Chemistry Reference
In-Depth Information
Sp
3
0.8
0.2
0.6
0.4
0.6
0.4
No films
0.8
GLCH
0.2
Sp
2
H
0.2
0.4
0.6
0.8
FIGURE 8.44
Ternary phase diagram of amorphous hydrocarbon films. The three corners
correspond to pure diamond (
sp
3
), graphite (
sp
2
), and hydrogen films. The abbreviations
used are GLCH (graphite-like hydrogenated carbon film), a-C:H (amorphous hydrogenated
carbon film), ta-C (tetrahedral amorphous carbon film), and ta-C:H (tetrahedral amorphous
hydrogenated carbon film). The shaded area in the corner is the region where no stable films
can be deposited.
(up to 30 at.%) hydrocarbon films are usually referred to as diamond-like carbon
(DLC) or hard a-C:H films [293]. The available experimental data can be most easily
compared by plotting the
sp
3
,
sp
2
, and hydrogen contents in a ternary phase diagram
as introduced by Smith [303]. Later Jacob et al. [294] used the published data and
found that only within a limited region of the parameter range, a stable a-C:H films
can be produced.
Figure 8.44 shows the ternary phase diagram of hydrocarbon films. The three
corners of this diagram correspond to pure graphitic carbon (
sp
2
), diamond (
sp
3
),
and hydrogen. The shaded area in the rightcorner is the region where no stable films
can be deposited. Depending on the hydrogen content and the relative abundance of
sp
2
/
sp
3
-bonded carbon, the films can be classified into different categories. Broadly,
films which have relatively high
sp
3
bonded carbon content are called DLC films and
the ones with relatively high
sp
2
carbon content are called graphite-like carbon (GLC)
films. Amorphous carbon films that do not contain hydrogen and have
sp
3
-bonded
carbon content greater than 60% are called tetrahedral amorphous carbon (ta-C)
films. If such a ta-C film is hydrogenated with hydrogen content
20-40 at.%, it is
called diamond-like hydrogenated carbon (DLCH) film. A ta-C:H film is amorphous
and hydrogenated (H-content 25-30 at. %) with
sp
3
-bonded carbon content
∼
70%.
Similarly, a GLC film with H-content below 20 at.% and
sp
3
-bonded carbon content
lower than 20% is called graphite-like hydrogenated carbon (GLCH) film.
∼
