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Full-Text Articles in Engineering Science and Materials

Multiscale Simulations Of Dynamics Of Ferroelectric Domains, Shi Liu Jan 2015

Multiscale Simulations Of Dynamics Of Ferroelectric Domains, Shi Liu

Publicly Accessible Penn Dissertations

Ferroelectric materials exhibiting switchable polarization have been used as critical components in electronics, memory, actuators and acoustics, and electro-optics. The applications of ferroelectric materials heavily rely on the interactions between the polarization and external perturbations, such as electric field, stress, and temperature. It is therefore crucial to understand the dynamics of ferroelectric response at finite temperature. Despite the tremendous advance of computational power and the success of first-principles methods, large-scale simulations of dynamics in oxides at finite temperature can still only be performed using classical atomistic potential. We first develop a model potential based on principles of bond-valence and bond-valence ...


Improving The Signal-To-Noise Of Nanopore Sensors, Matthew Puster Jan 2015

Improving The Signal-To-Noise Of Nanopore Sensors, Matthew Puster

Publicly Accessible Penn Dissertations

Over the last five years, solid state nanopore technology advanced to rival biological pores as a platform for next generation DNA sequencing. Fabrication improvements led to a reduction in nanopore diameter and membrane thickness, offering high precision sensing. Custom electronics were developed concomitant with low capacitance membranes for low-noise, high-bandwidth measurements. These advances improved our ability to detect small differences between translocating molecules and to measure short molecules translocating at high speeds.

This work focuses specifically on the challenge of maximizing the signal magnitude generated by the solid state nanopore. One way that this can be achieved is by thinning ...


Surface Reconstructions Of Perovskite-Type Oxides: Their Exotic Structures And Modified Chemistry, John Mark Pinat Martirez Jan 2015

Surface Reconstructions Of Perovskite-Type Oxides: Their Exotic Structures And Modified Chemistry, John Mark Pinat Martirez

Publicly Accessible Penn Dissertations

The ability to manipulate the atomic and electronic structures and stoichiometry of surfaces is of utmost importance in optimizing heterogeneous catalysts. A critical requirement in this endeavor is a deep thermodynamic and kinetic understanding of surface reconstruction behavior, under various thermal and chemical constraints. We explore the reconstruction behaviors (structure and chemistry) of Ti-based perovskite type oxides: BaTiO3, PbTiO3 and SrTiO3. The former two exhibit ferroelectricity. We find that these oxides undergo surface reconstruction transformations that generally result in enrichment of their catalytically active component: Ti. These reconstructions show rich bonding and structural motifs that affect the ...


Engineering Novel Nanostructures Via Chemical And Morphological Transformations, Rahul Agarwal Jan 2015

Engineering Novel Nanostructures Via Chemical And Morphological Transformations, Rahul Agarwal

Publicly Accessible Penn Dissertations

Materials at the nanoscale have revolutionized the world around us by enabling the discovery of novel size dependent properties and experimental verification of untested theoretical concepts. However, most nanomaterials today are phases of matter that are well known and have been studied extensively at the bulk scale. For example, II-VI semiconductors, which are widely studied today at the nanoscale, were employed in photovoltaic applications at the microscale for nearly half a century. The question that arises is whether material processing at the nanoscale can allow us to go beyond the limitations of conventional synthesis techniques? We believe that the next ...


Chirality And Its Spontaneous Symmetry Breaking In Two Liquid Crystal Systems, Louis Kang Jan 2015

Chirality And Its Spontaneous Symmetry Breaking In Two Liquid Crystal Systems, Louis Kang

Publicly Accessible Penn Dissertations

Chirality, or handedness, is a key concept spanning all fields of natural science, from biology to mathematics. Chiral structures can arise from achiral building blocks that lack a handedness if their assembly is unstable to chiral deformations, a phenomenon called spontaneous symmetry breaking. We theoretically study the role of chirality in two systems composed of liquid crystals dissolved or suspended in water, and our results match those obtained experimentally by our collaborators. In the first system, we study achiral liquid crystals whose Frank twist modulus is much lower than their splay and bend Frank moduli and which are confined in ...


