Pulsed Laser Deposition

The PLD system comprises a ComPex 205 248-nm excimer laser plus optical elements and two vacuum chambers. It is located in Weniger 475. Safety procedures must be observed at all times.

The Thermionics chamber consists of two joined vacuum chambers, the main chamber and the load lock. The main chamber and the load lock are separated by a large gate valve which serves to isolate the two sections. The load lock and the main chamber are each served by two vacuum pumps, a turbo-molecular pump and a roughing pump working in series.

The load lock roughing and turbo pumps are manufactured by Alcatel. The roughing pump uses traditional hydrocarbon vacuum pump oil in its operation, and should be replaced every 6 months.

The Alcatel turbo pump has a more complicated maintenance schedule. There is no oil sump in the turbo pump like the roughing pump, and so there is no oil to be changed. However, it is essential that the internal bearings are regreased every 5000 Hours. The bearing life specification is 30,000 hours; however this assumes a constant operating condition (100% duty cycle) at high vacuum. The nature of operation for this pump does not meet that specification, since its speed is ramped up and down often. The greatest amount of wear to a turbo pump occurs when its rotational speed is changing, especially at low speeds.

Bearing failure of this particular pump is known to happened at late as 20,000 hours, and as early as 6,000 hours. This is why the bearing maintenance should be performed at 5000 hours. The turbo pump controller is configured to to remind the user when this interval is met or exceeded.

The 3 mirrors used in the optical tower are from OptoSigma (part no. 034-0185 and ). These mirrors are made of a borosilicate glass (BK7) and are designed specifically for KrF laser use at 45 degrees incidence. When configured in this way, the reflectance should be > 99%. The mirrors on the lowest two tiers of the optics tower are arranged at this angle of incidence. The mirror on the highest tier of the optics tower is setup such that the angle of incidence is 30 degrees.

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The two focusing lenses (one for each chamber) used are of the plano-convex type, and are made of UV grade fused silica. The lenses used have no coatings, and have different focal lengths. The lens used with the Thermionics chamber is OptoSigma part no. 014-1315.

There are many windows on the thermionics chamber. However, there are two UV grade laser windows. Each of these is mounted in a ConFlat flange. Each of the laser windows are made of fused silica, and measuring with the Coherent power meter, have a loss of approximately 10%.

Clean windows (how often) Check on the sample holder screw (which one?) heating