Advanced Materials Research Vol. 1024

Abstract: Polyacrylonitrile (PAN) based polymer electrolytes composed of PAN, lithium tetrafluoroborate (LiBF₄), ethylene carbonate (EC) and dimethyl phthalate (DMP) were prepared by solution casting technique. The variation of conductivity with LiBF₄ concentrations of the prepared films has been studied using AC impedance spectroscopy. The conductivity of the films is charge concentration dependent and the highest room temperature conductivity of 1.08 ×10^-2 S cm^-1 is achieved for the film with optimum composition. The thermal activated conductivity of the films obeys Arrhenius rule in the temperature range from 303 K to 353 K. The electrochemical stability of the PAN-based films has been investigated using linear sweep voltammetry (LSV) with three electrodes system. The films were found to be electrochemically stable up to 4.4 V. The reversibility of the lithium ions conduction in the polymer electrolyte films have been studied using cyclic voltammetry (CV).

Abstract: Normal 0 false false false MicrosoftInternetExplorer4 Layered cathode materials are important for Li-ion battery application due to their high theoretical specific capacity. Efforts have been made to synthesize mixed-metal cathode materials such as LiNi_1/3Co_1/3Mn_1/3O₂ based materials with promising electrochemical characteristics. This is to lower the expensive Co content and help to stabilize the materials. Substitution of these materials with chromium producing LiNi_0.3Co_0.3Mn_0.3Cr_0.1O₂ material will also improve the stability of the cathodes. In this work, pure and single phase LiNi_0.3Co_0.3Mn_0.3Cr_0.1O₂ material was successfully synthesized using a combustion method. The samples were then annealed at 900 °C for 24, 48 and 72 h. From the charge-discharged measurements, it was found that the performance of the LiNi_0.3Co_0.3Mn_0.3Cr_0.1O₂ cathode material annealed at 900 °C for 24 h shows the best performance. /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;}

Abstract: Blue phosphor Sr₂MgSi₂O₇:Eu, Dy (SMS) has been widely used in the applications of painting, watches, clock displays and emergency signboards due to its long afterglow property, long term chemical and physical stability. In this work, solid state reaction method was used in the synthesis of SMS phosphor. The reductive atmosphere was generated by combustion of the raw materials in a graphite crucible. This approach was less costly as compared to the conventional solid state reaction which uses a mixture of hydrogen and nitrogen gas. The PL measurement shows a blue emission at wavelength of 466 nm when excite the SMS phosphor with Xenon lamp at wavelength of 325nm. This emission was attributed to Eu²⁺ subshells 4f⁶5d¹ to 4f⁷ transition. In addition, the strongest PL emission was obtained with the excitation source of 428 nm. X-ray diffraction analysis shows that SMS phosphor consist of tetragonal structure of Sr₂MgSi₂O₇ and monoclinic structure α-SrSiO₃.

Abstract: Poly (methyl) methacrylate (PMMA)-based gel polymer electrolytes (GPEs) containing magnesium triflate, Mg (CF₃SO₃)₂ salt were prepared using solution casting technique. Different concentrations of Mg (CF₃SO₃)₂ ranging from 5 wt.% to 30 wt.% have been added into a mixture of ethylene carbonate (EC) and propylene carbonate (PC) with a fixed mass ratio of 2:1. These free-standing GPE films were characterized using electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV) and cyclic voltammetry (CV). The highest ionic conductivity of 1.27 x 10^-3 S cm^-1 is obtained from the GPE film containing 20 wt.% of Mg (CF₃SO₃)₂ salt. The electrochemical window stability has been found in the range of-2.5 V to 2.5 V for the highest conducting GPE film. This value is considerably high enough for the GPE film to be used as electrolyte in magnesium rechargeable batteries.

Abstract: As a transparent conducting oxide, Cd:ZnO system is considered potential candidate for optoelectronic applications alternate to Al:ZnO. However instability issue of the Cd:ZnO system is under debate. Here we investigate effect of Cd impurities on physical properties of ZnO in wurtzite (WZ) as well as zincblende (ZB) geometries. Density functional theory (DFT) based full potential linearized augmented plane wave plus local orbital FP-L(APW+lo) method has been adapted for these investigations. To calculate the total energy of the system, exchange correlation energy term is evaluated at the level of GGA. For the more realistic band gap calculation, GGA in addition to mBJ exchange potential has been employed. From our calculations, it is observed, Cd:ZnO is more stable in ZB structure than that of WZ. The Cd substitution ZnO has a tendency to convert the hexagonal geometry into cubic. It is also observed, doping of the Cd impurities strongly influence the electronic structures resulting into the narrowing energy band gap.