Engineering A Library Of Anisotropic Building Blocks For Dna-Programmed Colloidal Self-Assembly, James Thomas Mcginley Jan 2015

Engineering A Library Of Anisotropic Building Blocks For Dna-Programmed Colloidal Self-Assembly, James Thomas Mcginley

Publicly Accessible Penn Dissertations

Programmable DNA interactions are an effective and versatile tool in the field of colloidal directed self-assembly. Colloidal systems are programmed by manipulating a variety of tunable parameters, such as particle sizes and DNA interaction strengths, and can self-assemble into a large and growing variety of colloidal crystal and gel structures. Since isotropically-interacting spherical particles generally form close-packed structures, the production and use of building blocks with anisotropic interactions, such as polyhedral particles, colloidal clusters, and patchy colloids, has been a rich research area in recent years.

This work represents a true expansion of the capabilities of DNA-directed colloidal assemblies, and ...


Development Of Bond-Order Potentials For Body-Centered-Cubic Transition Metals And Their Application In Atomistic Studies Of Plastic Properties Mediated By Dislocations, Yi-Shen Lin Jan 2015

Development Of Bond-Order Potentials For Body-Centered-Cubic Transition Metals And Their Application In Atomistic Studies Of Plastic Properties Mediated By Dislocations, Yi-Shen Lin

Publicly Accessible Penn Dissertations

ABSTRACT

DEVELOPMENT OF BOND-ORDER POTENTIALS FOR BODY-CENTERED-CUBIC TRANSITION METALS AND THEIR APPLICATION IN ATOMISTIC STUDIES OF PLASTIC PROPERTIES MEDIATED BY DISLOCATIONS

Yi-Shen Lin

Professor Vaclav Vitek

Bond-order potentials (BOPs), based on the tight binding (TB) approach for the evaluation of bonding, are an real-space method. They are eminently suitable for atomistic simulations of extended defects in transition metals in which the bonding is mixed nearly free electron and covalent. The latter requires a rigorous quantum mechanical treatment performed within the TB. In this Thesis, new BOPs were developed for non-magnetic BCC transition metals, V, Nb, Ta, Cr, Mo and W ...


Dynamics In Polymer Nanocomposites Containing Fixed And Mobile Nanoparticles, Chia-Chun Lin Jan 2015

Dynamics In Polymer Nanocomposites Containing Fixed And Mobile Nanoparticles, Chia-Chun Lin

Publicly Accessible Penn Dissertations

This dissertation describes experimental studies on the dynamics of polymer nanocomposites (PNC), namely, center-of-mass (COM) polymer diffusion in PNCs, and COM nanoparticle (NP) diffusion in polymer melts. Elastic recoil detection (ERD) is used for polymer diffusion studies and Rutherford backscattering (RBS) is used for NP diffusion studies. Diffusion of the tracer polymer, deuterated poly(methyl methacrylate) (dPMMA) is slowed down in a PMMA matrix filled with hydroxyl-capped spherical silica nanoparticles. A confinement parameter, ID/2Rg, where ID is interparticle distance and 2Rg is probe size is defined to account for the NP crowding effect. For highly crowded region where ID ...


Crystal-Amorphous Transformation Via Defect-Templating In Phase-Change Materials, Pavan Nukala Jan 2015

Crystal-Amorphous Transformation Via Defect-Templating In Phase-Change Materials, Pavan Nukala

Publicly Accessible Penn Dissertations

Phase-change materials (PCM) such as GeTe and Ge-Sb-Te alloys are potential candidates for non-volatile memory applications, because they can reversibly and rapidly transform between a crystalline phase and an amorphous phase with medium-range order. Traditionally, crystal-amorphous transformation in these materials has been carried out via melt-quench pathway, where the crystalline phase is heated beyond its melting point by the rising edge of an electric pulse, and the melt phase is quenched by the falling edge into a glassy phase. Formation of an intermediate melt phase in this transformation pathway requires usage of large switching current densities, resulting in energy wastage ...


