Solid State Phenomena Vols. 124-126

Abstract: Indium zinc oxide (IZO) thin films were deposited on a glass substrate by radio frequency (rf) reactive magnetron sputtering method. As the rf power increased, the deposition rate and resistivity increased while the optical transmittance decreased owing to the increase of grain size. With increasing gas pressure, the resistivity increased and the transmittance decreased. Atomic force microscopy and scanning electron microscopy were employed to observe the film surface. The IZO films displayed a resistivity of 3.8 × 10-4 Ω cm and a transmittance of about 90% in visible region.

Abstract: A nano-size zinc oxide was formulated for the effective removal of a very low concentration of sulfur compounds (H2S, COS) contained in a gasified fuel gas and their reactivity was also investigated in this study. They were prepared by a matrix-assisted method with various precursors. An active carbon was used for a matrix and zinc nitrate, zinc chloride, and zinc sulfate were selected as precursors. Zinc nitrate was the best precursor for the formulation of the nano-size zinc oxide in the experiments. The size of the formulated nano-size zinc oxides was in the range of 20-30 nm and its surface area was about 56.2 m2/g. From TGA(thermal gravity analysis) test, it was found that its sulfur capacity was about 5.83 gS/100 g-sorbent and sulfur absorption rate was about 0.363 gS/min·100 g-sorbent. Their reactivity increased with the smaller size and the larger surface area of the sorbents. Most prepared nano-size zinc oxides showed an excellent performance for the removal of not only H2S but also COS. Their absorption rate was faster than commercial zinc oxides. In order to investigate the sulfur absorption characteristics of zinc oxide, a experiments for the nano-size zinc oxides formulated from zinc nitrate precursors were carried out in a packed-bed reactor system over the temperature of 500
. It was concluded that the zinc oxide prepared by zinc nitrate as a precursor showed the highest sulfur removing capacity.

Abstract: Si electrode with different amount of polymer binder was fabricated by ball milling. With increasing of polymer content, not only porosity but also the first charge capacity of Si electrode was increased. The Si electrode enhanced electrical conductivity showed high first capacity of 3644mAh/g and improved cycle performance. Si electrode having good electrochemical property could be fabricated by controlling amount of polymer.

Abstract: Si and Si/Ni thin film electrodes less than 1
m in total thickness were fabricated on the roughened Cu substrate by rf sputtering. Their surface morphology and crystalline structure were carefully investigated by means of FESEM and XRD. The morphology of films is dependent on the surface feature of substrate, and the grown films were amorphous. The initial capacity and the irreversible capacity loss of a Li/Si film cell were improved with insertion of a Ni buffer layer. The effect of the film morphology on the electrochemical properties of cells was demonstrated based on the observations of film electrodes.

Abstract: A-Si:H/Si wafer heterojunction solar cells with different ZnO:Al sputtering conditions were fabricated and the effects of sputtering conditions on device performance were evaluated. Various sputter condition(substrate temperature RT~200’C, working pressure 0.5mTorr~15mTorr, thickness 60~100nm) were tested and optimized as 130’C, 0.5mTorr, 80nm by measuring reflectance and sheet resistance of ZnO:Al layer on corning glass. However, when optimal ZnO:Al condition was applied to solar cells, series resistance was high which led to device efficiency ~10%. Dark I-V curves of with and w/o ZnO layer showed large difference, which means there is a kind of barrier to current flow between ZnO:Al and a-Si:H layer. Modified condition with double layer scheme was applied and lower series resistance and device efficiency above 12% could be reached. The improvement may be due to either suppression of Si oxide formation or less defect formation by impinging atoms.

