Effect of oxygen pressure on the grain and domain structure of polycrystalline 0.85PbMg(1/3)Nb(2/3)O(3)-0.15PbTiO(3) thin films studied by scanning probe microscopy

0.85PbMg(1/3)Nb(2/3)O(3)-0.15PbTiO(3) ferroelectric-relaxor thin films have been deposited on La(0.5)nSr(0.5)CoO(3)/(1 1 1) Pt/TiO(2)/SiO(2)/Si by pulsed laser ablation at various oxygen partial pressures in the range 0.05 to 0.4 Torr. All the films have a rhombohedral perovskite structure. The grain morphology and orientation are drastically affected by the oxygen pressure, studied by x-ray diffraction and scanning electron microscopy. The domain structure investigations by dynamic contact electrostatic force microscopy have revealed that the distribution of polar nanoregions and their dynamics is influenced by the grain morphology, orientation and more importantly, oxygen vacancies. The correlation length extracted from autocorrelation function images has shown that the polarization disorder decreases with oxygen pressure up to 0.3 Torr. The presence of polarized domains and their electric field induced switching is discussed in terms of internal bias field and domain wall pinning. Film deposited at 0.4 Torr presents a curious case with unique triangular grain morphology and large polarization disorder.

Effect of Oxygen Pressure on Structural and Magnetic Properties of YIG Thin Films

The effect of oxygen pressure (P-O2) on the Yttrium Iron Garnet (YIG) thin films were grown on silicon substrate by rf sputtering method was studied. The as-deposited films at 300K were amorphous in nature. The crystallization of these films was achieved by annealing at a temperature of 800 degrees C/1hr in air. The structural, microstructural and magnetic properties were found to be dependent on P-O2.

Effect of low oxygen pressure on structural and magnetic properties of quenched SrFe12O19 thin films

Strontium hexaferrite thin films have been grown on glass substrates at room temperature in oxygen environment by pulsed laser deposition method. The effect of oxygen pressure (p(o2)) on the structural and magnetic properties has been investigated. The as-deposited films were found to be amorphous in nature. The crystallization of these films was achieved by annealing at a temperature of 850 A degrees C in air. The thickness of the film increased with p(o2). The film grown at p(o2) = 0.455 Pa had a clear hexagonal structure. The values of coercivity for the films were found to increase with p(o2).

Effect of Pressure on Polymer Ignition

Auto-ignition temperature of polystyrene, poly(vinyl chloride) and carboxy terminated polybutadiene has been measured at various oxygen pressures (1-28 atm) in a high pressure differential thermal analysis assembly at a heating rate of 10°C/min. The exothermic peak appears between 250-350°C in polystyrene and poly(vinyl chloride) and between 150-200°C for carboxy terminated polybutadiene. Ignition appears to be controlled by in situ forma tion and degradation of polymeric peroxides. Inverse dependence of ignition temperature on oxygen pressure is explained by the rate equation which con siders that ignition of a particular sample, of a fixed geometry, occurs when gasification rate reaches a unique critical value.

High-pressure kinetics of oxidative copolymerization of styrene with alpha-methyl styrene

This is the first report on the study carried out on high-pressure free-radical initiated oxidated copolymerization of styrene (STY) with alpha-methylstyrene (AMS) at various temperatures (45-65degreesC) at constant pressure (100 psi) and then at various pressures (50-300 psi) keeping the temperature (50degreesC) constant. The compositions of the copolyperoxides obtained from the H-1 NMT spectra were utilized to determine the reactivity ratios of the monomers. The reactivity ratios indicate that STY forms an ideal copolyperoxide with AMS and the copolyperoxide is richer in AMS. The effect of temperature and oxygen pressure in the reactivity ratios of the monomers was studied. The rates of copolymerization (R-p) were used to determine the overall activation energies (E-a) and activation volume (DeltaV(#)) of copolymerization. The unusually higher values of the DeltaV(#) may be due to the pressurizing fluid oxygen which itself is a reactant in the copolymerization, the side reactions, and the chain-transfer reactions occuring during copolymerizations.

