Materials & Nanotechnology

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Research from the Department of Materials & Nanotechnology. The interdisciplinary department website may be found at https://www.ndsu.edu/materials_nanotechnology/

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Agricultural Residues and Other Carbon-Based Resources as Feedstocks for Supercapacitor Electrodes
(North Dakota State University, 2017) Wang, Yong
Agricultural residues are generally considered as renewable, economical and environmental-friendly sources to produce carbon-based materials with many advanced applications. Agricultural residues and by-products generated from the agricultural industry, such as distiller's dried grains with solubles (DDGS), are produced every year on a large scale but lack of proper utilization. As a result, seeking high-value applications based on agricultural residues is essential for the promotion of the economy in agricultural states like North Dakota, USA. With the fast development of nanotechnology in recent years, carbon-based nanomaterials have attracted intense research interests in the fields of chemistry, materials science and condensed matter physics due to many unique properties (e.g., chemical and thermal stability, electrical conductivity, mechanical strength, etc.). The development of low-cost nanomaterials using agricultural residues as feedstocks can be a promising route for the sustainable development of the agricultural industry. In this dissertation, the preparation of carbon-based materials from agricultural residues is explored. Many advanced applications are investigated, especially in the field of energy storage devices. The development of porous activate carbons were investigated in detail, and their application as electrode materials of supercapacitors was demonstrated. Hydrothermal carbonization of biomass to produce carbonaceous materials was also covered in this dissertation. In addition to traditional raw materials such as cellulose produced from wood industry, novel material sources such as bacterial cellulose were used to prepare nanocomposites that can be used for the electrodes of supercapacitors. This dissertation contributes to the sustainable development of the agricultural industry in North Dakota.
Bending and Force Recovery in Polymer Films and Microgel Formation
(North Dakota State University, 2018) Elder, Theresa Marie
To determine correlation between geometry and material three different model films: polymethylsiloxane (PDMS), polystyrene (PS), and polycarbonate (PC), were singly bent and doubly bent (forming D-cones). Bends were chosen as they are fundamental in larger complex geometries such as origami and crumples. Bending was carried out between two plates taking force and displacement measurements. Processing of data using moment equations yielded values for bending moduli for studied films that were close to accepted values. Force recovery showed logarithmic trends for PDMS and stretched exponential trends for PS and PC. In a separate experiment a triblock copolymer of polystyrene–polyacrylic acid–polystyrene was subjected to different good and bad solvent mixing with any resulting particle morphology examined. Particles formed more uniformly with high water concentration, particles formed with high toluene concentration and agitation yielded three separate morphologies.
Biomimetic Nanoclay Scaffolds for Bone Tissue Engineering
(North Dakota State University, 2014) Ambre, Avinash Harishchandra
Tissue engineering offers a significant potential alternative to conventional methods for rectifying tissue defects by evoking natural regeneration process via interactions between cells and 3D porous scaffolds. Imparting adequate mechanical properties to biodegradable scaffolds for bone tissue engineering is an important challenge and extends from molecular to macroscale. This work focuses on the use of sodium montmorillonite (Na-MMT) to design polymer composite scaffolds having enhanced mechanical properties along with multiple interdependent properties. Materials design beginning at the molecular level was used in which Na-MMT clay was modified with three different unnatural amino acids and further characterized using Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD). Based on improved bicompatibility with human osteoblasts (bone cells) and intermediate increase in d-spacing of MMT clay (shown by XRD), 5-aminovaleric acid modified clay was further used to prepare biopolymer (chitosan-polygalacturonic acid complex) scaffolds. Osteoblast proliferation in biopolymer scaffolds containing 5-aminovaleric acid modified clay was similar to biopolymer scaffolds containing hydroxyapatite (HAP). A novel process based on biomineralization in bone was designed to prepare 5-aminovaleric acid modified clay capable of imparting multiple properties to the scaffolds. Bone-like apatite was mineralized in modified clay and a novel nanoclay-HAP hybrid (in situ HAPclay) was obtained. FTIR spectroscopy indicated a molecular level organic-inorganic association between the intercalated 5-aminovaleric acid and mineralized HAP. Osteoblasts formed clusters on biopolymer composite films prepared with different weight percent compositions of in situ HAPclay. Human MSCs formed mineralized nodules on composite films and mineralized extracellular matrix (ECM) in composite scaffolds without the use of osteogenic supplements. Polycaprolactone (PCL), a synthetic polymer, was used for preparing composites (films and scaffolds) containing in situ HAPclay. Composite films showed significantly improved nanomechanical properties. Human MSCs formed mineralized ECM on films in absence of osteogenic supplements and were able to infiltrate the scaffolds. Atomic force microscopy imaging of mineralized ECM formed on composite films showed similarities in dimensions, arrangement of collagen and apatite with their natural bone counterparts. This work indicates the potential of in situ HAPclay to impart polymeric scaffolds with osteoinductive, osteoconductive abilities and improve their mechanical properties besides emphasizing nanoclays as cell-instructive materials.
