Chemical Engineering Faculty Research and Publications

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  • ItemOpen Access
    Rational Modification of a Metallic Substrate for CVD Growth of Carbon Nanotubes
    (2018-03-12) Li, Xu; Baker-Fales, Montgomery; Almkhelfe, Haider; Gaede, Nolan R.; Harris, Tyler S.; Amama, Placidus B.
    Growth of high quality, dense carbon nanotube (CNT) arrays via catalytic chemical vapor deposition (CCVD) has been largely limited to catalysts supported on amorphous alumina or silica. To overcome the challenge of conducting CNT growth from catalysts supported on conductive substrates, we explored a two-step surface modification that involves ion beam bombardment to create surface porosity and deposition of a thin AlxOy barrier layer to make the surface basic. To test the efficacy of our approach on a non-oxide support, we focus on modification of 316 stainless steel (SS), a well-known inactive substrate for CNT growth. Our study reveals that ion beam bombardment of SS has the ability to reduce film thickness of the AlxOy barrier layer required to grow CNTs from Fe catalysts to ∼ 5 nm, which is within the threshold for the substrate to remain conductive. Additionally, catalysts supported on ion beam-damaged SS with the same AlxOy thickness show improved particle formation, catalyst stability, and CNT growth efficiency, as well as producing CNTs with higher quality and density. Under optimal reaction conditions, this modification approach can lead to CNT growth on other nontraditional substrates and potentially benefit applications that require CNTs be grown on a conductive substrate.
  • ItemOpen Access
    Bulk (100) scandium nitride crystal growth by sublimation on tungsten single crystal seeds
    (2018-09-20) Al-Atabi, Hayder A.; Khan, Neelam; Nour, Edil; Mondoux, Joseph; Zhang, Yi; Edgar, James H.; edgarjh
    Scandium nitride single crystals (14–90 μm thick) were grown on a tungsten (100) single crystal substrate by physical vapor transport in the temperature range of 1850 °C–2000 °C and pressure of 15–35 Torr. Epitaxial growth was confirmed using in-plane ϕ scan and out-of-plane x-ray diffraction techniques which revealed that ScN exhibits cube-on-cube growth with a plane relationship ScN (001) ǁ W (001) and normal direction ScN [100] ǁ W [110]. Atomic force microscopy revealed that the surface roughness decreased from 83 nm to 18 nm as the growth temperature was increased. The x-ray diffraction rocking curve (XRC) widths decreased with temperature, indicating that the crystal quality improved as the growth temperature increased. The lowest XRC FWHM was 821 arcsec which is so far the lowest value reported for ScN. Scanning electron microscopy exhibited the formation of macrosteps and cracks on the crystal surface with the latter due to the mismatch of ScN and tungsten coefficients of thermal expansion.
  • ItemOpen Access
    Catalysts-Looking Back and Peering Ahead
    (2017-01-26) Hohn, Keith L.; hohn; Hohn, Keith L.
    I am pleased to report on the latest happenings at Catalysts. It is gratifying to me to look back at where we’ve been and what we’ve accomplished, but also inspiring to peer ahead to how we will grow and improve.
  • ItemOpen Access
    Energy, Transportation, Air Quality, Climate Change, Health Nexus: Sustainable Energy is Good for Our Health
    (2016-02-16) Erickson, Larry E.; Jennings, M.; lerick; Erickson, Larry E.
    The Paris Agreement on Climate Change has the potential to improve air quality and human health by encouraging the electrification of transportation and a transition from coal to sustainable energy. There will be human health benefits from reducing combustion emissions in all parts of the world. Solar powered charging infrastructure for electric vehicles adds renewable energy to generate electricity, shaded parking, and a needed charging infrastructure for electric vehicles that will reduce range anxiety. The costs of wind power, solar panels, and batteries are falling because of technological progress, magnitude of commercial activity, production experience, and competition associated with new trillion dollar markets. These energy and transportation transitions can have a very positive impact on health. The energy, transportation, air quality, climate change, health nexus may benefit from additional progress in developing solar powered charging infrastructure.
