WorldCat Identities

Dai, Hongjie 1966-

Works: 20 works in 20 publications in 2 languages and 27 library holdings
Roles: Thesis advisor
Publication Timeline
Most widely held works about Hongjie Dai
Most widely held works by Hongjie Dai
Single-walled carbon nanotubes (SWNTs) as near infrared fluorescent imaging agents in biological systems by Kevin David Welsher( )
1 edition published in 2010 in English and held by 2 WorldCat member libraries worldwide
The near infrared range has long been known to be advantageous for biological imaging and sensing applications. In particular, the second near infrared window (1000 nm -- 1400 nm, NIR II) is characterized by low endogenous autofluorescence and deep tissue penetration due to reduced tissue scatter. To address the dearth of fluorophores in this window, this work focuses on utilizing the intrinsic near infrared photoluminescence of semiconducting single walled carbon nanotubes (SWNTs) to take advantage of this unique spectral region. First, SWNTs are made bio-inert and applied as fluorescent probes for highly specific cellular targeting using antibodies such as Rituxan and Herceptin. These probes were then used for the first whole animal fluorescent imaging using SWNTs in vivo following tail vein injection, including the observation of high SWNT accumulation in tumors. By implementing a surfactant exchange method to improve the fluorescence yield of SWNTs solubilized by phospholipid-polyethylene glycol, high magnification intravital microscopy of tumor vessels beneath thick skin was achieved. Further improvements were made to improve the fluorescence yield of the SWNT probes by utilizing a density gradient separation method which removed poorly fluorescent short tubes and nanotube bundles. Another separation method, ion-exchange chromatography was applied to isolate single chirality SWNTs and perform multicolor NIR imaging in vitro and in vivo. Finally, these bright, biocompatible nanotube fluorophores were used to achieve video rate imaging of mice in vivo during tail vein injection for dynamic contrast enhanced imaging through principal component analysis. The emission in the NIR II region allowed crisp anatomical resolution, confirmed by mock tissue phantom studies and Monte Carlo simulation
New methods for extracting ultrafast water dynamics at interfaces by Emily Elizabeth Fenn( )
1 edition published in 2012 in English and held by 1 WorldCat member library worldwide
Water dynamics near interfaces and in confined systems, as manifested by vibrational relaxation, orientational relaxation, and spectral diffusion of the water hydroxyl stretch (5% HOD in H2O), are measured via infrared (IR) pump-probe and 2D IR vibrational echo techniques. It is shown that a two component model for population and orientational relaxation accurately describes the dynamics for systems comprised of two types of hydrogen bonding ensembles: waters that are hydrogen bonded to other waters and waters at an interfacial region. Through a combination of spectroscopic and data analysis techniques, the dynamics of these two environments become separable. This two component model is successfully applied to binary mixtures of water and tetraethylene glycol dimethyl ether. The effects of confinement on water dynamics are studied by examining water inside of reverse micelles made with the surfactant Aerosol-OT (AOT), which contains charged head groups. Large reverse micelles (diameter [greater than or equal to] 4.6 nm) can be decomposed into two separate environments: a bulk water core and an interfacial water shell. Each region has distinct dynamics that can be resolved experimentally using the two component model. The core follows bulk water dynamics while interfacial water shows slower dynamics that are independent of size for large reverse micelles. To explore how the chemical composition of the interface influences dynamics, the dynamics of water in AOT reverse micelles are compared to water dynamics in reverse micelles made from the neutral surfactant Igepal CO-520. It is found that the presence of an interface plays the major role in determining interfacial water dynamics and not the chemical composition. A two component model is also developed for spectral diffusion. The two component model for spectral diffusion is an extended version of the center line slope (CLS) analysis procedure, originally developed for single ensemble systems. The modified two component CLS procedure allows the CLS behavior of water at the interface to be back-calculated from known parameters. From the interfacial CLS, the interfacial frequency-frequency correlation function, which describes spectral diffusion, can be determined. It is found that, similar to orientational relaxation behavior in large AOT reverse micelles, the interfacial FFCF does not vary with increasing reverse micelle size
Characterization and application of vertical nanopillar-based sensors for probing cellular functions by Lindsey Hanson( )
1 edition published in 2014 in English and held by 1 WorldCat member library worldwide
Vertically aligned nanopillars can serve as excellent electrical, optical and mechanical platforms for biological studies. To date, the interface between cells and nanopillars, particularly the conformation of the cell membrane and nucleus, has not been well characterized despite its importance to the choice of feasible applications for nanopillar substrates to cellular studies. We characterized the cell-nanopillar interface by fluorescence, scanning electron and transmission electron microscopy on nanopillars with a range of diameters, pitch and heights. We found that the cell membrane wraps around the entirety of the nanopillar without loss of membrane integrity, contrary to prior suggestions. We also observed that the membrane-surface gap of both cell bodies and neurites is smaller for nanopillars than for a flat substrate. These results support a tight interaction between the cell membrane and the nanopillars and previous findings of excellent sealing in electrophysiology recordings using nanopillar electrodes. Subsequently, we took advantage of the cell-nanopillar interface to develop applications of nanopillar arrays to mechanical and optical measurements in living cells. We observed that vertical nanopillar arrays significantly deform the nuclear envelope, and the extent of deformation is sensitive to both the stiffness of the nucleus and the stiffness of the cytoskeleton. Thus, nanopillar