Abstract
The characterisation of metallic nano-structures is of great importance as their optical properties are strongly dependent on their size and shape. Inaccurate size or shape characterisation can result in misleading measurements in applications such as bio-imaging and sensing. Characterisation techniques such as dynamic light scattering, electron microscopy or atomic force microscopy are commonly used; however, performing sub-surface measurements (inside semi-transparent objects) or in liquid media are very challenging. Here, we use time-resolved pump-probe spectroscopy to characterise the size and shape of metallic nano-structures in a water surrounding medium by using their vibrational modes. We show that this technique can achieve size measurements with a precision of 3 nm for the largest nano-structures which are in agreement with electron microscopy images. Furthermore, we demonstrate the ability to probe individual nano-structures despite being located in the same optical point spread function (PSF). Combining the high precision and sub-optical measurements provided by this technique with the ability to insert metallic nano-structures inside biological samples might open a way to perform 3D characterisation measurements.
Highlights
IntroductionMetallic nano-structures have been widely applied in bioimaging, sensing and nonlinear optics.[1,2,3,4,5] Accurate characterisation of these nano-structures is important since their optical and electronic properties are strongly dependent on their size and shape.[6,7] Characterisation methods such as extinction measurements,[8,9,10] direct imaging by scanning and transmission electron microscopy (SEM, TEM)[11,12,13] and atomic force microscopy (AFM)[14,15] are commonly used
Measuring nano-structures inside a semi-transparent object or surrounded by a liquid medium is challenging as a vacuum environment and conductive substrates are needed by electron microscopy and sub-surface measurements cannot be performed by atomic force microscopy (AFM)
We show that the size and shape of metallic nano-structures can be characterised by using time-resolved pump–probe spectroscopy delivered through a conventional optical microscope
Summary
Metallic nano-structures have been widely applied in bioimaging, sensing and nonlinear optics.[1,2,3,4,5] Accurate characterisation of these nano-structures is important since their optical and electronic properties are strongly dependent on their size and shape.[6,7] Characterisation methods such as extinction measurements,[8,9,10] direct imaging by scanning and transmission electron microscopy (SEM, TEM)[11,12,13] and atomic force microscopy (AFM)[14,15] are commonly used. We show that the size and shape of metallic nano-structures can be characterised by using time-resolved pump–probe spectroscopy delivered through a conventional optical microscope. The measured vibrational modes are related to the diameter, length and width of each individual
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