Magnetron Sputter deposition of a 48-member cuprate superconductor library: Bi2Sr2YxCa1-xCu2Oy (0.5 <= x <= 1) linearly varying in steps of 0.01

TL;DR

This study demonstrates the successful fabrication of a 48-member cuprate superconductor library using magnetron sputtering, enabling detailed exploration of composition-dependent properties and phase space mapping.

Contribution

It introduces a novel spatial composition spread method for creating a dense library of cuprate superconductors with controlled composition variation.

Findings

Crystalline order develops with linear c-axis contraction as Y-content increases.

Films show preferred orientation for thinner samples.

The composition variation allows detailed phase space mapping.

Abstract

Using magnetron sputtering, a spatial composition spread approach was applied successfully to obtain 48-member libraries of the Bi2Sr2YxCa1-xCu2Oy (0.5<= x <=1)cuprate superconducting system. The libraries of each system were deposited onto (100) single crystal MgO, mounted on a water cooled rotating table, using two targets: the antiferromagnetic insulator Bi2Sr2YCu2Oy (P=98 W RF) and the hole doped superconductor Bi2Sr2CaCu2Oy (P=44 W DC). A low chamber pressure of 0.81 mTorr argon is used to reduce scattering by the process gas. To minimize oxygen resputtering a substrate bias of -20 V was used as well as a process gas free of oxygen. A rapid thermal processor is used to post-anneal the amorphous deposited films. A step annealing regime was used, with a ramp rate of 5 degrees C/s for heating and cooling, with a first plateau at 780 C held for 200 s, and a second at 875 C held for 480 s. X-ray diffraction reveals that the films develop crystalline order with the c-axis lattice parameter contracting linearly from 30.55 Angstroms (x=0.5) to 30.24 Angstroms (x=1.0) with increasing Y-content, consistent with bulk values. The crystallized films are polycrystalline, developing preferred orientation (c-axis parallel to the substrate) for thinner members of the library. There is a change of 0.01 in doping per library member which will enable further studies to densely map phase space.