Chemistry Reference
In-Depth Information
Figure 3.6. Schematic representation of an apparatus for production of sublimation
crystals in a horizontal arrangement. The total length is typically 400 mm. Adapted
from Laudise
et al.
, 1998.
obtained only the well-known triclinic phase. This implies that with CEC different
regions of the parameter hyperspace can be explored.
Dry preparation methods
Physical vapour growth
Physical vapour growth in horizontal and vertical systems has been successfully
used to grow mm-cm sized single crystals of single-component compounds, e.g.,
α
-6T, pentacene, anthracene and CuPc (Kloc
et al.
, 1997; Laudise
et al.
,
1998). A scheme of the apparatus used in a horizontal arrangement for producing
sublimation crystals is shown in Fig. 3.6.
The source and the deposition regions are in separate tubes within the outer
reactor tube. The starting material, usually in the form of purified powder, can be
easily inserted with this geometry and both the final resulting residual material as
well as the crystals can be removed without difficulty after growth. In this scheme,
heating is applied by a resistance wire wound around the tubes designed in such
a way that reproducible temperature gradients are achieved. Gas inlet and outlet
tubes allow the introduction of inert gases such as argon, helium and nitrogen, as
well as hydrogen. With the valves the growth can be performed either in a closed
configuration (valves closed) enhancing convection or in an open configuration
(valves open), precisely regulating the gas flow.
Table 3.1 displays experimental growth conditions for organic semiconductors,
leading to high-quality single crystals. As for most growth methods the working
conditions are critical and this is best illustrated here for pentacene (Mattheus
-4T,
α
