skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Creating Ruddlesden-Popper phases by hybrid molecular beam epitaxy

Abstract

The synthesis of a 50 unit cell thick n = 4 Sr{sub n+1}Ti{sub n}O{sub 3n+1} (Sr{sub 5}Ti{sub 4}O{sub 13}) Ruddlesden-Popper (RP) phase film is demonstrated by sequentially depositing SrO and TiO{sub 2} layers in an alternating fashion using hybrid molecular beam epitaxy (MBE), where Ti was supplied using titanium tetraisopropoxide (TTIP). A detailed calibration procedure is outlined for determining the shuttering times to deposit SrO and TiO{sub 2} layers with precise monolayer doses using in-situ reflection high energy electron diffraction (RHEED) as feedback. Using optimized Sr and TTIP shuttering times, a fully automated growth of the n = 4 RP phase was carried out over a period of >4.5 h. Very stable RHEED intensity oscillations were observed over the entire growth period. The structural characterization by X-ray diffraction and high resolution transmission electron microscopy revealed that a constant periodicity of four SrTiO{sub 3} perovskite unit cell blocks separating the double SrO rocksalt layer was maintained throughout the entire film thickness with a very little amount of planar faults oriented perpendicular to the growth front direction. These results illustrate that hybrid MBE is capable of layer-by-layer growth with atomic level precision and excellent flux stability.

Authors:
; ; ;  [1]
  1. Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States)
Publication Date:
OSTI Identifier:
22594446
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 109; Journal Issue: 4; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CALIBRATION; DEPOSITS; ELECTRON DIFFRACTION; FILMS; LAYERS; MOLECULAR BEAM EPITAXY; MOLECULAR BEAMS; NITRATES; PERIODICITY; PEROVSKITE; REFLECTION; SHUTTERS; STRONTIUM OXIDES; STRONTIUM TITANATES; THICKNESS; TITANIUM OXIDES; TRANSMISSION ELECTRON MICROSCOPY; X-RAY DIFFRACTION

