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Department Library

2020

Spencer Roberts (Senior Thesis, August 2020, Advisor: Robert Davis )

Abstract

Neural probes allow researchers and medical professionals to read neural activity and send signals directly to the brain. However, mechanical stiffness mismatch between neural probes and brain tissue leads to chronic irritation and trauma, which eventually causes loss of signal. Viable long-term commercial implants will require flexible probes that match the brain’s stiffness. We have designed a carbon nanotube (CNT) based neural probe array that has high spatial resolution and high-aspect ratio flexible probes that have tunable stiffness via carbon infiltration. In this work, we characterize the Young’s modulus of our CNT probes at various infiltration levels using a dual deflection wire test. Results indicate that the minimum modulus of the probes is about 678 MPa, which is comparable to contemporary flexible polymer probes, indicating probable long-term biocompatibility without sacrificing spatial resolution or aspect ratio.

Tyler Richard Westover (Masters Thesis, April 2020, Advisor: Robert Davis )

Abstract

DNA origami templates have been studied due the versatility of shapes that can be designed and their compatibility with various materials. This has potential for future electronic applications. This work presents studies performed on the electrical properties of DNA origami templated gold nanowires. Using a DNA origami tile, gold nanowires are site specifically attached in a “C” shape, and with the use of electron beam induced deposition of metal, electrically characterized. These wires are electrically conductive with resistivities as low as 4.24 x 10-5 Ω-m. During moderate temperature processing nanowires formed on DNA origami templates are shown to be affected by the high surface mobility of metal atoms. Annealing studies of DNA origami gold nanowires are conducted, evaluating the effects of atom surface mobility at various temperatures. It is shown that the nanowires separate into individual islands at temperatures as low as 180° C. This work shows that with the use of a polymer template the temperature at which island formation occurs can be raised to 210° C. This could allow for post processing techniques that would otherwise not be possible.

2019

Camille Baird (Senior Thesis, April 2019, Advisor: Robert Davis )

Abstract

Porous micro-resonators show promising results for applications in chemical and bio-sensing. Rings and disks resonating in the wine-glass mode or radial contour mode have been designed and fabricated using a highly tunable microfabrication process to undergo further testing for quality factors and viability for sensing applications in fluid environments. Narrow anchors from the resonating structure to mounted pads have been placed at nodal points of the modes of vibration to reduce clamping losses during testing.

2018

Sterling Baird (Senior Thesis, September 2018, Advisor: Robert Davis )

Abstract

The high theoretical gravimetric energy density (Wh/kg) of lithium-sulfur batteries holds promise for battery applications such as UAVs, electric vehicles, and military applications. Here, we report the use of a carbon nanotube based interfacial layer in conjunction with highly scalable sulfur cathodes using the doctor-blade coating technique for high capacity, highly coulombic efficient lithium-sulfur batteries. The interfacial layer consists of vertically-aligned multi-walled carbon nanotubes and a conductive nonporous layer which aids in polysulfide trapping. We observe a high initial discharge capacity of 930 mAh/g-S and high coulombic efficiencies above 93% without the use of gas-forming additives such as lithium nitrate. Ratio effects between sulfur, electrolyte, and lithium reveal correlations to lower capacity with higher sulfur loading, higher capacity with stronger electrolyte to sulfur ratios, and increased cycle life with greater lithium overcapacity. Overcharge experiments reveal that a 15% overcharge cut-off provides reasonable efficiency (~87%), and cycle life. Addition of 1% selenium to the cathode composition increased discharge voltages, but slightly decreased capacity and did not have a discernable effect on rate capability at 1C. Addition of PEO/LiTFSI/HNT binder stabilized cycling, but decreased capacity in some instances. Enhanced diffusion pathways and electrolytic contact had a positive correlation with capacity, suggesting that micro-patterned carbon nanotube architectures may play a unique role in lithium-sulfur batteries.

Annie Laughlin (Senior Thesis, July 2018, Advisor: Robert Davis )

Abstract

Modern advancements in technological fields including electric vehicles and high powered laptops rely on battery storage. Lithium is useful in creating high capacity batteries because it has high energy density. However, when cycling a battery at a fast rate, the lithium becomes unstable due to the small amount of accessible energy on the surface of the lithium electrode. The solution to this problem is to increase the surface area of the lithium electrode through electrodeposition techniques onto a carbon scaffolding. This increases the current density limit. Electrodeposition is beneficial because the user can control how much lithium is deposited onto the substrate. This enables researchers to cycle high capacity batteries at an accelerated rate.

Kevin Robert Laughlin (Masters Thesis, August 2018, Advisor: Robert Davis )

Abstract

We have fabricated nanofuses from thin-film, arc-evaporation carbon for use in permanent data storage. Thin film carbon fuses have fewer fabrication barriers and retain the required resistivity and structural stability to work as a data storage medium. Carbon thin films were characterized for their electrical, microstructural, and chemical bonding properties. Annealing the thin-film carbon in an argon environment at 400°C reduced the resistivity from about 4*10-2 Ω cm as deposited down to about 5*10-4 Ω cm, allowing a lower blowing voltage. Nanofuses with widths ranging from 200 nm down to 60 nm were fabricated and tested. They blow with voltages between 2 V and 5.5 V, and the nanofuses remain stable in both a "1" and a "0" state under a constantly applied read voltage of 1 volt for over 90 hours, corresponding to a cumulative time of >1012 reads.

