title: Metal-filled carbon nanotube based optical nanoantennas: bubbling, reshaping, and in situ characterization.
abstract: Controlled fabrication of metal nanospheres on nanotube tips for optical antennas is investigated experimentally. Resembling soap bubble blowing using a straw, the fabrication process is based on nanofluidic mass delivery at the attogram scale using metal-filled carbon nanotubes (m@CNTs). Two methods have been investigated including electron-beam-induced bubbling (EBIB) and electromigration-based bubbling (EMBB). EBIB involves the bombardment of an m@CNT with a high energy electron beam of a transmission electron microscope (TEM), with which the encapsulated metal is melted and flowed out from the nanotube, generating a metallic particle on a nanotube tip. In the case where the encapsulated materials inside the CNT have a higher melting point than what the beam energy can reach, EMBB is an optional process to apply. Experiments show that, under a low bias (2.0-2.5 V), nanoparticles can be formed on the nanotube tips. The final shape and crystallinity of the nanoparticles are determined by the cooling rate. Instant cooling occurs with a relatively large heat sink and causes the instant shaping of the solid deposit, which is typically similar to the shape of the molten state. With a smaller heat sink as a probe, it is possible to keep the deposit in a molten state. Instant cooling by separating the deposit from the probe can result in a perfect sphere. Surface and volume plasmons characterized with electron energy loss spectroscopy (EELS) prove that resonance occurs between a pair of as-fabricated spheres on the tip structures. Such spheres on pillars can serve as nano-optical antennas and will enable devices such as scanning near-field optical microscope (SNOM) probes, scanning anodes for field emitters, and single molecule detectors, which can find applications in bio-sensing, molecular detection, and high-resolution optical microscopy.
authors.affiliation: Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Fan
authors.forename: Xinyong
authors.initials: X
authors.lastname: Tao
authors.forename: Xudong
authors.initials: X
authors.lastname: Cui
authors.forename: Xudong
authors.initials: X
authors.lastname: Fan
authors.forename: Xiaobin
authors.initials: X
authors.lastname: Zhang
authors.forename: Lixin
authors.initials: L
authors.lastname: Dong