Using the Carbon coater

In order for the deposition rate to be reproducible the following steps should be taken:

1. Adjust the current (50-100 Amps is enough) while the chamber is empty and then load the sample and deposit without changing the current.
2. The machine can only handle pulses up to and around 6 seconds in length before it becomes overheated. If longer pulses are used let the machine cool down for a few second between the pulses. It may also be necessary to reshape the rod between each of the pulses.
3. Using several small pulses instead of a few long ones helps making the deposition rate reproducible.

• The machine is overheated and needs to cool down for a while.
• The thin part of the carbon rod is expended and the two carbon rods are no longer in contact, i.e. no current flows through them.

If the carbon rods are still in contact when the thin parts have been expended it will result in the machine becoming overheated more rapidly.

If the current through the carbon rods is too large they will become overheated faster. The thin point also risk breaking. A large current will also result in large particles shooting from the rods that might hit the sample.

There is a "custom made" sample holder (made of Cu) that allows the sample to be placed above the carbon source instead of below thus lowering (but not eliminating) the risk of the sample being struck by large carbon particles.

One way of estimating the thickness of the carbon layer is by observing its colour. To do this it is best to place a "dummy sample" (an empty substrate or a piece of paper as recommended by the manufacturer) inside the chamber when depositing. By observing the colour of the dummy sample and comparing it with a sample with the desired thickness a fairly good result can be achieved.

When using the carbon coater we got the following results.

The diameter of the thin point was 1,1 mm and the sample was placed in the custom sample holder roughly 3 cm from the rod.

When using 3-second pulses our deposition rate is nonlinear and so far we have not gotten any reliable results.

It could also bee a good idea to try a slightly lower current since there are quite a lot of big particles flying around at 50 Amps and above when using longer pulses, lower current results in lower deposition rate but less particles. Lower than 40-45 amps results in no deposition at all.