Electrodeposited Metallic Nanowires as a Scanning Probe Tip
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1206-M18-03
Electrodeposited Metallic Nanowires as a Scanning Probe Tip Munekazu Motoyama1 and Friedrich B. Prinz 1,2 1 Department of Mechanical Engineering, Stanford University Stanford, CA 94305, USA 2 Department of Materials Science Engineering, Stanford University Stanford, CA 94305, USA ABSTRACT This paper describes lateral deformations of electrodeposited Ni nanowires as an atomic force microscope (AFM) probe tip. The maximum end deflections for nanowires to break the elasticity, which beam mechanics indicates, were applicable to our observed results. INTRODUCTION One-dimensional (1-D) nanostructures such as nanowires and nanotubes have attracted a great deal of interest in their unique physical properties such as the electronic conductivity and mechanical strength (1,2). Hence, extensive works have been devoted to applications to not only electronic devices, but also nanoscientific tools. For instance, carbon nanotube (CNT) atomic force microscope (AFM) probes have been already commercialized as probes to obtain higher resolutions in topography measurements (3,4). Previously, we reported the production method of metal nanowire AFM probes by electrochemical deposition using nanoporous templates (5). Excellent electronic conductivity can be expected for a metal nanowire as a scanning probe tip. Moreover, the tip geometry is a needle-like shape. Hence, more laterally confined electric fields can be generated compared to a conventional pyramidal AFM probe tip geometry. Ferromagnetic nanowires can also be expected as a magnetic force microscope (MFM) tip because their magnetization direction is preferentially oriented in their axes (1), thereby having a high sensitivity. Moreover, metal nanowire probe with insulated lateral surface can be used for scanning electrochemical microscopy (SECM) with nanoscopic resolution while retaining the ability as an AFM probe (6). On the other hand, mechanical properties of metal 1-D nanostructures have been of particular interest for many authors. AFM techniques have been used for measurements of mechanical properties of nanowires (7,8,9). Tested nanowires were always distributed on substrate surfaces. Metal nanowire AFM probes may provide us a different approach to measurements of mechanical properties of single metal nanowires. As introduced above, metal nanowire scanning probes have a lot of possibilities in surface science as well as nanomaterials science. Here we consider lateral deformations and bending stiffness of nanowire AFM tip based on classical beam mechanics, following the previous report (5).
THEORY Ni nanowires were electrodeposited through a polycarbonate track-etched membrane fixed at the tip of an AFM probe. The template membrane contained 200-nm-diameter pores. The detailed procedure was reported in previous work (5). A free-standing nanowire can be approximated as having an inverted-conical shape because track-etched polymer membranes typically contain cigar-shaped pores (10), whereby the free ends of halfway-grown nanowires are slightly wider than the fix
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