Abstract: Non-stoichiometric Zn4-xSb3 compounds with x=0~0.5 were prepared by vacuum melting at 1173K and annealing solidified ingots at 623K. Electrical resistivity and Seebeck coefficient at 450K increased from 1.8
cm and 145K-1 for Zn4Sb3(x=0) to 56.2
cm 350K-1 for Zn3.5Sb3(x=0.5) due to the decrease of the carrier concentration. Hall mobility and carrier concentration was 31.5cm2V-1s-1 and 1.32X1020cm-3 for Zn4Sb3 and 70cm2V-1s-1 and 2.80X1018cm-3 for Zn3.5Sb3. Electrical resistivity of Zn4-xSb3 with x=0~0.2 showed linearly increasing temperature dependence, whereas those of Zn4-xSb3 with x=0.3~0.5 above 450 K tended to decrease. Thermal conductivity of Zn4Sb3 was 8.5mWcm-1K-1 at room temperature and that of Zn4-xSb3 with x≥0.3 was around 11mWcm-1K-1. Maximum ZT of Zn4Sb3 was obtained around 1.3 at 600K. Zn4Sb3 with x=0.3~0.5 showed very small value of ZT=0.2~0.3.

Abstract: Al doped Li(Ni1/3Co1/3Mn1/3-xAlx)O2 (x=0.005, 0.01, 0.05) and Li(Ni1/3-x/2Co1/3Mn1/3-x/2Alx)O2 (x=0.01, 0.05) cathode materials for lithium ion batteries were synthesized using an ultrasonic spray pyrolysis and heat treatment. The substitution with Al reduced the content of Mn3+, promoted grain growth, and broadened the particle size distribution of synthesized powders. The initial discharge capacity of cells made with 0.5 mol% Al doped Li(Ni1/3Co1/3Mn1/3-0.005Al0.005)O2 powder was as high as that of the undoped (~180 mAhg-1, 3.0
4.5 V), and showed an excellent cycle stability. The improvement of the cycle stability was considered to be due to the decrease of Mn3+ in Li(Co1/3Ni1/3Mn1/3-xAlx)O2 by Al doping.

Abstract: To improve ion mobility in solid inorganic electrolyte for lithium ion battery, the hybrid electrolytes were developed in the form of the organic-inorganic meso-scale hybridization by the infiltration of liquid electrolyte into meso-porous inorganic glass membrane. Glass electrolyte membranes with nanopores were prepared by spinodal decomposition and subsequent acid leaching. The most suitable glass electrolyte membranes could be fabricated from the 7.5Na2O-46.25B2O3 -46.25SiO2 (mol%). The effect of leaching temperature, leaching time and leaching acids on the preparation of the membranes were investigated. The microstructure of the cross-section of 7.5Na2O-46.25B2O3-46.25SiO2 glass electrolytes were examined with a scanning electron microscope. Then, liquid electrolyte was infiltrated by dipping method into etched glasses electrolyte. Full cells were fabricated by LiCoO2 for cathode materials and MCMB for anode materials. Conductivity and charge-discharge test of the porous glass electrolyte membrane was measured.

Abstract: To find out suitable Si surface treatment and heat treatment conditions, acid treatment of Si wafer was done for lithium polysilicate electrolyte coating on Si wafer. In case of HCl treatment, the wet angle of a sample is 30o, which is the smallest wet angle of other acid in this experiment. Acid treatment time is 10 min, which is no more change of wet angle. Lithium polysilicate electrolyte was synthesized by hydrolysis and condensation of lithium silicate solution using perchloric acid. Thermal analysis of lithium polysilicate electrolyte shows the weight loss of ~23 % between 400 and 500
, which is due to the decomposition of LiClO4. The XRD patterns of the obtained lithium polysilicate electrolyte also show the decrement of LiClO4 peak at 400
. The optimum heat treatment temperature is below 400
, which is the suitable answer for lithium polysilicate electrolyte.

Abstract: Ag deposited Si/C composite was studied as the anode. In order to enhance the electrochemical properties of Si electrodes, which show poor cyclability as an anode in lithium ion secondary battery, the deposition of Ag prepared by electroless deposition method on the surface of the Si/C composite powder produced by high energy ball milling. Si/C composite shows overall fade in capacity which is caused by Si pulverization. However, The Ag deposited Si/C composite improves cyclability and exhibits capacity of ~590mAh/g after 30th cycle. Scanning electron microscopy(SEM) and X-ray diffraction(XRD) measurement are adapted to inspect the deposition process.