Publications

2017
N. Poudel, Liang, S. - J., Choi, D., Hou, B., Shen, L., Shi, H., Ang, L. K., Shi, L., and Cronin, S., “Cross-plane Thermoelectric and Thermionic Transport across Au/h-BN/Graphene Heterostructures,” Scientific Reports, vol. 7, pp. 14148, 2017. Publisher's Version
M. R. Tucker, Shirota, C., Lambercy, O., Sulzer, J. S., and Gassert, R., “Design and characterization of an exoskeleton for perturbing the knee during gait,” IEEE Transactions on Biomedical Engineering, vol. 64, no. 10, pp. 2331-2343, 2017.
N. Khusnatdinov, Resnick, D. J., Singhal, S., Grigas, M. M., and Sreenivasan, S. V., “Development Of An Inkjet-enabled Adaptive Planarization Process,” SPIE Photomask Technology Conference, vol. 10451. SPIE, Monterey CA, 2017. Publisher's VersionAbstract
Nanoimprint lithography manufacturing utilizes a patterning technology that involves the field-by-field deposition and exposure of a low viscosity resist deposited by jetting technology onto the substrate. The patterned mask is lowered into the fluid which then quickly flows into the relief patterns in the mask by capillary action. Following this filling step, the resist is crosslinked under UV radiation, and then the mask is removed, leaving a patterned resist on the substrate. The technology faithfully reproduces patterns with a higher resolution and greater uniformity compared to those produced by photolithography equipment. Throughputs of 80 wph have been demonstrated, and mix and match overlay of 3.7nm 3 sigma has been achieved. The technology has already been successfully applied as a demonstration to the fabrication of advanced NAND Flash memory devices. A similar approach can also be applied however to remove topography on an existing wafer, thereby creating a planar surface on which to pattern. In this paper, a novel adaptive planarization process is presented that addresses the problems associated with planarization of varying pattern densities, even in the presence of pre-existing substrate topography. The process is called Inkjet-enabled Adaptive Planarization (IAP). The IAP process uses an inverse optimization scheme, built around a validated fluid mechanics-based forward model that takes the pre-existing substrate topography and pattern layout as inputs. It then generates an inkjet drop pattern with a material distribution that is correlated with the desired planarization film profile. This allows a contiguous film to be formed with the desired thickness variation to cater to the topography and any parasitic signatures caused by the pattern layout. In this work, it was demonstrated that planarization efficiencies of up to 99.5% could be achieved, thereby reducing an initial similar to 100nm wafer topography down to as little as 0.6nm.
R. Edupuganti, Taliaferro, J. M., Wang, Q., Xie, X., Cho, E. J., Vidhu, F., Ren, P., Anslyn, E. V., Bartholomeusz, C., and Dalby, K. N., “Discovery of a potent inhibitor of MELK that inhibits expression of the anti-apoptotic protein Mcl-1 and TNBC cell growth,” Bioorganic & Medicinal Chemistry, vol. 25, no. 9, pp. 2609-2616, 2017.
Z. Sun, Espinoza, N. D., Balhoff, M. T., and Dewers, T. A., “Discrete element modeling of micro-scratch tests: investigation of mechanisms of CO2 alteration in reservoir rocks,” Rock Mechanics and Rock Engineering, vol. 50, pp. 3337–3348, 2017.
Z. Sun, Balhoff, M. T., Espinoza, N. D., and others,Discrete element modeling of micro-scratch tests on rocks altered by CO 2,” in 51st US Rock Mechanics/Geomechanics Symposium, 2017.
S. Misra, Torres-Verdín, C., Homan, D., and Rasmus, J., “Dispersive and directional effective electrical conductivity and dielectric permittivity of conductive-mineral-bearing samples derived from multi-frequency tensor electromagnetic induction measurements,” Geophysics, vol. 82, no. 4, pp. D211-D223, 2017.
