# Engineering Science and Materials Commons™

Articles 1 - 30 of 108

## Full-Text Articles in Engineering Science and Materials

Effect Of Annealing On The Contact Resistance Of Aluminum On A P-Type Substrate, Shrey Shah, George Patrick Watson Nov 2019

#### Effect Of Annealing On The Contact Resistance Of Aluminum On A P-Type Substrate, Shrey Shah, George Patrick Watson

##### Protocols and Reports

Aluminum contacts are widely used to form both ohmic and rectifying contacts. The process to form these contacts involves annealing, thus it is important to study the effect of annealing on the electrical properties of the contacts. Here, we present a way to measure the contact resistance of aluminum contacts formed on a p-type silicon substrate. It was found the contact resistivity decreased by an average of 18%. It was thus found that annealing at 400°C in a forming gas environment improves the electrical properties of aluminum contacts.

Oct 2019

#### Influence Of Flow Rate, Nozzle Speed, Pitch And The Number Of Passes On The Thickness Of S1805 Photoresist In Suss Microtec As8 Spray Coater, Rohan Sanghvi, Gyuseok Kim

##### Tool Data

S1805 positive photoresist has been deposited on single crystalline Si wafers using a Suss MicroTec Alta Spray. The inﬂuence of ﬂow rate, nozzle speed, pitch and number of passes on the thickness of the photoresist was studied. Results show that the thickness of S1805 is linearly proportional to the ﬂow rate and number of passes, and inversely proportional to the nozzle speed and pitch.

Correction Of Pattern Size Deviations In The Fabrication Of Photomasks Made With A Laser Direct-Writer, Ningzhi Xie, George Patrick Watson Oct 2019

#### Correction Of Pattern Size Deviations In The Fabrication Of Photomasks Made With A Laser Direct-Writer, Ningzhi Xie, George Patrick Watson

##### Protocols and Reports

When using Heidelberg DWL66+ laser writer to fabricate the photomask, the pattern feature dimensions may have deviations. These deviations can be caused by the lithography process and the undercut in the metal etch process. The same deviation value of 0.8µm was found to appear in all the patterns independent of the pattern original size and local pattern density. To overcome this universal deviation, a universal bias is suggested to be applied to the original patterns during the data preparation for the lithography process. In order to ensure this pre-exposure bias method can work, both the laser direct-write exposure conditions ...

Progress Report I: Fabrication Of Nanopores In Silicon Nitride Membranes Using Self-Assembly Of Ps-B-Pmma, Unnati Joshi, Vishal Venkatesh, Hiromichi Yamamoto Mar 2019

#### Progress Report I: Fabrication Of Nanopores In Silicon Nitride Membranes Using Self-Assembly Of Ps-B-Pmma, Unnati Joshi, Vishal Venkatesh, Hiromichi Yamamoto

##### Protocols and Reports

This progress report describes fabrication of silicon nitride membranes from Si wafers using cleanroom techniques, and of nanopore preparation via a self-assembled PS-b-PMMA film. A 36.9 µm thick membrane is successfully prepared by KOH wet etching. The membrane is a layered structure of 36.8 µm thick Si and 116 nm thick silicon nitride. It is also exhibited that in the 47 nm thick PS-b-PMMA film, the nanopore structure is observed in the vicinity of a dust particle, but most of the area indicates lamellar domain structure. The thickness of PS-b-PMMA film will ...

#### Alternating Multiblock Polyethylenes With Associating Groups: Self-Assembled Nanoscale Morphologies And Ion Transport, Lu Yan

##### Publicly Accessible Penn Dissertations

Single-ion conductors based on block copolymers (BCPs) are promising solid-state electrolytes for energy storage systems. Their ability to self-assemble into distinct nanostructures can provide both high ion transference numbers and strong mechanical integrity. Connecting the microphase-separated morphologies to the ion transport properties in BCP electrolytes as well as designing polymers to produce specific ion-conducting domain remain a critically important challenge.

