Synthesis and electrical properties of cubic NaxWO3Na_{x}WO_{3} thin films across the metal-insulator transition

Highly oriented (1 0 0) $Na_{x}WO_{3}$ thin films were fabricated in the composition range 0.1 \leq x \leq 0.46 by pulsed laser deposition technique. The films showed transition from metallic to insulating behaviour at a critical composition between x = 0.15 and 0.2. The pseudo-cubic symmetry of $Na_{x}WO_{3}$ thin films across the transition regionis desirable for understanding the composition controlled metal-insulator transition in the absence of any structural phase transformation. The electrical transport properties exhibited by these films across the transition regime were investigated. While the resistivity varied as T-2 at low temperatures in the metallic regime, avariable range hopping conduction was observed for the insulating samples. For metallic compositions, a non-linear dependence of resistivity in temperature was also observed from 300 to 7 K, whose exponent varied with the composition of the film

Synthesis and electrical properties of cubic Na<SUB>x</SUB>WO<SUB>3</SUB> thin films across the metal-insulator transition

Highly oriented (1 0 0) NaxWO3 thin films were fabricated in the composition range 0.1 &#8804; x &#8804; 0.46 by pulsed laser deposition technique. The films showed transition from metallic to insulating behaviour at a critical composition between x = 0.15 and 0.2. The pseudo-cubic symmetry of NaxWO3 thin films across the transition region is desirable for understanding the composition controlled metal-insulator transition in the absence of any structural phase transformation. The electrical transport properties exhibited by these films across the transition regime were investigated. While the resistivity varied as T2 at low temperatures in the metallic regime, a variable range hopping conduction was observed for the insulating samples. For metallic compositions, a non-linear dependence of resistivity in temperature was also observed from 300 to 7 K, whose exponent varied with the composition of the film

The suppression of structural phase transformation in LaVO<SUB>3</SUB> and La<SUB>1-x</SUB>Sr<SUB>x</SUB>VO<SUB>3</SUB> thin films fabricated by pulsed laser deposition

Highly oriented (100) thin films of LaVO3 and La1-xSrxVO3 have been fabricated by pulsed laser deposition in a reducing atmosphere. The films show a transition from insulating to metallic behaviour in the composition region of x, 0.175&lt;x&lt;0.200. In the single crystals of the antiferromagnetic insulating phase, a first-order structural phase transition is observed few degrees below the magnetic transition, which manifests itself as a kink in the temperature dependence of resistivity. In the highly oriented thin films of LaVO3 and La1-xSrxVO3 fabricated on lattice matched substrates in this study, the structural phase transformation in the insulating phase has been suppressed. The electrical conduction is found to take place via hopping through localized states at low temperatures. The metallic compositions show a non-linear (T1.5) behaviour in the temperature dependence of resistivity. V (2p) core level spectra of these films show a gradual change in the relative intensities of V3+ and V4+ ions as the value of x increases

Strain-induced metallic behavior in PrNiO<SUB>3</SUB> epitaxial thin films

Electrical transport properties of RNiO3 (R=Pr, Nd, Sm) thin films grown by pulsed laser deposition have been studied. RNiO3 films grow in the (1 0 0) direction on a LaAlO3 (1 0 0) substrate. Unlike the polycrystalline solid, PrNiO3 films showed metallic behavior. The first-order metal-to-insulator transition observed in polycrystalline solids is suppressed in RNiO3 films. The effect of lattice strain in the films influencing the transport properties has been studied by varying the thickness of PrNiO3 film on LaAlO3 (1 0 0) and also by growing them on SrTiO3 (1 0 0) and &#945;-Al2O3 ( 1 1 0 2) substrates. Deviation in the transport properties is explained due to the strain-induced growth of the films. Further, we show that the transport property of a LaNiO3 film is also influenced by a similar strain effect

Strain-induced Metallic Behavior in PrNiO3PrNiO_3 Epitaxial Thin Films

Electrical transport properties of $RniO_3$ (R=Pr, Nd, Sm) thin films grown by pulsed laser deposition have been studied. RNiO3 films grow in the (1 0 0) direction on a $LaAlO_3$ (1 0 0) substrate. Unlike the polycrystalline solid, $PrNiO_3$ films showed metallic behavior. The first-order metal-to-insulator transition observed in polycrystalline solids is suppressed in $RniO_3$ films. The effect of lattice strain in the films influencing the transport properties has been studied by varying the thickness of $PrNiO_3$ film on $LaAlO_3$ (1 0 0) and also by growing them on $SrTiO_3$ (1 0 0) and $\alpha-Al_2O_3 (1 \={1}02)$ substrates. Deviation in the transport properties is explained due to the strain-induced growth of the films. Further, we show that the transport property of a $LaNiO_3$ film is also influenced by a similar strain effect

