Characterization and Photoconductive Properties of Highly Oriented Thin Films of Oxotitanium Phthalocyanine Prepared by
- PDF / 409,623 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 84 Downloads / 236 Views
HISATOMO YONEHARA AND CHYONGJIN PAC Kawamura Institute of Chemical Research, 631 Sakado, Sakura, Chiba 285, Japan
ABSTRACT Thin films of oxotitanium phthalocyanine were grown on optical flat PYREX glass substrates at 0.05 - 1.5 nm/s under 2x10-4 Pa. The films were analyzed by X-ray diffraction patterns (XRD) and polarized absorption spectra to reveal a preferred molecular orientation in the films evaporated at 0.05 nm/s, but amorphous nature of the films prepared at higher deposition rates. All the films were changed in the crystallinity to a-form microcrystals upon exposure to vapor of methylene chloride or tetrahydrofuran. XRD analysis of the vapor-treated films at 0.05 nm/s showed only an intense peak at 20 = 7.500, demonstrating that the (010) face of the ax-form crystal is highly oriented perpendicularly to the substrate surface. The molecular orientation was again demonstrated by polarized absorption spectra. The photoconductive behavior of the films was found to depend on the deposition rates as well as on the vapor treatment.
INTRODUCTION Phthalocyanine compounds are functional dyes with high thermal and chemical stabilities, which have been utilized as carrier generation materials with high quantum yields in the nearinfrared region [1]. Among them, oxotitanium phthalocyanine (TiOPc) is one of the most sensitive organic photoreceptors used in electrophotographic laser printers [1]. Extensive studies have been performed on photoconductive properties of TiOPc materials with different crystal forms dispersed in polymer binders [2-4], suggesting important roles of molecular stacking habits in the solid state [4]. Since TiOPc fine particles are randomly oriented in polymerdispersed films, it is hard to understand the photoconductive nature of TiOPc associated with molecular orientation and/or crystalline alignment. Although the controlled growth of organic assemblies can be achieved in Langmuir-Blodgett films [5] and also by molecular-beam epitaxy [6], little has been reported on the photoconductive behavior of such controlled films, probably because of experimental difficulties. From practical viewpoints, usual vacuum-deposition techniques should be useful in obtaining rich information on relationships between photoconductivity and molecular orientations, if solid films of different molecular assemblies can be fabricated under controlled deposition. While photoconductivity of vacuum-deposited TiOPc films has been reported [7-9], few systematic study has been carried out to explore structure-activity relationships for TiOPc solid films. In the present investigation, we have found that highly oriented thin films of TiOPc can be fabricated under controlled vacuum deposition and that the dark conductive and photoconductive properties of vacuum-deposited TiOPc films depend on the crystalline forms and alignments of microcrystals associated with molecular arrangement.
301 Mat. Res. Soc. Symp. Proc. Vol. 328. ©1994 Materials Research Society
EXPERIMENT Pure TiOPc was synthesized according to a new method develope
Data Loading...
