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Lithium ion transport was accelerated within graphite by controlling its d-spacing as well as its functional groups. By oxidizing bare graphite under a mild condition, expanded graphites (EG* where * = functional groups) were obtained with increasing d-spacing from 0.3359 nm to 0.3395 nm as well as with functional groups formed on the plane or at the edges of graphites. The subsequent thermal reduction of EG* led to an insignificant change of d-spacing (0.3390 nm), simultaneously eliminating a portion of the functional groups (EG). The enlargement of d-spacing reduced kinetic hindrance of lithium ion movement within the expanded graphites (EG* and EG) by reserving more space for the ionic transport route. In addition, the activation energy of lithium ion intercalation in EG* was reduced by surface charge polarization of graphites induced by hydrogen bonds between oxygen atoms of carbonates in electrolytes and hydrogen atoms of surface functional groups of the expanded graphites, even if the degree of graphitization decreased. Re-graphitization induced by the subsequent thermal reduction increased delithiation capacities (Q[sub dLi]) of EG as an anode for lithium ion batteries especially at high currents: Q[sub dLi] at 50 C = 243 mA h g[sup -1] for EG versus 66 mA h g[sup -1] for bare graphite. [ABSTRACT FROM AUTHOR]

In order to obtain optimum growth conditions for desired thickness and more effective silicon feedstock usage, effects of processing parameters such as preheated substrate temperatures, time intervals, moving velocity of substrates, and Ar gas blowing rates on silicon ribbon thickness were investigated in the horizontal growth process. Most of the parameters strongly affected in the control of ribbon thickness with columnar grain structure depended on the solidification rate. The thickness of the silicon ribbon decreased with an increasing substrate temperature, decreasing time interval, and increasing moving velocity of the substrate. However, the blowing of Ar gas onto a liquid layer existing on the surface of solidified ribbon contributed to achieving smooth surface roughness but did not closely affect the change of ribbon thickness in the case of a blowing rate of ≥ 0.65 Nm³/h because the thickness of the solidified layer was already determined by the exit height of the reservoir. [ABSTRACT FROM AUTHOR]

Abstract  A homogeneous Eu2W2O9 phase with small grains (∼4.0μm) was formed for the specimens fired below 1175°C. As the firing temperature was increased above 1150°C, grain growth occurred and the grain shape changed from faceted to round. The excitation spectra of the Eu2W2O9 phosphor were similar to those of the Eu2(WO4)3 phosphor, but the absorption band due to the O2−→W6+ ligand to metal charge transfer was shifted to lower energies and the 7Fo→5H3 and 7Fo→5F2,4 transitions were not found. The intensity of the excitation and emission spectra of the Eu2W2O9 phosphor considerably increased with increasing firing temperature, due to the increased grain size and changed grain shape. The intensity of the red emission band of the Eu2W2O9 phosphor was higher than that of the Eu2(WO4)3 phosphor. Moreover, the addition of LiCl to the Eu2W2O9 phosphors considerably enhanced the intensity of their emission spectra, probably due to the increased grain size. Therefore, LiCl-added, Eu2W2O9 phosphor is a promising candidate material for red color emission. [ABSTRACT FROM AUTHOR]

BaTi4O9 thin films were grown on a Pt/Ti/SiO2/Si substrate using rf magnetron sputtering and the structure of the thin films were then investigated. For the films grown at low temperature (≤350°C), an amorphous phase was formed during the deposition, which then changed to the BaTi5O11 phase when the annealing was conducted below 950°C. However, when the annealing temperature was higher than 950°C, a BaTi4O9 phase was formed. On the contrary, for the films grown at high temperature (>450°C), small BaTi4O9 grains were formed during the deposition, which grew during the annealing. The homogeneous BaTi4O9 thin films were successfully grown on Pt/Ti/SiO2/Si substrate when they were deposited at 550°C and subsequently rapid thermal annealed at 900°C for 3 min. [ABSTRACT FROM AUTHOR]

A high capacitance density of 4.84 fF/μm2 and a low leakage current density of 4.28 fA/pF•V were obtained for a 138-nm-thick crystalline BaSm2Ti4O12 (BST) film. The 100-nm-thick amorphous BST film exhibited a high capacitance density of 3.91 fF/μm2 and a low leakage current of 1.24 fA/pF•V. The crystalline BST film had quadratic and linear voltage coefficient of capacitance (VCC) of -295 ppm/V2 and 684 ppm/V, respectively, and a temperature coefficient of capacitance (TCC) of -136 ppm/°C at 100 kHz. The amorphous BST film also showed quadratic and linear VCCs of 48.6 ppm/V2 and -738 ppm/V, respectively, with a low TCC of 169 ppm/°C at 100 kHz. [ABSTRACT FROM AUTHOR]

The dielectric and electrical properties of a BaTi4O9 film were investigated in order to evaluate its potential use in metal-insulator-metal (MIM) capacitors for rf/mixed signal integrated circuits. A high capacitance density of 4.62 fF/μm2 along with a low tan δ of 0.0025 were obtained at 100 kHz. A high capacitance density of 4.12 fF/μm2 and a high quality factor of 322 were also achieved at 2 GHz. The leakage current density was approximately 1 nA/cm2 at ±2 V. Small linear and quadratic voltage coefficients of capacitance of 110 ppm/V and 40.05 ppm/V2, respectively, and a small temperature coefficient of capacitance of -92.157 ppm/°C at 100 kHz were obtained. These results demonstrate that the BaTi4O9 film is a good candidate material for MIM capacitors. [ABSTRACT FROM AUTHOR]

Silicon nanoparticles (Si NPs) were simply mixed with carbon nanofibers (CNFs) without any chemical process at various weight ratios, and the electrochemical properties of these nanoparticles as anode materials were investigated in lithium-ion batteries (LIBs). To study the effects of the physical incorporation of CNFs on the volumetric variations in Si NPs, the dilations of full cells were measured. The measured volumetric change of the anode using a mixture of Si NPs and CNFs was smaller than that calculated from the theoretical volumetric changes of Si and graphite. Although the reversible capacity of Si NPs faded sharply, the fading was mitigated by increasing the mixing ratio of CNFs. In particular, the Si NP/CNF mixture prepared at weight ratio retained a reversible capacity of >800 mAh/g with a capacity retention of 53.2% even after 100 cycles. CNFs alleviated stress and strain during the charge–discharge process even though there was no tight chemical bonding with Si NPs. [ABSTRACT FROM AUTHOR]

Electron beam melting (EBM) systems have been used to improve the purity of metallurgical grade silicon feedstock for photovoltaic application. Our advanced EBM system is able to effectively remove volatile impurities using a heat source with high energy from an electron gun and to continuously allow impurities to segregate at the top of an ingot solidified in a directional solidification (DS) zone in a vacuum chamber. Heat in the silicon melt should move toward the ingot bottom for the desired DS. However, heat flux though the ingot is changed as the ingot becomes longer due to low thermal conductivity of silicon. This causes a non-uniform microstructure of the ingot, finally leading to impurity segregation at its middle. In this research, EB power irradiated on the silicon melt was controlled during the ingot growth in order to suppress the change of heat flux. EB power was reduced from 12 to 6.6 kW during the growth period of 45 min with a drop rate of 0.125 kW/min. Also, the silicon ingot was grown under a constant EB power of 12 kW to estimate the effect of the drop rate of EB power. When the EB power was reduced, the grains with columnar shape were much larger at the middle of the ingot compared to the case of constant EB power. Also, the present research reports a possible reason for the improvement of ingot purity by considering heat flux behaviors. [ABSTRACT FROM AUTHOR]