EFFECT OF GRAVITY ON COPPER PHTHALOCYANINE THIN-FILMS .2. SPECTROSCOPIC EVIDENCE FOR A NEW ORIENTED THIN-FILM POLYMORPH OF COPPER PHTHALOCYANINE GROWN IN A MICROGRAVITY ENVIRONMENT

A series of closed-cell physical vapor transport (PVT) experiments were conducted in both low earth orbit on the Space Shuttle Orbiter and in the laboratory as ground controls using the 3M-PVTOS (PVT of organic solids) apparatus. The experiments used PVT as a process to deposit oriented organic thin films of phthalocyanine and perylene compound derivatives on epitaxially active substrates sealed within demountable ampoules. In a series of three papers, of which this is the second, the complete characterization of the microscopic physical structure and macroscopic optical properties of the thin films produced using copper phthalocyanine as the organic source material is presented, and detailed comparisons are made between the microgravity-grown and unit-gravity (laboratory) grown samples. In the first paper it was shown that the films grown in low earth orbit are radially more uniform and optically homogeneous, and smoother over the submillimeter to submicron scale range. In this second paper of the series comparisons of the microgravity and unit gravity films are made using the results from applications of external reflection-absorption IR spectroscopy, grazing incidence X-ray diffraction, and visible-near-IR reflection-absorption spectroscopy. All three techniques appear mutually consistent in implying that the microgravity-grown films contain predominantly a new polymorphic form of CuPc designated here as M-CuPc, whereas the ground controls contain mixtures of α and β polymorphs and occasionally the new polymorph. Furthermore, the space-grown films are more highly uniaxially oriented in general with the molecular stacking b axis orientation of the crystalline domains in the "standing" mode relative to the surface for the microgravity-grown films, but parallel to the substrate in the unitgravity-grown films, with a larger fraction of the film material uniaxially oriented in the space-grown samples. To our knowledge, these experiments are the first time that an organic pigment film has been deposited by closed-cell PVT. © 1990.