Now showing items 1-20 of 20

    • Design and Characterization of a High Vacuum Metals Deposition System based on Electron Beam Evaporation 

      Ramírez Porras, Arturo; Avendaño Soto, Esteban Damián; Araya Pochet, José (2010-08-03)
      We describe a high vacuum metals deposition system based ona variation of a pendant-drop type electron beam evaporator.This system uses a Molybdenum crucible as an evaporantinstead of a rod or wire usually used in ultrathin ...
    • Detection of the adsorption of water monolayers through the ion oscillation frequency in the magnesium oxide lattice by means of low energy electron diffraction 

      Guevara Bertsch, Milena; Ramírez Hidalgo, Gustavo; Chavarría Sibaja, Andrés; Avendaño Soto, Esteban; Araya Pochet, José; Herrera Sancho, Óscar Andrey (2016-03)
      We investigate the variation of the oscillation frequency of the Mg2+ and O2− ions in the magnesium oxide lattice due to the interactions of the surface with water monolayers by means of Low Energy Electron Diffraction. ...
    • Diseño y caracterización de un enfriador de átomos de tipo “desacelerador Zeeman” 

      Guevara Bertsch, Milena; Salfenmoser, Lena; Chavarría Sibaja, Andrés; Avendaño Soto, Esteban Damián; Herrera Sancho, Óscar Andrey (2016)
      Nosotros presentamos un método que utiliza simultáneamente dos modelos matemáticos, con el objetivo de optimizar el diseño de un desacelerador Zeeman, con miras a la implementación de átomos ultrafríos a la física del ...
    • El Eclipse total de Sol del 11 de Julio de 1991: Aspectos Generales. 

      Azofeifa Alvarado, Daniel E.; Fernández Rojas, Walter; Villalobos M., José Alberto (San José, CR: Editorial de la Universidad de Costa Rica, 1992)
      El 11 de junio de 1991 ocurrió un eclipse total de sol, el cual se pudo observar en casi todo el territorio de Costa Rica. El presente artículo explica en que consistió el fenómeno y describe las características principales ...
    • Electronic structure of silicon-based nanostructures 

      Guzmán Verri, Gian Giacomo; Lew Yan Voon, Lok Chong (2007-08-30)
      We have developed a unifying tight-binding Hamiltonian that can account for the electronic properties of recently proposed Si-based nanostructures, namely, Si graphene-like sheets and Si nanotubes. We considered the sp3s∗ ...
    • Estimation of Silicon Nanocrystalline Sizes from Photoluminescence Measurements of RF Co-Sputtered Si/SiO2 Films 

      Ramírez Porras, Arturo; Fonseca, L. F.; Resto, O. (Materials Research Society Symposium Proceedings 737 (2003), 2003)
      A stochastic distribution of nanocrystalline sizes model is applied to fit photoluminescence (PL) spectra of luminescent Si nanocrystals in a Si/SiO2 matrix synthesized by RF co-sputtering on the top of quartz substrates. ...
    • Landau theory and giant room-temperature barocaloric effect 

      Corrales Salazar, A.; Brierley, Richard T.; Littlewood, Peter B.; Guzmán Verri, Gian Giacomo (2017-10-17)
      The structural phase transitions of MF3 (M = Al, Cr, V, Fe, Ti, Sc) metal trifluorides are studied within a simple Landau theory consisting of tilts of rigid MF6 octahedra associated with soft antiferrodistortive optic ...
    • Large isotropic negative thermal expansion above a structural quantum phase transition 

      Handunkanda, Sahan U.; Curry, Erin B.; Voronov, Vladimir; Said, Ayman H.; Guzmán Verri, Gian Giacomo; Brierley, Richard T.; Littlewood, Peter B.; Hancock, Jason N. (2015-10-01)
      Perovskite structured materials contain myriad tunable ordered phases of electronic and magnetic origin with proven technological importance and strong promise for a variety of energy solutions. An always-contributing ...
    • Light Reflection by Cuticles of Chrysina Jewel Scarabs: Optical Measurements, Morphology Characterization, and Theoretical Modeling 

      Vargas Castro, William E.; Hernández Jiménez, Marcela; Libby Hernández, Eduardo; Azofeifa Alvarado, Daniel E.; Barboza Aguilar, Cinthya; Solís Blanco, Ángel Arturo (2016)
      Cuticles of some Chrysina scarabs are characterized by flat, graded, and twisted structures of nanosized chitin fibrils. As inferred from SEM images, each species has its own spatial period or pitch P which is dependent ...
    • Negative Thermal Expansion in Open Perovskites near the Precipice of Structural Stability 