Development of Bio-based Wood Adhesive by Using Cellulose Nanofiber Reinforcement and Crosslinking Agent for Improved Bonding Strength
(North Dakota State University, 2017) Oh, Myungkeun
Engineered woods, plywood, particle board, and oriented strand board, are widely used as a low-cost wood replacement in many applications. Many of the currently used wood adhesives contain chemicals that are harmful to human health and the environment. Increasing environmental and human health concerns have made the development of safe bio-based adhesives a priority. In this study, two plant proteins, zein from corn and wheat gluten, were used to develop wood adhesives. To increase their bond strength, cellulose nanofibers were added to create nanocomposite adhesives and a crosslinking agent was also used. Single-lap shear test, flexural and internal bond tests were performed on dry and water-immersed samples to measure the bond strength. Fractured bond surfaces were studied using optical observation and scanning electron microscopy (SEM) to determine bond failure mechanisms. Thermal and chemical properties of the adhesives were evaluated using thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR), respectively.
The Development, Characterization and Testing of Mg-rich Primers
(North Dakota State University, 2012) Battocchi, Dante
Aluminum alloys are widely used in aircraft industry for their strength and light weight. Those alloys that are hardened by precipitation, especially the Copper-rich of the 2000 series, are prone to corrosion and are protected against it using chromate containing coatings. The primary component of these coating systems is Chromium 6+ (CrVI) that has been found to be very toxic in the environment and carcinogenic, toxic and mutagenic in humans. The Mg-rich primer development is the result of a successful multi-year project funded by the US Air-force with its objective the replacement of coatings based on CrVI with a class of coatings less toxic and with comparable protective performances. The Mg rich primer fulfilled the USAF requirements and it is currently undergoing commercial and military qualifications testing. The use of Mg as one of the active pigments in coatings allows the primer to protect the underlying Al sacrificially, not considered possible for this substrate until now. Mg is anodic to most of the other structural metals and when particulate Mg became available commercially, the concept of the primer was first developed by analogy to Zn-rich coatings for steel. When Mg and Al are in contact and immersed in a corrosive environment, magnesium corrodes preferentially and protects the aluminum.
The Effects of Doping on the Lithium Ionic Conductivity of LLZO Solid-State Electrolyte
(North Dakota State University, 2020) Altayaran, Fadhilah Ahmed
Lithium-ion batteries (LIBs) employing solid-state electrolytes are considerably safer and might potentially generate a higher energy density compared. The goal of this thesis is to investigate the synthesis and stability of doped Li₇La₃Zr₂O₁₂ (LLZO). The reason of adopting LLZO is to presents a high conductivity, good electrochemical stability against metallic lithium. The investigation method involves preparing LLZO powder, pressing it to pellets, sintering the pellets at 1230 ºC and coating metal electrodes on them, followed by the measurement of the lithium ionic conductivity through Electrochemical Impedance Spectroscopy, Scanning Electron Microscopy, and X-ray diffraction. Doping has proven to be an effective way to improve the lithium ionic conductivity. In our research, multi-doped LLZO with Al and Ta and F presented the highest conductivity σ = 1.67×10-4 Scm-1 at room temperature. Our study suggests that the adoption may lead to a significant increase in the lithium ionic conductivity of LLZO solid-state electrolyte.
