T. Santhosh Kumar

Structural and dielectric studies of Co doped MgTiO3 thin films fabricated by RF magnetron sputtering

We report the structural, dielectric and leakage current properties of Co doped MgTiO3 thin films deposited on platinized silicon (Pt/TiO2/SiO2/Si) substrates by RF magnetron sputtering. The role of oxygen mixing percentage (OMP) on the growth, morphology, electrical and dielectric properties of the thin films has been investigated. A preferred orientation of grains along (110) direction has been observed with increasing the OMP. Such evolution of the textured growth is explained on the basis of the orientation factor analysis followed the Lotgering model. (Mg1-xCox)TiO3 (x = 0.05) thin films exhibits a maximum relative dielectric permittivity of ɛr = 12.20 and low loss (tan δ ∼ 1.2 × 10−3) over a wide range of frequencies for 75% OMP. The role of electric field frequency (f) and OMP on the ac-conductivity of (Mg0.95Co0.05)TiO3 have been studied. A progressive increase in the activation energy (Ea) and relative permittivity ɛr values have been noticed up to 75% of OMP, beyond which the properties starts d...

Effect of annealing and atmosphere on the structure and optical properties of Mg2TiO4 thin films obtained by the radio frequency magnetron sputtering method

In this article, nanocrystalline Mg2TiO4 (MTO) thin films were deposited on quartz substrates with a thickness ranging from 200 to 300 nm at ambient temperature by the radio frequency magnetron sputtering method. These films were kept under O2 standard cubic centimeters per minute (SCCM) and, post deposition, annealing in air at 500°C for 1 h. The structure of the sintered target and films were analysed by X-ray diffraction (XRD). The XRD patterns indicated that these films are amorphous structurally, and annealing process induces the formation of crystalline phase. The microstructure and surface morphology of the MTO films were studied by field emission scanning electron microscopy and atomic force microscopy. The post-deposition annealing resulted in an amorphous-crystalline phase transition in the films, which is accompanied by an increase in the refractive index and decrease in the optical bandgap. The annealed films exhibit a refractive index of 1.98–2.03 (at 600 nm) with an optical bandgap values between 4.44 and 4.58 eV. The increase of refractive index for annealed films can be attributed to increase of crystalline nature and packing densities. The O2 SCCM and annealing also greatly affected the photoluminescence spectra. In addition, the characteristic emission sharp peak and shoulder peaks at 357, 409 and 466 nm were detected.

Structural, optical and microwave dielectric studies of Co doped MgTiO3 thin films fabricated by RF magnetron sputtering

We report the structural, optical, and microwave dielectric characteristics of (Mg0.95Co0.05)TiO3 (MCT) thin films deposited onto amorphous SiO2 (a-SiO2) substrates by RF magnetron sputtering for the first time. The role of the oxygen mixing percentage (OMP) on the growth, morphology, optical, and microwave dielectric properties of MCT thin films has been investigated. The as-deposited MCT films were x-ray amorphous and crystallined after annealing at 700 °C for 1 h in air. A preferred orientation of grains along the (110) direction has been observed with increasing OMP. Such a textured growth is explained by calculating the orientation factors from the Lotgering model. The dispersion in a refractive index with wavelength has been explained using a single oscillator dispersion model. Both the refractive index and bandgap of the films increases on annealing. The annealed films exhibit refractive indices in the range of 1.88–2.08 at 600 nm with an optical bandgap value between 3.95–4.16 eV. The increase in the refractive index is attributed to the improvement in packing density and crystallinity, and decrease in the porosity ratio, whereas the increase in bandgap is due to the decrease in intermediary energy levels within the optical bandgap. (Mg0.95Co0.05)TiO3 thin films exhibited a progressive increase in the dielectric properties with OMP and a maximum dielectric constant of r = 17.3 and low loss (tanδ ~ 1.1 × 10−3) at a spot frequency of 10 GHz for the films deposited at 75% OMP, beyond which they decreased. The improvement in dielectric properties with an increase in OMP has been correlated to the preferred orientation growth, reduction in oxygen vacancies, and strain. The prepared MCT thin films are suitable candidates for anti-reflection coatings and complementary metal-oxide semiconductor (CMOS) applications.

Effect of Process Parameters and Post Annealing Temperature on Structural and Optical Properties of MgTiO3 Thin Films Deposited by RF Magnetron Sputtering

MgTiO3 (MTO) thin films have been deposited on to SiO2 substrates at ambient temperature by RF magnetron sputtering at different oxygen mixing percentage (OMP). The MTO target has been synthesized by mechanochemical synthesis method and sintered at 1,350 °C for 3 h. The phase purity of the sputtering target was confirmed from X-ray diffraction pattern and it could be refined to \( R\bar{3} \) space group with lattice parameters a = b = 5.0557(12) A, c = 13.9003(9) A. The effect of annealing on crystal structure, and optical properties of MTO thin films studied systematically. The as deposited films were X-ray amorphous irrespective of the processing parameters and exhibit refractive index in the range of 1.84–1.97 at 600 nm with an optical absorption edge value in between 3.72 and 3.78 eV. On annealing at 700 °C for 1 h, the films were polycrystalline accompanied by an increase in refractive index and band gap and decrease in transmittance. The increase in the refractive index and band gap on annealing can be attributed to the improvement in packing density and crystallinity decrease in porosity ratio.

Irreversible thermochromic response of RF sputtered nanocrystalline BaWO4 films for smart window applications

We report irreversible thermochromic behaviour of BaWO4 (BWO) films for the first time. BWO films have been deposited at different substrate temperatures (RT, 200, 400, 600 and 800 °C) using RF magnetron sputtering in pure argon plasma. BWO films deposited at 800 °C exhibit crystalline nature. Also, BWO films deposited in the temperature range of 400 - 600 °C exhibit WO3 as a secondary phase and its weight percentage decreases with an increase in deposition temperature, whereas the films deposited at 800 °C exhibited pure tetragonal phase. FESEM images revealed that as the average particle sizes of the films are higher as compared with the thickness of the films and is explained based on Avrami type nucleation and growth. The transmittance of the films decreases with an increase in deposition temperature up to 600 °C and increases thereafter. Films deposited at 600 °C show ≤ 20% transmittance, looking at the films deposited at room temperature and 800 °C exhibits 90 and 70%, respectively. The refractive i...