Abstract: The (100) and (111) crystalline cubic silicon nitride (3C-SiC) thin films have been epitaxially deposited on (100) silicon substrate with the thickness of 0.5 µm and 1.0 µm. The effects of the different growth of 3C-SiC are considered as the most critical factor in determining the mechanical properties by comparing with bulk value such as Young’s modulus (~455 GPa) and hardness (~42 GPa). This paper evaluates the mechanical characteristic of the 3C-SiC-on-Si wafers to improve the 3C-SiC thin film quality. The aim is to employ the thin film as the flexible diaphragm in the MEMS capacitive pressure sensor for extreme environment. The surface morphology of thin layer of grown 3C-SiC wafers are characterized by X-ray diffraction (XRD), Infinite Focus Microscopy (IFM), scanning electron microscopy (SEM) and nano-indentation test. The results show the superior mechanical strengths of both (100) and (111) 3C-SiC thin films over (100) Si. To conclude, these results show that (100) and (111) 3C-SiC are indeed high quality thin film mechanically compare to (100) Si thin film, and is suitable to employed as the flexible diaphragm of the MEMS capacitive pressure sensor for extreme environments.

Abstract: In this work, effects of post-deposition annealing (PDA) time (15, 30, and 45 min) in nitrous oxide ambient on Y₂O₃ film deposited on Si substrate using RF-magnetron sputtering have been systematically studied. Y₂O₃/Si system subjected to PDA time at 15 and 30 min has demonstrated a negative flatband voltage shift but a change to positive flatband voltage shift was observed when PDA time was prolonged to 45 min. The shift from negative to positive flatband voltage with enhancement of PDA time could be related to the accumulation of nitrogen in the Y₂O₃ gate that acted as negatively trap charge. It was perceived that sample subjected to PDA time at 30 min has demonstrated the best leakage current density-breakdown voltage (J-V_B) characteristic. A correlation between the J-V_B characteristics with effective oxide charge, slow trap density, interface trap density, and total interface trap density has been discussed.

Abstract: Metal-oxide-semiconductor characteristics of MOD-derived lanthanum cerium oxide (La_xCe_yO_z) film deposited on n-type Si substrate have been studied. Post-deposition annealing of the oxide was performed in argon atmosphere for a dwell time, ranging from 15 to 120 min at a fixed temperature of 400°C. Results demonstrated presence of positively charged oxygen vacancies in all of the oxides post-deposition annealed for different dwell time. Acquisition of the lowest effective oxide charge as well as the lowest interface trap density and total interface trap density in oxide annealed for 120 min has led to the attainment of the highest breakdown voltage, surpassing other oxides.

Abstract: In and Ag co-doped ZnS photocatalysts were successfully prepared by hydrothermal method to extend the light absorption of ZnS to the visible light region. The concentration of In was constant while for Ag was varied to optimize the photocatalytic activity. The In and Ag co-doped ZnS photocatalysts showed smaller band gap energy compared to single doped In (0.1)-ZnS and undoped ZnS. The photocatalytic activity of In and Ag co-doped ZnS photocatalysts was evaluated from the amount of hydrogen produced. The hydrogen evolution rate from aqueous solution containing Na₂SO₃ and Na₂S as sacrificial reagent under visible light irradiation obtained from In and Ag co-doped ZnS is higher compared to the single doped In (0.1)-ZnS when optimum amount of Ag dopant was added. The highest photocatalytic activity is observed for In (0.1),Ag (0.01)-ZnS with hydrogen production rate of 26.82 μmol/h. The higher performance of this photocatalyst is ascribed to the extended visible light absorption, efficient charge separation as well as improved electron transfer associated with synergistic effect of appropriate amount of In and Ag co-doped ZnS.

Abstract: We report on miniaturized silicon field emitter arrays for the application in compact and energy-saving vacuum-microelectronic devices, e.g. sensors or x-ray tubes. Since standard silicon semiconductor technology has been used for the fabrication, they may be easily integrated with other silicon based circuits and devices on the same chip. The silicon tip geometry and the operating conditions were optimized in order to obtain highly uniform and stable electron field emission from large area cathode arrays. A series of uniform hexagonal tip arrays containing each 547 tips were fabricated and characterized. The electron emission properties of both individual tips as well as of complete emitter arrays were investigated. A saturation level in the voltage-current characteristics was found, which can be explained by the limitation of the supply of electrons due to the p-type silicon wafer material. When operating the arrays in the current saturation regime at an emission current of ~ 1 nA per tip, a highly stable and low noise emission can be observed.