Materials Science & Engineering Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2792

Browse

Search Results

Now showing 1 - 10 of 22

CHEMICAL SENSING WITH A TUBE-IN-A-TUBE NANOSTRUCTURE
(2022) Barnes, Benjamin; Wang, YuHuang; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Carbon nanotube field-effect transistors (FETs) exhibit exceptional electrical properties such as ballistic conductance and record-high carrier mobility that make them attractive for potential applications in chemical sensing. Successfully translating these properties to FET chemical sensors may advance the fields of medical diagnosis and in vivo chemical detection for a revolutionary impact on public health and personalized medicine. To this end, we must address multiple challenges for electrical detection, including 1) the need for simultaneous rapid detection and sensitivity to trace amounts of target molecules, 2) the need for detection in high ionic strength conditions, which tend to dampen the field-effect. 3) New fabrication routes are needed for producing FET chemical sensors at scale without compromising their superior electrical properties, and 4) new device form factors are needed for in vivo biosensing that combine these favorable electrical characteristics with biocompatibility, mechanical flexibility, and chemical sensitivity. The commonality in these seemingly diverse challenges is a lack of structure control at multiple length scales, from 10-9 m to 1 m. Particle length and surface defects at the single-nanostructure or nanometer-level dictate the electrical properties and target-probe kinetics, and therefore provide a fundamental lower limit of signal transduction. Furthermore, controlling the surface chemical properties at this scale can be used to tune sensing characteristics in high ionic strength conditions. Controlling the interactions and positioning of multiple nanostructures within a device (on the micrometer scale) dictate sensing time, detection range, and signal transduction. At the bulk level, up to the millimeter scale, the assembly of nanostructures into organized films and coatings dictates whether sensing properties can be preserved when fabricating devices at scale. Additionally, at this scale, device form factors must be considered, which determine the biocompatibility and sensitivity in the case of implantable FET sensors. In this work, I will address the challenge of structure control at multiple length scales using Tube-in-a-tube (Tube^2) nanostructures as a test platform. Tube^2 nanostructures are double-wall carbon nanotubes (DWCNTs) with heavily functionalized outer walls and semiconducting inner walls. This combination enables the use of outer wall surface chemistry modifications to address chemical selectivity and ionic screening challenges, while preserving the electrical transport properties of the inner wall for sensitive signal transduction.
ATOMIC LAYER DEPOSITION OF LEAD ZIRCONATE-TITANATE AND OTHER LEAD-BASED PEROVSKITES
(2019) Strnad, Nicholas Anthony; Phaneuf, Raymond J; Polcawich, Ronald G; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Lead-based perovskites, especially lead zirconate-titanate (PbZrxTi1-xO3, or PZT), have been of great technological interest since they were discovered in the early 1950s to exhibit large electronic polarization. Atomic layer deposition (ALD) is a thin-film growth technique capable of uniformly coating high aspect-ratio structures due to the self-limited nature of the precursor chemisorption steps in the deposition sequence. In this thesis, a suite of related processes to grow lead-based perovskites by ALD are presented. First, a new process to grow ferroelectric lead titanate (PbTiO3, or PTO) by ALD using lead bis(3-N,N-dimethyl-2-methyl-2-propanoxide) [Pb(DMAMP)2] and tetrakis dimethylamino titanium [TDMAT] as the lead and titanium cation precursors, respectively, is discussed. A 360-nm thick PTO film grown by ALD displayed a maximum polarization of 48 µC/cm2 and remanent polarization of ±30 µC/cm2. Second, a new process (similar to the ALD PTO process) to grow PZT by ALD is demonstrated by partial substitution of TDMAT with either tetrakis dimethylamino zirconium or zirconium tert-butoxide. The 200 nm-thick ALD PZT films exhibited a maximum polarization of 50 µC/cm2 and zero-field dielectric constant of 545 with leakage current density < 0.7 µA/cm2. Third, a new ALD process for antiferroelectric lead hafnate (PbHfO3, or PHO) is presented along with electrical characterization showing a field-induced antiferroelectric to ferroelectric phase transition with applications for capacitive energy storage. Finally, ALD lead hafnate-titanate (PbHfxTi1-xO3, or PHT), considered to be an isomorph of PZT, is demonstrated by combining the process for PTO and PHO. The thin-film PHT grown by ALD is shown to have electronic properties that rival PZT grown at compositions near the morphotropic phase boundary (MPB). The processes for both ALD PZT and PHT are shown to yield films with promising properties for microelectromechanical systems (MEMS) actuators and may help to dramatically increase the areal work density of such devices.
