Structural Characterization and Thickness Profile of Pulsed Laser-Deposited KY3F10: Ho3+ Thin Films

Abstract

Thin films of KY3F10 : Ho3+ have been successfully prepared by the pulsed laser deposition with a Nd-YAG laser (266 nm, pulse duration of 10 ns, repetition rate of 2 Hz) on a 1 cm × 1 cm silicon substrate in vacuum and for different target-to-substrate distances. The X-ray diffraction (XRD) results show that the films crystallized in the tetragonal polycrystalline phase of KY3F10 (in agreement with JCPDS card No. 27-0465). Theoretical predictions of the thickness profile have been presented, by using some experimental parameters used in the deposition. Assuming the ellipsoidal expansion of the plasma plume, the thickness profiles of films have been estimated from the solution of the gas dynamical equations for the adiabatic expansion of the plasma plume into vacuum. The results show the strong forward direction of the plume and are in a good agreement with experimental results. Both theoretical and experimental results show a decrease in the film thickness for relatively larger values of the target-to-substrate distance, and this could be attributed to a decrease in the deposition rate at such larger distances. Moreover, for a single film, the thickness also decreases for relatively larger radial angles with respect to the normal to the substrate. K e y w o r d s: thickness profile, gas dynamic equations, plasma plume. IntroductionPulsed laser deposition (PLD) is a thin film deposition technique, which has been a popular, versatile, and highly flexible method for the thin film growth for various materials [1][2][3]. Using this technique, the advantage of controlling a thin film stoichiometry accurately can be achieved by controlling the deposition parameters. The expansion of a laser-induced plasma plume increases on its way from the target to the substrate. This varies the particle flux of the target species over the substrate area, which makes the different parts of the same film to have slightly different thicknesses. It is reported that, near the axis of the plasma plume, the angular distribution of the flux species is proportional to cos , where ≫ 1 and is the radial angle with respect to the normal to the substrate [4]. The cause for this strong forward direction is the strong differences in pressure gradients in axial and radial directions. R.K. Singh and J. Narayan investigated the problem of the angular distribution of the mass flow in the plasma expansion, c ○ N. GEMECHU, T. ABEBE, 2018 by using the isothermal solution of the following gas dynamical equations with Gaussian pressure and density profiles [5]:where , , , and are the density, pressure, velocity, and entropy, respectively. However, since there exists a considerable temperature gradient inside the plasma plume [4,6], the consideration of isothermal solutions is inadequate for the description of PLD. S.I. Anisimov et al. considered the adiabatic expansion of a plume, which is a more realistic situation [4] and described the ellipsoidal expansion of a plasma plume in to vacuum by the above gas dynamic equations as well. By assuming that the...

Effect of Thermal Annealing on Thermoluminescence Glow Curves of KY3F10:Ho3+

“…The annealing temperature critically affects the luminescent behavior of a material, and the annealing brings about an enhancement or decline in the intensity of TL glow peaks of many TL materials [4][5][6][7][8]. Particularly, in this study of a KY 3 F 10 : Ho 3+ phosphor powder, we observed an enhancement in its TL intensity following the thermal annealing and a shift of the temperature of each TL peak to the higher temperature region.…”

“…One of the reasons for shifts in the peak temperatures after the annealing can be due to the cluster formation. The formation of the clusters of traps instead of randomly distributed defects causes a variation in the kinetics of the trapping and recombination processes [1][2][3][4][5].…”

“…DEBELO, S. HAILEMARIAM, 2020 kinetic parameters that include the trap depth (E), order of kinetics (b), and frequency factor (s). The study of relatively deep trapping-defect states in various phosphors, as well as the TL dating of solid-state materials, is closely related to the position of the trapping levels within the forbidden gap [3][4][5][6][7][8][9][10].…”