Showing papers by "J.-M. Liu published in 2002"

Formation of Ni germano-silicide on single crystalline Si/sub 0.3/Ge/sub 0.7//Si

Abstract: We have studied the Ni and Co germano-silicide on Si/sub 0.3/Ge/sub 0.7//Si. The Ni germano-silicide shows a low sheet resistance of 4-6 /spl Omega///spl square/on both P/sup +/N and N/sup +/P junctions, which is much smaller than Co germano-silicide. In addition, small junction leakage currents of 3/spl times/10/sup -8/ A/cm/sup 2/ and 2/spl times/10/sup -7/ A/cm/sup 2/ are obtained for Ni germano-silicide on P/sup +/N and N/sup +/P junctions, respectively. The good germano-silicide integrity is due to the relatively uniform thickness as observed by cross-sectional TEM.

Grain boundaries and low-field transport properties in colossal magnetoresistance materials

Abstract: The grain-boundary structure and the temperature dependence of resistivity were investigated for (1-x)LCMO + xYSZ, where LCMO and YSZ represent La2/3Ca1/3MnO3 and yttria-stabilized zirconia, respectively. It is shown that the YSZ doped samples for x 2%. The metal-insulator transition temperature (Tp) decreases for x 2% as x is increased. LFMR increases with x for x 2%. The experimental observations are discussed on the basis of scanning electron microscopy (SEM) analysis, which reveals YSZ appearing at the grain boundaries of LCMO for x 2%.

Phase separation and insulator-metal behaviour in highly Ba2+-doped La1-xBaxMnO3 compounds

Abstract: Investigations of structural and transport features of La1-xBaxMnO3 with x = 1/3 and 2/3 are performed. The x = 2/3 sample is shown to be phase separated into a mixture of La2/3Ba1/3MnO3 and BaMnO3 with the same volume fractions, ~50%. In this two-phase system, La2/3Ba1/3MnO3 regions are connected in a percolative manner, so the electrical transport is dominated by flow along these percolative paths. Using the recently proposed random resistor network based on electronic phase separation between ferromagnetic metallic and paramagnetic insulating domains, we show that the model can yield results in quantitative agreement with the resistance versus temperature dependence measured for the x = 1/3 and 2/3 samples by using the metallic number density as a fitting parameter. This approach suggests a simple quantitative picture that can be used to explain the insulator-metal behaviour in La1-xBaxMnO3 with higher x.

The orientation-selective growth of LaNiO3 films on Si(100) by pulsed laser deposition using a MgO buffer

Abstract: Highly (100)-oriented, (110)-oriented and polycrystalline LaNiO3 (LNO) films were successfully prepared on Si(100) using an oriented MgO film as a buffer. It was somewhat surprising to find that that the orientation relation between the LNO film and the corresponding MgO buffer was: LNO(100)\MgO(110), LNO(110)\MgO(111) and LNO(polycrystalline)\MgO(100). The crystalline quality of the LNO films was shown to be sensitive to the preparation conditions of the MgO buffer. The film surface was very smooth, without micrometer-sized droplets being observed. All LNO films were of metallic conductivity, with a room-temperature resistivities of approximately 250, 280 and 420 μΩ cm for the (110)-oriented, (100)-oriented and polycrystalline LNO, respectively.

Oxygen-deficiency-activated anomalous transport in La2/3Sr1/3MnO3-δ thin films deposited by laser ablation

Abstract: The transport in oxygen-deficient polycrystalline La2/3Sr1/3MnO3-δ thin films deposited on Si(111) substrates using laser ablation is studied by measuring the resistivity and ac magnetic susceptibility over the range 2-300 K. The oxygen deficiency results in a serious shift of the insulating-metal (IM) transition toward the low-temperature side and anomalous transport behaviour over the low-temperature range. The ac susceptibility measurement reveals that, upon cooling, the sample exhibits a ferromagnetic transition, a weak anomaly at the IM transition and an antiferromagnetic (AFM) transition which may mainly arise from the charge ordering. Partial melting of the AFM state under a low magnetic field of 750 Oe is observed at 4.2 K.