Publications

2018
S. Y. Shin, Deshpande, A., and Sulzer, J., “Design of an Underactuated, Adaptable Electromechanical Gait Trainer for People with Neurological Injury,” Journal of Mechanisms and Robotics, 2018.
Z. Sun, Tang, H., Espinoza, N. D., Balhoff, M. T., and Killough, J. E., “Discrete element modeling of grain crushing and implications on reservoir compaction,” Journal of Petroleum Science and Engineering, 2018. Publisher's Version
J. Zhao, Wang, G., del Mundo, I. M., McKinney, J. A., Lu, X., Bacolla, A., Boulware, S. B., Zhang, C., Zhang, H., Ren, P., and others,Distinct Mechanisms of Nuclease-Directed DNA-Structure-Induced Genetic Instability in Cancer Genomes,” Cell reports, vol. 22, pp. 1200–1210, 2018.
J. Chen, Hamann, D. M., Choi, D. S., Poudel, N., Shen, L., Shi, L., Johnson, D. C., and Cronin, S. B., “Enhanced Cross-plane Thermoelectric Transport of Rotationally-disordered SnSe2 via Se Vapor Annealing,” Nano Letters, vol. 18, no. 11, pp. 6876–6881, 2018. Publisher's Version
X. Xu, Kwon, H., Gawlik, B., Estakhri, N. M., Alu, A., Sreenivasan, S. V., and Dodabalapur, A., “Enhanced Photoresponse in Metasurface-Integrated Organic Photodetectors,” Nano Lett., vol. 18, no. 6, pp. 3362-3367, 2018. DOIAbstract
In this work, we experimentally demonstrate metasurface-enhanced photoresponse in organic photodetectors. We have designed and integrated a metasurface with broadband functionality into an organic photodetector, with the goal of significantly increasing the absorption of light and generated photocurrent from 560 up to 690 nm. We discuss how the metasurface can be integrated with the fabrication of an organic photodiode. Our results show large gains in responsivity from 1.5x to 2X between 560 and 690 nm.
E. Fleming, Kholmanov, I., and Shi, L., “Enhanced specific surface and thermal conductivity in ultrathin graphite foams grown by chemical vapor deposition on sintered nickel powder templates,” Carbon, vol. 136, pp. 380-386, 2018. Publisher's Version
J. Chen, Kim, J., Poudel, N., Hou, B., Shen, L., Shi, H., Shi, L., and Cronin, S., “Enhanced thermoelectric efficiency in topological insulator Bi2Te3 nanoplates via atomic layer deposition-based surface passivation,” Applied Physics Letters, vol. 113, pp. 083904, 2018. Publisher's Version
W. Lin, Bergquist, A. M., Mohanty, K. K., and Werth, C. J., “Environmental impacts of replacing slickwater with low/no-water fracturing fluids for shale gas recovery,” ACS Sustainable Chemistry & Engineering, vol. 6, no. 6, pp. 7515-7524, 2018. Publisher's VersionAbstract
The environmental impacts of a typical hydraulic fracturing operation for shale gas recovery were evaluated using life cycle assessment, with energy demands for well drilling and fracturing determined from GHGfrack model. Dominant environmental impacts stem from well construction, which are >63% in all categories (e.g., global warming and eutrophication), and mainly due to diesel fuel combustion and steel production. The relative impacts related to water use (i.e., fracturing fluid components, water/wastewater transportation, and wastewater disposal) are relatively small, ranging from 5 to 22% of total impacts in all categories; freshwater consumption for fracturing is also a small fraction of available water resources for the shale play considered. The impacts of replacing slickwater with CO2 or CH4-foam fracturing fluid (≤10 vol % water) were evaluated; total impacts decrease <12%, and relative impacts related to water use decrease to 2–9% of total impacts. Hence, switching to a foam-based fracturing fluid can substantially decrease water-related impacts (>60%) but has only marginal effects on total environmental impacts. Changes in lateral well length, produced to fresh-water ratios, fracturing fluid composition, and LCA control volume do not change these findings. More benefits could potentially be realized by considering water versus foam-related impacts of ecological health and energy production.
