Survey of Materials for Nanoskiving and Influence of the Cutting Process on the Nanostructures Produced

Abstract

This paper examines the factors that influence the quality of nanostructures fabricated by sectioning thin films with an ultramicrotome ("nanoskiving"). It surveys different materials (metals, ceramics, semiconductors, and conjugated polymers), deposition techniques (evaporation, sputter deposition, electroless deposition, chemical-vapor deposition, solution-phase synthesis, and spincoating), and geometries (nanowires or two-dimensional arrays of rings and crescents). It then correlates the extent of fragmentation of the nanostructures with the composition of the thin films, the methods used to deposit them, and the parameters used for sectioning. There are four major conclusions. (i) Films of soft and compliant metals (those that have bulk values of hardness less than or equal to those of palladium, or e500 MPa) tend to remain intact upon sectioning, whereas hard and stiff metals (those that have values of hardness greater than or equal to those of platinum, or g500 MPa) tend to fragment. (ii) All conjugated polymers tested form intact nanostructures. (iii) The extent of fragmentation is lowest when the direction of cutting is perpendicular to the exposed edge of the embedded film. (iv) The speed of cutting-from 0.1 to 8 mm/s-has no effect on the frequency of defects. Defects generated during sectioning include scoring from defects in the knife, delamination of the film from the matrix, and compression of the matrix. The materials tested were: aluminum, titanium, nickel, copper, palladium, silver, platinum, gold, lead, bismuth, germanium, silicon dioxide (SiO 2 ), alumina (Al 2 O 3 ), tin-doped indium oxide (ITO), lead sulfide nanocrystals, the semiconducting polymers poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV), poly(3-hexylthiophene) (P3HT), and poly(benzimidazobenzophenanthroline ladder) (BBL), and the conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS).

Free-standing NiTi alloy nanowires fabricated by nanoskiving

“…28 When nanoskiving was undertaken for pure Ni and pure Ti, the Ti nanowires typically fragmented whereas the Ni nanowires did not readily fragment so that intact Ni nanowires were produced that were markedly longer than Ti nanowires. 2,5 The structure of Ti is hexagonal close-packed (HCP) and the structure of Ni is face-centered cubic (FCC). The inherent number of available slip systems in Ti is three and there are twelve for Ni.…”

Bottom‐Up Molecular Tunneling Junctions Formed by Self‐Assembly

“…It combines the deposition of thin film with the mechanical sectioning of thin films embedded in a polymer matrix by ultramicrotomy. [128][129][130] It involves three major steps: 1) depositing a thin metallic, semiconducting, or polymeric film onto a substrate; 2) embedding the film in an epoxy or thiolene polymer block; [131] and 3) sectioning the block into slabs using an ultramicrotome, which is pictured in Figure 11. The operation is based on the controlled mechanical advance of a sample arm that holds the sample to be sectioned.…”

Single-Nanowire strain sensors fabricated by nanoskiving

“…In this technique, the offcuts (the “slabs”) contain consecutive cross sections (quasi copies) of the parent structure. This process is highly amenable to the reproducible fabrication of long, but thin nanowires ( h, w < 150 nm), i.e., by sectioning thin films [4–6]. After sectioning the block, the slabs float on a water bath where they can be harvested in a thin film of water suspended in a loop tool, or lifted out from underneath the surface of the water using a flat substrate.…”

“…Nanoskiving has the useful characteristic that it converts films, which are thin in the vertical dimension, into wires and other structures that are thin in the lateral dimension [7]. Moreover, it is possible to place the fabricated objects on any surface that can be wet by water [6]. The ease of use (no lithography) and length of the nanowires make nanoskiving favorable compared chemical synthesis, [26] synthesis in templates, [27] and lithographic techniques [28].…”