  • ItemOpen Access
    Development of transparent microwell arrays for optical monitoring and dissection of microbial communities
    (2016-08-01) Halsted, M.; Wilmoth, J. L.; Briggs, P. A.; Hansen, Ryan R.; Briggs, D. P.; Timm, A. C.; Retterer, S. T.; rrhansen; Hansen, Ryan R.
    Microbial communities are incredibly complex systems that dramatically and ubiquitously influence our lives. They help to shape our climate and environment, impact agriculture, drive business, and have a tremendous bearing on healthcare and physical security. Spatial confinement, as well as local variations in physical and chemical properties, affects development and interactions within microbial communities that occupy critical niches in the environment. Recent work has demonstrated the use of silicon based microwell arrays, combined with parylene lift-off techniques, to perform both deterministic and stochastic assembly of microbial communities en masse, enabling the high-throughput screening of microbial communities for their response to growth in confined environments under different conditions. The implementation of a transparent microwell array platform can expand and improve the imaging modalities that can be used to characterize these assembled communities. Here, the fabrication and characterization of a next generation transparent microwell array is described. The transparent arrays, comprised of SU-8 patterned on a glass coverslip, retain the ability to use parylene lift-off by integrating a low temperature atomic layer deposition of silicon dioxide into the fabrication process. This silicon dioxide layer prevents adhesion of the parylene material to the patterned SU-8, facilitating dry lift-off, and maintaining the ability to easily assemble microbial communities within the microwells. These transparent microwell arrays can screen numerous community compositions using continuous, high resolution, imaging. The utility of the design was successfully demonstrated through the stochastic seeding and imaging of green fluorescent protein expressing Escherichia coli using both fluorescence and brightfield microscopies. (C) 2016 American Vacuum Society.
  • ItemOpen Access
    Remembering ICC 16
    (2016-09-27) Hohn, Keith L.; hohn; Hohn, Keith L.
    Every four years, a group of outstanding individuals, the best in their field, come together from all over the world. These individuals have spent years learning their craft, and now they assemble to show what they can do. Such a gathering happened in 2016.
  • ItemOpen Access
    Towards sustainable agriculture: fossil-free ammonia
    (2017-05-01) Pfromm, Peter H.; pfromm; Pfromm, Peter H.
    About 40% of our food would not exist without synthetic ammonia (NH3) for fertilization. Yet, NH3 production is energy intensive. About 2% of the world's commercial energy is consumed as fossil fuels for NH3 synthesis based on the century-old Haber-Bosch (H.-B.) process. The state of the art and the opportunities for reducing the fossil energy footprint of industrial H.-B. NH3 synthesis are discussed. It is shown that even a hypothetical utterly revolutionary H.-B. catalyst could not significantly reduce the energy demand of H.-B. NH3 as this is governed by hydrogen production. Renewable energy-enabled, fossil-free NH3 synthesis is then evaluated based on the exceptional and continuing cost decline of renewable electricity. H.-B. syngas (H2, N2) is assumed to be produced by electrolysis and cryogenic air separation, and then supplied to an existing H.-B. synthesis loop. Fossil-free NH3 could be produced for energy costs of about $232 per tonne NH3 without claiming any economic benefits for the avoidance of about 1.5 tonnes of CO2 released per tonne NH3 compared to the most efficient H.-B. implementations. Research into alternatives to the H.-B. process might be best targeted at emerging markets with currently little NH3 synthesis capacity but significant future population growth such as Africa. Reduced capital intensity, good scale-down economics, tolerance for process upsets and contamination, and intermittent operability are some desirable characteristics of NH3 synthesis in less developed markets, and for stranded resources. Processes that are fundamentally different from H.-B. may come to the fore under these specific boundary conditions.
  • ItemOpen Access
    Self-healing in B12P2 through Mediated Defect Recombination
    (2016-11-09) Huber, S. P.; Gullikson, E.; Frye, Clint D.; Edgar, James H.; van de Kruijs, R. W. E.; Bijkerk, F.; Prendergast, D.; edgarjh; Frye, Clint D.; Edgar, James H.
