Recent Submissions

  • Synthesis of [Si1-xGex]136 type II clathrates (0.1<x<0.5): alloyed semiconductor cages in crystalline vs. amorphous products

    Raharjo, Taufik; Toberer, Eric; Koh, Carolyn A.; Krishna, Lakshmi
    The unique thermal, electrical, optical, and structural properties of Group IV clathrates have brought them to the forefront of potential renewable energy opportunities. Specifically, the semiconductor capabilities of crystalline alloyed silicon-germanium clathrate are especially promising due to the tenability of these properties for photovoltaics or thermoelectrics. However, a successful crystalline clathrate has yet to be formed at all molar compositions of SiGe. Therefore, understanding the critical parameters which control the formation of a crystalline alloyed SoGe clathrate are indispensable to employing these materials for semiconductor applications.
  • Nanoethics and policy education effectiveness

    Zilliox, Skylar Huzyk; Smith Rolston, Jessica; Packard, Corinne E.; Mitcham, Carl
    Nanotechnology (NT), as a new and potentially revolutionary technology, provides the opportunity to examine the complex interaction between society and technology. The Nano-Science, Technology, Ethics, and Policy (NanoSTEP) project at Colorado School of Mines (CSM) seeks to: (1) increase engineering students' understanding of society, policy, and ethics; and (2) use nanotechnology as a framework to better understand the role of ethics and policy education in an engineering curriculum.
  • Development of neutron radiography capabilities using a radioisotope neutron source

    Robinson, Shawn; King, Jeffrey C.
    The purpose is to develop neutron radiography capabilities using an existing radioisotope neutron source. This project involved the use of foil activation, collimator and sample holder design, film development, as well as the addition of radiation shielding. Design and modeling was done at the Colorado School of Mines, and the experiments we conducted at the Denver Federal Center at the USGS Triga Reactor, building 15.
  • Development of high-pressure rate rules for alkyl + O2 reactions

    Goffinett, Quinton T.; Villano, Stephanie M.; Cartensen, Hans-Heinrich; Dean, Anthony M.
    The need for increased engine performance / efficiency and new alternative fuels has proven kinetic modeling studies to be a valuable tool to assess new fuels and find optimal operating conditions. Research is geared toward verifying rate constants in key reaction pathways for low temperature hydrocarbon oxidation mechanisms. Obstacles to overcome are: the thousands of species involved in each combustion, the tens-of-thousands of reaction pathways available, the limited experimental data available and high-level calculations restricted to small molecules. The strategy was to use abinitio computational methods to calculate rate constants for smaller species, and then generalize the results on a per-site basis for larger species. Results suggest that the direct use of HP rate rules is sufficient to describe reactions under most conditions relevant to combustion/ignition engine problems. Future research efforts are directed toward refining data by improving thermodynamic profiles for reactants and transition states.
  • Scalable nanoparticle arrays for thin-film solar cells

    Yeoh, Phoebe; Ma, Fuduo; Wu, Ning
    Thin film solar cells use less material than conventional solar cells, making them a viable option for cheaper solar electricity. Unfortunately, their thinness also hinders them from trapping and absorbing longer light wavelengths, making them less efficient. Monolayered, non-close packed nanoparticle arrays placed within the cell help to scatter longer wavelengths within the cell and allows them to be absorbed. One method for creating these arrays is called Monolayered Self-assembly at Liquid-liquid Interfaces (SALI). A charged substrate is immersed in a water-hexane interface. Oppositely charged particles suspended in an alcohol and water spreading solvent are injected at the interface using a needle. The particles spread and are trapped at the interface in an ordered array, and the substrate is lifted to deposit the particle array upon it. By testing different experimental parameters' effects in creating arrays at the water-hexane interface, the goal is to understand how such arrays form and make the SALI method suitable for large-scale implementation. This work was done primarily with positively charged amidine latex particles of about 1 micron in diameter.
  • Study of the impact of porosity on coking sensor performance, A

