Operation of the Bio-Rad PT7125 Barrel


Before plasma processing your sample it must be dried either in an oven or under a flow of dry nitrogen. When you start the vacuum pump should be on, the power light on the instrument should be lit, the pump button should be pressed and the chamber should be evacuated (at less than 0.1 mbar) if the instrument is turned off or in a different state contact the SAF explaining the problem.

1) To vent the chamber press the pump button to release it and then the vent button (it should light up). Air should be heard rushing into the chamber after about 20 seconds the door will fall slightly open. Press the vent button once (it should now not be lit).

2) Place your sample(s) in the centre of the chamber.

3) While holding the chamber door shut, depress the pump button. The door should, after a few seconds, be held shut by the pressure differential across it. To also evacuate the oxygen line press the gas 1 button (the light will only be on if the chamber pressure is below 0.6 mbar). Check the red arrow on the gas 1 control valve is horizontal and pointing to the left, do not adjust it if it is (if it is not close it by turn ing it fully clockwise and then open it until the red arrow is in the correct orientation). The chamber will now take about 1 hr to evacuate.

4) Once the gas 1 light is lit and the pressure is below 0.1 mbar, open the oxygen cylinder set the regulator to 0.5 bar and check all valves between it and the plasma etcher are open. The chamber pressure should increase slightly (if the pressure rises above 0.6 mbar the control valve will automatically shut and the gas 1 button will become unlit).

5) Once the pressure has stabilised press the standby button once (it should light). The power dial should be turned fully anticlockwise, press the RF and auto/man buttons once (both buttons should light up) then increase the power until the forward power gauge is reading about 45 W, the reflected power gauge should read about 5 W and a grey/blue discharge should be observed through the window (if the discharge is pink, a nitrogen plasma, you have not purged all the air form the system so switch off the RF, auto/man and standby buttons and leave the system to purge for about an hour and then start from the beginning of step 5; if the distcharge is bright blue your sample is wet and you need to decide whether you wish to proceed or stop the treatment). Either time the processing by selecting the time required on the timer and switching the man/reset switch or by manually timing it. If you use the timer at once the selected interval has elapsed the RF will be automatically turned of and a buzzer will sound. Switch off the RF, auto/man and standby buttons and turn the power dial fully anticlockwise. Close the oxygen cylinder and switch off the gas 1 button.

6) To recover your sample repeat step 1, and then remove your sample. To keep the chamber as clean as possible it should be evacuated at all times so while holding the chamber door shut, depress the pump button. The door should, after a few seconds, be held shut by the pressure differential across it. It is now ready for the next user.