Stefan Lehnardt (Capstone, April 2018, Advisor: Robert Davis )

Abstract

Single-layer graphene consists of a single layer of sp2-bonded carbon atoms and exhibits many remarkable properties. It is the strongest material ever measured with a tensile strength of 90 GPa. As a single layer of atoms, however, single-layer graphene cannot cope with macroscopic forces and its applications are limited. Multi-layer graphene combines many layers of graphene and may be able to withstand forces that single-layer graphene cannot. To determine whether or not multi-layer graphene, (MLG) is suitable for a given application, it is important to know its mechanical properties and how they compare to those of single-layer graphene. This report focuses on the burst pressure of MLG membranes as grown on modified nickel substrates suspended over openings in silicon.

2017

Tyler Stevens (Senior Thesis, April 2017, Advisor: Robert Davis )

Abstract

EBID allows metals to be directly written to a substrate in order to connect to randomly oriented devices. When depositing with the precursor Trimethyl(Methylcyclopentadienyl)Platinum(IV), the deposited metal has a resistivity a few orders of magnitude higher than pure platinum. Therefore, the leads are highly resistive and present problems in experimental electrical measurements. By introducing an anneal with an alumina coating, the resistivity can be lowered to 1.32E−6 Ω𝑚, which is only 12 times above the resistivity of bulk platinum.

2016

Nathan Edward Boyer (Masters Thesis, June 2016, Advisor: Robert Davis )

Abstract

Carbon nanotube (CNT)/polymer composite sheets can be extremely high strength and lightweight, which makes them attractive for fabrication of mechanical structures. This thesis demonstrates a method whereby smooth, thin CNT/polymer composite sheets can be fabricated and patterned on the microscale using a process of photolithography and plasma etching. CNT/polymer composites were made from CNTs grown using chemical vapor deposition using supported catalyst growth and floating catalyst growth. The composite sheets had a roughness of approximately 30nm and were about 61¼m or 261¼m depending on whether they were made from supported catalyst grown or floating catalyst grown CNTs. The composites were patterned using an oxygen plasma as the etchant and a hard mask of silicon nitride.

Julia Grimes (Capstone, April 2016, Advisor: Robert Davis )

Abstract

For this project we not only wanted to create pre-class exercises that would help introductory level physics students learn basic physics principles before coming to class, but we also wanted to get feedback from the students so that we knew how to make the exercises more useful for their learning. We conducted interviews with students from the Physics 121 and Physics 140 classes and gave pre and post interview surveys to all who were willing to take them. Based on the feedback that we got from the students who were interviewed, the students felt like the idea behind the exercises was great. Even if they found the exercises to be frustrating, they still thought that idea and purpose for making them was very useful and hoped that we would continue to improve them to make them even better for students in the future. The data and feedback we collected gave us an overwhelming response that the students want more explanations and feedback when they are taking the exercises. We also had a majority of students who said that the most useful part of the exercises for them were the videos that gave explanations to the problems that they needed to solve. Along with this feedback, we were able to come up with a list of other helpful aspects students saw, issues they came up against, and changes that they saw we could make to help improve the exercises. This is discussed and presented in the paper.

Reese Petersen (Senior Thesis, April 2016, Advisor: Robert Davis )

Abstract

Dense arrays of carbon nanotubes (CNTs) were covered conformally with 14 nm of nanocrystalline carbon via chemical vapor deposition, followed by 14 nm of hafnium dioxide (HfO2) via atomic layer deposition (ALD) for creating dielectric capacitors with high areal capacitance. These coated carbon nanotube arrays were analyzed via scanning electron microscope imaging, energy dispersive x-ray spectroscopy, and transmission electron microscope imaging. HfO2 was found throughout the array but appeared to be thinner than 14 nm near the bottom of the array. We recommend a lower pyrolytic carbon deposition temperature and shorter CNT arrays for more uniform ALD.

Clarissa Veach (Senior Thesis, April 2016, Advisor: Robert Davis )

Abstract

Ion-exchange chromatography is a purification method for biological molecules commonly performed on functionalized Si monoliths. A potential method of ion-exchange chromatography is presented using a Si coated CNT structure as the chromatography matrix. Surface area and binding capacity calculations were made to determine the advantage of using these structures in place of those commonly used. It was found that the surface are of the CNT structure is approximately 0.58m^2 for a 1 cm^2 filter area. This results in a binding capacity for the antibody Immunoglobulin G of 5.67*10^14 particles/cm^2. When a quaternary ammonium substituted agarose polymer coating was applied to a Si plate it was found that the thickness was 1.8nm.

2015

Lawrence Kent Barrett (Masters Thesis, December 2015, Advisor: Robert Davis )

Abstract

Silicon has the highest theoretical capacity of any known anode material, and silicon coated carbon nanotubes (Si-CNTs) have shown promise of dramatically increasing battery capacity. However, capacity fading with cycling and low rate capability prevent widespread use. Here, three studies on differing aspects of these batteries are presented. Here, three studies on differing aspects of these batteries are presented. The first examines the rate capability of these batteries. It compares the cycling of electrodes hundreds of microns thick with and without ten micron access holes to facilitate diffusion. The holes do not improve rate capability, but thinner coatings of silicon do improve rate capability, indicating that the limiting mechanism is the diffusion through the nanoscale bulk silicon. The second attempts to enable stable cycling of anodes heavily loaded with silicon, using a novel monolithic scaffolding formed by coating vertically aligned carbon nanotubes (VACNTs) with nanocrystalline carbon. The structure was only able to stabilize the cycling at loadings of carbon greater than 60% of the electrode by volume. These electrodes have volume capacities of ~1000 mAhr/ml and retained over 725 mAhr/ml by cycle 100. The third studies the use of an encapsulation method to stabilize the solid electrolyte interphase (SEI) and exclude the electrolyte. The method was only able to stabilize cycling at loadings below 5% silicon, but exhibits specific capacities as high as 3000 mAhr/g of silicon after 20 cycles.

