2011 Research Highlight

The novel properties of meta-materials enable new technologies such as electromagnetic cloaks, flat near- and far-field focusing lenses, and transformation optics devices. MRSEC researchers’ nature-inspired design techniques and accurate fabrication methods minimize loss in this polarizationinsensitive free-standing gold-polyimide-gold meta-material which has both a zero refractive index and high transmission at 1.5μm. The vertical sidewalls eliminate bianisotropy. Low-loss meta-materials could enable a new generation of practical optical devices

MRSEC researchers have developed the materials necessary to embed GHz speed electronic photodetectors into micron diameter channels in optical fibers. Electronic devices are usually made on planar chips or more recently by coating the outside of tiny semiconductor nanowires with layers of new semiconductors to form interfaces known as junctions. Junctions are at the heart of modern optoelectronic devices, such as solar cells, diode lasers, and photodetectors.

Graphene, a sheet of carbon atoms arranged in a honeycomb lattice, possesses many excellent properties that are potentially useful in electronic, optical and mechanical applications. Attaching other chemical species onto the graphene plane offers an effective route to alter and engineer the properties of graphene. NSF-supported researchers have demonstrated that graphene covered dilutely with covalently bonded fluorine adatoms is vastly different from its pristine counterpart.

Polymer-dispersed liquid crystals (PDLCs) are used in numerous applications including smart windows, displays, micro-lenses, lasers, and data storage due to their excellent electro-optical properties. Besides electrical and optical driving, LC re-alignment based on the acousto-optic effect has also been demonstrated, where acoustic waves change the optical axis, thus changing the transmitted light intensity.

Insoluble polymer films depolymerize to release soluble monomeric products when exposed to a specific analyte. These depolymerization products create a concentration gradient that pumps fluids and insoluble particles away from the bulk polymer by diffusiophoresis, thereby amplifying the original signal.

These pumps can be designed to respond to a variety of analytes ranging from small molecules to enzymes in the next generation of smart micro/nanoscale devices.

Angew. Chem. 2012

Silver-CdS-Gold trimers fabricated by quenched electrostatic assembly (shown at left) act as catalytic motors that can be switched on by light. CdS is a semiconductor with a band gap of 2.4 eV which corresponds to blue-green light. With its low native conductivity, no electrons can pass through CdS, so that the motor is not active initially. By exposing CdS to blue light, we raise the number of carriers to lower its resistivity, and thus activate the motor.

MRSEC researchers have discovered a missing spatial operation in nature called rotationreversal symmetry that reverses the sense of all static rotations in a crystal. Certain minerals, organic crystals or metamaterials are composed of subunits that can exist in two states: clockwise or counter-clockwise rotated. The symmetry of a crystal lattice helps determine the material’s properties, and certain properties can only exist in lattices with special symmetries.

The Penn State MRSEC (NSF DMR-0820404) completed its fourth science museum kit as part of its longstanding partnership with The Franklin Institute. Hidden Power focuses on the ways various energy sources are converted to electricity, and vice versa. A hands-on, interactive approach conveys key concepts in the materials science and nanotechnology of solar panels, piezoelectricity, thermoelectricity, light emitting diodes, batteries, turbines, and efficiency.

Interfacing topological insulators with superconductivity provides a possible route towards an analog of Majorana fermions in condensed matter. We have carried out two key steps in the search for these exotic quantum excitations. We demonstrated proximity-induced superconductivity in topological insulator (Bi2Se3) nanoribbons interfaced with super-conducting electrodes. We also provided tantalizing evidence for the possible presence of vortices in the topological insulator.

D. M. Zhang, et al., Phys. Rev. B 84, 165120 (2011)

Selected as Editor's Suggestion

MRSEC researchers working in an international collaboration with French scientists at ESPCI (Paris Tech) have discovered that rocket-shaped metallic micro-rods can be propelled through fluids using ultrasound, with fast translation towards the tapered end and rapid rotation & assembly of rods into circular chains that move like conveyer belts.