SYNTHETIC DEVELOPMENT AND ELECTRODE PROCESSING OF LOW-DIMENSIONAL NANOMATERIALS FOR ADVANCED ELECTROCHEMICAL SYSTEMS
(2018) Lacey, Steven David; Hu, Liangbing; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Future advancements in terms of energy storage systems (lithium-ion batteries [LIBs] and beyond) rely on the development of novel materials, innovative electrode/device architectures, and scalable processing techniques or a combination thereof. In this thesis, each of these three facets will be explored to elucidate material-structure-property relationships of novel low-dimensional nanomaterials (LDNMs; i.e. 2D to 0D) and their assembled electrode/device architectures from a fundamental perspective or through performance demonstrations in conventional (LIBs) as well as advanced battery chemistries (e.g. lithium-oxygen batteries [LOBs]). The first part of the thesis employs an advanced in-situ/operando technique with a newly developed planar microbattery platform to study alkali-metal-ion battery operation at the nanoscale with a model intercalation (2D) material: molybdenum disulfide. By coupling an atomic force microscope (AFM) with an open liquid electrochemical cell, real-time topographical observations, including structural evolution and concomitant solid electrolyte interphase (SEI) formation, can be readily achieved for numerous electrode-electrolyte systems. The second portion focuses on the development and importance of nanoporous carbon-based materials (2D holey graphene [hG], hG/nanohybrids, and holey graphene oxide) to fabricate unique electrode architectures via alternative electrode processing techniques (dry/cold pressing, extrusion-based 3D printing) for LIBs and beyond. Material properties, such as nanoporosity and surface chemistry, enable the processability of these LDNMs into structurally-conscious, additive-free electrode designs and lead to improved overall electrochemical performance, especially for high-energy dense applications such as LOBs. The final portion of this thesis reports a novel high temperature synthesis technique, referred to as carbothermal shock (CTS), capable of combining up to 8 immiscible elements into a single solid solution (0D) nanoparticle on carbon supports. Through exploratory studies, the synthetic capabilities and potential applications of CTS are identified by developing and evaluating novel multimetallic solid solution nanoparticles for both catalytic and energy-related applications, including LOBs.
MULTI-FUNCTIONAL NANOSTRUCTURED FILMS FROM CELLULOSE NANOFIBERS
(2017) Jang, Soo-Hwan; Hu, Liangbing; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Cellulose nanofibrils (CNF) are one of most popular materials in nanotechnologies due to its favorable properties, such as biodegradability and high mechanical performance. However, their nano-/microscopric structure is not fully understood. In this thesis, we studied the structural features of CNF by using atomic force microscopy (AFM) and scanning electron microscopy (SEM), and then assessed the dimensions of single fibers from different wood species. We studied the dependence of cellulose nanopaper strength and toughness on the size of cellulose fibers using dynamic mechanical analysis (DMA). Interestingly, we found that both the strength and toughness increased as the fiber aspect ratio increased. Additionally, stability tests of carbon nanotubes and cellulose nanofibrils (CNT-CNF) solution were conducted by rheological measurement. The solution showed high stability and no visible precipitation. Based on these properties, we fabricated functionalized nanostructured films from CNF and observed promising results from the novel materials.
Understanding the Reaction Mechanism of Nanocomposite Thermites
(2015) Egan, Garth Christopher; Zachariah, Michael R; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Nanocomposite energetics are a relatively new class of materials that combine nanoscale fuels and oxidizers to allow for the rapid release of large amounts of energy. In thermite systems (metal fuel with metal oxide oxidizer), the use of nanomaterials has been illustrated to increase reactivity by multiple orders of magnitude as a result of the higher specific surface area and smaller diffusion length scales. However, the highly dynamic and nanoscale processes intrinsic to these materials, as well as heating rate dependencies, have limited our understanding of the underlying processes that control reaction and propagation. For my dissertation, I have employed a variety of experimental approaches that