In situ nanomechanics
Tensile testing of a 150 nm Cu nanowhisker
A pure single crystalline copper nanowhisker is tested under tensile load inside of a scanning electron microscope to measure the mechanical behavior. A nanomanipulator (right) provides the actuation, while a microelectromechanical device (left) measures load. The stress strain behavior is shown simultaneously. The strength is as much as 1,000 times higher than an equivalent bulk piece of Cu – this is achieved by simply changing the size.
Tensile testing of a 300 nm Cu nanowhisker
A pure single crystalline copper nanowhisker is tested under tensile load inside of a scanning electron microscope to measure the mechanical behavior. A novel nanomechanical transducer (bottom) provides the actuation and load measurement.
In situ bending of a nickel titanium shape memory alloy micropillar
A micropillar (approximately 1 micron in diameter) fabricated using focused ion beam machining is bent inside of a scanning electron microscope. The pillar appears to be permanently deformed, but subsequent heating causes the pillar to undergo a reverse phase transformation and recover to its original shape. This material can be used as small-scale actuators in tiny micro- and nanomachines.
Grain growth in nanocrystalline aluminum
In situ straining of a thin film of nanocrystalline aluminum in a transmission electron microscope reveals a dynamic world at small scales, in particular how individual crystallites (grains) grow under the influence of stress. The grains were originally 50-100 nm in size. Collaboration with Dr. Marc Legros (CEMES-CNRS, Toulouse).
Micro- and nanomanipulation
Pick and place of nanowires
This procedure was performed in a dual-beam scanning electron and focused ion beam microscope to harvest and prepare nanowires for tensile testing. Attachment is accomplished by locally depositing Pt “tape” and cutting by the use of the focused ion beam. The wire has a diameter of about 150 nm -- almost 1,000 times smaller than a human hair.
In situ bending of a Cu nanowhisker in a scanning electron microscope
Bending of a nanowhisker in situ in a scanning electron microscope. The bending occurs due to the presence of an electric field, and the whisker is moved through the field, causing more bending. After moving the whisker back, it returns to its original shape, even after large amounts of deformation.
Wrinkling in thin films
Wrinkling of a thin film under applied stress -- finite element simulation
This is a finite element simulation of a freestanding 150 nm thin film with patterned holes to introduce spatial variations of stress and strain around the holes. An applied remote tensile stress causes the film to wrinkle due to the small thickness of the film. These wrinkles can be used as a mechanical assay to measure strain.
Wrinkling of a thin film under applied stress -- 2 angled holes
This is a freestanding 150 nm thin Al film with patterned holes to introduce spatial variations of stress and strain around the holes. Two holes are placed at an angle from each other, resulting in a concentrated region of shear stress between the holes. Watch as the wrinkling evolves!
Wrinkling of a thin film under applied stress - 4 holes
This is a freestanding 150 nm thin Al film with 4 patterned holes to introduce a different stress field.
Small scale image-based strain measurements
In situ local strain measurement of a nanowire
In situ straining of a 70 nm Cu nanowhisker in a scanning electron microscope. Digital image correlation is used to calculate the displacement field along the wire during testing. The gradient of the displacement field along the wire axis gives the strain.
4-point bending of a thermal barrier coating microbeam
Thermal barrier coatings are used as protective ceramic layers, for example on turbine blades in the hot section of jet engines. These coatings allow for higher operating temperatures in the engines and higher efficiency. This movie shows a microbending experiment of a ceramic topcoat to measure the mechanical response of the coating. Displacement and strain fields were computed using digital image correlation and are superimposed on the images.
Teaching at Penn
Levitation of a YBCO Superconductor via the Meissner Effect
Levitation of a rare earth magnet above a YBCO high critical temperature superconductor via the Meissner effect. The superconductor discs were synthesized by Penn undergraduate students as part of the course MSE 250, Nanoscale Materials Laboratory. The discs are brought to the superconducting state by pouring liquid nitrogen over the material.