arrays constitute a novel approach for non-invasive, subcellular perturbation of nuclear mechanics and open up exciting new possibilities for the study of nuclear mechanotransduction in live cells. In addition to serving as mechanical probes, we developed a nanopillar-based platform for single molecule measurements in live cells. With a diameter much smaller than the wavelength of visible light, a transparent silicon dioxide nanopillar embedded in a nontransparent substrate restricts the propagation of light and affords evanescence wave excitation along its vertical surface. We showed that nanopillar illumination can be used for in vitro single molecule detection with high background. In addition, the tight interface between vertical nanopillars and live cells allows them to function as highly localized light sources inside the cell. Overall, nanopillar arrays are a powerful platform for studying cell function through electrical, optical and mechanical measurements
Orientational dynamics in water/cosolvent mixtures by Adam Lynn Sturlaugson( )
1 edition published in 2013 in English and held by 1 WorldCat member library worldwide
The design and characterization of new solvent systems is an ever growing field of research. As such, understanding how macroscopic solvent properties emerge from molecular structure and dynamics is foundational for rational solvent system design. Of particular interest are water/cosolvent systems since they can display a wide variety of desirable characteristics. Water is inexpensive, safe, and well understood, and a large volume of research is devoted to the dynamics in water/cosolvent systems, with recent focus on the influence of cosolvents on the dynamics of water. In this thesis, optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments on two water/cosolvent systems are presented. The OHD-OKE experiment is a well-established pump-probe pulsed laser technique that can measure orientational relaxation. The experimental setup described here has been improved substantially over previous versions and is demonstrated capable of measuring dynamics over seven decades in time and eight decades in signal amplitude. The broad time window is obtained through the use of regeneratively amplified pulses and continuous wave probing, while the large signal range is accessed by incorporating balanced detection, digital lock-in amplification, polarization modulation phase cycling, and beam geometry optimization. The signal from water in the OHD-OKE is small; thus, the dynamics primarily track the motions of the cosolvent. The first water/cosolvent system studied here is a model water/polyether binary mixture. Polyethers are a large class of compounds with applications including medicine, cosmetics, and electrochemistry. Based on previous studies, some have suggested that there are significant polyether conformational changes as the water content is increased. However, rotational diffusion measurements from the OHD-OKE, translational diffusion measurements from NMR, and detailed hydrodynamic calculations, both as a function water concentration and temperature, show that such claims are unwarranted. The rotational diffusion of the polyether, which is sensitive to molecular shape, is in good agreement with the hydrodynamic calculations, both as a function of water concentration and temperature. In contrast, the translational dynamics are only hydrodynamic at high water concentrations. The water poor mixtures are anomalously fast, which we hypothesize is due to the free volume of the system. Careful analysis of the hydrodynamic calculations support this hypothesis, showing that voids in the liquid can impact the translation of the anisotropic polyether molecules more than they impact the rotational diffusion, as measured by OHD-OKE. The second system studied consists of a series of water/ionic liquid (IL) mixtures. Research in and application of ILs has exploded in the past decade, but their use as pure solvents is often limited by their high viscosities and extremely hygroscopic nature. The influence of water on the orientational dynamics of alkylmethylimidazolium tetrafluoroborate ILs is studied as a function of water concentration and cation alkyl chain length. For low water concentrations or short-chain cations, the dynamics are single exponential and follow Debye-Stokes-Einstein (DSE) behavior. However, the long-chain ILs at high water concentrations show clearly biexponential behavior, with the slow component of the dynamics showing anti-DSE behavior. We attribute the slow component to overall cation reorientation due to alkyl tail aggregates and the onset of water-induced gelation (as seen in similar water/IL systems) and the fast component to the wobbling-in-a-cone motions of the charged headgroup of the cation. We hypothesize that this specific water/tetrafluoroborate IL system studied does not gel because it phase separates before the enough water can be added to induce gelation. These results should have implications for rational water/IL cosolvent system design
Inorganic/graphene hybrid nanomaterials for electrochemical energy storage and conversion by Hailiang Wang( )
1 edition published in 2012 in English and held by 1 WorldCat member library worldwide
The increasing demand for energy together with the growing concerns about air pollution and global warming has stimulated intensive research on energy processes ranging from production, conversion, storage, transmission and consumption. Energy storage is to become more and more important with the gradual shift from fossil fuels to renewable energy sources which are temporally intermittent and geographically localized. On the other hand, electric vehicles are now a trend in the automobile industry with the goal to cut emission and reduce oil consumption. It is thus crucial to develop electrochemical energy conversion and storage devices such as batteries and supercapacitors with high specific energy and power, long cycle life, low cost and safety. We aim to design and synthesize novel nanostructured electrode materials and electrocatalysts by using chemically derived graphene sheets as growth substrates for electrochemical functional materials. The unique chemical interactions between graphene and the active nanomaterials affect the morphology and size of the nanomaterials, enhance electron transport, stabilize the nanomaterials during cycling, and generate synergistic effects in electrocatalysis, leading to superior electrochemical performance. We have grown nanocrystals of hydroxides, oxides, chalcogenides and phosphates with controlled morphology, sizes and structures on graphene, affording materials that can be readily integrated in current lithium ion batteries, alkaline batteries and supercapacitors to boost their performance, as well as materials that support rising technologies such as Li-S and Li-air batteries. The novel materials we have studied also allow for deepening our understanding in materials chemistry and electrochemistry
