Three-dimensional interconnected silica nanotubes templated from hyperbranched nanowires.

Figure 1. Flowchart of the fabrication process for interconnected silica nanotubes from hyperbranched PbSe nanowires. Inorganic nanofluidic devices, such as nanopores, nanochannels, and nanotubes (NTs) have been actively studied in bioseparation, bioanalysis, fluidic transistors, power generation, and fast mass transport. Compared to biological nanopores, inorganic nanofluidic devices have been demonstrated to be robust, to have easily tuned surfaces and to be integrable into arrays. One of the most powerful nanofluidic device fabrication methods is templating against a porous membrane or chemically synthesized or lithographically patterned nanowires (NWs). NTs or nanochannels made in this way have controllable dimensions, with diameters down to several nm and lengths up to tens of mm. Herein, we exploit hyperbranched PbSe NWs as templates to produce 3D interconnected hyperbranched silicon dioxide (silica) NTs by simple coating and etching steps. The obtained NTs with a thick enough shell retain the orientation of the original hyperbranched arrays and are either parallel or perpendicular to each other. These hyperbranched NTs afford interesting opportunities for constructing new 3D nanofludic devices. The fabrication process for silica hyperbranched NTs is shown in Figure 1. Hyperbranched PbSe NWs were grown on Si (100) substrates using vapor transport growth. Each hyperbranched PbSe NW exhibits 908 orientation between branches because of the epitaxial relationship. The details of hyperbranched NW growth can be found elsewhere. The samples with hyperbranched NWs were then coated by plasma enhanced chemical vapor deposition (PECVD) of silica. The deposition temperature was 350 8C. The growth rate for a silicon oxide layer based on thin-film deposition on silicon (100) substrate is around 6 nm min . Silica layers with different thickness (30 nm and 80 nm) were deposited on different samples of hyperbranchedNWs to evaluate the effect of silica thickness on the morphologies of the final silica NTs.