Controlled Layer-by-Layer Formation of Ultrathin Oxide Films on Silver Island Films for Surface-Enhanced Raman Scattering Measurement

Abstract

Methods for the controlled deposition of ultrathin metal oxide layers onto silver island films for surface-enhanced Raman scattering (SERS) measurements are reported. Two related deposition techniques are explored for thin film growth: a surface sol-gel method and atomic layer deposition. Both methods exhibit excellent control of the deposited film thickness to atomic level precision while conformally coating the complex structures found in silver island films. Coating of metal oxide films onto silver substrates provides a method for monitoring the distance dependence of SERS enhancements and offers a platform for exploring adsorption and interaction of analytes on dielectric surfaces. Analysis of the distance dependence of the Raman signal with increasing film thickness yields estimated silver particle sizes that are in agreement with microscopy, which is consistent with the layer-by-layer growth mechanism of uniform metal oxide films on the silver substrate. These methods can be easily extended to grow a variety of laminar or mixed metal oxide films for the exploration of interfacial phenomena.

Ag Nanorods Coated with Ultrathin TiO2 Shells as Stable and Recyclable SERS Substrates

“…It has been long recognized that the Raman enhancement of metal nanostructures depends strongly on the distance between metal surfaces and adsorbed molecules 19 42 43 . We therefore investigated the TiO 2 layers’ effect on the sensitivity of SERS substrates, using crystal violet (CV) as a model analyte.…”

“…In addition to sensitivity and stability, the recyclable property of SERS substrates is also meaningful for routine applications 19 43 45 . In our study, the self-cleaning performances of Ag@TiO 2 NRs were investigated through UV light-assisted photocatalytic bleaching of organic molecules adsorbed on the substrates.…”

Silver Nanorods Wrapped with Ultrathin Al2O3 Layers Exhibiting Excellent SERS Sensitivity and Outstanding SERS Stability

“…For example, coating Ag islands with Al 2 O 3 films could maintain their SERS activity for a period of 34 days 29 ; coating Ag nanorods with TiO 2 thin films by glancing angle deposition (GLAD) technique could sustain their morphology and stabilize the SERS performance at 100 °C (above which coalescence of Ag nanorods was observed) 31 . However, 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. It is therefore highly demanded to find ways to deposit protective layers that completely cover Ag nanostructures at relatively low temperatures to maintain their morphological features, with a precise control of the coating thickness to prohibit sharply decreasing the SERS sensitivity but meanwhile thick enough to make them robust against temperature.…”

Ag Nanorods-Oxide Hybrid Array Substrates: Synthesis, Characterization, and Applications in Surface-Enhanced Raman Scattering

“…Several approaches have been exploited to produce oxide layers over AgNR arrays. Because SERS is a highly localized effect that depends significantly on the distance between metal surfaces and target molecules [ 62 , 63 , 64 ], the oxide shells should be thin enough so as not to eliminate the SERS enhancement. In this regard, atomic layer deposition (ALD) holds great potential in the oxide formation of AgNRs-oxide hybrid substrates.…”