Aubrey Hatch (Senior Thesis, August 2015, Advisor: Robert Davis )

Abstract

Our group and others have developed micro filters that can be fabricated using standard photolithography techniques. Our filters are made with the negative photoresist SU-8 and consist of two layers: a thinner membrane layer, and a thicker support layer. The thinner membrane layer is important for filtration, but by itself is very fragile. The support layer enables the filter to withstand higher pressures without bursting and means it is much less fragile to handle. However the support layer covers some of the pores of the membrane layer decreasing the open area of the filter. The goal of my research is to create a support layer with inward sloping side walls. Since these walls are narrower at the bottom, fewer pores will be covered and overall open area will increase. These walls have been fabricated using a simple diffraction grating. The widths at the bottom of the structure ranged from 20.59 microns to 22.69 microns at an exposure dose of 135 mW/cm^2. This is a 24%-31% decrease in size from the regular 30 micron length. I conclude that the inward slope of the walls is caused by how the diffraction grating changes the intensity of the light being used for exposure.

Steven Noyce (Senior Thesis, August 2015, Advisor: Robert Davis )

Abstract

Porous cantilever resonator sensors offer detection of trace chemical concentrations in otherwise difficult sensing environments such as gases or liquids. Fabrication of such devices has traditionally been difficult because microfabrication processes that can acheive high aspect ratios are not generally compatible with porous materials. Here we report the fabrication of porous resonators made from a carbon infiltrated carbon nanotube structure. Resulting structure densities are tunable in the range of 10^2 to 10^3 kg/m^3. We perform resonance measurements on these structures in vacuum, air, and water. We also present initial use of these devices as sensors.

2014

Lawrence Barrett (Senior Thesis, August 2014, Advisor: Robert Davis )

Abstract

High-aspect-ratio metallic microstructures have a variety of potential applications in sensing and actuation. However, fabrication remains a challenge. We have fabricated Ni microstructures with over 20:1 aspect ratios by electroplating patterned, carbon-coated, carbon-nanotube forests (CNTs) using a nickel chloride bath. Pulse plating allows nickel ions to diffuse into the interior of the forest during off portions of the cycle. Done properly, this solves the problem of the formation of an external crust which otherwise blocks Ni deposition in the interior of the structures. Thus, densities of 86±3% of bulk Ni for the composite structures are achieved. Cantilever structures do not yield under load but break. Measurements of the material properties of this composite material indicate an elastic modulus of approximately 42 GPa and a strength of 400 MPa. We demonstrate the utility of this method with a simple MEMS magnetic actuator consisting of a proof mass and two flexures. We achieved 7 mN actuation forces.

Bryce Clay (Senior Thesis, August 2014, Advisor: Robert Davis )

Abstract

Silica aerogel is a novel material with many applications. There is potential for use as a thermal barrier. Aerogel was prepared from TEOS using a two-step, acid-base catalyzed process. A viscometer was prepared and used to ensure optimal viscosity during spinning. Thin films were produced by spin casting on silicon wafers at various spin speeds. Films were characterized by uniformity and thickness.

2013

Adam Konneker (Senior Thesis, April 2013, Advisor: Robert Davis )

Abstract

Here we report the synthesis of vertically aligned and three-dimensional patterned silicon-carbide nanowires (SiCNWs). The SiCNWs were formed by thermally annealing silicon-carbon core-shell nanotubes (Si/CNTs) in argon. The Si/CNTs were fabricated based on a carbon nanotube templated microfabrication process (CNT-M), in which a vertically aligned and patterned carbon nanotube (CNT) growth was followed by low pressure chemical vapor deposition (LPCVD) of silicon. The carbon nanotube forests were grown from a patterned catalyst layer resulting in high aspect ratio three dimensional microscale structures up to 500 microns tall with vertical sidewalls. Silicon LPCVD layers were deposited conformally, coating the nanotubes well into the interior of the structure. A thermal annealing of the structure converts the Si/CNTs to SiCNWs. This combination of CNT-M fabrication, LPCVD silicon deposition, and annealing yields a unique fabrication approach resulting in porous three dimensional silicon carbide structures with precise control over shape and porosity.

2012

David B Brough (Masters Thesis, December 2012, Advisor: Robert Davis )

Abstract

The material properties of low stress silicon nitride make it a possible replacement material for beryllium in X-ray windows. In this study, X-ray windows made of LPCVD deposited low stress silicon nitride are fabricated and characterized. The Young’s modulus of the LPCVD low stress silicon nitride are characterized and found to be 226±23 GPa. The residual stress is characterized using two different methods and is found to be 127±25 MPa and 141±0.28 MPa. Two support structure geometries for the low stress silicon nitride X-ray windows are used. Xray windows with thicknesses of 100 nm and 200 nm are suspended on a silicon rib support structure. A freestanding circular geometry is used for a 600 nm thick X-ray window. The 100 nm and 200 nm thick low stress silicon nitride X-ray windows with a silicon support structure are burst tested, cycling tested and leak rate tested. The average burst pressure for the 100 and 200 nm films on a silicon support structure are 1.4 atm and 2.2 atm respectively. Both 100 nm and 200 nm windows are able to withstand a difference in pressure of 1 atm for over 100 cycles with a leak rate of less than 10-10 mbar-L/s. The low stress silicon nitride with 100 nm and 200 nm thicknesses, the 600 nm freestanding low stress silicon nitride windows and freestanding 8 micron thick beryllium windows are mechanical shock resistance tested. The support structure low stress silicon nitride and beryllium windows are tested with an applied vacuum. The freestanding 600 nm thick low stress silicon nitride windows burst at 0.4 atm and are therefore mechanical shock wave tested without an applied vacuum. The support structure low stress silicon nitride windows fractured when subjected to an acceleration of roughly 5,000 g. The 8 micron thick beryllium windows are subjected to accelerations of over 30,000 g without fracturing. A quasistatic model is used to show that for low stress silicon nitride with a freestanding circular geometry, an acceleration of 106 g is required to have the same order of magnitude of stress caused by a pressure differential of 1 atm. Low stress silicon nitride can act as a replacement for beryllium in X-ray windows, but the support geometry, residual stress, and strength of the material need to be optimized.