Electrical transport properties of LaNi<SUB>1-x</SUB>M<SUB>x</SUB>O<SUB>3</SUB> (M = Co, Mn) thin films fabricated by pulsed laser deposition

Highly oriented thin films of LaNi1-xMxO3 (M = Mn, Co) are grown on LaAlO3(100) substrate by pulsed laser deposition. They undergo a metal to insulator transition when the Mn or Co concentration is increased. The observed conduction pattern is highly sensitive to the doping concentration in these thin films. The conduction pattern also varies as the doping element is varied from Mn to Co. There is a large dominance of electron-lattice interactions in the conduction mechanism of the charge carriers. While the metallic thin films of LaNi1-xCoxO3 show a linear variation of resistivity with temperature, LaNi1-xMnxO3 thin films exhibit a prominent square-root dependence of resistivity on temperature. At high concentrations of Mn or Co, the conduction takes place via a polaron hopping mechanism, which suggests that lattice polarization may be present in these films. The change observed in the transport properties is attributed to the charge disproportionation between the Ni3+-Ni2+ pairs, which are favoured more in Mn doped thin films. The photoelectron spectroscopic studies give evidence of charge disproportionation present in these films

The effect of strain on nonlinear temperature dependence of resistivity in SrMoO3SrMoO_3 and SrMoO3−xNxSrMoO_{3-x}N_x films

Highly oriented $SrMoO_3$ thin films have been fabricated by pulsed laser deposition of $SrMoO_4$ in hydrogen. The films are found to grow along the (1 0 0) direction on $LaAlO_3$ (1 0 0) and $SrTiO_3$ (1 0 0) substrates. The method has been extended for the fabrication of oxynitride thin films, using ammonia as the reducing medium. The resistivity measurements show nonlinear temperature dependent $(T^n)$ behaviour in the temperature interval of 10–300 K. The conduction mechanism is largely affected by the strain due to the substrate lattice. A combination of $T$ and $T^2$ dependence of resistivity on temperature is observed for films having lesser lattice mismatch with the substrate. The X-ray photoelectron spectroscopic studies confirm the formation of $SrMoO_3$ and $SrMoO_{3-x}N_x$ films

The suppression of structural phase transformation in LaVO3LaVO_{3} and La1−xSrxVO3La_{1-x}Sr_{x}VO_{3} thin films fabricated by pulsed laser deposition

Highly oriented (100) thin films of $LaVO_{3}$ and $La_{1-x}Sr_{x}VO_{3}$ have been fabricated by pulsed laser deposition in a reducing atmosphere. The films show a transition from insulating to metallic behaviour in the composition region of x, 0.175 < x < 0.200. In the single crystals of the antiferromagnetic insulating phase, a first-order structural phase transition is observed few degrees below the magnetic transition, which manifests itself as a kink in the temperature dependence of resistivity. In the highly oriented thin films of $LaVO_{3}$ and $La_{1-x}Sr_{x}VO_{3}$ fabricated on lattice matched substrates in this study, the structural phase transformation in the insulating phase has been suppressed. The electrical conduction is found to take place via hopping through localized states at low temperatures. The metallic compositions show a non-linear $(T^{1.5})$ behaviour in the temperature dependence of resistivity. V (2p) core level spectra of these films show a gradual change in the relative intensities of $V^{3+}$ and $V^{4+}$ ions as the value of x increases

Assembly of Iron Oxide Nanocrystal Superstructures

In this work we report on the self-assembly of monodisperse iron oxide nanocrystals on silica-coated Au surfaces achieved by magnetic field-assisted solution deposition techniques and discuss the effects of the interactions that contribute to promote their ordered arrangement into small clusters, chain-like structures or high-density particle multilayer superlattices. The results highlight the roles of inter-particle and nanocrystal-substrate interactions in controlling the nucleation and growth of self-assembled clusters and superstructures made of spherical magnetic nanocrystals

Structure and electrical properties of sodium tungsten bronzes thin films

Highly oriented thin films of $Na_xWO_3 (x=0.25–0.7)$ are grown on sapphire (1 1 0 2) and $SrTiO_3$ (1 0 0) substrates by pulsed laser deposition. The colour of the films changes from blue through red to bronze yellow on varying the sodium content. The films are composed of particles less than 100 nm size. As in bulk $Na_xWO_3$, the resistivity is found to decrease on increasing the sodium content, and at around x=0.25, a non-metal to metal transition is clearly observed. The conductivity measurement of Na_0_._2_5WO_3 shows a crossover from temperature-activated Arrhenius behaviour at high temperatures to a variable range hopping mechanism near 70 K. The metallic samples show linear dependence of resistivity above 50 K. XPS studies confirm the presence of sodium in +1 and tungsten in +5 and +6 oxidation states