have allowed me to probe these processes at heating rates representative of free combustion with the goal of understanding the fundamental mechanisms. Dynamic transmission electron microscopy (DTEM) was used to study the in situ morphological change that occurs in nanocomposite thermite materials subjected to rapid (10^11 K/s) heating. Aluminum nanoparticle (Al-NP) aggregates were found to lose their nanostructure through coalescence in as little as 10 ns, which is much faster than any other timescale of combustion. Further study of nanoscale reaction with CuO determined that a condensed phase interfacial reaction could occur within 0.5-5 µs in a manner consistent with bulk reaction, which supports that this mechanism plays a dominant role in the overall reaction process. Ta nanocomposites were also studied to determine if a high melting point (3280 K) affects the loss of nanostructure and rate of reaction. The condensed phase reaction pathway was further explored using reactive multilayers sputter deposited onto thin Pt wires to allow for temperature jump (T-Jump) heating at rates of ~5x10^5 K/s. High speed video and a time of flight mass spectrometry (TOFMS) were used to observe ignition temperature and speciation as a function of bilayer thickness. The ignition process was modeled and a low activation energy for effective diffusivity was determined. T-Jump TOFMS along with constant volume combustion cell studies were also used to determine the effect of gas release in nanoparticle systems by comparing the reaction properties of CuO and Cu2O.
ALD-ENABLED CATHODE-CATALYST ARCHITECTURES FOR LI-O2 BATTERIES
(2015) Schroeder, Marshall Adam; Rubloff, Gary W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The Li-O2 electrochemical redox couple is one of the prime candidates for next generation energy storage. Known for its impressive theoretical metric for specific energy, even current practically obtainable values are competitive with state of the art Li-ion intercalation chemistries and the achievable performance of batteries featuring this nascent technology will continue to improve as fundamental scientific challenges in each component of the device are addressed. The positive electrode is particularly complicated by its role as a scaffold for oxygen reduction and evolution, exhibiting sluggish kinetics, poor chemical stability, and limited cyclability due to parasitic side reactions. Fortunately, recent Li-O2 research has shown some success in improving the performance and cyclability of these O2 cathodes by shifting toward nanostructured architectures with catalytic functionalizations. Atomic layer deposition (ALD) is one of the most promising enabling technologies for fabricating these complex heterostructures. Offering precise control of film thickness, morphology, and mass loading with excellent conformality, this vapor-phase deposition technique is applied in this work to deposit thin film and particle morphologies of different catalyst chemistries on mesostructured carbon scaffolds. This thesis dissertation discusses: (1) development of a lab-scale infrastructure for assembly, electrochemical testing, and characterization of Li-O2 battery cathodes including a custom test cell and a state of the art integrated system for fabrication and characterization, (2) design, fabrication, testing, and post-mortem characterization of a unique 3D cathode architecture consisting of vertically aligned carbon nanotubes on an integrated nickel foam current collector, (3) atomic layer deposition of heterogeneous ruthenium-based catalysts on a multi-walled carbon nanotube sponge to produce a freestanding, binder-free, mesoporous Li-O2 cathode with high capacity and long-term cyclability, (4) evaluation of dimethyl sulfoxide as an electrolyte solvent for non-aqueous Li-O2 batteries, and (5) investigation of the relative importance of passivating intrinsic defects in carbon redox scaffolds vs. introduction of heterogeneous OER/ORR catalysts for improving the long-term stability and cyclability of these Li-O2 electrodes.
RANDOM NETWORKS OF ONE-DIMENSIONAL CONDUCTIVE NANOMATERIALS: FABRICATION, PROPERTIES, AND APPLICATIONS
