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.
This method can create the LSMO nanoparticles uniformly on a STO single-crystal substrate. Also, the GBCO film can be obtained through the same method in the same vacuum chamber. The main advantage of this technology is that LSMO nanoparticles with uniform size and high-quality superconducting GBCO film can be deposited in the same vacuum chamber.
This method can provide insight into film deposition area, nanoparticle growth area, et cetera. It can also be applied to metal film deposition, metal nanoparticle deposition, et cetera. This method will allow researchers to become familiar with vacuum equipment and learn more about film growth technology.
First, sequentially clean strontium titanium oxide single-crystal substrates in isopropanol and deionized water for 10 minutes each at room temperature in an ultrasonic bath. Then, dry the substrates with nitrogen. This promotes uniform covering of the substrate and good film adherence.
Mount the 001-oriented STO substrates in substrate holders with silver powder conductive glue. Load the holders into a vacuum chamber. Mount an LSMO target in a 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. Then, close the vacuum chamber, and pump down. Once the vacuum is lower than one times 10 to the minus four pascals, heat the substrate to 850 degrees Celsius using a heating rate of 15 degrees Celsius per minute.
Set the target substrate distance to eight centimeters. Next, set the mass flow controller to 10 standard cubic centimeters per minute of oxygen and five standard cubic centimeters per minute of argon as the working gas flow. Before deposition, pre-sputter the LSMO target for 20 minutes at 30 watts.
To obtain a chamber pressure of 25 pascals, adjust the molecular pump splint valve. If the instant value becomes larger than 25 pascals, rotate it counterclockwise. If it becomes smaller than 25 pascals, rotate it clockwise.
Following this, check that the substrate temperature remains at 850 degrees Celsius and is stable. Increase the power of the magnetron from 30 to 80 watts. After the plasma is stabilized, open the shutter and deposit LSMO on the heated substrate.
Once the deposition is complete, close the shutter and shut off power to the magnetron. Then, close the gas valve, and shut off the heater power. After cooling the samples to room temperature, vent the chamber with dry nitrogen.
Then, open the chamber, and remove the samples. Mount the gadolinium barium copper oxygen target in the magnetron injection gun, and then reassemble the gun. Deposit the gadolinium barium copper oxygen films as previously described, using similar conditions except for the sputtering time, which should be 30 minutes.
Next, decrease the sample temperature to 500 degrees Celsius. Then, open the gas valve for oxygen to give a chamber pressure of 75, 000 pascals, and hold the samples at this temperature for one hour. After cooling the samples to room temperature, vent the chamber with dry nitrogen.
Then, open the chamber, and remove the samples. The AFM image of an LSMO nanoparticle on STO substrates shows uniform growth. The XRD patterns of gadolinium barium copper oxygen films fabricated on undecorated and LSMO nanoparticle-decorated STO substrates are shown here.
The superconducting transition temperature was close to 90.5 kelvin for the gadolinium barium copper oxygen film and 90.3 kelvin for the LSMO films, which indicates that the nanoparticles don't harm the superconducting property for the films. By comparison, the magnetization hysteresis loop area is much bigger, from zero to six tesla, at 30, 50, and 77 kelvin for films fabricated on LSMO-decorated substrates. The gadolinium barium copper oxygen film deposited on an LSMO-decorated substrate possesses a higher critical current density from 1.3 to six tesla at 30 kelvin and from zero to six tesla at 77 kelvin.
At 30 kelvin, the decorated sample has a larger pinning force density above 1.3 tesla. At 77 kelvin, the density moved to a higher H value for the decorated sample. The angular dependence of the critical current density at 3 tesla and 77 kelvin for the LSMO-decorated film shows an increase along the c-axis, suggesting that it is more effective at a magnetic field orientation parallel to the c-axis direction.
This method involves many steps and details, so visual demonstration is critical for understanding and mastering this method. After its development, this method makes it possible to deposit oxide films and nanoparticles, as well as metal films and nanoparticles. After its development, this method makes it possible to deposit oxide films and nanoparticles, as well as metal films and nanoparticles.
