Dissertations / Theses on the topic 'SCIENCE / Nanoscience'

Nous examinons une question que l'avènement des nanotechnologies rend de plus en plus pressante pour la philosophie des sciences. Elle prend les allures d'une critique de cette dernière en se fondant sur quelques théories philosophiques, représentatives et suffisamment originales sur la science, développées par Thomas Kuhn, Imre Lakatos, Ian Hacking et Serge Robert. Les différents discours sur les nanos et plus précisément le concept de nanotechnologie se sont révélés, à tout le moins, polysémiques et décrivent parfois prématurément une activité qui n'existe pas encore. Ainsi, nous avons requalifié le concept de nanotechnologie en « nanotechnoscience ». Puis nous avons confronté les philosophies des sciences que nous avons retenues aux fins de les mettre à l'épreuve de ce qui apparaît comme un impensé de leurs philosophies, notamment la dimension technologique de la science souvent connue et reconnue, mais « sous-traitée » et reléguée au mieux au second plan. Nos recherches ont donc porté sur chacune des philosophies que nous avons annoncées, sur les nanotechnosciences elles-mêmes, la philosophie de la technologie, mais aussi sur celle naissante des technosciences et des nanotechnosciences sans oublier notre ouverture à des fins heuristiques sur la philosophie du langage d'Austin et la praxéologie de Denis Vernant. Dans cette étude, nous avons traité d'étymologie, d'histoire du préfixe nano et de définition. Puis, nous avons examiné attentivement les différentes philosophies des sciences par lesquelles il nous a paru pertinent d'examiner les nanotechnosciences émergentes afin de voir ce qui dans ces doctrines permettrait d'envisager une réflexion philosophique sur les nanos. Sachant que ces pensées privilégient la représentation sur l'intervention, nous nous sommes posés la question de la place de la technologie dans ces systèmes philosophiques avec l'idée que la technologie est une condition nécessaire quoique non suffisante de toute philosophie à prétention technoscientifique ou nanotechnoscientifique. C'est dans cette optique que nous avons sollicité la théorie des paradigmes, puis celle du falsificationnisme sophistiqué revu et corrigé par le correctionnisme de Robert avant de tenter l'interventionnisme de Hacking. Nous avons pu constater l'omniprésence de la technologie tout comme l'hétérogénéité de la place qui lui est accordée dans ces théories philosophiques. Ainsi de Kuhn à Hacking, la reconnaissance du rôle et de la place de la technologie va crescendo, au point de nous inviter à penser les nanotechnosciences en termes d'« actes de discours ». L'enchevêtrement ou l'entrelacement entre science et technologie nous a inspiré deux analogies : la première avec l'idée de « contexte de performance oral » de Mamoussé Diagne analogue elle-même à la seconde, la performativité introduite et initiée par les réflexions d'Austin sur le discours ordinaire. Notre investigation prend les allures d'une mise à l'épreuve de toutes ces philosophies à l'aune de la place qu'occupe la technologie dans leurs systèmes respectifs. Nous avons eu recours à l'analyse comparative des discours philosophiques sur la science ainsi que ce que nous avons appris sur les pratiques scientifiques, le tout complété par une approche lexicométrique basée sur le corpus des principaux ouvrages de Kuhn, Lakatos, Robert et Hacking. Notre démarche nous a amené à mettre en cause l'étymologie du préfixe nano trop hâtivement attribuée au grec alors qu'il serait plus à propos de la considérer comme latine, puis nous avons tenté d'établir l'idée que les « nanotechnologies » n'existent pas et que ce que l'on appelle bien souvent ainsi relève d'un abus de langage et d'une sorte d'anachronisme inversée. De cette critique nous avons tenté de tirer des leçons qui ont inspiré la requalification conceptuelle de l'activité qu'est censé désigner ce morphème en « nanotechnoscience » que nous avons redéfini en tenant compte de plusieurs facteurs déterminants
This thesis focuses on the consideration of a question that the advent of what is called nanotechnology makes it increasingly urgent to philosophy in general and the philosophy of science in particular because of the inexistence of the “nanotechnology” stricto sensu, the lack of good definition and the default of something like a “nanophilosophy”. We critique the latter based on some philosophical, representative and sufficiently original theories of science, developed by Thomas Kuhn, Imre Lakatos, Ian Hacking and Serge Robert. Different discourses on nanos and more specifically the concept of nanotechnology proved, at least, polysemous and sometimes describe an activity which in the strict sense does not exist prematurely. Thus, we have reclassified the concept of nanotechnology "nanotechnoscience" and proposed a more rigorous definition emphasizing the hybrid nature of this activity, both theoretical and practical, scientific and technological. Then we compared the philosophies of science that we have selected to make them confront what appears to be an unthought of their philosophies, including the technological dimension of science often known and recognized, but "outsourced" and relegated to better secondary. Our research has therefore focused on each of the philosophies that we announced on the nanotechnosciences themselves, philosophy of technology, but also on emerging technosciences and nanotechnoscience not forgetting our opening for heuristic purposes on the philosophy of language of Austin and praxeology of Denis Vernant. Then, we carefully examined the different philosophies of science which seemed appropriate to consider the emerging nanotechnosciences so as to see what in these doctrines would help envisaging a philosophical reflection on the Nano. Knowing that these thoughts favor representing rather than intervening, we questioned the role of technology in these philosophical systems with the idea that technology is a necessary though not sufficient condition for any claim of technoscientific or nanotechnoscientific philosophy. It is in this context that we solicited the paradigms theory, then the sophisticated falsificationism reviewed and corrected by Robert's correctionism before attempting interventionism Hacking's interventionism. During this exercise we have seen the pervasiveness of technology as well as the heterogeneity of the place it is granted in these philosophical theories. The entanglement or intertwining between science and technology inspired us two analogies: the first with the idea of "context of oral performance" by Mamoussé Diagne, analogous itself to the second, performativity introduced and initiated by Austin's reflections on ordinary language. Our investigation takes on the appearance of a testing of all these philosophies in terms of the place of technology in their respective systems. To achieve this, we resorted to the comparative analysis of philosophical discourse on science and what we have learned about scientific practices, complemented by a lexicometric approach based on the corpus of the principal works published from Kuhn, Lakatos, Robert and Hacking. From our critique we have tried to draw lessons that inspired the conceptual requalification of the activity that this morpheme is intended to mean into "nanotechnoscience" which we have redefined. This established at the end of this analysis, we could say that neither the philosophy of Kuhn or Lakatos, nor that of Robert leave enough space for technology to position itself as philosophies of technosciences. The one which seems the most appropriate is the interventionism defended by Hacking, but which Gilbert Hottois criticized for not having taken the step that would have led to a philosophy of authentic technosciences. It was then that tracks to Bacon and Peirce are suggested respectively by Hacking and Schmidt and Nordmann

Mesoporous silicate have widespread potential applications, such as drug delivery, supports for catalysis, selective adsorption and host to guest molecules. Most important in the area of scientific research and industrial applications is their demand due to its extremely high surface areas (> 800m ²g⁻¹) and larger pores with well defined structures.

Mesoporous silicate (MCM-41) samples were prepared by hydrothermal method under various chemo-physical conditions and various experimental methods such as small angle X-rays scattering (SAXS), Nitrogen adsorption-desorption analysis at 77 K, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were employed to investigate the changes in the structural morphology and subtle lattice parameter changes. With regards to the subtle changes in the structural characteristics of the synthesized mesoporous silicate, we seek to understand the electron density function changes as the synthesis parameter are varied from low molar concentration of ATAB/Si to higher concentration, the system becoming more acidity due to increase in the hydrolysis time of pH regulator as a result of increased production of ethanol and acetic acid and the changes due to extended reaction time.