Adam Konneker (Senior Thesis, December 2012, Advisor: Robert Davis )

Abstract

Anthony Craig Pearson (PhD Dissertation, August 2012, Advisor: Robert Davis )

Abstract

Bottom-up self-assembly can be used to create structures with sub-20 nm feature sizes or materials with advanced electrical properties. Here I demonstrate processes to enable such selfassembling systems including block copolymers and DNA origami, to be integrated into nanoelectronic devices. Additionally, I present a method which utilizes the high stability and electrical conductivity of graphene, which is a material formed using a bottom-up growth process, to create archival data storage devices. Specifically, I show a technique using block copolymer micelle lithography to fabricate arrays of 5 nm gold nanoparticles, which are chemically modified with a single-stranded DNA molecule and used to chemically attach DNA origami to a surface. Next, I demonstrate a method using electron beam lithography to control location of nanoparticles templated by block copolymer micelles, which can be used to enable precise position of DNA origami on a surface. To allow fabrication of conductive structures from a DNA origami template, I show a method using site-specific attachment of gold nanoparticles to and a subsequent metallization step to form continuous nanowires. Next, I demonstrate a longterm data storage method using nanoscale graphene fuses. Top-down electron beam lithography was used to pattern atomically thin sheets of graphene into nanofuses. To program the fuses, graphene is oxidized as the temperature of the fuse is raised via joule heating under a sufficiently high applied voltage. Finally, I investigate the effect of the fuse geometry and the electrical and thermal properties of the fuse material on the programming requirements of nanoscale fuses. Programming voltages and expected fuse temperatures obtained from finite element analysis simulations and a simple analytical model were compared with fuses fabricated from tellurium, a tellurium alloy, and tungsten.

Anthony D Willey (Masters Thesis, December 2012, Advisor: Robert Davis )

Abstract

A method is described for ultrasonically spraying thin films of carbon nanotubes that have been suspended in organic solvents. Nanotubes were sonicated in N-Methyl-2-pyrrolidone or N-Cyclohexyl-2-pyrrolidone and then sprayed onto a heated substrate using an ultrasonic spray nozzle. The solvent quickly evaporated, leaving a thin film of randomly oriented nanotubes. Film thickness was controlled by the spray time and ranged between 200–500 nm, with RMS roughness of about 40 nm. Also described is a method for creating thin (300 nm) conductive freestanding nanotube/polymer composite films by infiltrating sprayed nanotube films with polyimide.

Kyle Zufelt (Senior Thesis, August 2012, Advisor: Robert Davis )

Abstract

An issue that often impacts x-ray and electron analysis of electron microscopy samples is the presence of high-Z atoms in the chosen substrate. In many cases, it is also desirable that the chosen substrate be resistant to chemicals and various processing methods. We present an all-carbon transmission electron microscope (TEM) grid made by carbon nanotube templated microfabrication (CNT-M). Several membranes were deposited on the grids, including Formvar, amorphous carbon, silicon dioxide, and alumina. These grids provide a significant advantage in analytical TEM applications due to the absence of high-Z atoms and the improved chemical resistivity which allows for a wider range of sample preparation and processing techniques.

2011

Taylor Bradham (Capstone, April 2011, Advisor: Robert Davis, David Long, BYU Electrical Engineering Dept. )

Abstract

I participated in the Mechanical Engineering Capstone. The 200+ students who participate are split into group of 5-7 members. Each group bids on three projects they find interesting and feel their unique skill set would allow them to complete to project better than any other group. The group I was placed in won the bid for a project sponsored by L-3 Communications based out of Salt Lake City. The project objective was to design a device that reflects a laser beam onto a wall and be able to move quickly and accurately according to user input. I personally was given ownership of testing the accuracy, speed, and acceleration specs of the project, as well as oversee the development of algorithms for the movement of the reflective surface. Based on the criterion set forth by our sponsor the project was a success, and the concept has been approved for further development.

Brian S Davis (Masters Thesis, August 2011, Advisor: Robert Davis )

Abstract

Dielectrophoresis has been used as a technique for the parallel localization and alignment of both semiconducting and metallic carbon nanotubes (CNTs) at junctions between electrodes. A variation of this technique known as Floating Potential Dielectrophoresis (FPD) allows for a selflimiting number of CNTs to be localized at each junction, on a massively parallel scale. However, the smallest FPD geometries to date are restricted to conductive substrates and have a lower limit on floating electrode size. We present a geometry which eliminates this lower limit and enables FPD to be performed on non-conducting substrates. We also discuss experiments clarifying the self-limiting mechanism of CNT localization and how it can be used advantageously as devices are scaled downward to smaller sizes.

