Controlled Growth of Aligned Polymer Nanowires

Abstract

We have developed a one-step method to fabricate large-scale polymer nanowire (PNW) arrays of any organic materials, with a good control over the density and length. The PNWs are formed by ion etching a polymer film that is covered with a thin layer of metal nanoparticles, which serves as the "mask" for creating the surface roughness required for creating the PNWs. Our study demonstrates an effective approach for creating functional organic NW arrays for applications in sensors, electronics, biomaterials, and energy materials.Nanowires (NW) of semiconductor and functional oxides are the fundamental units for fabricating nanoscale devices for photonics, electronics, sensors, bioscience, and energy science. 1-7Growth of orientation-, dimensionality-, and location-controlled NWs is the key for controlling the performance of nanodevices toward nanomanufacturing.8-10 NW arrays of inorganic materials are usually grown by physical approach via a vapor-liquid-solid (VLS) 11 or vapor-solid-solid (VSS) 12,13 process at high temperature and a wet chemical approach using solvent-thermal or hydrothermal process.14-16 The alignment of inorganic NWs is usually achieved using either catalyst-guided growth together with the epitaxial relationship with the substrate or the template technique. 17,18 Polymer-based NWs have potential applications in sensors, organic light-emitting diodes (OLEDs), field-effect transistors (FETs) and solar cells, but the growth of aligned organic NW arrays of a general material is challenging. [19][20][21][22] Although approaches have been demonstrated using an anodic aluminum oxide (AAO) template-based technique, 23 the alignment of the NWs after removing the template is rather distorted and bunched. 24,25 A new technique is required to fabricate polymer NW (PNW) arrays with good control over orientation, dimensionality, and location.Recently, we have demonstrated a novel technique for fabrication of patterned and aligned polymer nanowire arrays on a wafer-level substrate of any material.26 By creating a designed pattern on a spin-coated polymer film using techniques such as stamping or microtip writing, plasma etching results in the formation of aligned PNW arrays distributed according to the pattern. It is suggested that the formation mechanism of the NWs is due to a dependence of the size of the ion sample interaction volume on the local incident angle of the ion at the modulated surface. This establishes a new technique for largescale fabrication of organic NW arrays.In this paper, we expand the technique for fabricating aligned NWs of any polymer with a control over the growth density and length to meet the needs of future device fabrications.Instead of using surface roughness first created on the polymer film surface, we deliberately sputtered a thin layer of metal nanoparticles on the substrate, which serve as the "nanomasks" for ion irradiation, resulting in the initial roughness for further etching. Polymer NWs to be presented include but are not limited to PMMA (poly(methyl methacrylate)), ...

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