Materials Science Forum Vols. 475-479

Abstract: In this paper, the effect of a thin interlayer of Pt on thermal stability of NiSi films on Si(111) has been studied. The Ni/Pt/Si(111) bilayered samples with the same film thickness were annealed by rapid thermal annealing at 640 °C-900 °C. Both the X-ray diffraction analysis and four-probe measurements show a remarkable improvement in the thermal stability NiSi as a result of Pt interlayer. The possible reason for the enhanced NiSi thermal stability is attributed to the formation of the Ni(Pt)Si solid solution and its preferred orientation, leading to the decrease in the driving force of NiSi2 nucleation and the increase in the interfacial energy change respectively. The experimental results are explained in terms of Miedema’s Model and Thomas-Fermi-Dirac (TFD) equations in detail.

Abstract: A novel electric-pulse-induced reversible resistance (EPIR) change effect was observed in Ag/Ln1-xCaxMnO3/Pt (Ln= Pr, La) sandwich structure at room temperature without applied magnetic field. The Ln1-xCaxMnO3 films were grown on Pt/Ti/SiO2/Si substrate. The resistance of the Ag/Ln1-xCaxMnO3/Pt sandwich structure increases and reaches at a saturated high resistance state after applying a certain number of electric-pulse from Pt bottom electrode to Ln1-xCaxMnO3 layer, while it decreases and switches to a saturated low resistance state when the pulse polarity reversed. It is also found that the EPIR effect in the /Ln0.7Ca0.3MnO3/Pt system exhibits “fatigue” behavior, that is, for the high resistance state activated by electric-pulse, along the time after pulsing, the resistance decreases slowly after a certain stable stage; otherwise, the resistance change ratio decreases as the number of the high-low resistance switching circle increases. For the fatigue phenomenon with time, a resistance change with three stages was observed and a simple mechanism of the EPIR was proposed.

Abstract: Carbon-doped b-FeSi2 films synthesized by ion implantation are investigated with the aim to fabricate high-quality semiconducting b-FeSi2 layer on silicon substrate. According to transmission electron microscopy cross-section observations, carbon-doped films, with homogeneous thickness and smooth b/Si interface, have higher quality than binary Fe-Si films. In particular, annealing at 500 °C ~ 700 °C leads to the formation of a flat and continuous b-type silicide layer. Improved thermal stability of the b phase is also found. Optical emission spectroscopy measurements show that the doping influences only slightly the band gap values.

Abstract: In this paper, we report the growth of NaxCoO2 thin films by pulsed-laser deposition (PLD). It is shown that the concentration of sodium is very sensitive to the substrate temperature and the target-substrate distance due to the evaporation of sodium during the deposition. α'-phase Na0.75CoO2 and γ-phase Na0.71CoO2 thin films can be obtained with different conditions. Correspondingly, the surface morphology of the films changes from flake-like to particle-like. The temperature dependence of resistivity for the films prepared with the optimal condition shows metallic behavior, consistent with the data of NaxCoO2 single crystals. This work demonstrates that PLD is a promising technique to get high quality NaxCoO2 thin films.

Abstract: Amorphous thin Films of Ti51.78 Ni22.24Pd25.98 alloys were deposited onto 2 inch diameter n-type (100)Si wafer by r.f. magnetron sputtering. The crystallization temperature from an amorphous state to crystallization of free-standing thin film was found to be 553.1oC, but that of non-free-standing thin film on Si wafer was found to be higher from X-ray diffraction experiment. The film heated 1 h at 550 oC was partly crystallized but at 650 oC was almost whole crystallized. The film heated 1 h at 750 oC quite crystallized and some precipitation appear. Heated 50 h at 450 oC before crystallization the films would be accelerate B19' but restrain B19 formation in succeeding heat-treatment.

Abstract: Solidification and cooling of a continuously cast steel slab and the heating of the mould is a very complicated problem of transient heat and mass transfer. This original three-dimensional (3D) numerical model is capable of simulating the temperature field of a caster. The numerical computation has to take place simultaneously with the data acquisition—not only to confront it with the actual numerical model, but also to make it more accurate throughout the process. The utilization of the numerical model of solidification and cooling plays an indispensable role in practice. An important step in this analysis is to determine the necessary quantities in the course of concasting. The software enables data acquisition in real time, which is necessary for optimization. This is ensured by the correct process procedure: real process → input data → numerical analysis → optimization → correction of process. This procedure is necessary for optimization (i.e. maximization of the quality of the process)—especially when reacting to specific needs and conditions in the operation.