Directed Assembly of Nanoelements Using Electrostatically Addressable Templates
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Directed Assembly of Nanoelements Using Electrostatically Addressable Templates Xugang Xiong1, Prashanth Makaram1, Kaveh Bakhtari1, Sivasubramanian Somu1, Ahmed Busnaina1, Jason Small1, N. McGruer1 and Jingoo Park2 1 Northeastern University, Boston, MA 02115, U.S.A. 2 Hanyang University, Ansan, 425-791, Korea ABSTRACT Directed assembly of nanoparticles and single wall carbon nanotubes (SWNTs) using electrostatically addressable templates has been demonstrated. Nanoparticles down to 50 nm are assembled on the Au micro and nanowires of the templates in a DC and AC electric fields. The nanoparticles can be assembled in monolayers and thicker layers. Single wall carbon nanotubes (SWNTs) are also assembled without alignment on Au wires using the nanotemplate. As the size of the template wires is reduced to nanoscale dimensions, an AC electric field proves to be more effective for nanoparticle assembly than a DC electric field. INTRODUCTION Manufacturing using nanoparticles or carbon nanotubes as building blocks to construct nano-structures or devices requires massive high rate/high volume assembly strategies. One of the fundamental problems is how to assemble oriented nanoelements onto predefined locations with accurate control. Single particle manipulation with a SPM (scanning probe microscope) tip can be precise [1,2], but it is slow and not suitable for large scale assembly as required for nanomanufacturing. Directed self-assembly is a promising technique for making nano-structures or devices over large scale. The assembly process involves many forces such as electrostatic, van der Waals, hydrophobic or hydrophilic interactions. Nanoelements need to be mobile in order to be transported under such interactions in liquid or gas phases. Electric fields have been used to manipulate nanoparticles or carbon nanotubes with partial success [3-6]. In this paper, we present an electric field (DC or AC field) assisted approach for directed assembly of nanoelements using templates (Figure 1). Nanoparticles were assembled using electrophoresis in dc assembly. The dominant force in AC field assisted assembly is dielectrophoresis (DEP) force, which has been studied extensively elsewhere [5-11]. We used lithographically fabricated metallic nanowires as templates for the directed assembly of nanoparticles. a)
b)
Figure 1. Schematic of field-assisted self-assembly of nanoparticles using (a) DC field and (b)
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AC field. EXPERIMENTAL Nanotemplates were fabricated using e-beam lithography techniques with nanowires widths down to 50 nm. Microtemplate electrodes (6 nm Cr/40 nm Au in thickness) were fabricated on Si/SiO2 wafer using standard lithographic processes. The width and spacing of these electrodes were 2 µm and 70 µm, respectively. Fluorescent polystyrene latex (PSL) nanoparticles (300nm and 50nm) from Duke Scientific, Inc. were used in these experiments. In DC field assembly, particles suspensions were diluted in DI water with a concentration of ~7.1×108 particles/mL for 300nm PSL and ~9.8×1010 par
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