To this end, nanolaminates of ZnO, Al2O3, ZrO2 thin films have been deposited at varying sequences and thicknesses on silicon substrates and high temperature (M50) bearing steels by atomic layer deposition (ALD). The top lubricious, nanocrystalline ZnO layer was structurally-engineered to achieve low surface energy {0002}-orientated grain that provided low sliding friction coefficients (0.2 to 0.3), wear factors (range of 10-7 to 10-8 mm3/Nm) and good rolling contact fatigue resistance. The Al2O3 was intentionally made amorphous to achieve the {0002} preferred orientation while {101}-orientated tetragonal ZrO2 acted as a high toughness/load bearing layer. It was determined that the ZnO defective structure (oxygen sub-stoichiometric with growth stacking faults) aided in shear accommodation by re-orientating the nanocrystalline grains where they realigned to create new friction-reducing surfaces. Specifically, high resolution transmission electron microscopy (HRTEM) inside the wear surfaces revealed in an increase in both partial dislocation and basal stacking fault densities through intrafilm shear/slip of partial dislocations on the (0002) planes via a dislocation glide mechanism. This shear accommodation mode mitigated friction and prevented brittle fracture classically observed in higher friction microcrystalline and single crystal ZnO that has potential broad implications to other defective nanocrystalline ceramics. Overall, this work has demonstrated that environmentally-robust, lubricious ALD nanolaminates of ZnO/Al2O3/ZrO2 are good candidates for providing low friction and wear interfaces in moving mechanical assembles, such as fully assembled rolling element bearings and microelectromechanical systems (MEMS) that require thin (~10-200 nm), uniform and conformal films.

The objective of this dissertation is to develop amorphous metal thin films (AMTFs) for two-terminal electrical device and nanolaminate applications. Two AMTFs, ZrCuAlNi and TiAl, are investigated in both two-terminal electrical device and nanolaminate applications. Material properties including composition, atomic order, surface morphology, surface potential, and electrical resistivity are explored. Application of AMTFs as electrodes in tunneling MIM diodes leverages the ultra-smooth AMTF surface morphology which results from the amorphous atomic order of AMTFs. Analysis methodologies using tunneling MIM diode I-V characteristics are described. A methodology used to estimate potential barrier heights is applied to tunneling MIM diode with differing lower electrode material, upper electrode material and upper electrode deposition technique. A second methodology used to estimate relative tunneling MIM diode insulator thickness is also presented. The presented I-V characteristic analysis methodologies illustrate that tunneling MIM diodes fabricated with AMTF lower electrodes possess tunable I-V characteristics. Nanolaminates are layered materials fabricated with alternating dissimilar thin-film layers. The flexibility of AMTF nanolaminates is illustrated through the presentation of amorphous metal/oxide nanolaminates fabricated with differing AMTFs and aqueous solution deposited oxides. TEM and XPS depth profile analysis of realized nanolaminates are presented. The optical dielectric response of ZrCuAlNi/aluminum phosphate oxide (AlPO) and TiAl/AlPO nanolaminates are evaluated through polarized reflectance measurements and effective medium theory. The optical dielectric response of the nanolaminates differ from the optical dielectric response of the component layers. ZrCuAlNi/AlPO and TiAl/AlPO nanolaminates therefore satisfy the definition of metamaterials. / Graduation date: 2012 / Access restricted to the OSU Community at author's request from May 9, 2012 - May 9, 2013

No description available.

Metastable (Ti,Si)N alloy and TiN/SiNx multilayer thin solid films as well as SiNx/TiN surfaces have been explored. Cubic Ti1-xSixN (0≤x≤0.14) films deposited onto cemented carbide (WC-Co) substrates by arc evaporation exhibited a competitive columnar growth mode where the structure transforms to a feather-like nanostructure with increasing Si content as revealed by x-ray diffraction and transmission electron microscopy. X-ray photoelectron spectroscopy revealed the presence of Ti-N and Si-N bonding, but no amorphous Si3N4. Band structure calculations showed that phase separation of NaClstructure Ti1-xSixN solid solution into cubic SiN and TiN phases is energetically favorable. The metastable microstructure, however, was maintained for the Ti0.86Si0.14N film annealed at 900°C, while recrystallization in the cubic state took place at 1100°C annealing during 2h. The Si content influenced the film hardness close to linearly, by combination of solid-solution hardening in the cubic state and defect hardening. For x=0 and x=0.14, nanoindentation gave a hardness of 29.9±3.4 GPa and 44.7±1.9 GPa, respectively. The hardness was retained during annealing at 900°C. Nanostructured materials, e.g., nanocomposites and nanolaminates, are defined by internal interfaces, of which the nature is still under debate. In this work two-phase model systems were explored by depositing SiNx/TiN nanolaminate films, including superlattices containing cubic SiNx, by dual target reactive magnetron sputtering. It is demonstrated that the interfacial phase of SiNx onto TiN(001) and TiN(111) can be crystalline, and even epitaxial with complex surface reconstructions. Using in situ structural analyses combined with ab initio calculations, it is found that SiNx layers grow epitaxially, giving rise to strong interfacial bonding, on both TiN(001) and TiN(111) surfaces. In addition, TiN overlayers grow epitaxially on SiNx/TiN(001) bilayers in nanolaminate structures. These results provide insight into the development of design rules for novel nanostructured materials. / Report code: LiU-TEK-LIC-2006:51.

