Effect of TiO₂ arrays on surface enhanced Raman scattering (SERS) performance for Ag/TiO₂ substrates

Abstract

Ag/TiO2 nanostructure arrays were constructed on fluorine-doped tin oxide (FTO) via a controllable hydrothermal route and a magnetron sputtering method with a variety of TiO2 arrays decorated by Ag nanoparticles. Effects of different TiO2 arrays on the microstructure, composition, and optical properties of the samples were revealed. As surface enhanced Raman scattering (SERS) active substrates, we discussed the sensitivity and reproducibility of Ag/TiO2 nanostructure arrays for Rhodamine 6G (R6G) molecule detection. It was found that TiO2 nanosheet (TiO2(S)) array as a supporting made Ag nanoparticles have a uniform and continuous distribution, which achieved much higher SERS signals. The obtained Ag/TiO2(S) substrate had an improved enhancement factor of 4.31 × 105 compared with the other Ag/TiO2 nanostructure arrays of nanorods, nanotubes, and nanotrees. Furthermore, Ag/TiO2(S) active substrate showed good reproducibility with low relative standard deviation values. Such a remarkable SERS activity could be due to the synergistic effect of electromagnetic enhancement and charge transfer enhancement. Moreover, the TiO2(S) array with high-exposed {101} facets provided a large adhesion area and generated a strong interaction with external atoms, which would produce high-density ‘hot spots’ of SERS.

Facile Method to Fabricate Cactus-like Ag NPs/CuO/Cu2O Nanocomposites for Recyclable SERS Detection of Trace Carbendazim Residues

“…The light absorption properties of the as-prepared substrates were tested by the UV–vis absorption spectra. As shown in Figure A, except for the Cu foam, all of the CACNs show a strong visible light absorption in the range from 400 to 830 nm, which is attributed to the narrow band gap of both Cu 2 O and CuO, as well as the local surface plasmon resonance of Ag NPs. , Moreover, an absorption peak centered at ∼484 nm could be observed in the UV–vis spectrum of 10-CACN, as indicated within the black circle, due to the localized surface plasma resonance effect of Ag NPs. , Particularly, 10-CACN exhibits optimal absorption properties even at the near-infrared region, which could be attributed to high-density CuO/Cu 2 O nanothorns and Ag NPs. Moreover, the band gap of the CACN can be determined based on the Tauc equation ((α h ν) 2 vs h ν) (eq ), as shown in Figure B. false( α italichv false) n = A ( hv ‐ E g ) where α is the absorption coefficient that can be obtained from UV–vis spectra, h v and E g represent the photon energy and the optical band gap energy, respectively, n equals 1/2 for direct transition and 2 for indirect transition.…”

“…As shown in Figure 8A, except for the Cu foam, all of the CACNs show a strong visible light absorption in the range from 400 to 830 nm, which is attributed to the narrow band gap of both Cu 2 O and CuO, as well as the local surface plasmon resonance of Ag NPs. 32,55 Moreover, an absorption peak centered at ∼484 nm could be observed in the UV−vis spectrum of 10-CACN, as indicated within the black circle, due to the localized surface plasma resonance effect of Ag NPs. 69,70 Particularly, 10-CACN exhibits optimal absorption properties even at the near-infrared region, which could be attributed to high-density CuO/Cu 2 O nanothorns and Ag NPs.…”

“…Three-dimensional (3D) nanostructures can greatly improve SERS sensitivity due to their large specific surface area for adsorbing more analyte molecules and a lot of hot spots along the three-dimensional structure. ,, Therefore, the development of 3D metal/semiconductor nanocomposites is an effective strategy to obtain SRES substrates with high sensitivity and recyclability. Many studies on the fabrication of 3D metal/semiconductor recyclable SERS substrates have been reported recently, including Au or Ag NPs/TiO 2 , − − Au or Ag NPs/ZnO, − Au or Ag NPs/MoS 2 , ,− ,− Au or Ag NPs/g-C 3 N 4 , − − and Au or Ag NPs/CuO and/or Cu 2 O. ,− Here, we summarize the relevant published work, involving the fabrication methods, probe molecules, and relevant parameters, as given in Table . It can be seen that although the as-prepared SERS substrates have been applied for the detection of various molecules with high sensitivity, the fabrication methods are relatively complex, where two steps at least are required, generally including (i) fabricating the semiconductor nanostructures and (ii) decorating the Au or Ag NPs onto the semiconductor nanostructures via physical or chemical processes.…”

Regulating thermal diffusion of gold thin films at solid-state interfaces for site-selective decoration of gold nanoparticles on titania nanotubes as an efficient SERS sensing platform

“…26,27 It is evident that the morphology, size, density of Au nanoparticles, and the hybrid pattern with semiconductors have a great influence on the hotspot region and SERS activity of the composite substrate. 28 In view of the shadow effect and high curvatures of TiO 2 nanotubes in the array, the coating of a uniform Au thin film is still challenging. Besides, the Au nanoparticles formed by dewetting of the Au thin film cannot be distributed closely enough to form a large number of hot spots throughout the TiO 2 nanotube array.…”

Unique gap-related SERS behaviors of p-aminothiophenol molecules absorbed on TiO2 surface in periodic TiO2/Ni nanopillar arrays

“…Despite many reports about the sensitive detection with metal/semiconductor composite substrates, the research on regulation and controlling of semiconductors in SERS substrates is still far behind that of metals. Fortunately, in recent years, researchers have found that semiconductors also can be modulated in some parameters (size [23][24][25][26][27], thickness [28][29][30][31][32] and morphology [27,33]), and hence to promote their CT resonance enhancement and further optimize their SERS activities [26,34], just like the regulation of noble metals [35,36]. For example, Lombardi et al [23] optimized the size of ZnSe nanoparticles and obtained an enhancement factor of 2 × 10 6 .…”