Nanowires: A route to efficient thermoelectric devices

Miniaturization of electronic devices aims at manufacturing ever smaller products, from mesoscopic to nanoscopic sizes. This trend is challenging because the increased levels of dissipated power demands a better understanding of heat transport in small volumes. A significant amount of the consumed energy is transformed into heat and dissipated to the environment. Thermoelectric materials offer the possibility to harness dissipated energy and make devices less energy-demanding. Heat-to-electricity conversion requires materials with a strongly suppressed thermal conductivity but still high electronic conduction. Nanowires can meet nicely these two requirements because enhanced phonon scattering at the surface and defects reduces the lattice thermal conductivity while electric conductivity is not deteriorated, leading to an overall remarkable thermoelectric efficiency. Therefore, nanowires are regarded as a promising route to achieving valuable thermoelectric materials at the nanoscale. In this paper, we present an overview of key experimental and theoretical results concerning the thermoelectric properties of nanowires. The focus of this review is put on the physical mechanisms by which the efficiency of nanowires can be improved. Phonon scattering at surfaces and interfaces, enhancement of the power factor by quantum effects and topological protection of electron states to prevent the degradation of electrical conductivity in nanowires are thoroughly discussed

Raman and infrared studies of La_1-ySr_yMn_1-xM_xO_3 (M=Cr, Co, Cu, Zn, Sc or Ga): Oxygen disorder and local vibrational modes

We present results of our study of polarized Raman scattering and infrared reflectivity of rhombohedral ceramic La_1-ySr_yMn_1-xM_xO_3 manganites in the temperature range between 77 and 320K. In our samples, a part of the Mn atoms is substituted by M = Cr, Co, Cu, Zn, Sc, or Ga with x in the range 0 -- 0.1. The hole concentration was kept at the optimal value of about 32% by tuning the Sr content y. We have monitored the distortions of the oxygen sublattice by the presence of broad bands in the Raman spectra, the increase of d.c. resistivity extracted from the infrared reflectivity, and the change of the critical temperature of the ferromagnetic transition. Our results support the idea, that these properties are mainly determined by the radius of the substituent ion, its electronic and magnetic structure playing only a minor role. Furthermore, the Raman spectra exhibit an additional A_g-like high frequency mode attributed to the local breathing vibration of oxygens surrounding the substituent ion. Its frequency and intensity strongly depend on the type of the substituent. In the Co-substituted sample, the mode anomalously softens when going from 300 to 77K. The frequency of the bulk A_{1g} mode depends linearly on the angle of the rhombohedral distortion.Comment: 11 pages, 11 Figures, best-fit values table added, a discussion adde

Developing a community profile tool for improving health in New Mexico rural communities.

Presented at: 2016 Annual Conference of the New Mexico Public Health Association; April 12-13, 2016; Las Cruces, NM.https://digitalrepository.unm.edu/prc-posters-presentations/1031/thumbnail.jp

Parental feeding responses to experimental short-term partner removal in a species with male and female brood desertion

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Usage of tobacco cessation helpline (QUITNOW) in rural New Mexico.

Presented at: Society for Advancement of Chicanos/Hispanics and Native Americans in Science; October 29-31, 2015; Washington, DC.https://digitalrepository.unm.edu/prc-posters-presentations/1050/thumbnail.jp

Measuring tobacco cessation helpline (1-800-QUIT NOW) usage in rural and urban areas of New Mexico.

Presented at: 2016 Annual Conference of the New Mexico Public Health Association; April 12-13; Las Cruces, NM.https://digitalrepository.unm.edu/prc-posters-presentations/1035/thumbnail.jp

Aplicación de la función densidad electrónica para diferenciar la estructura de la corrensita y de la clorita-clorita hinchable

El estudio por difracción de rayos X de interestratificados de minerales de la arcilla es de gran utilidad en la investigación geológica de los materiales arcillosos. El analisis de los espectros de difracción de interestratificados regulares utilizando los metodos de "tanteo" de determinación de estructuras cristalinas asi como los basados en la transformada de Fourier, permite obtener una información mas relacionada con el interestratificado que con la muestra arcillosa global en el caso de estudiar muestras no puras, mejor que los métodos quimicos en los que se basan un gran número de conclusiones de tipo estructural. La aplicación de la transformada de Fourier para la función de mezcla asi como de la función densidad electrónica pone de manifiesto que las estructuras de los interestratificados regulares de cloritaclorita hinchable y de clorita-esmectita son distintas, a pesar de ser utilizada indistintamente por algunos autores la denominación de corrensita para ambos interestratificados

Phonon-induced optical superlattice

We demonstrate the formation of a dynamic optical superlattice through the modulation of a semiconductor microcavity by stimulated acoustic phonons. The high coherent phonon population produces a folded optical dispersion relation with well-defined energy gaps and renormalized energy levels, which are accessed using reflection and diffraction experiments

High accuracy Raman measurements using the Stokes and anti-Stokes lines

We show that by measuring the separation between the Stokes and anti-Stokes peaks excited by two different laser lines we obtain a very precise determination of absolute phonon energies. The method is useful for measuring small changes of these energies with strain, temperature, laser power, etc. It doubles the changes and avoids the necessity of using the reference lines in the Raman spectra. The method can be applied for the determination of phonon deformation potentials, for the characterization of strained heteroepitaxial layers, and for micro-Raman analysis of strain in silicon integrated circuits. We give examples of phonon shifts in Si, Ge, GaAs, InAs, and GaP as a function of applied biaxial strain, laser power, and [email protected] ; [email protected]