Electrochemical Impedance Spectroscopy Study of the Ultraviolet Exposure of Ballistic Resistant Polymer Matrix Composites
(North Dakota State University, 2012) Pavlacky, Drew Adam
This study examined the effect of ultraviolet radiation on ballistic resistant polymer matrix composites. Two composite systems studied included a phenolic matrix with either S2 Glass® or Kevlar® fiber laminates. These composites were weathered in ultraviolet conditions and the effects were quantified with multiple destructive and non-destructive testing. Electrochemical impedance spectroscopy (EIS) was used as a non-destructive evaluation method which is a commonly used experiment in the corrosion community. Circuit modeling the EIS spectra produced both resistive and capacitive characteristics inherent of the composite materials. Surface characterization was performed to determine if degradation was occurring at the composite surface. Techniques included: color, gloss, surface profilometry, and water contact angle. Tensile and flexural destructive experimentation revealed the influence of the ultraviolet exposure on the mechanical properties. It was determined that the resistive portion of the EIS response correlated well with the ultimate tensile strength of the S2 Glass® fiber composites.
An Electron Energy-Loss Spectroscopic Investigation of Molecular Interactions at Hydroxyapatite-Collagen Interfaces in Healthy and Diseased (Osteogenesis Imperfecta) Human Bone and Biomineralized Tissue-Engineered Bone
(North Dakota State University, 2018) Payne, Scott Andrew
At its primary level (nm scale) bone is a nanocomposite consisting of a mineral (hydroxyapatite) phase which gives bone its strength and an organic (type I collagen) phase giving bone its fracture toughness. Hydroxyapatite, (HAP) Ca10(PO4)6(OH)2, is the most abundant mineral in the human body. Bone tissue has a complex hierarchical structure spanning multiple length scales (cm to nm). Characterization of mineral composition in biomineralized tissues such as bone at their primary level, is very challenging and requires instrumentation with nanometer-scale spatial resolution. Transmission electron microscopy (TEM) combines high spatial resolution with visual correlation of diffraction and elemental-composition data. Electron energy-loss spectroscopy (EELS) is a sensitive technique used to probe electronic structure at the molecular level. TEM-based EELS is the only available technique that can provide information about the chemical and coordination environment of minerals with nm scale spatial resolution. Prior studies in our group has developed a method to create biomimetic HAP using biomineralization routes inside the clay galleries of montmorillonite clay modified with amino acids (in-situ HAPclay). Incorporation of in-situ HAPclay into polymer scaffolds and seeding with human mesenchymal stem cells has enabled the cells towards differentiation into osteoblastic lineages without differentiating media. Because of the importance of these materials for bioengineering applications, TEM-EELS was used to evaluate differences and similarities among HAP, biomimetic in-situ HAPclay, modified MMT clay, and β-tricalcium phosphate. Osteogenesis imperfecta (OI), also known as brittle bone disease, is an inheritable disease characterized by increased bone fragility, low bone mass, and bone deformity caused primarily by mutation in collagen type I genes and is expressed as changes in structure and mechanics at the macrostructural level of bone. Therefore the mineralization of HAP in OI bone and the molecular basis of OI bone disease makes this an interesting system for molecular-level investigations. Small changes in the valence band and outer electronic structures of the diseased bone have been revealed through EELS. These small changes observed in the electron energy-loss spectra of the OI bone appear to play important biological roles towards development of the disease.
Evaluating Mechanisms of Metastasis of Prostate Cancer to Bone Using 3D Bone-Mimetic Tissue Engineered Scaffolds
(North Dakota State University, 2018) Molla, MD Shahjahan
The complex nature of cancer metastasis necessitates the development of a cancer model based on specific metastatic stages. In this dissertation, we report a polymer-nanoclay based in vitro tumor model which recapitulates early stage of prostate cancer skeletal metastasis. A unique cell culture system termed as ‘sequential culture’ has been applied to create a bone-mimetic niche for colonization of prostate cancer cells. Sequentially cultured MDA PCa 2b cells with MSCs formed self-organized multicellular tumoroids with distinct tight cellular junctions and hypoxic core regions. Further, the sequentially cultured PC-3 cell formed multicellular tumoroid like clusters. We performed immunocytochemical confocal microscopy, qRT-PCR, ELISA assays, nanomechanical evaluation and SEM imaging to characterize our tumor model. We observed that in the in vitro model that MSCs differentiated to matured osteoblasts, EMT (epithelial to mesenchymal transition) was inhibited, MET was enhanced, and hypoxia increased angiogenesis when prostate cancer cells were sequentially cultured with MSCs. We also studied the effect of prostate cancer metastasis on bone microenvironment using different prostate cancer cell lines. We found that the less metastatic MDA PCa 2b cells inhibited mineralized collagen formation whereas, highly metastatic PC-3 cells enhanced mineralized collagen formation. All the experimental results indicated osteoblastic bone formation by PC-3 cells and osteolytic bone resorption by MDA PCa 2b cells. Cancer metastasis is a complex process requiring dramatic remodeling of the cell cytoskeleton. Bone metastasis is characterized by complex biochemical, morphological, pathophysiological, and genetic changes to cancer cells as they colonize at remote bone sites. These changes can be captured in sum by changes to nanomechanical properties of cancer cells during metastasis. Using a specially designed nanoindentation apparatus, we observed significant softening of prostate cancer cells during MET and then further softening during the disease progression at the metastatic site. We observed a substantial reduction in elastic modulus of prostate cancer cells during MET arising from actin reorganization and depolymerization. This is the first study that reveals changes to nanomechanical characteristics of prostate cancer cells with correlation to cytoskeletal changes during MET and progression of the disease at the metastatic bone site.