    The icosahedral boride B12P2 has been reported to exhibit “self-healing” properties, after transmission electron microscopy recordings of sample surfaces, which were exposed to highly energetic particle beams, revealed little to no damage. In this work, employing calculations from first-principles within the density functional theory (DFT) framework, the structural characteristics of boron interstitial and vacancy defects in B12P2 are investigated. Using nudged elastic band simulations, the diffusion properties of interstitial and vacancy defects and their combination, in the form of Frenkel defect pairs, are studied. We find that boron icosahedra maintain their structural integrity even when in a degraded state in the presence of a vacancy or interstitial defect and that the diffusion activation energy for the recombination of an interstitial vacany pair can be as low as 3 meV, in line with the previously reported observation of “self-healing”.
  • ItemOpen Access
    Detection of defect populations in superhard semiconductor boron subphosphide B12P2 through X-ray absorption spectroscopy
    (2017-03-06) Huber, S. P.; Gullikson, E.; Meyer-Ilse, J.; Frye, Clint D.; Edgar, James H.; van de Kruijs, R. W. E.; Bijkerk, F.; Prendergast, D.; edgarjh; Frye, Clint D.; Edgar, James H.
    Recent theoretical work has shown for the first time how the experimentally observed property of “self-healing” of the superhard semiconductor boron subphosphide (B12P2) arises through a process of mediated defect recombination. Experimental verification of the proposed mechanism would require a method that can detect and distinguish between the various defect populations that can exist in B12P2. X-ray absorption near-edge spectroscopy (XANES) is such a method and in this work we present experimentally collected spectra of B12P2samples with varying crystalline qualities. By simulating the X-ray spectroscopic signatures of potential crystallographic point defects from first-principles within the density functional theory framework, the presence of defect populations can be determined through spectroscopic fingerprinting. Our results find an increasing propensity for the presence of phosphorus vacancy defects in samples deposited at lower temperatures but no evidence for comparable populations of boron vacancies in all the samples that have been studied. The absence of large amounts of boron vacancies is in line with the “self-healing” property of B12P2.
  • ItemOpen Access
    Determining crystal phase purity in c-BP through X-ray absorption spectroscopy
    (2017-02-02) Huber, S. P.; Medvedev, V. V.; Gullikson, E.; Padavala, Balabalaji; Edgar, James H.; van de Kruijs, R. W. E.; Bijkerk, F.; Prendergast, D.; edgarjh; Padavala, Balabalaji; Edgar, James H.
    We employ X-ray absorption near-edge spectroscopy at the boron K-edge and the phosphorus L2,3-edge to study the structural properties of cubic boron phosphide (c-BP) samples. The X-ray absorption spectra are modeled from first-principles within the density functional theory framework using the excited electron core-hole (XCH) approach. A simple structural model of a perfect c-BP crystal accurately reproduces the P L2,3-edge, however it fails to describe the broad and gradual onset of the B K-edge. Simulations of the spectroscopic signatures in boron 1s excitations of intrinsic point defects and the hexagonal BP crystal phase show that these additions to the structural model cannot reproduce the broad pre-edge of the experimental spectrum. Calculated formation enthalpies show that, during the growth of c-BP, it is possible that amorphous boron phases can be grown in conjunction with the desired boron phosphide crystalline phase. In combination with experimental and theoretically obtained X-ray absorption spectra of an amorphous boron structure, which have a similar broad absorption onset in the B K-edge spectrum as the cubic boron phosphide samples, we provide evidence for the presence of amorphous boron clusters in the synthesized c-BP samples.
  • ItemOpen Access
    Membrane Technology for the Recovery of Lignin: A Review
    (2016-09-06) Humpert, D.; Ebrahimi, M.; Czermak, Peter; pczermak; Czermak, Peter
    Utilization of renewable resources is becoming increasingly important, and only sustainable processes that convert such resources into useful products can achieve environmentally beneficial economic growth. Wastewater from the pulp and paper industry is an unutilized resource offering the potential to recover valuable products such as lignin, pigments, and water [1]. The recovery of lignin is particularly important because it has many applications, and membrane technology has been investigated as the basis of innovative recovery solutions. The concentration of lignin can be increased from 62 to 285 g.L-1 using membranes and the recovered lignin is extremely pure. Membrane technology is also scalable and adaptable to different waste liquors from the pulp and paper industry.