Optical And Structural Studies Of Shape-Controlled Semiconductor Nanocrystals And Their Self-Assembled Solids, Benjamin Tavenner Diroll Jan 2015

Optical And Structural Studies Of Shape-Controlled Semiconductor Nanocrystals And Their Self-Assembled Solids, Benjamin Tavenner Diroll

Publicly Accessible Penn Dissertations

Colloidal nanocrystals are prominent candidates to displace current electronic active layers in solid-state device technologies and offer a body of physics which diverges from those of bulk materials and discreet molecules. Realizing the potential of colloidal nanocrystals may transform the costs and performance of common technologies, but understanding of the relationship between particle size, shape, uniformity, and composition and outputs like physical properties or device performance is often incomplete. This work uses the controlled synthesis of anisotropic colloidal nanocrystals to implement characterization techniques including X-ray diffraction and simulation, which allows an ensemble-level description of particle structure, as well as polarized ...


Form And Function: X-Ray Scattering And Spectroscopy Of Transition Metal-Based Nanoparticles, Vicky V T Doan-Nguyen Jan 2015

Form And Function: X-Ray Scattering And Spectroscopy Of Transition Metal-Based Nanoparticles, Vicky V T Doan-Nguyen

Publicly Accessible Penn Dissertations

In recent decades, nanoparticles have been found to possess unique, tunable properties with an enormous variety of applications. The atomic and nanoscale structures govern these functional properties, and structural deviations from the bulk, in part, are responsible for the vast technological uses of nanoparticles. This dissertation tackles the understanding of structure in a number of metal, metal phosphide, and metal oxide nanoparticle systems. Additionally, the syntheses of monodispersed nanoparticle systems allow for correlating their structure with functional properties. Real space analysis using pair distribution functions of monometallic (Ni, Pd) nanoparticles of less than 5 nm in diameter revealed a deviation ...


The Optoelectronic Properties Of Surface-Modified Semiconductor Nanocrystal Solids, Earl D. Goodwin Jan 2015

The Optoelectronic Properties Of Surface-Modified Semiconductor Nanocrystal Solids, Earl D. Goodwin

Publicly Accessible Penn Dissertations

Colloidal semiconductor nanocrystals have emerged as fascinating new materials and gained interest in the last 30 years because of their size, shape, and compositionally tunable electronic and optical properties as well as their potential to serve as artificial atoms. Challenges and opportunities have arisen when assembling nanocrystals into nanocrystal solids for electronic and optoelectronic applications, largely because of the significant influence of nanocrystal surface chemistry on the electronic, optical, and structural properties of nanocrystal solids. In order to assemble nanocrystal solids for high performance devices, we must understand and be able to control the effects of nanocrystal surface organic capping ...


Surface Chemistry Mediated Assembly Of Polymer-Grafted Nanorods In Solution And Polymer Matrices, Robert Charles Ferrier Jan 2015

Surface Chemistry Mediated Assembly Of Polymer-Grafted Nanorods In Solution And Polymer Matrices, Robert Charles Ferrier

Publicly Accessible Penn Dissertations

In the dissertation, I investigate ways to assemble nanorods, typically made of gold, in solution and polymer matrices by controlling surface chemistry. Gold nanorods were anisotropically functionalized with polymer on the side and alkane dithiol on the end causing the gold nanorods to spontaneously assemble in solution. The assembly could be tuned by controlling the incubation time which affected the solution absorbance due to plasmon coupling. Linked gold nanorods were cast in polymer thin films and their optical properties were imparted to the film. This anisotropic functionalization method was utilized to placed DNA or peptides on the ends of the ...


Electronic And Structural Investigation Of Nanocrystal Thin Films Tuned Via Surface Chemistry, Elizabeth Ashley Gaulding Jan 2015

Electronic And Structural Investigation Of Nanocrystal Thin Films Tuned Via Surface Chemistry, Elizabeth Ashley Gaulding

Publicly Accessible Penn Dissertations

Monodisperse colloidal nanocrystals (NCs) provide an opportunity to access physical properties that cannot be realized in bulk materials, simply by tuning the particle size or shape. These NCs form the basis of an artificial periodic table that can be used as building blocks to engineer a new class of solid-state materials with emergent properties. The monodispersity offers a structural advantage for assembling NCs into an ordered superlattice, in addition to a narrow distribution of band energies which in principle promote more efficient transport when the NCs are electronically coupled in a thin film solid after undergoing surface chemistry treatments. However ...


