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., a-4T, a-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. 

Thin-film formation is described as a sequential process which includes nucleation, coalescence and subsequent thickness growth, whereby all states can be influenced by deposition parameters, such as temperature, pressure, gas flow rate, etc. [3,4], For physical vapour deposition (PVD) processes, significant works have been published and progess made in understanding the microstructure evolution of the films. In the atomistics of growth processes, there exists much in common bewteen CVD and PVD. Theories from PVD processes can thus be used to analyse the microstructure evolution of CVD processes [5, 6],... 

Condensation, nucleation and growth phenomena have been investigated both theoretically and experimentally for films made under conditions typical for physical vapour deposition in high vacuum. A number of papers concerning this topic are listed in ref. [42]. 

Interest in the crucial processes of nucleation and the growth of solids from fluid phases has a long and multidisciplinary history [50-53]. This research topic involves chemistry, chemical physics, material science, chemical engineering and physics, and, as a consequence, both theoretical and experimental studies were carried out by specialists in these fields. Thus, the following discussion does not pretend to be an exhaustive literature coverage of what is known about nucleation and growth, but rather, through recent articles, tries to review contributions especially relevant to controlled chemical vapour deposition of nanoparticles, always from a multidisciplinary point of view. 

Growth of crystals from vapour may be divided into two categories depending on whether the change, vapour—> crystal, is physical or chemical. When the composition of the vapour and the crystal is the same, the process is physical examples are sublimation-condensation and sputtering. The process is termed chemical when a chemical reaction occurs during the growth in such a case, the composition of the solid is different from the vapour. The use of chemical vapour deposition (CVD) as a... 

The rapid development of solid state physics and technology during the last fifteen years has resulted in intensive studies of the application of plasma to thin film preparation and crystal growth The subjects included the use of the well known sputtering technique, chemical vapour deposition ( CVD ) of the solid in the plasma, as well as the direct oxidation and nitridation of solid surfaces by the plasma. The latter process, called plasma anodization 10, has found application in the preparation of thin oxide films of metals and semiconductors. One interesting use of this technique is the fabrication of complementary MOS devices11. Thin films of oxides, nitrides and organic polymers can also be prepared by plasma CVD. 

The study of crystallization and alteration processes of natural and artificial snow crystals has been a subject of interest for several decades. Nakaya was the first who investigated the relations between growth forms and experimental conditions (temperature and water vapour saturation relative to ice). Although many laboratory" " and theoretical studies on ice crystals have been carried out since his seminal work, snow crystal growth is still not completely understood. Experimental studies are challenged by the complexity of the physical processes influencing the crystal growth, which are further complicated by effects of chemical impurities. ... 

Compared with other vapour-phase deposition methods, CVD method is perhaps the most complex. Unlike growth by physical deposition such as evaporation or Molecular Beam Epitaxy (MBE), this method requires numerous test runs to determine and reach suitable growth parameters, especially for single-crystal growth. The complexity of this method results from the following facts ... 

Figure 6.5 is reprinted from Chemical Physics Letters, Vol. 299, Pan Z W Pan, S S Xie, B H Chang, L F Sun, W Y Zhou and G Wang, Direct growth of aligned open carbon nanotubes by chemical vapour deposition, pp. 97-102, 1999, with permission from Elsevier. 

Ice crystals can grow in two simple distinct ways either by the freezing of liquid water or by direct sublimation from the vapour phase. In each case the mechanisms which determine the rate and habit of growth are the transport of water molecules to the point of growth and their accommodation into the growing interface, together with the transport of latent heat away from this interface. Many different physical situations can occur, of course, but they are all controlled by these basic mechanisms. 

Physical property measurements of rare earth elements and intermetallic compounds can be particularly sensitive to metallurgical factors such as impurity concentrations, phase distribution and crystallinity. For this reason, it is extremely important to perform measurements on well-characterised materials, and if possible on single crystals, produced under controlled conditions from the purest possible constituents. With this aim in view, this chapter is concerned with the preparation and crystal growth of the rare earth elements and their intermetallie compounds by solid state, melt and vapour eondensation growth techniques. 

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