Citation Formats

Haislmaier, Ryan C., Stone, Greg, Alem, Nasim, and Engel-Herbert, Roman, E-mail: rue2@psu.edu. Creating Ruddlesden-Popper phases by hybrid molecular beam epitaxy. United States: N. p., 2016. Web. doi:10.1063/1.4959180.
Haislmaier, Ryan C., Stone, Greg, Alem, Nasim, & Engel-Herbert, Roman, E-mail: rue2@psu.edu. Creating Ruddlesden-Popper phases by hybrid molecular beam epitaxy. United States. doi:10.1063/1.4959180.
Haislmaier, Ryan C., Stone, Greg, Alem, Nasim, and Engel-Herbert, Roman, E-mail: rue2@psu.edu. 2016. "Creating Ruddlesden-Popper phases by hybrid molecular beam epitaxy". United States. doi:10.1063/1.4959180.
@article{osti_22594446,
title = {Creating Ruddlesden-Popper phases by hybrid molecular beam epitaxy},
author = {Haislmaier, Ryan C. and Stone, Greg and Alem, Nasim and Engel-Herbert, Roman, E-mail: rue2@psu.edu},
abstractNote = {The synthesis of a 50 unit cell thick n = 4 Sr{sub n+1}Ti{sub n}O{sub 3n+1} (Sr{sub 5}Ti{sub 4}O{sub 13}) Ruddlesden-Popper (RP) phase film is demonstrated by sequentially depositing SrO and TiO{sub 2} layers in an alternating fashion using hybrid molecular beam epitaxy (MBE), where Ti was supplied using titanium tetraisopropoxide (TTIP). A detailed calibration procedure is outlined for determining the shuttering times to deposit SrO and TiO{sub 2} layers with precise monolayer doses using in-situ reflection high energy electron diffraction (RHEED) as feedback. Using optimized Sr and TTIP shuttering times, a fully automated growth of the n = 4 RP phase was carried out over a period of >4.5 h. Very stable RHEED intensity oscillations were observed over the entire growth period. The structural characterization by X-ray diffraction and high resolution transmission electron microscopy revealed that a constant periodicity of four SrTiO{sub 3} perovskite unit cell blocks separating the double SrO rocksalt layer was maintained throughout the entire film thickness with a very little amount of planar faults oriented perpendicular to the growth front direction. These results illustrate that hybrid MBE is capable of layer-by-layer growth with atomic level precision and excellent flux stability.},
doi = {10.1063/1.4959180},
journal = {Applied Physics Letters},
number = 4,
volume = 109,
place = {United States},
year = 2016,
month = 7
}
  • We report an atomic layer epitaxial growth of Ruddlesden-Popper (RP) thin films of SrO(SrTiO{sub 3}){sub n} (n = ∞, 2, 3, 4) by means of metalorganic aerosol deposition (MAD). The films are grown on SrTiO{sub 3}(001) substrates by means of a sequential deposition of Sr-O/Ti-O{sub 2} atomic monolayers, monitored in-situ by optical ellipsometry. X-ray diffraction and transmission electron microscopy (TEM) reveal the RP structure with n = 2–4 in accordance with the growth recipe. RP defects, observed by TEM in a good correlation with the in-situ ellipsometry, mainly result from the excess of SrO. Being maximal at the film/substrate interface, the SrO excess rapidlymore » decreases and saturates after 5–6 repetitions of the SrO(SrTiO{sub 3}){sub 4} block at the level of 2.4%. This identifies the SrTiO{sub 3} substrate surface as a source of RP defects under oxidizing conditions within MAD. Advantages and limitations of MAD as a solution-based and vacuum-free chemical deposition route were discussed in comparison with molecular beam epitaxy.« less
  • The local epitaxial growth of pulsed laser deposited Ca{sub 2}MnO{sub 4} films on polycrystalline spark plasma sintered Sr{sub 2}TiO{sub 4} substrates was investigated to determine phase formation and preferred epitaxial orientation relationships (ORs) for isostructural Ruddlesden-Popper (RP) heteroepitaxy, further developing the high-throughput synthetic approach called Combinatorial Substrate Epitaxy (CSE). Both grazing incidence X-ray diffraction and electron backscatter diffraction patterns of the film and substrate were indexable as single-phase RP-structured compounds. The optimal growth temperature (between 650 °C and 800 °C) was found to be 750 °C using the maximum value of the average image quality of the backscattered diffraction patterns. Films grew inmore » a grain-over-grain pattern such that each Ca{sub 2}MnO{sub 4} grain had a single OR with the Sr{sub 2}TiO{sub 4} grain on which it grew. Three primary ORs described 47 out of 49 grain pairs that covered nearly all of RP orientation space. The first OR, found for 20 of the 49, was the expected RP unit-cell over RP unit-cell OR, expressed as [100][001]{sub film}||[100][001]{sub sub}. The other two ORs were essentially rotated from the first by 90°, with one (observed for 17 of 49 pairs) being rotated about the [100] and the other (observed for 10 of 49 pairs) being rotated about the [110] (and not exactly by 90°). These results indicate that only a small number of ORs are needed to describe isostructural RP heteroepitaxy and further demonstrate the potential of CSE in the design and growth of a wide range of complex functional oxides.« less
  • The authors have synthesized two new lithium-containing oxides which are related to Ruddlesden-Popper phases, Li{sub 4}Sr{sub 3}Nb{sub 5.77}Fe{sub 0.23}O{sub 19.77} and Li{sub 4}Sr{sub 3}Nb{sub 6}O{sub 20}, with partial occupancy of the 12-coordinated sites by Sr, for the first time by direct solid-state reaction. While the single crystal and powder X-ray diffraction data indicate that these oxides crystallize in tetragonal cells (space group I4/mmm; a = 3.9585(2) {angstrom}, c = 25.915(3) {angstrom} and a = 3.953(2) {angstrom}, c = 26.041(5) {angstrom} for the respective oxides), the electron diffraction of some of the crystallites shows supercell reflections with a {approx} {radical}2a{sub p},more » c {approx} 25.9 {angstrom}, probably indicating a twisting of the NbO{sub 6} octahedra in the ab-plane. Although, these oxides show no significant lithium ionic conduction at room temperature, they show distinct conductivity values at elevated temperatures.« less
  • The room-temperature crystal structures of the n = 3 Ruddlesden-Popper phases Ca/{sub 4}-Mn{sub 2}FeO{sub 9.75} and Sr{sub 4}Mn{sub 2}FeO{sub 9.80} have been refined from neutron and X-ray powder diffraction data. Both adopt space group I4/mmm with (a,c) = (Ca, 3.73683(1), 27.0860(1) {angstrom}), (Sr, 3.83393(1), 27.8148(1) {angstrom}). In both compounds the cation site at the center of the perovskite blocks is preferentially occupied by Fe (Ca, Mn:Fe = 0.424:0.576(4)), and the anion vacancies are found around this site. The occupied anion sites show static disorder in Ca{sub 4}Mn{sub 2}FeO{sub 9.75} but not in Sr{sub 4}Mn{sub 2}FeO{sub 9.80}. Both compounds are electricalmore » insulators which order antiferromagnetically at T{sub N} = 75 K (Ca) or 90 K (Sr). Susceptibility and M(H) data suggest that not all the Mn and Fe cations take part in the long-range magnetic ordering, and there is evidence of a spin glass transition in both compounds at {approximately}11 K. The magnetic structure of Ca{sub 4}Mn{sub 2}FeO{sub 9.75} at 5 K has been determined by neutron diffraction. No ordered moment was detected on the Mn/Fe site at the center of the perovskite blocks; 0.74(1) {micro}{sub B} per transition metal cation was measured at the sites on the block edges. Possible causes of magnetic frustration in this crystal structure are considered. Ca{sub 4}Mn{sub 2}FeO{sub 9.75} has a magnetoresistance of {minus}4% at 137 K in a 14 T field.« less
  • The crystal chemistry of the system LaO{sub 1.5}-CaO-CuO at the 1:1:2 composition was studied at high pressures with the goal of stabilizing new perovskite cuprates with two-dimensional ordering of La, Ca cations and oxygen vacancies. Several phases, including the perovskites La{sub 4}Ca{sub 4}Cu{sub 8}O{sub 20}, La{sub 4}Ca{sub 4}Cu{sub 88}O{sub 18} and the Ruddlesden-Popper (RP) phase La{sub 2}Ca{sub 2}Cu{sub 3}O{sub 8}, containing three copper oxide layers (n = 3), were revealed for the first time. The results are very sensitive to experimental conditions, and a variety of reaction channels are observed at the 1:1:2 composition depending on the choice of totalmore » pressure, p{sub O}{sub 2}, temperature, and annealing conditions. The perovskite-related phases at this composition exhibited A-site cation disorder and three-dimensional ordering of oxygen vacancies. The Ruddlesden-Popper phase required the substitution of Sr on the A-sites to be metastably retained at room temperature. Due to its thermal instability, the RP phase could not be doped to a carrier concentration at which superconductivity might be observed.« less