Abstract
Silver nanostructures have been considered as promising substrates for surface-enhanced Raman scattering (SERS) with extremely high sensitivity. The applications, however, are hindered by the facts that their morphology can be easily destroyed due to the low melting points (~100 °C) and their surfaces are readily oxidized/sulfured in air, thus losing the SERS activity. It was found that wrapping Ag nanorods with an ultrathin (~1.5 nm) but dense and amorphous Al2O3 layer by low-temperature atomic layer deposition (ALD) could make the nanorods robust in morphology up to 400 °C, and passivate completely their surfaces to stabilize the SERS activity in air, without decreasing much the SERS sensitivity. This simple strategy holds great potentials to generate highly robust and stable SERS substrates for real applications.
Highlights
Silver nanostructures have been considered as promising substrates for surface-enhanced Raman scattering (SERS) with extremely high sensitivity
A drawback of this coating approach is the giant decrease in SERS sensitivity, which is caused by the coating layers that separate the target molecules from Ag nanostructures[29,33,34], and by the possible morphology changes of silver created during coating process
In order to find an appropriate deposition temperature at which morphology changes of Ag nanorods can be avoided during atomic layer deposition (ALD) processing, we heated the as-deposited Ag nanorods in the ALD chamber at temperatues of [50, 80] and 100 °C for 8 minutes, separately, without purging the ALD precursors
Summary
Silver nanostructures have been considered as promising substrates for surface-enhanced Raman scattering (SERS) with extremely high sensitivity. We employed atomic layer deposition (ALD) technique to prepare ultrathin Al2O3 films that fully wrapping Ag nanorods at a temperature of 50 °C, and investigated the coating influences on the morphological stability of Ag nanorods at elevated temperatures in air, as well as their SERS sensitivity and activity at ambient conditions.
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