ICMCTF2015 Session FP: Symposium F Poster Session

In recent years much attention has been given to High Power Impulse Magnetron Sputtering (HIPIMS) as one of the advanced technologies within the PVD Industry. The advantages of HIPIMS technology stem from the very high ionisation rate of the sputtered flux as compared to traditional Direct Current Magnetron Sputtering (DCMS). HIPIMS can be used to change the microstructure of the coating leading to many unique properties, such as increased density and higher hardness [1,2].

The Closed Field Unbalanced Magnetron Sputtering Ion Plating (CFUBMSIP) configuration increases ion bombardment of the growing film and offers further potential benefits when combined with HIPIMS. Low friction graphite based coatings [3] have been selected to study the combination of the HIPIMS technique with traditional DCMS under the CFUBMSIP configuration. Many parameters including the HIPIMS pulse width, frequency and power, substrate bias, DCMS contribution and chamber pressure have been varied to optimise the properties of the coatings. At the same time the Optical Emission Spectum (OES) has been monitored to observe the level of ionisation in the chamber. The mechanical properties of the coatings have been evaluated by Rockwell, Pin-on-Disc and Hardness testing, while SEM has been used to observe the microstructure of the coatings.

This study shows that with carefully optimised parameters the coating hardness can be increased by more than 20% with the addition of HIPIMS whilst maintaining equivalent friction coefficients and wear characteristics. The combination of HIPIMS with DCMS can be used to minimise the reduction in deposition rate whilst achieving a high level of ionisation and a coating with dense microstructure. However further work will be required to incorporate the HIPIMS technique into an industrial scale process.

References

[1] A. P. Ehiasarian et al, J. Appl. Phys. 109, 104314 (2011)

[2] G. Greczynski et al, Surface & Coatings Tech. 205 (2010) 118-130

[3] S. K. Field et al, Tribology Int. 37 (2005) 949-956

The proton exchange fuel cell is one of the candidate devices as a clean energy source. The fuel cell generates the electric power with the electrchemical reaction of hydrogen and oxygen atoms. The platinum catalyst, supported on carbon fine powder, is generally used to enhance the electrochemical reaction and to increase the output power of the fuel cell. The reduction of the platinum catalyst in the used amount is one of the important research subjects to popularize the fuel cell, because the platinum is high cost material.

In this study, the platinum particles was successfully formed on the surface of carbon nanotubes (CNTs) as the catalyst of fuel cell by the in-liquid plasma. Moreover, the proton exchange fuel cell was formed using the platinum catalyst supported on the CNTs.

Two platinum wires were placed in water dispersed with CNT of 18.9 mg as electrodes. The in-liquid plasma was formed in the CNT dispersion by applying pulse high voltage of 7 kV between the platinum electrodes. The generated plasma spattered the surface of the platinum electrodes into the water. Therefore, the platinum particle was formed on the CNT surface in the water. The weight of spattered platinum increased from 7 mg to 24 mg with an increase in the applying time of high voltage from 0 minute to 20 minutes.

The platinum particles supported on the CNT were used as catalyst of the proton exchange fuel cell. The open voltage of the fuel cell was 0.8 V. The maximum power of 54 mW/cm2 was observed with the platinum spattered at 7 mg. The maximum power increased up to 160 mW/cm2 with an increase in the weight of the spattered platinum.

Carbon Nanotube (CNT) has received an extensive attention because of its superior mechanical, electrical and thermal properties. These properties make CNT an attractive filler for composite materials to be used in many applications such as coating materials for bipolar plates (BP) of fuel cell (FC). However, CNTs have a strong tendency to bundle together through van der walls interactions, which limit the possibility of using CNT in applications. Therefore, appropriate dispersion process has to be applied in order to utilize the unique properties of CNT.

In this study, multi-walled carbon nanotubes have been dispersed in water with surfactant by using wet jet milling process to break CNT agglomerate and the effect of wet jet mill process in CNT dispersion was investigated. Hence, the study aims to attain the optimum parameters of CNT dispersion to be used as coating composite to protect BP of FC from surface corrosion.

