Graphene-MnO2 composites are reduced from GO-MnO2 using various concentrations of hydrazine hydrate with a fixed reduction time to optimize the hydrazine concentration to obtain excellent electrochemical performance. Changes in the oxygen-containing functional groups are observed as the concentration of hydrazine is varied. These changes affect the electrical conductivity and density of MnO2 nanoneedles, which impact the surface area and can significantly affect the supercapacitive performance. The characterization of morphology and microstructure of the as-prepared composites demonstrates that MnO2 is successfully formed on the GO surface and GO is successfully reduced by using hydrazine hydrate as a reducing agent. The capacitive properties of the graphene-MnO2 electrodes which reduced 50 mM of hydrazine (RGO-MnO2(50)) show a low sheet resistance value as well as a high surface area, resulting in excellent electrochemical performance (383.82 F g(-1) at a scan rate of 10 mV s(-1)). It is anticipated that the formation of nanoneedle structures of MnO2 on graphene oxide surfaces utilizing the 50 mM hydrazine reduction procedure is a promising fabrication method for supercapacitor electrodes.
The oblique angle deposition of Ag with different deposition rates and substrates was studied for surface-enhanced Raman spectroscopy (SERS) efficiency. The deposition rate for the Ag substrate with maximum SERS efficiency was optimized to 2.4 Å/s. We also analyzed the morphology of Ag nanorods deposited at the same rate on various substrates and compared their SERS intensities. Ag deposited on SiO2, sapphire, and tungsten showed straight nanorods shape and showed relatively high SERS efficiency. However, Ag deposited on graphene or plasma-treated SiO2 substrate was slightly or more aggregated (due to high surface energy) and showed low SERS efficiency.
We report the method of fabrication of nano-gaps (known as hot spots) in Ag thin film using a sodium chloride (NaCl) sacrificial layer for Raman enhancement. The Ag thin film (20-50 nm) on the NaCl sacrificial layer undergoes an interfacial reaction due to the AgCl formed at the interface during water molecule intercalation. The intercalated water molecules can dissolve the NaCl molecules at interfaces and form the ionic state of Na and Cl, promoting the AgCl formation. The Ag atoms can migrate by the driving force of this interfacial reaction, resulting in the formation of nano-size gaps in the film. The surface-enhanced Raman scattering activity of Ag films with nano-size gaps has been investigated using Raman reporter molecules, Rhodamine 6G (R6G).
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