Abstract
High-temperature surface-enhanced Raman scattering (SERS) sensing is significant for practical detections, and pinhole-containing (PC) metal@oxide structures possessing both enhanced thermal stability and superior SERS sensitivity are served as promising SERS sensors at extreme sensing conditions. Through tuning the Al2O3 precursors’ exposure time during atomic layer deposition (ALD), Al2O3 shells with different amount of pinholes were covered over Ag nanorods (Ag NRs). By virtue of these unique PC Ag@Al2O3 nanostructures, herein we provide an excellent platform to investigate the relationship between the pinhole rate of Al2O3 shells and the melting behavior, high-temperature SERS performances of these core-shell nanostructures. Pinhole effect on the melting procedures of PC Ag@Al2O3 substrates was characterized in situ via their reflectivity variations during heating, and the specific melting point was quantitatively estimated. It is found that the melting point of PC Ag@Al2O3 raised along with the decrement of pinhole rate, and substrates with less pinholes exhibited better thermal stability but sacrificed SERS efficiency. This work achieved highly reliable and precise control of the pinholes over Al2O3 shells, offering sensitive SERS substrates with intensified thermal stability and superior SERS performances at extreme sensing conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1390-0) contains supplementary material, which is available to authorized users.
Highlights
High-temperature surface-enhanced Raman scattering (SERS) detection is a vital part for practical sensing, which can be employed for monitoring many in situ reactions, e.g., thermal crystallization [1], structural variations [2, 3], and chemical reactions [4, 5] at elevated temperatures
To explore the relationship between the exposure time of atomic layer deposition (ALD) precursors and Al2O3 pinhole rate, we introduced acridine, a SERS probe molecule that can directly interact with Ag surface instead of Al2O3 layers [11–13]
Because of the saturation of 1 × 10−2 M acridine over uncoated Ag Ag nanorods (NRs), we further utilized the acridine spectra from different substrates to estimate the pinhole rate of Al2O3 shells, via dividing acridine Raman intensity at 1403 cm−1 from PC Ag@Al2O3 substrates by that from uncoated Ag nanorods (Ag NRs)
Summary
High-temperature surface-enhanced Raman scattering (SERS) detection is a vital part for practical sensing, which can be employed for monitoring many in situ reactions, e.g., thermal crystallization [1], structural variations [2, 3], and chemical reactions [4, 5] at elevated temperatures. Core-shell nanostructures of metal core covered with protective oxide layer have been proposed as good SERS substrates for high-temperature Raman sensing [2, 3, 5, 8–10]. Up to now, the accurate control and measurements of the oxide pinhole rate, as well as the comprehensive investigation of the melting procedures and thermal stability of PC metal@oxide substrates, have not been investigated in detail. In this regard, we introduced atomic layer deposition (ALD) technique to cover Ag NRs with Al2O3 shells (Ag@Al2O3) of different pinhole amount and experimentally analyzed the Al2O3 pinholes’ influence on the melting behavior of PC Ag@Al2O3 substrates. The melting process of PC Ag@Al2O3 was monitored via their reflectivity
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