Caleb Hustedt (Senior Thesis, August 2011, Advisor: Robert Davis )

Abstract

Graphene is an exciting material that stands to have a large impact on the scientific community. Unfortunately, graphene cannot be fully utilized due to its small scale and time consuming production. Graphene grown by chemical vapor deposition solves these issues but comes with a cost of decreased mechanical and electrical properties due to defects. However, the exact properties of CVD graphene are not well quantified. In order to measure the qualities of CVD graphene it must be suspended. Carbon infiltrated carbon nanotube forests were fabricated with holes 2-20um in size. Imaging showed CVD graphene was suspended over up to 50 percent of the holes.

David McKenna (Senior Thesis, August 2011, Advisor: Robert Davis )

Abstract

Carbon nanotube templated microfabrication (CNT-M) is a method developed to create microstructures of various materials. Here we investigate the application of CNT-M in the creation of tungsten metal microstructures with applications in MEMS. The CNT-M method involves the growth of patterned vertically aligned carbon nanotubes to form a 3D framework that is subsequently infiltrated with a filler material for added strength. We employed an organo-metallic chemical vapor infiltration (CVI) process using tungsten carbonyl (W(CO)6) to infiltrate the carbon nanotube framework with tungsten metal. In this way microstructures can be created for applications that take advantage of the characteristics of tungsten such as its high melting temperature, anti-corrosivity and high yield strength.

Jun Song (PhD Dissertation, October 2011, Advisor: Robert Davis )

Abstract

A process, called carbon nanotube templated microfabrication (CNT-M) makes high aspect ratio microstructures out of a wide variety of materials by growing patterned vertically aligned carbon nanotubes (VACNTs) as a framework and then infiltrating various materials into the frameworks by chemical vapor deposition (CVD). By using the CNT-M procedure, a partial Si infiltration of carbon nanotube frameworks results in porous three dimensional microscale shapes consisting of silicon-carbon nanotube composites. The addition of thin silicon shells to the VACNTs enables the fabrication of robust silicon nanostructures with flexibility to design a wide range of geometries. Nanoscale dimensions are determined by the diameter and spacing of the resulting silicon/carbon nanotubes while microscale dimensions are controlled by the lithographic patterning of CNT growth catalyst. The characterization and application of the new silicon nanomaterial, silicon-carbon core-shell nanotube (Si/CNT) composite, is investigated thoroughly in the dissertation. The Si/CNT composite is used as thin layer chromatography (TLC) separation media with precise microscale channels for fluid flow control and nanoscale porosity for high analyte capacity. Chemical separations done on the CNT-M structured media outperform commercial high performance TLC media resulting from separation efficiency and retention factor. The Si/CNT composite is also used as an anode material for lithium ion batteries. The composite is assembled into cells and tested by cycling against a lithium counter electrode. This CNT-M structured composite provides an effective test bed for studying the effects of geometry (e.g. electrode thickness, porosity, and surface area) on capacity and cycling performance. A combination of high gravimetric, volumetric, and areal capacity makes the composite an enabling materials system for high performance Li-ion batteries. Last, a thermal annealing to the Si/CNT composite results in the formation of silicon carbide nanowires (SiCNWs). This combination of annealing and Si/CNTs yields a unique fabrication approach resulting in porous three dimensional silicon carbide structures with precise control over shape and porosity.

Cary Tippets (Senior Thesis, August 2011, Advisor: Robert Davis )

Abstract

Photovoltaic cells have the possibility of drastically changing electricity production. Unfortunately, solar cells produced power still remain more than five times cost of traditional power sources. Inexpensive materials and production methods are needed to over come this cost barrier, without the sacrifice of efficiency. Cupric Oxide (CuO) is a possible absorption material that has several promising electrical and optical characteristics. CuO deposited by spray pyrolysis is shown to have a 3% change in resistance when exposed to light. Post deposition annealing is shown to increase this photoconductivity to 4% . Transmission spectra show CuO thin films are strong absorbers below wavelengths of 700 nm.

Taylor Wood (Honors Thesis, August 2011, Advisor: Robert Davis )

Abstract

Microdevices such as accelerometers and force sensors are changing the face of technology. Unfortunately, the type of material a device is made of considerably limits the extent of its practical applications and impedes microdevices from being used to their full potential. Carbon nanotubes (CNTs) contain many interesting physical properties and present an exciting material for use as a nanoframework to shape and reinforce the structure of microdevices. In this study, we use a method of growing, infiltrating, and characterizing carbon nanotube templated structures for use in microfabrication. Carbon nanotubes are first grown by Fe-catalyzed chemical vapor deposition after which infiltration of amorphous carbon (a-C) proceeds by chemical vapor deposition. a-C fills the spaces in between the CNTs, creating a CNT/nanotube composite material. Using cantilever structures fabricated from different Fe-catalyst thicknesses and different a-C infiltration times, we measure the extension vs. applied force of the cantilevers. We then use this material to calculate the Young’s modulus and yield stress of the nanocomposite. Young’s modulus values for our material ranged from 1.67 – 7.87 GPa, depending on sample preparation conditions. Yield stress values of the composite material ranged from 53.7 – 147 MPa, depending on sample preparation conditions. Our results show that a thicker Fe-catalyst layer results in higher Young’s modulus and yield stress values. Furthermore, our data indicate that the a-C infiltration time has little effect on the resultant materials properties of the nanocomposite. Our data characterize this material as a flexible material with moderate strength. We hope that with further optimization, it will soon be used in the fabrication of industrial devices.