Variation of the partial thermodynamic properties of oxygen with composition in YBa2Cu3O7−δ

The variation of equilibrium oxygen potential with oxygen concentration inYBa 2Cu3O7-δhas been measured in the temperature range of 773 to 1223 K. For temperatures up to 1073 K, the oxygen content of theYBa 2Cu3O7-δsample, held in a stabilized-zirconia crucible, was altered by coulometric titration. The compound was in contact with the electrolyte, permitting direct exchange of oxygen ions. For measurements above 1073 K, the oxide was contained in a magnesia crucible placed inside a closed silica tube. The oxygen potential in the gas phase above the 123 compound was controlled and measured by a solid-state cell based on yttria-stabilized zirconia, which served both as a pump and sensor. Pure oxygen at a pressure of 1.01 × 105 Pa was used as the reference electrode. The oxygen pressure over the sample was varied from 10-1 to 105 Pa. The oxygen concentrations of the sample equilibrated with pure oxygen at 1.01 × 105 Pa at different temperatures were determined after quenching in liquid nitrogen by hydrogen reduction at 1223 K. The plot of chemical potential of oxygen as a function of oxygen non-stoichiometry shows an inflexion at δ ∼ 0.375 at 873 K. Data at 773 K indicate tendency for phase separation at lower temperatures. The partial enthalpy and entropy of oxygen derived from the temperature dependence of electromotive force (emf ) exhibit variation with composition. The partial enthalpy for °= 0.3, 0.4, and 0.5 also appears to be temperature dependent. The results are discussed in comparison with the data reported in the literature. An expression for the integral free energy of formation of YBa2Cu3O6.5 is evaluated based on measurements reported in the literature. By integration of the partial Gibbs’ energy of oxygen obtained in this study, the variation of integral property with oxygen concentration is obtained at 873 K.

Thermodynamics of GdMnO3 and GdMn2O5 phases determined by the EMF method

Using solid oxide galvanic cells of the type: MnO + Gd2O3 + GdMnO3/O-2/Ni + NiO and Mn3O4 + GdMnO3 + GdMn2O5/O-2/air the equilibrium oxygen pressure for the following reactions :MnO + 1/2Gd(2)O(3) + 1/4O(2) = GdMnO3 1/3Mn(3)O(4) + GdMnO3 + 1/3O(2) = GdMn2O5 was determined in the temperature range from 1073 to 1450 K. From the determined equilibrium oxygen partial pressure the corresponding G i b b s free energy change for these reactions was derived: Delta G(f,GdMnO3)(0) (+/- 425J) 132721(+/ - 2240) +51.91(+/ - 0.81)T Delta G(f,GdMn2O5)(0)(+/- 670J) 121858(+/ - 6176) + 79.52(+/ - 4.83)T From these data, standard G i b b s energies, enthalpies and entropies of formation of GdMnO3 and GdMn2O5 from component oxides and from the elements are derived. Thermodynamic data tables for the two ternary phases are compiled from 298.15 to 1400 K.

Study of the electrical properties of pulsed laser ablated (Ba0.5Sr0.5)TiO3 thin films

The laser ablated barium strontium titanate (BST) thin films were characterized in terms of composition, structure, microstructure and electrical properties. Films deposited at 300 degrees C under 50 mTorr oxygen pressure and 3 J cm(-2) laser fluence and further annealed at 600 degrees C in flowing oxygen showed a dielectric constant of 467 and a dissipation factor of 0.02. The room-temperature current-voltage characteristics revealed a space charge limited conduction (SCLC) mechanism, though at low fields the effect of the electrodes was predominant. The conduction mechanism was thoroughly-investigated in terms of Schottky emission at low fields, and bulk-limited SCLC at high fields. The change over to the bulk-limited conduction process from the electrode-limited Schottky emission was, attributed to the process of tunneling through the electrode interface at high fields resulting into the lowering of the electrode contact resistance and consequently giving rise to a bulk limited conduction process. The predominance of SCLC mechanism in the films suggests that the bulk properties are only revealed if the depletion width at the electrode interface is thin enough to allow the tunneling process to take place. This condition is only favorable if the him thickness is high or if the doping concentration is high enough. In the present case the film thickness ranged from 0.3 to 0.7 mu m which was suitable to show the transition mentioned above. (C) 1999 Elsevier Science S.A. All rights reserved.