Fast dynamics of aqueous biological molecules investigated with 2D IR spectroscopy by Jean K Chung( )
1 edition published in 2012 in English and held by 1 WorldCat member library worldwide
Proteins are dynamic structures that are in constant fluctuations, and their ability to undergo structural changes is critical to their function. However, their fastest dynamics in thermal equilibrium have remained largely unexplored. In this work, studies that examine the dynamics of aqueous proteins using two-dimensional infrared echo spectroscopy (2D IR) are presented. In particular, investigations of fast fluctuations in proteins and peptides within the context of structural changes upon denaturation are discussed. 2D IR is a nonlinear optical spectroscopic technique that can measure ultrafast dynamics of complex molecules in the picoseconds regime, timescales ~6-10 orders of magnitude faster than nuclear magnetic resonance. In addition, the relatively low energy mid-IR laser pulses used in this study probe the relevant nuclear degrees of freedom without significantly perturbing the protein structure or dynamics. Brief descriptions of the experimental setup and methods, as well as analysis and interpretation, are given
A self assembly approach to localization and patterning of optically resolved single molecules by Randall Mark Stoltenberg( )
1 edition published in 2011 in English and held by 1 WorldCat member library worldwide
Directed assembly of single molecules is a central theme in nanotechnology. This body of work was inspired by a specific challenge involving ordered deposition of single DNAs on surfaces for massively parallel single molecule DNA sequencing via fluorescence microscopy. A potential 10-fold gain in data density is possible if single molecules can be forced into a regular array rather than randomly deposited. The dimensions of such an array are difficult to achieve with conventional lithography techniques. On one end, molecules must be separated by sufficient distance so their optical signatures do not overlap. This distance is on the order of hundreds of nanometers. On the other end, the attachment points for the molecules must have molecular dimensions. Bridging these two length scales is a formidable task. The ability to place nanometer scale objects with nanometer precision can been achieved through atomic force microscopy, scanning tunneling microscopy, optical tweezers, and ebeam lithography. All of these techniques, however, are serial in nature and hence do not serve the intended gain in data density. Another approach toward directed patterning of single molecules is through self-assembly. In this work, self-assembly of block copolymers is explored as a means to addressing the molecular and optical resolution length scales simultaneously. First, the challenge of molecular patterning for single molecule fluorescence microscopy is explored theoretically and the limits of this approach are defined. Block copolymers are introduced as a possible solution to generating the correct surface patterns for improved data density, and experimental results are compared to theoretical predictions. Second, the surface chemistry of these arrays is characterized, and I will show they can be selectively functionalized in preparation for directed assembly of DNAs. Third, these arrays are integrated into single molecule fluorescence imaging experiments to determine their potential for improved data density. What emerges from this work is not only a viable platform for increased single molecule fluorescence data density, but also a deeper understanding of the requirements for directed self-assembly of single molecules
Cohesion and decohesion kinetics of polymer solar cells by Christopher Bruner( )
1 edition published in 2014 in English and held by 1 WorldCat member library worldwide
Polymer organic solar cells (OSCs) possess many desirable properties include low temperature solution processibility of photoactive materials and the utilization of flexible substrates for conformal OSC design. However, challenges remain that may inhibit their adoption and implementation. Among these are thermochemical stability, optimized power conversion efficiency, and mechanical reliability. Indeed, for organic solar cells to be used on flexible substrates, mechanical reliability of the individual layers and interfaces is pertinent. In this dissertation, quantitative micromechanical testing techniques were employed to help characterize the mechanical reliability of the layers and interfaces for polymer OSCs. From testing, it was determined that the polymer:fullerene photoactive layer consistently failed cohesively. The cohesive strength of most photoactive layers generally ranged from 0.5 to 2.0 Joules per square meter. However, by using thermal annealing, manipulating the photoactive layer structure, and selecting polymer molecular weight, cohesion values as high as 17 Joules per square meter could be achieved. Indeed, polymer molecular weight affected cohesion the most due to significant plasticity within the photoactive layer. Conversely, improved cohesion did not always result in improved device electronic performance. By optimizing cohesion and efficiency, we are able to come closer to design guidelines for mechanically robust and efficient solar cells. Finally, because OSCs must operate in the environment at temperatures as high as 65 C, we analyzed OSCs under dry, inert environmental conditions and showed how temperature affects the decohesion kinetics within the device. It was demonstrated that the decohesion rate generally accelerated with increasing test temperature. We were able to develop a viscoelastic kinetic model that was able to describe and predict decohesion for these devices. This collective work and modeling will provide greater insight into the practical limitations of OSC design and will aid in future development of OSCs with greater mechanical reliability and in-service lifetimes
