Probing Spin-State Switching in Fe(phen)₂(NCS)₂ Thin Film Nanocrystals on Different Substrates by Electrical Conductivity Measurements.

Spin-state switching mechanism is investigated by measuring the temperature of the electrical conductivity of spin crossover (SCO) material Fe(phen)2(NCS)2 thin films grown on glass, quartz and silicon substrates. The morphology characterized by scanning electron microscopy, clearly reveals the growth of thin films of thickness ~300 nm comprising of nanocrystals, size and distribution of which is dependent on the nature of substrates. The film on quartz is found to have the most uniform growth of nanocrystals of size ~22 nm with a homogeneous distribution. All the films retain the orthorhombic crystal structure as that of bulk with slight distortions in lattice plausibly arising out of the strain. Spin state switching between LS and HS is clearly revealed by the hysteresis loop observed in the temperature dependence of the electrical conductivity in its heating and cooling cycle. The critical temperature of transition between HS and LS states is found to be 162 K, 193 K and 217 K for film on glass, quartz and Si respectively. Film on quartz is found to exhibit a wide hysteresis loop of width ~60 K while that of on silicon exhibits higher transition temperature with narrow hysteresis loop ~14 K. The results are found to be quite inspiring to tune the SCO characteristics to develop molecular switch and memory devices close to room temperature.