Electronic properties of evaporated thin films of bis(1,2-benzoquinone dioximato)metal(II), M(bqd)2(M = Ni, Pd and Pt)

Abstract

Thin films of bis(1,2-benzoquinone dioximato)metal(II), M(bgd)₂, where the metal(II) or M is Ni, Pd or Pt, gives a divalent d⁸ metal ion, have been prepared by evaporation onto a quartz or a glass substrate held at room temperature in a vacuum (ca. 1.33 × 10^–4 Pa). X-Ray diffraction profiles, electronic absorption spectra, UV photoelectron spectra and electrical resistivities of these complex thin films have been measured to study the characteristics of their electronic properties. The lowest absorption bands of the three kinds of complex films were observed at about 0.99, 1.93 and 1.49 eV for Pt(bqd)₂, Pd(bqd)₂ and Ni(bqd)₂, respectively. Those bands for Pt(bqd)₂ and Pd(bqd)₂ were assigned to the electronic transitions from the levels ndz₂ to (n+1)p_Z(n= 4 and 5). The threshold ionization energies of the thin films were 4.96, 5.31 and 5.23 eV for Pt(bqd)₂, Pd(bqd)₂ and Ni(bqd)₂, respectively. The magnitudes of both energy values are in the order Pd > Ni > Pt for M in M(bqd)₂. The electrical resistivity of the thin film of Pt(bqd)₂ was measured to be 6.3 × 10⁴Ω cm with a thermal energy gap of 0.34 eV, which was obtained from the activation energy for its electric conduction in the temperature range from 140 K to room temperature. On the other hand, the energy gap of Pt(bqd)₂ was estimated to be Δε= 0.84 eV from the energy diagram derived for its external photoelectric process on the basis of the band model for an intrinsic semiconductor.