This Ph.D. research tries to understand the influence of various parameters like surfactant-Si molar ratio, reaction time, and the hydrolysis of the pH regulator on the orderliness/disorderliness of the lattice order, lattice spacing and electron density function. The stages during synthesis are carefully selected to better understand where the greater influence on the overall structural morphology exist so as to be able to ne tune this parameter for any desired specification and application.

The SAXS measurement were conducted on a HECUS S3-Micro X-ray system at Rensselaer Polytechnic Institute, Troy, NY. while the data evaluation and visualization were carried in 3DView 4.2 and EasySWAXS software. The electron density functions were generated with a proprietary software called edens.

In this dissertation, the following observations have been revealed resulting from SAXS measurement.

1. As one increases the hydrolysis duration of ethyl acetate, a gradual collapse of the lattice spacing of the mesoporous silcate MCM-41 is observed. We found from SAXS that there is a slight right shift of the spectra toward the higher q-values indicating that we are gradually losing orderliness in the lattice spacing and hexagonal structure of the mesoporous silica. Also, the intensity of the peak of second and third peaks are diminutive when compared to sample with shorter hydrolysis time.

2. A comparison of the SAXS spectra for the different molar concentration sample reveals that the 0:5M samples shows a deteriorating structural characteristics as compared to the 0:25 and 0:75M samples respectively and a clear decrease in the (100) reflection planes. Also noticed is the slight rightward shift in the overall spectrum prole. This observation suggest that further analysis is needed so as to better understand the result.

3. We establish that during MCM-41 synthesis, longer reaction time is needed to produce quality sample with well defined structurally characteristic for its intended application because according to spectrum for the sample with a longer reaction time (aging), a shift towards the lower q-values indicates that a sample with a larger lattice parameter and wall thickness but the intensities of its peak are diminishing when compared to the other of relatively shorter reaction time.

Other complementary techniques were used to corroborated the result obtained from SAXS. Nitrogen adsorption-desorption analysis at 77K was used to generate the isotherms while B.E.T method was used in conjunction with the isotherms to obtained the very important surface area information. SEM provide a visual structural morphology of the samples and FTIR gave the fingerprint detail of the bonds and vibration types between particle present.

This thesis offers a mixed-method exploratory investigation of global scientific mobility. Contextualised as an important factor in the development of national capacities in science and innovation, global scientific mobility has so far remained a relatively underdeveloped subject in current scholarship. In this doctoral research, the focus on the impact of global scientific mobility that entails change of affiliation on (1) research practice, in particular, boundaries of academic activities, and (2) career development trajectories, increasingly affected by globalisation, is assumed. This research responds to the interest among academic and policy communities in the role of human resources in science-driven economic growth. It integrates three sets of literature, encompassing systems approach to studying learning and innovation; transnational approach to migration studies, and social studies of science that focus on academic citizenship, to explain global transformations in scientific mobility flows across countries and regions; and the post-migration impact of scientists in host organisations and communities. Empirically, this research focuses on career trajectories and elements of academic practice of Russian-speaking nanoscientists educated in post-Soviet countries and working abroad. The Soviet Union was an internationally isolated research system and developed peculiar norms of organisation, communication and governance of science. After the breakdown, post-Soviet countries experienced large-scale human capital flight. Nanotechnology is a generic technology, thought to aggregate advanced use-inspired areas of physics, chemistry and engineering. Around the world, nanotechnology has significant political importance. Policy and public-driven emerging technology agendas reveal contribution of competent post-Soviet scientists, but also elicit differences in approaches and rewards. This study finds significant transformations in scientific mobility flows caused by globalisation-induced opportunities. As relocation becomes easier to accomplish, scientists increasingly build their careers not only in multiple organisations, but also in multiple countries. At the same time, national differences in career development paths and norms of academic community membership have significant influence on career development opportunities of scientists. However, unique skills developed during mobility open up alternative options for globally mobile Russian-speaking nanoscientists, such as engagement in transnational science diaspora networks. This research contributes to understanding of scientific mobility as a simultaneous, continuous, network-based process. It further provides insight into development of multidisciplinary research area that encompasses broader understanding of roles, activities, contributions and opportunities of foreign-born scientists in the globalising world.

Carbon nanotubes (CNTs) are materials with significant potential applications due to their desirable mechanical and electronic properties, which can both vary based on their structure. Electronic applications for CNTs are still few and not widely available, mainly due to the difficulty in the control of fabrication. Carbon nanotubes are grown in batches, but despite many years of research from their first discovery in 1991, there are still many unanswered questions regarding how to control the structure of CNTs. This work attempts to bridge some of the gap between question and answer by focusing on the catalyst particle used in common CNT growth procedures. Ostwald ripening studies on iron nanoparticles are performed in an attempt to link catalyst morphology during growth and CNT chirality (the structure aspect of a nanotube that determines its electrical properties). These results suggest that inert gas dynamics play a critical role on the catalyst morphology during CNT growth. A novel method for CNT catalyst activation by substrate manipulation is presented. Results of this study build upon prior knowledge of the role of the chemistry of the substrate supporting CNT catalysts. By bombarding sapphire, a substrate known to not support CNT growth, with an argon ion beam, the substrate is transformed into an active CNT growth support by modifying both the structure and chemistry of the sapphire surface. Finally, catalyst formation is studied with transmission electron microscopy by depositing an iron gradient film in order to identify a potential critical catalyst size and morphology for CNT growth. A relationship between catalyst size and morphology has been identified that adds evidence to the hypothesis that a catalysts activity is determined by its size and ability to properly reduce.

The nematic phases of liquid crystals have been the most thoroughly investigated since the founding of the liquid crystal field in the early 1900’s. The resulting technologies, most notably the liquid crystal display, have changed our world and spawned an entire industry. Consequently, the recent identification of a new type of nematic – the twist-bend nematic – was met with as much surprise as excitement, as it melds the fluid properties and environmental responsiveness of conventional nematics with the intrinsic polarization and complex ordering of bent-core liquid crystals. I summarize the history of the twist-bend nematic phase, charting the development of our understanding from its first identification to the present day. Furthermore, I enumerate and highlight my own efforts in the field to characterize the behavior and nanoscale organization of the twist-bend phase.

Characterization of magnetic domain structure is essential to understand and manipulate the magnetic properties of materials. In this thesis, we have utilized Lorentz Transmission Electron Microscopy (LTEM) in combination with image simulations based on micromagnetic models, to investigate the magnetic domain structure of a unique nano-chessboard structure consisting of L1 0 and L1₂ phases in a Co₄₀Pt₆₀ alloy. We have shown high-resolution LTEM images of nano-size magnetic features acquired through spherical aberration correction in Lorentz Fresnel mode. Phase reconstructions based on the transport of intensity equation has been carried out to fully understand the magnetic domain structure and to extract quantitative information, including direction of magnetic induction and magnetic domain wall width, from the Lorentz TEM images. The experimental Fresnel images of the nano-chessboard structure show zig-zag shaped magnetic domain walls at the inter-phase boundaries between L10 and L1₂ phases. A circular magnetization distribution with vortex and anti-vortex type arrangement is evident in the phase reconstructed magnetic induction maps as well as simulated maps. The magnetic contrast in experimental LTEM images has been properly interpreted with the help of magnetic induction maps simulated for various relative electron beam-sample orientations inside TEM. Apart from the nano-chessboard structure, this alloy shows other interesting microstructural features such as anti-phase boundaries, tweed structure, coarse L10 plates, and macro-twins all of which have been characterized using conventional bright field/dark field TEM imaging and compared with their respective Lorentz TEM images. The magnetic domain wall widths obtained for each microstructure has been compared and the influence of microstructure and the particle size on wall widths has been discussed.