(2014) Preston, Colin; Hu, Liangbing; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Random networks of one-dimensional conductive nanomaterials are unique structures that exhibit nominal properties useful in flexible thin-film electronics; however, a greater understanding of these properties is necessary to enable high performance device functionality. This thesis presents a comprehensive investigation into the various mechanisms that determine certain characteristics of random networks composed of either carbon nanotubes or silver nanowires. In Chapter 1 we outline the motivation and structure of the dissertation. In Chapter 2, we explore the properties of carbon nanotube spray-coatings, and their application as conductive electrodes for various devices. In this chapter, an ink composed of originally grown nanotubes with a tailored wall number is demonstrated to enable spray-coatings with conductivities reaching 2100 S/cm, which is the highest conductivity for spray-coated carbon nanotube random networks from surfactant-free inks. In Chapter 3, we introduce a synthesis technique to form a new nanostructure of boron-doped few walled carbon nanotubes directed at lowering the bulk resistivity of the nanotube growth yield. An investigation into the structure, morphology, and composition of the boron-doped nanotubes is conducted and compared to undoped few walled nanotubes from the previous chapter. In Chapter 4, we explore the properties of random networks of originally grown Ag NWs and their application towards transparent conducting electrodes for thin-film solar cells. The impact of transmission haze in transparent conducting electrodes is investigated, which provides evidence that the current performance metric of transparent conducting electrodes is insufficient at evaluating their performance in thin-film solar cell devices. In Chapter 5, we expound upon our evidence that transmission haze is a beneficial property for transparent conducting electrodes in thin-film solar cells by introducing a novel Ag NW paper hybrid network that form a transparent conducting electrode with exceptional properties. The combined high transmittance, low sheet resistance, and high transmission haze measured and studied in this new Ag NW paper structure suggests that is the highest performing transparent conducting electrode for thin-film solar cells. In Chapter 6, we consider the impact of this dissertation on the current thin-film technology. Future experiments that may supplement the results in this thesis were also suggested in this chapter.
Heat dissipation in current carrying multiwalled carbon nanotubes
(2014) Voskanian, Norvik; Cumings, John; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Understanding thermal transport is of great interest in combatting the excess heat generated in current electronic circuits. In this dissertation we provide insight and progress in thermal transport in current carrying MWCNT. Chapter 1 gives an overview of the work presented in this dissertation, quickly discusses the motivation for studying heat dissipation in current carrying carbon nanotubes, and outlines the key findings. The chapter outlines the unique remote heating phenomena observed in Joule heated MWCNTs, as well as, the process in which the research led to the discovery of a detection method for near-field heat transfer. The physical properties of carbon nanotubes are discussed in Chapter 2 and the relevant heat transfer mechanisms are introduced. Chapter 3 outlines some of the previous experimental work in studying thermal properties of nanotubes. The results presented in this dissertation rely on previously measured thermal conductivity and thermal contact resistance for nanotubes and thus a discussion of these results is critical. The fabrication process for the measured devices is presenter in Chapter 4. In addition, chapter 4 provides a detailed discussion of the measurement technique employed to probe the thermal properties of the devices presented in Chapter 5 and 6. Chapter 5 discusses the findings in regard to heat dissipation for a current carrying MWCNT supported on a SiN substrate. The results provide definitive proof of substrate heating via hot electrons; a process which can not be explained using traditional Joule heating model and requires the presence of an additional remote heating mechanism. Analysis of the results indicate a reduction in remote Joule heating which led to a series of controlled experiments presented in Chapter 6 in an effort to study substrate thermal conductivity, kSiN, variations as a function of voltage. In this chapter we outline the experimental and simulated results which indicate the remarkable ability of our technique to detect near-field thermal radiation. The enhanced thermal transport via near-field radiation is of great interest for scientific and engineering purposes but its detection has proven difficult. This thesis provides evidence of the sensitivity of the electron thermal microscopy technique to measure near-field radiation.
REAL-TIME INVESTIGATION OF INDIVIDUAL SILICON NANOSTRUCTURED ELECTRODES FOR LITHIUM-ION BATTERIES
