Gallium oxide (Ga2O3) thin films
were produced
by sputter deposition by varying the substrate temperature (T
s) in a wide range (T
s = 25–800 °C). The structural characteristics and optical
properties of Ga2O3 films were evaluated using
X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive
X-ray spectrometry (EDS), Rutherford backscattering spectrometry (RBS),
and spectrophotometric measurements. The effect of growth temperature
is significant on the chemistry, crystal structure, and morphology
of Ga2O3 films. XRD and SEM analyses indicate
that the Ga2O3 films grown at lower temperatures
were amorphous, while those grown at T
s ≥ 500 °C were nanocrystalline. RBS measurements indicate
the well-maintained stoichiometry of Ga2O3 films
at T
s = 300–800 °C. The spectral
transmission of the films increased with increasing temperature. The
band gap of the films varied from 4.96 to 5.17 eV for a variation
in T
s in the range 25–800 °C.
A relationship between microstructure and optical property is discussed.
Dysprosium-doped nickel-ferrite (NiFe 1.925 Dy 0.075 O 4 ) thin films were fabricated using sputterdeposition using a stoichiometric bulk target prepared by the solid state chemical reaction. The structural, electrical and optical properties of NiFe 1.925 Dy 0.075 O 4 thin films were studied in detail. The grain-size (L) and lattice-expansion effects are significant on the electrical and optical properties of NiFe 1.925 Dy 0.075 O 4 films. Air annealing (T a ) at 450-1000 uC results in the formation of nanocrystalline NiFe 1.925 Dy 0.075 O 4 films, which crystallize in the inverse spinel structure, with L = 5-40 nm. The lattice constant of NiFe 1.925 Dy 0.075 O 4 increases compared NiFe 2 O 4 due to Dydoping. Electrical conductivity of NiFe 1.925 Dy 0.075 O 4 films (at 300 K) decreases from 1.07 V 21 m 21 to 3.9 6 10 23 V 21 m 21 with increasing T a (450 to 1000 uC). Conductivity was found to decrease exponentially with decreasing the temperature from 300 K to 120 K indicating the characteristic semiconducting nature of all the films. Band gap increases from 3.17 to 4.08 eV for NiFe 1.925 Dy 0.075 O 4 films with increasing T a from 450 to 1000 uC. A correlation between grain-size, electrical conductivity and optical band gap in nanocrystalline NiFe 1.925 Dy 0.075 O 4 films is established.
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