In light of their escalating exposure to possible environmental toxicants, there are many biological systems that need to be evaluated in a resource and time efficient manner. Understanding how toxicants behave in relation to their physicochemical properties and within complex biological media is especially important toward developing a stronger scientific foundation of these systems so that adequate regulatory decisions may be made. While there are many emerging methods available for the detection and characterization of these chemicals, nanotechnology has presented itself as a promising alternative toward creating more efficient assays. In particular, metallic nanoparticles and thin films exhibit unique optical properties that allow for highly sensitive and multiplexed studies to be performed. These plasmonic materials often preclude the use of molecular tags and labels, enabling direct characterizations and enhancing the throughput of biomolecular studies. However, their lack of specificity toward certain targets and potential toxicity has thus far precluded their widespread use in toxicity testing.

The cell membrane, a natural signal transducer, represents one of the fundamental structures for biological recognition and communication. These interfaces principally function as a selective barrier to exogenous materials, including ions, signaling molecules, growth factors, and toxins; therefore, understanding interactions at membrane interfaces is a vital step in elucidating how biological responses are effected. Supported lipid bilayers, which may easily be tailored in composition and complexity, are ideal interfaces for coupling to plasmonic assays since they may be supported in close proximity to metallic nanoparticles and thin films, where measurements are most sensitive. This research will focus on the coupling of plasmonic materials and biomimetic interfaces to increase the sensitivity, efficiency, and throughput of conventional toxicity assays. The fabrication of new plasmonic materials for membrane-based assays is presented, as well as method developments in membrane array formation and opportunities for hyphenation with complementary analytical techniques.

Given a rapidly developing world, the need exists for inexpensive renewable energy alternatives to help avoid drastic climate change. Photovoltaics have the potential to fill the energy needs of the future, but significant cost decreases are necessary for widespread adoption. Semiconductor nanocrystals, also known as quantum dots, are a nascent technology with long term potential to enable inexpensive and high efficiency photovoltaics. When deposited as a film, quantum dots form unique nanocomposites whose electronic and optical properties can be broadly tuned through manipulation of their individual constituents.

The contents of this thesis explore methods to understand and optimize the optoelectronic properties of PbSe quantum dot films for use in photovoltaic applications. Systematic optimization of photovoltaic performance is demonstrated as a function of nanocrystal size, establishing the potential for utilizing extreme quantum confinement to improve device energetics and alignment. Detailed investigations of the mechanisms of electrical transport are performed, revealing that electronic coupling in quantum dot films is significantly less than often assumed based on optical shifts. A method is proposed to employ extended regions of built-in electrical field, through controlled doping, to sidestep issues of poor transport. To this end, treatments with chemical redox agents are found to effect profound and reversible doping within nanocrystal films, sufficient to enable their use as chemical sensors, but lacking the precision required for optoelectronic applications. Finally, a novel doping method employing "redox buffers" is presented to enact precise, stable, and reversible charge-transfer doping in porous semiconductor films. An example of oxidatively doping PbSe quantum dot thin films is presented, and the future potential for redox buffers in photovoltaic applications is examined.

Carbon nanotubes are a relatively new area of research which has gained significant attention in published literature. One reason for this interest is their use in multi-phase composites, specifically where they can enhance traditional polymer matrices. Many authors have attempted to adapt conventional micromechanical analyses reserved for microfibers to the nano scale. A review of these works is presented. In depth analysis is provided on one of these two phase (nanotube and matrix) models, the Anumandla-Gibson model, originally published in 2006. A discussion of its strengths and sensitivities is given, with numerical data to support the conclusions. It is extended to three-phase composites through the use of classical laminated plate theory. A literature survey is conducted to gather published two and three-phase experimental results for comparison. Two phase experimental results agree well with the present model, whereas three phase data was limited, but initial comparisons were promising.

Low-k dielectrics have been incorporated into advanced computer chip technologies as a part of the continuous effort to improve computer chip performance. One drawback associated with the implementation of low-k dielectrics is the large leakage current which conducts through the material, relative to silica. Another drawback is that the breakdown voltage of low-k dielectrics is low, relative to silica [1]. This low breakdown voltage makes accurate reliability assessment of the failure mode time dependent dielectric breakdown (TDDB) in low-k dielectrics critical for the successful implementation of these materials. The accuracy with which one can assess this reliability is currently a topic of debate.

These material drawbacks have motivated the present work which aims both to contribute to the understanding of electronic conduction mechanisms in low-k dielectrics, and to improve the ability to experimentally characterize changes which occur within the material prior to TDDB failure. What follows is a study of the influence of an applied magnetic field on the conductivity of a low-k dielectric, or in other words, a study of the material’s magnetoresistance.

This study shows that low-k dielectrics used as intra-level dielectrics exhibit a relatively large negative magnetoresistance effect (∼2%) at room temperature and with modest applied magnetic fields (∼100 Oe). The magnetoresistance is attributed to the spin dependence of trapping electrons from the conduction band into localized electronic sites. Mixing of two-electron spin states via interactions between electron spins and the the spins of hydrogen nuclei is suppressed by an applied magnetic field. As a result, the rate of trapping is reduced, and the conductivity of the material increases.

This study further demonstrates that the magnitude of the magnetoresistance changes as a function of time subjected to electrical bias and temperature stress. The rate that the magnetoresistance changes correlates to the intensity with which the material was stressed. It is postulated that the change in magnetoresistance which occurs as a result of bias temperature stress could be used as an alias for measuring the degradation which contributes to TDDB.

Finally, it is shown that the magnetoresistance behavior is non-monotonic. That is, for small values of applied magnetic field (∼2 Oe) the conductivity initially decreases, while for further increase of the magnetic field the conductivity increases to a saturation. The non-monotonic behavior is consistently described in the context of competing spin mixing mechanisms.

Our need to reduce global energy use is well known and without question, not just from an economic standpoint but also to decrease human impact on climate change. Emerging advances in this area result from the ability to tailor-make materials and energy-saving devices using solution–phase chemistry and deposition techniques. Colloidally synthesized nanocrystals, with their tunable size, shape, and composition, and unusual optical and electronic properties, are leading candidates in these efforts. Because of recent advances in colloidal chemistries, the inventory of monodisperse nanocrystals has expanded to now include metals, semiconductors, magnetic materials, and dielectric materials. For a variety of applications, an active layer composed of a thin film of randomly close-packed nanocrystals is not ideal for optimized device performance; here, the ability to arrange these nano building units into mesoporous (2 nm < d < 50 nm) architectures is highly desirable. Given this, the goal of the work in this dissertation is to determine and understand the design rules that govern the interactions between ligand-stripped nanocrystals and polymeric materials, leading to their hierarchical assembly into colloidal nanocrystal frameworks. I also include the development of quantitative, and novel, characterization techniques, and the application of such frameworks in energy efficiency devices such as electrochromic windows.

Understanding the local environment of nanocrystal surfaces and their interaction with surrounding media is vital to their controlled assembly into higher-order structures. Though work has continued in this field for over a decade, researchers have yet to provide a simple and straightforward procedure to scale across nanoscale material systems and applications allowing for synthetic and structural tunability and quantitative characterization. In this dissertation, I have synthesized a new class of amphiphilic block copolymer architecture-directing agents based upon poly(dimethylacrylamide)-b-poly( styrene) (PDMA-b-PS), which are strategically designed to enhance the interaction between the hydrophilic PDMA block and ligand-stripped nanocrystals. As a result, stable assemblies are produced which, following solution deposition and removal of the block copolymer template, renders a mesoporous framework. Leveraging the use of this sacrificial block copolymer allows for the formation of highly tunable structures, where control over multiple length scales (e.g., pore size, film thickness) is achieved through the judicious selection of the two building blocks. I also combine X-ray scattering, electron imaging, and image analysis as novel quantitative analysis techniques for the physical characterization of the frameworks.

Last, I demonstrate the applicability of these porous frameworks as platforms for chemical transformation and energy efficiency devices. Examining the active layer in an electrochromic window, I show a direct comparison between, and improved performance for, devices built from both randomly close-packed nanocrystals and those arranged in mesoporous framework architectures. I show that the framework also serves as a scaffold for in-filling with a second active material, rendering a dual–mode electrochromic device. These results imply that there may exist a broad application space for these techniques in the development of ordered composite architectures.