2010

Jonathan D Abbott (Masters Thesis, April 2010, Advisor: Robert Davis )

Abstract

A highly durable optical disk has been developed for data archiving. This optical disk uses tellurium as the write layer and carbon as a dielectric and oxidation prevention layer. The sandwich style CTeC film was deposited on polycarbonate and silicon substrates by plasma sputtering. These films were then characterized with SEM, TEM, EELS, ellipsometry, ToF-SIMS, etc, and were tested for writability and longevity. Results show the films were uniform in physical structure, are stable, and able to form permanent pits. Data was written to a disk and successfully read back in a commercial DVD drive.

Nicholas Morrill (Senior Thesis, August 2010, Advisor: Robert Davis )

Abstract

2009

Scott Black (Capstone, July 2009, Advisor: Robert Davis, Richard Vanfleet )

Abstract

A new growth recipe for height maximization of carbon nanotubes (CNTs) by thermal chemical vapor deposition is found using an ethylene purity of 99.5%. This new recipe yields fast growthrates with average growth heights of 1146 μm in 10 minutes of growth. The CNT forest growth is very uniform but also has tears in structures, bowed vertical growth, and rough sidewalls indicating a poor quality CNT forest. These poor features seem to be a result of the thickness of the iron catalyst layer. With a thicker catalyst layer, high quality CNT forests may potentially be grown using 99.5% pure ethylene with faster growth rates than the current standard growth recipe for CNTs using 99.95% pure ethylene.

David Brown (Honors Thesis, April 2009, Advisor: Robert Davis )

Abstract

Polymer surfaces made hydrophilic by timed exposure to UV light can be characterized by measuring their water contact angle. Additionally, adhesive force of the roughened and functionalized surfaced can be measured via a vertical peel test. Water contact angle and peel force for a given surface exhibit a linear relationship. We suggest that one can conceivably be used to predict the other. Our work focused on octydecyltrichlorosilane (OTS), which was laid down by solution chemistry and modified by exposure to UV light. Preparation, treatment, and characterization methods are described to encourage further study.

Hiram Jacob Conley (Masters Thesis, July 2009, Advisor: Robert Davis )

Abstract

Placement of single walled carbon nanotubes is demonstrated through massively parallel indirect dielectrophoresis (MPID). MPID is shown to be able to control the placement of carbon tubes as well as the number of tubes placed. Lumped element analysis for AC circuits is used to model MPID. This model allows for predictions of the number of tubes that will be captured in a trap. This model has been consistent with experimental data of numbers of nanotube placed in a junction. Carbon nanotubes placed with MPID are shown to be electrically active.

Brian Davis (Honors Thesis, April 2009, Advisor: Robert Davis )

Abstract

Chemical surface patterning at the nanoscale is an important component of the chemically directed assembly of sensitive biological molecules or nanoscale electrical devices onto surfaces. Here we present a scanning probe lithography technique that allows for patterning of aqueous polymers on glass or silicon dioxide surfaces. The surfaces were functionalized by covalently bonding a silane monolayer with a known surface charge to either a borosilicate glass slide or thermal oxide on a silicon wafer. A polymer layer less than 2 nm in thickness was then electrostatically bound to the silane layer, passivating the functionalized surface. An Atomic Force Microscope (AFM) probe was used to mechanically remove a portion of the polymer layer, exposing the functional silane layer underneath. Employing this method we made chemically active submicron regions. These regions were backfilled with a fluorescently-tagged polymer. Chemical differentiation was verified through tapping mode AFM and optical fluorescence microscopy. Lines with a pitch as small as 20 nm were observed with AFM height and phase mode data. Scribing forces were measured as low as 0.3 μN. Scribing was successful in ambient conditions as well as in aqueous solution, thus allowing patterning of sensitive biological molecules in their native environments. No instabilities in the created patterns were noted during observation periods of several months.

David Jones (Senior Thesis, August 2009, Advisor: Robert Davis )

Abstract

We present a scalable procedure for the fabrication of transistors from puri- ed (7; 6) carbon nanotubes. CoMoCAT nanotubes are puri ed via isopycnic centrifugation and dielectrophoretically placed between electrodes. The resul- tant devices display on/o ratios as high as 103 and resistances as low as 106. Approximately 50% of all the devices display an on/o ratio greater than 10. The potential for higher yields is discussed.

Emmalee Jones (Capstone, April 2009, Advisor: Robert Davis, Richard Vanfleet )

Abstract

The purpose of the capstone project was to develop a less costly process of patterning vertical structures in amorphous silicon for use in photovoltaics. Two processes were followed in trying to develop the mold. The first process centered on using a 3 micron layer of photoresist SU-8 10, a viscous polymer creating a pattern using lithography and spun on hydrogen silsesquioxane (HSQ) to create a reusable reverse glass mold. This process resulted in an unusable pattern with unclean lines and definition. A second process was planned after the failure of the first process. The second process centered on polyimide, a different polymer, using lithography to create a reusable reverse mold. The initial results with polyimide are promising and will continue to be investigated.

2008

Katherine Hurd (Senior Thesis, August 2008, Advisor: Robert Davis )

Abstract

Carbon nanotube forests condense when they are saturated with a solvent and then dried. While larger features readily condense into patterned features, smaller features require more delicate shrinking conditions and are highly de- pendant on temperature, solvent type, solvent vapor density, and heating rate. Through optimization of these parameters, nanotube forests can be success- fully densi ed so that they maintain their original patterns, simply becoming thinner and denser. Shrinking micrometer-scaled features allow us to use larger patterns to create extremely small features up to one hundred times smaller than the original features.