Electronic And Plasmonic Properties Of Nano-Sized Gold/Strontium Titanate Interface, Jiechang Hou Jan 2015

Electronic And Plasmonic Properties Of Nano-Sized Gold/Strontium Titanate Interface, Jiechang Hou

Publicly Accessible Penn Dissertations

In this thesis, nano-sized metal/oxide interfaces are fabricated to determine the size dependence of electronic and resistive switching properties, effect of atomic structure on the orientation dependence of electronic properties, and mechanisms of plasmon-induced current enhancement.

A combination of drop-casting and high temperature annealing enables orientation control over nano-sized metal/oxide interfaces. To examine the electronic properties, individual Au nanoparticle/SrTiO3 interfaces with sizes ranging from 20 to 150 nm are characterized via conductive atomic force microscopy, for two distinct interface orientations. Current-voltage characterization enables the determination of dominant electron transport mechanisms. The development of a depletion region results ...


Manipulation Of Light-Matter Interaction In Two-Dimensional Systems Via Localized Surface Plasmons, Joohee Park Jan 2015

Manipulation Of Light-Matter Interaction In Two-Dimensional Systems Via Localized Surface Plasmons, Joohee Park

Publicly Accessible Penn Dissertations

Localized surface plasmons (LSPs), which are collective charge oscillation confined by metallic nanoparticles, gained much interest in the field of optoelectronics due to its ability to confine light down to nanoscale without a diffraction limit. As light-matter interaction in nanoscale is becoming more important due to the demand in scaling down the optoelectronic devices, my thesis describes the work on manipulation of such light-matter interaction enabled by LSPs. First, periodically patterned two-dimensional arrays of bowties were investigated to study the localized surface plasmon (LSP) resonances via reflection measurements and numerical simulations. Due to the grating created by arrays of bowties ...


Optomechanical Devices And Sensors Based On Plasmonic Metamaterial Absorbers, Hai Zhu Jan 2015

Optomechanical Devices And Sensors Based On Plasmonic Metamaterial Absorbers, Hai Zhu

Publicly Accessible Penn Dissertations

Surface plasmon resonance is the resonant oscillations of the free electrons at the interface between two media with different signs in real permittivities, e.g. a metal and a dielectric, stimulated by light. Plasmonics is a promising field of study, because electron oscillations inside a subwavelength space at optical frequencies simultaneously overcome the limit of diffraction in conventional photonics and carrier mobilities in semiconductor electronics. Due to the subwavelength confinement, plasmonic resonances can strongly enhance local fields and, hence, magnify light-matter interactions. Optical absorbers based on plasmonic metamaterials can absorb light resonantly at the operating wavelengths with up to 100 ...


Fabrication And Actuation Of Hierarchically-Patterned Polymer Substrates For Dynamic Surface And Optical Properties, Elaine Lee Jan 2015

Fabrication And Actuation Of Hierarchically-Patterned Polymer Substrates For Dynamic Surface And Optical Properties, Elaine Lee

Publicly Accessible Penn Dissertations

Switchable optical materials, which possess reversible color and transparency change in response to external stimuli, are of wide interest for potential applications such as windows and skylights in architectural and vehicular settings or optical sensors for environmental monitoring. This thesis considers the tuning of optical properties by tailoring and actuating responsive materials. Specifically, we demonstrate the design and fabrication of tilted pillar arrays on wrinkled elastomeric polydimethylsiloxane (PDMS) as a reversibly switchable optical window. While the original PDMS film exhibits angle-dependent colorful reflection due to Bragg diffraction of light from the periodic pillar array, the tilted pillar film appears opaque ...


Synthesis And Characterization Of Transition Metal Based Metal Oxide And Metallic Nanocrystals For Ac Magnetic Devices And Catalysis, Hongseok Yun Jan 2015

Synthesis And Characterization Of Transition Metal Based Metal Oxide And Metallic Nanocrystals For Ac Magnetic Devices And Catalysis, Hongseok Yun

Publicly Accessible Penn Dissertations

The d-block elements are very important in magnetics, electronics, catalysis, and biological systems. The synthesis and characterization of nearly monodisperse d-block element based nanocrystals with a precise control over the size, composition, and shape are important to utilize the nanocrystals in such applications. The goals of my thesis are to synthesize d-block transition metal based nanocrystals and understand their magnetic and catalytic properties. I present the size- and composition-dependent AC magnetic permeability of superparamagnetic iron oxide nanocrystals for radio frequency applications. The nanocrystals are synthesized through high-temperature solvothermal decomposition, and their stoichiometry is determined by Mossbauer spectroscopy. Size-dependent magnetic permeability ...