Functionally relevant solvation dynamics in the protein interior by William James Childs( )
1 edition published in 2010 in English and held by 1 WorldCat member library worldwide
Functionally relevant solvation dynamics in the protein interior Stanford University, 2010. The role of solvent in the kinetics and thermodynamics of charge transfer reactions in simple solvents is well studied. However, biologically relevant systems often involve chemical reactions not in simple aqueous environments, but within a protein interior that constitutes an organized solvent environment. The role of the protein environment during catalysis and charge transfer reactions continues to be debated. To determine the role of the protein environment during charge transfer reactions, experiments presented in this dissertation were designed to measure the time-resolved response of a protein environment to sudden electronic perturbation. Specifically, time-resolved fluorescence measurements were used to determine the solvation response of a chromophore bound in the protein interior. An unnatural amino acid containing a fluorescent side chain, aladan, was synthetically incorporated into seven sites of a small globular protein, GB1, in order to determine the degree of solvation in different regions of a single protein. In all regions, the solvation dynamics showed an ultra-fast solvation response on the subpicosecond timescale. However, in addition to the subpicosecond dynamics, buried sites also showed relatively long solvation behavior over nanoseconds. mPlum, a variant of the red-fluorescent protein DsRed, was produced by a directed evolution experiment in the Roger Tsien lab. Ultra-fast fluorescence upconversion experiments measured a solvation response in mPlum. Examining the comprehensive library of mutants generated by the directed evolution experiment identified a single hydrogen bond between glutamic acid 16 and the chromophore to be the origin of the solvation process. The possibility of localizing a solvation response to a single interaction is only possible in an organized solvent system like a protein interior. The catalytic relevance of solvation dynamics was studied with a light-driven reaction analog for isomerisation of [delta]5-3-ketosteroids in ketosteroid isomerase. The light-driven analog consists of a photoacid bound to the active site of ketosteroid isomerase. In the ground state, the photoacid electrostatically resembles the reaction intermediate. In the excited state, the photoacid resembles the starting material. The solvation response recorded from the fluorescing photoacid shows a dramatically reduced solvation capacity and slower dynamics than observed with the same fluorophore in solution. Solvation within the protein occurs on the nanosecond timescale compared to picoseconds in solution. The active site of ketosteroid isomerase does show dynamic electrostatic behavior during the simulated reaction; however, the response is among the slowest recorded. The resistance to electrostatic perturbation suggests an electrostatically preorganized environment which does not significantly reorganize during catalysis
Multifunctional graphitic carbon nanomaterials for imaging, drug delivery and photothermal therapy by Sarah Paige Sherlock( )
1 edition published in 2011 in English and held by 1 WorldCat member library worldwide
In recent years there has been a growing interest in utilizing nanomaterials for drug delivery and biomedical imaging applications. This work focuses on the development of two multifunctional graphitic-carbon based nanomaterials capable of acting as both drug delivery agents and as contrast agents for either magnetic resonance imaging or near-infrared fluorescence imaging. Both of these agents heat under near-infrared light and are capable of loading chemotherapy drugs making them multifunctional in nature. The first material discussed is a FeCo-graphitic carbon nanocrystal loaded with doxorubicin. Addition of near-infrared photothermal therapy significantly increases the cellular toxicity of these nanocrystals in vitro. Treatment of breast cancer tumors in mice using combined nanocrystal drug delivery and photothermal therapy resulted in complete tumor regression in 45% of mice. The imaging capability of these nanocrystals is demonstrated through high-resolution magnetic resonance imaging of microvessels in rabbits. The potential long-term biodistribution and safety of this material is evaluated. The second graphitic-carbon nanomaterial used in this work is single-walled carbon nanotubes. This material is developed as a deep-tissue fluorescent imaging agent due to their inherit photoluminescence beyond 1 micron. This light emission is demonstrated to be particularly useful for in vivo imaging by minimizing light scattering by tissues leading to crisp anatomical resolution
Ultrafast studies of ionic liquids and the role of nanostructural organization by Kendall Stanley Fruchey( )
1 edition published in 2011 in English and held by 1 WorldCat member library worldwide
Ionic liquids are a quickly emerging class of neoteric solvents composed of organic and inorganic ions that remain liquid at room temperature. Their properties are diverse and often unique, bridging the continuum between polar and nonpolar, molecular and ionic. One property which has garnered special attention is the possibly ubiquitous existence of ordering in the bulk liquid, known as nanostructural organization. Resulting from the energetics of balancing the strong electrostatics of ions with steric considerations, it has been suggested that ionic liquids with sufficiently large alkyl substitutions should form distinct regions of polar and non-polar groups within the bulk solvent structure. The characteristics of this ordering, and even its very existence, have been heavily debated topics in ionic liquid research. Two ultrafast fluorescence experiments are discussed which attempt to assess the extent and role of nanostructural organization in the solvent properties of prototypical ionic liquids. Additionally, an Optical Kerr Effect study is described with the aim of understanding the role of Li in ionic liquid electrolytes. Time dependent fluorescence depolarization measurements studied the rotational friction experienced by small charged and nonpolar dye molecules in a series of ionic liquids with increasing alkyl chain lengths. Two distinct behaviors were observed. For a