Catalytic oxidative polymerization of 1,1-diphenylethylene at ambient temperature and potential application of peroxide macroinitiator

The Co(II)TPP(Py) complex was used as an efficient dioxygen carrier for the radical polymerization of 1,1-diphenylethylene (DPE), which has a low ceiling temperature, at ambient temperature and low oxygen pressure. The mechanism of polymerization is discussed' on the basis of kinetic data, W-vis, ESR, and H-1 NMR studies. The rate of polymerization (RP) and number-average molecular weights (M) of poly(1,1-diphenylethylene peroxide) (PDPEP) are higher and the polydispersity is lower than in 2,2'-azobis(isobutyronitrile) (AIBN) initiated polymerization. PDPEP was further. used as a macroinitiator for the polymerization of MMA. The polymerization obeys classical kinetics. The K-2 value of the PDPEP has been determined from the slope of R-P(2) VS [M](2)[I], which reveals that it can also be used at higher temperature for the polymerization. An "active" PMMA was also synthesized, containing initiating segments in the polymer backbone.

Study of pulsed laser ablated CaBi2Ta2O9 thin films

Polycrystalline CaBi2Ta2O9 thin films were grown on Pt/TiO2/SiO2/Si (100) substrates using a pulsed laser deposition technique. The influence of substrate temperature and oxygen pressure on crystallization and orientation of the films was studied. In-situ films deposited under a combination of higher substrate temperature and lower oxygen pressure exhibited a preferred c-axis orientation. Micro-Raman spectroscopy was used for complete understanding of phase evolution of CBT films. Thin films deposited at higher substrate temperatures showed larger grain size and higher surface roughness, observed by atomic force microscopy. The values of maximum polarization (2Pmnot, vert, similar13.4 μC/cm2), remanent polarization (2Prnot, vert, similar4.6 μC/cm2) and the coercive field Ec was about 112 kV/cm obtained for the film deposited at 650°C and annealed at 750°C. The room temperature, dielectric data revealed a dependence on the grain size.

Thermodynamics of SmMnO3 and SmMn2O5 phases determined by the E.M.F. method

Streszczenie angielskie: Using solid oxide galvanic cells of the type: MnO + Sm2O3 + SmMnO3 / O-2/ Ni + NiO and Mn3O4 + SmMnO3 + SmMn2O5 / O-2 / air the equilibrium oxygen pressure for three-phase equilibria described by the following reactions of formation of ternary phases: MnO + 1/2Sm2O3 + 1/4O2 = SmMnO3 1/3Mn3O4 + SmMnO3 + 1/3O2 = SmMn2O5 was determined in the temperature range from 1173 to 1450 K. From the obtained experimental data the corresponding Gibbs free energy change for above reactions of phases formation was derived: ΔG0f,SmMnO3(+/ - 250J) = -131321(+/ - 2000) + 48.02(+/ - 0:35)T / K ΔG0f,SmMn2O5(+/ - 2000 J) = -107085(+/ - 2200) + 69.74(+/ - 1:70)T / K Using obtained results and available literature data, thermodynamic data tables for the two ternary phases have been compiled from 298.15 to 1400 K. Streszczenie polskie: W pracy przedstawiono wyniki badań dotyczące własności termodynamicznych manganinów samaru, wyznaczone metodą pomiaru SEM ogniw ze stałym elektrolitem: MnO + Sm2O3 + SmMnO3 / O-2/ Ni + NiO ogniwo I Mn3O4 + SmMnO3 + SmMn2O5 / O-2 / powietrze ogniwo II oraz określono równowagowe ciśnienie parcjalne tlenu dla reakcji tworzenia SmMnO3 i SmMn2O5 w zakresie temperatur 1173�1450 K: MnO + 1/2Sm2O3 + 1/4O2 = SmMnO3 1/3Mn3O4 + SmMnO3 + 1/3O2 = SmMn2O5 Z tych danych doświadczalnych wyznaczono zależności temperaturowe energii swobodnych tworzenia powyższych manganinów samaru: ΔG0f,SmMnO3(+/ - 250J) = -131321(+/ - 2000) + 48.02(+/ - 0:35)T / K ΔG0f,SmMn2O5(+/ - 2000 J) = -107085(+/ - 2200) + 69.74(+/ - 1:70)T / K W tablicach I i II zamieszczono dane termodynamiczne dla dwóch potrójnych faz otrzymane poprzez kompilacje własnych danych doświadczalnych z danymi literaturowymi.

