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(Color online) Schematic diagram of two-step lithography process utilizing a nanopatterned tungsten (W) film as a protective layer. Spin-coated double layer electron resist on (a) BiFeO3/SrRuO3/SrTiO3, (b) electron beam lithography, (c) sputter-deposition of a W layer, (d) lift off of the resist layer, (e) FIB lithography, and (f) chemical removal of the W layer. (g) Schematic showing the rotation and strain of the out-of-plane lattice vector due to asymmetric in-plane expansion of the BFO film when the planar film constraint is removed from the sides of the nanostructure upon fabrication.
(Color online) Overview scan of multiple patterned BFO devices showing nano-XRD results [(b)-(d)] and a reference SEM image (a). The BFO (002) diffracted x-ray intensity is shown in (b), the 2θ center of mass variation (COM) in (c), and the χ COM variation in (d). A rotation of the out-of-plane lattice vector (C-axis) from the center of each object towards all released edges is indicated by the left-right/blue-red angular (COM) distribution of 2θ (c) and the up-down/blue-red angular COM distribution of χ (d).
(Color online) Overview of x-ray diffraction scan, comparing a single patterned BFO nanostructure [(d)-(f)] with the unpatterned planar film [(a)-(c)]. The BFO (002) x-ray diffraction signal from the nanostructure exhibits a generally lower intensity, higher 2θ value, and increased 2θ and χ variance in comparison with the unpatterned planar film (common linear scale bars are included for comparison). The average domain size indicated by this variance is comparable between the nanostructure and the planar film regions.
(Color online) Results of nanofocused x-ray diffraction lattice mapping in a single 500 nm BFO nanostructure [(b)-(d)] compared to the ferroelectric domain structure observed via PFM (a). Repeated 2D lateral scans were taken while varying the sample angle across the BFO (002) rocking curve, from which (b) the integrated intensity, (c) out-of-plane lattice strain, and (d) out-of-plane lattice (C-axis) rotation were extracted. The lattice constant of the film in the nanostructure is relaxed relative to the planar film by a strain value of as much as −1.8% Δc/c, with a strain distribution that generally corresponds to the ferroelectric domain structure (shown in (a)).
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