Densely mapping the phase diagram of the cuprate superconductor $La_{2-x}Sr_{x}CuO_{4}$ $(0 \leq x \leq 0.18)$, using a spatial composition spread approach*

Densely mapping the phase diagram of cuprate superconductors is the key to deciphering the normal state properties of these materials. A spatial composition spread approach was used to successfully deposit a 52-member composition spread library of $La_{2-x}Sr_{x}CuO_{4}$ $(0 \leq x \leq 0.18)$. Two home made targets of $La_{2}CuO_{4}$ and $La_{1.82}Sr_{0.18}CuO_{4}$ were sputtered using 41 W RF and 42 W DC bias,respectively, at process gas pressure of 15 mTorr argon. A linear composition variation was produced by using specially designed masks in front of the $La_{2}CuO_{4}$ and $La_{1.82}Sr_{0.18}CuO_{4}$ targets. The libraries were sputtered onto $LaSrAlO_{4}$(001), $SrTiO_{3}$(100) and MgO(100)substrates through a 52-slot shadow mask, and post annealed in a two step sequence - $800^{o}C$ for 1 h then at $950^{o}C$ for 2 h - in a tube sealed with oxygen gas. XRD and WDS analysis revealed the expected doping variation. Resistivity measurements reveal expected features such as a suppression of superconductivity near $\frac{1}{8}$ (x = 0.125) doping and a novel one - that superconductivity appears near 3\% (x=0.03) doping. The work present a powerful approach to studying the phase diagram of existing superconductors as well as offering a method to search for new materials.