ELECTRICAL-CONDUCTIVITY OF NH2-SUBSTITUTED NI(II)-PHTHALOCYANINE

It is found that substitution of NH2 groups into positions 4, 4', 4", 4"' of Ni(II)-phthalocyanine (NH2-NiPc) transforms Ni(II)-phthalocyanine (NiPc) from a compound falling in the insulator (sigma almost-equal-to 10(-12) OMEGA-1 cm-1) to semiconductor (sigma almost-equal-to 10(-4) OMEGA-1 cm-1) range of electrical conductivities. The change in the conductivity reaches about 8 orders of magnitude, being dependent on the ambient conditions. The samples of NH2-NiPc exposed to air show up to 3 orders of magnitude higher conductivity than those examined immediately after evaporation under vacuum almost-equal-to 10(-3) Pa. Surface-and sandwich-mode conductivity measurements are performed showing similar activation energies of the current within the range 0.05 to 1.0 eV dependent on the temperature range and the ambient. Applying Auger spectroscopy NH2-NiPc is found to contain over 50% more oxygen than NiPc. It is, therefore, suggested that the larger conductivity of NH2-NiPc is due to its greater ability to absorb oxygen. Possible reasons of this property are discussed, the more open crystal structure, as one of them, is confirmed by separated XANES studies of the local structure at Ni atom in both the compounds. The temperature behaviour of the conductivity of NH2-NiPc under vacuum is discussed in terms of an interplay between electrode injection and bulk-generated carriers contributing to the measured current, the injection dominating at low temperatures.