Reactive Phase Formation Research Articles

Preparation and Basic Properties of BaTiO3-BaPbO3 Multilayer Thin Films by Metal-Alkoxides Method

Preferentially oriented barium titanate (BTO)-barium metaplumbate (BPO) multilayer thin films were prepared by the metal-alkoxides method on MgO single crystals. The BPO layer is an electrode for the BTO layer. Thin films were deposited on cleaved MgO (100) substrates by spin coating. A BTO film of 0.4 µm thickness on the BPO layer shows a dielectric constant of about 400 at room temperature. No formation of reaction phases between BTO and BPO, fired at 800°C to yield a well-crystallized BTO film, was detected in X-ray diffraction analysis.

Amorphous phase formation and initial interfacial reactions in the platinum/GaAs system

We have investigated the amorphous phase formation and initial crystalline reactions at Pt/GaAs interfaces via high-resolution transmission electron microscopy (HRTEM) and in situ HRTEM. A 3-nm-thick amorphous intermixed layer consisting of three elements, platinum, gallium, and arsenic formed at the Pt/GaAs interface during the deposition of a 500-Å-thick Pt film. The interlayer grew in a planar fashion in an amorphous state upon low temperature (e.g., 200 °C) annealing by a solid-state amorphization reaction. This reaction occurs with a driving force of a negative heat of mixing, and by the dominant diffusion of Pt to the GaAs substrate, which was verified by in situ HRTEM. Following the growth of the amorphous interlayer, the Pt3Ga and PtAs2 phases nucleated within the amorphous layer and grew at the Pt and GaAs sides, respectively. The relative mobility of the three constituents at the low temperature, the structure of the crystalline intermetallic compounds, and local thermodynamical equilibrium are responsible for the sequence of the crystalline phase formation. After a complete reaction at 400 °C for 20 min, we observed the formation of a layered structure of PtGa/PtAs2/GaAs as the final structure. In situ HRTEM experiments also demonstrated growth of the amorphous intermixed layer and crystalline reaction between the Pt film and the GaAs, which is consistent with the results from the ex situ annealing treatment.

Effect of Microstructure on Phase Formation in Reaction of The Nb/Al Multilayer Thin Films

AbstractWe investigated the phase formation sequence in the reaction of multilayer thin films of Nb/Al with overall compositions of 25 and 33 at.% AI. We report novel phenomena which distinguish thin-film reactions unequivocally from those in bulk systems. For sufficiently thin layers composition and stability of product phases are found to deviate significantly from that predicted from the equilibrium phase diagram. We demonstrate that in the Nb/Al system the length scales below which such deviations occur is about 150 nm. We believe that these phenomena occur due to the importance of grain boundary diffusion and hence microstructure in these thin films.

Thermodynamic analysis and technology of preparation of high‐Tc superconducting system YBa2Cu3O7−x

AbstractBy modeling the equilibrium state of the phase formation reaction of High‐Tc superconducting phase 1:2:3 (YBa2Cu3O7−x) and using the results of P‐T−x correlation investigation of some authors, the variation of Gibbs free energy (ΔGm) versus temperature has been calculated. On the basis of the variation of ΔGm, the technology procedure of preparation of phase 1:2:3 with desired x has been established to meet requirement of basic investigation and application of High‐Tc superconductors YBa2Cu3O7−x.

Solid-phase reactions between (100) GaAs and thin-film refractory metals (Ti, Zr, V, Nb, Cr, Mo, and W)

Recently, there has been an increased interest in the applications of refractory metals as gate materials for the self aligned gate process in the fabrications of GaAs field effect transistors. In this study, we systematically investigated the thermally induced interface interactions between (100) GaAs substrates and thin films of refractory metals (Ti, Zr, V, Nb, Cr, Mo, and W). Depth profilings of the M/GaAs interfaces were obtained using conventional and heavy ion Rutherford backscattering spectrometry. Phase identifications were achieved by x-ray diffraction. Results on the phase formation sequence, reaction kinetics, the distribution, composition and structure of the reacted phases and the interface reactivity of these contacts will be presented. Correlations between metal properties (electronegativity and metal-metal bond strength) and kinetics of the reactions (activation energy and reactivity of the interfaces) will also be discussed.

ChemInform Abstract: A KINETIC STUDY OF THE GAS PHASE FORMATION AND DECOMPOSITION REACTIONS OF NITROUS ACID

AbstractDie kinetischen Untersuchungen der Zersetzungs‐ bzw. Bildungsreaktionen A und Bvon Salpetriger Säure in der Gasphase werden in einem Pyrex‐ Reaktor bei HONO‐Partialdrücken zwischen 0,05 und 1,0 Torr und im Gesamtdruck‐ bereich von 5‐50 Torr mit Hilfe eines massenspektrometrischen Detektors (Elektronenstoßionenquelle) durchgeführt.

A kinetic study of the gas phase formation and decomposition reactions of nitrous acid

The kinetics of the gas phase decomposition and formation reactions of nitrous acid, 2HONO = NO + NO/sub 2/ + H/sub 2/O (k/sub 1/, k/sub 2/), have been investigated in a Pyrex reactor at HONO partial pressures of 0.05 to 1.0 Torr and total pressures of 5 to 50 Torr using a mass spectrometer detector. The reactions were determined to be heterogeneous under all surface conditions tested. The best upper limits to the homogeneous rate constants at 300/sup 0/K were k/sub 1/ less than or equal to 1 x 10/sup -20/ cm/sup 3//molecule s and k/sub 2/ less than or equal to 4.4 x 10/sup -40/ cm/sup 6//molecule/sup 2/s. The kinetics of the heterogeneous reactions were examined, and a rate law is proposed.

Effect of Starting Materials on the Formation of Zn<sub>2</sub>SnO<sub>4</sub> Crystals by Vapor Phase Method and Formation Reaction

Effect of Starting Materials on the Formation of Zn<sub>2</sub>SnO<sub>4</sub> Crystals by Vapor Phase Method and Formation Reaction