Influence of Substrate on the Transportation Properties of Co/Alq₃ Granular Films on a Si Wafer

A series of Co_0.48(Alq₃)_0.52 granular films were deposited on silicon substrates using the co-evaporating technique. A crossover of magnetoresistance (MR) from negative to positive was observed in the samples, due to conducting channel switching. The transport properties of samples are greatly influenced by hydrofluoric acid pretreatment, as a result, positive MR decreases drastically and the temperature dependence of resistance changes a lot near room temperature. The result indicates that the native oxide layer plays an important role in the transport mechanism. Moreover, different resistivities of Si substrates influence the current distribution of conducting channels, leading to different transport behaviors accordingly.