In-situ doser checking | SPMwiki

There are two gas lines on STM chamber which could be used for in-situ dosing experiments. We can directly introduce gas onto the sample surface while keeping the tip on the same scanning area. This is a crucial approach to study the intercation between the adsorbates and substrates.

These two gas lines just sit near the both sides of the LN2 shield. And there are also two holes on both sides of the shield which are cover by movable shutters.The problem is that the focus of the gas line to the hole may be not so well and gas molecule was impossible to dose onto the surface. But we can use a ‘frozen water spot’ to check the focus of the gas line.

The main idea of this method is dosing water directly onto the shield and see the frozen spot on the shield.

Before you plan to warm up the system,and adjust the gas lines. You can dosing lots of water onto the cold shield, then you will see the phenomenon as the picture bellow.

The frozen water spot is out of the hole on the shield , so the gas line should be bended to the left side.

After you finished the adjustments, you can cool down the shield to low temperature and check the focus again berfore baking out. The following picture shows the focus of the gas line. And it looks much better than before.

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