Surface-enhanced Raman scattering from transition metals with special surface morphology and nanoparticle shape

Abstract

This discussion focuses on our recent approaches at aiming to optimize surface-enhanced Raman scattering (SERS) activity for transition metals (group VIII B elements), by intentionally fabricating desired surface nanostructures or synthesizing nanoparticles. The SERS activity of transition metals critically depends on the surface morphology of electrodes and on size, shape and aggregation form of nanoparticles. A correct surface roughening procedure for transition-metal electrodes is indispensable for fabricating cauliflower-like nanostructures that show a higher SERS activity. Two more methods have been explored to synthesize nanoparticles, i.e., cubic nanoparticles and gold-core palladium-shell nanostructures, respectively. Their SERS activities are considerably higher than those of normal spherical mono-metallic nanoparticles. To explain these observations, a preliminary theoretical calculation, using the three-dimensional finite difference time domain (3D-FDTD) method, was performed to evaluate the local electromagnetic field on transition metal surfaces. The result is in good agreement with the experimental data.

Tip-enhanced Electron Emission Microscopy Coupled with the Femtosecond Laser Pulse

“…Calculations are carried out using the finite-difference in time-domain (FDTD) [29][30][31][32] technique for the current experimental condition. The curvature radius of the tungsten tip and its cone angle are assumed to be 50 nm and 35º, respectively.…”

Can Mixed-Metal Surfaces Provide an Additional Enhancement to SERS?

“…[25][26][27][28] In subsequent extensive work of Weaver, Tian, Dai, et al, fabrication techniques for producing transition-and mixed-metal substrates were considerably improved and their surface enhancements were explored in great detail. [29][30][31][32][33][34][35][36][37][38] Their work was motivated by the concept of SERS borrowing, originally put forward by Van Duyne and Haushalter. 39 SERS borrowing refers to the fact that dopant metals are poor SERS substrates by themselves.…”

Application of well-defined indium tin oxide nanorods as Raman active platforms

“…Although not as extensively explored as the aforementioned metals, some research efforts are made to obtain SERS of transition metals such as Pt, Rh, Pd, Fe, Co, and Ni. 3,[10][11][12][13] And more recently, other systems involving either a metal oxide thin film or a hybrid system of a metal nanoparticle/metal oxide thin film have been demonstrated as SERS-active materials. 7,[14][15][16][17][18][19] Plasmonic characteristics similar to those observed from noble metals are found in some transparent conducting metal oxides such as indium tin oxide, fluorine-doped tin oxide, and aluminum-doped zinc oxide.…”

“…28 For example, SERS activities of cubic or cauliflower-like particles are much greater than that of spherical ones under the same excitation condition. 3,12 The threedimensional finite difference time domain (3D-FDTD) theory, calculating local electromagnetic fields of transition metal surfaces when compared to the free electron metals, has effectively explained the experimentally observed phenomena. 3,12,22,29 The increased electromagnetic fields of non-spherical particles are often referred to as the lighting rod effect near structures of high curvature on a surface.…”

“…3,12 The threedimensional finite difference time domain (3D-FDTD) theory, calculating local electromagnetic fields of transition metal surfaces when compared to the free electron metals, has effectively explained the experimentally observed phenomena. 3,12,22,29 The increased electromagnetic fields of non-spherical particles are often referred to as the lighting rod effect near structures of high curvature on a surface. The large anisotropy of the ITO NRs (with an aspect ratio larger 1:375 (width:length)) used in our SERS measurements may intensify this effect even further, leading to higher SERS activity than their isotropic zero-dimensional counterparts and the two dimensional ITO thin films.…”