1wt% of CNT and surfactant in water were ultrasonically agitated for 3 minutes and then dispersed using wet jet milling process at an ejection pressure of 50Mpa for 1-10 cycle repetitions (number of passes). Dispersion fluid of Polytetrafluoroethylene (PTFE) was mixed with 50wt% of CNT dispersion to form CNT/PTFE resin dispersion. CNT/PTFE resin dispersion was ultrasonically agitated for 20 minutes and applied to glass substrate. The sample was dried for 30 minutes then heated at 350 for 5 minutes. Finally, the result was examined by viscometer, four-point probe, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

CNT dispersion showed linear decrease in viscosity by increasing wet jet mill processing pass number. At the first processing pass, CNT dispersion was 24.6 mPa.s then dropped gradually until reached low viscosity of 3.60 mPa.s by the 10^th processing pass. CNT/PTFE composite film formed from the CNT dispersion showed electrical conductivity, while PTFE film was extremely low conduction. The electrical conduction of CNT/PTFE film depended on wet jet mill processing pass number. CNT/PTFE composite film showed linear increase in electrical conductivity by increasing wet jet mill processing pass number. At the first processing pass, CNT/PTFE dispersion reached the conductivity of 9.45 S/cm. CNT/PTFE conductivity increased up to 41.32 S/cm with the increase in wet jet mill processing pass number of 10 pass. This result shows that an electrical network of CNT was uniformly formed after increasing processing pass number.

Next approach will be changing the ejection pressure and increasing pass number to evaluate CNT/PTFE dispersion. Then CNT/PTFE composite film will be applied as anticorrosion coating to BP of FC

Zinc oxide (ZnO) exhibits n-type conduction and has the band gap energy of 3.37 eV, which is transparent to visible light. On the other hand, cupric oxide (CuO) exhibits p-type conduction and has the band gap energy of ~1.35 eV, which is very close to ~1.4 eV at which the maximum energy conversion efficiency has been predicted from the Shockley-Queisser limitation theory for the single pn junction solar cells. We have reported the shape controllability of vertically aligned ZnO NRs prepared by the CBD techniques using zinc chloride (ZnCl₂) and zinc acetate dihydrate [Zn(CH₃COO)₂・2H₂O] as source materials [1]. Moreover, the cone-shaped ZnO nanorods (NRs)/CuO heterojunctions with rectifying behaviors on their current density (J) – voltage (V) curves were successfully grown on the Au seed layers by CBD using Zn(CH₃COO)₂・2H₂O and copper (II) nitrate trihydrate [Cu(NO₃)_2・3H₂O] [2]. In the present paper, fabrication of the ZnO NRs and the ZnO/CuO heterojunctions by CBD growth technique using zinc nitrate hexahydrate [Zn(NO₃)_2・6H₂O] and Cu(NO₃)_2・3H₂O, and controllability of their structural, optical and electrical properties will be discussed.

The ZnO NRs were grown on various substrate materials, i.e. alkali-free glass coated with and without Au film, Au/Ti/Si(100) film and CuO/Au/Si(100) film, by CBD using the mixed aqueous solution of Zn(NO₃)₂・6H₂O and hexamethylenetetramine (HMT) or the Zn(NO₃)₂・6H₂O aqueous solution in which pH value was adjusted to be 10 by the use of ammonia solution. The Zn concentration in the aqueous solution was varied in the range of 0.01-0.1 M. Growth time was changed in the range from 15 to 180 min.

It was confirmed that the vertically aligned ZnO NRs can be grown on the Au seed layer by CBD using the Zn(NO₃)₂・6H₂O aqueous solution as well as using the aqueous solutions of ZnCl₂ and of Zn(CH₃COO)₂・2H₂O. Both the higher concentrations of the aqueous solutions and the longer growth times were favorable for obtaining the vertically aligned ZnO NRs. The vertically aligned ZnO NRs were also obtained on the CuO/Au/Si(100) films as with the case of the Au seed layers. With increasing the concentration of the mixed aqueous solution, shapes of the ZnO NRs on the CuO layer change from cones to cylinders together with the increase in diameter and length, and the density of the NRs becomes higher. These results indicate that the accurate concentration control of the aqueous solution is one of the important factors for the achievement of the shape control growth of the ZnO NRs.

[1] T. Terasako et al.: Thin Solid Films 549 (2013) 292. [2] T. Terasako et al.: Sol. Energy Mater. Sol. Cells (to be published)

All-solid-state batteries are attractive to next generation battery due to their high safety, durability and energy density. However, all-solid-state battery has problem with low Li ion conduction pathway between cathode particles. To solve this problem, a composite electrode consists of a cathode material and a solid electrolyte is synthesized for increased Li ion pathway.

In this study, a composite electrode has been manufactured using a solid electrolyte Li-B-W-O (LBWO) and a cathode material LiCoO₂ (LCO) by liquid phase sintering method. Liquid phase sintering method has advantages such as high distribution of melted solid electrolyte in the composite and its simple synthesis process. The LCO cathode material and melted LBWO solid electrolyte interfaces were investigated by Scanning Electron Microscopy. X-ray diffraction and Transmission Electron Microscopy were applied to analyze the LBWO coated LCO composite electrodes. The ion conductivity of the sintered composite electrode was 3 × 10^-6 S cm^-1 when its thickness was 150 μm. The synthesized composite electrode composed of LCO and LBWO by liquid phase sintering method is expected to be a promising candidate for all-solid-state batteries.

