Sol-Gel Derived SnO2 Nanometric Fibers
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1017-DD12-30
Sol-Gel Derived SnO2 Nanometric Fibers Kristjan Saal, Tanel T‰tte, Madis Paalo, Rasmus Talviste, Sergei Vlassov, and Ilmar Kink Laboratory of Low Temperatures, Institute of Physics University of Tartu and Estonian Nanotechnology Competence Center, 142 Riia St, Tartu, 51014, Estonia
ABSTRACT The applicability of Sn(OBu)4 based viscous oligomeric concentrates in fabrication of thin oxide fibers and needles is demonstrated. Influence of several crucial parameters like viscosity of the concentrate, humidity of surrounding atmosphere and pulling speed on formation of the structures is discussed. We show that the method enables to obtain fibers less than a micron in diameter and needles with tip radii down to 15 nm, i.e. in range that is of considerable interest for many nanotechnological applications. INTRODUCTION Fabrication of ultra-thin optical fibers has attracted growing attention since the early 1990s, when nanometer-range sharp silica fibers were demonstrated to act as near-field optical microscopy sensors [1,2]. Recently, silica fibers only some tens of nanometers in diameter were demonstrated as promising components in future microphotonic devices [3]. In these cases the fibers were formed by melt pulling at temperatures as high as 2000 K. However, there are lowtemperature alternatives for preparation of the fibers, namely, methods that base on sol-gel chemistry [4]. Although sometimes the fibers obtained by these methods have non-circular and/or irregular cross-section, or/and larger diameter (typically some tens of microns) they offer significant advantages, namely they can be easily doped in order to improve certain properties, like conductivity, hardness, flexibility, or give some new properties, like fluorescence. The theoretical and practical limits of the sharpness and diameter of sol-gel fibers have been poorly studied and thus their potential in microphotonics remains obscure. In our earlier works we have shown that high viscosity transition metal alkoxide concentrates can be used as precursors for preparation of ultra-sharp needles [5,6]. We also demonstrated that the needles could be applied as scanning tunneling and near-field photon-imaging microscopy probes. Their advantages are related to their higher refractive index, hardness and florescent properties [7]. The preparation method is sketched in Eq. 1:
M(OR)4 + H2O metal alkoxide OR (-MO-)n
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