J. K. Bean, Bhandari, S., Bilotto, A., and Hildebrandt Ruiz, L., “Formation of Particulate Matter from the Oxidation of Evaporated Hydraulic Fracturing Wastewater,” Environmental Science & Technology, vol. 52, no. 8, pp. 4960-4968, 2018. Publisher's Version
M. Sivaguru, Saw, J. J., Jr., J. W. C., Lieske, J. C., Krambeck, A. E., Romero, M. F., Chia, N., Schwaderer, A. L., Alcalde, R. E., Bruce, W. J., Wildman, D. E., Fried, G. A., Werth, C. J., Reeder, R. J., Sanford, R. A., and Fouke, B. W., “Geobiology reveals how human kidney stones dissolve in vivo,” Scientific Reports, vol. 8, pp. 13731, 2018. Publisher's VersionAbstract
More than 10% of the global human population is now afflicted with kidney stones, which are commonly associated with other significant health problems including diabetes, hypertension and obesity. Nearly 70% of these stones are primarily composed of calcium oxalate, a mineral previously assumed to be effectively insoluble within the kidney. This has limited currently available treatment options to painful passage and/or invasive surgical procedures. We analyze kidney stone thin sections with a combination of optical techniques, which include bright field, polarization, confocal and super-resolution nanometer-scale auto-fluorescence microscopy. Here we demonstrate using interdisciplinary geology and biology (geobiology) approaches that calcium oxalate stones undergo multiple events of dissolution as they crystallize and grow within the kidney. These observations open a fundamentally new paradigm for clinical approaches that include in vivo stone dissolution and identify high-frequency layering of organic matter and minerals as a template for biomineralization in natural and engineered settings.
I. Shovkun and Espinoza, N. D., “Geomechanical implications of dissolution of mineralized natural fractures in shale formations,” Journal of Petroleum Science and Engineering, vol. 160, pp. 555–564, 2018. Publisher's Version
Google Scholar Profile”. 2018. Link to Google Scholar
C. Faxon, Dhulipala, S. V., Allen, D. T., and Hildebrandt Ruiz, L., “Heterogeneous Production of Cl2 from Particulate Chloride Measured in Environmental Chamber Experiments,” American Institute of Chemical Engineers Journal, Futures Issue: Reaction Engineering, Kinetics, and Catalysis, 2018. Publisher's Version
Z. Pan, Xu, X., Chung, C. -jui, Dalir, H., Yan, H., Chen, K., Wang, Y., Jia, B., and Chen, R. T., “High-Speed Modulator Based on Electro-Optic Polymer Infiltrated Subwavelength Grating Waveguide Ring Resonator,” Laser & Photonics Reviews, 2018. Publisher's VersionAbstract
Silicon‐organic hybrid integrated devices show great potential in high‐speed optical interconnects and sensors. In this paper, a high‐speed modulator based on an electro‐optic (EO) polymer (SEO125) infiltrated sub‐wavelength grating (SWG) waveguide ring resonator is presented. The core of the SWG waveguide consists of periodically arranged silicon pillars along the light propagation direction, which provides large mode volume overlap with EO polymer. The optimized SWG shows a mode volume overlap of 36.2% with a silicon duty cycle of 0.7. The 3‐dB modulation bandwidth of the fabricated modulator is measured to be larger than 40 GHz occupying an area of 70 μm x 29 μm, which is the largest bandwidth and the most compact footprint that has been demonstrated for ring resonators on the silicon‐organic hybrid platform.
