Thermal stability of mesoporous silica-coated gold nanorods with different aspect ratios

The effect of different temperatures (up to 900 degrees C) on the morphology of mesoporous silica-coated gold nanorods was systematically investigated. Gold nanorods with different aspect ratios (AR ranging from 2.5 to 4.3) were coated with a 15 nm thick mesoporous silica shell. Silicon supported monolayers of the particles were annealed in the temperature range of 300-900 degrees C. The resulting changes in particle morphology were investigated using scanning electron microscopy and visible wavelength extinction spectroscopy. The silica coating generally improved the stability of the nanorods from ca. 250 degrees C by several hundreds degree Celsius. For nanorods with AR < 3 the shape and the aspect ratio change is only moderate up to 700 degrees C. At 900 degrees C these nanorods became spherical. For nanorods with AR>3, lower stability was found as the aspect ratio decrease was more significant and they transformed into spherical particles already at 700 degrees C. It was confirmed by investigating empty silica shells that the observed conformal change of the shell material when annealing core/shell particles is dictated by the deformation of the core particle. This also implies that a significant mechanical stress is exerted on the shell upon core deformation. In accordance with this, for the highest aspect ratio (AR similar to 4) nanorod the shell breaks up at 900 degrees C and the gold cores were partially released and coalesced into large spherical particles. (C) 2014 Elsevier B.V. All rights reserved.