Methanol sensing characteristics in undoped and (Zn, Mn) doped Fe(phen)2(NCS)2 spin-crossover thin films

Abstract

The methanol sensing properties of spin-crossover (SCO) complex Fe(phen)2(NCS)2 thin, as well as those of thin films doped with Zn or Mn are demonstrated here. The synchrotron x-ray diffraction (SXRD) data clearly confirms the crystal structure of the SCO complex. The microstructure studied by transmission electron microscopy (TEM) clearly shows the formation of cuboid-shaped growth of nanocrystals and is similar for all the samples. The optical photographs of the samples show an evident change in color from reddish-purple color to pink upon exposure to methanol vapor. The optical absorption band (∼540 nm) in the presence of methanol of the SCO films is shifted to a longer wavelength with exposure time. The methanol sensitivity of SCO films is further investigated using electrical resistance measurements, which reveal that the response differs between Zn and Mn doped films and undoped ones. The difference in electronegativity of metals plausibly alters the polaron hopping transport in the SCO films and explains the observed variation of resistance with methanol exposure. The data suggest that using spin-crossover materials may be pretty important in designing smart sensors in the future.