PDF icon PDF
In-plane thermal conductivity measurement with nanosecond grating imaging tehchnique
J. Jeong, Chen, K., Walker, E. S., Roy, N., He, F., Liu, P., Willson, G. C., Cullinan, M., Bank, S. R., and Wang, Y., “In-plane thermal conductivity measurement with nanosecond grating imaging tehchnique,” Nanoscale and Microscale Thermophyical Engineering, vol. 22, no. 2, pp. 83-96, 2018. Publisher's VersionAbstract
We develop a nanosecond grating imaging (NGI) technique to measure in-plane thermal transport properties in bulk and thin-film samples. Based on nanosecond time-domain thermoreflectance (ns-TDTR), NGI incorporates a photomask with periodic metal strips patterned on a transparent dielectric substrate to generate grating images of pump and probe lasers on the sample surface, which induces heat conduction along both cross- and in-plane directions. Analytical and numerical models have been developed to extract thermal conductivities in both bulk and thin-film samples from NGI measurements. This newly developed technique is used to determine thickness-dependent in-plane thermal conductivities (κx) in Cu nano-films, which agree well with the electron thermal conductivity values converted from four-point electrical conductivity measurements using the Wiedemamn–Franz law, as well as previously reported experimental values. The κx measured with NGI in an 8 nm x 8 nm GaAs/AlAs superlattice (SL) is about 10.2 W/m⋅K, larger than the cross-plane thermal conductivity (8.8 W/m⋅K), indicating the anisotropic thermal transport in the SL structure. The uncertainty of the measured κx is about 25% in the Cu film and less than 5% in SL. Sensitivity analysis suggests that, with the careful selection of proper substrate and interface resistance, the uncertainty of κx in Cu nano-films can be as low as 5%, showing the potential of the NGI technique to determine κx in thin films with improved accuracy. By simply installing a photomask into ns-TDTR, NGI provides a convenient, fast, and cost-effective method to measure the in-plane thermal conductivities in a wide range of structures and materials.
PDF icon PDF
D. S. Choi, Poudel, N., Park, S., Akinwande, D., Cronin, S. B., Watanabe, K., Taniguchi, T., Yao, Z., and Shi, L., “Large Reduction of Hot Spot Temperature in Graphene Electronic Devices with Heat-Spreading Hexagonal Boron Nitride,” ACS Applied Materials & Interfaces, vol. 10 , pp. 11101–11107, 2018. Publisher's Version
J. A. Valdez and Tinney, C. E., “Measurements of a Mach 3 jet using high-speed optical flow techniques,” AIAA/CEAS Aeroacoustics Conference, AIAA Paper 2018-3148. Atlanta, Georgia, USA, 2018.Abstract
The design and construction of various high-speed digital optical flow techniques forstudying the aeroacoustics and turbulence dynamics, as it relates to supersonic/hypersonicflow phenomena, is discussed. The three systems comprise retroreflective shadowgraphy, a z-type schlieren and a focused schlieren system. The performance of the three systems are examined using an axisymmetric Mach 3 flow, which has received considerable attention at the University of Texas at Austin for understanding the sound produced by flows with supersonic convective acoustic Mach numbers. Various techniques to aid in the setup of optical elements in conjunction with the high resolution digital cameras, capable of producing a million frames per second, are described. Various analysis methods are then employed (wavenumer-frequency transforms and wavelet analysis) to quantify the dynamical nature of the flow and sound field produced by this supersonic nozzle.
