Intense Plasmon-Induced Magneto-Optical Activity in Substoichiometric Tungsten Oxide (WO3–x) Nanowires/Nanorods

In this article, intense magneto-optical (MO) activity is demonstrated for plasmonic tungsten oxide WO 3– x nanowires/nanorods by magnetic circular dichroism (MCD) spectroscopy. One-dimensional WO 3– x nanoarchitectures are prepared by a solvothermal process using WCl 6 and pure ethanol or an ethanol/PEG (polyethylene glycol) mixture, and their crystalline phases are identified as monoclinic W 18 O 49 (WO 2.72 ). Some of them tend to form urchinlike assemblies, but the presence of PEG makes not only the lengths of nanowires very short (to form nanorods) but also the sizes of assemblies rather small. We observe a broad absorption band ranging from visible to near-IR (NIR) region, but most impressively, an intense MCD response is found for the nanowires/nanorods, which can substantially be ascribed to circular modes of localized surface plasmon of one-dimensional W 18 O 49 nanostructures. The MO activity, defined as the maximum MCD amplitude normalized to absorption, exceeds that of typical Ag nanospheres that are one of the best magnetoplasmonic nanomaterials with very high performance. We believe that such anisotropic oxide nanomaterials with strong plasmon-induced MO activity will be highlighted as potential substitutes for noble metals and will expand promising new applications in the fields of semiconductor-based nanophotonics and MO devices.