When processing polymer samples in sputtering or ALD processes, they melt or degrade at a much lower temperature than their melting point.
Does it depend also on the composition of the material? (for example the polystyrene melts at 180 ºC with 1 mbar when it is supposed to melt at 240 ºC). Or it is just a matter of pressure?
If it´s that, is there any relation between both properties that could be used to avoid the problem or it is a question of test and error?
It is not so simple. For each material there is a phase diagram which describes the relation between different phases (solid, liquid and gaseous). These diagrams shows phase in which material exists at given temperature and pressure. There are of course borders of the phase regions which describe pressure-temperature conditions of the phase transition. There can be also special situations when the substance can exist at given pressure and temperature in all three phases (for example: triple point of water). These phase diagrams are plotted as a result of many experimental measurements.
Thank you very much! I will try to find the phase diagram for the PS and check the relation.
Hi Ana, polystyrene is a thermoplastic polymer, it is in a solid (glassy) state at room temperature but begins to soften and flow if heated above approx. 100 °C, its glass transition temperature. It becomes rigid again when cooled, which will encourage crystallization. So depending on your processing temperature, you could be reaching the softening point.
Another thing to consider, are your polymer films ultrathin, for example 100nm or less. It has been shown that when polymer films are ultrathin, there is a drastic change in cohesive energy as the surface area to volume ratio greatly increases. This can result in a depression of the melting temperature and glass transition temperature. (see Gibbs-Thomson Equation for the structural melting point depression).
Ana,It is possible to increase the "melting point". By depositing thin ALD oxide at lower temperature and then increasing temperature to final deposition range. The thin ALD film makes molecule movement harder and the "melting " point increase a bit.
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