The Next Generation Science Standards represent a significant challenge for K-12 school reform in the United States in the science, technology, engineering and mathematics (STEM) disciplines (NSTA, 2012). One important difference between the National Science Education Standards (NRC, 1996) and the Next Generation Science Standards (Achieve, 2013) is the more extensive inclusion of nanoscale science and technology. Teacher PD is a key vehicle for implementing this STEM education reform effort (NRC, 2012; Smith, 2001). The context of this dissertation study is Project Nanoscience and Nanotechnology Outreach (NANO), a secondary level professional development program for teachers that provides a summer workshop, academic year coaching and the opportunity for teacher participants to borrow a table-top Phenom scanning electron microscope and a research grade optical microscope for use in their classrooms. This design-based descriptive case study examined the thinking of secondary teachers in the 2012 Project NANO cohort as they negotiated the inclusion of novel science concepts and technology into secondary science curriculum. Teachers in the Project NANO 2012 summer workshop developed a two-week, inquiry-based unit of instruction drawing upon one or more of nine big ideas in nanoscale science and technology as defined by Stevens, Sutherland, and Krajcik (2011). This research examined teacher participants' metastrategic thinking (Zohar, 2006) which they used to inform their pedagogical content knowledge (Shulman, 1987) by focusing on the content knowledge teachers chose to frame their lessons, their rationales for such choices as well as the teaching strategies that they chose to employ in their Project NANO unit of instruction. The study documents teachers various entry points on a learning progression as teachers negotiated the inclusion of nanoscale science and technology into the curriculum for the first time. Implications and recommendations for teacher professional development are offered.

Viable methods for bacterial biofilm remediation require a fundamental understanding of biofilm mechanical properties and their dependence on dynamic environmental conditions. Mechanical test data, quantifying elasticity or adhesion, may be used to perform physical modeling of biofilm behavior, thus enabling the development of novel remediation strategies. To achieve real-time, dynamic measurements of these properties, a novel analysis platform consisting of a microfluidic flowcell device has been designed and fabricated for in situ analysis using atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM). The flowcell consists of microfluidic channels for biofilm establishment that are then converted into an open architecture, laminar flow channel for AFM measurement in a liquid environment. Computational fluid dynamics (CFD) was used to profile fluid conditions within the device during biofilm establishment. The validity of the AFM nanoindentation measurement mechanism was confirmed in the context of the system through the elastic characterization of several non-living reference materials. Force-mode AFM was used to measure the elastic properties of mature Pseudomonas aeruginosa PAO1 biofilms and observe a dynamic response to a chemical antagonist. Elastic moduli ranging from 0.58 to 2.61 kPa were determined for the mature biofilm, which fall within the range of moduli previously reported by optical, rheometric, and microindentation techniques. A modified version of the flowcell was employed to perform similar elastic characterization of mouse submandibular glands (SMGs), demonstrating the adaptability of the system to perform ex situ analyses of a broader set of biological materials. These results demonstrate the validity of the microfluidic flowcell system as an effective platform for future investigations of the mechanical and morphological response of biofilms and other soft biomaterials to dynamic environmental conditions.

In the past decades, nanostructured materials have opened new and fascinating avenues for research. Nanopolycrystalline solids, which consist of nano-sized crystalline grains and significant volume fractions of amorphous grain boundaries, are believed to have substantially different response to the thermal-mechanical-electric-magnetic loads, as compared to the response of single-crystalline materials. Nanopolycrystalline materials are expected to play a key role in the next generation of smart materials.

This research presents a framework (1) to generate full atomistic models, (2) to perform non-equilibrium molecular dynamics simulations, and (3) to study multi-physics phenomena of nanopolycrystalline solids. This work starts the physical model and mathematical representation with the framework of molecular dynamics. In addition to the latest theories and techniques of molecular dynamics simulations, this work implemented principle of objectivity and incorporates multi-physics features. Further, a database of empirical interatomic potentials is established and the combination scheme for potentials is revisited, which enables investigation of a broad spectrum of chemical elements (as in periodic table) and compounds (such as rocksalt, perovskite, wurtzite, diamond, etc.). The configurational model of nanopolycrystalline solids consists of two spatial components: (1) crystalline grains, which can be obtained through crystal structure optimization, and (2) amorphous grain boundaries, which can be obtained through amorphization process. Therefore, multi-grain multi-phase nanopolycrystalline material system can be constructed by partitioning the space for grains, followed by filling the inter-grain space with amorphous grain boundaries.

Computational simulations are performed on several representative crystalline materials and their mixture, such as rocksalt, perovskite and diamond. Problems of relaxation, mechanical loading, thermal stability, heat conduction, electrical field response, magnetic field response are studied. The simulation results of the mechanical, thermal, electrical and magnetic properties are expected to facilitate the rational design and application of nanostructured materials.

The isolation of single layers of van der Waals materials has shown that their properties can be significantly different compared to their bulk counterparts. These observations, illustrates the importance of interface interactions for determining the materials properties even in weakly interacting materials and raise the question if materials properties of single layer van der Waals materials can be controlled by appropriate hetero-interfaces. To study interface effects in monolayer systems, surface science techniques, such as photoemission spectroscopy and scanning probe microscopy/spectroscopy, are ideally suited. However, before these characterization methods can be employed, approaches for the synthesis of hetero-van der Waals systems must be developed, preferably in-situ with the characterization methods, i.e. in ultra-high vacuum. Therefore, in this thesis, we explored novel approaches for creating van der Waals heterostructures and characterized fundamental structural and electronic properties of such systems. Specifically, we developed an approach to decouple graphene from a Ir(111) growth substrate by intercalation growth of a 2D-FeO layer, and we investigate van der Waals epitaxy of MoSe2 on graphite and other transition metal dichalcogenide substrates. For the Ir(111)/2D-FeO/graphene heterostructure system, we first demonstrated the growth of 2D-FeO on Ir(111). The FeO monolayer on Ir(111) exhibits a long range moiré structure indicating the locally varying change of the coordination of the Fe atoms with respect to the substrate Ir atoms. This variation also gives rise to modulations in the Fe2+-O2- separation, and thus in the monolayer dipole. We demonstrated that this structure can be intercalated underneath of graphene grown on Ir(111) by chemical vapor deposition. The modulation of the dipole in the 2D-FeO moiré structure consequently gives rise to a modulated charge doping in the graphene. This effect has been studied by C-1s core level broadening. In general, this study demonstrates that modulated substrates can be used to periodically modify 2D materials. Growth of transition metal dichalcogenides (TMDCs) by molecular beam epitaxy (MBE) is a very versatile approach for growing TMDC heterostructures. However, there may be unforeseen challenges in the synthesis of some of these materials. Here we show that in MBE growth of MoSe2, the formation of twin grain boundaries is very abundant. While this is detrimental in our efforts for characterizing interface properties of TMDC heterostructures, however the twin grain boundaries have exciting properties. Since the twin grain boundaries are aligned in an epitaxial film we were able to characterize their properties by angle resolved photoemission spectroscopy (ARPES), which may be the first time a material’s line defects could be studied by this method. We demonstrate that the line defects are metallic and exhibit a parabolic dispersing band. Because of the 1D nature of the metallic lines, embedded in a semiconducting matrix, the electronic structure follows a Tomonaga Luttinger formalism and our studies showed strong evidence of the predicted so-called spin charge separation in such 1D electron systems. Moreover, a metal-to-insulator Peierls transition has been observed in this system by scanning tunneling microscopy as well as in transport measurements. Finally, we have shown that the defect network that forms at the surface also lends itself for decoration with metal clusters. Although unexpected, the formation of grain boundary networks in MoSe2 marks the discovery of a new material with exciting quantum properties.

