The effect of gas and pressures on morphological and optical properties of C60 cluster films

C60 cluster films have been prepared by thermal evaporation in nitrogen or argon atmosphere. Surface morphologies and optical properties of C60 cluster films were studied with scanning electron microscope, ultraviolet-visible spectroscopy and ellipsometry. The average diameter of the surface particles of C60 cluster films increases with pressure. The UV/VIS absorption spectrum of C60 films grown in N2 or Ar atmosphere are significantly different from that of C60 films grown in vacuum. The three feature peaks of C60 films have obvious red shift. The value of red shift of three feature peaks is 6.0, 19.0 and 20.5 nm for C60 films deposited in an Ar pressure of 16 kPa, and 8.0, 28.0 and 28.5 nm for C60 films deposited in an N2 pressure of 16 kPa. The value of red shift increases with increasing wavelength. The refractive index n varies from 1.49 to 1.42 for C60 films deposited in Ar atmosphere and from 1.46 to 1.07 for C60 films deposited in N2 atmosphere with gas pressure varying from 4 to 16 kPa. The bandgap of C60 films deposited in Ar and N2 atmosphere is 2.24 and 2.09 eV, respectively. They are larger than that of C60 films (2.02 eV) deposited in vacuum. These results indicate that the optical properties of C60 cluster films are related to the nature of gas and pressure during deposition. The effects of gas and pressure on surface morphology and optical properties have been studied.