Combining non-conducting polyethylene (PE) blocks that alternate with short strongly-interacting ionic blocks leads to a wide range of intriguing nanoscale phase-separated morphologies. Depending on the PE block lengths, these alternating multiblock copolymers exhibit amorphous or semicrystalline morphologies and their ionic ...

#### Designing Colloidal Nanomaterials For Electronic And Optoelectronic Devices Through Surface Modification, Tianshuo Zhao

##### Publicly Accessible Penn Dissertations

Colloidal quantum dots (QDs) are nanometer-sized semiconductors synthesized by wet chemical methods and stabilized by surface ligands in solvents. They are prized for the size-dependent electronic band structures, giving rise to tunable optical properties. Their solution form is also suitable for large-area and low-cost fabrication processes. These unique characteristics make this class of materials promising as building blocks for next-generation thin-film electronic and optoelectronic devices. However, the construction of QD based devices requires precise control of their material properties, including carrier mobility, lifetime, doping concentration and energy positions of the conduction and valence band edges. The large surface-to-volume ratio allows ...

#### Alignment And Morphological Effects Of Nanoplates In Lamellar Diblock Copolymer Thin Films, Nadia Krook

##### Publicly Accessible Penn Dissertations

The ability to disperse inorganic nanoparticles (NPs) of various shapes, sizes, and compositions in polymeric matrices enables researchers to continuously engineer new material combinations with different resulting properties. Polymer nanocomposites (PNCs) can be further customized for specific applications by intentionally organizing and orienting NPs within these hybrid materials. Despite significant advances in the field of PNCs, full control over the orientation of embedded anisotropic NPs, specifically nanoplates, is not well-established without employing multistep processes. Capturing either in-plane (parallel) or out-of-plane (vertical) orientation of nanoplates in thin polymer films through a scalable method would create new opportunities for developing coating technologies ...

Jan 2019

#### Continuum Modeling Of Cell-Extracellular Environment Interaction, Xuan Cao

##### Publicly Accessible Penn Dissertations

To perform functions such as proliferation, differentiation, and locomotion, living cells establish stable attachments to the extracellular matrix (ECM) via the formation of specialized receptor mediated contact foci, through which they sense the mechanical stimuli from the ECM and adapt their cytoskeleton structures. The cellular contraction, on the other hand, may induce dramatic structural changes to the local extracellular environment, particularly for the fibrous matrices. The main goal of this thesis is to understand the cell-ECM interaction and cell-cell interaction, which lays the foundation to address the role of mechanical stimuli in several physiological and pathological processes such as cell ...

#### Investigation Of Ferroelectric Perovskite Oxides For Photovoltaic Applications, Liyan Wu

##### Publicly Accessible Penn Dissertations

Ferroelectric materials have been demonstrated to be promising in developing emerging photovoltaic technologies because of the various mechanisms that allow above-bandgap photovoltages and higher efficiencies. However, the wide bandgaps of conventional ferroelectric oxides limit their utilization of the solar spectrum. This thesis focused on the identification of chemical substituents capable of reducing the bandgap of ferroelectric perovskite oxides, while retaining a robust polarization. Building upon the discovery of (1−x)KNbO3-xBa(Ni1/2Nb1/2)O2.75 solid solutions which have bandgaps compatible with traditional semiconductors, new families of Ni- and Ni/Nb-substituted BaTiO3 were fabricated through solid state methods. The ...

#### Diverse Colloidal Crystals And Clusters Formed By Dna-Grafted Spheres Via Self-Assembly, Yifan Wang

##### Publicly Accessible Penn Dissertations

Meta-materials with novel photonic, phononic, thermal, and mechanical properties are considered as future materials for new applications. Colloidal crystals are meta-materials made from assemblies of building blocks that are not found in naturally occurring materials. Unlike atoms and molecules, such building blocks could be obtained from DNA-coated colloids which have feasible and adjustable interaction strengths as well as facilitating a further DNA-induced self-assembly into different geometries and structures. This DNA colloidal self-assembly prototyping process could be utilized as a fast and effective way for fabricating different structures, which shed light on the industrial production of the meta-materials.

