Supported by NSF DMR Yale University Creating new devices using oxide materials Boron is surprising versatile in the bonding networks it forms in its crystalline, molecular, and nanoscale phases. Here we focus on boron nanostructures in the form of sheets and nanotubes. 2nm Boron sheets and nanotubes: buckling and bonding Sohrab Ismail-Beigi, Yale University, DMR Hui Tang and Sohrab Ismail-Beigi, Physical Review B 82, (2010). Atomically thin boron sheets form complex structures with triangular and hexagonal motifs. They also tend to pucker (have corrugated surfaces), so when two sheets come together, they bond together to make a double- layered structure. This is in contrast to carbon sheets (graphene) that have a simple, flat, hexagonal structure and bond very weakly. Top view of a sheet A double-layered sheet (side view) Boron nanotubes show similar behaviors. When formed with single-layered walls, they have buckled surfaces: the buckling is important as it makes small diameter nanotubes semiconducting. Nanotubes made of double- layered sheets are more stable, have bonds between the layers, and are generally metallic. Metallic boron nanotubes have the potential to act as light-weight and highly conductive nanoscale wires. Side (left) and axial (right) view of a semiconducting nanotube with a single- layered wall: atoms buckling outwards/inwards are blue/gold Axial view of a metallic double-walled nanotube displaying inter-wall bonds

Supported by NSF DMR Yale University Creating new devices using oxide materials Hui Tang and Sohrab Ismail-Beigi, Physical Review B 80, (2009). Atomically thin boron sheets provide a poignant example when compared to the better known carbon-based graphene and nanotubes. Boron and carbon are neighbors on the periodic table but their stable sheet structures differ greatly. On the left is the stable honeycomb structure of carbon (graphene) which turns out to be highly unstable for boron. On the right is a stable boron sheet. Interestingly, it is composed of triangles and hexagons. 2nm Metal Doping of Boron Nanostructures Sohrab Ismail-Beigi, Yale University, DMR Nanoscale materials can present novel properties due to the small length scales and confined dimensions. In particular, the types of bonds that form between atoms may change dramatically. This is because, in a nanomaterial, the constituent atoms find themselves in significantly different environments compared to their usual three dimensional crystalline arrangements. This triangle/hexagon motif generalizes to situations when metal atoms are added to boron nanostructures (doping). Metal doping may potentially create new superconductors or light-weight hydrogen storage materials. On the left is the structural motif of the crystalline superconductor MgB 2 (Mg in blue, B in grey). However, this structure is not stable for MgB 2 sheets: they prefer the more complex structure on the right. How these structures change with metal content and how that affects the materials properties are open questions.

Supported by NSF DMR Yale University Teaching materials science using modern electronics Modern electronics, e.g. a smart phone, relies heavily on science and engineering: semiconductors (diodes, transistors), magnetism (hard drives), photoelectric effect (digital camera), photon generation and lasers (LEDs, CD/DVD drives), light polarization (LCD), etc. The immediacy and applicability makes electronics a great tool for teaching science and technology. Sohrab Ismail-Beigi, Kenneth Spinka, Christine Broadbridge, Jacquelynne Garofano A Yale professor and a New Haven public high school science teacher collaboratively develop web pages, presentations, teaching modules, lesson plans, and hands-on kits appropriate for high school students and teachers. CRISP (Yale’s NSF MRSEC) has purchased kits for loan to New Haven area teachers who can check them out for class use. Teaching materials science using modern electronics: websites Sohrab Ismail-Beigi, Yale University, DMR Web page segment: our own SEM images of CD/DVD surface and explanations of how CD/DVD data is stored and read

Supported by NSF DMR Yale University Teaching materials science using modern electronics Modern electronics, e.g. a smart phone, relies heavily on science and engineering: semiconductors (diodes, transistors), magnetism (hard drives), photoelectric effect (digital camera), photon generation and lasers (LEDs, CD/DVD drives), light polarization (LCD), etc. The applicability makes electronics a great tool for teaching science and technology. Based on this idea, teaching material is being developed by a Yale professor and a New Haven public high school science teacher. With organizational support from CRISP (Yale’s NSF MRSEC), a first workshop introducing this approach took place on March 24, 2010 and was attended by New Haven area science teachers and involved short lectures, discussions, plenty of questions, use of hands-on kits, and pizza. Teaching materials science using modern electronics: workshops Sohrab Ismail-Beigi, Yale University, DMR Sohrab Ismail-Beigi, Hui Tang, Kenneth Spinka, Christine Broadbridge, Jacquelynne Garofano Workshop participants disassemble and examine a hard drive as part of the kit Short lecture on magnetic storage, magnetic grains, and magnetic materials Successful disassembly of a DVD drive