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Silver nanodecahedra and nanoplates were successfully fabricated using a simple solution method, where silver nitrate (AgNO3) was reduced with sodium borohydride (NaBH4) at melting ice temperature. Green light-emitting diode (green LED, wavelength λG = 520 nm) was irradiated into the reaction system to control the morphology of the product. The synthetic procedure was a combination of two processes including the formation of silver seeds and subsequent photomediated crystal growth. This article also presents a mechanism study of the photomediated growth of silver nanoplates and nanodecahedra. In these processes, citrate ions were used as a morphology-controlled reagent and polyvinyl pyrrolidone as a capping agent. The growth process was evaluated by dynamic light scattering and ultraviolet/visible spectra measurements. The obtained silver nanoparticles (AgNPs) possessed various shapes, including triangular, truncated triangular, hexagonal and decahedron depending on the time duration of LED irradiation. Triangular nanoplates or decahedral nanoparticles (80–100 nm) were obtained when the silver colloid was exposed to green LED irradiation for different times (30 min—76 h). The average width and thickness of such nanoparticles were estimated to be approximately 80 nm and 20 nm, respectively. The technology uniqueness in this work is that we can change the morphology of silver from plate to decahedron via prolonging the LED illumination period from 140 min to 76 h instead of changing the light wavelength or temperature of the reaction solution. The surface-enhanced Raman scattering (SERS) experiment was carried out to measure Rhodamine 6G (R6G) concentrations plated on the silicon substrates. Silver nanodecahedra can detect the low concentration of R6G (10−8 M), while silver nanoplates can detect a higher R6G concentration of 10−6 M. Silver nanodecahedra could be used as an effective SERS substrate for ultrasensitive detection. [ABSTRACT FROM AUTHOR]

It is generally understood that the chemical enhancement process is essential in surface-enhanced Raman scattering (SERS) of semiconductor-based substrates. Understanding the chemical enhancement mechanism is one of the most significant issues in improving the SERS activity of semiconductor substrates and designed hybrid substrates. Nevertheless, understanding the chemical enhancement process, on the other hand, remains controversial and elusive. In this study, ZnO semiconductor microstructures are prepared to investigate SERS activities in probing methylene blue (MB). The SERS mechanism is well elucidated based on the chemical enhancement mechanism related to both the formation of charge-transfer band and charge transfer from the second ionization of the oxygen vacancy defect (V o ••) to lowest unoccupied molecular orbital (LUMO) of MB. Remarkably, the charge-transfer band was evidenced by examining the ground state absorption spectra with a large band centred at 600 nm. These explanations are consistent with the strong SERS substrate behaviour of ZnO microstructures, with the SERS enhancement factor (EF) of ZnO plate substrates being highest among four investigated samples (ZnO tube, hexagonal, plate and flory-rod) at 2.9 × 104 at a concentration of MB of 10−4 M. To the best of our knowledge, this is the first investigation of detecting MB molecules using a pure semiconductor surface with a strong SERS activity. [Display omitted] • We have successfully fabricated various morphologies of semiconductor ZnO microstructures by hydrothermal route, including tube, hexagonal, plate and flory-like structures. • These products were studied surface-enhanced Raman scattering (SERS) behaviour for probing methylene blue (MB) molecules with the enhancement factor (EF) achieving 2.9 × 104 (10−4 M). • The charge-transfer band corresponding to the interaction between the ZnO surface and the MB molecule was evidenced by examining the ground state absorption spectra with a large band centred at 600 nm. • The SERS mechanism is well elucidated based on the chemical enhancement mechanism related to both the formation of charge-transfer band and charge transfer. • The combination of the existence of charge-transfer band and charge-transfer resonance leads to the large enhancement factor of using pure ZnO as SERS surface. [ABSTRACT FROM AUTHOR]