University of California

Sanjay Govindjee

Richard S Muller

Hyuck Choo

James Demmel

David Garmire

Robert O Ritchie

Siva Wu

Shilpa N Raja

Peter Ercius

Andrew C K Olson

Danylo Zherebetskyy

Paul Alvisatos

Nanoscale stress-sensing can be used across fields ranging from detection of incipient cracks in structural mechanics to monitoring forces in biological tissues. We demonstrate how tetrapod quantum dots (tQDs) embedded in block-copolymers act as sensors of tensile/compressive stress. Remarkably, tQDs can detect their own composite dispersion and mechanical properties, with a switch in optomechanical response when tQDs are in direct contact. Using experimental characterizations, atomistic simulations and finite-element analyses, we show that under tensile stress, densely-packed tQDs exhibit a photoluminescence peak shifted to higher energies ('blue-shift') due to volumetric compressive stress in their core; loosely-packed tQDs exhibit a peak shifted to lower energies ('red-shift') from tensile stress in the core. The stress-shifts result from the tQD's unique branched morphology in which the CdS arms act as antennas that amplify the stress in the CdSe core. Our nanocomposites exhibit excellent cyclability and scalability with no degraded properties of the host polymer. Colloidal tQDs allow sensing in many materials to potentially enable auto-responsive, smart structural nanocomposites that self-predict impending fracture.

Mechanisms of local stress sensing in multifunctional polymer films using fluorescent tetrapod nanocrystals

The present invention provides a device for in-situ monitoring of material, process and dynamic properties of a MEMS device. The monitoring device includes a pair of comb drives, a cantilever suspension comprising a translating shuttle operatively connected with the pair of comb drives, structures for applying an electrical potential to the comb drives to displace the shuttle, structures for measuring an electrical potential from the pair of comb drives; measuring combs configured to measure the displacement of the shuttle, and structures for measuring an electrical capacitance of the measuring combs. Each of the comb drives may have differently sized comb finger gaps and a different number of comb finger gaps. The shuttle may be formed on two cantilevers perpendicularly disposed with the shuttle, whereby the cantilevers act as springs to return the shuttle to its initial position after each displacement.

Integrated MEMS metrology device using complementary measuring combs

Growing community of inventors

Lafayette, CA, United States of America

Sanjay Govindjee