Synthesis, structural analysis, spectrophotometric measurements and semiconducting properties of 3-phenyl azo-4-hydroxycoumarin thin films
A B S T R A C T
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 10
5
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, s
, 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.