      Occhialini, Connor A.; Guzmán Verri, Gian Giacomo; Handunkanda, Sahan U.; Hancock, Jason N. (2018)
      Negative thermal expansion (NTE) describes the anomalous propensity of materials to shrink when heated. Since its discovery, the NTE effect has been found in a wide variety of materials with an array of magnetic, electronic ...
    • Negative thermal expansion near two structural quantum phase transitions Connor 

      Guzmán Verri, Gian Giacomo; Hancock, Jason N. (2017-12-18)
      Recent experimental work has revealed that the unusually strong, isotropic structural negative thermal expansion in cubic perovskite ionic insulator ScF3 occurs in excited states above a ground state tuned very near a ...
    • Pressure dependence of ferroelectric quantum critical fluctuation 

      Coak, Matthew J.; Haines, Charles Robert Sebastian; Liu, Cheng; Guzmán Verri, Gian Giacomo; Saxena, Siddharth S. (2019-12-13)
      Phase transitions to a long-range-ordered state driven by a softened phonon mode are ubiquitous across condensed matter physics, but the evolution of such a mode as the system is tuned to or from the transition has never ...
    • Quantum Ferroelectric Instabilities in Superconducting SrTiO3 

      Arce Gamboa, José Rafael; Guzmán Verri, Gian Giacomo (2018)
      We examine the effects of strain and cation substitution on the superconducting phase of polar semiconductors near a ferroelectric quantum phase transition with a model that combines a strong coupling theory of ...
    • Random Electric Field Instabilities of Relaxor Ferroelectrics 

      Guzmán Verri, Gian Giacomo; Arce Gamboa, José Rafael (2017-06-13)
      Relaxor ferroelectrics are complex oxide materials which are rather unique to study the effects of compositional disorder on phase transitions. Here, we study the effects of quenched cubic random electric fields on the ...
    • Room temperature gas-solid reaction of titanium on glass surfaces forming a very low resistivity layer 

      Solís Sánchez, Hugo; Clark Binns, Neville; Azofeifa Alvarado, Daniel E.; Avendaño Soto, Esteban (2016-09)
      Titanium films were deposited on quartz, glass, polyamide and PET substrates in a high vacuum system at room temperature and their electrical resistance monitored in vacuo as a function of thickness. These measurements ...
    • Stochastic approach to the smart quantum confinement model in porous silicon 

      Ramírez Porras, Arturo; Weisz, S. Z. (Surface Science 515 (2002) L509-L513, 2002)
      A model that encompasses two approaches to explain the photoluminescence in p-type porous silicon is proposed. The model considers a stochastic distribution of nanocrystallite sizes within the porous matrix and explain the ...
    • Structure factor of a relaxor ferroelectric 

      Guzmán Verri, Gian Giacomo; Varma, Chandra M. (2015-04-14)
      We study a minimal model for a relaxor ferroelectric including dipolar interactions, and short-range harmonic and anharmonic forces for the critical modes as in the theory of pure ferroelectrics together with quenched ...
    • Study of oxide bands in p-type porous silicon layers 

      Rojas Fernández, Yoselin; Hernández López, María José; Ramírez Porras, Arturo (2019)
      The interest in developing fast and reliable chemical and biochemical sensors in an inexpensive way is something that has attracted a lot of efforts in the last decades. One of the potential material candidates is ...
    • Vacuum treatment to stabilize oxidation at low temperature region in porous silicon 

      Allen, Kevin; Pereira Cubillo, Juan Sebastián; Ramírez Porras, Arturo (2020)
      Oxidation in porous silicon is studied for as-etched samples and samples subjected to high vacuum at room temperature. Attenuated Total Reflectance (ATR) measurements in infrared spectroscopy for temperatures ranging from ...
    • Why is the electrocaloric effect so small in ferroelectrics? 

      Guzmán Verri, Gian Giacomo; Littlewood, Peter B. (2016-05-19)
      Ferroelectrics are attractive candidate materials for environmentally friendly solid state refrigeration free of greenhouse gases. Their thermal response upon variations of external electric fields is largest in the vicinity ...