charged pyranine-derivative dye, strong interaction between the dye molecules and ionic liquid leads to a greater rotational friction than the Debye-Stokes-Einstein hydrodynamic theory predicts. The magnitude of this increase scales with the size of the ionic liquid cation. For the nonpolar dye perylene, the rotational friction was less than the slip boundary condition of hydrodynamic theory. Moreover, increasing alkyl chain length causes the rotational behavior to converge on that experienced by the dye in a purely alkane environment. The causes of these trends are discussed, leading to the conclusion that different regions of the nanostructured environment are being assessed. The nonpolar dye is segregated into the nonpolar region of the ionic liquid, so that the rotation friction describes the structure of this region. The charged dye is interacting with the ions in the hydrophilic region. The results shed light on some aspects of nanostructural organization as it applies to ionic liquids as solvents. To assess the spatial characteristics of nanostructural organization, donor-donor excitation transfer was examined. The time dependence of the excitation transfer is strongly sensitive to the distribution of donors and acceptors in solution. Using a dye molecule that is anticipated to segregate into the nonpolar regions, the altered distribution of dye molecules resulting from nanostructural organization will be evident in the excitation transfer. Fluorescence depolarization can be used to monitor the excitation transfer. Observables for an isotropic and structured distribution of dye were calculated, and compared to fluorescence experiments. Based on the fits, an upper bound on the radius of 6-8Å is placed on the size of the hydrophobic regions of nanostructural orgaization, modeled as spheres. The transport properties of ionic liquids as electrolytes are strongly and negatively affected by the addition of lithium. To understand this, Optical Heterodyne Detected Optical Kerr Effect studies were performed on a pure and lithium loaded imidazolium ionic liquid. Mode-coupling theory was tested in the pure liquid, and found to be capable of describing the dynamics. Mode-coupling theory was then used to understand the results in the lithium loaded samples. Changes in parameters from the mode-coupling theory fits occur at a lithium mole fraction of 0.2. This is discussed in terms of outside MD simulations to understand and substantiate the changes in ionic liquid structure leading to the loss of ion mobility
Synthesis, properties and electronics of graphene nanoribbons by Xinran Wang( )
1 edition published in 2010 in English and held by 1 WorldCat member library worldwide
Graphene, a two-dimensional single atomic layer of graphite, has emerged as a material with interesting physical and chemical properties and high potential for various applications such as sensors, transparent electrodes and electronics. Due to high carrier mobility (up to ~15,000cm2/Vs), graphene has gained much interest as a possible candidate to extend beyond silicon complementary metal-oxide-semiconductor (CMOS) technology for future nano-electronics. Bulk graphene is a semi-metal with zero bandgap, not suitable for high on/off ratio transistors. However, narrow (~ a few nanometer) graphene nanoribbons (GNRs) have been theoretically predicted to be semiconductors that afford high performance room temperature field-effect transistors (FETs). This thesis focuses on the synthesis, physical and chemical properties and electronic devices of GNRs down to a few nanometers wide. We address several critical issues towards large scale graphene electronics and propose a roadmap to achieve this goal. In the first part of this thesis, I will show a chemical route to produce GNRs with width below 10 nanometers, as well as single ribbons with varying widths along their lengths or containing lattice defined graphene junctions. The GNRs were solution phase derived, stably suspended in solvents with noncovalent polymer functionalization, and exhibited ultra-smooth edges with possibly well defined zigzag or armchair edge structures. Electrical transport experiments showed that the bandgaps of these GNRs are inversely proportional to the widths, which confirms that quantum confinement is responsible for the bandgap opening. Unlike single-walled carbon nanotubes (SWNTs), all of the GNRs narrower than ~5nm are semiconductors that afford graphene FETs with on/off ratios of higher than ~105 at room temperature. We then study the chemically derived narrow semiconducting GNR-FETs on 10nm SiO2 systematically. We find that the on state current density can be as high as ~2000[mu]A/[mu]m, carrier mobility is ~200cm2/Vs and scattering mean free path is ~10 nm. Scattering mechanisms by edges, acoustic phonon, and defects are discussed. The semiconducting GNR-FETs are comparable to small diameter (d~1:2 nm) semiconducting SWNT-FETs in on-state current density and on/off ratio. In the second part of this thesis, I will talk about complementary electronics of GNRs. As made GNR device are usually p-doped by adsorbates, but for device applications, it would be useful to access the n-doped material. Individual graphene nanoribbons could be covalently functionalized by nitrogen species through high-power electrical joule heating in NH3, leading to n-type electronic doping consistent with theory. The formation of the carbon-nitrogen bond should occur mostly at the edges of graphene where chemical reactivity is high. We fabricate the first n-type graphene FET that operates at room temperature. Spectroscopic study of graphene oxide (GO) annealed in NH3 provides direct evidence of nitrogen incorporation and sheds light on the possible configurations of nitrogen in carbon networks. In the third part of this thesis, I study the interface between graphene and high dielectric constant (high-k) metal oxides, which are widely used in current silicon technology as gate dielectrics of transistors. We use atomic layer deposition (ALD) to deposit the metal oxides. We find that ALD of metal oxides gives no direct deposition on defect-free pristine graphene. On the edges and defect sites, however, dangling bonds or functional groups can react with ALD precursors to afford active oxide growth. This leads to an interesting and simple way to decorate and visualize defects in graphene. By noncovalent functionalization of graphene with carboxylate-terminated perylene molecules, one