Quantum mechanics, arguably one of the greatest achievements of modern physics, has not only fundamentally changed our understanding of nature but is also taking an ever increasing role in engineering. Today, the control of quantum systems has already had a far-reaching impact on time and frequency metrology. By gaining further control over a large variety of different quantum systems, many potential applications are emerging. Those applications range from the development of quantum sensors and new quantum metrological approaches to the realization of quantum information processors and quantum networks. Unfortunately most quantum systems are very fragile objects that require tremendous experimental effort to avoid dephasing. Being able to control the interaction between a quantum system with its local environment embodies therefore an important aspect for application and hence is at the focus of this thesis.
Physics

This thesis is concerned with the study of biomedical scientific research work that is intensely distributed, i.e. socially distributed across multiple institutions, sites, and disciplines. Specifically, this PhD probes the ways in which scientists co-operating on multi-sited crossdisciplinary projects, design, use and maintain information-based resources to conduct and coordinate their experimental activities. The research focuses on the roles of information artefacts, i.e. the tools, media and devices used to store, track, display, and retrieve information in paper or electronic format, in helping the scientists integrate their activities to achieve concerted action. To examine how scientists in globally distributed settings organise and co-ordinate their scientific work using information artefacts, a multi-method multi-sited study informed by different ethnographic perspectives was conducted focused on a large European crossdisciplinary translational research project in nanodiagnostics. Situated interviews with project scientists, participant observations and participatory learning exercises were designed and deployed. From the data analysis, several abstractions were developed to represent how the joined utilisations of key information artefacts support the co-ordination of experimental activities. Subsequently, a framework was developed to highlight key interactional strategies that need to be managed by experimenters when using artefacts to organise their work cooperatively. This framework was then used as a guiding device to identify innovative ways to design future digital interactive systems to support the co-ordination of intensely distributed scientific work. From this study, several key findings came to light. We identify the role of the experimental protocol acts as a co-ordinative map that is co-designed dynamically to disseminate various instantiations of experimental executions across sites. We have also shed light on the ways the protocol, the lab book and the material log are used jointly to support the articulation of scientific work. The protocol and the lab book are used both locally and across co-operating sites to support four repeatability and reproducibility levels that are key to experimental validation. The use of the local protocol / lab book dyads at each site is further integrated with that of a centralised material log artefact to enable a system of exchange of scientific content (e.g. experimental processes, intermediate results and observations) and experimental materials (both physical materials and key information). We have found that this integration into a co-ordinative cluster supports awareness and the articulation of experimental activities both locally and across remote labs. From this understanding, we have derived several sensitising tensions to frame the strategies that scientific practitioners need to manage when designing their multi-sited experimental work and technologists should consider when designing systems to support them: (1) formalisation / flexibility; (2) articulability / local appropriateness; (3) scrutiny / tinkering; (4) accountability / applicability; (5) traceability / improvisation and (6) lastingness / immediacy. Lastly, based on these tensions, we have suggested a number of implications for the design of interactive information artefacts that can help manage both local and multi-sited co-ordination in intensely distributed scientific projects.

Les simulations moléculaires sont devenues un outil essentiel en biologie, chimie et physique. Malheureusement, elles restent très coûteuses. Dans cette thèse, nous proposons des algorithmes qui accélèrent les simulations moléculaires en regroupant des particules en plusieurs objets rigides. Nous étudions d'abord plusieurs algorithmes de recherche de voisins dans le cas des grands objets rigides, et démontrons que les algorithmes hiérarchiques permettent d'obtenir des accélérations importantes. En conséquence, nous proposons une technique pour construire une représentation hiérarchique d'un graphe moléculaire arbitraire. Nous démontrons l'usage de cette technique pour la mécanique adaptative en angles de torsion, une méthode de simulation qui décrit les molécules comme des objets rigides articulés. Enfin, nous introduisons ARPS - Adaptively Restrained Particle Simulations ("Simulations de particules restreintes de façon adaptative") - une méthode mathématiquement fondée capable d'activer et de désactiver les degrés de liberté en position. Nous proposons deux stratégies d'adaptation, et illustrons les avantages de ARPS sur plusieurs exemples. En particulier, nous démontrons comment ARPS permet de choisir finement le compromis entre précision et vitesse, ainsi que de calculer rapidement des proprietésstatiques d'équilibre sur les systèmes moléculaires.

An atomic force microscopy beam-like cantilever is combined with an electrical tuning fork to form a shear force probe that is capable of generating an acoustic response from the mesoscopic water layer under ambient conditions while simultaneously monitoring force applied in the normal direction and the electrical response of the tuning fork shear force probe. Two shear force probes were designed and fabricated. A gallium ion beam was used to deposit carbon as a probe material. The carbon probe material was characterized using energy dispersive x-ray spectroscopy and scanning transmission electron microscopy. The probes were experimentally validated by demonstrating the ability to generate and observe acoustic response of the mesoscopic water layer.

Polymer blending facilitates the combination of the attractive attributes of two or more polymers while compensating for the unfavorable ones. Most polymers are thermodynamically incompatible with one another, and their blending yields a two-phase microstructure. This morphology generally determines the mechanical and rheological properties of the blend system which then determine its applications. Morphology development typically involves deformation of the dispersed phase followed by drop breakup. However, drop coalescence competes with this process, and ultimately a balance must be reached between these two competing processes. Extensional flow fields are known to promote drop breakup and are especially important for blends with high viscosity ratios, that is for blends where the viscosity of the dispersed phase is at least about 3.8 times greater than that of the matrix phase. Coalescence may be attenuated by compatibilizers that modify the interface between the polymer phases. Nanoparticles with tuned surface chemistry may also be used as compatibilizers. A combination of extensional flow and nanoparticle stabilization should, therefore, result in a fine, stable morphology.

To begin the investigation toward the effects of extensional flow blending with and without the incorporation of nanoparticles, preliminary results were obtained using two different polymer blend systems: polycarbonate (PC)/styrene acrylonitrile (SAN) and polystyrene (PS)/linear low-density polyethylene (LLDPE). However, the majority of the presented results involve blends of high-density polyethylene (HDPE) dispersed in PS. With this blend system, with the material grades selected, the viscosity ratio exceeded 3.8 over the entire domain of deformation rates anticipated in the processing used. Coarse blends of various compositions were formulated using shear flow in an internal mixer or in a twin-screw extruder. These blends were subjected to extensional flow in converging dies of different geometries and where more than one stretching episode was possible; the temperature, total strain, and flow rate were varied, among other factors, in a systematic manner. Experiments were repeated in the presence of various grades of fumed nanosilica of different sizes and surface treatments, which imparted different surface tension and relative surface polarity (hydrophilic versus hydrophobic) for the nanoparticles. The mixing sequence was varied including premixing the nanosilica into the thermodynamically non-preferred polymer phase.

Scanning electron microscopy (SEM) was used to determine the size and size distribution of the dispersed polymer phase. The material was typically sectioned in the flow direction, but sectioning in the direction perpendicular to flow and etching, or selectively dissolving, one phase or the other was also investigated. The primary effect of extensional flow blending was to reduce the volume-average diameter of the dispersed polymer phase, especially with increasing strains and flow rates, or strain rates, which is directly dependent on both. Finding suitable conditions for the nanoparticles to selectively localize at the HDPE/PS interface was challenging, but relatively small amounts of nanoparticles dispersed in the PS matrix decreased the volume-average diameter of HDPE drops. When the nanosilica was preloaded into the HDPE dispersed phase, very coarse initial blends were produced which then exhibited dramatic decreases in phase size with extensional flow. These and other results are properly organized and presented.

