The figure below shows XPS and ATR-FTIR analysis of carboxylic acid group-containing plasma polymer coatings on LDPE for different duty cycle for a fixed time. I have made following speculations from FTIR and XPS results. Please give your views about these statements with references.
1. ATR-FTIR The oxygen-containing group's intensity increases by lowering duty cycle show high retention of these groups. These results only give qualitative information of oxygen-containing groups so the falls in coating thickness cannot be interrupted from FTIR analysis in this case (the same experiment shows thickness decreases from 40 nm 5 nm by lowering duty cycle).
2. XPS
The sudden rise in C/O peak ratio at 10% DC is due to LDPE contribution for lower coating thickness (5 nm range). As XPS is more surface sensitive technique, so it shows the effect of thickness loss along with retention of oxygen-containing groups.
The absolute intensity in XPS is affected by many factors such as the surface roughness. Therefore, it should be preferable to compare a given atomic ratio (O/C, for instance) instead of following the absolute intensity. The modification of the surface may be accompanied of a serious modification of its roughness.
The absolute intensity in XPS is affected by many factors such as the surface roughness. Therefore, it should be preferable to compare a given atomic ratio (O/C, for instance) instead of following the absolute intensity. The modification of the surface may be accompanied of a serious modification of its roughness.
If the coating thickness is less than 1.0 micrometer, your interpretation is rational.
Ana Maria Thank you very much for your correction.
I have modified question according to C/O atomic ratio. (Please see second attached graph).
The C/O ratio for 10% duty cycle is still substantial, showing the contribution of LDPE substrate carbon. Please give your kind view about the hypothesis mentioned in the question.
Dear Pudun Zhang,
Thanks for your valuable comment, I also need references to support my interpretation.
I think that your explanation is plausible. I would advise the inclusion of error bars in your data points. I would say that the treatment is removing the carboxylic containg polymer coating the LDPE almost without modifying its composition; just the thickness is decreasing and when it reaches around 10 nm, in XPS you start to have signal coming from LDPE increasing dramatically the C/O atomic ratio measured by XPS.
Thanks, ana Maria for your valuable comments I also think at 10% duty cycle deposition is negligible due to longer off time. your opinion about surface roughness and XPS intensity relation is also worthy as I think it 'll help to prove inhomogeneity of polymer coating in 10 nm range.
I recommend our paper to read, it maybe help you.
`Structure of Plasma Deposited Poly (acrylic acid) Films´ Alaa Fahmy, Renate Mix, Andreas Schönhals, Jörg Friedrich, Plasma Processes and Polymers, 8, 147, 2011;
I recommend our paper to read, it maybe help you.
Structure of Plasma Deposited Poly (acrylic acid) Films, Alaa Fahmy, Renate Mix, Andreas Schönhals, Jörg Friedrich, Plasma Processes and Polymers, 8, 147, 2011;
Professor Alaa Fahmy thank you very much for your reply.
I already studied your articles about plasma polymerization. In fact, your articles have led me to do these experiments.
But this case is a bit different from those articles. Those articles explained the retention of carboxylic groups for lower duty cycle and showed same information from XPS and FTIR results as coating thickness is 150 nm. So there is no influence of substrate was observed in XPS results.
In my case thickness is around 10 nm. So I observed the influence of substrate in XPS results but not in FTIR results for low duty cycle. So I predicted that as XPS is surface sensitive technique, so O/C ratio is less due to substrate influence but in FTIR C=O peak is still high showing retention of the functional group even for low thickness.
Please give your views about this justification.
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