can coat graphene with densely packed polar groups for uniform ALD of high-k dielectrics. Uniform high-k coverage is achieved on large pieces of graphene sheets with a size of greater than 5 [mu]m. This method opens the possibility of integrating ultrathin high-k dielectrics in future graphene electronics. Finally, I will describe a scalable lithographic approach to make GNRs narrower than 10nm for future logic applications. We devise a gas phase chemical approach to etch and shrink graphene from the edges without damaging its basal plane. The reaction involves high temperature oxidation of graphene in a slight reducing environment to afford controlled etch rate ([less than or equal to] ~1nm/min). We then fabricate ~20-30nm wide GNR arrays by electron beam lithography, and use the gas phase etching chemistry to narrow the ribbons down to <10nm. Parallel arrays of ultra-narrow GNRs are obtained. For the first time, high on/off ratio up to ~104 has been achieved at room temperature for field effect transistors built with sub-5nm wide GNR semiconductors derived from lithographic patterning and narrowing. Controlled chemical etching could play important roles in tailoring the dimensions of graphene for large scale device integration
Nanomaterials for biological imaging and biomedical diagnostic applications by Scott Michael Tabakman( )
1 edition published in 2011 in English and held by 1 WorldCat member library worldwide
This thesis describes the use of inorganic nanomaterials for spectroscopic applications in biomedical imaging in vitro and ex vivo as well as in diagnostic sensor applications. Nanomaterials exhibit unique electronic, optical, magnetic, and chemical properties due to their small size and low dimensionality compared with their bulk counterparts. Exploitation of these phenomena has been the subject of much research in the past few decades, since Feynman famously informed us that there is "Plenty of Room at the Bottom." Components of relatively large chemical systems, quantum physical systems, and biomolecules converge in the nanometer size range, the so-called "nano-bio interface." Control of objects on this length scale affords a wealth of potential applications in biomedicine. However, inorganic nanomaterials and biological systems are not without their incompatibilities. Chemical modification and surface engineering are necessary to successfully employ nanomaterials in biological applications. To exploit the inherent optical properties of single-walled carbon nanotubes (SWNTs) in sensitive and multiplexed medical imaging and diagnostic applications, they must be rendered biocompatible by non-covalent modification. Indeed, it is shown that a suspension of SWNTs via functional amphiphiles affords a supramolecular complex that may be interfaced with biological systems. Resonance Raman scattering molecular imaging of cancer in vitro is demonstrated. The simple chemical structure and high Raman scattering cross section of SWNTs is exploited to prepare a library of SWNT labels for Raman-based immunostaining of ex vivo cancer tissue. Furthermore, the benefits and pitfalls of Raman scattering compared with traditional fluorescence methodologies are discussed. In addition to the optical properties of SWNTs, gold (and silver) nanoparticles possess unique localized surface plasmon resonances in the visible and near-infrared. Coupling of electromagnetic radiation to these plasmon modes effectively increases the local field strength within several nanometers from the nanoparticle surface, enhancing proximal optical phenomena, producing the surface-enhanced Raman scattering (SERS) effect, as well as plasmon-enhanced fluorescence. In order to prepare plasmonic films for SERS and fluorescence-enhancing applications, novel chemical and physical approaches will be presented. Biocompatible SWNTs conjugated to target-specific biomolecules are employed as Raman scattering labels in a SERS-based immunoassay. The combination of the SERS effect with the large Raman scattering intensity of SWNTs affords a protein assay capable of fM detection in microarray format. In addition to SERS, fluorescence-enhancement owing to chemically prepared plasmonic gold films was also realized. The enhancement of both the local electric field and NIR fluorescence emission rate via the coupling of scattering nanoparticle plasmon modes can lead to NIR fluorescence enhancement (NIR-FE) under appropriate conditions. Here, those conditions are optimized to yield the NIR-FE effect in the context of microarray immunoassays. The rapid and simple methodology developed affords high sensitivity detection of cancer and autoimmune disease biomarkers, offering a broad dynamic range applicable to a wide variety of assays. Comparisons are drawn between the SERS and NIR-FE methodologies, along with a discussion of their merits and future research directions
Structure design of silicon anodes for high energy lithium batteries by Nian Liu( )
1 edition published in 2014 in English and held by 1 WorldCat member library worldwide
More than two centuries old, battery technology has never attracted so much attention as it is today from all over academia, industry, government, and general public. Its extended application in our daily life, from portable electronic devices, electric vehicles, to power grid storage is driving the urgent need for major breakthroughs, in energy density, cycle life, and cost. One of the materials of choice is silicon. Silicon anodes have an order of magnitude higher capacity than state-of-the-art graphite anodes, providing great promise for use not only in Li-ion, but also in next generation high energy Li-S and Li-O2 batteries. However, Si anodes of conventional structure have very short cycle life, because the volume change of Si upon cycling leads to fracture and unstable interfaces. In this dissertation, I employed nanoscale materials design to overcome these problems, by rationally making accurate void space available inside the structure, and limiting the surfaces that are exposed to the electrolyte. The first-generation "yolk-shell" anode prevents fracture, stabilizes the interface, and significantly extends cycle life at small mass loading. Then I designed a second-generation "pomegranate" anode that has reduced interface side-reaction, increased energy density, and enhanced electrode-level conductivity. This design performs excellently even at mass loading as high as commercial batteries. Moreover, its fabrication is highly scalable. Next, I developed a method that produces the key source material for the above designs, Si nanoparticles, from rice husks, an agricultural byproduct with extremely high annual yield, and low cost. Finally, a prelithiation method has been developed for silicon anodes so that it could be paired with high-energy sulfur cathodes to make a full battery. Such a combination can give almost 400% the energy of state-of-the-art Li-ion batteries, enabling the next generation of battery technology
