Chien-Chon Chen

Fabrication of long TiO2 nanotube arrays in a short time using a hybrid anodic method for highly efficient dye-sensitized solar cells

We report a simple hybrid anodic method, with initial potentiostatic anodization followed by galvanostatic anodization, to grow much longer titania nanotube (TNT) arrays in a much shorter anodization period (t). The length of the TNT arrays (L) depends linearly on t and is controlled by the electric current; the growth rates are 5.3, 10.7 and 20.3 μm h−1 for current densities 3.7, 5.6 and 7.5 mA cm−2, respectively. The produced TNT films of L = 15–57 μm sensitized with N719 dye were fabricated into devices for photovoltaic characterization. The NT-DSSC devices show systematically improved cell performance depending on L, reflecting the excellent intrinsic light-scattering property of the NT-DSSC devices to harvest increased sunlight with long TNT arrays. The great effective surface area inside TNT arrays has been shown to significantly increase the dye loading, which might help to enhance the cell performance of the device with co-sensitizing of different dyes for improved efficiency of light harvesting in the future. The best performance of the NT-DSSC device was achieved at L ∼ 30 μm with a spacer of similar thickness, giving JSC = 14.63 mA cm−2, VOC = 0.741 V, FF = 0.70, and η = 7.6%, which is unprecedented for a back-illumination DSSC.

Fabrication of single-crystal tin nanowires by hydraulic pressure injection

Tin (Sn) nanowires, with 15 and 60 nm average diameter and up to 10 µm in length, were fabricated by an injection process using a hydraulic pressure method. The Sn melt was injected into an anodic aluminium oxide (AAO) template and solidified to form nanowires. By back etching the aluminium substrate and barrier layer, the nanowire array ends were partially exposed from the bottom face of the AAO template. The filling ratio of nanowires inside and through the thickness of the AAO template was found to be close to 100%. The nanowires were also found to be dense and continuous with uniform diameter throughout their length. Transmission electron microscope (TEM) and x-ray diffraction (XRD) studies on the 60 nm diameter nanowires revealed that the nanowires were single crystals with body-centred-tetragonal (bct) structure predominantly growing along the [100] direction. The current method of synthesizing nanowires is straightforward, low-cost and suitable for low-melting point (<650 °C) metals including low-melting point alloys with stoichiometric composition.

Evaluation of Fluorine Ion Concentration in TiO2 NT Anodization Process

Studies have shown that fluorine ions play a significant role in the initiation and growth of TiO 2 nanotubes. As fluorine is doped in titanium nanotubes (Ti0 2 NTs), fluoride gases form during Ti0 2 NT anodization. The concentration of fluorine in an electrolyte decreases as the anodization period increases. Maintaining a constant concentration of fluorine levels is a challenging task. In this paper, we discuss and calculate the quantity of fluorine reduced in an electrolyte given various electrolyte temperatures, sample sizes, and anodization time effects. According to thermodynamic calculations, F, FO, and FO 2 have relatively low vapor pressures but HF, H 2 F 2 , H 3 F 3 , H 4 F 4 , H 5 F 5 , H 6 F 6 , and H 7 F 7 have relatively high vapor pressures during anodization. The effects of fluorine contained in TiO 2 NT (12.2 wt %) and vaporized from the electrolyte can cause the fluorine concentration in the electrolyte to decrease.

Anisotropic O 2p-Mn 3d unoccupied states in La1−xMnO3: an X-ray absorption spectroscopy study

We have studied La 1-x MnO 3 thin films, which show the metal-insulator transition similar to La 1 x Ca x MnO 3 . The transport and magnetic properties are measured. X-ray absorption spectroscopy is employed to investigate the electronic structure. Surprisingly, the electronic structure of La 1-x MnO 3 shows large anisotropy. Our results suggest that La 1-x MnO 3 is unique among manganites.

Highly sensitive arrayed indium-antimony nanowires for infrared detection

The objective of this study is to achieve a high sensitive infrared detector by fabricating highly ordered array of indium-antimony (In-Sb) nanowires which is a semiconductor material. The approach is to investigate an infrared detector with arrayed nanowires which can transport signals in one dimension to obtain high efficiency and sensitivity compared with In-Sb by using traditional thin film fabrications. This research expects to provide an infrared detector by fabricating III-V alloy nanowires to highly improve the resolution of infrared signal. To develop scaled-up functional devices, highly ordered nanowire arrays are essential building blocks. Many candidate materials (metals, alloys, oxides and semiconductors) have been studied for various potential applications in nanotechnology and have shown some promising results. The solid metallic nanowires have been exploited for a wide range of applications to take the advantages of their large length/diameter aspect ratio. Further development to synthesize nanowires efficiently at lower cost is the direction for manufacturing next generation nanodevices. In this study, various diameters of ordering nanowires, from 10 nm to 500 nm, were fabricated and evaluated the performance of the sensitivity of infrared detection. Moreover, a 1 inch plate, which can be regarded as a device, with nanowires array was fabricated by designing a new type of processing chamber.

The effect of nitrogen-doped ATO nanotubes on radical multiplication of buffer media by visible light photocatalysis rather UV

The use of TiO2 in photodynamic therapy for the treatment of cancer has generally been studied in cultured cancer cells in serumcontaining RPMI 1640 medium under visible light application rather than ultraviolet (UV) light. An ordered channel array of N-doped anodic titanium dioxide (ATO) has been successfully made for visible light application. ATO nanotubes in the anatase form with a length of 10 µm are more effective than nanotubes of 1.8 µm in length as a photocatalyst for radical multiplication in buffer solution by generating hydroxyl radicals and superoxide radical anions under UV-A exposure. Only the N-doped ATO is applicable to visible light photocatalysis for radical multiplication in RPMI 1640 + 1% FBS and acrylamide, a free radical carrier.