Strain accommodation through facet matching in La1.85Sr0.15CuO4/Nd1.85Ce0.15CuO4 ramp-edge junctions

Abstract

Scanning nano-focused X-ray diffraction and high-angle annular dark-field scanning transmission electron microscopy are used to investigate the crystal structure of ramp-edge junctions between superconducting electron-doped Nd1.85Ce0.15CuO4 and superconducting hole-doped La1.85Sr0.15CuO4 thin films, the latter being the top layer. On the ramp, a new growth mode of La1.85Sr0.15CuO4 with a 3.3° tilt of the c-axis is found. We explain the tilt by developing a strain accommodation model that relies on facet matching, dictated by the ramp angle, indicating that a coherent domain boundary is formed at the interface. The possible implications of this growth mode for the creation of artificial domains in morphotropic materials are discussed.

Three-dimensional graphoepitaxial growth of oxide films by pulsed laser deposition

“…1306 This approach provides excellent agreement with the observed 1307 tilt angle between the SICPs of two layers. Similar results can 1308 be obtained for twin boundaries [39], where facet matching is 1309 the obvious mechanism of strain accommodation on the grain 1310 boundaries. References [11] and [40] also point out matching 1311 at higher symmetries (symmetric [11] and asymmetric [40] 1312 boundaries) as an alternative to the simple geometrical match-1313 ing at the film-substrate interface.…”

“…Hoek et al [39] provide another example of a more compli-1295 cated mechanism matching top and bottom layers. The SICPs 1296 of La(Sr)CuO 4 grown on a 26°ramp etched of Nd(Ce)CuO 4 1297 demonstrated a 3.3°inclination to the SICPs of the bottom 1298 layer.…”

“…The geometry of growth and the behavior 1300 of the inclination are similar to that discussed in our study, but 1301 application of the simple geometrical model gives a smaller 1302 tilt angle of 2.8°. Authors [39] suggest a more sophisticated 1303 mechanism of matching of corresponding facets, say, (3 0 19), 1304 of the top and bottom layers during growth, with simultaneous 1305 matching of both in-plane and out-of-plane lattice constants. 1306 This approach provides excellent agreement with the observed 1307 tilt angle between the SICPs of two layers.…”

Ramp-edge junctions between superconducting Nd1.85Ce0.15CuO4and La1.85Sr0.15CuO4

“…During sample fabrication the quality of the layers is monitored by x-ray diffraction (XRD) and atomic force microscopy (AFM). Global XRD 2 q q spectra and local scans using a nano-focused x-ray beam [15] reveal no additional phases other than NCO, NCCO and LSCO.…”

“…After each ion milling step, the etch depth is verified by AFM and the surface topography of the films is measured. The ramp angle is determined to be around 26°from a HAADF-STEM cross-section [15] and from AFM measurements after ion milling. HAADF-STEM and nano-focused XRD measurements were performed to investigate the interface structure of the ramp-edge structures [15].…”