Synthesis, structural analysis, spectrophotometric measurements and semiconducting properties of 3-phenyl azo-4-hydroxycoumarin thin films
3-phenyl azo-4-hydroxycoumarin, PAHC, compound was synthesized by reacting aniline diazonium salt
with 4-hydroxy coumarin. The thin
films of PAHC were prepared on the glass and quartz substrates by
thermal evaporation technique under vacuum pressure 105 mbar. The structure of thin
films was
characterized using X-ray diffraction, XRD, and Fourier transformation infrared, FTIR, techniques. The
XRD pattern for the pristine PAHC thin
film showed nanocrystallites distributed in amorphous matrix.
Annealing at 423 K improved the crystallinity of
films and the crystallite size is in the range 23–36 nm.
FTIR showed different vibrational modes, observed in infrared spectra of the powder, pristine and
annealed thin
films, were assigned to the molecular bonding structure of PAHC compound. The optical
properties of PAHC thin
films were investigated by the spectrophotometer measurements of the pristine
and annealed PAHC
films in the range 200–2100 nm. The refractive and absorption indices of the pristine
and annealed PAHC
films were calculated from measured transmittance and reflectance data. The results
showed that the refractive and absorption indices of thin
films are influenced with increasing annealing
temperature. The direct allowed transitions were the most probable transition and the optical band gap
was found to vary from 2.14 to 2.21 eV with increasing annealing temperature. The single oscillator model
was applied in the normal region of dispersion spectrum to determine the dispersion parameters and it is
noted that they are decreased with annealing temperature. The AC electrical conductivity, sAC, and the
real and imaginary parts of dielectric constants measurements were investigated in temperature range
304–413 K and frequency range 0.1–100 kHz; they confirmed semiconductor behavior of the PAHC
films