C. E. Tinney, Hill, B., Valdez, J., Sirohi, J., and Cameron, C., “Drone acoustics at static thrust conditions,” American Helicopgter Society 73rd Annual Forum. Fort Worth, Texas, USA, 2017.Abstract
Multirotor drones are becoming increasingly popular in both the civilian and military sectors of our society. These compact gadgets come in a variety of sizes with the smallest ones measuring less than two inches in diameter, while larger ones can be in excess of five feet. Surprisingly, very little is known about their acoustical footprint, which is becoming a topic of broad importance given that these vehicles most often operate in populated areas. Thus, the objective of this paper is to provide a first principles understanding of the acoustical characteristics of hovering drones. To accomplish this, a new test stand was constructed at the Applied Research Laboratories at The University of Texas at Austin for studying various multirotor drone configurations. The drone test stand is capable of powering up to eight DC electric motors with adjustable arms that allow different rotor diameters to be tested. Rotor diameters ranging from 8 in to 12 in are studied and with configurations comprised of an isolated rotor, a quadcopter configuration and a hexacopter configuration. A six degree-of-freedom load cell is used to assess the aerodynamic performance of each drone configuration. Meanwhile, an azimuthal array of 1/2-inch microphones is placed between 2 and 3 hub-center diameters from the drone center thereby allowing the acoustic near-field to be quantified. The analysis is performed using standard statistical metrics such as Sound Pressure Level and Overall Sound Pressure Level and is presented to demonstrate the relationship between the number of rotors, the drone rotor size and it’s aerodynamic performance (thrust) relative to the far-field noise.
C. E. Tinney, Scott, K., Routon, M., Sirohi, J., and Ruf, J., “Effect of aeroelasticity on vibroacoustic loads during startup of large area ratio nozzles,” 23rd AIAA/CEAS Aeroacoustics Conference, AIAA Paper 2017-3361. Denver, Colorado, USA, 2017.Abstract
The vibroacoustic loads that form during the startup of both rigid and compliant wallhigh area ratio nozzles is investigated. The rigid wall nozzle is fabricated from 6061 aluminum while the compliant wall nozzles are formed from urethane-based elastomers in order to invoke aeroelastic coupling between the nozzle wall and the internal flow. Single point measurements of the nozzle lip displacement are synchronized with a pressure field microphone located behind the nozzle where the base of a vehicle would reside. Particularattention is drawn to the sound field during transition from free-shock separated flow torestricted shock separated flow, as well as the end-effects regime loads. The findings revealthe sensitivity of the vibroacoustic loads to the aeroelasticity of the nozzle wall duringcritical stages in the startup process.
E. J. Guiltinan, Cardenas, B. M., Bennett, P. C., Zhang, T., and Espinoza, N. D., “The effect of organic matter and thermal maturity on the wettability of supercritical CO2 on organic shales,” International Journal of Greenhouse Gas Control, vol. 65, pp. 15–22, 2017.
P. Sayar and Torres-Verdín, C., “Effective-medium modeling of velocity dispersion and attenuation in isotropic rocks.,” Geophysics, vol. 82, no. 2, pp. D133-D154, 2017.
P. Sayar and Torres-Verdín, C., “Effective-medium modeling of velocity dispersion and attenuation in isotropic rocks.,” Geophysics, vol. 82, no. 2, pp. D133-D154, 2017.