In this work ...

#### Improving Performance Of Infiltrated Sofc Cathodes Via Scaffold Engineering And Catalyst Surface Engineering, Yuan Cheng

##### Publicly Accessible Penn Dissertations

Solid Oxide Fuel Cells (SOFCs) are energy-generating devices operating at elevated temperatures. At their cathode sides, oxygen molecules reduce into oxygen ions and then transport to the anode side through a solid-state ceramic membrane (typically, Yttria-Stabilized Zirconia (YSZ)). At their anode side, the fuels react with the oxygen ions and then release electrons to the external circuit. Always, it is the cathode that has the slowest reaction kinetics, such it contributes the largest resistance in the entire device.

The state-of-the-art cathode materials are typically perovskite-phase ceramic materials, such as Strontium-doped Lanthanum Manganate (LSM), Strontium-doped Lanthanum Ferrite (LSF) and Strontium-doped Lanthanum ...

Jan 2019

#### A Computational And Experimental Study Of Polymer Conformation And Diffusion Under Confinement, James F. Pressly

##### Publicly Accessible Penn Dissertations

Over the past several decades the use of polymers in applications such as microelectronics fabrication and nanocomposite materials has steadily increased. In these applications polymer chains are often confined to length scales comparable to their size. While it is well known that these confining environments alter polymer properties, a generalized understanding of how different confining geometries alter polymer behavior has not been established. Here we investigate changes to polymer conformation and diffusion under cylindrical and planar confinement using a combination of computational and experimental techniques. Using molecular dynamics simulations of polymer melts, we systematically examine changes in the polymer radius ...

Anisotropy And Aggregation In Self-Assembled Polymer Nanocomposites, Benjamin Joseph Lindsay Jan 2019

#### Anisotropy And Aggregation In Self-Assembled Polymer Nanocomposites, Benjamin Joseph Lindsay

##### Publicly Accessible Penn Dissertations

Polymer nanocomposites (PNC) are an exciting class of materials with a wide array of applications. Whether the desired application involves isotropic or anisotropic polymer and particle structures, controlling aggregation and/or anisotropy in PNCs remains crucial to engineering composites with desired properties. Many methods have been developed to address these challenges. Three methods of interest include 1) the inclusion of anisotropic particles in the PNC, 2) block copolymers used as anisotropic templates to pattern particles, and 3) particle surface chemistry modification to increase dispersion. Significant experimental progress has been made in all three of these methods, but deeper fundamental understanding ...

Jan 2019

#### Scale-Dependent Plasticity And Nanoindentation Creep Of Geologic Materials, Christopher Thom

##### Publicly Accessible Penn Dissertations

Nanoindentation is a commonly used technique in materials science that allows for the determination of the mechanical properties (e.g. hardness, elastic modulus, and creep) of single crystals and polycrystalline aggregates, but it has been severely underutilized for the study of geologic materials. In this dissertation, we demonstrate the effectiveness of nanoindentation for measuring the rheological behavior of a wide range of geologic materials. For all materials tested, including single crystals, polycrystalline samples, and two different natural fault surfaces, we identify an ‘indentation size effect,’ whereby the strength of the material increases with decreasing size of the indent. We explore ...

Jan 2019

#### Nonlinear Optical Responses In Type-Ii Weyl Semimetals, Gerui Liu

##### Publicly Accessible Penn Dissertations

Weyl semimetals are gapless topological states of matter with broken inversion and/or time reversal symmetry. In this thesis, we will firstly discuss the observation of a novel photogalvanic effect in type-II Weyl semimetals including $\rm T_d-MoTe_2$, $\rm Mo_{0.9}W_{0.1}Te_2$ and $\rm Mo_{0.3}W_{0.7}Te_2$. A circulating photocurrent is obtained under the illumination of normally incident light with circular polarization and the circulating current direction is opposite with different light helicity. Through temperature induced phase transition of $\rm MoTe_2$, this effect is further confirmed to exclusively occur in the Weyl phase ...

