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Isolated pyramids, 30–80 nm wide and 3–20 nm tall, form during sputter-annealing cycles on the Ge (110) surface. Pyramids have four walls with {19 13 1} faceting and a steep mound at the apex. We used scanning tunneling microscopy (STM) under ultrahigh vacuum conditions to periodically image the surface at ion energies between 100 eV and 500 eV and incremental total flux. Pyramids are seen using Ar+ between 200 eV and 400 eV, and require Ag to be present on the sample or sample holder. We suspect that the pyramids are initiated by Ag co-sputtered onto the surface. Growth of pyramids is due to the gathering of step edges with (16 × 2) reconstruction around the pyramid base during layer-by-layer removal of the substrate, and conversion to {19 13 1} faceting. The absence of pyramids using Ar+ energies above 400 eV is likely due to surface damage that is insufficiently annealed.
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Self-assembly and properties of domain walls in BiFeO3 layers grown via molecular-beam epitaxy
Bismuth ferrite layers, ∼200-nm-thick, are deposited on SrRuO3-coated DyScO3(110)o substrates in a step-flow growth regime via adsorption-controlled molecular-beam epitaxy. Structural characterization shows the films to be phase pure with substrate-limited mosaicity (0.012° x-ray diffraction ω-rocking curve widths). The film surfaces are atomically smooth (0.2 nm root-mean-square height fluctuations) and consist of 260-nm-wide [11¯1]o-oriented terraces and unit-cell-tall (0.4 nm) step edges. The combination of electrostatic and symmetry boundary conditions promotes two monoclinically distorted BiFeO3 ferroelectric variants, which self-assemble into a pattern with unprecedentedly coherent periodicity, consisting of 145 ± 2-nm-wide stripe domains separated by [001]o-oriented 71° domain walls. The walls exhibit electrical rectification and enhanced conductivity.
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- PAR ID:
- 10595065
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- APL Materials
- Volume:
- 7
- Issue:
- 7
- ISSN:
- 2166-532X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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