D. Choi, Poudel, N., Cronin, S. B., and Shi, L., “Effects of basal-plane thermal conductivity and interface thermal conductance on the hot spot temperature in graphene electronic devices,” Applied Physics Letters, vol. 110, pp. 073104, 2017. Publisher's Version
X. Chen, Jarvis, K., Sullivan, S., Li, Y., Zhou, J., and Shi, L., “Effects of grain boundaries and defects on anisotropic magnon transport in textured Sr14Cu24O41,” Phys. Rev. B, vol. 95, pp. 144310, 2017. Publisher's Version
J. Botto, Fuchs, S. J., Fouke, B. W., Clarens, A. F., Freiburg, J. T., Berger, P. M., and Werth, C. J., “Effects of Mineral Surface Properties on Supercritical CO2 Wettability in a Siliciclastic Reservoir,” Energy & Fuels, vol. 31, no. 5, pp. 5275-5285, 2017. Publisher's VersionAbstract
Wettability is a key reservoir characteristic influencing geological carbon sequestration (GCS) processes, such as CO2 transport and storage capacity. Wettability is often determined on a limited number of reservoir samples by measuring the contact angle at the CO2/brine/mineral interface, but the ability to predict this value remains a challenge. In this work, minerals comprising a natural reservoir sample were identified, and the influence of their surface roughness and mineralogy on the contact angle was quantified to evaluate predictive models and controlling mechanisms. The natural sample was obtained from the Mount Simon formation, a representative siliciclastic reservoir that is the site of a United States Department of Energy CO2 injection project. A thin section of the Mount Simon sandstone was examined with compound light microscopy and environmental scanning electron microscopy (ESEM) coupled with energy-dispersive X-ray spectroscopy (EDS). Quartz and feldspar were identified as dominant minerals and were coated with various reddish black precipitates consistent with illite clay and iron oxide hematite. Contact angle (θ) measurements were conducted for the four representative minerals and the Mount Simon sample over a range of pressures (2–25 MPa) at 40 °C. At supercritical conditions, all samples are strongly water-wet, with contact angles between 27° and 45°. Several predictive models for contact angle were evaluated for the mineral and Mount Simon samples, including the Wenzel and Cassie–Baxter models, plus newly proposed modifications of these that account for the fraction of different minerals comprising the reservoir sample surface, the surface roughness, and the extent that roughness pits are filled with brine. Modeling results suggest that the fraction of mineral surfaces containing roughness pits filled with brine is the most important reservoir characteristic that controls wettability in the Mount Simon sandstone, followed by surface mineralogy. To our knowledge, this is one of the few studies to investigate the effects of individual minerals on the wettability of a natural reservoir sample.
S. Deng, Wang, Q., and Ren, P., “Estimating and modeling charge transfer from the SAPT induction energy,” Journal of Computational Chemistry, 2017.
E. D. Maalouf and Torres-Verdín, C., “Estimation of rock stiffness coefficients in VTI formations using LWD acoustic measurements (Expanded Abstract),” Society of Petrophysicists and Well Log Analysts (SPWLA) 58th Ann. Logging Symposium. Oklahoma City, OK, June 17-21, 2017.
J. Selvakumar and Bakolas, E., “Evasion with Terminal Constraints from a Group of Pursuers using a
Matrix Game Formulation
,” American Control Conference. Seattle, WA, 2017.PDF icon jseb_acc17.pdf
K. Chen, Ghosh, R., Meng, X., Roy, A., Kim, J. - S., He, F., Mason, S. C., Xu, X., Lin, J. - F., Akinwande, D., Banerjee, S. K., and Wang, Y., “Experimental evidence of exciton capture by mid-gap defects in CVD grown monolayer MoSe2,” npj 2D Materials and Applications, vol. 1, pp. 1-15, 2017. Publisher's VersionAbstract
In two dimensional (2D) transition metal dichalcogenides, defect-related processes can significantly affect carrier dynamics and transport properties. Using femtosecond degenerate pump-probe spectroscopy, exciton capture, and release by mid-gap defects have been observed in chemical vapor deposition (CVD) grown monolayer MoSe2. The observed defect state filling shows a clear saturation at high exciton densities, from which the defect density is estimated to be around 0.5 × 1012/cm2. The exciton capture time extracted from experimental data is around ~ 1 ps, while the average fast and slow release times are 52 and 700 ps, respectively. The process of defect trapping excitons is found to exist uniquely in CVD grown samples, regardless of substrate and sample thickness. X-ray photoelectron spectroscopy measurements on CVD and exfoliated samples suggest that the oxygen-associated impurities could be responsible for the exciton trapping. Our results bring new insights to understand the role of defects in capturing and releasing excitons in 2D materials, and demonstrate an approach to estimate the defect density nondestructively, both of which will facilitate the design and application of optoelectronics devices based on CVD grown 2D transition metal dichalcogenides.
J. Shiriyev, Brick, Y., Zhang, P., Yilmaz, A. E., Torres-Verdín, C., Sharma, M., Hosbach, T., Oerkfitz, M. A., and Gabelmann, J., “Experiments and simulations of a prototype tri-axial electromagnetic induction logging tool for open-hole hydraulic fracture diagnostics,” Geophysics, vol. 83, no. 3, pp. D7-D81, 2017.

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