Surface Composition of TiO 2 -Zn Nanotubes by NanoSIMS
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Surface Composition of TiO2-Zn Nanotubes by NanoSIMS Indu B Mishra, Diana Khusnutdinova and William T Petuskey School of Molecular Sciences, Arizona State University
ABSTRACT Titania nanotubes were prepared by anodic oxidation of Ti. The titania surfaces were partially coated with Zn by reacting zinc acetate with the nanotubes and then annealed. [1] An annealed nanotube cluster was placed carefully on a silicon wafer using tweezers. Secondary electron images were acquired by bombarding with Cs+ and observing the ejected OZn- and OTirespectively. The SIMS analysis was done in ultra-high vacuum (~ 10-10 Torr). The location of before and after the SIMS analysis was confirmed by scanning electron microscopy (SEM). Specific areas with various orientations (vertical and horizontal orientations) of the nanotubes were selected for the NanoSIMS 50L analysis. The NanoSIMS 50L is made by Ametek Cameca, Gennevillieres, France and is capable of doing in situ isotopic analysis of surfaces at high spatial resolution (25 nm2). The average ZnO/TiO was ~1.8%, confirming the actual content of Zn used during synthesis of the nanotubes. Qualitatively, the TiO/ZnO ratio increased with increasing depth implying that ZnO concentration was decreasing as we probed into the nanotubes. INTRODUCTION Zwiling discovered Titania nanotubes, TiNT, first in 1997 [1] and since then TiNT has attracted attention throughout the globe. In the past few years there has been close to 8800 publications on TiNT. The synthesis of TiNT by chemical methods was reported by Kesuga et al. in 1999 [2]. Most extensively studied synthesis of titania nanotubes is by anodic oxidation of Ti foils in various media [3-5]. Titania nanotubes by hydrothermal methods [6] have developed over the years. TiNT, surface modified TiNT with metals [3, 7, 8] have found use as sensors for detecting hydrogen, oxygen and improvised explosives [3, 5, 9, 10]. Dye sensitized TiNT is extensively used as Gretzel cells in solar energy harvesting. [5, 11, 12] Dubnikova et al. [9] first showed in 2002 that some metals like Li+, K+, Zn++, Cd++, Co++, Ni++ form a complex with triacetone triperoxide (TATP). Following this Banerjee et al. in 2009, reported that Zn++ substituted titania (TiNT-Zn) forms a labile complex with TATP [3]. This complex formation results in a large change in the electrical conductivity compared to TiNT-Zn. This complex breaks down when subjected to high vacuum or UV pulse. This provided for the first time a solid state sensor for detecting TATP. For example base line current (amp) measured without exposure to TATP vapor is found to be 10-8 – 10-9 A which corresponds to resistivity of 108 – 109 Ωcm. When TATP is exposed to the TiNT-Zn, a sharp change in the current to 10-1 – 10-3 A corresponding with a resistivity of 101 to 103 Ωcm was observed. The experiment was carried out under ambient condition at ambient vapor pressure of TATP which is quite high. Thus the method provided a positive presence or absence of TATP. Subsequently Roy et al. reported similar effect with Co++
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