Method Article

Radio Frequency Magnetron Sputtering of GdBa2Cu3O7−δ/ La0.67Sr0.33MnO3 Quasi-bilayer Films on SrTiO3 (STO) Single-crystal Substrates

DOI:

10.3791/58069

⸱

April 12th, 2019

 ,  ,  ,  ,  ,  ,  ,  ,  ,  , 
1Department of Physics, Mathematics, Shanghai Key Laboratory of Materials Protection and Advanced Materials in Electric Power, Shanghai University of Electric Power, 2Key Laboratory of Artificial Structure and Quantum Control, Ministry of Education, Department of Physics, Shanghai Jiao Tong University, 3Shanghai Institute of Space Power-sources, 4Shanghai Key Laboratory of High Temperature Superconductors, Shanghai University

In This Article

Summary

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Here, we present a protocol to grow LSMO nanoparticles and (Gd) BCO films on (001) SrTiO3 (STO) single-crystal substrates by radio frequency (RF)-sputtering.

Abstract

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Here, we demonstrate a method of coating ferromagnetic La0.67Sr0.33MnO3 (LSMO) nanoparticles on (001) SrTiO3 (STO) single-crystal substrates by radio frequency (RF) magnetron sputtering. LSMO nanoparticles were deposited with diameters from 10 to 20 nm and heights between 20 and 50 nm. At the same time, (Gd) Ba2Cu3O7−δ ((Gd) BCO) films were fabricated on both undecorated and LSMO nanoparticle decorated STO substrates using RF magnetron sputtering. This report also describes the properties of GdBa2Cu3O7−δ/ La0.67Sr0.33MnO3 quasi-bilayer films structures (e.g., crystalline phase, morphology, chemical composition); magnetization, magneto-transport, and superconducting transport properties were also evaluated.

Introduction

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The hole-doped manganite La0.67Sr0.33MnO3 (LSMO) have unique properties such as wide-band gaps, half-metallic ferromagnetism, and entangled electronic states, which provide extraordinary opportunities for potential spintronic applications1,2,3,4. Currently, many researchers are endeavoring to take advantage of the unique properties of LSMO to inhabit the vortex movement for high temperature superconducting (HTS) films, such as (RE) Ba2Cu3O7−δ films (REBCO, RE= rare-earth element)5,6,7,8,9,10,11,12. Nanoscale decoration of the substrate surfaces with ferromagnetic nanoparticles will provide well-defined sites for inducing magnetic pinning centers of expected density13,14. However, the ability to control the density and geometry of the nanoparticles on highly textured surfaces, such as on single-crystal substrates and highly textured metal substrates is very difficult. Most commonly, nanoparticles are synthesized and coated on surfaces using metal organic decomposition methods15, and pulsed laser deposition methods16,17. Although pulse laser deposition methods can provide nanoparticles coated on various substrates, it is difficult to realize large area homogeneous nanoparticles deposition. As for metal organic decomposition methods, they are proper for large area deposition of nanoparticles. However, the nanoparticles are often non-uniform and easily damaged by small physical stresses.

Among these techniques, RF-magnetron sputtering has many advantages. Sputtering has a high deposition rate, low cost, and a lack of toxic gas emission. Also, it is easy to expand to large scale area substrates18,19. This method provides single-step formation of La0.67Sr0.33MnO3 (LSMO) nanoparticles, and the nanoparticles are easy to be deposited on single-crystal substrates. RF magnetron sputtering can create large area nanoparticles uniformly on a diverse range of substrates, irrespective of surface texture, and surface roughness20.The particle control can be achieved by adjust sputtering time. Homogeneity can be achieved by adjust target-substrate distance. The disadvantage of RF-magnetron sputtering is its lower growth rate for some oxides21. In this approach, target atoms (or molecules) are sputtered out of the target by argon ion, and then nanoparticles are deposited on substrates in the vapor phase22. Nanoparticles formation occurs on the substrate in a single step23. This method is theoretically applicable to any materials including superconducting thin film, resistance film, semiconductor film, ferromagnetic thin film etc. However, to date, reports about protocols for depositing ferromagnetic nanoparticles are very scarce.

Here, we demonstrate the deposition of GdBa2Cu3O7−δ/La0.67Sr0.33MnO3 quasi-bilayer films on SrTiO3 (STO) single-crystal substrates by RF magnetron sputtering method. Two kinds of target materials, GdBa2Cu3O7−δ and La0.67Sr0.33MnO3 target are used in the process. SrTiO3 (STO) single-crystal substrates were coated with GdBa2Cu3O7−δfilms and GdBa2Cu3O7−δ/La0.67Sr0.33MnO3 quasi-bilayer films.

In this protocol, GdBa2Cu3O7−δ/La0.67Sr0.33MnO3 Quasi-bilayer films are deposited with RF magnetron sputtering on STO (001) substrates. The target diameter is 60 mm and the distance between the target and substrates is about 10 cm. The heaters are bulbs positioned 1 cm above the substrates. The maximum temperature is 850°C in this system. There are 5 different substrates in this system. RF magnetron sputtering GdBa2Cu3O7−δ/La0.67Sr0.33MnO3 quasi-bilayer films consists of two steps, which are the preparation of substrates and the RF magnetron sputtering process. A picture of the sputtering system is shown in Figure S1.

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Protocol

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1. Substrate and Target Preparation

NOTE: This section describes the preparation of the sputter deposition chamber and the single crystal SrTiO3 (STO) substrates.

