Fabrication and convergent X-ray nanobeam diffraction characterization of submicron-thickness SrTiO3 crystalline sheets

Abstract

The creation of thin SrTiO3 crystals from (001)-oriented SrTiO3 bulk single crystals using focused ion beam milling techniques yields sheets with submicron thickness and arbitrary orientation within the (001) plane. Synchrotron x-ray nanodiffraction rocking curve widths of these SrTiO3 sheets are less than 0.02°, less than a factor of two larger than bulk SrTiO3, making these crystals suitable substrates for epitaxial thin film growth. The change in the rocking curve width is sufficiently small that we deduce that dislocations are not introduced into the SrTiO3 sheets. Observed lattice distortions are consistent with a low concentration of point defects.

Stressor-layer-induced elastic strain sharing in SrTiO3 complex oxide sheets

“…24 The sample was annealed at 1000 ºC for 50 h in order to reduce the distortion of the sheet due to ion-beam induced structural changes, following a procedure described in ref. 19. Previous studies have Indicated under these conditions, the strain in the STO sheet due to milling is on the order of 6 × 10 -4 .…”

“…19,25 FIB yielded STO sheets that have the same x-ray nanobeam diffraction rocking curve widths as the bulk unprocessed STO crystal. 19 A scanning electron microscope image of an STO sheet before the deposition of the SiN layers is shown in Fig. 1(b).…”

“…This control is achieved without changes in composition or increases in dislocation density, as evidenced by the observed rocking curve widths. 19 The approach can be extended to sheets of larger lateral size and can provide a route to complex oxides with improved properties for a range of technological applications in electronics and optics. The change in lattice parameter of the bare STO sheet arises from the FIB processing.…”

“…Thin complex oxide 4 sheets have been created by chemical exfoliation, epitaxial lift-off, and lithographic techniques. [16][17][18][19][20] The first two methods, however, face significant experimental challenges. Chemical exfoliation often results in an ensemble of micron-scale sheets rather than a thin layer with large lateral extent.…”

“…21 Strain of a similar magnitude was observed in previous studies of FIB-patterned STO, and has a magnitude consistent with the formation of point defects during ion-beam milling. 19 The strain measured from the STO sheet with the stressors has a different distribution than the sheet without the stressor, as shown in Fig. 4(a).…”