#### Selective Conversion Of Biomass Model Compounds Using Promoted Metal Catalysts, Cong Wang

##### Publicly Accessible Penn Dissertations

ABSTRACT

SELECTIVE CONVERSION OF BIOMASS MODEL COMPOUNDS USING PROMOTED METAL CATALYSTS

Cong Wang

Raymond J. Gorte

Extensive research and development have gone into modern biomass upgrading in order to mitigate the environmental concerns and other impending challenges associated with conventional fuels and chemicals. The phenolic and furanic compounds produced by primary upgrading processes represent a collection of biomass intermediates that still preserve the valuable chemical structures, but they require further upgrading due to unfavorable oxygen contents and unstable functional groups. This dissertation seeks to demonstrate the viability of utilizing bimetallic and metal-oxide-promoted metal catalysts to further upgrade biomass-derived oxygenates by ...

#### Atomic Force Microscopy-Based Investigation Of Plastic Deformation Mechanisms In Disordered Nanoparticle Packings, Joel Allen Lefever

##### Publicly Accessible Penn Dissertations

Understanding the plastic deformation mechanisms of disordered materials is a longstanding and complex problem in condensed matter physics and materials science. In particular, the elementary plastic rearrangement in a disordered material is believed to be the shear transformation zone, a localized cooperative motion of a handful of constituents. Although observed in mesoscale systems, the shear transformation zone has never been identified in an experiment at the nanoscale. In the present work, atomic force microscopy is used to probe the mechanical response of thin films of disordered nanoparticle packings that have been deposited by spin-coating and layer-by-layer deposition. Results demonstrate that ...

Jan 2018

#### Controlled Folding In Precisely Functionalized Polyethylenes: Designing Nanoscale Lamellar Structures For Ion Transport, Edward Boynton Trigg

##### Publicly Accessible Penn Dissertations

There is great societal need for improved energy storage technology, in applications ranging from electric vehicles to grid storage to emergency power systems. New polymeric membranes with enhanced ion conductivities are needed in batteries and fuel cells to improve these technologies. Despite decades of research, these membrane materials are still not adequate for commercial use. The primary metric that requires improvement is ion or proton conductivity of the membrane under desirable operating conditions.

Modifying linear polyethylene by the addition of precisely periodic functional groups leads to a rich array of intriguing morphologies and properties. Depending on the functional group chemistry ...

Jan 2018

#### Grain-Boundary Kinetics And Nonequilibrium Grain-Boundary Structure, Jian Han

##### Publicly Accessible Penn Dissertations

Microstructure of polycrystalline materials can be described as grain boundary (GB) networks; hence, GBs play major role in a wide-range of polycrystal properties. Control over GB kinetics provides effective means to tailor polycrystal properties through material processing. Understanding and prediction of GB kinetic behavior are always central problems in materials science. In this thesis, these are realized based on a mechanistic model. The mechanistic model describes a GB as intrinsic GB structure decorated by extrinsic defects. GB kinetics is described by the transition among all the stable/metastable intrinsic GB structures and the kinetics of GB defects. A major type ...

The Role Of Sliding Contact In Nanoscale Tribochemistry, Zachary Banks Milne Jan 2018

#### The Role Of Sliding Contact In Nanoscale Tribochemistry, Zachary Banks Milne

##### Publicly Accessible Penn Dissertations

In this dissertation, the results of experimental and theoretical studies exploring friction

and adhesion at the nanoscale are presented. Using a customized in situ transmission

electron microscopy nanoindentation methodology, it is observed that cohesion of silicon and

adhesion of silicon and diamond are strongly modied by the sliding speed and the normal

stress applied during sliding. This indicates that shear stress modulates the reactivity of the

surfaces. This is the rst time that tunable adhesion of hard contacts has been demonstrated

in situ.

If sliding experiments are performed in ultra-high vacuum and the interfacial shear stress

is low enough to ...