  1. Use 10 mm x 10 mm SrTiO3 (STO) single-crystal substrates during the RF magnetron sputtering process.
  2. Sequentially clean the substrates in isopropanol and deionized water for 10 min each at room temperature in ultrasonic bath. Then dry the substrates with nitrogen, which is for uniform covering of the substrate and good film adherence.
  3. Mount the (001) STO substrates in the substrate holders with silver powder conductive glue. Load these into the vacuum chamber.
  4. Mount the LSMO target in the magnetron injection gun, and then reassemble the gun. Test the resistance with an ohmmeter, to avoid a short circuit between the magnetron and the surrounding shield. Close the vacuum chamber is closed and pump down.
  5. Once the vacuum is lower than 1 x 10-4 Pa, heat the substrates to 850 °C using a heating rate of 15 °C/min. set the target-substrate distance to 8 cm.
  6. Set the mass flow controller to 10 sccm of O and 5 sccm of Ar as working gas flow. Use Ar/ O mixed gas to keep O cationic ratio (3) for La0.67Sr0.33MnO3 material during growth.
  7. Before the deposition, pre-sputter the LSMO target for 20 min at 30 W. High power will lead to cracks in the target and using low power will lead to more time for a clean surface, so we choose 20 min for 30 W.

2. LSMO Nanoparticle Deposition

NOTE: This section describes the deposition of the LSMO nanoparticles by RF-magnetron sputtering.

  1. To obtain a chamber pressure of 25 Pa, adjust the molecular pump splint valve. If the instant value is becoming larger than 25 Pa, rotate it counter-clockwise; if it is becoming smaller than 25Pa, rotate it clockwise. Continue until the pressure has settled to a stable value.
  2. Check that the substrate temperature remains at 850 °C and is stable.
  3. Increase the power of magnetron from 30 to 80 W. Wait for 10 min, until the plasma is stabilized.
  4. Open the shutter and deposit LSMO on the heated substrate.
    NOTE: We used sputtering times of 5, 10, 30, and 60 s for four samples.
  5. Close the shutter. Shut off power to the magnetron. Close the gas valve and shut off heater power.
  6. Cool the samples to room temperature. Unusually, this takes at least two hours in this system. Vent the chamber with dry nitrogen, open it, and remove the samples.

3. GdBa2Cu3O7−δ Film Deposition

  1. Mount the GdBa2Cu3O7−δtarget in the magnetron gun, then reassemble the gun. Deposit any (Gd) BCO films, using steps similar to steps 1.4-2.8. Use similar deposition conditions for (Gd) BCO films as for the LSMO nanoparticles, except for the sputtering time which should be 30 min. After this, the growth will be over, and next step is the post-annealing.
  2. Decrease the sample temperature to 500°C. Then, open the gas valve for oxygen to give a chamber pressure of 75,000 Pa. Hold the samples at this temperature for one hour.
    NOTE: The temperature for 500 °C and a chamber pressure of 75,000 Pa are for uniformly achieving LSMO nanoparticles.
  3. Cool the samples to room temperature. Vent the chamber with dry nitrogen, open it, and remove the samples.

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Results

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The thickness of (Gd) BCO films on both bare and LSMO decorated STO substrate was 500nm, which was measured by a surface profilometer. The film thickness was controlled by sputtering time. Figure 1a,b shows the AFM image of LSMO nanoparticle (sputtering time of 10 s) on 1.0 cm x 1.0 cm single-crystal STO substrates to prove that the LSMO nanoparticles grown on STO substrates uniformly. The surface and to measure the roughness of the films was...

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Discussion

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Here we have demonstrated that this method can be used to prepare LSMO ferromagnetic nanoparticles of uniform distribution on SrTiO3 (STO) single-crystal substrates. The (Gd) BCO films also can be deposited on both bare and LSMO decorated STO substrate. With an appropriate adjustment of deposited parameters, such as growth temperatures and target-substrate distance, this method ought to be useful for deposited different kinds of magnetic and non-magnetic particles or layers, for example, CeO2, YSZ (...

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Disclosures

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The authors have nothing to disclose.

Acknowledgements

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This work was supported by the National Natural Science Foundation of China (No. 51502168; No.11504227) and the Shanghai Municipal Natural Science Foundation (No.16ZR1413600).The authors gratefully thank the Instrumental Analysis Center of Shanghai Jiao Tong University and Ma-tek analytical lab for competent technical assistance.

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Materials

List of materials used in this article
NameCompanyCatalog NumberComments
Sputter Deposition SystemShenyang scientific instruments Limited by Share LtdBespoke
SrTiO3 Single Crystal SubstrateHefei Ke crystal material technology Co., LtdSingle-sided epi-polished(001) orientation
La0.67Sr0.33MnO3 sputtering targetHefei Ke crystal material technology Co., LtdBespoke60 mm diameter
GdBa2Cu3O7−δ sputtering targetHefei Ke crystal material technology Co., LtdBespoke60 mm diameter
Atomic Force MicroscopeBrükerDimension Icon
X-ray DiffractometerBrükerD8 Discover
Physical Property Measurement SystemQuantum DesignPPMS 9

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GdBa2Cu3O7 delta FilmsLa0 67Sr0 33MnO3 NanoparticlesSrTiO3 SubstratesOxide Film DepositionNanoparticle GrowthSuperconducting PropertiesMagnetization HysteresisCritical Current DensityAFM Imaging

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