David Hutchison (Senior Thesis, August 2008, Advisor: Robert Davis )

Abstract

We present a new technique using carbon nanotubes as a framework to make high aspect ratio structures from a variety of materials, and demonstrate its applicability to microelectromechanical systems. First, a \forest" of vertically- aligned carbon nanotubes (CNTs) is grown from a patterned catalyst film by chemical vapor deposition (CVD). Next, the spaces between CNTs are filled with silicon, silicon nitride, or other materials by CVD. Finally, parts of the structure may be released by a short reactive ion etch to expose an underlying sacrificial layer, followed by a wet etch of the sacrificial layer. In this way, structures as tall as 1 mm with minimum feature size of less than 3 m (dependent on design geometry) can be fabricated from a wide variety of materials.

Brendan Turner (Senior Thesis, April 2008, Advisor: Robert Davis )

Abstract

We investigated the role of sub-catalyst barrier layers in Vertically-aligned car- bon nanotube (VACNT) growth and explored its effect on VACNT structures. Al2O3 and several alternative barrier layers including native SiO2, thermally grown SiO2, and Ti were deposited on silicon wafers prior to Fe layer de- position. The effect of the barrier layers on VACNT growth characteristics, specifically: VACNT growth rate, carbon nanotube (CNT) size, density, and dimensional control of patterned vertical structures were examined. VACNT forest growth was characterized by scanning electron microscopy (SEM). The effect of the barrier layer on the Fe catalyst after both pre-growth annealing and CNT growth was characterized by atomic force microscopy (AFM) and transmission electron microscopy (TEM). TEM revealed that the Al2O3 bar- rier layer both reduced diffusion of the Fe into the Si substrate and played a significant role in particle formation resulting in small Fe nanoparticles. Ther- mal SiO2 provided a significant barrier to diffusion into the substrate but did not result in Fe nanoparticles as small as those on the Al2O3. Thinner Fe catalyst layers resulted in faster, denser, and better-aligned growth.

2007

Michael Clemens (Senior Thesis, August 2007, Advisor: Robert Davis )

Abstract

Aqueous suspensions of single-wall carbon nanotubes (SWNTs) extracted from the supernatant of ultra-centrifuged sodium cholate micelle SWNT mixtures are shown to be strongly heterogeneous with respect to the quantum yield of their constituents. This is shown by separating the suspended SWNTS through preparative ultracentrifugation in iodixanol density gradients followed by frac- tionation of the isopycnic layers. The fractions are optically characterized by photoluminescence and linear absorption spectroscopy. We nd that the most buoyant fractions with a density of 1.055  0.005 g/cm3 have the highest pho- toluminescence quantum yield  of 1.1%, a factor of 5 higher than that of the supernatant. Denser fractions with lower  make up for about 2/3 of these samples and contain mostly small ropes in which the quantum yield is reduced by nonradiative decay through coupling to metallic tubes.

Hiram Conley (Senior Thesis, August 2007, Advisor: Robert Davis )

Abstract

We developed a technique to image ribosomes with the Atomic Force Microscope( AFM) in a fluid environment. We imaged 30S, 50S, and 70S ribosomes in fluid and showed that our data is in agrement with crystallography data. This is an introductory work to enable our group to study ribosomes using the AFM

2006

Sterling Fillmore (Capstone, July 2006, Advisor: Robert Davis )

Abstract

A concise experiment is conducted in order to determine: 1.) the effect of the presence of the promoter thioglycolic acid on the density of ferritin while electrochemically adsorbed onto a gold electrode and 2.) the effect of cyclic voltammetry on the density of ferritin previously electrochemically adsorbed onto an atomically flat gold electrode. Atomic Force Microscopy is used to image adsorbed ferritin. It is shown that when ferritin is electrochemically adsorbed in the presence of thioglycolic acid, the density of adsorbed ferritin is increased by a factor of 1.5 for individual ferritin and 2.0 for ferritin clumps. It is determined that cyclic voltammetry reduces the amount of adsorbed ferritin by a factor of 2.0 if the ferritin was originally adsorbed in the presence of thioglycolic acid. It is also shown that ferritin density is not affected by cyclic voltammetry when the ferritin was adsorbed without the presence of thioglycolic acid.

Jacob Fluckiger (Senior Thesis, December 2006, Advisor: Robert Davis )

Abstract

An intriguing mechanical material would be an aluminum / carbon nanotube composite. It could combine the ultra high strength of carbon nanotubes with the ductility and manufacturability of aluminum. We are studying the formation of this metal matrix composite by electroplating aluminum on preformed carbon nanotube structures. In order to induce aluminum growth on the nanotubes, chemical modification of the nanotube surface is required. Surface chemical functionalization was performed by suspension and immersion in a succinic acid bath for the loose nanotubes and nanotube mats respectively. The active surfaces consisting of carboxyl groups should form a stable chemical bonds with the aluminum. Characterization of the chemically functionalized buckypaper by water contact angle and x-ray photo electron spectroscopy (XPS) measurements will be presented. Initial metallization studies will also be presented.

John-Mark Geiss (Capstone, December 2006, Advisor: Robert Davis, Matthew Linford )

Abstract

Chemomechanical functionalization of chemical surfaces is a field of chemistry and physics which has attracted a great deal of attention over the last decade. The atomic force microscope has played an instrumental role in the advancement of nanotechnology using such methods. In my research we investigated the effectiveness of depositing a stable Avidin protein monolayer on a silicon oxide surface. This was accomplished through a multi-step process involving surface chemistry. The atomic force microscope and ellipsometer were used in measuring the thickness and verifying the presence of each layer formed during this multi-step process.

