Yusuke Ichino1,2,Noriyuki Taoka1,Yoshiyuki Seike1,Tatsuo Mori1,Tomonori Arita3,2,Tomoya Horide3,2,Yutaka Yoshida3,2
Aichi Institute of Technology1,Japan Science and Technology Agency2,Nagoya University3
Yusuke Ichino1,2,Noriyuki Taoka1,Yoshiyuki Seike1,Tatsuo Mori1,Tomonori Arita3,2,Tomoya Horide3,2,Yutaka Yoshida3,2
Aichi Institute of Technology1,Japan Science and Technology Agency2,Nagoya University3
When BMO-doped REBCO superconducting thin films (BMO+REBCO films) are prepared by vapor-phase-epitaxy (VPE) such as PLD and MOCVD, BMO self-organizes into nanorods and/or nanoparticles in the REBCO matrix. On the other hand, only incoherent BMO nanoparticles are observed in the solid phase growth method such as MOD. These experimental results suggest that the kinetics of the raw material particles at the surface of the thin film crystal growth contribute significantly to the self-organization of BMO. In fact, it is known that BMO exhibits various nanostructures depending on the growth temperature (<i>T</i><sub>G</sub>), the volume fraction of BMO added (<i>V</i><sub>BMO</sub>), and the deposition rate (<i>DR</i>) in the VPE. Therefore, we have developed a BMO+REBCO thin film growth simulation considering the kinetics using the Monte Carlo (MC) method to investigate the effect of deposition conditions on the nanostructure and the formation mechanism of nanorods.<br/>As a result, the following trends were obtained.<br/>(1) When <i>T</i><sub>G</sub> is high and <i>DR</i> is low, nanorods are formed perpendicular and linear to the substrate surface. In addition, the diameter of the nanorods becomes thicker.<br/>(2) At a lower <i>T</i><sub>G</sub> and higher <i>DR</i> than (1), the nanorods are inclined and their diameters are narrower and their number density is higher.<br/>(3) When <i>DR</i> is high enough, nanoparticles consisting of short nanorods are observed.<br/>(4) Even if <i>DR</i> is high enough, linear nanorods can be obtained if <i>T</i><sub>G</sub> and <i>V</i><sub>BMO</sub> are sufficiently high.<br/>The above trends are qualitatively in good agreement with experimental results and reported cases.<br/>The time evolution of nanostructure formation can also be observed in the MC simulations. This indicates that nanorods are formed in the following steps. First, crystal nuclei of REBCO and BMO are generated on the substrate surface, from which crystal growth proceeds. Since the volume fraction of BMO is small, the BMO islands are eventually surrounded by the REBCO layer, and BMO can only grow in the direction perpendicular to the substrate surface. This process is repeated, consequently, BMO nanorods are formed. On the other hand, at low <i>T</i><sub><span style="font-size:10.8333px">G</span></sub> and high <i>DR</i>, more BMO crystal nuclei are generated, which slows down the growth rate of BMO islands in the vertical direction, resulting in tilted or shortened nanorods. In other words, the competition between REBCO and BMO growth rates results in the formation of various nanostructures.<br/>The above are mainly MC simulations in the VPE. On the other hand, the VLS growth method, which is a thin film growth method via thin liquid layer on a films surface, has the advantage that high-quality crystals can be fabricated even at high <i>DR</i>. However, it is difficult to control the BMO nanostructure. This is because the kinetics of the raw material particles is different from that of the VPE due to the presence of the thin liquid layer. Therefore, MC simulations concerning to the VLS growth method were developed and compared with the VPE for the formation of BMO nanostructures. MC simulations were also performed by intentionally adding screw dislocations to obtain a more detailed picture of the crystal growth environment.<br/>In this presentation, we will discuss the growth conditions, nanostructure formation, and thin film crystal growth environment.<br/><br/>Acknowledgment<br/>This work was partly supported by JST, CREST Grant Number JPMJCR2336, Japan.