Sr3Al2O6 PLD Target

Introduction to the Sr3Al2O6 

Sr3Al2O6 is a water soluble material which can be epitaxially deposited onto common perovskite substrate SrTiO3. Once grown, other lattice matched materials (mainly perovskite but also cubic materials can be grown on top of the Sr3Al2O6. The Sr3Al2O6 can be dissolved in water and the top layer is the freestanding which can either collected on a flexible substrate or caught on the water surface or transferred to another substrate such as silicon. Below is a video after dissolving the Sr3Al2O6 layer (deposited from one of our targets). Here we show the transfer of the epitaxial battery cathode free standing thin films onto on a flexible silicone coated PET substrate (readily available).

Crystal Structure of Sr3Al2O6 

Sr3Al2O6 forms a cubic unit cell (space group Pa3) with lattice constant a = 15.844 Å, which closely matches four unit cells of the most representative perovskite substrate SrTiO3 (STO = 3.905 Å, 4 × STO = 15.620 Å). This close resemblance in lattice forms the strong basis for the epitaxial growth of Sr3Al2O6 on SrTiO3

PLD Conditions for Epitaxial Growth of Sr3Al2O6 

Whilst initial repost show a very low oxygen background pressure (presumably as they were using RHEED) our technical staff find better films grown at higher oxygen background of 50-100 mTorr and a deposition temperature of 600-700C onto SrTiO3

Typical Substrates for Epitaxial Growth of Sr3Al2O6 

Sr3Al2O6 can readily be deposited on SrTiO3 with (100) having the least rough surface. but deposition onto STO (110) and (111) is also possible.

Solubility of Sr3Al2O6 

A key aspect of the Al-O network in Sr3Al2O6 is that they readily hydrolyze in water, therefore, the underlying SrTiO3 surface is completely free of any residues, recovering the atomically flat SrTiO3 surface. 

If you leave an uncovered Sr3Al2O6 (SAO) film in DI water it will dissolve in seconds. However when it is covered by an additional layer on top, it will take between 2-24 hours depending on the thickness of the SAO layer used (with thicker layers dissolving quicker), this is simply due to the access of the water to reach the later. In our work, we find that a layer of 20-50 nm is a good balance of a flat surface to grow additional layers from and a reasonable time for dissolving the layer.

SAO is hydroscopic so if you are no depositing anything on top then it will absorb water - keep dry if you are characterising it. Keep your target in a desiccator too!

Release of Free-standing thin films

This is the fun part. there are a few ways including adding PMMA on top, or catching on the surface or water, but the best we tried is the same as one tried in the initial work by Lu et al. Using a phone screen protector which is a thin flexible plastic with a layer of silicone on top, pressing that onto the top surface of your film (ensure no air bubbles or particles - just like when applying to your phone) then please into water. If you place into the water substrate down, the PET material of the phone cover makes it stay on the surface and it seems to dissolve quicker, assuming because there is a small amount of tension on it, one the SAO is dissolved the substrate falls to the bottom.

Other soluble interlayers

NaCl is a price example which was used a long time ago for a similar purpose. As NaCl is very soluble and the waters absorb a lot of water, this is a much trickier task to handle. There are several other materials which can be selectively dissolved but mainly using strong acids which limit the materials you can grow on top.