Seminar Thursday July 3, 2014

Speaker: Amy Pitman
Location: Physics 175
Time: 3:30,  July 03 2014

Abstract: A society driven by the need for newer and faster technology, we have constantly pushed for a continued technological revolution. As advances in electronics continue to increase at a near exponential rate, we get closer to the limits of our advances in both size and speed. A recently emerged technology known as Spintronics may provide the opportunity needed to continue the trend of decreasing size by utilizing electron spin in electronic materials. While retaining the operation of traditional electronics, Spintronics allows for the opportunity to exploit a second pair of states — spin-up and spin-down — and exponentially increasing the potential logic operations. These properties are only achieved when both semiconducting and ferromagnetic properties exist simultaneously. This work focuses on one sub-set of Spintronic materials, Dilute Magnetic Semiconductors (DMSs), a class of materials which consist of a semiconductor doped with a small amount of transition-metal atoms. The primary system of interest is the semiconductor MoS2 doped with cobalt. We determine the dopant sites via the local bonding environment using cobalt L2,3 x-ray experiments and calculations while sulphur L2,3 x-ray experiments provide an estimate of the band gap.


New Age Solar Cells: Dye-Sensitized and Nanocrystal Approaches

Who (supervisor): Paul Bazylewski (Gap Soo Chang)
Venue: PEGASUS Student Summer Seminar, July 5, 2012.
Abstract: Recently, organic semiconductor materials have received significant attention as potential solar cell materials. This is due to appealing properties that cannot be achieved with conventional inorganic semiconductors (silicon), such as low-cost solution based fabrication of large-area, mechanically flexible devices. Solution processing is low temperature and therefore ideal for flexible plastic substrates which cannot withstand the high temperatures required for inorganic processing. To date, significant progress has been made in polymer/small molecule bulk heterojunction (BHJ) organic photovoltaic (OPV) devices, achieving power conversion efficiencies (PCE) up to 8%. Although promising, this PCE falls below the benchmark for commercialization of ~10%. Therefore research has branched off to explore different device architectures and new materials, with the most successful approaches to date being dye-sensitized solar cells (DSSC) and hybrid nanocrystal-organic solar cells (HSC). These devices take advantage of organic dyes and unique properties of nanocystals such quantum confinement to improve PCE. This talk will outline the state of the art of these two new approaches, and introduce the research collaboration I am currently undertaking to develop high efficiency solar cell devices.

Plasma Ion Implantation for materials engineering

Who (supervisor): Sarah Purdy (Michael Bradley)
Venue: PEGASUS Student Summer Seminar, June 21, 2012.

Plasma Ion Implantation is a materials processing technique that can be used to modify the surface and subsurface structure of a material. A voltage bias applied to a conductive target immersed in plasma introduces a buried layer of impurities in the existing material. This processing technique has been applied to the modification of Si to produce silicon-based light emitting diodes (LEDs) with some success. Bulk silicon is not a light emitter due to its indirect band gap, but any photonic integration for multicore processing needs to be silicon based in order to be scalable for mass production. The work presented here is based on introducing carbon to a silicon wafer to introduce a buried layer of SiC – a known blue light emitter. With the introduction of a buried layer with significantly different stoichiometry from the native material, we see the appearance of delaminated blister features in the layer.

Band gap investigation of photocatalytic energy materials

Who (supervisor): Eamon McDermott (Alex Moewes)
Venue: PEGASUS Student Summer Seminar, June 14, 2012.
 Abstract: Eamon will give a brief overview of his research into the near-band gap electronic structure of energy materials, including semiconductor photocatalysts and lithium organics for use in alloying battery electrodes

Click here for a PDF version of Eamon’s talk

New model for polychlorinated biphenyls (PCBs)

Who (supervisor): Jay Forrest (Gap Soo Chang)
Venue:  PEGASUS Student Summer Seminar, May 17, 2012.
Abstract: Here we present a new model for the toxicity of polychlorinated biphenyls (PCB).  This model works on a first-principles basis, where it takes into account the basic electronic and electron transfer characteristics of the PCBs, investigated using Density Functional Theory.  The model shows bandgap as the overarching indicator of toxicity, but not the only factor.  Our model explains the why both para- positions are required for high levels of toxicity.  To rank the PCBs on a one-by-one basis, the dipole moment in relation to the most chemically active Cl-sites is critical.  The theory is consistent with accepted the Toxic Equivalency Factor (TEF) model for these molecules, and is also able to improve on it to rank the toxicity of PCBs of similar TEF.  This new model also includes a 13th dioxin-like PCB not under the TEF model, PCB 74.  The model is applied to bandgap measurements of a set of PCBs and the measurements are consistent with the model.  Bandgap measurements also indicate the bio-accumulative nature of PCBs.