  • ItemOpen Access
    Stochastic Assembly of Bacteria in Microwell Arrays Reveals the Importance of Confinement in Community Development
    (2016-05-06) Hansen, Ryan R.; Timm, A. C.; Timm, C. M.; Bible, A. N.; Morrell-Falvey, J. L.; Pelletier, D. A.; Simpson, M. L.; Doktycz, M. J.; Retterer, S. T.; rrhansen; Hansen, Ryan R.
    The structure and function of microbial communities is deeply influenced by the physical and chemical architecture of the local microenvironment and the abundance of its community members. The complexity of this natural parameter space has made characterization of the key drivers of community development difficult. In order to facilitate these characterizations, we have developed a microwell platform designed to screen microbial growth and interactions across a wide variety of physical and initial conditions. Assembly of microbial communities into microwells was achieved using a novel biofabrication method that exploits well feature sizes for control of innoculum levels. Wells with incrementally smaller size features created populations with increasingly larger variations in inoculum levels. This allowed for reproducible growth measurement in large (20 mu m diameter) wells, and screening for favorable growth conditions in small (5, 10 mu m diameter) wells. We demonstrate the utility of this approach for screening and discovery using 5 mu m wells to assemble P. aeruginosa colonies across a broad distribution of innoculum levels, and identify those conditions that promote the highest probability of survivial and growth under spatial confinement. Multi-member community assembly was also characterized to demonstrate the broad potential of this platform for studying the role of member abundance on microbial competition, mutualism and community succession.
  • ItemOpen Access
    Preliminary results on growing second generation biofuel crop miscanthus X Giganteus at the polluted military site in Ukraine
    (2020-01-01) Pidlisnyuk, V.; Trögl, J.; Stefanovska, T.; Shapoval, P.; Erickson, Larry E.; lerick; Erickson, Larry E.
    The semi-field research on using second-generation biofuel crop Miscanthus x giganteus for restoration of former military site in Kamenetz-Podilsky, Ukraine was carried out during two vegetation seasons. Despite high metal pollution of soil, in particular, by Fe, Mn, Ti, and Zr, no growth inhibition was observed. The concentrations followed pattern soil > roots > stems > leaves. Accumulation of particular metals in roots was different: Fe, Mn and Ti were accumulated rather palpably after the first vegetation season and less tangible after the second one. Cu, Pb and Zn were less accumulative in both vegetation seasons, and for As and Pb the accumulative concentrations were very small. Accumulations in the aboveground parts of the plant in comparison to roots were significantly lower in case of Fe, Ti, Mn, Cu, Zn, Sr and even statistically comparable to zero in case of As, Pb and Zr. Calculated translocation ratio of metals in the plant's parts preferably indicated lack of metals' hyper accumulation. Generally, no correlations were observed between concentrations of metals in the soil and in the upper plant's parts. The research confirmed the ability of Miscanthus x giganteus to grow on the military soils predominantly contaminated by metals. © by Josef Trögl 2016.