Experimental Evaluation of Multiscale Behavior of Human Bone
(North Dakota State University, 2014) Gu, Chunju
Bone is the most important structural member of the human body. It has a unique hierarchical structure and its primary constituents, collagen molecules and hydroxyapatite, are arranged in a staggered pattern at nanometer scale. Osteogenesis imperfecta (OI) is an inheritable disease characterized by the fragility of bones and other tissues rich in the type I collagen. OI provides an interesting platform for investigating how alterations of collagen at the molecular level cause changes in the structure of bone. In this dissertation, multi-scale-, particularly nanometer and sub-micro scale-, behaviors of both normal and OI (putative type I) human bones have been evaluated experimentally. Since chemical treatment influences collagen or mineral structure, we have used ―undisturbed bone samples‖ that are not subjected to any chemicals as previously done in literature. Photoacoustic-Fourier transform infrared spectroscopy (PA-FTIR) experiments reveal orientational differences in stoichiometry of hydroxyapatite. FTIR, electron microscopy, scanning probe microscopy, and nanomechanical tests also show that the OI disease results in a distorted microstructure in bone and that the mineralization of hydroxyapatite in OI is also altered. Modulus mapping test displays the distribution of mineralized fibril and extrafibrillar mineral according to the spatial variation of elastic properties. Dynamic nanomechanical behaviors of OI bone and normal bone indicates that the viscoelasticity of intact bone is mostly determined by the mineral. Also investigated are molecular composition and nanomechanical properties of different anatomical positions in the diaphysis of an OI human tibia. Our study on OI bone describes unique differences in collagen as previously described but also elaborates on unique influence of the non-collagenous proteins on mineralization of bone in OI. The fundamental premise of this work is investigation of the molecular basis of this highly debilitating bone disease.
First Principle Study on Interfacial Energetic Alignment and Charge Transfer in Quantum Dots Functionalized via Metal-Organic Dye
(North Dakota State University, 2016) Cui, Peng
Quantum dots (QDs) are promising materials for applications in solar energy conversion because of tunable band gap, multi-exciton generation, photon-upconversion, etc. One of the main challenges of increasing solar energy conversion is to extend the lifetime of photoexcited charge-carriers in conduction band, and one of the strategies is to functionalize QD with mediator molecules. Functionalizing QD with metal-organic dye serves as the additional channel of manipulating charge transfer – the key process increasing solar energy conversion. When metal-organic dye is attached to QD, the interfacial charge transfer direction as well as the rates are determined by a balance between the energetic alignment, QD-dye interaction as well as charge-carrier relaxation dynamics. In this dissertation, we explore the effect of dye functionalization on these elements. We change the metal ion, organic ligands as well as binding geometry of dye, size of QD, polarity of solvent, and use density functional theory to study their effects on energetic alignment. Embedding density functional calculation is used to study the dipole interaction between QD and dye providing additional controllability on charge transfer excitation. At last, we apply Tully surface hopping scheme in combining with density functional theory in time domain to study the charge-carrier relaxation dynamics and charge transfer across the heterogeneous interface in QD/dye nanocrystal composite.