2004

Jacob Hale (Senior Thesis, April 2004, Advisor: Robert Davis )

Abstract

n/a

Jorj Owen (Capstone, April 2004, Advisor: Robert Davis )

Abstract

This paper describes three advances in lab-on-a-chip technology. First, it is shown that chemomechanical surface patterning can be performed using a commercially available liquid handler that has undergone only minor modifications. These capabilities are demonstrated by making and then characterizing smaller hydrophobic corrals, made with a diamond tip, than have previously been reported. Hydrophobic corrals are small enclosures on a surface that are ringed by hydrophobic lines. They hold droplets of high surface tension solutions. They allow a surface to be subdivided into individually addressable elements, thus providing a platform for conducting many simultaneous surface experiments with small (down to ca. 1 μL) liquid volumes. An important consequence of this work is that it makes chemomechanical surface patterning, which is a valuable and straightforward method for surface modification, much more accessible to the technical community. Second, it is shown that an entire array of hydrophobic corrals can be simultaneously coated with polyelectrolyte multilayers, but that the hydrophobic corrals still retain the ability to hold liquids after this deposition. The robotic arm of the liquid handler is again employed to manufacture this ultrathin film. Finally, as a demonstration of the capability of this technology to create complex patterned arrays on surfaces from solution for biological or nanostructured materials applications, and again employing the liquid handler, polyelectrolyte-coated hydrophobic corrals are individually addressed and loaded with a solution containing gold nanoparticles for independently specified times. The density and morphology of deposited nanoparticle monolayers were studied by scanning electron microscopy. The deposition of gold nanoparticles onto a chip occurred at a constant rate (0.5 %/min) over the range of times studied.

Melinda Tonks (Honors Thesis, March 2004, Advisor: Robert Davis )

Abstract

Jed D Whittaker (Masters Thesis, December 2004, Advisor: Robert Davis )

Abstract

Carbon molecules were grown over a lithographically defined se of trenches. After finding a nanotube that crossed one or more trenches, we used an atomic force microscope (AFM) to measure the amount of force required to make a single-walled carbon nanotube slip along the silicon dioxide trench tops. This measurement was made by pushing down the tube with the AFM probe until slip was observed in the force-distance curve. The change in suspended length of the slipped tube was calculated from the force-distance curve. The nanotubes slipped at an axial tension of 8 nN. Pushing was also done on tubes after being selectively coated with silicone dioxide, physically attaching them to the trench tops, with a slipping tension of 12 nN. Carbon nanotubes were also grown on AFM probes by chemical vapor deposition, and selectively coated with silicon dioxide. Under the right conditions the deposition selectively coated the nanotubes where they were in contact with the probe, but not where they extended off the tip.

Degao Xu (PhD Dissertation, December 2004, Advisor: Robert Davis )

Abstract

Conductive Atomic Force Microscope (c-AFM) was used to measure the conductivity of single horse spleen ferritin (HoSF) and azotobacter vinelandii bacterial ferritin (AvBF) molecules deposited on flat gold surfaces. A 500µm diameter gold ball was also used as a contact probe to measure the conductivity of a thin film of ferritin molecules. The average current measured for holo HoSF was 13 and 5 times larger than that measured for apo HoSF as measured by c-AFM at 1V and gold ball at 2V and respectively, which indicates that the core of ferritin is more conductive than the protein shell and that conduction through the shell is likely the main factor limiting electron transfer. With 1 volt applied, the average electrical currents through single holo HoSF and single apo HoSF molecules were 2.6 pA and 0.19 pA respectively. Measurements on holo AvBF showed it was more than 10 times as conductive as holo HoSF, indicating that the protein shell of AvBF is more conductive than that of HoSF. The increased conductivity of AvBF is attributed to heme groups in the protein shell.

2003

Travis S Hughes (Masters Thesis, December 2003, Advisor: Robert Davis )

Abstract

We repot the observation of the Influenza A M2 incorporated in a DPPC supported planar bilayer (SPB) on mica, formed by use of a modified vesicle fusion method from proteoliposomes using contact mode atomic force microscopy (AFM). M2’s extra-bilayer domains were observed as particles 1-1.5 nm in height above the bilayer surface. Movement of M2 independent of the probe tip was observed with a calculated lateral diffusion coefficient of ~5_10-14cm2/s and a mobile fraction of ~80%. Protein-protein interaction was also observed. Incubation of proteoliposomes in a hypertonic solution and increased DPPD: M2 weight ratios improved SPB formation by M2/DPPC proteoliposomes.

Jed Whittaker (Senior Thesis, April 2003, Advisor: Robert Davis )

Abstract

2002

Dan Allen (Senior Thesis, April 2002, Advisor: Robert Davis )

Abstract

Brent Alan Wacaser (Masters Thesis, December 2002, Advisor: Robert Davis )

Abstract

Surface modification and patterning at the nano-scale is a new frontier in science with significant possible applications in biomedical technology, sensors, and nanoelectronics. Here we show that an atomic force microscope (AFM) can be employed to simultaneously pattern and functionalize hydrogen-terminated silicon (111) surfaces. The AFM probe was used to break Si-H and Si-SI bonds in the presence of reactive molecules, which covalently bonded to the scribed Si surface. Functionalized patches and patterned lines of molecules were produced. Line widths down to 30 nm were made by varying the force at the tip. These of flight secondary ion mass spectroscopy. The forces required to produce the features were analyzed and discussed.

2001

Matthew Housley (Honors Thesis, June 2001, Advisor: Robert Davis )

Abstract

Dale Kitchen (Senior Thesis, July 2001, Advisor: Robert Davis )

Abstract

Ryan Monson (Honors Thesis, May 2001, Advisor: Robert Davis )

Abstract

Brent Alan Wacaser (Honors Thesis, May 2001, Advisor: Robert Davis )

Abstract