Coloration and oxygen vacancies in wide band gap oxide semiconductors: Absorption at metallic nanoparticles induced by vacancy clustering - A case study on indium oxide
Résumé
In this paper, we show by optical and electron microscopy based investigations that vacancies in oxides may cluster and form metallic nanoparticles that induce coloration by extinction of visible light. Optical extinction in this case is caused by generation of localized surface plasmon resonances at metallic particles embedded in the dielectric matrix. Based on Mie's approach, we are able to fit the absorption due to indium nanoparticles in In2O3 to our absorption measurements. The experimentally found particle distribution is in excellent agreement with the one obtained from fitting by Mie theory. Indium particles are formed by precipitation of oxygen vacancies. From basic thermodynamic consideration and assuming theoretically calculated activation energies for vacancy formation and migration, we find that the majority of oxygen vacancies form just below the melting point. Since they are ionized at this temperature they are Coulomb repulsive. Upon cooling, a high supersaturation of oxygen vacancies forms in the crystal that precipitates once the Fermi level crosses the transition energy level from the charged to the neutral charge state. From our considerations we find that the ionization energy of the oxygen vacancy must be higher than 200 meV.
Mots clés
Indium nanoparticles
Localized surface plasmon resonance
Metallic nanoparticles
Optical and electron microscopies
Particle distributions
Transition energy levels
Oxygen vacancies
Activation energy
Energy gap
Indium compounds
Ionization
Light absorption
Nanoparticles
Oxide semiconductors
Plasmons
Precipitation (chemical)
Surface plasmon resonance
Wide band gap semiconductors
Absorption measurements
Dielectric matrixes