Academic Appointments


  • Engr Res Assoc, Mechanical Engineering

Professional Education


  • Ph.D., Stanford University, Mechanical Engineering (2016)
  • Ph.D. minor, Stanford University, Electrical Engineering (2016)
  • M.S., Stanford University, Civil and Environmental Engineering (2011)
  • B.S., Tsinghua University, Environmental Engineering (2009)

All Publications


  • Extending the limits of Pt/C catalysts with passivation-gas-incorporated atomic layer deposition NATURE CATALYSIS Xu, S., Kim, Y., Park, J., Higgins, D., Shen, S., Schindler, P., Thian, D., Provine, J., Torgersen, J., Graf, T., Schladt, T. D., Orazov, M., Liu, B., Jaramillo, T. F., Prinz, F. B. 2018; 1 (8): 624–30
  • Direct and continuous strain control of catalysts with tunable battery electrode materials SCIENCE Wang, H., Xu, S., Tsai, C., Li, Y., Liu, C., Zhao, J., Liu, Y., Yuan, H., Abild-Pedersen, F., Prinz, F. B., Norskov, J. K., Cui, Y. 2016; 354 (6315): 1031-1036

    Abstract

    We report a method for using battery electrode materials to directly and continuously control the lattice strain of platinum (Pt) catalyst and thus tune its catalytic activity for the oxygen reduction reaction (ORR). Whereas the common approach of using metal overlayers introduces ligand effects in addition to strain, by electrochemically switching between the charging and discharging status of battery electrodes the change in volume can be precisely controlled to induce either compressive or tensile strain on supported catalysts. Lattice compression and tension induced by the lithium cobalt oxide substrate of ~5% were directly observed in individual Pt nanoparticles with aberration-corrected transmission electron microscopy. We observed 90% enhancement or 40% suppression in Pt ORR activity under compression or tension, respectively, which is consistent with theoretical predictions.

    View details for DOI 10.1126/science.aaf7680

    View details for PubMedID 27885028

  • Variation of Energy Density of States in Quantum Dot Arrays due to Interparticle Electronic Coupling. Nano letters Logar, M., Xu, S., Acharya, S., Prinz, F. B. 2015; 15 (3): 1855-1860

    Abstract

    Subnanometer-resolved local electron energy structure was measured in PbS quantum dot superlattice arrays using valence electron energy loss spectroscopy with scanning transmission electron microscopy. We found smaller values of the lowest available transition energies and an increased density of electronic states in the space between quantum dots with shorter interparticle spacing, indicating extension of carrier wave functions as a result of interparticle electronic coupling. A quantum simulation verified both trends and illustrated the wave function extension effect.

    View details for DOI 10.1021/nl5046507

    View details for PubMedID 25670055

  • Effects of size polydispersity on electron mobility in a two-dimensional quantum-dot superlattice PHYSICAL REVIEW B Xu, S., Thian, D., Wang, S., Wang, Y., Prinz, F. B. 2014; 90 (14)
  • Electrical Properties of Ultrathin Platinum Films by Plasma-Enhanced Atomic Layer Deposition ACS APPLIED MATERIALS & INTERFACES Kim, H. K., Kaplan, K. E., Schindler, P., Xu, S., Winterkorn, M. M., Heinz, D. B., English, T. S., Provine, J., Prinz, F. B., Kenny, T. W. 2019; 11 (9): 9594–99

    Abstract

    The ability to deposit thin and conformal films has become of great importance because of downscaling of devices. However, because of nucleation difficulty, depositing an electrically stable and thin conformal platinum film on an oxide nucleation layer has proven challenging. By using plasma-enhanced atomic layer deposition (PEALD) and TiO2 as a nucleation layer, we achieved electrically continuous PEALD platinum films down to a thickness of 3.7 nm. Results show that for films as thin as 5.7 nm, the Mayadas-Shatzkes (MS) model for electrical conductivity and the Tellier-Tosser model for temperature coefficient of resistance hold. Although the experimental values start to deviate from the MS model below 5.7 nm because of incomplete Pt coverage, the films still show root mean square electrical stability better than 50 ppm over time, indicating that these films are not only electrically continuous but also sufficiently reliable for use in many practical applications.

