The Effect of Annealing Temperature on the Plasma Edge in Reflectance Spectra of Al/Al 2 O 3 Composites Synthesized by T
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The Effect of Annealing Temperature on the Plasma Edge in Reflectance Spectra of Al/Al2O3 Composites Synthesized by Thermal Oxidation of Aluminum Thin Films Kamal Kayed 1
&
Lubna Alberni 1
Received: 19 April 2020 / Accepted: 29 June 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this study, the structural and optical properties of aluminum oxide thin films were investigated. Aluminum oxide thin films were prepared on silicon and glass substrate by DC magnetron sputtering of aluminum targets with subsequent thermal oxidation of the aluminum-deposited thin films. Important result obtained included the presence of a plasma edge for the individual aluminum atoms. In addition, the temperatures that resulted in the highest concentration of surface plasmons were determined. On other hand, the relationship between the plasma edge and the optical energy gap was investigated. Keywords Silver oxide . Thin film . DC magnetron sputtering . Annealing . Plasmon . Plasma edge
Introduction Silver oxide thin films gained the attention of many research groups in recent years [1–13], mainly because they exhibit significant applications in gas sensors, passivation, organic field-effect transistors, perovskite solar cells, organic lightemitting diode encapsulation, optical data storage, and surface plasmon optics, etc. There are numerous deposition techniques for obtaining Al2O3 thin films as thermal evaporation [2],atomic layer deposition (ALD) [13–15], magnetron sputtering [16, 17], pulsed-laser deposition (PLD) [18], spray pyrolysis [19, 20], and sol-gel coating [21]. Valence electrons in any conductor act like free electrons, where the collision among the electrons is similar among gas molecules that are described in the kinetic theory of gases [22]. Optical properties of metals are produced due to the interaction between the fallen photons on the surface and the electronic cloud [22]. Optical reflectivity is considered the most important physical property of the metal layers, which generally relates to the interaction between the light and the free electrons which could be expressed by the equation of dispersion as follows [22, 23]:
sffiffiffiffiffiffiffiffiffiffiffiffiffiffi 4πN e2 ωp ¼ ε∞ m*
ð1Þ
where N is the concentration of conducting electrons, e the electron charge, ∞ the high frequency (visible wavelength), ɛ the dielectric constant, and m* the electron effective mass. Both electron concentration and electron effective mass affect this plasma edge [22] and could be directly determined from the reflecting spectra where dramatic change of reflectivity happens at the plasma edge as a result of photon reflection from the conduction band electron plasma oscillations [23]. Furthermore, equation indicates that, when carrier concentration and hence typically the conductivity are increased, the plasma edge moves to high frequencies (shorter wavelengths) [23]. In this paper, we are interested in identifying the factors affecting the plasma edge formed in the reflectance spectra of aluminum oxide thin films prepared
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