Modification and manipulation of one-dimensional carbon materials for electronics by Justin Wu( )
1 edition published in 2014 in English and held by 1 WorldCat member library worldwide
As Moore's Law demands ever smaller transistors, it becomes necessary to solve the deleterious effects of scaling. Graphene, with its intrinsically two-dimensional nature, offers a potential solution to the short channel effects seen with traditional geometries and materials. Using a 2D material, or one-dimensional in the form of either graphene nanoribbons (GNRs) or single walled carbon nanotubes (SWNTs), instead of bulk Si allows for an intrinsically compact device geometry, which should offer the ability to maintain high gate control far into the sub-10 nm regime. Graphene based materials also show considerably higher carrier mobility than Si. It is anticipated then that SWNT/Graphene transistors will show significantly better metrics in both speed and energy delay than Si based transistors. There are critical challenges that currently prevent the wider implementation of carbon electronics, the lack of bandgap in graphene, the roughness of GNRs, and the variability of SWNTs. This thesis will describe several projects aimed at addressing these challenges by modification and manipulation of these carbon materials. In the first project described in this thesis, we cover high-field transport in GNRs on silicon dioxide, up to breakdown. Next, in the third chapter, we investigate chlorine plasma reaction with graphene and GNRs and compare with hydrogen and fluorine plasma reactions. In the fourth chapter, we investigate the effect of uniaxial strain (0%-6%) introduced into individual GNRs by atomic force microscopy (AFM). In the fifth chapter, we characterize ~98% pure semiconducting single walled carbon nanotubes (s-SWNTs) obtained by gel filtration of arc-discharge grown SWNTs with diameters in the range of 1.2-1.6 nm. In the sixth chapter, we present a process where highly pure s-SWNTs are separated from bulk materials and self-assembled into densely aligned rafts driven by depletion attraction forces. In the seventh chapter, s-SWNTs are self-assembled using these same depletion attraction forces into rafts along lithographically defined patterns of narrow pitch of 100 and 200 nm
Nanotechnology enabled biomedical fluorescence imaging in the second near-infrared window by Guosong Hong( )
1 edition published in 2014 in English and held by 1 WorldCat member library worldwide
Fluorescence imaging in the second near-infrared window (NIR-II, 1.0-1.7 microns) has many salient advantages over the visible (400-750 nm) and the traditional near-infrared (NIR-I, 750-900 nm) windows owing to the reduced photon scattering and negligible tissue autofluorescence. However, NIR-II fluorescence imaging has been limited by the scarcity of materials with sufficient NIR-II fluorescence quantum efficiency, and single-walled carbon nanotube (SWNT) had been the only fluorophore for biological imaging in the NIR-II window. This work aims to enhance the intrinsic NIR-II fluorescence of SWNTs, apply SWNTs for in vivo imaging of real-world medical problems in animal models and develop new NIR-II fluorophores other than SWNTs. First, a plasmonic gold substrate is used to enhance the intrinsically low NIR-II fluorescence of SWNTs and to improve the sensitivity of cancer cell imaging using SWNTs as molecular targeting probes. The sensitive distance dependence of fluorescence enhancement of SWNTs is then exploited to probe the trans-membrane motion of single nanotube molecules and reveal the internalization pathway as receptor-mediated endocytosis. The biocompatible SWNTs are further applied to an in vivo animal model of lower limb ischemia, where we demonstrate microvascular imaging and hemodynamic measurement using NIR-II fluorescence, with improved spatial resolution over X-ray computer tomography (CT) and broader dynamic range of blood flowmetry than ultrasound. In a rationally chosen sub-region of NIR-II in the 1.3-1.4 micron range, chemically separated SWNTs allow for non-invasive brain vascular imaging through intact scalp and skull with sub-10 micron resolution at millimeter depth of penetration. Lastly, two new materials, Ag2S quantum dots (QDs) and conjugated copolymers are developed to expand the toolbox of NIR-II fluorophores. The Ag2S QDs afford in vitro targeted cancer cell imaging and in vivo mouse imaging with high tumor uptake. The high fluorescence quantum yield of the conjugated copolymer allows for ultrafast dynamic NIR-II imaging of the arterial blood flow with waveform cardiac cycles revealed in hemodynamic analysis. The many benefits of NIR-II fluorescence imaging demonstrated in this work based on the development of a handful of biocompatible NIR-II nanomaterials bode well for future biological research and clinical applications with this new imaging technique
Catalysis on platinum surfaces probed using synchrotron-based core-level spectroscopies by Daniel James Miller( )
1 edition published in 2013 in English and held by 1 WorldCat member library worldwide
Probing chemical reactions on solid surfaces in situ remains a major challenge in heterogeneous catalysis, because most methods of surface characterization require ultrahigh vacuum (UHV) conditions. In addition, the effects of morphology, particle size, and chemical composition are frequently difficult to disentangle due to sample heterogeneity. This work addresses these limitations by applying synchrotron-based core-level spectroscopies to well-defined systems based on single crystals. With a view to developing improved electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells, the behavior of oxygenated species on the Pt(111) and Pt/Rh(111) surfaces was examined in situ under both electrochemical and ambient-pressure conditions using high-energy-resolution fluorescence-detection x-ray absorption spectroscopy (HERFD XAS) and ambient-pressure x-ray photoelectron spectroscopy (APXPS), respectively
