Growth and physical properties of crystalline rubrene - BOA Bicocca ...

Chapter 3
Experimental techniques
The experimental work described in this thesis required the use of a wide
variety of sample preparation and measurement techniques, that will all be
introduced in this chapter, along with the principles behind their function-
ing, when relevant for the results presented in the following chapters. The
sample preparation techniques include the growth of single crystals and epi-
taxial thin films of rubrene and other organic materials; the characterization
techniques that will be described in the following sections instead include
various atomic force microscope based techniques and structural characteri-
zation by means of X-ray diffraction.
3.1 Sample preparation
3.1.1 Crystal growth
The most efficient and reproducible method to grow organic molecular
crystals of oligoacenes such as rubrene or tetracene is the physical vapor
transport (PVT) method[75, 76]. In figure 3.1 the scheme of the apparatus
used to grow crystals using such a system is reported in its vertical config-
uration. In our case, the apparatus used to grow crystals with the vertical
physical vapor transport method consists of a quartz tube with a closed ex-
tremity and with two openings at the other extremity. On the bottom of
the tube a crucible is placed containing the starting material for the growth
of the crystal. A smaller tube, inserted from the topmost opening of the
larger tube is used to convey an inert gas flux (usually He, Ar or N 2 ) to-
ward the source material. The gas is then expelled through a second opening