Plasma

For one of my experiment, I need to create oxygen plasma. This post is about creating oxygen plasma


Introduction 

Plasma is one of the fundamental state of matter when molecules exist as ions. Plasma is created in low pressure typically of the order of 0.2mbar by applying high DC, AC or Rf voltage. In the plasma state O2- and O- ions are formed.

Experiment

For creating plasma, I am using a vacuum chamber of my thermal physical vapor deposition system. I will connect a oxygen cylinder to the vent port of the system to introduce oxygen into the chamber. I will use a flow controller or regulator to control the flow of oxygen. I am planning to use a pure aluminum wire which will act as electrode. Since the voltage for creating plasma is hazardous, I am going to use a interlock which will disable the plasma supply whenever I will open the chamber. This will prevent me to accidentally touch active wire antenna.

1) Aluminum Electrode

I am planning to use 99.9% pure aluminum wire of diameter ~1.5mm as plasma electrode. I am ordering it from here

http://www.sigmaaldrich.com/catalog/product/sial/310360?lang=en&region=US

Another source of getting pure Aluminum electrodes/wires etc is -

http://www.americanelements.com/aluminum-electrode.html

Another source of ordering Al rods is -

http://www.espimetals.com/index.php/online-catalog/824-Aluminum%20%28Al%29,

I am planning to order 0.5" rod.

2) Power Supply

There are three ways to create plasma, one is DC plasma where you need to apply high DC voltage, other is apply AC high voltage and the third is to apply Rf power. First, I will try DC plasma then AC plasma.

For creating plasma, + of the power supply is connected to anetena (or metal electrode) and ground is connected to the vacuum chamber. I am not very confident at this stage to connect one terminal of AC to vacuum chamber so first I will try DC voltage, were connecting the ground to chamber is much more safe. For power supply, I am using PS350 high voltage power supply system from stanford research system. (http://www.thinksrs.com/products/PS300.htm). After being successful with this, I will also try other much cheaper high voltage transformers.

Working with High Voltages -

WARNING

High voltage cables can store charge if they are disconnected from the supply while the high voltage is on. The charge on the cable can cause injury or damage even after the cable is disconnected from the unit

Please make certain that the high voltage is completely discharged before changing the cable.

There are special type of cables called "High Voltage Cables" which should be used instead of normal BNC when working with high voltages. These cables mate with special connectors designed for high voltages only. These are MHV connectors and SHV connectors. Note that MHV connectors looks similar to BNC connectors but should not be confused with.

For high voltage cable I am ordering this one -

http://fieldcomponents.com/SHVP-RG58-SHVP-Length.html

Another option is from Kiethly , this one

http://www.keithley.com/products/accessories/cables/?mn=248-SHV

I will also need a BNC to male SHV connector

Source yet to find.