Doctor of Philosophy
Department of Chemical Engineering
Vikas Berry
Placidus Amama
The evolution of unique electrical, optical, thermal, mechanical, and chemical properties in two-dimensional (2D) nanomaterials due to the atomic confinement in the z-direction has ignited tremendous technology promises. With that promise comes a challenge of incorporating 2D nanomaterials into practical applications, enabling their large-area growth and using covalent or van der Waal bonding to extent and control their properties in electronic applications. This PhD thesis establishes the following results: (a) successfully developing of scalable processes for direct growth of large-area graphene, h-BN, and MoS₂-on-h-BN on SiO₂/Si substrate, (b) demonstrating an electronic sensor for the defection of molecular motion by covalently interfacing 2D nanomaterials with photo-mechanical molecules, and (c) establishing the modulation of structural, electrical, thermal properties of 2D nanomaterials by covalently interfacing metal nanoparticles with 2D nanomaterials. A promising scalable route for large-area growth of 2D nanomaterial on a dielectric substrate is to perform chemical vapor deposition (CVD). Via two patented processes, we have synthesized graphene films directly on a SiO₂ substrate via carbon-diffusion through copper grains, and h-BN film on SiO₂ substrate via surface oxide assisted mechanism. The continuous graphene film grown with large coverage on SiO₂ substrate possessed a crystalline sp² domain size of 140 nm with low defect density (as indicated by low Raman I[subscript]D/I[subscript]G~0.1). The sheet resistance of this turbostratic stacking graphene was ~4 kOhm/sq, with a charge carrier mobility of ~250 cm²V⁻¹s⁻¹. Unprecedented, large coverage of directly grown h-BN film on SiO₂ substrate was demonstrated. This h-BN film showed a 6-fold smoothness enhancement compared to that of SiO₂ substrate. Such smoothness and the nature of free dangling bond of h-BN film reduced Coulombic long range scattering, leading to the 5-fold enhancement in the conductivity of the MoS₂, which is directly grown on the underlying h-BN platform. The next-generation molecular electromechanical systems require controlled manipulation and detection of molecular motion to build systems which respond to molecular mechanics. To achieve this, we covalently interfaced photo-mechanical molecules (azobenzene) (density = 2.5 nm⁻²) onto trilayer graphene (37.5% sp² coverage), where high sensitivity of this trilayer graphene due to high quantum capacitance (6.3 microF/cm²) and carrier confinement was leveraged. This enabled graphene to sensitively detect azobenzene isomerization, where one hundred molecules generated one charged carriers in the graphenic platform (2.44 x 10¹² holes/cm²). As mentioned before, surface modification of 2D nanomaterials opens an avenue to incorporate them into rational applications. We demonstrated the ability to interface noble metal nanoparticles (gold, silver) selectively onto a MoS₂ lattice (60° angular displacement) via both diffusion limited aggregation and instantaneous reaction arresting (using microwaves). Such gold nanoparticle interfaces allowed the modulation of electrical, and thermal properties, confirmed by Raman, electrical, and thermal studies. Consequently, a remarkably capacitive interaction between gold and thin MoS₂ sheet showed a 9-fold increase of effective gate capacitance with low Schottky barrier (14.52 meV), and a 1.5-fold increase in thermal conductivity with a low carrier-transport thermal-barrier (44.18 meV). This long-term work has established the following points: 1) Scalable routes for the growth of 2D nanomaterials, which can be extended to synthesize complex hetero/lateral architectures for integrated thin film circuitries. Furthermore, 2) covalent functionalization of 2D nanomaterials with nanoparticles and molecular systems can futuristically develop rational interfaces with other 2D heterostructures, and molecular machines.

Graphene materials, exhibiting outstanding mechanical properties, are excellent candidates as reinforcement in high-performance polymer nanocomposites. In this dissertation, advanced atomic force microscopy (AFM) techniques are applied to study the nanomechanics of graphene/polymer nanocomposites, specifically the graphene/polymer interfacial strength and the stress transfer at the interface.;Two novel methods to directly characterize the interfacial strength between individual graphene sheets and polymers using AFM are presented and applied to a series of polymers and graphene sheets. The interfacial strength of graphene/polymer varies greatly for different combinations. The strongest interaction is found between graphene oxide (GO) and polyvinyl alcohol (PVA), a strongly polar, water-based polymer. On the other hand, polystyrene, a non polar polymer, has the weakest interaction with GO. The interfacial bond strength is attributed to hydrogen bonding and physical adsorption.;Further, the stress transfer in GO/PVA nanocomposites is studied quantitatively by monitoring the strain in individual GO sheet inside the polymer via AFM and Raman spectroscopy. For the first time, the strains of individual GO sheets in nanocomposites are imaged and quantified as a function of the applied external strains. The matrix strain is directly transferred to GO sheets for strains up to 8%. at higher strain levels, the onset of the nanocomposite failure and a stick-slip behavior is observed. This study reveals that GO is superior to pure graphene as reinforcement in nanocomposites. These results also imply the potential to make a new generation of nanocomposites with exceptional high strength and toughness.;In the second part of this dissertation, AFM is used to study the structure of silk proteins and the morphology of spider silks. For the first time, shear-induced self-assembly of native silk fibroin is observed. The morphology of the Brown Recluse spider silk is investigated and a novel silk/GO nanocomposite is proposed.;Finally, the growth, capacitance and frequency response of vertically oriented graphene sheets prepared by radio frequency plasma-enhanced chemical vapor deposition and used in electric double layer capacitors (EDLC) are presented. These capacitors exhibit the highest frequency response observed, to date, for carbon based materials, providing EDLC suitable for AC filtering. The results also suggest mechanisms other than surface area are operative in the double layer charge storage, such as a stronger polarization from graphene edges and vacancies.

Doctor of Philosophy
Department of Physics
Bruce M. Law
Three diverse first author surfaces science experiments conducted by Sean P. McBride 1-3 will be discussed in detail and supplemented by secondary co-author projects by Sean P. McBride, 4-7 all of which rely heavily on the use of an atomic force microscope (AFM). First, the slip length parameter, b of liquids is investigated using colloidal probe AFM. The slip length describes how easily a fluid flows over an interface. The slip length, with its exact origin unknown and dependencies not overwhelming decided upon by the scientific community, remains a controversial topic. Colloidal probe AFM uses a spherical probe attached to a standard AFM imaging tip driven through a liquid. With the force on this colloidal AFM probe known, and using the simplest homologous series of test liquids, many of the suspected causes and dependencies of the slip length demonstrated in the literature can be suppressed or eliminated. This leaves the measurable trends in the slip length attributed only to the systematically varying physical properties of the different liquids. When conducting these experiments, it was realized that the spring constant, k, of the system depends upon the cantilever geometry of the experiment and therefore should be measured in-situ. This means that the k calibration needs to be performed in the same viscous liquid in which the slip experiments are performed. Current in-situ calibrations in viscous fluids are very limited, thus a new in-situ k calibration method was developed for use in viscous fluids. This new method is based upon the residuals, namely, the difference between experimental force-distance data and Vinogradova slip theory. Next, the AFM’s ability to acquire accurate sub nanometer height profiles of structures on interfaces was used to develop a novel experimental technique to measure the line tension parameter, τ, of isolated nanoparticles at the three phase interface in a solid-liquid-vapor system. The τ parameter is a result of excess energy caused by the imbalance of the complex intermolecular forces experienced at the three phase contact line. Many differences in the sign and magnitude of the τ parameter exist in the current literature, resulting in τ being a controversial topic.