    Garbiso, Markus A.; Wheeler, Jeffey L.; Porter, Jason M.
    Fuel reforming systems transform hydrocarbon fuels (e.g. gasoline and methane) into synthesis gas (CO and O2). One problem in fuel reforming systems is if the concentration of carbon is too high, solid carbon starts to coat (coking) and damage the catalyst. A solution to prevent coking is a Wheatstone bridge circuit printed onto a ceramic wafer. When coke starts to deposit on Ni/YSZ, a measurable change in voltage occurs. When coking starts to form on a nickel catalyst, carbon nanofibers start to bridge nickel particles. The sensor is tested in an environmental cell with a methane and carbon dioxide atmosphere. Increasing the porosity of the sensor catalyst caused: monotonic sensor response, improved repeatability, and slower sensor response. Future work might be to investigate why nanofibers didn't form, but still worked.
  • Silyl ether passivation of silicon quantum dots via catalytic dehydrocoupling reactions

    Sharps, Meredith; Zhou, Tianlei; Sellinger, Alan
    Silicon quantum dots (SiQD) have been researched as potential materials for use in solar cells, photovoltaic devices, organic light emitting diodes, luminescent markers for biological imaging, and ink-jet printable displays. Passivation of the SiQDs with organic ligands can be used to protect the dots from oxidation, improve solubility, and stabilize luminescence by tuning the distance of the electronic band gap. Passivating the dots with silyl ethers is not a new process, but the state-of-the-art method requires chlorosilane precursors, resulting in the production of toxic and corrosive HCl gas. Our method utilizes a palladium catalyzed process for the direct conversion of a silyl hydride to silyl ether. This process eliminates the Si-Cl generation step and produces a milder by-product, hydrogen gas. This project looks at the formation of Si-O-C bonds and the more hydrolytically stable Si-O-Si bonds developed using this method.
  • Electrospinning lithium silicide and lithium germanide encapsulated carbon nanofibers for lithium ion batteries

    Taylor, Lauren; Cloud, Jacqueline E.; Yang, Yongan
    Lithium silicide and lithium germanide encapsulated carbon nanofibers were explored for use in next generation lithium ion batteries. Both silicon and germanium have high theoretical charge capacities in comparison to the currently used graphite anode, but increase in volume by up to 400% during lithiation. This expansion and contraction breaks the electrical connection and causes destruction of the solid electrolyte interface (SEI) within the battery, decreasing its cyclability. This research attempts to solve the volume expansion problem by creating a material that is already at its expanded state. During delithiation void spaces are created to accompany lithium in future cycles.
  • Characterization of rapidly thermally annealed Cu doped ZnTe thin films

    Davis, Kendall; Li, JiaoJiao; Beach, Joseph; Wolden, Colin Andrew; Ohno, Timothy R.
    CdTe solar cells can be produced inexpensively and Cu doped ZnTe films are used as back-contact interfacial layers for CdTe because they are p-type and have a small valence band discontinuity with CdTe1, which can improve grain quality and reduce defects. This research demonstrated that RTP annealing can improve device performance. A better understanding of the electrical effects of RTP annealing could lead to further enhanced cells. Glass slides were cut and cleaned for use as substrates. Thin films of Cu doped ZnTe were then deposited on each substrate in a vapor transport depositor. The ZnTe and Cu were co-deposited at a pressure of 6x10-6 and a temperature of 100 degree C, with thicknesses of 150nm (ZnTe) and 15nm (Cu), for a total film thicknesses of 165nm. Samples were loaded into a Rapid Thermal Processor where they were annealed in 2 torr of Ar gas from 150 degree C to 550 degree C in increments of 50 degree C, for 30 seconds. Samples with concentrations of Cu would be expected to display lower resistances, and vice versa. Carrier Density increases by orders of magnitude after RTP at 500 degree C for the samples high in ZnTe. This corresponds to the temperature at which ZnTe began to evaporate from the samples. The type switches between measurements, depending on field strength and processing conditions. This occurrence could be due to a number of effects, most notably lack of uniformity in the films and or the contact geometry. The gradient of copper could also contribute to a photo voltage. The sample crystalllinity and composition also may contribute.
  • Incorporation of silicon nanoparticles into silicon based solar cells

