Tuning of plasmon resonance of gold nanorods by controlled etching

Production of gold nanorods with preset geometric characteristics is of fundamental importance for many fields of application, because even slight variations in their absolute sizes or axial ratio may noticeably change the positions and intensities of the maxima in the resonance absorption and scattering of light. In this work, a method has been proposed for tuning the plasmon resonance of gold nanorods in a wide wavelength range via their controlled etching along the major axis with a complex of Au 3+ ions and cetyltrimethylammonium bromide. The synthesized gold nanorods possess longitudinal plasmon resonance at a wavelength of 920 nm, an average thickness of 16 nm, and an axial ratio of about 5. A chloroauric acid solution added to a colloid of the nanorods etches their ends and decreases the axial ratio thereof, while their thickness remains unchanged, thereby shifting the longitudinal plasmon resonance toward shorter wavelengths. The axial ratio of resulting nanoparticles and the position of plasmon resonance are entirely determined by the ratio between gold atoms in the initial nanorods and gold ions in the solution. This makes it possible to vary the axial ratio from 5 to 1 and finely tune plasmon resonance in a wavelength range from 920 to 520 nm. It has also been shown that the proposed method can be used for controlled etching of gold nanospheres.