Flexible Nanocomposite Thin Films for Electronic Devices
(North Dakota State University, 2019) Alzaid, Meshal Mufleh
Electronic technology is moving towards flexible, durable, and smaller devices with multifunctional capability. To accelerate this movement, creating materials with outstanding properties is critical. Nanocomposites based on single wall carbon nanotubes (SWCNTs) have received considerable attention because of their unique mechanical and electrical properties. When SWCNTs are formed as a sheet, they provide large contact area and ease of control, especially when incorporated into a flexible format. However, when SWCNT films are adhered to an elastic substrate, there are challenges with their use in flexible electronics, such as a reduction Young’s modulus under deformation. SWCNT films can undergo plastic behavior at even a small strain because individual SWCNTs slide past each other in response to deformation. To address these challenges, a strain-induced elastic buckling instability for mechanical measurements (SIEBIMM) method was used to query SWCNT film mechanics. The buckling wavelength and the film thickness are two main factors that influence the mechanics of nanocomposite thin films adhered to elastomeric substrates. SWCNT films coated with a second nanomaterial, such as a polymer thin film or nanocrystals (NCs), have shown a significant enhancement in elasticity. The studies described in this dissertation demonstrate that polymer thin film can reduce the strain softening of SWCNT films, where both yield strain and Young’s modulus increase with the introduction of SWCNT-polymer layers. Specifically, the films started to exhibit a strong synergy between SWCNT and polymer at a film thickness of around 20 nm, which is attributed to the thickness approaching the characteristic interfacial width between the two materials. Both a ‘passive’ polymer thin film (for example, polystyrene-PS) and an ‘active’ polymer thin film, the conducting polymer poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS), were investigated, spanning a bilayer to the bulk limit of SWCNT-polymer multilayers. In addition, ultrathin SWCNT films coated with colloidal NCs have also been investigated. We have utilized two approaches to coat SWCNT films with NCs: Langmuir-Blodgett (LB) and spray coating. Both Si and CdSe nanocrystals showed a roughly two-fold enhancement in film elasticity, which was attributed to an excluded volume effect that prevents the SWCNT rearrangement under an applied strain.
The Free and Restricted Diffusion of Silicon Nanocrystal Clusters
(North Dakota State University, 2015) Elbaradei, Ahmed Bahgat
Biological applications for silicon nanocrystals (SiNCs) have recently gained more attention because of silicon’s low toxicity. But, to be able to use SiNCs in applications such as biological sensors, labeling or drug delivery we need to understand their transport in different environments and their interaction with cell membrane. I will review some different methods for the synthesis of, and I will give an accounting of encapsulating SiNCs with PEGylated phospholipids to make them soluble in water. I also studied the free diffusion of these micelles in water, as well as their restricted diffusion and interaction with giant unilamellar vesicles (GUVs). I studied their restricted diffusion in oil emulsions. I was able to calculate the diffusion coefficient for a large number of micelles moving freely in water. I also measured the effect of water on the SiNC micelles intensity and observed the difference between the restricted diffusion in liposomes and emulsions.
An Insilico Design of Nanoclay Based Nanocomposites and Scaffolds In Bone Tissue Engineering
(North Dakota State University, 2016) Sharma, Anurag
A multiscale in silico approach to design polymer nanocomposites and scaffolds for bone tissue engineering applications is described in this study. This study focuses on the role of biomaterials design and selection, structural integrity and mechanical properties evolution during degradation and tissue regeneration in the successful design of polymer nanocomposite scaffolds. Polymer nanocomposite scaffolds are synthesized using aminoacid modified montmorillonite nanoclay with biomineralized hydroxyapatite and polycaprolactone (PCL/in situ HAPclay). Representative molecular models of polymer nanocomposite system are systematically developed using molecular dynamics (MD) technique and successfully validated using material characterization techniques. The constant force steered molecular dynamics (fSMD) simulation results indicate a two-phase nanomechanical behavior of the polymer nanocomposite. The MD and fSMD simulations results provide quantitative contributions of molecular interactions between different constituents of representative models and their effect on nanomechanical responses of nanoclay based polymer nanocomposite system. A finite element (FE) model of PCL/in situ HAPclay scaffold is built using micro-computed tomography images and bridging the nanomechanical properties obtained from fSMD simulations into the FE model. A new reduction factor, K is introduced into modeling results to consider the effect of wall porosity of the polymer scaffold. The effect of accelerated degradation under alkaline conditions and human osteoblast cells culture on the evolution of mechanical properties of scaffolds are studied and the damage mechanics based analytical models are developed. Finally, the novel multiscale models are developed that incorporate the complex molecular and microstructural properties, mechanical properties at nanoscale and structural levels and mechanical properties evolution during degradation and tissue formation in the polymer nanocomposite scaffold. Overall, this study provides a leap into methodologies for in silico design of biomaterials for bone tissue engineering applications. Furthermore, as a part of this work, a molecular dynamics study of rice DNA in the presence of single walled carbon nanotube is carried out to understand the role played by molecular interactions in the conformation changes of rice DNA. The simulations results showed wrapping of DNA onto SWCNT, breaking and forming of hydrogen bonds due to unzipping of Watson–Crick (WC) nucleobase pairs and forming of new non-WC nucleobase pairs in DNA.