A two-step process including the deposition of a ZnO seed layer followed by the growth of ZnO nanowires using a solution process was developed to grow ZnO nanowires on glass substrate. The ZnO seed layers were prepared using various precursor solutions through a spin coating method. T he use of various precursor solutions allows the formation of seed layers exhibiting as many different characteristics as possible. Effects of the precursor preparation, including precursor type and concentration on the growth and characteristics of the obtained ZnO nanowires are presented and discussed. In particular, we report an unusual growth kinetics in which the lengthening of the nanowires is proportional to t^1.5. A growth model is therefore proposed.

Self-assembled multilayer structures ha ve been observed. Such self-assembled structures occur not in only metal-carbon systems but also ceramic-carbon, alloys, and metal-ceramic systems. In the carbon-metal systems, different groups h ave investigated a-C:Cu, a-C:Au, a-C:Ag, a-C:Fe a-C:H/Ti, a-C:H/W, a-C:H/Mo, and a-C:Cr thin films using different deposition techniques. Regardless of the differences in the metal type and the deposition technique used in these groups, it appears that not all the deposition conditions, including the metal type, lead to the formation of such interesting microstructures. It is also noted that although the self-assembled layered structure s were found in different processes with different materials, and explained by different models, effects of the growth parameters and the growth mechanism have not been fully understood. In this research, we have used a reactive magnetron sputter deposition technique for the preparation of a-C:H/Me thin films under various deposition conditions. As for the types of metals investigated, the research has covered a wider range of metals, including Al, Si, Fe, Ni, Cu, and Pt, than that of the other groups. Various types of metal containing amorphous hydrogenated carbon thin films (a-C:H/Me) have been grown on different substrates using one single target, a rotating but not revolving substrate, and constant feed gas compositions in a conventional reactive sputter deposition chamber. Meanwhile, the growth and characteristics of metal containing amorphous hydrogenated carbon thin films (a-C:H/Me) were studied. In order to explain the formation of th e distinct structures, correlations were first made among the deposition rate, the composition, the crystallinity, the surface chemistry, and the microstructure of a-C:H/Me thin films. A growth mechanism based on the considerations of clustering of carbon and metal, segregation of carbon, catalytic effects of metal, formation of carbide, energy of adatoms, and surface diffusion of metal and carbon, has been developed.

Mg₄Nb₂O₉ thin films were grown on Si (100) substrate by radio frequency magnetron sputtering. The structure and surface morphology have been studied by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). From the results of SEM, indicated that the grain size of the film changed with an increase annealing temperature. The electrical properties were also measured using capacitance–voltage (C–V) and current–voltage (I–V) measurements on a metal–insulator–semiconductor (MIS) capacitor structure.

In this study, the resistive switching (RS) behavior of Al/Gd₂O₃/Si MIS capacitor is introduced with rectification effect. The n-type semiconducting Gd₂O₃ thin films are deposited on p-Si substrates by RF magnetron sputtering. The physical properties of Gd₂O₃ thin films at various annealing conditions are discussed. The experimental results showed that more oxygen vacancies exist in the N₂-H₂-annealed samples than the air-annealed samples. In addition, the effects of annealing temperature on electrical properties of the Al/Gd₂O₃/Si MIS capacitors are also discussed. According to the results, all of these devices are electrical rectified which is controlled by p-n junction for these devices. Finally, the RS characteristic of Al/Gd₂O₃/Si MIS capacitors is studied. The RS phenomenon with the rectification effect over 6 orders and ON/OFF ratio over 4 orders can be obtained.

Metallized polyethylene terephthalate (PET) could be used as a low-cost solar reflector for demanding applications such as mirrors for concentrating solar power systems. However, there application has been somewhat limited due to atmospheric corrosion especially in regions that have significant amounts of salt. To attempt to develop low-cost durable solar reflectors we have deposited hydrophobically functionalized silica coatings on metallized PET substrates using a sol-gel process. We have fabricated coatings with thicknesses in the range of 0.2 microns to 0.8 microns and investigated the corrosion resistance of pristine and mechanically degraded films by exposure to salt-spray. Mechanical degradation due to deformation of the substrate and coating system was investigated by stretching films using a miniature tensile testing machine and attached microscope. Both stretched and unstretched samples were exposed to salt-spray and the effect of exposure time on reflectivity and contact angle measured. Microscopy and surface analysis were used to determine corrosion behavior. We also simulated the impact of cleaning the mirrors using a custom built reciprocating-sliding tribology tester and then exposing worn and pristine samples to salt-spray and the effect of exposure time on reflectivity and contact angle measured.