Chemistry Reference
In-Depth Information
characteristic absorption bands of the asymmetric and symmetric C-H stretching
vibrations (2950-2700 cm
−
1
) as well as the C-H deformation vibration (1460 cm
−
1
)
of the
polymer. The ratio spectrum in Figure 8.32b, generated from IR
spectra before and after plasma treatment, contains all the changes due to the oxygen
plasma treatment. The strong polymer degradation/etching from the negative bands
in the spectral range of the C-H vibrations is clearly seen. Furthermore, different
oxygen-containing structures were produced in the top polymer interface. In the
wave number range between 3500 and 3000 cm
−
1
, the O-H stretching vibrations
of the hydroxyl groups appear broadened due to hydrogen bonds. Additionally, the
carbonyl group (C
−
(CH
2
)
n
−
O stretching) is observed around 1750 cm
−
1
. The wide spectral
range of the carbonyl group reveals a variety of C
=
O structures with slightly different
characteristic frequencies. In the fingerprint region from 1400 to 1000 cm
−
1
, there are
many overlapped bands associated with C-O stretching vibrations, O-H deformation
in alcohols, as well as C-O stretching vibrations in esters and ethers. The absorption
around 960 cm
−
1
can be interpreted as C-H stretching vibration from cross-linked
(C
=
C) molecular structure. The formation of polar oxygen-containing groups causes
the enhancement of surface energy.
In a similar way, the treatment of polysterene thin films in a low pressure (5Pa)
capacitively coupled 13.56 MHz discharge in different process gases (H
2
,O
2
,CF
4
)
observedbyinsituATRleadstochemicalmodificationofthesurface[153].H
2
plasma
destroys aromatic ring structures, and new aliphatic C-H structures are formed. CO
and OH functional groups are observed in O
2
plasma treated polysterene, and CF
x
groups are formed by CF
4
plasma.
=
8.2.3.2 Metals
Surface modification of metals include
•
Cleaning of metal surfaces
•
Change of the chemistry by, e.g., oxidation, nitriding
•
Surface polishing
Tools for surface modification comprise not only low pressure up to atmospheric
pressure plasmas, but also microplasmas in liquid ambience in plasma electrolysis.
8.2.3.2.1 Plasma Cleaning
Plasma cleaning of work pieces is a precision cleaning due to the low rate involved.
Cleaning of metals from organic surface layers by nontoxic reaction gases as oxygen
leads to an environmentally safe process with low thermal stress of the surface
[164]. The application of an oxygen plasma causes the formation of CO
2
,CO,
and H
2
O. The mechanism includes chemical reactions of hydrocarbons with O
2
molecules, O atoms, and also ozone. Investigations of cleaning experiments using
O
2
/Ar mixtures show a synergetic effect of Ar ion and O
2
flux to the surface. The
removal of a hydrocarbon film will be determined by ion impact-induced defects
on the surface, which can easily react with the oxygen [165]. Also collisions with
adsorbed O
2
molecules that react with the surface and ion-enhanced chemical erosion
where ion bombardment enhances the reactivity of O
2
are discussed. The cleaning