Investigating the Reduction of Fogging Behavior of Natural Fiber-Filled Polymers
(North Dakota State University, 2021) Thanki, Nidhi Modha
Synthetic fibers such as glass and carbon are used as reinforcement in polymer composites due to their high strength and modulus. However, synthetic fibers are non-biodegradable and contribute to high costs. In literature, various natural fibers, including banana and sisal fiber, as reinforcement in a polymer matrix, are investigated for mechanical and thermal properties to overcome this challenge. Nevertheless, natural fibers bring their issues such as degradation and emissions of Volatiles Organic Compounds (VOCs), resulting in the fogging phenomena when exposed to heating-cooling cycles. In this study, effectiveness of addition of porous fillers in reducing VOCs emissions in biocomposites reinforced with natural fibers is investigated. Mechanical testing exhibited that adding the porous filler into the biocomposites did not hinder mechanical properties. It is hypothesized that adding the porous filler in the biocomposites could reduce the VOCs emission due to the pore structures absorbing the VOCs.
Laser-Assisted Advanced Assembly for MEMS Fabrication
(North Dakota State University, 2014) Atanasov, Yuriy Andreev
Micro Electro-Mechanical Systems (MEMS) are currently fabricated using methods originally designed for manufacturing semiconductor devices, using minimum if any assembly at all. The inherited limitations of this approach narrow the materials that can be employed and reduce the design complexity, imposing limitations on MEMS functionality. The proposed Laser-Assisted Advanced Assembly (LA3) method solves these problems by first fabricating components followed by assembly of a MEMS device. Components are micro-machined using a laser or by photolithography followed by wet/dry etching out of any material available in a thin sheet form. A wide range of materials can be utilized, including biocompatible metals, ceramics, polymers, composites, semiconductors, and materials with special properties such as memory shape alloys, thermoelectric, ferromagnetic, piezoelectric, and more. The approach proposed allows enhancing the structural and mechanical properties of the starting materials through heat treatment, tribological coatings, surface modifications, bio-functionalization, and more, a limited, even unavailable possibility with existing methods. Components are transferred to the substrate for assembly using the thermo-mechanical Selective Laser Assisted Die Transfer (tmSLADT) mechanism for microchips assembly, already demonstrated by our team. Therefore, the mechanical and electronic part of the MEMS can be fabricated using the same equipment/method. The viability of the Laser-Assisted Advanced Assembly technique for MEMS is demonstrated by fabricating magnetic switches for embedding in a conductive carbon-fiber metamaterial for use in an Electromagnetic-Responsive Mobile Cyber-Physical System (E-RMCPS), which is expected to improve the wireless communication system efficiency within a battery-powered device.
Lattice Gases with Molecular Dynamics Collision Operator
(North Dakota State University, 2018) Parsa, Mohammad Reza
The purpose of this dissertation is to provide a direct microscopic underpinning for lattice Boltzmann (and lattice gas) methods. Lattice gases are idealized discrete models that conserve mass and momentum. These conservation laws imply, through the formalism of kinetic theory, that on a macroscopic scale these methods recover the continuity and Navier-Stokes equations. As part of the kinetic theory approach, an ensemble average of the lattice gas is taken leading to a lattice Boltzmann equation. These lattice Boltzmann equations can be implemented directly leading to the new how ubiquitous lattice Boltzmann methods. In this dissertation we step away from justifying lattice Boltzmann methods and the ability of recovering suitable macroscopic equations. Rather, their correspondence to coarse-grained Molecular Dynamics simulations is examine and can be cast in the form of a lattice gas evolution equation. We call this lattice gas the Molecular Dynamic Lattice Gas (MDLG). We use this MDLG to derive the exact formulation for lattice Boltzmann equilibrium distributions, relaxation parameters, and fluctuating properties.
