Welcome to the Greer Group

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Introduction [top]

The Greer Group research focuses on the problems of unraveling the physical origins of size-dependent strength in nano-scale solids, where the presence of surfaces causes the emergence of unexpected deformation mechanisms in response to mechanical deformation.

Nano-Louvre: overplated 50 nm Au nanopillar.
(image courtesy D. Jang)

It has been shown that when the sample size is reduced not only vertically (i.e. thin films) but also laterally, the mechanical properties of single crystals, for example, drastically differ from those of their bulk counterparts. They are thought to arise from the distinct defect behavior that emerges as a result of reducing material dimensions to the nano-scale and manifest themselves by causing unusual mechanical properties.

These characteristics include avalanche-like stochastic stress-strain signature, size-dependent strength, and tension-compression asymmetry - prevalent only in those structures where the surface area is significantly higher than their volume, i.e. sub-micron scale.

While these studies provide a powerful foundation for the fundamental deformation processes operating in these materials at small scales, they are a far reach from representing real materials, whose microstructure is often complex, containing boundaries and interfaces.

Nano-popsicles: overplated nano-twinned Cu nanopillars.
(image courtesy D. Jang)

In fact, both homogeneous interfaces (grain boundaries, twin boundaries, etc.) and heterogeneous interfaces (phase boundaries, precipitate-matrix boundaries, and free surface) in size-limited features are crucial elements in structural reliability of most modern materials.

Establishing the link between the observed mechanical properties and microstructural evolution remains a grand challenge, and one of my major research goals is in establishing a more quantified, predictive relationship between the competing factors of intrinsic and extrinsic limitations on the overall material properties.

Our key research thrusts lie in the development of innovative experimental approaches that enable us to assess nano-scale mechanical properties, and in subsequent design and fabrication of new, innovative materials with tunable desired properties.

Main research activities [top]

  1. Mechanical properties and deformation mechanisms of nano-scale materials
  2. Radiation damage tolerance in interface-containing metallic nano structures
  3. Materials with controlled microstructural architecture: energy sciences and structural applications
  4. Deformation response of vertically aligned carbon nanotube (VACNT) forests
  5. Mechanical stability of polymer-embedded Si nanowire arrays for flexible solar panels
  6. Innovative materials for low-temperature electronics for space applications
  7. Bio-inspired design of damage-tolerant materials
  8. Characterization of energy dissipation processes in gravitational measurements in LIGO
  9. Transport across grain boundaries in Ceria
  10. Mechanical-electrical coupling in graphene-based devices

Stress-strain response of a carbon nanotube foam (CNTs) under compression (courtesy S. Hutchens).

TEM images of nano-twinned Cu nanopillars (courtesy D. Jang).

Group News
May. 2012: Congratulations to Zach for passing his candidacy!
Apr. 2012: Congratulations to David for receiving the NSF Graduate Research Fellowship and to Lucas for being named for honorable mention! We're proud of both of them!
Mar. 2012: Congratulations to Wendy for passing her candidacy!
Mar. 2012: Robert, Dongchan, and Chris Weinberger present talks at the annual TMS meeting in Orlando.
Feb. 2012: Congratulations to Shelby and Liz for winning the Materials Today cover art competition with their image of CNTs! Read the article here.
Dec. 2011: Congratulations to Zach for passing his qualifying exams!
Nov. 2011: Ultralight Metallic Microlattices, published in Science, makes the headlines on the Caltech homepage, and is featured on major news outlets! Links: BBC MSNBC
Nov. 2011: Congratulations to Seok-Woo for receiving the prized Kavli Nanoscience Institute post-doctoral fellowship!
Oct. 2011: Congratulations to Clara for winning the 2011 Goldhirsh-Resnick Fellowship, and Nisha for passing her qualifying exams!
Oct. 2011: Julia receives the 2011 Sia Nemat-Nasser Early Career Award from ASME for her research in physical origins of size dependent mechanical properties in nano-scale solids.
Aug. 2011: Congratulations to Ju-Young who just became a faculty member at the Ulsan National Institute of Science and Technology (UNIST) in Korea!
Aug. 2011: Julia (with great help from Christy, Joanna, Robert, and Dongchan) hosted a Small-Scale Metallic Glass workshop at Caltech on Aug. 8th and 9th. Highlights included an inspirational keynote presentation by Bill Johnson, outstanding talks by all invited speakers, and a Brazilian BBQ dinner at Porto Alegre! Group photo can be found here.
July 2011: Julia "raps" about nanomechanics while playing Bach's Partita No. 2 at the Inaugural MUSE/IQUE concert on the Beckmann Lawn directed by Rachael Worby and featuring the legendary soprano Jessye Norman. See LA Times press releases here and here, or watch the video!
July 2011: The group welcomes Lucas Meza, a 1st year Ph.D. student in Mechanical Engineering.
May 2011 : Shelby Hutchens successfully defends her PhD thesis! Congratulations to Julia Greer on winning the DOE Early Career Award & Congratulations to Shelby on receiving the 2011 DTK Prize in Nanotechnology!
Apr. 2011: Congratulations to Allison Kunz and Xun (Wendy) Gu for winning the National Defense Science and Engineering Graduate (NDSEG) Fellowship!
Feb. 2011: Ju-Young, Dongchan (invited), Allison, and Sid present talks/posters at the TMS meeting in San Diego. Julia receives the Young Leaders for Professional Development award at TMS (SMD).
Jan. 2011: Shelby presents a talk in the Jim Knowles Symposium at Caltech.
Jan. 2011: Julia presents a keynote talk at the Symposium in Honor of W.D. Nix at Plasticity '11 conference (Puerto Vallarta)
Jan. 2011: Greer group welcomes Wendy Gu (Chem. E., 1st year Ph.D. student).