Abstract
Core@shell Ag@C nanocubes (NCs) with a cubic silver core (~60 nm of side length) and a coating of ultrathin amorphous carbon (~4 nm) have been synthesized on a large scale by a one-pot hydrothermal method. The carbon layer not only protects the Ag@C nanocubes from oxidation under hydrothermal condition, but also stabilizes the structure of Ag cores. Considering that optical properties of nanostructured metals strongly depend on the temperature for SERS measurement, in this work we systemically investigate the relationship between the orientation of molecules adsorbed on Ag@C NCs and temperature by SERS spectra. Results suggest that the adsorbed 4-MBA molecules prefer a flat orientation on the NC surface with temperature decreasing. In addition, Ag@C NCs after one-year storage in water still maintain high SERS-active capability. Our synthesized Ag@C NCs with excellent and stable optical properties can be potentially applied in the field of sensor and ultrasensitive spectral analysis.
Highlights
In our work, we developed a hydrothermal method to grow Ag@C NCs with very narrow size distribution and high property-stability in water, which show extraordinary electromagnetic field due to the antenna effect
The excited electron can be transferred from the surface plasmon (Eplasmon) of Ag NC to the LUMO energy level of 4-MBA molecule when under laser illumination
In a strongly acidic environment, C-C bonds of 4-MBA molecules are mainly in the protonated form which is related to the low temperature effect
Summary
We developed a hydrothermal method to grow Ag@C NCs with very narrow size distribution and high property-stability in water, which show extraordinary electromagnetic field due to the antenna effect. The merit of our method is that the crystal growth is well controlled, leading to cubic Ag crystals with uniform size. The structure and optical properties of Ag@C NCs were characterized using SEM The temperature-dependent orientation of molecules adsorbed onto Ag@C NCs was revealed by means of changing temperatures from 10 K to 190 K in SERS measurement. The stability of Ag@C NCs in the water solution has been investigated by analyzing the sample after storage in water for 12 months. High SERS activity of Ag@C NCs was well maintained with aging
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