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The origin of alternating wavy dark-bright stripe-like contrast in strain contrast transmission electron microscopy images of NiCo2O4 (NCO) epitaxial thin films grown by pulsed laser deposition has been investigated. The nanoscale stripe-like pattern is determined to be associated with coexisting rock salt (RS) and inverse spinel crystal phases. The presence of two different phases, not addressed in previous reports, is experimentally confirmed by both electron diffraction and high resolution transmission electron microscopy imaging. First principles based calculations, together with compressive strain present in the films, support the formation of such coexisting crystallographic phases in NCO. Similar microstructural patterns and RS structure are not observed in epitaxial films of two other oxides of the spinel family, namely, NiFe2O4 and CoFe2O4. A correlation between the coexisting structures and the macroscopic physical properties of NCO is discussed. [ABSTRACT FROM AUTHOR]

Yttrium titanate (Y2Ti2O7) thin films, having pyrochlore-type structure, were synthesized in single phase by sol-gel synthesis technique. Single-phase formation was confirmed by X-ray diffraction (XRD) study. Surface morphology of thin films was studied by using FESEM and average grain size was found to be in nanometer range. Retention of stoichiometry in thin films was confirmed by EDX analysis. Optical property of Y2Ti2O7 thin films was studied with the help of UV-Vis spectrometer and the energy band gap was found to be ∼3.5 eV. Dielectric properties of thin films are also studied and discussed in details. [ABSTRACT FROM AUTHOR]

We present control over the ambipolar nature of Te in ZnO and the corresponding optical band gap in epitaxial thin film grown by pulsed laser deposition. Experimentally, the decrease in band gap is found to be strongly dependent on the Te concentration for TeO compared to TeZn. Emission at 3 eV for TeZn, irrespective of Te content is explained by first principle calculation considering Zn vacancy in the lattice. An experimental band bowing parameter of ∼7 eV is obtained for TeO and is in agreement with modified Becke-Johnson potential (mBJLDA) based theoretical calculation. The physical insight into the nature of band bowing is elucidated. [ABSTRACT FROM AUTHOR]

We have investigated the Te atom incorporation, solubility, structural features and the corresponding optical property of epitaxial ZnO:Te thin film grown on c -plane sapphire by pulsed laser deposition. Incorporation of Te at the oxygen (Te O ) or zinc (Te Zn ) site can be controlled through the deposition scheme to transfer Te during the film growth. Solubility of Te at the oxygen site is strongly dependent on the growth temperature and a maximum of ~4 at% Te is obtained at 400 °C with the film remained to be in epitaxial form. Lowering the temperature further increases Te incorporation but films turn out to be amorphous. For Te at the Zn site a maximum of ~3.4 at% is achieved with the film to be in the epitaxial form with tilt and phase separation is observed beyond this composition. Band gap decreases with Te incorporation both in the oxygen and zinc sites but decrease in band gap is found to be pronounced and composition dependent for the former case. [ABSTRACT FROM AUTHOR]

Crystallographic phase separation and optical properties of ZnO1-xSx (x=0.1-0.3) alloy thin films grown by pulsed laser deposition (PLD) on c-plane sapphire substrate have been investigated with and without using ZnO buffer layer between the film and substrate. ZnO buffer layer assists in lattice matching of the alloy thin film and influences the phase separation and incorporation of S in this system. ZnO0.7S0.3 thin film separated into four different phases when directly grown on c-plane sapphire compared to two when grown using ~8 nm thick ZnO buffer layer. ZnO0.88S0.12 thin film showed a single phase with tilt between crystallites but forms epitaxial film without any tilt on ZnO buffer layer. Incorporation of S is close to the targeted value for the films grown with the buffer layer. With the help of buffer layer we have been able to grow epitaxial film up to 17 at% S. Band gap for each alloy phase has been determined by low loss electron energy loss spectroscopy and a band bowing parameter of ~5 eV is obtained. [ABSTRACT FROM AUTHOR]

It is found that the oxygen vacancy (VO) defect concentration affecting the separation between individual species in LiZn-Lii complex influences the optical emission property of Li0.06Zn0.94O epitaxial thin film grown by pulsed laser deposition. The film grown under low oxygen partial pressure (n-type conductivity)/higher partial pressure (resistive-type) has broad emission at ∼2.99 eV/∼2.1 eV and a narrower emission at 3.63 eV/3.56 eV, respectively. First principle based mBJLDA electronic structure calculation suggests that the emission at 2.99 eV is due to the LiZn-Lii pair complex and the emission at 2.1 eV is when the component species are away from each other. [ABSTRACT FROM AUTHOR]

Co vacancy (VCo) induced robust room temperature ferromagnetism (Ms ∼ 60 emu/cm3 and coercivity ∼ 603 Oe) is experimentally realized in rock-salt CoO epitaxial thin film (∼110 nm) grown by pulsed laser deposition. Co charge state is found to be higher ∼+3.2 (from Co L3/L2 white line ratio) and this is due to the VCo induced charge transfer from the neighboring Co-3d to O-2p states in order to compensate for the hole formation. O-K and cathodoluminescence spectra corroborate the existence of VCo and higher charge state. Temperature dependent magnetization and exchange bias experiments confirm the coexistence of ferromagnetic and antiferromagnetic phases. [ABSTRACT FROM AUTHOR]

We report on detailed microstructural and atomic ordering characterization by transmission electron microscopy in epitaxial LiFe 5 O 8 (LFO) thin films grown by chemical vapor deposition (CVD) on MgO (001) substrates. The experimental results of LFO thin films are compared with those for bulk LFO single crystal. Electron diffraction studies indicate weak long-range ordering in LFO (α-phase) thin films in comparison to bulk crystal where strong ordering is observed in optimally annealed samples. The degree of long-range ordering depends on the growth conditions and the thickness of the film. Annealing experiment along with diffraction study confirms the formation of α-Fe 2 O 3 phase in some regions of the films. This suggests that under certain growth conditions γ-Fe 2 O 3 -like phase forms in some pockets in the as-grown LFO thin films that then convert to α-Fe 2 O 3 on annealing. [ABSTRACT FROM AUTHOR]