Juan A. Sans

Oscillations studied with the smartphone ambient light sensor

This paper makes use of a smartphones ambient light sensor to analyse a system of two coupled springs undergoing either simple or damped oscillatory motion. The period, frequency and stiffness of the spring, together with the damping constant and extinction time, are extracted from light intensity curves obtained using a free Android application. The results demonstrate the instructional value of mobile phone sensors as a tool in the physics laboratory.

Ordered helium trapping and bonding in compressed arsenolite: Synthesis of As4O6 2He

The compression of arsenolite (cubic As2O3) has been studied from a joint experimental and theoretical point of view. Experimental X-ray diffraction and Raman scattering measurements of this molecular solid at high pressures with different pressure-transmitting media have been interpreted with the help of ab initio calculations. Our results confirm arsenolite as one of the softest minerals in absence of hydrogen bonding and provide evidence for helium trapping above 3 GPa between adamantane-type As4O6 cages, thus leading to a new compound with stoichiometry He2As4O6. Helium trapping alters all properties of arsenolite. In particular, pressure-induced amorphization, which occurs in pure arsenolite above 15 GPa, is impeded when He is trapped between the As4O6 cages; thus resulting in a mechanical stability of He2As4O6 beyond 30 GPa. Our work paves the way for the modification of the properties of other molecular solids by compression depending on their ability to trap relatively small atomic or molecular species and form new compounds. Furthermore, our work suggests that compression of molecular solids with noble gases as helium could result in unexpected results compared to other pressure-transmitting media.

SnS Thin Films Prepared by Chemical Spray Pyrolysis at Different Substrate Temperatures for Photovoltaic Applications

The preparation and analysis of morphological, structural, optical, vibrational and compositional properties of tin monosulfide (SnS) thin films deposited on glass substrate by chemical spray pyrolysis is reported herein. The growth conditions were evaluated to reduce the presence of residual phases different to the SnS orthorhombic phase. X-ray diffraction spectra revealed the polycrystalline nature of the SnS films with orthorhombic structure and a preferential grain orientation along the (111) direction. At high substrate temperature (450°C), a crystalline phase corresponding to the Sn2S3 phase was observed. Raman spectroscopy confirmed the dominance of the SnS phase and the presence of an additional Sn2S3 phase. Scanning electron microscopy (SEM) images reveal that the SnS film morphology depends on the substrate temperature. Between 250°C and 350°C, SnS films were shaped as rounded grains with some cracks between them, while at substrate temperatures above 400°C, films were denser and more compact. Energy-dispersive x-ray spectroscopy (EDS) analysis showed that the stoichiometry of sprayed SnS films improved with the increase of substrate temperature and atomic force microscopy micrographs showed films well covered at 350°C resulting in a rougher and bigger grain size. Optical and electrical measurements showed that the optical bandgap and the resistivity decreased when the substrate temperature increased, and smaller values, 1.46xa0eV and 60 Ωxa0cm, respectively, were attained at 450°C. These SnS thin films could be used as an absorber layer for the development of tandem solar cell devices due to their high absorbability in the visible region with optimum bandgap energy.

Pressure-Driven Isostructural Phase Transition in InNbO4: In Situ Experimental and Theoretical Investigations

The high-pressure behavior of technologically important visible-light photocatalytic semiconductor InNbO4, adopting a monoclinic wolframite-type structure at ambient conditions, was investigated using synchrotron-based X-ray diffraction, Raman spectroscopic measurements, and first-principles calculations. The experimental results indicate the occurrence of a pressure-induced isostructural phase transition in the studied compound beyond 10.8 GPa. The large volume collapse associated with the phase transition and the coexistence of two phases observed over a wide range of pressure shows the nature of transition to be first-order. There is an increase in the oxygen anion coordination number around In and Nb cations from six to eight at the phase transition. The ambient-pressure phase has been recovered on pressure release. The experimental pressure-volume data when fitted to a Birch-Murnaghan equation of states yields the value of ambient pressure bulk modulus as 179(2) and 231(4) GPa for the low- and high-pressure phases, respectively. The pressure dependence of the Raman mode frequencies and Grüneisen parameters was determined for both phases by experimental and theoretical methods. The same information is obtained for the infrared modes from first-principles calculations. Results from theoretical calculations corroborate the experimental findings. They also provide information on the compressibility of interatomic bonds, which is correlated with the macroscopic properties of InNbO4.

Diseño y evaluación de un laboratorio virtual de vectores en 3D

En Fisica, un gran numero de magnitudes son vectores, y su uso requiere operaciones tipicas tales como: suma, resta, multiplicacion por un escalar, producto escalar, producto vectorial y producto mixto. Se trata de conceptos basicos en todos los cursos de Fisica General para grados en Ingenieria. Sin embargo, algunos estudiantes carecen de una comprension profunda de las operaciones vectoriales y sus propiedades. En este trabajo presentamos un laboratorio virtual (desarrollado utilizando la herramienta “Easy Java Simulations”) para el estudio y comprension de estos conceptos. El usuario puede introducir las componentes de los vectores de entrada y obtiene una representacion 3D, que puede escalar y girar para una mejor visualizacion. Se puede seleccionar cualquiera de las operacionesxa0antes mencionadas, y se muestra el resultado tanto numerica como grafica-mente. El usuario puede tambien modificar cualquiera de los vectores repre-sentados. De esta forma, el laboratorio virtual proporciona una visualiza-cion en tiempo real de como el cambio afecta al resultado. Tambien se incluye la posibilidad de modificar unicamente el modulo o la orientacion. Para comprobar la eficiencia del laboratorio virtual, se han analizado los resultados obtenidos por dos grupos de estudiantes (laboratorio virtual vs. recursos tradicionales). Tambien se ha realizado una encuesta de opinion. Palabras clave: laboratorio virtual, Fisica, Easy Java, analisis vectorial.