| The preparation of thin films via the physical vapor transport (PVT) method is a process that allows source material molecules a high degree of structural organization during condensation. This is because PVT is a relatively slow process. However, PVT, being described by fluid dynamics, is strongly influenced by external forces, such as that of gravity, and the physical dimensions (aspect ratio) of the container in which the deposition takes place. A previous work, based on the organic thin films preparation of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) by the PVT method, confirmed the influences of gravity and aspect ratio on the microstructure of the films, and has inspired the current work. This consists of the study of gravity and aspect ratio effects on the nucleation phase growth of N,N'-Bis-(3-methyphenyl)-N,N-bis-phenylbenzidine (TPD) via the PVT method. The nucleation phase represents the start of thin film growth and occurs during a short time lapse. Such experiments are therefore compatible with the short duration microgravity conditions available onboard parabolic flights. In this work, the deposition of TPD on indium tin oxide (ITO) covered substrates has been carried out on Earth by varying experiment orientation in relation to gravity, aspect ratio and the duration of deposition. Two technical challenges encountered were the control of TPD evaporation and condensation within a short time lapse, and rendering the ground based experiment compatible with parabolic flight conditions. These two issues, as well as the results and the perceived influences of gravity and aspect ratio, are presented in detail. A discussion concerning the links between results and influences is based on PVT theory, the thermodynamics of nucleation processes, and particle size distribution. |