  • ItemOpen Access
    Hydride CVD Hetero-epitaxy of B12P2 on 4 H-SiC
    (2017-02-01) Frye, C.D.; Saw, C.K.; Padavala, Balabalaji; Nikolić, R.J.; Edgar, James H.; edgarjh
    Icosahedral boron phosphide (B12P2) is a wide bandgap semiconductor (3.35 eV) that has been reported to “self-heal” from high-energy electron bombardment, making it attractive for potential use in radioisotope batteries, radiation detection, or in electronics in high radiation environments. This study focused on improving B12P2 hetero-epitaxial films by growing on 4 H-SiC substrates over the temperature range of 1250–1450 °C using B2H6 and PH3 precursors in a H2 carrier gas. XRD scans and Laue transmission photographs revealed that the epitaxial relationship was View the MathML source. The film morphology and crystallinity were investigated as a function of growth temperature and growth time. At 1250 °C, films tended to form rough, polycrystalline layers, but at 1300 and 1350 °C, films were continuous and comparatively smooth (View the MathML source). At 1400 or 1450 °C, the films grew in islands that coalesced as the films became thicker. Using XRD rocking curves to evaluate the crystal quality, 1300 °C was the optimum growth temperature tested. At 1300 °C, the rocking curve FWHM decreased with increasing film thickness from 1494 arcsec for a 1.1 μm thick film to 954 arcsec for a 2.7 μm thick film, suggesting a reduction in defects with thickness.
  • ItemOpen Access
    A fast and simple assay to quantify bacterial leukotoxin activity
    (2016-11-01) Oppermann, Tobias; Schwarz, Stefan; Busse, Nadine; Czermak, Peter; pczermak
    Background: Mannheimia haemolytica is the primary bacterial pathogen in causing bovine respiratory disease with tremendous annual losses in the cattle industry. The leukotoxin from M. haemolytica is the predominant virulence factor. Several leukotoxin activity assays are available but not standardized regarding sample preparation and cell line. Furthermore, these assays suffer from a high standard error, a prolonged time consumption and often complex sample pretreatments, which is important from the bioprocess engineering point of view. Results: Within this study, an activity assay based on the continuous cell line BL3.1 combined with a commercial available adenosine triphosphate viability assay kit was established. The leukotoxin activity was found to be strongly dependent on the sample preparation. Furthermore, the interfering effect of lipopolysaccharides in the sample could be successfully suppressed by adding polymyxin B. We reached a maximum relative P95 value of 14%, which is more than seven times lower compared to current available assays as well as a time reduction up to 88%. Conclusion: Ultimately, the established leukotoxin activity assay is simple, fast and has a high reproducibility. Critical parameters regarding the sample preparation were characterized and optimized making complex sample purification superfluous.
  • ItemOpen Access
    CVD growth and properties of boron phosphide on 3C-SiC
    (2016-09-01) Padavala, Balabalaji; Frye, C.D.; Wang, Xuejing; Raghothamachar, Balaji; Edgar, James H.; edgarjh
    Improving the crystalline quality of boron phosphide (BP) is essential for realizing its full potential in semiconductor device applications. In this study, 3C-SiC was tested as a substrate for BP epitaxy. BP films were grown on 3C-SiC(100)/Si, 3C-SiC(111)/Si, and 3C-SiC(111)/4H-SiC(0001) substrates in a horizontal chemical vapor deposition (CVD) system. Films were produced with good crystalline orientation and morphological features in the temperature range of 1000–1200 °C using a PH3+B2H6+H2 mixture. Rotational twinning was absent in the BP due to the crystal symmetry-matching with 3C-SiC. Confocal 3D Raman imaging of BP films revealed primarily uniform peak shift and peak widths across the scanned area, except at defects on the surface. Synchrotron white beam X-ray topography showed the epitaxial relationship between BP and 3C-SiC was (100)(100)〈011〉〈011〉BP||(100)(100)〈011〉〈011〉3C-SiC and (111)(111)View the MathML source〈112̅〉BP||(111)(111)View the MathML source〈112̅〉3C-SiC. Scanning electron microscopy, Raman spectroscopy and X-ray diffraction analysis indicated residual tensile strain in the films and improved crystalline quality at temperatures below 1200 °C. These results indicated that BP properties could be further enhanced by employing high quality bulk 3C-SiC or 3C-SiC epilayers on 4H-SiC substrates.