Inkjet Printing Of Ag Nanoparticles Using Dimatix Inkjet Printer, No 2, Ming Yuan Chuang May 2017

#### Inkjet Printing Of Ag Nanoparticles Using Dimatix Inkjet Printer, No 2, Ming Yuan Chuang

##### Protocols and Reports

This report describes the rheological analysisof the present Ag nanoparticle ink, and confirms that it is suitable for the piezoelectric drop-on-demand printing for both of 1 pL and 10 pL cartridges. The satellite drops and the splashing on the substrate are also discussed for optimization of the nozzle temperature and the jetting voltage. The minimum horizontal and vertical line widths are shown to be 30 and 40 µm, respectively, but the average minimum single line width is estimated to be ~50 µm. The non-uniform width lines are suggested to arise from the bulge instability. Furthermore, it is indicated that the ...

Inkjet Printing Of Ag Nanoparticles Using Dimatix Inkjet Printer, No 1, Amal Abbas, Inayat Bajwa Jan 2017

#### Inkjet Printing Of Ag Nanoparticles Using Dimatix Inkjet Printer, No 1, Amal Abbas, Inayat Bajwa

##### Protocols and Reports

Ag nanoparticle inkjet printing on polyimide and polyethylene terephthalate films has been performed using Dimatix inkjet printer at Quattrone Nanofabrication Facility. This article describes selection of Ag nanoparticle inks and reports the progress of optimization of drop spacing, drop frequency, droplet size, and waveform for high resolution features, and furthermore reveals the pros and cons of Dimatix inkjet printing. In addition, the resistivity of Ag nanoparticle line sintered was determined to be ~2.2 x 10-5 Ωm. The adhesion and bending tests indicated that Ag nanoparticle pattern sintered on PI and PET films had exceptional mechanical stability.

Mechanics Of Colloidal Assemblies, Daniel James Strickland Jan 2017

#### Mechanics Of Colloidal Assemblies, Daniel James Strickland

##### Publicly Accessible Penn Dissertations

Amorphous solids -- solids that lack long-range order of their constituent particles -- are common in both nature and industry. Window glass, dense polymers, and food grains are three examples of amorphous solids familiar to us. In many amorphous solids, shear banding -- plastic deformation in which strain is accumulated in a thin band of the material -- is common. Consequently, many amorphous solids are brittle, a trait which has limited the technological adoption of otherwise promising materials such as metallic glasses. Therefore, a fundamental understanding of shear banding -- i.e., the progression from particle level plastic events to a macroscopic shear band, identification ...

#### Quantum Electronic Interference In Nano Amorphous Silicon And Other Thin Film Resistance Memory, Yang Lu

##### Publicly Accessible Penn Dissertations

This thesis describes conductivity in amorphous semiconductors and insulators—some doped with metals, in which elastic electrons can random walk across a transport length of ~10 nm. At low temperatures, back diffusion of coherent electrons causes constructive quantum interference that leads to reduced diffusivity/conductivity. Rich physics also arises in this so-called weak-localization (WL) regime from electron-phase mutilation by spin-orbit interaction (weak-antilocalization or WAL) and magnetic modulation, and from Friedel-oscillation-enhanced backscattering and Zeeman splitting (electron-electron-interaction or EEI). Conductivity is analyzed by a new tool to eliminate contact resistance without using the four-point-probe method.

The Aharonov-Bohm oscillation in magnetoresistance affords the ...

Engineering Plasmonic Nanocrystal Coupling Through Template-Assisted Self-Assembly, Nicholas J. Greybush Jan 2017

#### Engineering Plasmonic Nanocrystal Coupling Through Template-Assisted Self-Assembly, Nicholas J. Greybush

##### Publicly Accessible Penn Dissertations

The construction of materials from nanocrystal building blocks represents a powerful new paradigm for materials design. Just as nature’s materials orchestrate intricate combinations of atoms from the library of the periodic table, nanocrystal “metamaterials” integrate individual nanocrystals into larger architectures with emergent collective properties. The individual nanocrystal “meta-atoms” that make up these materials are themselves each a nanoscale atomic system with tailorable size, shape, and elemental composition, enabling the creation of hierarchical materials with predesigned structure at multiple length scales. However, an improved fundamental understanding of the interactions among individual nanocrystals is needed in order to translate this structural ...