Engineering Extracellular Matrix Signals Into Fibrous Hyaluronic Acid Hydrogels, Ryan Joseph Wade Jan 2015

Engineering Extracellular Matrix Signals Into Fibrous Hyaluronic Acid Hydrogels, Ryan Joseph Wade

Publicly Accessible Penn Dissertations

Hydrogels have gained widespread use in biomedical applications for their ability to mimic certain features of the natural extracellular matrix (ECM) including tissue-like mechanics, water-swollen environments, and biodegradability. Despite these advantages, hydrogels typically do not present the fibrous architecture of natural ECM, even though this structure can guide cell behavior and tissue function. With this in mind, the overall goal of this dissertation is the translation of hydrogels from hyaluronic acid (HA) macromers into more complex, fibrous networks with spatiotemporal control. First, HA macromers that contain protease-cleavable and fluorescent peptides were synthesized and shown to form both isotropic hydrogels and ...


Nanophotonics Of 2-Dimensional Materials, Jason C. Reed Jan 2015

Nanophotonics Of 2-Dimensional Materials, Jason C. Reed

Publicly Accessible Penn Dissertations

2-Dimensional materials are of great interest because of novel and intriguing properties that emerge at the monolayer limit in comparison to bulk materials. To that end, this thesis is split into the study of two different 2-dimensional materials in the realm of nanophotonics. First, graphene is utilized for both passivating the surface of metallic nanoparticles from oxidation and as a platform for functionalization and integration into specific molecule sensing. The nanoparticles act as plasmonic nanoantennas, enhancing the electric field near the surface of the antenna. It is shown that graphene-encapsulated silver nanoantennas are oxidation resistant and optically stable over a ...


The Effect Of Cell Contractility And Packing On Extracellular Matrix And Soft Tissue Rheology, Anne Sofieke Geertruide Van Oosten Jan 2015

The Effect Of Cell Contractility And Packing On Extracellular Matrix And Soft Tissue Rheology, Anne Sofieke Geertruide Van Oosten

Publicly Accessible Penn Dissertations

In the past decades it has become clear that the mechanical properties of tissues are important for healthy functioning. The mechanical properties of tissues and their load-bearing components found in the extracellular matrix (ECM) have been tested mechanically to provide more insight. However, there is a discrepancy between tissue and ECM mechanics. In this thesis this discrepancy is investigated with a novel multiaxial rheology method, which addresses a physiologically relevant combination of shear and axial strains. Blood clots are used to study the effect of cell traction and cell packing on ECM mechanics.

The results show that ECM networks compression ...


Structure-Property Relationships Of Imidazolium-Containing Polymer Systems: Homopolymers, Block Copolymers, And Block Copolymer/Ionic Liquid Mixtures, Sharon Sharick Jan 2015

Structure-Property Relationships Of Imidazolium-Containing Polymer Systems: Homopolymers, Block Copolymers, And Block Copolymer/Ionic Liquid Mixtures, Sharon Sharick

Publicly Accessible Penn Dissertations

Advanced solid-state polymer electrolytes for electrochemical and energy storage applications are needed to replace conventional liquid electrolytes that are unstable, flammable, and volatile. In particular, a fundamental understanding of morphology-ionic conductivity relationships is necessary to improve the ionic conductivity of ion-containing polymer systems. To this end, we investigate the structure-property relationships of homopolymer and block copolymer systems containing imidazolium-based ionic liquids (ILs). We first explore the effects of anion type and pendant alkyl chain length on the morphologies and properties of polymerized ionic liquid (PIL) homopolymers with bound cations. In both acrylate-based and vinylimidazolium PIL homopolymers, nanoscale segregation of polar ...