ICMCTF2014 Session FP: Symposium F Poster Session

Zinc acetate dihydrate and copper (II) nitrate trihydrate were used as Zn and Cu sources, respectively. The pH values of the aqueous solutions were adjusted to 10-10.5 by the use of ammonia solution. The Au/Ti/Si(100) wafers and glass substrates were used as the substrate materials. The bath temperature was changed in the range of 70-90 ℃. Growth times for the CuO and ZnO layers were 60 and 20 min, respectively. After each CBD process, post-annealing treatment was carried out at 250 ℃ in the air.

The X-ray diffraction patterns of the CuO/glass films were dominated by the (002) peaks. It was confirmed that as-deposited CuO films do not exhibit p-type conduction without the post-annealing treatment. For the CuO/glass films, Hall mobilities were distributed in the range of 8.9-33.6 cm²/Vs, and the carrier concentration p varied in the range from 2.9×10¹⁶ to 3.6×10¹⁸ cm^-3.

SEM observations revealed the successful growth of ZnO nanorods with 500-1400 nm in length and 270-700 nm in width on the top of the CuO layers composed of the columnar grains with approximately 400 nm in width. The current density-voltage curves for the p-CuO/n-ZnO heterojunctions exhibited rectifying characteristics. However, the extremely large ideality factors of 3.17-4.15 have been obtained so far, indicating that there is a lot room for improvement of the interface states between the p-CuO layer and the n-ZnO layers. With respect to this problem, the effect of the insertion of the intermediate layer between the p-CuO layer and the n-ZnO is also under investigation.

Dye-sensitized solar cells (DSSCs) have attracted attention because of their low cost, eco-friendliness, low incident-light-angle dependence, and high efficiency. In DSSCs, nanostructured ZnO or TiO₂ photoanode layers are essential part to increase the dye adsorption and photoconversion efficiency by enhancing electron transfer. Several attempts have been made to improve the electron transport efficiency of those photoanode layers using one-dimensional (1D) nanostructures or 3D porous structures with a thin shell (i.e., the inverse opal structure) to provide fast electron transport paths. For the preparation of the nanostructures, atomic layer deposition (ALD) has many advantages, including excellent step coverage and conformality, accurate thickness control, exceptional composition control for nanostructures, and uniformity over large areas. Herein, a simple and versatile template assisted approach was investigated to prepare ZnO nanostructured photoanodes on large area for low cost dye-synthesized solar cells (DSSC). As a low cost nanostructured template, the paper that composed of cellulose nanofibers was utilized. After the low temperature atomic layer deposition (LT-ALD) of ZnO on the paper followed by calcination, the porous and fibrous nanostructures of paper was able to be successfully replicated. Due to the low thermal stability and complex interconnected nature of cellulose nanofibers in the paper, the use of LT-ALD process of ZnO was inevitable. In the presentation, the optimization of both LT-ALD ZnO and calcination processes will be discussed in terms of the microstructure and photoelectrochemical characteristics. Also, the feasibility of using our approach will be demonstrated by fabricating DSSCs.

In this work, we applied a novel treatment of supercritical fluid to fabrication ZnO nanotubes and successfully demonstrated that using supercritical CO2 fluid mixed with ethanol solution can oxidize and transform the DC-sputtered zinc film for synthesizing ZnO nanotubes. The treatment process was kept at 60 ^oC and 3000 psi for 1 hour. The morphology of ZnO nanotubes was uniform with diameter of 10 nm and 3-nm thickness of tube, which observed in the images of scanning electron microscopy and transmission electron microspore. Besides, the distribution of ZnO nanotubes was clustered and high density, fully grown on the surface of subtract. These ZnO nanotubes were analyzed by the N & K analyzer, photoluminescence (PL), scanning electron microscope (SEM) and Transmission electron microscope (TEM) to investigate the characteristics of the optical, morphology and crystal structures.