<p>Metastable (Ti,Si)N alloy and TiN/SiNx multilayer thin solid films as well as SiNx/TiN surfaces have been explored. Cubic Ti1-xSixN (0≤x≤0.14) films deposited onto cemented carbide (WC-Co) substrates by arc evaporation exhibited a competitive columnar growth mode where the structure transforms to a feather-like nanostructure with increasing Si content as revealed by x-ray diffraction and transmission electron microscopy. X-ray photoelectron spectroscopy revealed the presence of Ti-N and Si-N bonding, but no amorphous Si3N4. Band structure calculations showed that phase separation of NaClstructure Ti1-xSixN solid solution into cubic SiN and TiN phases is energetically favorable. The metastable microstructure, however, was maintained for the Ti0.86Si0.14N film annealed at 900°C, while recrystallization in the cubic state took place at 1100°C annealing during 2h. The Si content influenced the film hardness close to linearly, by combination of solid-solution hardening in the cubic state and defect hardening. For x=0 and x=0.14, nanoindentation gave a hardness of 29.9±3.4 GPa and 44.7±1.9 GPa, respectively. The hardness was retained during annealing at 900°C.</p><p>Nanostructured materials, e.g., nanocomposites and nanolaminates, are defined by internal interfaces, of which the nature is still under debate. In this work two-phase model systems were explored by depositing SiNx/TiN nanolaminate films, including superlattices containing cubic SiNx, by dual target reactive magnetron sputtering. It is demonstrated that the interfacial phase of SiNx onto TiN(001) and TiN(111) can be crystalline, and even epitaxial with complex surface reconstructions. Using in situ structural analyses combined with ab initio calculations, it is found that SiNx layers grow epitaxially, giving rise to strong interfacial bonding, on both TiN(001) and TiN(111) surfaces. In addition, TiN overlayers grow epitaxially on SiNx/TiN(001) bilayers in nanolaminate structures. These results provide insight into the development of design rules for novel nanostructured materials.</p> / Report code: LiU-TEK-LIC-2006:51.

Graphene-based conductor materials (GCMs) consist of stacked and decoupled layers of graphene flakes and could potentially transfer graphene’s outstanding material properties like its exceptional electrical conductivity to the macro scale, where alternatives to the heavy and expensive metallic conductors are desperately needed. To reach super-metallic conductivity however, a systematic electrical conductivity optimization regarding the structural and physical input parameters is required. Here, a new trend in the field of process and material optimization are data-based models which utilize data science methods to quickly identify and abstract information and relationships from the available data. In this work such data-based models for the conductivity of a real GCM thin-film sample are build on data generated with an especially improved and extended version of the network simulation approach by Rizzi et al. [1, 2, 3]. Appropriate methods to create data-based models for GCMs are thereby introduced and typical challenges during the modelling process are addressed, so that data-based models for other properties of GCMs can be easily created as soon as sufficient data is accessible. Combined with experimental measurements by Slawig et al. [4] the created data-based models allow for a coherent and comprehensive description of the thin-films’ electrical parameters across several length scales.:List of Figures List of Tables Symbol Directory List of Abbreviations 1 Introduction 2 Simulation approaches for graphene-based conductor materials 2.1 Traditional simulation approaches for GCMs 2.1.1 Analytical model for GCMs 2.1.2 Finite element method simulations for GCMs 2.2 A network simulation approach for GCMs 2.2.1 Geometry generation 2.2.2 Electrical network creation 2.2.3 Contact and probe setting 2.2.4 Conductivity computation 2.2.5 Results obtained with the network simulation approach 2.3 An improved implementation for the network simulation 2.3.1 Rizzi’s implementation of the network simulation approach 2.3.2 An network simulation tool for parameter studies 2.3.3 Extending the network simulation approach for anisotropy investigations and multilayer flakes 3 Data-based material modelling 3.1 Introduction to data-based modelling 3.2 Data-based modelling in material science 3.3 Interpretability of data-based models 3.4 The data-based modelling process 3.4.1 Preliminary considerations 3.4.2 Data acquisition 3.4.3 Preprocessing the data 3.4.4 Partitioning the dataset 3.4.5 Training the model 3.4.6 Model evaluation 3.4.7 Real-world applications 3.5 Regression estimators 3.5.1 Mathematical introduction to regression 3.5.2 Regularization and ridge regression 3.5.3 Support Vector Regression 3.5.4 Introducing non-linearity through kernels 4 Data-based models for a real GCM thin-film 4.1 Experimental measurements 4.2 Simulation procedure 4.3 Data generation 4.4 Creating data-based models 4.4.1 Quadlinear interpolation as benchmark model 4.4.2 KR, KRR and SVR 4.4.3 Enlarging the dataset 4.4.4 KR, KRR and SVR on the enlarged training dataset 4.5 Application to the GCM sample 5 Conclusion and Outlook 5.1 Conclusion 5.2 Outlook Acknowledgements Statement of Authorship