Developing novel carbon nanomaterials for tumor imaging and photothermal therapy by Joshua Tucker Robinson( )
1 edition published in 2012 in English and held by 1 WorldCat member library worldwide
Reliable, unambiguous cancer detection is important for successful cancer treatment. Current imaging modalities lack either the resolution or signal-to-background to reliably identify tumors below 1 mm3. Positron emission tomography (PET), Magnetic resonance imaging (MRI), and fluorescence imaging all attempt to image a contrast agent which is overly abundant at the site of a tumor while present at significantly lower levels in healthy, cancer-free tissue. Ideally, this contrast agent could serve, not only to identify cancer, but as a non-invasive treatment to eliminate the cancer. In this work, we present single-walled carbon nanotubes (SWNTs) as a potential diagnostic/therapeutic 'theranostic' agent that addresses many of the issues that face other contrast agents. SWNTs possess many unique optical properties; they have intrinsic fluorescence in the Near-Infrared (NIR) with a several hundred nanometer Stokes shift. The ability to excite SWNTs between 700-1000 nm (NIR-I) allows for superior depth penetration in vivo because of the minimal absorption of light by biological tissue and water in this region. SWNTs emit fluorescence between 1000-1400 nm (NIR-II), a region with low scattering by endogenous tissues, which enables rapid, sub 100 micron resolution whole-animal imaging. Because of the large Stokes shift, filter sets can be coordinated to eliminate virtually all auto-fluorescence. Utilizing these techniques, we present data supporting the superiority of SWNTs as in vivo fluorophors because they allow for images with a higher combined resolution and depth penetration than most other currently available modalities. In order to be useful for cancer imaging, however, an imaging contrast agent must be able to achieve high accumulation at the site of the cancer compared with non-specific uptake. By tailoring and optimizing the size and composition of the surfactant coating in this work, SWNTs achieved the highest tumor uptake of any intravenously injected nanoparticle. The high tumor accumulation of SWNTs is visually represented by crisp, well-defined images of tumors in vivo with little to no signal in other organs or skin. The speed of fluorescent imaging allowed us to take 100 ms frame-rate videos of SWNTs after intravenous injection; a mathematical technique called Principal Component Analysis (PCA) is used to separate the components of the SWNT fluorescence over time. Due to differential blood flow through cancerous and healthy tissue, we clearly identified tumor masses within minutes of injecting the SWNTs using PCA, as opposed to waiting for hours or days for typical contrast agents to have significant tumor accumulation. While SWNTs have sufficient light absorption in NIR-I for fluorescent imaging, the majority of the light absorbed (> 99%) undergoes non-radiative relaxation, resulting in heat generation. By irradiating mice with a relatively low power of 808 nm laser light, SWNTs heated and ablated tumors with no observable damage to healthy tissue. This approach to cancer therapy, known as photothermal therapy, has had a recent push into using nanoparticles, specifically gold nanorods/nanoparticles as photothermal agents. Our SWNTs, because of their higher light absorption and tumor accumulation, are able to use 70% lower laser power and 90% lower dose than the previous standard for photothermal therapy, which is important when considering toxicity and the safe limit for human exposure to laser light. Additional nanomaterials that share optical and pharmacokinetic properties with SWNTs are explored in this work as well. We synthesized the first examples of biocompatible graphite oxide and graphene oxide. These low cost, industrially scalable two-dimensional carbon-based nanomaterials maintain SWNTs high light absorption in the Near-Infrared region. We selectively targeted graphene oxide to cancer cells followed by subsequent photothermal destruction of the cancerous cells, making this an economical alternative to SWNTs for photothermal therapy. Near-Infrared Quantum Dots, composed of a silver sulfide core surrounded with a branched Poly(ethylene glycol) coating, are optically similar to SWNTs, with large Stokes shift, NIR-I excitation, and NIR-II fluorescence emission. These quantum dots were shown to have ultra-high tumor accumulation and minimal accumulation in other organs. Preliminary excretion and retention studies in this work indicated that, most likely because of their smaller hydrodynamic radius, these quantum dots are more easily able to 'escape' the liver and spleen and be excreted quicker than SWNTs. The final thrust of this work lies in separating bulk SWNTs into their single-chiralities. This holds enormous potential for lowering the dose of SWNTs necessary for biomedical treatment; by removing the SWNTs that do not contribute to the optical absorption/fluorescence for NIR imaging (> 90%) the dose for imaging and photothermal therapy can be further lowered by an order of magnitude, minimizing toxicity concerns
Development of a resonance ionization spectroscopy ion-transport probe for the enriched xenon observatory by Maria Montero Diez( )
1 edition published in 2012 in English and held by 1 WorldCat member library worldwide
The Enriched Xenon Observatory (EXO) is a series of experiments seeking to measure the neutrino mass through observation of neutrinoless double beta decay (0nbb). The next generation of 0nbb experiments aims to probe Majorana neutrino masses at or below 10 meV. To reach this sensitivity, ton-scale detectors are needed with lower radioactive backgrounds than the best ones operating today. The EXO collaboration is developing a novel strategy for a virtually background-free search for the 0nbb of Xe-136, based around detecting individual Ba-136 ions resulting from such decays. This dissertation details the efforts to develop a barium tagging technique which uses resonance ionization spectroscopy (RIS) to selectively and efficiently ionize barium atoms for injection and detection in an ion trap. A simple radionuclide-driven single-ion source has been developed to push the technology to high efficiency with a small number of ions
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