An inter-MRSEC collaboration between the University of Chicago and the Pennsylvania State University led to the discovery of a new technique that enables bidirectional control of the chemical potential in a topological insulator (TI).

There is an abiding interest in using nanocrystals as laser gain media due to their tunable emission wavelengths, low cost, and solution processability. However, it has been proven difficult to achieve low lasing thresholds suitable for practical applicatons.  MRSEC members Engel and Talapin showed that colloidal semiconductor nanoplatelets (NPLs) with electronic structure of quantum wells can produce optical gain and lase in the red, yellow, green, and blue regions of the visible spectrum with low thresholds and high gains, both a significant improvement over colloidal quantum dots [1].

We introduced the concept of plate mechanical metamaterials [1] and its initial realization in the form of freestanding corrugated plates made out of ultrathin films. We used atomic layer deposition (ALD) and microfabrication techniques to make robust plates out of a single continuous ALD layer with lateral dimensions of up to 2 cm and a thickness as low as 25 nm, creating the thinnest freestanding plates that can be picked up by hand [1].

The NSF has awarded additional funds to support helium conservation in the Property Measurement Shared Experimental Facility (SEF). The SEF hosts over a dozen low temperature measurement capabilities requiring liquid helium.

Optimum function of plasmonic nanocrystal in assembly requires precision control of separation. Often, larger separations are desired while still maintaining order. With our COMPASS collaborators, Hough and Donnio, IRG-4 has developed a new class of building blocks that incorporate dendrimer ligands. Dendrimer-nanocrystal building blocks have diameters controlled by dendrimer “generation.” This work was published in  J. Am. Chem. Soc. 137, 10728–10734 (2015).

A metal spoon can bend in half without breaking because of defects in its crystalline structure.  By contrast, a metal spoon with atoms in a disordered structure—a metallic glass spoon—would break via a catastrophic brittle fracture.  Here we show that disordered packings of particles ranging in size from atoms, as in a metallic glass, to nanoparticles to micron-sized colloids to centimeter-sized granular particles, show universal behavior in their microscopic structure and dynamics and in their macroscopic mechanical response, even for systems with extremely different interactions between

To increase our online presence, we are recording nearly all outreach presentations and making them available on our website (www.lrsm.upenn.edu/outreach/videos). These include Science Cafes, PREM seminars (given usually in Spanish), and various other events.

Harvard hosted its first ever “Top Chef” competition, as part of Science and Cooking: From Haute Cuisine to Soft Condensed Matter, now in its sixth year as a highly popular undergraduate course at Harvard. Created and taught by Michael Brenner and David Weitz, the course enrolls several hundred undergraduates each fall, and is also offered as a free online course through the EdX portal.

Shape morphing systems may find potential application in smart textiles, autonomous robotics, biomedical devices, drug delivery and tissue engineering. Lewis and Mahadevan at the Harvard MRSEC have developed 4-D printing by creating a hydrogel-cellulose fibril ink that could be printed to induce a programmable shape change as recently reported in Nature Materials.

A dendrimer is a synthetically made branched molecule. In this work, a family of amphiphilic Janus dendrimers bearing precise carbohydrate residues arranged in a defined sequence – glycodendrimers – were used to make vesicles that could be agglutinated by naturally occurring lectins that binds to carbohydrates. The lectins, called galectins, are human adhesion and growth regulatory lectins. Very small differences in the chemistry of different galectin were detected through differences in agglutination with different Janus glycodendrimers.