Patterning and epitaxy of large-area arrays of nanoscale complex oxide epitaxial heterostructures

Patterning and epitaxy of large-area arrays of nanoscale complex oxide epitaxial heterostructures

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A combination of block copolymer (BCP) lithography and solid-phase epitaxy can be employed to form large areas, on the order of square centimeters, of a high density of epitaxial crystalline complex oxide nanostructures.We have used BCP lithography with a poly(styrene-block-methyl methacrylate) (PS-b-PMMA) copolymer to template a nanohole array either directly on an (001)-oriented SrTiO3 (STO) single crystal substrate or on a 20 nm-thick Si3N4 layer deposited on the STO substrate.BCPs with the selected compositions assembled in a cylindrical phase with 16 ngetikin nm diameter PMMA cylinders and a cylinder-to-cylinder spacing of 32 nm.The substrate was modified with an energetically non-preferential polymer layer to allow for the vertical alignment of the cylinders.

The PMMA cylinders were removed using a subtractive process, leaving an array of cylindrical holes.For BCPs assembled on Si3N4/STO, the pattern was transferred to the Si3N4 layer using reactive ion etching, exposing the underlying STO substrate in the nanoholes.An amorphous LaAlO3 (LAO) layer was deposited on the patterned Si3N4/STO at room temperature.The amorphous LAO read more epitaxially crystallized within the nanoscale-patterned holes with fully relaxed lattice parameters through solid phase epitaxy, resulting in the formation of nanoscale LAO/STO epitaxial heterostructures.