Mechanical Properties of Multilayers of Carbon Nanotube Polystyrene Nanocomposites
(North Dakota State University, 2017) Almutairi, Eid Ali
We have studied the mechanical behavior of multi-layered composite films comprised of single-wall carbon nanotubes and polystyrene polymer, where we focused on three targeted layer thicknesses; 10 nm, 20 nm, and 40 nm. The approach we used is the Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIFMM) technique, which allows us to measure the Young modulus of the films as a function of layer thickness and the number of layers by inducing a compressive stress in the films at different strains; 1 %, 2.5 %, 5 %, 7.5 %, and 10 %. Polystyrene was added in an effort to reduce the plasticity of the carbon nanotube films by filling the pores of the nanotube network. We found that the strongest synergistic effect in this regard occurred for the composite with a layer thickness near 20 nm, while the composite films have reached bulk behavior by the sixth layer.
Multicomponent Doped Barium Strontium Titanate Thin Films for Tunable Microwave Applications
(North Dakota State University, 2014) Alema, Fikadu Legesse
In recent years there has been enormous progress in the development of barium strontium titanate (BST) films for tunable microwave applications. However, the properties of BST films still remain inferior compared to bulk materials, limiting their use for microwave technology. Understanding the film/substrate mismatch, microstructure, and stoichiometry of BST films and finding the necessary remedies are vital. In this work, BST films were deposited via radio frequency magnetron sputtering method and characterized both analytically and electrically with the aim of optimizing their properties. The stoichiometry, crystal structure, and phase purity of the films were studied by varying the oxygen partial pressure (OPP) and total gas pressure (TGP) in the chamber. A better stoichiometric match between film and target was achieved when the TGP is high (> 30 mTorr). However, the O2/Ar ratio should be adjusted as exceeding a threshold of 2 mTorr in OPP facilitates the formation of secondary phases. The growth of crystalline film on platinized substrates was achieved only with a lower temperature grown buffer layer, which acts as a seed layer by crystallizing when the temperature increases. Concurrent Mg/Nb doping has significantly improved the properties of BST thin films. The doped film has shown an average tunability of 53%, which is only ~8 % lower than the value for the undoped film. This drop is associated with the Mg ions whose detrimental effects are partially compensated by Nb ions. Conversely, the doping has reduced the dielectric loss by ~40 % leading to a higher figure of merit. Moreover, the two dopants ensure a charge neutrality condition which resulted in significant leakage current reduction. The presence of large amounts of empty shallow traps related to NbTi localize the free carriers injected from the contacts; thus increase the device control voltage substantially (>10 V). A combinatorial thin film synthesis method based on co-sputtering of two BST sources doped with Mg/Nb and Ce, respectively, was applied. The composition and the dielectric properties of the deposited film were correlated and the optimal concentration of dopants corresponding to high tunability and low dielectric loss was determined in a timely fashion.
Non-Thermal Plasma Synthesis of Luminescent Silicon Nanocrystals from Cylclohexasilane
(North Dakota State University, 2019) Pringle, Todd Andrew
In this report we establish cyclohexasilane (CHS) as a reliable precursor for non-thermal plasma synthesis of high quality photoluminescent silicon nanocrystals (SiNCs). We demonstrate that this synthesis approach can produce high quality, size tunable silicon quantum dots with quantum yields exceeding 60% as synthesized (subsequent work in our group has measured over 70% quantum yield after density gradient ultracentrifugation size purification).After a brief background on non-thermal plasma synthesis, the characterization methods used in this study, and an overview of CHS, we report at length on our development of the apparatus used, and our exploration of the controllable processing parameters of the synthesis method. We describe our successes and challenges with size tuning, sample collection, and passivation. Finally, we discuss preliminary studies we performed to identify promising future research areas. Novel reactor designs, blue light passivation, and magnetic confinement of plasma are described briefly to entice future researchers.

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