C. E. Schaefer, Ho, P., Berns, E., and Werth, C. J., “Mechanisms for abiotic dechlorination of TCE by ferrous minerals under oxic and anoxic conditions in natural sediments,” Environmental Science & Technology, 2018. Publisher's VersionAbstract
Bench-scale experiments were performed on natural sediments to assess abiotic dechlorination of trichloroethene (TCE) under both aerobic and anaerobic conditions. In the absence of oxygen (<26 µM), TCE dechlorination proceeded via a reductive pathway generating acetylene and/or ethene. Reductive dechlorination rate constants up to 3.1 x 10-5 d-1 were measured, after scaling to in situ solid water ratios. In the presence of oxygen greater than 120 µM, TCE dechlorination proceeded via an oxidative pathway generating formic/glyoxylic and glycolic/acetic acids, and oxidative dechlorination rate constants (again scaled to in situ conditions) up to 7.4 x 10-3 d-1 were measured. These rates correspond to half-lives of 60 and 0.25 years for abiotic TCE dechlorination under anaerobic and aerobic conditions, respectively, indicating the potentially large impact of aerobic TCE oxidation in the field. For both reductive and oxidative TCE dechlorination pathways, measured first-order rate constants increased with increasing ferrous iron content, suggesting the role of iron oxidation. Hydroxyl radical formation was measured and increased with increasing oxygen and ferrous iron content. Rate constants associated with TCE oxidation products increased with increasing hydroxyl radical generation rates, and are zero in the presence of a hydroxyl radical scavenger, suggesting that oxidative TCE dechlorination is a hydroxyl radical driven process.
S. Qu, Hu, M. - B., Wang, Y., and Song, T., “Modeling the influences of Ag or Au nanoparticles on the solar energy absorption and photocatalytic properties of N-TiO2,” Optics Communications, vol. 407, pp. 375-380, 2018. Publisher's VersionAbstract
Metallic nanoparticles have unique optical properties such as localized surface plasmon resonance (LSPR) effect, which can be used to improve the energy absorption and photocatalytic properties of semiconductor bases. In this paper, we construct a model to study the influence of Ag or Au nanoparticles (cubes or spheres) on the solar energy absorption and photocatalytic properties of nitrogen doped TiO2 (or N-TiO2). Effects of specific nanoparticle coupling parameters, such as particle shape, size, doping period (metal–metal distance) and separation distance (metal–semiconductor distance), on the properties of N-TiO2 are studied in detail. We show that the photocurrent improvement can be optimized by setting suitable geometric parameters. In particular, the separation distance between metallic nanoparticles and N-TiO2D should be around 6–7 nm, and the period of doping P should be around 360 nm. The silver cubes with edge length  show the best performance. The results can help the design of solar energy materials, in which metallic nanoparticles may play an important role.
A. Cherala and Sreenivasan, S. V., “Molecular dynamics modeling framework for overcoming nanoshape retention limits of imprint lithography,” Microsystems & Nanoengineering, vol. 4, no. 3, 2018. Publisher's VersionAbstract
Complex nanoshaped structures (nanoshape structures here are defined as shapes enabled by sharp corners with radius of curvature <5 nm) have been shown to enable emerging nanoscale applications in energy, electronics, optics, and medicine. This nanoshaped fabrication at high throughput is well beyond the capabilities of advanced optical lithography. While the highest-resolution e-beam processes (Gaussian beam tools with non-chemically amplified resists) can achieve <5 nm resolution, this is only available at very low throughputs. Large-area e-beam processes, needed for photomasks and imprint templates, are limited to similar to 18 nm half-pitch lines and spaces and similar to 20 nm half-pitch hole patterns. Using nanoimprint lithography, we have previously demonstrated the ability to fabricate precise diamond-like nanoshapes with similar to 3 nm radius corners over large areas. An exemplary shaped silicon nanowire ultracapacitor device was fabricated with these nanoshaped structures, wherein the half-pitch was 100 nm. The device significantly exceeded standard nanowire capacitor performance (by 90%) due to relative increase in surface area per unit projected area, enabled by the nanoshape. Going beyond the previous work, in this paper we explore the scaling of these nanoshaped structures to 10 nm half-pitch and below. At these scales a new "shape retention" resolution limit is observed due to polymer relaxation in imprint resists, which cannot be predicted with a linear elastic continuum model. An all-atom molecular dynamics model of the nanoshape structure was developed here to study this shape retention phenomenon and accurately predict the polymer relaxation. The atomistic framework is an essential modeling and design tool to extend the capability of imprint lithography to sub-10 nm nanoshapes. This framework has been used here to propose process refinements that maximize shape retention, and design template assist features (design for nanoshape retention) to achieve targeted nanoshapes.

Pages