Electronic and optical properties of lead iodide

ABSTRACT: Lead iodide (PbI2) is a very important material with a technological applicability as a room-temperature radiation detector. It is a wide-band-gap semiconductor (Eg.2 eV) with high environmental stability efficiency. The performance of the detector cannot be fully understood unless its electronic and optical properties are determined. Recently, its band-gap energy and thermal properties were determined by photoacoustic spectroscopy. A single crystal of PbI2 was grown by the Bridgman method with the c-axis oriented perpendicular to the growth axis. The purpose of this work is to obtain the electronic structure of PbI2, its dielectric functions e 1 and e 2 by ellipsometry and theoretically by full-potential linear muffin-tinorbital ~FPLMTO! method, and the temperature dependence of the measured band-gap energy by optica absorption. The obtained Eg(T) can be fitted by two different methods, leading to Eg ~0 K! and Eg ~300 K!

Uma abordagem diferente na estatística do experimento Millikan

The classic Millikan experiment to determine the electron charge is very interesting from the point of view of statistics of experimental measurements. In a physics laboratory it is suggested to divide the obtained values of the electric charge by the value of an electron charge, and it is possible to experimentally establish that the oil droplets carry integer numbers of electrons. This work presents a new statistical algorithm for the treatment of measurements and for determining the best value of the electron charge in a Millikan experiment.A experiência clássica de Millikan para a determinação da carga do elétron é muito interessante do ponto de vista de estudos estatísticos de medidas experimentais. Em uma experiência didática de laboratório de física, é sugerido dividir os valores da carga elétrica obtida pelo valor da carga do elétron e, desta forma, estabelecer experimentalmente que as gotas de óleo carregam números inteiros de elétrons. Este trabalho apresenta um algoritmo estatístico novo para tratamento das medidas e para o cálculo do melhor valor da carga do elétron em um experimento Millikan

Gap energy studied by optical transmittance in lead iodide monocrystals grown by Bridgman's Method

The bandgap energy as a function of temperature has been determined for lead iodide. The monocrystal was obtained in a vacuum sealed quartz ampoule inside a vertical furnace by Bridgman's method. The optical transmittance measurement enables to evaluate the values of Eg. By a fitting procedure of Eg as a function of temperature is possible to extract the parameters that govern its behavior. The variation of Eg with temperature was determined as: Eg(T) = Eg(0) - <FONT FACE="Symbol">a</FONT>T2/(<FONT FACE="Symbol">a</FONT> + T), with: Eg(0) = (2.435 <FONT FACE="Symbol">±</FONT> 0.008) eV, <FONT FACE="Symbol">a</FONT> = (8.7 <FONT FACE="Symbol">±</FONT> 1.3) x 10-4 eV/K and <FONT FACE="Symbol">a</FONT> = (192 <FONT FACE="Symbol">±</FONT> 90) K. The bandgap energy of lead iodide at room temperature was found to be 2.277 <FONT FACE="Symbol">±</FONT> 0.007 eV