    View details for DOI 10.1021/acsami.8b21054

    View details for Web of Science ID 000460996900096

    View details for PubMedID 30707831

    View details for PubMedCentralID PMC6407042

  • Nanostructuring Strategies To Increase the Photoelectrochemical Water Splitting Activity of Silicon Photocathodes ACS APPLIED NANO MATERIALS Hellstern, T. R., Nielander, A. C., Chakthranont, P., King, L. A., Willis, J. J., Xu, S., MacIsaac, C., Hahn, C., Bent, S. F., Prinz, F. B., Jaramillo, T. F. 2019; 2 (1): 6–11
  • Methodology for Studying Surface Chemistry and Evolution during the Nucleation Phase of Atomic Layer Deposition Using Scanning Tunneling Microscopy JOURNAL OF PHYSICAL CHEMISTRY C Thian, D., Yemane, Y. T., Xu, S., Prinz, F. B. 2017; 121 (49): 27379–88
  • Building upon the Koutecky-Levich Equation for Evaluation of Next-Generation Oxygen Reduction Reaction Catalysts ELECTROCHIMICA ACTA Xu, S., Kim, Y., Higgins, D., Yusuf, M., Jaramillo, T., Prinz, F. B. 2017; 255: 99–108
  • Atomically Flat Silicon Oxide Monolayer Generated by Remote Plasma JOURNAL OF PHYSICAL CHEMISTRY C Thian, D., Yemane, Y. T., Logar, M., Xu, S., Schindler, P., Winterkorn, M. M., Provine, J., Prinz, F. B. 2016; 120 (15): 8148-8156
  • Oscillatory barrier-assisted Langmuir-Blodgett deposition of large-scale quantum dot monolayers APPLIED SURFACE SCIENCE Xu, S., Dadlani, A. L., Acharya, S., Schindler, P., Prinz, F. B. 2016; 367: 500-506
  • Self-limiting atomic layer deposition of barium oxide and barium titanate thin films using a novel pyrrole based precursor JOURNAL OF MATERIALS CHEMISTRY C Acharya, S., Torgersen, J., Kim, Y., Park, J., Schindler, P., Dadlani, A. L., Winterkorn, M., Xu, S., Walch, S. P., Usui, T., Schildknecht, C., Prinz, F. B. 2016; 4 (10): 1945-1952

    View details for DOI 10.1039/c5tc03561a

    View details for Web of Science ID 000371671400003

  • Quantifying Geometric Strain at the PbS QD-TiO2 Anode Interface and Its Effect on Electronic Structures NANO LETTERS Trejo, O., Roelofs, K. E., Xu, S., Logar, M., Sarangi, R., Nordlund, D., Dadlani, A. L., Kravec, R., Dasgupta, N. P., Bent, S. F., Prinz, F. B. 2015; 15 (12): 7829-7836

    Abstract

    Quantum dots (QDs) show promise as the absorber in nanostructured thin film solar cells, but achieving high device efficiencies requires surface treatments to minimize interfacial recombination. In this work, lead sulfide (PbS) QDs are grown on a mesoporous TiO2 film with a crystalline TiO2 surface, versus one coated with an amorphous TiO2 layer by atomic layer deposition (ALD). These mesoporous TiO2 films sensitized with PbS QDs are characterized by X-ray and electron diffraction, as well as X-ray absorption spectroscopy (XAS) in order to link XAS features with structural distortions in the PbS QDs. The XAS features are further analyzed with quantum simulations to probe the geometric and electronic structure of the PbS QD-TiO2 interface. We show that the anatase TiO2 surface structure induces PbS bond angle distortions, which increases the energy gap of the PbS QDs at the interface.

