Estudio de la influencia del dopaje con praseodimio sobre las propiedades estructurales y ópticas de películas delgadas de MoO3 preparadas por spray pirólisis

Abstract

Estudio de la influencia del dopaje con praseodimio sobre las propiedades estructurales y ópticas de películas delgadas de MoO3 preparadas por spray pirólisis. De las micrografías obtenidas se evidencia la formación de granos de dimensiones nanométricas y micrométricas. En las películas dopadas, a temperatura de 473 K se presentas fracturas y poros en la superficie que van desapareciendo con el aumento de la temperatura, volviéndose más evidentes en las películas con mayor porcentaje de dopante. Se obtiene una variación en la transmitancia de las películas dopadas en comparación con las que no se doparon. Para las películas sin dopar la transmitancia disminuye entre las temperaturas de 473 K y 573 K, para las temperaturas de 623 K y 673 K es mayor la transmitancia. Se encontró que la región de absorción se presenta en regiones más altas de longitud de onda para las películas entre 2% y 4% de dopaje. Se dio una variación del gap entre 3.90 eV y 3.95 eV en la película de 673 K. Se realizaron medidas de fotoluminiscencia, pero debido a la poca concentración de Pr en cada una de las muestras y que la luz de excitación no tenía suficiente energía, no se obtuvo señal de recombinación.

Abstract: Since its creation in 2006, the Materials Group with Technological Applications of the Department of Physics of the National University of Colombia, has been investigating the development and characterization of thin films of different materials grown under different techniques. In this work, MoO3 films doped at different concentrations of praseodymium Pr were deposited under the pyrolysis spray technique. It was made from heptamolybdate solutions of Ammonium 4 - hydrated, Praseodymium nitrate and citric acid, with dopant concentration of 0%, 2%, 4%, 6% and 10% in relation to the atomic concentration of Mo, a substrate temperature of 473, 523, 573, 623 and 673 K and with a volume of the spray solution amount of 10 ml. The samples with 0% doping have a white appearance and as the temperature of the substrate increased they became a little more transparent, the other samples with doping equal to or greater than 2% have a dark appearance, which were clarified to a dark gray tone as the substrate temperature was increased. Using the X-ray scattered electron spectroscopy (EDAX) analysis technique, it was evidenced that, in all the depositions, films doped with Praseodymium were grown, the percentage of atomic weight in the film decreasing with the substrate temperature, with which each One of the precursor solutions was suitable for depositing the films. Based on the technique of X-ray diffraction, it was identified that at substrate temperature below 573 K the undoped films grow in an amorphous form. At temperatures above 573 K, the poly-crystalline phase α - MoO3 is obtained, which is destroyed by the introduction of the Praseodymium, becoming amorphous at high temperatures as the percentage of the dopant increases. There is a preferential growth in the films along the direction (h00). From the micrographs obtained, the formation of grains of nanometric and micrometric dimensions is evident. In the doped films, at a temperature of 473 K, there are fractures and pores on the surface that disappear with the increase in temperature, becoming more evident in films with a higher percentage of dopant. A variation in the transmittance of the doped films is obtained in comparison with those that were not doped. For the films without doping the transmittance decreases between the temperatures of 473 K and 573 K, for the temperatures of 623 K and 673 K the transmittance is higher. It was found that the absorption region occurs in higher regions of anda length for films between 2% and 4% doping. There was a in gap variation for the 673 K film between 3.90 eV and 3.95 eV. Photoluminescence measurements were made, but due to the low concentration of Pr in each of the samples and that the excitation light did not have enough energy, no recombination signal was obtained.