Formation of Thick Dense Yttrium Iron Garnet Films Using Aerosol Deposition

The overall goal of the experiment is to deposit a several micron, thick, dense, polycrystalline film of atrium iron garnet onto a sapphire substrate using a room temperature deposition technique. This is achieved by mounting a prepared substrate onto the translation stage attached to the top cap of the apparatus, then placing the top cap on the deposition chamber and attaching the motor cables as a second step load powder process To possess the desired agglomeration size into the aerosol chamber, put the aerosol chamber top cap in place and connect it via a nozzle with the deposition chamber. Next, establish a pressure gradient between the chambers and start gas flow into the aerosol chamber.

Combine this with the action of a vibration plate to create an aerosol that passes through the nozzle into the deposition chamber. Deposition of the glomerate proceeds by fracture, deformation, and fusing of the crystalite resulting in the formation of a thick, dense film on the substrate. The main advantage of this technique over existing methods is that it can produce very thick, dense films without the need to heat the substrate or the precursor material from a production standpoint.

Aerosol deposition also has the advantage of being done in a relatively low vacuum environment and it can deposit at a very high rate. At the core of this experiment is the aerosol deposition setup. This schematic view of the equipment identifies the principle components.

Place the powder to be aerosolized into the aerosol chamber and inject flow controlled carrier gas into the chamber by maintaining a pressure difference between the aerosol chamber and the deposition chamber. Create a flow of aerosol through the nozzle control deposition onto a sample in the deposition chamber. Using a translation stage for this video, the first step will be to mount a prepared substrate on the translation stage.

The translation stage is part of the top cap assembly. First place double-sided copper tape near the center of the stage. Next, get a cleaned and dried substrate and place it on the tape near the center of the stage.

This six millimeter by six millimeters sapphire substrate is in position. For the next steps in the protocol. Continue by using calipers to collect data needed to help align the spray nozzle.

Do this by measuring and recording the distance from one edge of the mounting stage to the nearest and farthest edges along one direction. Perform a similar measurement along the perpendicular direction. After making the measurements, transport the top cap with the translation stage and sample to the deposition chamber.

Lower the top cap into place and put the translation stage and sample into the chamber. Once this is done, secure the top cap in by clamping the flange to seal it. Then attach the controller cables for the translation motors.

Now move on to preparing the aerosol chamber seen here with its top section off. Get 100 to 150 grams of sied and dried atrium iron garnet powder. Distribute the powder over the bottom section of the aerosol chamber.Next.

For this setup, put a filter declogging attachment in place. Get the main body of the aerosol chamber and lower it onto the bottom section. Continue by clamping the main body to the bottom section.

Then attach the aerosol pressure gauge to the side port. Now get the nozzle inlet section and use a quick fit clamp to secure it to the top port of the main body of the aerosol chamber. When this is ready, raise the nozzle inlet tube to the inlet port on the deposition chamber.

Finish by securing the top and bottom fitting. Start establishing a pressure gradient by isolating the roughing pump from the rest of the system. Then turning it on.

Open a bypass line to perform the initial pump down to ensure a better controlled pump down. Turn on the deposition chamber illumination light at the computer. Set the pressure monitoring and stage controller software without starting either as pumping continues.

Monitor the system pressure. When the pressure reaches 150 to 200 tor, adjust the bypass line pump down rate to one tor per second. Once the pressure drops below 100 tor, start the pressure monitoring and stage controller software.

When the pressure is about one tor close the valves to the bypass line. Continue by opening the main pumping valve. As pumping continues, move to deposition chamber and tighten the clamp to the top cap.

The next step is to turn on the blower pump and open the ultra high purity nitrogen gas cylinder to provide the carrier gas at the computer. Use the stage controller software graphical interface to position the substrate as seen through the viewport. First place the substrate over the nozzle.

Once in place, lower the substrate until it contacts the nozzle. Then move the substrate 7.5 millimeters in the vertical direction to its position. Close the main pumping line and check that the leak rate is less than about three millitorr per second.

Before proceeding, continue by setting the deposition chamber butterfly valve to its 500 TOR preset value. Set the flow rate of the mass flow controller, but do not turn it on. Program a function generator to set the vibrational frequency of the agitator and turn it on.

Start the nitrogen gas flow. Then count down three seconds before starting the stage controller macro on the computer. Adjust the gas flow rate to keep the desired constant pressure difference.

In this case, about 500 tor. Make use of the viewport to visually monitor the deposition. At the end of the deposition, note the exact runtime.

Shut off the nitrogen gas, the function generator and the pumps. Open the deposition chamber. Butterfly valve, completely open the bypass valve to the deposition chamber.

Turn the house nitrogen gas regulator to zero and redirect the gas into the deposition chamber. Close the main pumping valve while slowly increasing the house gas pressure. Return to the computer to use the stage controller software to home the nozzle, and then close the program.

When the pressure is above 100 tor, stop the pressure monitoring software. Continue to adjust the house gas as necessary until the system reaches atmosphere. To recover the sample, detach the cables for the translation motors from the top of the deposition chamber.

Remove the top cap from the deposition chamber and take it to a workbench. At the bench, orient the top cap to gain access to the sample. Unmount the sample to prepare it for characterization.

This is a scanning electron micrograph of an atrium Iron Garnet film on a sapphire substrate. The deposition sweep moved at 0.65 millimeters per second and covered an area of 75 square millimeters. The film is somewhat rough and well compacted with few voids.

The dense nature of the film is also seen in this scanning electron micrograph of the cross section of the film. On the sapphire substrate, the main image shows the edge of the as deposited sample as formed during deposition. It is not a cleaved section of the film.

The inset is a magnified view of the cross section. A step was created by removing a portion of the film along one edge. The data in black gives the step height of the film.

The red line indicates an average film thickness of about 11 micrometers. The roughness is about 1.4 micrometers. In this plot, Pharaoh magnetic resonance absorption, derivative data is in black, and a Lian derivative line shape fit to the data is in red.

Both the signal location and shape for the data are comparable to typical spectra. For Polycrystalline Atrium Iron Garnet grown using other methods. The good Lian Fit suggests a uniform film.

After watching this video, you should have a good understanding of how the aerosol deposition process works and how to perform aerosol deposition using this system.