NetNotes
to ensure that the partial pressure of water is much below (orders of magnitude) the chamber pressure of your scope. Also, you need to take into account the thermal conductivity of the sample you are examining. Remember that the temperature of the exposed surface can be well above the cooling temperature of the stage itself. Remember that the beam will also cause local heating of the sample. In my TEM, I have seen ice evaporate under the beam when the stage temperature was reading <-100ºC. Henk Colijn
colijn.1@osu.edu Fri Dec 23 I will second Henk’s comments that the beam will lead to localized increased temperatures. You will have to play around with the conditions to get what you want. We have a Peltier stage on our Quanta. I’m not sure that ours has as much as a -50ºC to 70ºC range. I think our cooler allows 25ºC deviations up or down from ambient and that is relative to a temperature conditioned water bath. I am not sure you would need the -180ºC model. I would ask you to consider the full process of your experiments. How will you introduce your samples? Do you have a cryo transfer system? How will you prepare your samples for examination? That could be in-situ but probably elsewhere. Do you have an SEM capable of low-vacuum or environ- mental mode? Henk, you spoke of keeping the vapor pressure of the water in the sample far below the pressure of the chamber. Are you dealing with a high-vacuum-only instrument? Couldn’t that still result in problems? If the partial pressure of water in your vacuum is below the vapor pressure of water at the sample temperature, the water in the sample would still sublime. Granted, if the temperature is very low, that should be a slow process. Conversely, if the partial pressure of water in your chamber is higher that the vapor pressure of water at sample temperature, then you would have frost build up on the sample through deposition. It will be a tricky business. Warren Straszheim
wesaia@iastate.edu Fri Dec 23
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