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Galvanic synthesis of three-dimensional and hollow metallic nanostructures.

Park SH, Son JG, Lee TG, Kim J, Han SY, Park HM, Song JY - Nanoscale Res Lett (2014)

Bottom Line: Finally, the wet etching process of remaining silver resulted in the formation of 3D-NPG.During the GRR process, the application of bias voltage to the cathode decreased the porosity of 3D-NPG in the voltage range of 0.2 to -0.62 V.The 3D-NPG nanostructures were found to effectively enhance the SERS sensitivity of rhodamine 6G (R6G) molecules with a concentration up to 10(-8) M.

View Article: PubMed Central - PubMed

Affiliation: Korea Research Institute of Standard and Science, Daejeon, 305-340, Republic of Korea, psh@kriss.re.kr.

ABSTRACT
We report a low-cost, facile, and template-free electrochemical method of synthesizing three-dimensional (3D) hollow metallic nanostructures. The 3D nanoporous gold (3D-NPG) nanostructures were synthesized by a galvanic replacement reaction (GRR) using the different reduction potentials of silver and gold; hemispherical silver nanoislands were electrochemically deposited on cathodic substrates by a reverse-pulse potentiodynamic method without templates and then nanoporous gold layer replicated the shape of silver islands during the GRR process in an ultra-dilute electrolyte of gold(III) chloride trihydrate. Finally, the wet etching process of remaining silver resulted in the formation of 3D-NPG. During the GRR process, the application of bias voltage to the cathode decreased the porosity of 3D-NPG in the voltage range of 0.2 to -0.62 V. And the GRR process of silver nanoislands was also applicable to fabrication of the 3D hollow nanostructures of platinum and palladium. The 3D-NPG nanostructures were found to effectively enhance the SERS sensitivity of rhodamine 6G (R6G) molecules with a concentration up to 10(-8) M.

No MeSH data available.


Variation of SERS spectra with the R6G concentrations and cyclic voltammograms. (a) SERS spectra with the R6G concentrations of (i) 10-6, (ii) 10-7, and (iii) 10-8 M on 3D-NPG nanostructures and (iv) 10-6 M on PNPG film, respectively. (b) Cyclic voltammograms measured for (i) bare Au film, (ii) PNPG film, and (iii) 3D-NPG nanostructures in N2-saturated 0.1 M H2SO4 for the sake of measuring each rESA. The insets denote top-view SEM images of PNPG and 3D-NPG, respectively.
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Fig7: Variation of SERS spectra with the R6G concentrations and cyclic voltammograms. (a) SERS spectra with the R6G concentrations of (i) 10-6, (ii) 10-7, and (iii) 10-8 M on 3D-NPG nanostructures and (iv) 10-6 M on PNPG film, respectively. (b) Cyclic voltammograms measured for (i) bare Au film, (ii) PNPG film, and (iii) 3D-NPG nanostructures in N2-saturated 0.1 M H2SO4 for the sake of measuring each rESA. The insets denote top-view SEM images of PNPG and 3D-NPG, respectively.

Mentions: Figure 7a shows the SERS spectra of R6G adsorbed on the 3D-NPG nanostructures and PNPG film with the R6G concentration in the range of 10-6 to 10-8 M. All the SERS peaks for 3D-NPG nanostructures are clearly distinguished by 633 nm laser and assigned to the characteristics of R6G Raman spectra [31, 32]. In comparison, the SERS intensity of R6G on PNPG film is approximately 40 times lower than that on 3D-NPG nanostructures, even though the surface areas of both nanostructures are almost similar to each other, according to rESA measurement (the below inset of Figure 7b). The rESA was evaluated by cyclic voltammograms in N2-saturated 0.1 M H2SO4, as shown in Figure 7b. The similar surface areas of 3D-NPG and PNPG are due to the less formation of nanopores around 3D hollow nanostructures, as shown in the inset of Figure 7b. Generally, the higher SERS intensity is known to come from nanpore size, ratios of ligaments to nanopores, and surface roughness [12, 13]. However, in the present study, the difference of pore sizes between 3D-NPG and PNPG was not so large, approximately 3 nm. This suggests that the SERS enhancement for 3D-NPG nanostructures might be due to other effects. One possible reason is supposed to be the polygonal edges of 3D-NPG (see the inset of Figure 7b). Previously, it was reported that high index gold nanocrystals exhibit more efficient SERS activity than spherical gold nanocrystals and an electromagnetic field enhancement effect arises because the electric field localizes more easily at the edges of nanocrystals [33]. And, the SERS spectra of 10-6 M R6G were measured at random points over the whole substrate. The SERS enhancement was highly reproducible at random five points over the whole substrate, as shown in the SERS spectra (Additional file 1: Figure S6). Thus, ultra-thin 3D-NPG nanostructures were easily fabricated by the bottom-up process providing a uniform SERS substrate without hot spots.Figure 7


Galvanic synthesis of three-dimensional and hollow metallic nanostructures.