Indium gallium zinc oxide (IGZO), with high transparency, remarkable saturation mobility (μ_sat), low operation voltage and low density-of-states (DOS), has been utilized as a substitute for poly-Si in thin-film transistor (TFT). Even though the amorphous IGZO that fabricated by conventional dc magnetron sputtering as well as many other coating methods are satisfactory in its properties for practical application, literatures have shown that additional substrate heating or post-annealing can enhance the saturation mobility, operational stability and electrical conductivity. For fulfilling the flexible display purpose, as the aim of this study, high power impulse magnetron sputtering (HIPIMS) technique known to provide high density plasma is employed so as to form high-quality IGZO film on polymeric flexible substrate at a relatively low substrate temperature. By regulating the output waveform of the HIPIMS power supply, the optical and electrical characteristics of the obtained IGZO were investigated to associate with film microstructure.

Experimental results reveal that the as-prepared IGZO film is very morphologically dense. The saturation mobility, the electrical conductivity and the optical transmittance are dependent on the output waveform and are discussed. The characteristics of the TFT device using IGZO layer as the channel layer is also explored.

In this contribution, we describe measurements of the ionized metal flux fraction, the ratio between ionized and neutral metal species, arriving to the substrate in High Power Impulse Magnetron Sputtering (HiPIMS). The ionized metal flux fraction is determined from the deposition rate of ions and neutrals. In order to determine the respective rates, a combination of a retarding field and by a quartz crystal microbalance (QCM) was used. Two different sensors were tested. A standard QCM equipped with a set of grids and an alternative grid-less sensor which was developed in order to increase the sensitivity. The grid-less sensor uses magnetic field to repel electrons and the bias voltage is applied directly to the QCM top electrode.

We report results for two materials, Ni and Ti. Ti was characterized both in nonreactive (Ar) and reactive (Ar+O2) atmosphere. Measurements with the QCM analyzer showed an ionized fraction of up to 50% for Ni. Somewhat higher values, exceeding 60%, were measured for Ti. In this case, shorter on times lead to higher ionized fraction at the same deposition rate and average discharge power. In reactive sputtering of Ti, substantially higher ionized fraction was observed in the oxide mode as compared to the metal mode. Already at lower values of the peak power, there was a significant fraction of Ti ions in the oxide mode.

In this work, the (Cu, Zn) metal and (Cu, Zn) oxide nanowire arrays were fabricated through template-assisted electrochemical deposition method, which was controlled the pulse duration. The pulse potentials of (Cu-Zn) nanowire were -0.18 and -1.26 V/SCE, respectively. The microstructure and chemical composition of (Cu, Zn) nanowire arrays were characterized by field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM) equipped energy dispersive x-ray spectrometer (EDS). The SEM results indicated that the Cu-Zn nanowire arrays were assembled into the nanochannel of porous alumina template with diameter of 90-100 nm. SEM results shown the bamboo-like (Cu, Zn) multilayer structure was observed at 40 (Cu) and 20 (Zn) seconds pulse deposition. With the increasing of pulse potential duration, segments with homogeneous shape of Cu-Zn nanowires were disappeared to form the continuous shape. Growth mechanism of structural nanowire during electrochemical deposition was assumed to base on the reduction potential. During the various annealing time of segmented Cu-Zn nanowire process, the (Cu, Zn) oxide nanowire structures were exhibited segmented nanowire and continuous nanowire. In texture formation of (Cu, Zn) oxide nanowire was proposed on the Zn diffused into Cu oxide of heating process. The crystallinity of (Cu, Zn) oxide nanowire was characterized as single crystal. The application on water splitting characterization was obtained maximum photocurrent density of (Cu,Zn) oxide and Cu₂O-ZnO bamboo-like structure were 0.07 mA/cm² and 0.11 mA/cm², and the conversion efficiency were 0.1 % and 0.13 %, respectively.