    Grovogui, Jann; Kendrick, Chito; Collins, Reuben T.
    In this project, silicon based solar cells were developed using active layers that consisted of Amorphous Silicon as well as Silicon Nanoparticles (Silicon Quantum Dots). The ultimate goal of this project was to fabricate a working solar cell with an active layer that incorporated Silicon Nanoparticles in an attempt to improve cell functionality.
  • Experimental investigation of endothermic fuel cracking for cooling hypersonic vehicles

    Bogin, Gregory E.; Saldana, Mario H.; Sardin, Juliette
    The Air Force's scramjet (supersonic combustion ramjet) is a jet engine in which combustion takes place in supersonic airflow. As scramjet flight speeds increase to supersonic and hypersonic regimes, the temperature of the ram air taken on board the vehicle becomes too high to cool the structure. Therefore, it is necessary to use a fuel that undergoes endothermic cracking as the primary coolant. The primary focus of this project is to develop a fundamental understanding of the coupled homogeneous and heterogeneous reactions that occur during endothermic fuel cracking; which will be partly accomplished through the investigation of gas-phase and surface reaction interactions in a high pressure flow reactor.
  • Lithium silicide encapsulated porous carbon thin films for lithium ion batteries

    Bjarnason, Elsie V.; Yoder, Tara S.; Yang, Yongan
    Improved energy storage is a critical component of reaching an energy-sustainable future. Lithium ion batteries are very promising due to their relatively high energy density, slow loss of charge when idle, and essentially no memory effect. However, their charge capacity, cyclability, and energy and power densities need to be improved to meet our energy demands. In order to accomplish this goal, new electrode materials are being investigated. Silicon is promising in that it has a charge capacity six times higher than graphite, the currently used material; however, silicon has poor cyclability due to its extreme volumetric expansion during lithiation, which causes a loss of electrical contact and a cyclic gain and loss of a solid-electrolyte interface (SEI).
  • Etch resistant Zn1-xMgxO alloys as an e'-acceptor for dye sensitized solar cells

    Meing, Erich; Brenner, Thomas; Collins, Reuben T.; Furtak, Thomas E.
    In DSSCs, dyes are used to photosensitize a nanoporous electrode, most commonly TiO2. Light excites the dye, which then transfers an electron to the metal oxide electrode. The electron then travels to the conducting contact and through the external circuit. An electrolyte surrounding the electrode replenishes the electron deficiency in the dye. Zinc oxide has been explored as an alternative electron acceptor material to TiO2 because of its abundance of easily synthesized nanostructures. However, ZnO suffers from Zn-Dye aggregate formation. The carboxyl groups of the dye are acidic and form aggregates through etching of the surface. Aggregates prevent efficient transfer of electrons to the ZnO matrix which instead decays through fluorescence. Aggregate formation can be identified through photoluminescence spectroscopy. Previous work on Zn1-xMgxO nanotips suggested that this alloy is more resistant to etching than ZnO4. Zn1-xMgxO showed improved etch-resistance in another project, which makes it a promising replacement for ZnO in DSSCs. The sensitization and aggregate formation of N3 dye on Zn1-xMgxO is investigated in this poster.
  • Functional mesoporous silica nanoparticles for the selective sequestration of fatty acids

