Lowcost Plasmacleaner

Plasmacleaners are a very useful and important tool in research and technology. They provide very efficient cleaning of solid surfaces and allow functionalizing numerous materials. However, these devices easily cost several thousands of dollars and are certainly not within the budget of hobbyists or highschools.

I will present the construction of a low-cost version of a plasma cleaner that allows to clean materials such as glass slides and functionalize them in a hydrophilic state. This may be useful for the development of low electronics and in-class experiments.

Most professional plasma cleaners produce a low energy (~5 W) RF plasma. However, RF electronics (amplifiers and Tuners) can be pricy. I have thus decided to produce an AC discharge plasma.

1. Tupperware container (I got these ones here but you can go with any sealable plastic box)

2. Threaded rod

3. Two-component epoxy glue

4. 12 V, 2 A DC Power Supply (I used this one here)

5. 12 V CCFL Inverter (I ordered them on Amazon)

6. Vacuum gauge (This is not necessary but it is nice to measure the final pressure. I used this one here, which had happened to be in the lab)

7. Brass T-fitting (I used this one here)

8. Barb fitting (I used this one here)

9. Vacuum pump. I had an old oil rotary pump in the lab so I don't have any suggestions here. However, the pump needs to be able to evacuate the container to <0.5 torr.

The total costs of the equipment were around 80 CAD but I had a pump and vacuum gauge lying around. However, I am convinced that one can assemble the device for ~200 CAD. One can certainly save some money on the plastic container and the vacuum gauge.

First, cut two ~10 cm long pieces from the threaded rod. Next, drill two holes on either side of the container. Make sure that the diameter of these holes is just big enough to tightly fit the threaded rods. This makes it easier to seal the container. Drill another hole into the lid of the container with a diameter matching your T-fitting. In my case, this was a diameter of 1/2 inches. Insert the threaded rods and the pipe fitting into the lid and the container. They will seal well if you drilled the holes precisely. You may improve the sealing with Teflon tape or you can glue everything with a two-component epoxy. Make sure to give the epoxy enough time to harden out. Finally, connect the barb to the t-fitting.

Congratulation! You have finished constructing the vacuum chamber.

Connect each output wire of the CCFL converter to the threaded rods respectively. These converters produce a high-frequency AC signal (900 V, 25 kHz). It thus doesn't matter how you assign the wires to the threaded rod. Then, connect the input of the CCFL converter to the 12 V power supply. Don't turn it on yet!!

This part really depends on your pump. I am currently using the apparatus with a pump that comes with Japanese screw-fittings. However, I was also operating the chamber with a rotary vane pump with a kf-outlet. Other (cheaper) pumps may have variable connectors.

It worked for me to connect the pump and the chamber with a 1" hose sealed with vacuum grease and gear clamps. This brings the pressure down to <0.5 torr within 20 s.

However, connecting the pump and the chamber may need some improvisation.

First, turn on the pump and wait until the pressure drops below 1 torr. Most cheaper gauges can not measure this range precisely. You may place a beaker with water inside the chamber. Boiling water indicates that you achieve less than 50 torrs. You won't be able to get the pressure this low if there is any leakage. So doublecheck the screws and pipefittings for proper sealing.

Now you may turn on the power supply if the pressure is low enough. You should see a bright purple/pink glow between both electrodes as you can see on the pictures.

Congratulations! You have just created a plasma!

Well, that's really up to you. I am using the device to clean silicon wafers, glass slides, and PCBs. The device may also be interesting for in-class use: You can use it to study basic aspects of plasma physics or prepare more advanced class experiments. Equipped with a Langmuir-probe, you may characterize the plasma and measure its electron temperature and plasma potential.

I use the device myself in lectures to demonstrate the 'dancing droplets' experiment demonstrated by the Prakash-lab in Standford (https://www.nature.com/articles/nature14272).