Ordered assemblies of nanoparticles, such as nanorods or nanoprisms, can have useful optoelectronic properties. However, covering relatively large areas with such neatly aligned nanoparticles is still challenging.

Feng Bai, Henan University and Collaborative Innovation Center of Nano Functional Materials and Applications, Kaifeng, China, Hongyou Fan, The University of New Mexico and Sandia National Laboratories, Albuquerque, USA, and colleagues have made large-area arrays of vertically aligned gold nanorods (GNRs). The team used nanorods of uniform size, coated with cetylmethylammonium bromide (CTAB) and sodium oleate (NaOL). A suspension of the GNRs in water was then prepared and the water was slowly evaporated under a controlled external humidity of 96 %. After drying, the surfactant was washed off and the resulting GNR arrays were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD).

The GNRs were hexagonally close packed in macroscopic, homogeneous arrays with diameters of about 2 mm. The team used the GNR arrays in surface-enhanced Raman scattering (SERS) experiments and found that they have excellent detection sensitivity and reproducibility. According to the researchers, the method can be extended to other nanoparticle systems.

• Fabrication of Large-Area Arrays of Vertically Aligned Gold Nanorods,
  Wenbo Wei, Yuru Wang, Juanjuan Ji, Shanshan Zuo, Wentao Li, Feng Bai, Hongyou Fan,
  Nano Lett. 2018.
  https://doi.org/10.1021/acs.nanolett.8b01584