Plasma polymer adhesion promoters for metal-polymer systems - Polyimides and Other High Temperature Polymers - page 363

Similar to the OH derivatization, NH 2 labelling was performed as a gas-phase reac-
tion. The samples were exposed to PFBA vapour for 20 h. Then the samples were
degassed at a pressure of 10 -5 Pa for 8 h to remove the unreacted PFBA. These la-
belling reactions were examined with 4,4´diaminodiphenylmethane as model and
reached yields in the range of 80%, which are much higher than described in [37].
2.4.3. Derivatization of COOH groups
Carboxylic groups were identified by labelling with vapours of trifluoroethanol in
presence of di- tert -butyldiimide and pyridine for 8 to 20 h [38]:

Afterwards the samples were degassed at a pressure of 10 -5 Pa to remove non-
reacted components. The yield of this reaction was about 90% (see also [38, 39]).

2.5. Self-exciting electron resonance spectroscopy (SEERS)
SEERS and its basic theory are connected with the use of a diode-type radio-
frequency reactor. In such a reactor, the self-excited electron vibrations of the
plasma depend specifically on electron density and collision rate and can be
mathematically described in a theory (developed by ASI for the Hercules sensor
system, ASI company, Berlin, Germany). The electron vibrations of the plasma
were detected with a sensor in the wall of the reactor and analysed. The SEERS
theory is based on the non-linearity of the space charge sheath at the r.f. electrode
that provides harmonics with the modulated sheath width and produces high-
frequency oscillations in the bulk plasma. The idea of the method is to use the high
self-excited (high frequency) damped oscillations of the bulk plasma, which are
generated at every peak voltage of the sinusoidal power supply. A computerized
hydrodynamic model of the plasma bulk is used, which takes into account the non-
linear behaviour of the modulated sheath width. Using this plasma theory it is pos-
sible to evaluate the above-mentioned plasma parameters by using the sensor signal.
In contrast to Langmuir plasma probes and optical methods, the SEERS method is
not influenced by the continuously growing plasma polymer deposit whether on the
sensor or at the walls of the reactor. It would be expected that the electron density
n e and electron collision rate µ e should be closely related to the generation of free

radicals which are known to be necessary for further polymerisation reactions in the
plasma-off period. The data acquisition time of less than 1 µs for one measurement
allows monitoring the relevant plasma parameters also in pulsed plasmas.