Acta Optica Sinica, Volume. 41, Issue 17, 1730003(2021)
Enhancement of Raman Spectra Based on Optical Trapping of Gold Nanocubes
Fig. 1. Schematic diagrams of experimental system and sample. (a) Schematic diagram of experimental system, L1, L2: beam expanding lens, F1: excitation filter, F2: emission filter, DBS: dichroic mirror, BS: beam splitter, L3, L4: focusing lens; (b) structure of sample chamber; (c) SEM image of gold nanocubes; (d) SEM image of gold nanospheres
Fig. 2. Dark field imaging of gold nanoparticles trapped by laser (scale bar is 5 μm). Arrow represents the position of the focal spot, circles represent gold nanoparticles. (a1)--(a5) Dark field imaging of gold nanocubes trapped by laser; (b1)--(b5) dark field imaging of gold nanospheres trapped by laser
Fig. 3. Raman signal intensities in different kinds of aqueous solution at different times. Raman spectra of 4-MBA in (a1) aqueous solution of gold nanocubes and (a2) aqueous solution of gold nanospheres; Raman spectra of 4-MBA in (b1) aqueous solution of gold nanocubes and (b2) aqueous solution of gold nanospheres at initial time, where vertical dashed lines make positions of two Raman characteristic peaks and their corrsponding Raman shifts are 1078 cm-1 and 1594 cm-1, respectively
Fig. 4. Raman signal (Raman shift is 1078 cm-1) intensitis of 4-MBA in solutions of gold nanocubes and gold nanospheres vary with time after laser is turned on
Fig. 5. Optical forces on particles in two typical states. When electric field E (along the y-direction) is parallel to (a1) side or (b1) diagonal of gold nanocube,for y=0, (a2)(b2) relationship between Fx(x) and x (dot line), (a3)、(b3) relationship between Fz(x) and x (dot line); for x=0, (a2)(b2) relationship between Fy(y) and y (diamond line), (a3)(b3) relationship between Fz(y) and y (diamond line); (a4) (b4) relationship between Fx and D (dot line) when the center of gold nanocube is located at x=200 nm and y=0, relationship between Fy and D (diamond line) when the center of gold nanocube is located at x=0 and y=200 nm, and relationship between Fz and D (triangle line) when the center of gold nanocube is located at x=0 and y=0
Fig. 6. Velocity distributions of photothermal convection in cavity caused by aggregated gold nanocubes, arrows indicate directions of velocity. (a) Side view; (b) top view
Fig. 7. Distributions of f for different numbers of nanoparticles on x-y plane. (a1)--(a3) Distributions of f for single particle; (b1)--(b3) distributions of f for two particles; (c1)--(c3) distributions of f for 9 gold nanospheres; (d1)--(d3) distributions of f for 9 gold nanocubes
Fig. 8. fSERS for different metal structures. fSERS for different numbers of gold nanocubes and nanospheres. Data in dotted box are the results for the case that number of particles increases gradually while arrangement of particles with the previous number remains unchanged; (b) fSERS corresponding to two gold nanocubes with typical structure of "edge close to surface" as shown in
Fig. 9. Raman enhancement factor fSERS for different M when g=20 nm. Circular curve and rectangular curve correspond to structure with two gold nanospheres and structure with two gold nanocubes, respectively (electric field E of incident laser along the y-direction). Ordinate value of circular curve is magnified 5 times to show the details
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Sheng Rong, Hongshuang Liu, Ying Zhong, Haitao Liu. Enhancement of Raman Spectra Based on Optical Trapping of Gold Nanocubes[J]. Acta Optica Sinica, 2021, 41(17): 1730003
Category: Spectroscopy
Received: Feb. 5, 2021
Accepted: Mar. 29, 2021
Published Online: Sep. 3, 2021
The Author Email: Liu Haitao (liuht@nankai.edu.cn)