The major trend in the current research activity on SOFCs focuses on decreasing the operating temperature to the range 500-700ºC to reduce system and material costs and improve lifetime. Currently, Yttrium Stabilized Zirconia (YSZ) with 8 or 10% yttria is the most common electrolyte. To ensure sufficient ionic conduction operating temperatures ranging from 800 to 1000 ºC must be used. These high temperatures place stringent requirements on the cell components, such as chemical stability in oxidizing and reducing environments, chemical stability of contacting materials and thermomechanical compatibilities. Exotic and costly materials have to be used, such as lanthanum chromite for current collectors. As a result, actual SOFCs concepts often fail to meet the expected durability requirements and their costs per W are still several times higher than economically feasible values.

The development of Intermediate Temperature SOFCs (IT-SOFCs) may be achieved by different strategies, including the development of new electrolyte materials, with better performance at intermediate temperatures, and reducing the electrolyte thickness to decrease the ohmic drop at the electrolyte. Silicate-based materials have attracted considerable interest as potential low cost electrolyte materials. Their ionic conductivity is higher than the conventional YSZ electrolyte at low temperatures (e.g. 0.01 S/cm at 700 °C) and comparable to CGO at 600 ºC. Despite silicon oxide volatilization from the surface layers under reducing conditions, which results in conductivity degradation with time at temperatures above 1100 K, the silicate-based solid electrolytes possess a promising combination of transport properties, thermal expansion and stability, enabling their use for IT SOFCs operating at 500–700 ºC. Lanthanum silicate has a hexagonal structure with oxygen channels aligned with the c axis of the cell which are preferential conduction paths for the ions. As a result the ionic conductivity of lanthanum silicate is 10 times higher along the c axis than in perpendicular directions. In this work lanthanum silicate electrolyte films deposited by magnetron sputtering with preferentially oriented grains in such a way that the c axis of the crystals is aligned with the conduction direction.

Satellite structures demand high strength and stiffness for dimensional stability and survival of both launch and orbital environments. The use of carbon nanotube-based sheets for composite laminates is currently being evaluated to replace carbon fiber composites in high strength / high modulus applications such as the skeletal support of next generation spacecraft. In this study, improvements in the purification of commercial, continuous carbon nanotube (CNT) reinforcement were made and their effects on the resulting composite laminate were investigated. CNT sheet purification was performed with a series of oxidative thermal treatments with concomitant purity assessment using thermal, elemental, and electron imaging techniques. Purification of the CNT fabric purification shows encouraging results in terms of reducing the amount of metal catalyst while minimizing oxidation of the CNT sidewalls as evidenced in X-ray photoelectron spectroscopy. Moreover, this treatment decreases the CNT fabric density by ∼8%, and increases the thermal oxidation temperature by 40°C. We were successful in isolating and imaging individual multiwalled tubes of the purified sheet material which confirmed that the purification process was not deleterious to the surface morphology. Post-treatment steps (i.e. chemical sizing and plasma treatment) of the purified sheet were employed as noninvasive techniques which successfully enhanced the wetting and bonding properties without structural degradation of CNT material. This purification route is efficient and can be used to improve and maximize surface wetting and bonding of resin to carbon nanotube sheets in order to improve processability and mechanical properties.

Boron Nitride (BN) is a potential material for optoelectronic, piezoelectric sensors and high power electronic applications. However, BN is especially difficult to synthesize by thermal CVD in other phase than the poorly crystallized turbostratic phase (t-BN), between amorphous and hexagonal phases (h or r-BN). Recent attempts to obtain epitaxial layers of hexagonal BN phase with triethyl boron [1] and diborane [2] as boron source and NH3 as nitrogen source have succeeded. The growth rates allowing epitaxial growth of BN was below 200 nm/h.

Based on the results obtained in aluminum nitride layer at high temperature using AlCl3 has aluminum source [3], the epitaxial growth of BN is recently investigated via the same chemical pathway. Growth of BN at high temperature (1000-1700°C) on various substrates (lab-made AlN templates on c-saphire, W and Cr) has been studied using NH3, BCl3 and H2. The experiment set-up consists of a vertical water-cooled quartz reactor with an induction-heated graphite susceptor covered with AlN. Influence of the substrate temperature and N/B ratio in the gas phase on the quality of the grown BN layer have been investigated. As-grown BN layers have been characterized by Field Emission Scanning Electron Microscopy (FE-SEM) and X-ray diffraction (XRD) and Raman spectroscopy.

