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Title: Van der Waals epitaxy and remote epitaxy of LiNbO 3 thin films by pulsed laser deposition
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Award ID(s):
1719875 1712752
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Journal Name:
Journal of Vacuum Science & Technology A
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Sponsoring Org:
National Science Foundation
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  1. Abstract One-dimensional c -axis-aligned BaZrO 3 (BZO) nanorods are regarded as strong one-dimensional artificial pinning centers (1D-APCs) in BZO-doped YaBa 2 Cu 3 O 7− x (BZO/YBCO) nanocomposite films. However, a microstructure analysis has revealed a defective, oxygen-deficient YBCO column around the BZO 1D-APCs due to the large lattice mismatch of ∼7.7% between the BZO (3a = 1.26 nm) and YBCO (c = 1.17 nm), which has been blamed for the reduced pinning efficiency of BZO 1D-APCs. Herein, we report a dynamic lattice enlargement approach on the tensile strained YBCO lattice during the BZO 1D-APCs growth to induce c -axis elongation of the YBCO lattice up to 1.26 nm near the BZO 1D-APC/YBCO interface via Ca/Cu substitution on single Cu-O planes of YBCO, which prevents the interfacial defect formation by reducing the BZO/YBCO lattice mismatch to ∼1.4%. Specifically, this is achieved by inserting thin Ca 0.3 Y 0.7 Ba 2 Cu 3 O 7− x (CaY-123) spacers as the Ca reservoir in 2–6 vol.% BZO/YBCO nanocomposite multilayer (ML) films. A defect-free, coherent BZO 1D-APC/YBCO interface is confirmed in transmission electron microscopy and elemental distribution analyses. Excitingly, up to five-fold enhancement of J c ( B ) at magnetic field Bmore »= 9.0 T// c -axis and 65 K–77 K was obtained in the ML samples as compared to their BZO/YBCO single-layer (SL) counterpart’s. This has led to a record high pinning force density F p together with significantly enhanced B max at which F p reaches its maximum value F p,max for BZO 1D-APCs at B // c -axis. At 65 K, the F p,max ∼158 GN m −3 and B max ∼ 8.0 T for the 6% BZO/YBCO ML samples represent a significant enhancement over F p,max ∼ 36.1 GN m −3 and B max ∼ 5.0 T for the 6% BZO/YBCO SL counterparts. This result not only illustrates the critical importance of a coherent BZO 1D-APC/YBCO interface in the pinning efficiency, but also provides a facile scheme to achieve such an interface to restore the pristine pinning efficiency of the BZO 1D-APCs.« less
  2. (Sc 2 O 3 ) x (Ga 2 O 3 ) 1−x was grown by molecular beam epitaxy at low temperatures (100 °C) using a variety of growth sequences to avoid surface segregation of Ga. Continuous and digital growth techniques always produced Ga segregation. This surface segregation was attributed to the stronger bond between the Sc and O compared to the Ga and O. A digital growth technique (alternate opening of Sc and Ga shutters with the O shutter open continuously during the growth) was unsuccessful in eliminating this effect. The segregation was eliminated using a growth technique in which the Ga shutter was closed for a set amount of time toward the end of the growth while the O and Sc shutters remained open. Characterization with reflection high energy electron diffraction, x-ray diffraction, and transmission electron microscopy revealed the growth of a fine-grained polycrystalline film under these conditions. A third growth technique was used that involved closing the Ga shutter for a set amount of time toward the end of the growth while the O and Sc shutters were open continuously. This technique was successful in depositing a uniform film. However, the breakdown field was only 1.40 MV/cm (at 1 mA/cm 2more »). The addition of Ga to Sc 2 O 3 diminished the insulating properties of the film. These initial experiments indicate that phase segregation is likely to be a major issue with most growth techniques and that alloying Ga 2 O 3 with elements other than Sc, such as Gd or Al, might be a more successful approach.« less