(2013) Karki, Khim Bahadur; Cumings, John; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Silicon-based anode materials are an attractive candidate to replace today's widely-utilized graphitic electrodes for lithium-ion batteries because of their high gravimetric energy density (3572 mAh/g vs. 372 mAh/g for carbon) and relatively low working potential (~ 0.5V vs. Li/Li+). However, their commercial realization is still far away because of the structural instabilities associated with huge volume changes of ~300% during charge-discharge cycles. Recently, it has been proposed that silicon nanowires and other related one-dimensional nanostructures could be used as lithium storage materials with greatly enhanced storage capacities over that for graphite in the next generation of lithium-ion batteries. However, the studies to date have shown that the nanomaterials, while better, are still not good enough to withstand a large number of lithiation cycles, and moreover, there is little fundamental insight into the science of the improvements or the steps remaining before widespread adoption. This dissertation seeks to understand the basic structural properties and reaction kinetics of one dimensional silicon nanomaterials, including Si-C heterostructures during electrochemical lithiation/delithiation using in-situ transmission electron microscopy (TEM). I present my work in three parts. In part I, I lay out the importance of lithium-ion batteries and silicon-based anodes, followed by experimental techniques using in-situ TEM. In part II, I present results studied on three different nanostructures: Si nanowires (SiNWs), Si-C heterostructures and Si nanotubes (SiNTs). In SiNWs, we report an unexpected two-phase transformation and anisotropic volume expansion during lithiation. We also report an electrochemically-induced weld of ~200 MPa at the Si-Si interface. Next, studies on CNT@α-Si heterostructures with uniform and beaded-string structures with chemically tailored carbon-silicon interfaces are presented. In-situ TEM studies reveal that beaded-string CNT@ α-Si structures can accommodate massive volume changes during lithiation and delithiation without appreciable mechanical failure. Finally, results on lithiation-induced volume clamping effect of SiNTs with and without functional Ni coatings are discussed. In Part III, a conclusion and a brief outlook of the future work are outlined. The findings presented in this dissertation can thus provide important new insights in the design of high performance Si electrodes, laying a foundation for next-generation lithium ion batteries.
Atomic Layer Deposition of Ru and RuO2: New Process Development, Fabrication of Heterostructured Nanoelectrodes, and Applications in Energy Storage
(2013) Gregorczyk, Keith E.; Rubloff, Gary W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The ability to fabricate heterostructured nanomaterials with each layer of the structure having some specific function, i.e. energy storage, charge collection, etc., has recently attracted great interest. Of the techniques capable of this type of process, atomic layer deposition (ALD) remains unique due to its monolayer thickness control, extreme conformality, and wide variety of available materials. This work aims at using ALD to fabricate fully integrated heterostructured nanomaterials. To that end, two ALD processes, using a new and novel precursor, bis(2,6,6-trimethyl-cyclohexadienyl)ruthenium, were developed for Ru and RuO2 showing stable growth rates of 0.5 Å/cycle and 0.4 Å/cycle respectively. Both process are discussed and compared to similar processes reported in the literature. The Ru process is shown to have significantly lower nucleation while the RuO2 is the first fully characterized ALD process known. Using the fully developed RuO2 ALD process, thin film batteries were fabricated and tested in standard coin cell configurations. These cells showed high first cycle gravimetric capacities of ~1400 mAh/g, which significantly degraded after ~40 cycles. Rate performance was also studied and showed a decrease in 1st cycle capacity as a function of increased rate. These results represent the first reports of any RuO2 battery studied beyond 3 cycles. To understand the degradation mechanisms witnessed in the thin film studies in-situ TEM experiments were conducted. Single crystal RuO2 nanowires were grown using a vapor transport method. These nanowires were cycled inside a TEM using Li2O as an electrolyte and showed a ~95% volume expansion after lithiation, ~26% of which was irreversible. Furthermore, a chemical irreversibility was also witnessed, where the reaction products Ru and Li2O remain even after full delithiation. With these mechanisms in mind heterostructured nanowires were fabricated in an attempt to improve the cycling performance. Core/shell TiN/RuO2 and MWCNT/RuO2 structures were fabricating using the ALD process developed in this work. While the TiN/RuO2 structures did not show improved cycling performance due to connection issues, the MWCNT/RuO2 structure showed a stable areal capacity of ~600 μAh/cm2 after ~20 cycles and were easily cycled 100 times.

Materials Science & Engineering Theses and Dissertations

Browse

Filters

Settings

Sort By

Results per page

Search Results