Abstract
Direct observation of the surface-enhanced Raman scattering (SERS) of molecules adsorbed on nano-sized zirconia (ZrO2) substrates was first reported without the need for the addition of metal particles. It was found that ZrO2 nanoparticles can exhibit unprecedented Raman signal enhancements on the order of 103 for the probe molecule 4-mercaptobenzoic acid (4-MBA). The dramatic effect of the calcination temperature on the ZrO2 nanoparticles was also investigated. The ZrO2 nanoparticles with the particle diameter of 10.5 nm, which were prepared by calcination at a temperature of 500°C, have the highest SERS activity. A comparison between the experimental and calculation results indicates that charge transfer (CT) effects dominate the surface enhancement. The plentiful surface state of ZrO2 active substrate that is beneficial to CT resonance occurs between molecules and ZrO2 to produce a SERS effect. The CT process depends, to a large extent, on the intrinsic properties of the modifying molecules and the surface properties of the ZrO2. This is a new SERS phenomenon for ZrO2 that will expand the application of ZrO2 to microanalysis and is beneficial for studying the basic properties of both ZrO2 and SERS.
Highlights
IntroductionThe large surface-enhanced Raman scattering (SERS) enhancement observed in metals and semiconductors is explained by the vibrational coupling of various resonances in the molecules of the semiconductor system, such as surface plasmons, excitons, charge transfer (CT), and molecular resonance (Yin et al, 2010; Li et al, 2011; Wang and Chen, 2011; Jiang et al, 2013; Wang et al, 2013, 2014, 2016; Huang et al, 2014; Kadkhodazadeh et al, 2014; Mogensen and Kneipp, 2014; Shiohara et al, 2014; Zhao et al, 2014; Shen et al, 2015; Scott and Carron, 2016; Fu et al, 2019)
The results show that the surface-enhanced Raman scattering (SERS) spectrum of 4-mercaptobenzoic acid (4-MBA) on ZrO2 is mainly due to the contribution of the charge transfer (CT) mechanism, and the intrinsic properties of the adsorbed molecules and the surface properties of the semiconductor have a significant effect on SERS
The plentiful surface state of the ZrO2 active substrate is beneficial for the occurrence of CT resonance between molecules and the ZrO2 to produce a SERS effect
Summary
The large surface-enhanced Raman scattering (SERS) enhancement observed in metals and semiconductors is explained by the vibrational coupling of various resonances in the molecules of the semiconductor system, such as surface plasmons, excitons, charge transfer (CT), and molecular resonance (Yin et al, 2010; Li et al, 2011; Wang and Chen, 2011; Jiang et al, 2013; Wang et al, 2013, 2014, 2016; Huang et al, 2014; Kadkhodazadeh et al, 2014; Mogensen and Kneipp, 2014; Shiohara et al, 2014; Zhao et al, 2014; Shen et al, 2015; Scott and Carron, 2016; Fu et al, 2019). Nano-sized zirconium dioxide (ZrO2) is one of the most important materials for the preparation of nano-ceramics, and it can prepare ceramic components with various functions (Li et al, 2017). It has applications and developments in solid oxide fuel cells, thermal barrier coating materials, catalyst carriers, lubricant additives, medical, gas sensitive, and wear resistant materials (Duan et al, 2017; Gan et al, 2017; Long et al, 2017; Xu et al, 2017; Wang et al, 2019). As a new type of high-performance ceramics, the use of highly sensitive SERS technology with in-situ characterization advantages to study the size effect of nano-sized ZrO2 is expected to promote the better performance of nano-ceramic materials to enable the emergence of new properties and functions
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