Remarkable SERS Detection by Hybrid Cu₂O/Ag Nanospheres

Abstract

Cu 2 O nanospheres (NSs) were synthesized by modifying the glucose reduction method. Based on this method, Cu 2 O/Au (Ag) NSs were further prepared by in situ reduction of HAuCl 4 (via electron beam evaporation of Ag). With Rhodamine 6G (R6G) as probe, the surface-enhanced Raman scattering (SERS) characteristics of the three samples were systematically studied. The experiment results showed that the enhancement factor (EF) of Cu 2 O/Au (Ag) NSs as 1.25 × 10 8 (2.74 × 10 9 ) and the ultralow detection limit (LOD) as 8.07 × 10 –12 (1.13 × 10 –13 ) M for R6G. The excellent performance of SERS may be due to the charge transfer (CT) between metal–semiconductor (MS) molecules and the strong electromagnetic field (E-field) of each hot spot. In addition, discrete dipole approximation (DDA) simulations were performed to simulate the E-field enhancement of the Cu 2 O and Cu 2 O/Au (Ag) NSs in a three-dimensional (3D) configuration. These further supported that the high SERS performance for R6G is because of the powerful E-field coupling between neighboring Au (Ag) NPs and the surface plasmon resonance (SPR) effect. The Cu 2 O/Ag NSs have potential in applications such as biomedicine, food safety, and environmental monitoring because of their high sensitivity and good reproducibility.

Laser Fabricated Cu2O‐CuO/Ag Nanocomposite Films for SERS Application**

“…Introducing Ag NWs into the Cu 2 O‐CuO film makes it possible to form a new charge transfer (CT) system due to the Fermi level of Ag being lower than the surface state energy level of CuO and Cu 2 O. The Fermi energy levels of Ag, CuO, and Cu 2 O are 4.26 eV, [21] 5.3 eV, [31] and 4.84 eV, [21] respectively. When an Ag NW is in contact with a p‐type semiconductor such as CuO or Cu 2 O, the charge distribution is readjusted to reach equilibrium of the Fermi level between Ag and Cu 2 O (or CuO).…”

“…For Ag‐Cu 2 O‐MBA system (see Figure 7a), the electrons of “new Fermi level” of Ag NWs excited by incident laser will inject into the conduction band (CB) of Cu 2 O and migrate towards lower energy levels (the surface‐state energy level E ss ) of Cu 2 O [3,34] . Meanwhile, the electrons on the valence band of Cu 2 O can only transfer to lower energy levels than CB because laser excitation energy (1.96 eV) is lower than the band gap (2.2 eV) [21] . As a result, these photoexcited electrons of Cu 2 O will be transferred into LUMO of the 4‐MBA molecules instead.…”

“…The superior properties such as low cost and enrich photochemical property lead CuO and Cu 2 O to a promising SERS substrate. At present, many efforts have been made to synthesis semiconductor nanomaterials for noble metals/semiconductor composite SERS substrates, like hydrothermal process, [11] glucose reduction method, [21] direct thermal annealing, [22] and plasma processing [23] . For example, thermal annealing is a single step‐approach allowing a controllable synthesis of various morphologies and plasma is even more facile and faster with a lot of opportunities for oxide growth control.…”

Trace Cd2+ Ions Detection on the Flower-Like Ag@CuO Substrate

“…The EF at 610 cm −1 was 3.99 × 10 10 . In comparison with other kinds of materials, we listed their EFs [ 15 , 16 , 17 , 18 , 19 , 29 ] in Table 1 . It was found that the EF of our proposed substrate was the highest, indicating that the Ag@CuO FM substrate achieved excellent SERS performance.…”

“…Consequently, precious metals are not the best choice for surface enhanced Raman scattering (SERS) substrate. It was documented that semiconductor nanomaterials (SNs) such as ZnO [ 15 ], Cu 2 O [ 16 ], and CuO [ 17 , 18 , 19 ] also produce weak SERS signals. The composite structure of precious metals and semiconductor nanomaterials has a better effect on SERS [ 20 ] because it has not only the electromagnetic enhancement effect between precious metal nanoparticles, but also the chemical enhancement one produced by SNs.…”