Bio


The Gu Group studies the mechanical behavior of nanomaterials. We work at the intersection of solid mechanics, materials science and nano-chemistry. We research the unique properties of nanoscale metals, ceramics and nano-architected composites in order to design strong, tough and lightweight structural materials, materials for extreme environments, and mechanically-actuated sensors. Our experimental tools include nanoindentation, electron microscopy, and colloidal synthesis.

Academic Appointments


Honors & Awards


  • Terman Faculty Fellow, Stanford Engineering (2017-2020)
  • National Defense Science and Engineering Graduate Fellowship, DoD (2011)
  • Fulbright Award, Fulbright (2009)

Professional Education


  • BS, University of California, Berkeley (2009)
  • MS/PhD, California Institute of Technology (2014)

2019-20 Courses


Stanford Advisees


  • Postdoctoral Faculty Sponsor
    Qi Li
  • Doctoral Dissertation Advisor (AC)
    David Doan, Mehrdad Kiani, Abhinav Parakh, Radhika Pramod Patil
  • Doctoral Dissertation Co-Advisor (AC)
    Chen Liu
  • Master's Program Advisor
    Delara Mohtasham, Tommy Pluschkell, Victor Zhang

All Publications


  • Tolerance to structural disorder and tunable mechanical behavior in self-assembled superlattices of polymer-grafted nanocrystals. Proceedings of the National Academy of Sciences of the United States of America Gu, X. W., Ye, X., Koshy, D. M., Vachhani, S., Hosemann, P., Alivisatos, A. P. 2017

    Abstract

    Large, freestanding membranes with remarkably high elastic modulus (>10 GPa) have been fabricated through the self-assembly of ligand-stabilized inorganic nanocrystals, even though these nanocrystals are connected only by soft organic ligands (e.g., dodecanethiol or DNA) that are not cross-linked or entangled. Recent developments in the synthesis of polymer-grafted nanocrystals have greatly expanded the library of accessible superlattice architectures, which allows superlattice mechanical behavior to be linked to specific structural features. Here, colloidal self-assembly is used to organize polystyrene-grafted Au nanocrystals at a fluid interface to form ordered solids with sub-10-nm periodic features. Thin-film buckling and nanoindentation are used to evaluate the mechanical behavior of polymer-grafted nanocrystal superlattices while exploring the role of polymer structural conformation, nanocrystal packing, and superlattice dimensions. Superlattices containing 3-20 vol % Au are found to have an elastic modulus of ∼6-19 GPa, and hardness of ∼120-170 MPa. We find that rapidly self-assembled superlattices have the highest elastic modulus, despite containing significant structural defects. Polymer extension, interdigitation, and grafting density are determined to be critical parameters that govern superlattice elastic and plastic deformation.

    View details for DOI 10.1073/pnas.1618508114

    View details for PubMedID 28242704

    View details for PubMedCentralID PMC5358368

  • Ultra-strong Architected Cu Meso-lattices Extreme Mechanics Letters Gu, X. W., Greer, J. R. 2015: 7-14
  • Mechanisms of Failure in Nanoscale Metallic Glass NANO LETTERS Gu, X. W., Jafary-Zadeh, M., Chen, D. Z., Wu, Z., Zhang, Y., Srolovitz, D. J., Greer, J. R. 2014; 14 (10): 5858-5864

    Abstract

    The emergence of size-dependent mechanical strength in nanosized materials is now well-established, but no fundamental understanding of fracture toughness or flaw sensitivity in nanostructures exists. We report the fabrication and in situ fracture testing of ∼70 nm diameter Ni-P metallic glass samples with a structural flaw. Failure occurs at the structural flaw in all cases, and the failure strength of flawed samples was reduced by 40% compared to unflawed samples. We explore deformation and failure mechanisms in a similar nanometallic glass via molecular dynamics simulations, which corroborate sensitivity to flaws and reveal that the structural flaw shifts the failure mechanism from shear banding to cavitation. We find that failure strength and deformation in amorphous nanosolids depend critically on the presence of flaws.

    View details for DOI 10.1021/nl5027869

    View details for Web of Science ID 000343016400060

    View details for PubMedID 25198652

  • Microstructure versus Flaw: Mechanisms of Failure and Strength in Nanostructures NANO LETTERS Gu, X. W., Wu, Z., Zhang, Y., Srolovitz, D. J., Greer, J. R. 2013; 13 (11): 5703-5709

    Abstract

    Understanding failure in nanomaterials is critical for the design of reliable structural materials and small-scale devices with nanoscale components. No consensus exists on the effect of flaws on fracture at the nanoscale, but proposed theories include nanoscale flaw tolerance and maintaining macroscopic fracture relationships at the nanoscale with scarce experimental support. We explore fracture in nanomaterials using nanocrystalline Pt nanocylinders with prefabricated surface notches created using a "paused" electroplating method. In situ scanning electron microscopy (SEM) tension tests demonstrate that the majority of these samples failed at the notches, but that tensile failure strength is independent of whether failure occurred at or away from the flaw. Molecular dynamics simulations verify these findings and show that local plasticity is able to reduce stress concentration ahead of the notch to levels comparable with the strengths of microstructural features (e.g., grain boundaries). Thus, failure occurs at the stress concentration with the highest local stress whether this is at the notch or a microstructural feature.

    View details for DOI 10.1021/nl403453h

    View details for Web of Science ID 000327111700111

    View details for PubMedID 24168654

  • Size-Dependent Deformation of Nanocrystalline Pt Nanopillars NANO LETTERS Gu, X. W., Loynachan, C. N., Wu, Z., Zhang, Y., Srolovitz, D. J., Greer, J. R. 2012; 12 (12): 6385-6392

    Abstract

    We report the synthesis, mechanical properties, and deformation mechanisms of polycrystalline, platinum nanocylinders of grain size d = 12 nm. The number of grains across the diameter, D/d, was varied from 5 to 80 and 1.5 to 5 in the experiments and molecular dynamics simulations, respectively. An abrupt weakening is observed at a small D/d, while the strengths of large nanopillars are similar to bulk. This "smaller is weaker" trend is opposite to the "smaller is stronger" size effect in single crystalline nanostructures. The simulations demonstrate that the size-dependent behavior is associated with the distinct deformation mechanisms operative in interior versus surface grains.

    View details for DOI 10.1021/nl3036993

    View details for Web of Science ID 000312122100057

    View details for PubMedID 23148764