Jan 2017

#### Cation Kinetics And Electric Field Effect In Zirconia, Yanhao Dong

##### Publicly Accessible Penn Dissertations

Cation diffusion controls mass transport and microstructural evolution in zirconia above 1200 oC. In past research, its experimentally measured activation energy of 5 eV cannot be reproduced by computer simulation, which gives >10 eV and a cation vacancy mechanism implicating enhanced diffusion in oxidizing atmosphere, contradicting experimental evidence. This thesis was undertaken to answer these questions and to explore new ground in cation kinetics.

To help search for low-energy configurations in zirconia alloys, we employed crystal chemistry to boost sampling efficiency, by >1,000 times, and obtained plausible “ground states” to launch ab-initio calculations for cation defects and migration. The ...

#### Understanding Dewetting Transitions On Nanotextured Surfaces: Implications For Designing Surfaces With Improved Wettability, Suruchi Fialoke

##### Publicly Accessible Penn Dissertations

Despite the early promise of superhydrophobic surfaces, their widespread technological adoption has been dawdled by the ease with which water can penetrate the surface texture, resulting in a breakdown of superhydrophobicity. Furthermore, this breakdown is believed to be irreversible, because large adhesion barriers impede the dewetting of the surface texture and the concomitant recovery of superhydrophobicity. Using molecular dynamics simulations in conjunction with advanced sampling techniques, in this thesis, we challenge this conventional argument. We show that while large barriers do typically impede the recovery of superhydrophobicity, it can nevertheless be recovered spontaneously on nanotextured surfaces, wherein collective water density ...

Interfacial Assembly In Aqueous Two Phase Systems, Sarah Danielle Hann Jan 2017

#### Interfacial Assembly In Aqueous Two Phase Systems, Sarah Danielle Hann

##### Publicly Accessible Penn Dissertations

Stabilizing bio-friendly and cyto-mimetic fluid structures has important implications for drug and gene delivery, micro bio-reactors, single cell and microniche studies, and as protocells. The majority of stabilization techniques have been developed for oil-in-water and water-in-oil emulsions, which have limitations in their application to biological systems due to the presence of the oil phase. The structures built in this thesis are therefore made within water-in-water dispersions. These all water dispersions are from aqueous mixtures of two polymers that demix to form two phases, termed aqueous two phase systems (ATPSs). ATPSs are comprised of two water-rich phases and are therefore excellent ...

Flexible, Photopatterned, Colloidal Cdse Semiconductor Nanocrystal Integrated Circuits, Franklin Scott Stinner Jan 2017

#### Flexible, Photopatterned, Colloidal Cdse Semiconductor Nanocrystal Integrated Circuits, Franklin Scott Stinner

##### Publicly Accessible Penn Dissertations

As semiconductor manufacturing pushes towards smaller and faster transistors, a parallel goal exists to create transistors which are not nearly as small. These transistors are not intended to match the performance of traditional crystalline semiconductors; they are designed to be significantly lower in cost and manufactured using methods that can make them physically flexible for applications where form is more important than speed. One of the developing technologies for this application is semiconductor nanocrystals.

We first explore methods to develop CdSe nanocrystal semiconducting “inks” into large-scale, high-speed integrated circuits. We demonstrate photopatterned transistors with mobilities of 10 cm2/Vs on ...

#### Experimental Investigation Of Polymer Adhesion Mechanics Using A Blister Contact Test, Nathan Ip

##### Publicly Accessible Penn Dissertations

The adhesion of thin layers of soft polymers is important in many applications, such as tapes, microtransfer printing, and bioinspired adhesives. Traditional adhesion tests based on probe contacts are not suitable for characterizing thin layers and common separation-based specimens, such as the peel test, have well-known limitations. The blister contact test (BCT) was developed in this dissertation to overcome the limitations of current methods and was used to investigate the adhesion and separation of several technologically relevant adhesive systems. In the BCT, a thin sheet was elastically deformed into adhesive contact with a reference substrate and the contact area was ...