Modification of Properties of Yttria Stabilized Zirconia Epitaxial Thin Films by Excimer Laser Annealing

Abstract

This study focuses on the ultrafast improvement of surface wettability, electrical, and room temperature magnetic characteristics of cubic zirconia single crystalline thin films after laser annealing. The point defects generated by the laser treatment are envisaged to play a critical role in altering the above properties. Yttria stabilized zirconia (YSZ) thin films were epitaxially grown on Si(100) substrates by pulsed laser deposition technique and subsequently annealed by a KrF excimer laser beam (τ = 25 ns) using low-energy laser pulses. An atomically sharp interface, parallel to the film free surface, between laser annealed layer and the pristine region was observed. The single crystalline nature of thin films was preserved following the laser treatment. The laser-solid interaction with YSZ led to the introduction of point defects, i.e., oxygen vacancies, resulting in a strained structure which, in turn, resulted in the formation of a tetragonal-like zirconia. With the increase of number of laser pulses the laser treated films got highly disordered due to the high concentration of the point defects, while maintaining their crystalline nature. Although the surface of the pristine sample showed weak hydrophilic characteristics (contact angle ∼ 73°), the laser annealed samples exhibited significantly improved hydrophilic characteristics. It was found that there is an optimum number of laser pulses where the maximum hydrophilicity (contact angle ∼ 22°) is obtained. The carrier concentration in the sample with the highest hydrophilicity was determined to be higher by about 5 orders of magnitude compared to the pristine sample. This sample possessed the lowest electrical resistivity. The laser annealed YSZ epilayers showed a superior room-temperature ferromagnetic behavior, compared to the pristine samples. A 2-fold enhancement in the magnetization of the samples was observed following the laser treatment which is a clear demonstration of the key role of defects and their transient distribution throughout the lattice. All these observations were correlated with the formation of point defects due to the photon interaction with YSZ and absorption of energy of the KrF laser photons to produce defects.

Surface Analysis and Optical Properties of Cu-Doped ZnO Thin Films Deposited by Radio Frequency Magnetron Sputtering

“…The FGG equation is given as: The wettability behavior of the surface is strongly related to the surface morphology of the sample surface [27]. The results of wettability tests are shown in the inset of Figure 2a-c. With an increasing R rms , a larger amount of air is expected to be trapped in the gap of the nanoislands [28], which, in turn, would greatly increase the contact area of the air-water interface (i.e., preventing the water droplets from penetrating into the air pockets), resulting in a larger contact angle (θ CA ), as displayed in the rougher sample (see the Cu-6% doping CZO thin film in Figure 2b). It is noted that similar phenomena were reported by Dave et al [29].…”

Unique redox properties in defective CeO2-x nanocrystallines synthesized by laser melting

“…The laser focused upon the pellets' top surface and the spot (75 μm in diameter and 50 W in laser power) moved along a scheduled path to fully melt the entire area. The energy density of the laser is about 600 J cm −2 , which is much higher than that normally used in laser ablation or annealing of ceramics [13,14]. The surface zone treated by laser was then carefully removed and ground into powder manually for characterization, and will be marked as "LT" in the following text.…”

Annealing-Driven Microstructural Evolution and Its Effects on the Surface and Nanomechanical Properties of Cu-Doped NiO Thin Films

“…Extrinsically, in addition to the effect of surface hierarchical modification (namely the increased surface roughness), described above [47], the improved crystallinity, and hence reduction of the defect concentration, may also play a role, as well. Indeed, as pointed out by Bayati et al [48], point defects, such as oxygen vacancies, were mainly responsible for the significant hydrophilicity (contact angle~22 • ) observed in their laser pulses irradiated yttria stablilized zirconia films. In our case here, the removal of the grown-in defects during deposition by annealing, thus, is expected to result in increasing surface hydrophobicity.…”