Growth of c-Axis-Oriented Superconducting KFe₂As₂ Thin Films

Abstract

KFe2As2, an iron-based superconductor, is expected to exhibit large spin Hall conductivity, and fabrication of high-quality thin films is requisite for evaluation of this effect and application to spintronics devices. Thin-film growth of KFe2As2 is difficult because of two intrinsic properties; its extremely hygroscopic nature and the high vapor pressure of potassium. We solved these issues by combining room-temperature pulsed laser deposition using K-rich KFe2As2 targets with thermal crystallization in KFe2As2 powder after encapsulation in an evacuated silica-glass tube with all of the processes conducted in a vacuum chamber and a dry Ar atmosphere in a glovebox. The optimized KFe2As2 films on (La,Sr)(Al,Ta)O3 single-crystal substrates were obtained by crystallization at 700 °C, and they were strongly c-axis oriented. The electrical measurements were performed with thin films protected by grease passivation to block reaction with the atmosphere. The KFe2As2 films exhibited a superconductivity transition at 3.7 K.

Superconductivity at 48 K of heavily hydrogen-doped SmFeAsO epitaxial films grown by topotactic chemical reaction using CaH2

“…b) represents the first approach, which is based on our previous reports on heteroepitaxial growth of materials composed of high vapor pressure elements such as K[29,30]. The precursor film (No.…”

Fabrication, Characterization, and Modulation of Functional Nanolayers

“…All of the setup processes must be conducted in a vacuum chamber and a dry Ar atmosphere in a glove box (Fig. 10.12) [61]. Optimized KFe 2 As 2 films on (La, Sr)(Al, Ta)O 3 single-crystal substrates are obtained by crystallization at 700°C.…”

“…Reprinted from ref. [61]. Copyright © 2014 American Chemical Society crystal structure of SnSe is changed from the thermal equilibrium GeS-type one to the RS-type one because the three-dimensional network of high-coordination number polyhedra [sixfold (PbSe 6 ) in the RS-type one] forms larger band dispersions than two-dimensional layered structures [threefold (SnSe 3 ) in the GeS-type one].…”

Novel solid-phase epitaxy for multi-component materials with extremely high vapor pressure elements: An application to KFe2As2

“…1(b) were performed in a dry and inert glove box. This tight sealing method prevents vaporization of K during high temperature 7 annealing even at 1000 °C for 30 min [Fig. 1(c) After annealing using the present technique, the stainless nuts were sintered to the stainless tube and could not be loosened.…”

“…4 This issue is much more serious for KFe 2 As 2 , because even low-temperature deposition including room temperature causes serious chemical composition deviation, producing an alkali metal-poor film. In 2014, we solved this issue by post-deposition thermal annealing in an evacuated silica-glass tube combined with a pulsed laser deposition (PLD), 7 in which the separation of the film deposition and thermal crystallization processes was the key to growing the target films, as also reported in Refs. 6, 8, and 9.…”