xv, 153 p. : ill. (some col.)
Lead sulfide nanocrystals (PbS-NCs) are an important class of semiconductor nanomaterials that are active in the near-infrared and exhibit unique properties distinct from their bulk analogues, notably, size tunability of the band gap and solution processability. One factor influencing PbS-NC properties is the presence of an organic ligand shell, which forms the interface between the nanocrystal core and its environment. The specific focus of this dissertation is how ionic functionalization of the ligand shell alters the physical and chemical properties of the resulting PbS-NC/ligand complex. Short-chain ligands can improve photoconductivity in PbS-NC thin films, but there are few solution-based preparations available. Chapter II demonstrates how ionic groups can enable functionalization of PbS-NCs with two short- chain thiol ligands - sodium 3-mercaptopropanesulfonate (MT) and sodium 2,3-dimercaptopropanesulfonate (DT) - via a solution-phase exchange procedure. Despite a structural similarity, DT-functionalized PbS-NCs (PbS-DT) are more stable to oxidation than MT-functionalized PbS-NCs (PbS-MT). The relative stabilities are explained in terms of different binding modes to the nanocrystal surface (bidentate vs. monodentate) and oxidation pathways (intermolecular vs. intramolecular). Toxicology studies on nanomaterials have been limited by the availability of water-soluble samples with systematically controlled structures. As examples of such materials, PbS-DT and PbS-MT nanocrystals are studied in Chapter III for their toxicological impacts on embryonic zebrafish. PbS-DT solutions induce less toxicity than PbS-MT solutions, which is explained in terms of the relative stabilities of the nanocrystal solutions. Finally, Chapter IV investigates the hitherto unexplored effects of ionic functionalization on the optical/electrical properties of PbS-NC thin films, with an emphasis on understanding how counter ions affect the photoconductivity of PbS-DT thin films. Films containing small counter ions exhibit increased dark conductivity and responsivity with time under an applied bias, whereas films containing larger or multivalent counter ions show a suppression of this behavior. These results are discussed in terms of ion motion and ion-assisted carrier injection at the PbS-NC/electrode interface. This dissertation includes previously published and unpublished co-authored material.
Committee in charge: David R. Tyler, Chair; Mark C. Lonergan, Advisor; Catherine J. Page, Inside Member; Andrew Marcus, Inside Member; Hailin Wang, Outside Member

Recent progress and a coordinated national research program have brought considerable effort to bear on the synthesis and application of carbon nanostructures for field emission. at the College of William and Mary, we have developed field emission arrays of vertically oriented graphene (carbon nanosheets, CNS) that have demonstrated promising cathode performance, delivering emission current densities up to 2 mA/mm2 and cathode lifetime >800 hours. The work function (&phis;) of CNS and other carbonaceous cathode materials has been reported to be &phis;∼4.5-5.1 eV. The application of low work function thin films can achieve several orders of magnitude enhancement of field emission.;Initially, the intrinsic CNS field emission was studied. The mean height of the CNS was observed to decrease as a function of operating time at a rate of ∼0.05 nm/h (I 1∼40 muA/mm2). The erosion mechanism was studied using a unique UHV diode design which allowed line-of-site assessment from the field emission region in the diode to the ion source of a mass spectrometer. The erosion of CNS was found to occur by impingement of hyperthermal H and O neutrals and ions generated at the surface oxide complex of the Cu anode by electron stimulated desorption. Techniques for minimizing this erosion are presented.;The Mo2C (&phis;∼3.7 eV) beading on CNS at previously reported carbide formation temperatures of ∼800??C was circumvented by physical vapor deposition of Mo and vacuum annealing at ∼300??C which resulted in a conformal Mo2C coating and stable field emission of 1∼50 muA/mm2. For a given applied field, the emission current was >102 greater than uncoated CNS.;ThO2 thin film coatings were presumed to be even more promising because of a reported work function of &phis; ∼2.6 eV. The fundamental behavior of the initial oxidation of polycrystalline Th was studied in UHV (p<1x10-11 Torr), followed by studies of thin film coatings on Ir and thermionic emission characteristics. Although a work function of 3.3 eV was determined by a RichardDushman plot, activation of the thin film was not achieved at T<1700??C. Rather, the deposited ThO2 film decomposed, surface diffused and aggregated into stable ThO2(111) crystallites.;Thin film ThO2 coatings deposited on CNS initially demonstrated excellent field emission (up to ∼2 muA/mm2) and apparently activated spontaneously without significant thermal energy. Fowler-Nordheim plots suggested a work function of &phis; ∼2.6 eV. Undesired beading and ThO2 surface diffusion away from active emission sites resulted in rapidly deteriorating performance at higher field emission currents. Techniques that should provide a more stable ThO2/CNS conformal coating are presented.;The impact of thin films of Mo2C and ThO2on the magnitude of field emission from carbon nanosheets (CNS) was substantial. For a given field emission current density, J ∼2 muA/mm 2, the necessary applied field for uncoated CNS was ∼12 V/mum, but only ∼8 V/mum when coated with Mo2C (&phis;∼3.7 eV) and ∼5 V/mum when coated with ThO2 (&phis;∼2,6 eV). The mechanism for enhanced emission and the stability of the coatings are discussed, with special focus on the activation of ThO2 thin films. The major limitation observed in these studies has been the difference in surface energy of the graphene and the coatings which resulted in a tendency for the films to bead and separate from active emission sites at elevated currents. Suggested techniques to prevent this unwanted surface diffusion are presented.

Recently, there has been growing interest in using transition metals (TM) for catalytic and electromagnetic applications, due to the ability of TMs to form stable compounds in multiple oxidation states. In this research, the focus has been on the synthesis and characterization of carbon-supported TM nanoparticles (NPs), specifically palladium (Pd) and gold (Au) NPs, for catalytic applications, and transition metal oxides (TMO) NPs, specifically Fe₃O₄ NPs for electromagnetic applications. Carbon supports have several advantages, such as enabling even distribution of particles, offering large specific surface area with excellent electron conductivity, and relative chemical inertness.

In this dissertation, for catalytic applications, emphasis was on removal of trichloroethylene (TCE) from groundwater. For this application, carbon-supported Pd/Au NP catalysts were developed. Pd was chosen because it is more active, stable and selective for desired end-products, and Au has shown to be a good promotor of Pd’s catalytic activity. Often, commercially available Pd-based catalysts are made using harsh chemicals, which can be harmful to the environment. Here, an environmentally friendly process with aspects of green chemistry was developed to produce carbon-supported Pd/Au NP catalysts. This process uses a combination of sonochemistry and solvothermal syntheses. The carefully designed carbon-supported Pd/Au NP catalyst material was systematically characterized, tested against TCE, and optimized for increased rate of removal of TCE. Electron microscopy and spectroscopy techniques were used to study the material including structure, configuration and oxidative state. The Pd/Au NPs were found mainly to form clusters with an aggregate-Pd_ShellAu_Core structure. Using state-of-the-art direct detection with electron energy loss spectroscopy, the Pd NPs were found to have an oxidative state of zero (0). The formation of the catalyst material was studied in detail by varying several synthesis parameters including type of solvent, sonication time, synthesis temperature etc. The most optimized catalyst was found remove TCE at double the rate of corresponding commercial Pd-based catalysts in a hydrogen headspace. This material was found to catalyze the removal of TCE via traditional hydrodehalogenation and shows promise for the removal of other contaminants such as trichloropropane (TCP), carbon tetrachloride (CT).

This green approach to make and optimize TM materials for specific applications was extended to TMOs, specifically magnetite (Fe₃O₄) and further developed for the application of electromagnetism. As catalysts, Fe₃O₄ is used for removal of p-nitrophenol from water. However, since the carbon-supported Pd/Au material system was developed and optimized for catalysis, here, carbon-supported Fe₃O ₄ NPs were developed for electromagnetic applications. There has been growing interest in tuning the magnetic properties of materials at room temperature with the use of external electric fields, for long-term applications in data storage and spintronic devices. While a complete reversible change of material properties has not yet been achieved, some success in partial switching has been achieved using multiferroic spinel structures such as Fe₃O ₄. These materials experience a change in magnetic moment at room temperature when exposed to the electric fields generated by electrochemical cells such as lithium ion batteries (LIBs) and supercapacitors (SC). In the past, a 1% reversible change was observed in Fe₃O₄ using LIBs. Here, building on the developments from previous material system, Fe ₃O₄ NPs were directly hybridized onto the graphene support in order to increase the observable change in magnetic moment. The material was systematically designed and tested for this application, including a study of the material formation. A simple, environmentally friendly synthesis using the solvothermal process was implemented to make the graphene-supported Fe ₃O₄ NPs. This new material was found to produce a reversible change of up to 18% in a LIB. In order to overcome some of the difficulties of testing with a LIB, a corresponding hybrid SC was designed, built and calibrated. The graphene-supported Fe₃O₄ NPs were found to produce a net 2% reversibility in the SC, which has not been reported before. The results from both the LIB and SC were analyzed to better understand the mechanism of switching in a spinel ferrite such as Fe₃O₄, which can help optimize the material for future applications.

