Nanocrystals in silicate glass as potential wells for charge carrier localization

Abstract

Background. Nanocrystals spontaneously appearing in silicate glass during its melting are considered as potential wells where free charge carriers are localized. For the first time the depth of these potential wells is estimated based on the duration of crystallization of silicate glasses at different temperatures. For silicate glass of different compositions, the depth of such potential wells was found to be equal to 0.26-0.87 eV, while the width of the band gap of the glass itself, determined by the edge of optical absorption, is more than 3 eV. Apparently, the optical width of the band gap of glass is an average value including the depth of potential wells. At the same time these wells are essential for the mechanism of electrical conductivity of thick-film resistors (silicate glasses doped with oxide compounds of ruthenium), creating conditions for variable range hopping (Mott mechanism). Study of the influence of the nanocrystalline structure on the depth of potential wells in the material under investigation, as well as the identification of the relationship between the nanoparticle size and the energetic characteristics of the system.

Materials and methods. X-ray diffraction methods were used in the study to determine the phase composition and sizes of the nanocrystals, as well as spectroscopic methods to investigate the energetic characteristics of the potential traps. Numerical calculations based on quantum-mechanical approaches were applied to model the electronic states. The experimental data were processed using statistical methods to ensure the reliability of the obtained results.

Results. The study established that a decrease in the size of the nanocrystals leads to an increase in the depth of the potential wells, which is attributed to quantum-size effects. X-ray diffraction analysis confirmed the formation of the nanocrystalline structure, while spectroscopic measurements showed a shift in the energy levels depending on the nanoparticle size. Numerical calculations are in agreement with the experimental data, confirming the influence of the nanocrystals on the electronic properties of the material.

Conclusion. The conducted study showed that the nanocrystalline structure significantly affects the depth of potential wells, which is associated with the manifestation of quantum-size effects. Both experimental and theoretical results confirmed that a decrease in the nanoparticle size leads to an increase in the energy gap and changes in the electronic properties of the material. The obtained data could be useful for the development of new nanostructured materials with specific energetic characteristics.