2012 Research Highlight

Graphene is a one-atom-thick planar sheet of carbon atoms. By incorporating nitrogen atoms into graphene, its physico-chemical properties could be altered depending on the doping configuration within the sub-lattices. MRSEC researchers developed a process to synthesize nitrogendoped graphene sheets with specific doping structures and used them as high-efficiency surface-enhanced Raman spectroscopy (SERS) substrate materials for the first time.

For the first time, MRSEC researchers have created single layers of a naturally occurring rare mineral called tungstenite or WS₂. The resulting sheets of stacked sulfur and tungsten atoms forms honeycomb patterns within triangular islands that have unusual light-emitting (photoluminescent) properties. These triangular structures could have many potential applications in optical light detection, light-emitting diodes, and lasers.

Using the new tools of metamaterials and transformation optics, MRSEC researchers have developed designs for miniaturized optical devices in chip-based optical integrated circuits, the analog of the integrated electronic circuits in computers and cell phones. A unified theory for designing practical devices on a single platform using transformation optics has been developed. These broadband, lossless all-dielectric-based gradient-index devices designed include beam collimators, beam splitters, waveguide crossings and waveguide couplers.

The resistance of a thin-film topological insulator Bi₂Se₃ shows an abrupt and prominent upturn when the electrodes (In, Al or W) becomes superconducting. In turn, the Bi2Se3 film weakens the superconductivity of the electrodes, significantly reducing both their transition temperature and the critical field. These results highlight the interplay of the Cooper pairs in the electrodes and the spin-polarized current of the surface states in Bi₂Se₃, an emerging material with fundamentally new electron-transport properties.

We have designed a set of microscale pumps that consist of insoluble polymer films that depolymerize to release soluble monomeric products when exposed to a specific analyte. Products formed as a result of the depolymerization reaction amplify the signal and create a concentration gradient that pumps fluids and insoluble particles away from the bulk polymer due to a diffusiophoretic mechanism. These pumps are tunable to respond to a variety of analytes, ranging from small molecules to enzymes.

Our knowledge of one-dimensional superconductivity to date is based on studies of nanowires just a few microns long. MRSEC researchers have now measured charge transport in an Indium- Gallium nanowire that is 150 nm across and exceptionally long: 6 millimeters. Protected within a hollow glass fiber, the nanowire shows an unusual superconducting transition, with steps at both 5K and 1.1K (close to T_c of pure Ga).

The ability to non-invasively and dexterously manipulate cells and other microparticles is critical for a wide variety of applications in biology, chemistry and medicine. MRSEC researchers have developed a novel acoustic manipulation platform – acoustic tweezers – which can trap and manipulate single microparticles, cells and entire organisms along programmed routes in two dimensions within a microfluidic chip. “PSU” is spelled by moving a bovine red blood cell. The organism C. elegans can be manipulated and immobilized.

Intrinsic magnetoelectric coupling describes the microscopic interaction between magnetic and electric polarization in a single-phase material. The control of the magnetic state of a material with an electric field is an enticing prospect for device engineering. MRSEC researchers are collaborators have demonstrated giant magnetoelectric cross-field control in a europium titanate film. In bulk form, EuTiO₃, is antiferromagnetic, but anti- and ferromagnetic interactions coexist between different europium neighbors.

The Penn State MRSEC is expanding its efforts to encourage diverse high school students to pursue degrees in STEM fields. Working with 70 Upward Bound Math and Science (UBMS) students from low-income and first generation college-bound families from underrepresented and underserved populations, MRSEC graduate students and faculty, along with Physics/MRSEC REU undergraduates, trained together in teams to prepare a full day of science outreach activities at the Central Pennsylvania Festival of the Arts Children and Youth Day.

The Penn State MRSEC received an overwhelming positive response to its first annual Women in STEM Mixer. This professional networking program connected 71 women and 7 men from a variety of STEM disciplines and multiple career stages, including undergraduates, graduate students, post-docs, research staff, faculty and industry representatives. After the short feature Setting up for Success: Promoting Yourself and Your Research, attendees participated in three randomly assigned small-group discussions, each lead by faculty and industry cohosts.