Studies on Field Dependent Domain Structures in Multi-Grained 0.85PbMg(1/3)Nb(2/3)O3-0.15PbTiO(3) Thin Films by Scanning Force Microscopy

0.85PbMg(1/3)Nb(2/3)O(3)-0.15PbTiO(3) (0.85PMN-0.15PT) ferroelectric relaxor thin films have been deposited on La0.5Sr0.5CoO3/(111) Pt/TiO2/SiO2/Si by pulsed laser ablation by varying the oxygen partial pressures from 50 mTorr to 400 mTorr. The X-ray diffraction pattern reveals a pyrochlore free polycrystalline film. The grain morphology of the deposited films was studied using scanning electron microscopy and was found to be affected by oxygen pressure. By employing dynamic contact-electrostatic force microscopy we found that the distribution of polar nanoregions is majorly affected by oxygen pressure. Finally, the electric field induced switching in these films is discussed in terms of domain wall pinning.

Influence of O-2 flow rate on HfO2 gate dielectrics for back-gated graphene transistors

HfO2 thin films deposited on Si substrate using electron beam evaporation, are evaluated for back-gated graphene transistors. The amount of O-2 flow rate, during vaporation is optimized for 35 nm thick HfO2 films, to achieve the best optical, chemical and electrical properties. It has been observed that with increasing oxygen flow rate, thickness of the films increased and refractive index decreased due to increase in porosity resulting from the scattering of the evaporant. The films deposited at low O-2 flow rates (1 and 3 SCCM) show better optical and compositional properties. The effects of post-deposition annealing and post-metallization annealing in forming gas ambience (FGA) on the optical and electrical properties of the films have been analyzed. The film deposited at 3 SCCM O-2 flow rate shows the best properties as measured on MOS capacitors. To evaluate the performance of device properties, back-gated bilayer graphene transistors on HfO2 films deposited at two O-2 flow rates of 3 and 20 SCCM have been fabricated and characterized. The transistor with HfO2 film deposited at 3 SCCM O-2 flow rate shows better electrical properties consistent with the observations on MOS capacitor structures. This suggests that an optimum oxygen pressure is necessary to get good quality films for high performance devices.

Selective growth of single phase VO2(A, B, and M) polymorph thin films

We demonstrate the growth of high quality single phase films of VO2(A, B, and M) on SrTiO3 substrate by controlling the vanadium arrival rate (laser frequency) and oxidation of the V atoms. A phase diagram has been developed (oxygen pressure versus laser frequency) for various phases of VO2 and their electronic properties are investigated. VO2(A) phase is insulating VO2(B) phase is semi-metallic, and VO2(M) phase exhibits a metal-insulator transition, corroborated by photoelectron spectroscopic studies. The ability to control the growth of various polymorphs opens up the possibility for novel (hetero) structures promising new device functionalities. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Dielectric investigation of high-k yttrium copper titanate thin films

We report on the first dielectric investigation of high-k yttrium copper titanate thin films, which were demonstrated to be very promising for nanoelectronics applications. The dielectric constant of these films is found to vary from 100 down to 24 (at 100 kHz) as a function of deposition conditions, namely oxygen pressure and film thickness. The physical origin of such variation was investigated in the framework of universal dielectric response and Cole-Cole relations and by means of voltage dependence studies of the dielectric constant. Surface-related effects and charge hopping polarization processes, strictly dependent on the film microstructure, are suggested to be mainly responsible for the observed dielectric response. In particular, the bulky behaviour of thick films deposited at lower oxygen pressure evolves towards a more complex and electrically heterogeneous structure when either the thickness decreases down to 50 nm or the films are grown under high oxygen pressure.