    View details for DOI 10.1021/acs.nanolett.5b02373

    View details for Web of Science ID 000366339600008

    View details for PubMedID 26554814

  • Electrochemical tuning of vertically aligned MoS2 nanofilms and its application in improving hydrogen evolution reaction PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Wang, H., Lu, Z., Xu, S., Kong, D., Cha, J. J., Zheng, G., Hsu, P., Yan, K., Bradshaw, D., Prinz, F. B., Cui, Y. 2013; 110 (49): 19701-19706

    Abstract

    The ability to intercalate guest species into the van der Waals gap of 2D layered materials affords the opportunity to engineer the electronic structures for a variety of applications. Here we demonstrate the continuous tuning of layer vertically aligned MoS2 nanofilms through electrochemical intercalation of Li(+) ions. By scanning the Li intercalation potential from high to low, we have gained control of multiple important material properties in a continuous manner, including tuning the oxidation state of Mo, the transition of semiconducting 2H to metallic 1T phase, and expanding the van der Waals gap until exfoliation. Using such nanofilms after different degree of Li intercalation, we show the significant improvement of the hydrogen evolution reaction activity. A strong correlation between such tunable material properties and hydrogen evolution reaction activity is established. This work provides an intriguing and effective approach on tuning electronic structures for optimizing the catalytic activity.

    View details for DOI 10.1073/pnas.1316792110

    View details for PubMedID 24248362

  • Efficiency enhancement of solid-state PbS quantum dot-sensitized solar cells with Al2O3 barrier layer JOURNAL OF MATERIALS CHEMISTRY A Brennan, T. P., Trejo, O., Roelofs, K. E., Xu, J., Prinz, F. B., Bent, S. F. 2013; 1 (26): 7566-7571

    View details for DOI 10.1039/c3ta10903h

    View details for Web of Science ID 000320245400004

  • Effects of QD Surface Coverage in Solid-State PbS Quantum Dot-Sensitized Solar Cells 39th IEEE Photovoltaic Specialists Conference (PVSC) Roelofs, K. E., Brennan, T. P., Trejo, O., Xu, J., Prinz, F. B., Bent, S. F. IEEE. 2013: 1080–1083
  • Nickel Silicide Nanowire Arrays for Anti-Reflective Electrodes in Photovoltaics ADVANCED FUNCTIONAL MATERIALS Dasgupta, N. P., Xu, S., Jung, H. J., Iancu, A., Fasching, R., Sinclair, R., Prinz, F. B. 2012; 22 (17): 3650-3657
  • CO2 and its correlation with CO at a rural site near Beijing: implications for combustion efficiency in China ATMOSPHERIC CHEMISTRY AND PHYSICS Wang, Y., Munger, J. W., Xu, S., McElroy, M. B., Hao, J., Nielsen, C. P., Ma, H. 2010; 10 (18): 8881–97
  • Catalytic performance of manganese cobalt oxides on methane combustion at low temperature APPLIED CATALYSIS B-ENVIRONMENTAL Li, J., Liang, X., Xu, S., Hao, J. 2009; 90 (1-2): 307–12
  • Effects of support acidity on the reaction mechanisms of selective catalytic reduction of NO by CH4 in excess oxygen FRONTIERS OF ENVIRONMENTAL SCIENCE & ENGINEERING IN CHINA Xu, S., Li, J., Yang, D., Hao, J. 2009; 3 (2): 186–93
  • Promotional Mechanism of Sulfation on Selective Catalytic Reduction of NO by Methane in Excess Oxygen: A Comparative Study of Rh/Al2O3 and Rh/Al2O3/SO42- JOURNAL OF PHYSICAL CHEMISTRY C Xu, S., Li, J., Yang, D., Hao, J. 2008; 112 (41): 16052–59

    View details for DOI 10.1021/jp806301z

    View details for Web of Science ID 000259943300022