Optical Transmissions

Artist Statement My art is deeply rooted in graphic design. Along the way I have experimented in block printing, screen printing, and painting. I use highly saturated colors and patterns to create optical illusions. One major influence on my work is the Op Art movement from the 1960s. From Op Art I take the ideas of how color and shape can work together to create visual effects. Music is another influence on my work. I try to create rhythms and the illusion of pulsating beats, visually. I want there to be a sensation of movement within the work where some parts of the artwork appear to advance and other parts to recede. My goal in art is to evoke a sense of visual excitement in the viewer through the use of color, shape, and pattern

Zintl Chemistry for Designing High Efficiency Thermoelectric Materials

Zintl phases and related compounds are promising thermoelectric materials; for instance, high zT has been found in Yb_(14)MnSb_(11), clathrates, and the filled skutterudites. The rich solid-state chemistry of Zintl phases enables numerous possibilities for chemical substitutions and structural modifications that allow the fundamental transport parameters (carrier concentration, mobility, effective mass, and lattice thermal conductivity) to be modified for improved thermoelectric performance. For example, free carrier concentration is determined by the valence imbalance using Zintl chemistry, thereby enabling the rational optimization of zT. The low thermal conductivity values obtained in Zintl thermoelectrics arise from a diverse range of sources, including point defect scattering and the low velocity of optical phonon modes. Despite their complex structures and chemistry, the transport properties of many modern thermoelectrics can be understood using traditional models for heavily doped semiconductors

Transport properties of the layered Zintl compound SrZnSb_2

Transport properties of the layered Zintl compound SrZnSb_2 have been characterized from room temperature to 725 K on polycrystalline samples. SrZnSb_2 samples were found to be p-type with a Hall carrier concentration of 5×10^(20) cm^(−3) at room temperature, and a small Seebeck coefficient and electrical resistivity are observed. A single band model predicts that, even with optimal doping, significant thermoelectric performance will not be achieved in SrZnSb_2. A relatively low lattice thermal conductivity is observed, κ_L~1.2 W m^(−1) K^(−1), at room temperature. The thermal transport of SrZnSb_2 is compared to that of the layered Zintl compounds AZn2Sb_2 (A=Ca,Yb,Sr,Eu), which have smaller unit cells and larger lattice thermal conductivity, κ_L~2 W m^(−1) K^(−1), at 300K. Ultrasonic measurements, in combination with kinetic theory and the estimated κ_L values, suggest that the lower κ_L of SrZnSb_2 is primarily the result of a reduction in the volumetric specific heat of the acoustic phonons due to the increased number of atoms per unit cell. Therefore, this work recommends that unit cell size should be considered when selecting Zintl compounds for potential thermoelectric application

Spin-dependent electron-hole capture kinetics in conjugated polymers

The recombination of electron-hole pairs injected in extended conjugated systems is modeled as a multi-pathway vibron-driven relaxation in monoexcited state-space. The computed triplet-to-singlet ratio of exciton formation times $r = \tau_T/\tau_S$ increases from 0.9 for a model dimer to 2.5 for a 32-unit chain, in excellent agreement with experiments. Therewith we rationalize recombination efficiency in terms of spin-dependent interstate vibronic coupling and spin- and conjugation-length-dependent exciton binding energies.Our model calculations for various length polymers indicate that the ratio of the singlet to triplet formation ratios, $r = \sigma_S/\sigma_T$, is inversely related to the ratio of the singlet and triplet binding energies, $\epsilon^b_S/\epsilon^b_T$

Thermoelectric properties of p-type LiZnSb: Assessment of ab initio calculations

In response to theoretical calculations on the thermoelectric performance of LiZnSb, we report the pertinent transport properties between room temperature and 523 K. Nominal LiZnSb samples are found to be p-type, with a carrier concentration in the range (4–7)×10^(20) cm^(−3). The thermoelectric figure of merit (zT) is found to be 0.02–0.08 at 523 K. Analysis of material transport parameters and previously reported ab initio calculations demonstrates that even with optimal doping, p-type LiZnSb is unlikely to achieve zT>0.2 at 523 K. The accuracy of the high zT estimate (zT>2) for n-type compositions from ab initio calculations is discussed within the current synthetic limits