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Program Highlights for year 2016

Persistent Optical Gating of a Topological Insulator

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).

Red, Yellow, Green, and Blue Lasing Using Colloidal Quantum Wells

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.

Top Chefs at the MRSEC

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.

Biomimetic 4-D Printing

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

Revealing Hidden Phases in Materials

Strong interactions at the interface between a crystalline film and substrate can impart new structure to thin films. Here, a germanium surface (purple atoms) squeezes a BaTiO3 thin film above, revealing a hidden phase not seen in the bulk. The hidden phase of BaTiO3 shows oxygen octahedra cages (shaded in aqua) alternating in size. By combining theory, synchrotron x-ray diffraction, and electron microscopy, a new materials design approach has uncovered hidden traits of a material that can be expressed through articulated forces at an interface.

Electrocatalytic Surfaces Using Bulk Metallic Glass Nanostructures

Metallic glass nanostructures provide a new platform for electrocatalytic applications. Several surface modification strategies that remove or add metal species (top images) improve the catalytic activity of metallic glass nanostructures. These strategies were demonstrated for three key electrocatalytic reactions important for renewable energy.

Leveraging MRSEC Equipment Purchases

Leveraged upgrades to Scanning Transmission Electron Microscope (S/TEM) and Focused Ion Beam System (FIB):

Efficient and uniform doping of zinc oxide nanocrystals via plasma synthesis

In solution-based synthesis, often doping efficiencies are low and dopants are excluded from the nanocrystals’ central cores. The research team developed a fundamentally different plasma-based process for synthesizing aluminum-doped zinc oxide nanocrystals.

How many electrons make a nanocrystal film metallic?

Understanding the transport of electrons in films of touching nanocrystals is of central importance for their future use in printed electronic devices such as light emitting diodes, solar cells, or transistors. The research team developed a new theory that describes the transition of the electron conduction in doped nanocrystal films from a semiconducting to a metallic behavior.