Epitaxial Growth by D.c. Magnetron Sputtering of Carbyne (Chaoite) Microcrystals on CVD-Deposited Polycrystalline Diamond - Polyynes: Synthesis, Properties, and Applications - page 43

FIGURE 3.6 SEM micrograph of a tungsten filament after carbonization treatment.

3.4 DEPOSITION AND CHARACTERIZATION OF CARBYNE

Carbyne layers were grown using the D.c. magnetron system described
above. A tungsten filament of 0.2mm in diameter was carbonized as shown
above, placed between the HOPG target and the Si wafer CVD-coated with
diamond, and heated to 2000-2400 C. The distance between the target and
the filament, and the distance between the filament and the substrate were
typically 50mm and 20-30mm, respectively. Sputtering was carried out
under pure argon gas pressure of 13 to 20 Pa. The background pressure
before sputtering was below 1.3

10 4 Pa. The temperature of the sub-
strate varied between 200 and 400 C. The power supplied to the graphite
target was between 450 and 600W, and the deposition time varied between
1 and 6 h.

Figure 3.7 shows a typical carbyne deposit formed on a CVD diamond-

coated Si(100) substrate with a power of 450W, substrate temperature
200-400 C, filament temperature 2400 C, deposition time 5 h.
As shown in Figure 3.7b the carbyne layer deposited consists of small
columnar crystallites about 1 m m long that are arranged more or less per-
pendicular to the substrate surface, i.e. (111) of diamond. These structures
closely resemble those reported by Onuma et al. [17] and Kawai et al. [18],
and attributed to chaoite, a carbyne polytype with an assumed chain length
of n

¼ 11 carbon atoms [12].

Grazing incidence x-ray diffraction (GIXD) measurements ( Figure 3.8 )

showed conclusively that well-crystallized carbyne (chaoite) has been

deposited. The interplanar spacings are listed in Table 3.1 , together with

interplanar spacings of chaoite taken from the literature [24,25]. As shown

in Table 3.1, the (hk.l) indexing of the interplanar spacings of References 24

and 25 are quite different. We intuitively tend towards that of References 25

since the orientation of the crystals predominately perpendicular to the sub-
strate surface suggests reflections with only l 0. This is also in accord with

the paper by El Goresy Donnay [20] on the ''Ries Crater
carbyne''. The intensity of the (111) diamond spacing at 206 pm shown

¼

seminal and