The focus of this dissertation was on the development of a methodology for carbon-supported TM and TMO NPs for specific applications. It is envisioned that this approach and strategy will contribute towards the future optimization of similar material systems for a multitude of applications.

In this study, one AP Biology curriculum unit and one general Biology curriculum unit that included tabletop Scanning Electron Microscope (SEM) technology provided by Project NANO, a grant-funded, collaborative initiative designed to integrate cutting-edge nanotechnology into high school classrooms were implemented at a public high school in rural Oregon. Nine students participated in the AP unit and 52 students participated in the general Biology unit. Each student completed an opinion-based pre and post survey to determine if using the SEM as a part of the curriculum unit had an impact on his or her interest in science or in nanoscience. Interviews were conducted to add to the data. The results indicate that using the SEM can increase a student's interest in science. Recommendations for improving student experience were identified.

Mechanical Engineering
M.S.
The study of nanomaterials is a developing science with potentially large benefits in the development of catalysts, optical and chemical sensors, and solid state memory devices. As several of these devices require large arrays of nanoparticles, one of the greatest obstacles in material characterization and device development is the reliable manufacture of nanopatterns over a large surface area. In addition, various applications require different nanoparticle size and density. High density arrays with small nanoparticle sizes are difficult to achieve over a large surface area using current manufacturing processes. Herein, Nanoimprint Lithography (NIL) and Dynamic Templating are combined to create a new manufacturing process capable of developing high density arrays with small nanoparticle sizes. The NIL process involves the stamping of a polymer coated substrate by a silicon stamp with patterned nanofeatures. The stamp is then removed, leaving the pattern in the polymer, which is first etched and then coated with a thin layer of metal, filling the recessed regions of the pattern. The excess polymer is dissolved, leaving a pattern of nanoparticles on the substrate matching the pattern on the stamp. When Dynamic Templating is applied, a very thin layer of metal can be coated, which forms small nanoparticle sizes when dewetted. A custom NIL system has been developed to combine these two processes together, which has now proven to yield consistent large-area, dense arrays with a small nanoparticle size. An array spacing of 700 nm has been achieved, along with a nanoparticle size of 90 nm. Arrays have been created in gold and palladium, where there is now the potential to combine them with other solution-based syntheses which should lead to complex nanoparticle geometries suitable for sensor applications.
Temple University--Theses

Being able to directly relate the final properties with the intimate structure provides a unique insight into the functionality of materials and devices, especially when compared to the necessarily statistical nature of the information that can be retrieved by macroscopic measurements. In particular, the scale reduction associated with the Nanoscience and Nanotechnology revolution demands characterization tools capable of reaching an unprecedented resolution, in a wide range of fields, not only for standard quality control, but in order to understand the properties of matter at the nanoscale. Going from bigger to smaller devices, but also from elemental building blocks (even atoms) to bigger assemblies, basic properties and device functionalities meet. With its ability to provide different kinds of information at a very high spatial resolution, state-of-the-art TEM and related techniques are in the core of this multidisciplinary and rapidly growing field. The first major topic is related to the assessment of local atomic ordering/disordering phenomena in functional materials. A series of rare earth niobates (RE3NbO7) will be studied in order to understand the microstructural origin of their proton conduction properties, that make them excellent candidates to be used as electrode materials in solid oxide fuel cells. Also, single crystals of the tetragonal tungsten bronze (TTB) Sr0.33Ba0.66Nb2O6 (SBN-67) will be studied by different TEM techniques in order to assess the possible short range structural and/or chemical disorder. These features are thought to be responsible for the observed macroscopic uniaxial polarization vector of the material as well as its relaxor properties. A second major topic of interest will be the phenomena taking place at interfaces. This includes the characterization of a set of LaNiO3 perovskite thin films grown on different substrates (LAO, LSAT, STO, YAO). The effect of the substrate-induced compressive/tensile strain, given by lattice mismatch, on the structure of the films will be assessed and related to the observed electric transport properties. The interfaces in a GaN/InAlN multilayered system designed as a Bragg reflector for laser cavities applications will be investigated in order to account for a lower than expected reflectivity of the devices. The presence of structural defects and the detection of intergrowth of wurtzite and zinc blende phases of GaN in thin films will be addressed. Also regarding interfaces and strain conditions, the characterization of the free surface of Nb2O5 nanorods, as a key point for their humidity sensing properties. Expanding on this, the strain state of Nb2O5 when grown on SnO2 nanowires will also be studied. The coupling of the sensing capabilities of Nb2O5 with the electrical transport properties of SnO2 is of particular interest for functional sensing devices. Therefore, defects at the interface and strain state are of capital interest in order to understand the band structure alignment of the system. Interfaces in lower dimensionality systems will also be studied, as in the case of Ag@Fe3O4 dimers for applications in magnetoplasmonics. The epitaxial quality, strain, and the possible chemical diffusion through the contact surface of the two phases of the dimer are key aspects in order to properly tailor their optical properties. The last major topic is the mapping of magnetic fields at the nanoscale. The magnetic configurations of different geometric arrangements of magnetite Fe3O4 nanocubes will be studied. This characterization is aimed at obtaining enhanced responses in magnetic hyperthermia treatments for cancer. Given the strong interrelationship between the problems under study, the chapter structure follows the dimensionality of the systems under study (3D, 2D, 1D and 0D systems).
La reducció en l'escala espacial associada a la revolució de la Nanociència i la Nanotecnologia fa necessari comptar amb una sèrie d'eines capaces d'assolir una resolució sense precedents en una gran varietat d'àress, ja no tan sols com a control de qualitat, sinó per tal d'entendre les propietats de la matèria a la nanoescala. La correlació de la configuració estructural, la composició química i les distribucions de càrrega amb les propietats funcionals és imprescindible pel disseny de nous dispositius, tant des de la perspectiva 'top down' (reducció de les dimensions dels dispositius) com de la perspectiva 'bottom up' (fabricació d'estructures complexes a partir de blocs més petits, fins i tot àtoms). La capacitat de la Microscòpia Electrònica de Transmissió (TEM) de proporcionar diferents tipus d'informació amb una alta resolució espacial, situa les tècniques avançades de TEM com a peça clau en el desenvolupament d'aquest camp multidisciplinari i creixent. L'objectiu principal d'aquesta tesi ha estat l'aplicació de tècniques quantitatives d'imatge TEM per la resolució de problemes en ciència dels materials. La tesi cobreix un espectre ampli pel que fa al tipus de materials estudiats i els seus camps d'aplicació. El Capítol 1 presenta una introducció general a la teoria de formació d'imatge aplicada a la microscopia TEM. S'hi exposen els diferents fenòmens d'interacció electró-matèria que són responsables dels diferents tipus de contrast que es poden trobar a les imatges TEM. El Capítol 2 presenta les tècniques experimentals que es faran servir en la caracterització dels materials, en concret la simulació d'imatges d'alta resolució (HRTEM), l'holografia electrònica i l'anàlisi de la fase geomètrica (GPA). S'hi pot trobar una descripció del marc teòric i dels fonaments experimentals, juntament amb un resum dels resultats més recents en aquests camps. Els resultats experimentals s'agrupen en els capítols posteriors segons la dimensionalitat dels sistemes estudiats. En ordre decreixent de dimensionalitat s'hi inclouen: materials massius (3D), capes primes (2D), nanofils (1D) i nanopartícules (1D).