The study shows that the t-BN phase is predominately obtained with BCl3 as boron precursor, whatever the temperature and the B/N ratio in the range studied, for a growth rate in the order of 1 µm/h. To stabilize the h-BN growth on hetero substrate, a very low supersaturation (consequently growth rate) of BCl3 must be used.

The influence of different anodization conditions on Ca- and P- incorporated titania nanotubes properties was evaluated. TiO₂ nanotubes were produced by potentiostatic anodization of Ti-cp in a viscous electrolyte containing HF and Ca and P ions, at different voltages (15 to 120 V) for different times (2 to 24 h), and annealed at 530 °C for 10 h. Characterization of the nanostructured oxide layer was conducted using scanning electron microscopy, glancing-angle X-ray diffraction, X-ray photoelectron spectroscopy, and contact angle measurements. During the anodization treatment, Ca and P ions were incorporated into the oxide layer. The results showed that the applied voltage and anodic oxidation duration have a large effect on the change in the characteristics of the nanotubes layer. The amount of anatase phase and morphology of the oxide layer were dependent on the voltage applied during the oxidation treatment. The size of the nanotubes was increased with increasing voltage of anodic oxidation. In addition, the resulting nanostructured layer have a superhydrophilic characteristic.

Keywords: TiO₂, nanotubes, anodization, wettability

Recently, high power impulse magnetron sputter (HiPIMS) process attracts attentions due to its ability for providing a highly ionized flux of sputtered species. The advantages of HiPIMS include low process temperature, well-adherent coating, better quality of the films, and droplet-free coating process. The deposition a uniform layer on substrate with complex shapes and trenches can also be achieved by HiPIMS. High density of peak current and peak power are the typical characteristics of HiPIMS. A low duty cycle (typically <5%) and the pulse duration approximately in a range between 10 and 1000 μs are commonly used in HiPIMS.

In this study, a HiPIMS system was used to deposit TiO₂ thin films. The used target is TiO₂ with a purity of 99.99% and a size of Ф150 x 5mm. Before the deposition, the I-V characteristics of the discharge are first measured to determine the duty cycle and the pulse duration. Duty cycles in the range of 1-5% and the pulse duration in the range of 25 to 200μs are used to investigate the I-V of the discharge. Besides, the optical emission spectroscopy (OES) is also used to diagnose the composition of the plasma. The voltage and the peak current in the range of 50 ~ 300 A were found increasing with decreasing the duty cycles and with increasing the pulse duration. The TiO₂ films was then deposited to discuss their crystalline structure, morphological features, and optical properties.

Keywords: TiO₂, HiPIMS, duty cycle, pulse duration

Submit to Poster Presentaion in Symposium F2. High Power Impulse Magnetron Sputtering (HIPIMS)

Ni-Mn-Al thin films have been deposited using DC/RF magnetron sputtering from three different targets of Ni, Mn and Al. The off-stoichiometric films have been deposited for 2 min, 5 min, 10 min and 15 min. The elemental composition analysis of Ni-Mn-Al thin films has been carried out using an energy dispersive X-ray analysis. T he XRD patterns of the films reveal cubic B2 structure. The observation of cubic structure shows that the films exhibit high temperature austenite phase at room temperature. To further confirm the phase present in the films, the crystal structure of the films has been examined by transmission electron microscopy. Magnetization versus temperature curves reveal martensitic transition from austenite phase to martensite phase below room temperature which is further confirmed by resistivity versus temperature measurements. A splitting between ZFC and FC curves is observed at low temperatures which have been further studied by ac susceptibility measurements. A spin glass behaviour is observed in the system which may be responsible for complex magnetic behaviour at low temperatures. A large exchange bias has been observed at low temperature (5 K) associated with the coexisting spin glass and antiferromagnetic exchange interactions. The exchange bias is found to be dependent on the thickness of the film. Nanoindention of thin films reveals high hardness of magnetically ordered films.