Park SH, Son JG, Lee TG, Kim J, Han SY, Park HM, Song JY - Nanoscale Res Lett (2014)

Variation of SERS spectra with the R6G concentrations and cyclic voltammograms. (a) SERS spectra with the R6G concentrations of (i) 10-6, (ii) 10-7, and (iii) 10-8 M on 3D-NPG nanostructures and (iv) 10-6 M on PNPG film, respectively. (b) Cyclic voltammograms measured for (i) bare Au film, (ii) PNPG film, and (iii) 3D-NPG nanostructures in N2-saturated 0.1 M H2SO4 for the sake of measuring each rESA. The insets denote top-view SEM images of PNPG and 3D-NPG, respectively.
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Related In: Results  -  Collection

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Fig7: Variation of SERS spectra with the R6G concentrations and cyclic voltammograms. (a) SERS spectra with the R6G concentrations of (i) 10-6, (ii) 10-7, and (iii) 10-8 M on 3D-NPG nanostructures and (iv) 10-6 M on PNPG film, respectively. (b) Cyclic voltammograms measured for (i) bare Au film, (ii) PNPG film, and (iii) 3D-NPG nanostructures in N2-saturated 0.1 M H2SO4 for the sake of measuring each rESA. The insets denote top-view SEM images of PNPG and 3D-NPG, respectively.
Mentions: Figure 7a shows the SERS spectra of R6G adsorbed on the 3D-NPG nanostructures and PNPG film with the R6G concentration in the range of 10-6 to 10-8 M. All the SERS peaks for 3D-NPG nanostructures are clearly distinguished by 633 nm laser and assigned to the characteristics of R6G Raman spectra [31, 32]. In comparison, the SERS intensity of R6G on PNPG film is approximately 40 times lower than that on 3D-NPG nanostructures, even though the surface areas of both nanostructures are almost similar to each other, according to rESA measurement (the below inset of Figure 7b). The rESA was evaluated by cyclic voltammograms in N2-saturated 0.1 M H2SO4, as shown in Figure 7b. The similar surface areas of 3D-NPG and PNPG are due to the less formation of nanopores around 3D hollow nanostructures, as shown in the inset of Figure 7b. Generally, the higher SERS intensity is known to come from nanpore size, ratios of ligaments to nanopores, and surface roughness [12, 13]. However, in the present study, the difference of pore sizes between 3D-NPG and PNPG was not so large, approximately 3 nm. This suggests that the SERS enhancement for 3D-NPG nanostructures might be due to other effects. One possible reason is supposed to be the polygonal edges of 3D-NPG (see the inset of Figure 7b). Previously, it was reported that high index gold nanocrystals exhibit more efficient SERS activity than spherical gold nanocrystals and an electromagnetic field enhancement effect arises because the electric field localizes more easily at the edges of nanocrystals [33]. And, the SERS spectra of 10-6 M R6G were measured at random points over the whole substrate. The SERS enhancement was highly reproducible at random five points over the whole substrate, as shown in the SERS spectra (Additional file 1: Figure S6). Thus, ultra-thin 3D-NPG nanostructures were easily fabricated by the bottom-up process providing a uniform SERS substrate without hot spots.Figure 7

Bottom Line: Finally, the wet etching process of remaining silver resulted in the formation of 3D-NPG.During the GRR process, the application of bias voltage to the cathode decreased the porosity of 3D-NPG in the voltage range of 0.2 to -0.62 V.The 3D-NPG nanostructures were found to effectively enhance the SERS sensitivity of rhodamine 6G (R6G) molecules with a concentration up to 10(-8) M.

View Article: PubMed Central - PubMed

Affiliation: Korea Research Institute of Standard and Science, Daejeon, 305-340, Republic of Korea, psh@kriss.re.kr.

ABSTRACT
We report a low-cost, facile, and template-free electrochemical method of synthesizing three-dimensional (3D) hollow metallic nanostructures. The 3D nanoporous gold (3D-NPG) nanostructures were synthesized by a galvanic replacement reaction (GRR) using the different reduction potentials of silver and gold; hemispherical silver nanoislands were electrochemically deposited on cathodic substrates by a reverse-pulse potentiodynamic method without templates and then nanoporous gold layer replicated the shape of silver islands during the GRR process in an ultra-dilute electrolyte of gold(III) chloride trihydrate. Finally, the wet etching process of remaining silver resulted in the formation of 3D-NPG. During the GRR process, the application of bias voltage to the cathode decreased the porosity of 3D-NPG in the voltage range of 0.2 to -0.62 V. And the GRR process of silver nanoislands was also applicable to fabrication of the 3D hollow nanostructures of platinum and palladium. The 3D-NPG nanostructures were found to effectively enhance the SERS sensitivity of rhodamine 6G (R6G) molecules with a concentration up to 10(-8) M.

No MeSH data available.