  • ItemOpen Access
    Nature of exciton transitions in hexagonal boron nitride
    (2016-03-01) Li, J.; Cao, X. K.; Hoffman, Timothy B.; Edgar, James H.; Lin, J. Y.; Jiang, H. X.; edgarjh
    In contrast to other III-nitride semiconductors GaN and AlN, the intrinsic (or free) exciton transition in hexagonal boron nitride (h-BN) consists of rather complex fine spectral features (resolved into six sharp emission peaks) and the origin of which is still unclear. Here, the free exciton transition (FX) in h-BN bulk crystals synthesized by a solution method at atmospheric pressure has been probed by deep UV time-resolved photoluminescence (PL) spectroscopy. Based on the separations between the energy peak positions of the FX emission lines, the identical PL decay kinetics among different FX emission lines, and the known phonon modes in h-BN, we suggest that there is only one principal emission line corresponding to the direct intrinsic FX transition in h-BN, whereas all other fine features are a result of phonon-assisted transitions. The identified phonon modes are all associated with the center of the Brillouin zone. Our results offer a simple picture for the understanding of the fundamental exciton transitions in h-BN. (C) 2016 AIP Publishing LLC.
  • ItemOpen Access
    Controlling condensation and frost growth with chemical micropatterns
    (2016-01-22) Boreyko, J. B.; Hansen, Ryan R.; Murphy, K. R.; Nath, S.; Retterer, S. T.; Collier, C. P.; rrhansen
    In-plane frost growth on chilled hydrophobic surfaces is an inter-droplet phenomenon, where frozen droplets harvest water from neighboring supercooled liquid droplets to grow ice bridges that propagate across the surface in a chain reaction. To date, no surface has been able to passively prevent the in-plane growth of ice bridges across the population of supercooled condensate. Here, we demonstrate that when the separation between adjacent nucleation sites for supercooled condensate is properly controlled with chemical micropatterns prior to freezing, inter-droplet ice bridging can be slowed and even halted entirely. Since the edge-to-edge separation between adjacent supercooled droplets decreases with growth time, deliberately triggering an early freezing event to minimize the size of nascent condensation was also necessary. These findings reveal that inter-droplet frost growth can be passively suppressed by designing surfaces to spatially control nucleation sites and by temporally controlling the onset of freezing events.
  • ItemOpen Access
    A New Year of Catalysts
    (2016-01-19) Hohn, Keith L.; hohn
    Excerpt: Welcome to a new year of Catalysts, an international, peer-reviewed open access journal. From time to time, I like to write about the status of the journal: what milestones have been reached, what special issues will be coming out, what conferences we will partner with, etc. As we turn to the New Year, this seems like an opportune time to provide an update on Catalysts.
  • ItemOpen Access
    Photocurrent response of B12As2 crystals to blue light, and its temperature-dependent electrical characterizations
    (2016-01-01) Gul, R.; Cui, Y.; Bolotnikov, A. E.; Camarda, G. S.; Egarievwe, S. U.; Hossain, A.; Roy, U. N.; Yang, G.; Edgar, James H.; Nwagwu, U.; James, R. B.; edgarjh
    With the global shortage of He-3 gas, researchers worldwide are looking for alternative materials for detecting neutrons. Among the candidate materials, semiconductors are attractive because of their light weight and ease in handling. Currently, we are looking into the suitability of boron arsenide (B12As2) for this specific application. As the first step in evaluating the material qualitatively, the photo-response of B12As2 bulk crystals to light with different wavelengths was examined. The crystals showed photocurrent response to a band of 407- and 470- nm blue light. The maximum measured photoresponsivity and the photocurrent density at 0.7 V for 470 nm blue light at room temperature were 0.25 A.W-1 and 2.47, respectively. In addition to photo current measurements, the electrical properties as a function of temperature (range: 50-320 K) were measured. Reliable data were obtained for the low-temperature I-V characteristics, the temperature dependence of dark current and its density, and the resistivity variations with temperature in B12As2 bulk crystals. The experiments showed an exponential dependence on temperature for the dark current, current density, and resistivity; these three electrical parameters, respectively, had a variation of a few nA to mu A, 1-100 mu and 7.6x10(5)-7.7x10(3), for temperature increasing from 50 K to 320 K. The results from this study reported the first photoresponse and demonstrated that B12As2 is a potential candidate for thermal-neutron detectors. (C) 2016 Author(s).