    Grant, Benjamin; Bharadwaj, Vivek; Maupin, C. Mark
    The use of seed and/or algae oil is an attractive alternative feedstock for the biofuels industry. Currently methods to sequester free fatty acids (FFAs) are expensive, but using mesoporous silica nanoparticles may provide a fast, efficient, and cost effective way to selectively sequester the FFAs from feedstock oils. The goal of this project is to illuminate why functionalized mesoporous silica nanoparticles are able to sequester certain FFAs. Presented here is the parameterization and molecular dynamics (MD) simulations of various common saturated, monounsaturated, and polyunsaturated FFAs. Density functional theory (B3LYP/CBSB7) has been used to optimize and calculate the charge distribution, which was transformed into a classical point charge representation using the restrained electrostatic potential method (RESP). Modifying the general amber force field (GAFF) with the new charge distribution has enabled the simulations of pure FFAs, FFAs in hexane, and a silicon dioxide porous material with a FFA-hexane mixture. The resulting densities for the pure FFAs are found to be in excellent agreement (within 5%) with the experiment values. Simulations have also elucidated the structural and energetic properties of pure FFAs, and FFAs in hexane in addition to insights on the sequestering capability of unmodified silicon dioxide pores.
  • Clathrate hydrate nucleation visualization

    Barnes, Brian C.; Sum, Amadeu K.; Richards, Alex
    Clathrate hydrates occur when water forms cages around natural gas molecules such as Methane. Nucleation refers to the process of cage formation by the water. Guest Coordination may provide the necessary cage stabilization. This poster graphically represents the nucleation process as well as cage geometry examples that utilize the concept of guest coordination for stability.
  • Defect analysis of phosphorus doped silicon quantum dots by electron spin resonance

    Kanten, Bethany; Riskey, Kory; Wheeler, Lance; Taylor, P. Craig
    Perfectly crystalline silicon with a dopant provides free carriers in solar materials. The crystalline structure of the lattice provides an ideal semiconductor. Quantum dots have a better ability to collect electrical current than amorphous silicon. Defects in silicon are defined as places where the crystalline lattice is not perfect such as a dangling bond. Electron Spin Resonance can be used to understand defects and discover the defect concentration of various silicon structures to determine their potential efficiency. Phosphorus doped silicon quantum dots were synthesized using silane and phosphine gases by plasma enhanced chemical vapor deposition (PECVD). Samples were doped to increasing levels of phosphorus: 0.01%, 0.1%, 1%, 10%. Samples were prepared both dry and in toluene solvent. All samples characterized at three temperatures: 300K, 77K, 12K.
  • Fabrication of ternary palladium alloy membranes for hydrogen production

    Brazel, Aisling; Lewis, Amanda; Way, J. Douglas; Wolden, Colin Andrew
    Demand for hydrogen, for use in fuels, fertilizers, and the production of ammonia, is increasing. Since 95% of all hydrogen produced in the United States is through the steam reformation of methane, with only a 50% conversion, a limited equilibrium in the water-gas shift, and an extensive, intensive separation train being required, the goal of this project is to introduce membrane reactors for H2 production. The ideal process stream reforms CH4 and +H20 through a high temperature, H2 permeable membrane to produce H2 and CO2. The advantages of this process are: continuous H2 removal; reduced temperature and increased pressure; high conversion percentage; and concentrated CO2 for sequestration. But the challenge is a lack of suitable membrane. A ternary palladium alloy membrane was fabricated by depositing Pd and Au layers by electroless plating. Ternary was added by DC magnetron sputtering and high temperature annealing for diffusion/alloy formation. Four metals were deposited in the alloy membrane: magnesium, ruthenium, zirconium, and molybdenum. The targets were successfully calibrated, and their deposition rate was calculated. Also successful was the fabrication of ternary palladium alloy membranes. These membranes are in the process of being annealed and tested for hydrogen permeation and resistance to corrosion by hydrogen sulphide.
  • Addition of carbon black as a conductive support to bimetallic catalysts for use in anion exchange membrane fuel cells

    Wheatle, Bill; Ngan, Christine; Herring, Andrew M.; Greenlee, Lauren F.
    The anion exchange membrane (AEM) fuel cell has the potential to become an important energy conversion technology. Unlike proton exchange membrane (PEM) fuel cells, AEMs do not use noble metal catalysts, allowing them to potentially become low-cost alternatives to PEMs. The purpose of this research is twofold: To increase the methanol oxidation current produced by the bimetallic catalyst used by AEM fuel cells; To reduce the catalyst ability to split water. To accomplish this, carbon black was added during various steps in catalyst processing.