Periodic ZnO-Elevated Gold Dimer Nanostructures for Surface-Enhanced Raman Scattering Applications (original) (raw)
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We fabricated surface-enhanced Raman scattering (SERS) substrates using gold nanoparticle (AuNP)-decorated zinc oxide (ZnO) nanorods (NRs). Prior to decoration with AuNPs, ZnO NRs on the glass substrate fabricated using the sol–gel method could enhance the SERS signal for detecting 10−5 M rhodamine 6G (R6G). Microscopic analysis revealed that the thermal-annealing process for fabricating the seed layers of ZnO facilitated the growth of ZnO NRs with the highly preferred c-axis (002) orientation. A decrease in the diameter of ZnO NRs occurred because of the use of annealed seek layers further increased the surface-to-volume ratio of ZnO NRs, resulting in an increase in the SERS signal for R6G of 10−5 M. To combine the localized surface plasmon resonance (LSPR) mode with the charge transfer (CT) mode, ZnO NRs were decorated with AuNPs through pulsed-laser-induced photolysis (PLIP). However, the preferred vertical (002) orientation of ZnO NRs was prone to the aggregation of AuNPs, which...
2015 28th IEEE International Conference on Micro Electro Mechanical Systems (MEMS), 2015
In recent years, the SERS-related materials research has gradually moved to the much cheaper semiconductor materials against the barriers from noble metals. [9-21] However, compared with noble metals, their relatively weak enhancement factor (EF) is not high enough for molecule to trace detection. Therefore, how to efficiently improve the SERS performance of semiconductors is the focus of a related study. Fortunately, scientists have found that some semiconductive materials could show great Raman scattering enhancement to trace of substances, reaching an ultralow limit of detection (LOD) and an ultrahigh EF. One excellent example is an urchin-like W 18 O 49 reported by Zhao and co-workers; the EF is up to the 3.4 × 10 5 level by means of the surface plasmon resonance. [17] And the single Cu 2 O superstructure particle reported by Guo and coworkers, obtaining an LOD of 10 −9 m and an EF of 8.0 × 10 5 , may be the best enhancement effect among the non-noble metal substrates reported so far. [14] Besides, considering promoting the interfacial charge-transfer process (ICTP) is an important premise to improve the sensitivity of semiconductorbased SERS, Guo's group further developed amorphous ZnO nanocages (a-ZnO NCs). Their study indicates that the remarkable SERS sensitivity can be obtained from the high-efficiency ICTP within the amorphous ZnO NCs-molecules system. [20] Based on previous research, the optimization of the geometry morphology and promotion of the ICTP between the semiconductor and molecules are considered two determining factors for EF improvement in semiconductor SERS. If we obtain an amorphous structure and simultaneously reduce the size of nanoparticles greatly, even to quantum size, we can achieve enhanced SERS. However, achieving both of them simultaneously is challenging. In our previous work, we have prepared 2D MoO 3 nanosheets that indicated excellent LSPR performance. [22] But due to the relatively larger size in the 2D region, its SERS is not so satisfied. In this work, we designed an alternative strategy to fabricate uniform amorphous molybdenum oxide quantum dots. By carrying out a series of efficient regulation strategies on the reaction system, this as-prepared peculiar nanostructure possesses excellent quantum size in uniformity, accompanied with an intensively enhanced plasmonic resonance property. Our experimental results demonstrate the
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We study the surface enhanced Raman scattering of Methylene Blue (MB) dye molecules induced by 3D array of “hot spots” made of vertical Au/ZnO core-shell nanorods coupled to self-assembled plasmonic Au nanoparticles. SERS substrates based on array of nanorods coupled to nanoparticles show much better performance compared with bare Au/ZnO nanorods. The hybrid 3D SERS substrate perfectly resolve Raman spectra of MB molecules chemisorbed from solutions with analyte concentrations of ∼10-7 M even upon washing of a sample i.e. when only chemisorbed molecules were remained. Raman signal enhancement results from the superposition of two effects, namely, the ability of a plasmonic coupled system to enhance the Raman scattering via local field enhancement and from the large 3D surface which provides more adsorption sites compared with traditional 2D surfaces.
Surface enhanced Raman scattering of light by ZnO nanostructures
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Raman scattering (including nonresonant, resonant, and surface enhanced scattering) of light by optical and surface phonons of ZnO nanocrystals and nanorods has been investigated. It has been found that the nonresonant and resonant Raman scattering spectra of the nanostructures exhibit typical vibrational modes, E 2 (high) and A 1 (LO), respectively, which are allowed by the selection rules. The deposition of silver nanoclusters on the surface of nanostructures leads either to an abrupt increase in the intensity (by a factor of 10 3 ) of Raman scattering of light by surface optical phonons or to the appearance of new surface modes, which indicates the observation of the phenomenon of surface enhanced Raman light scattering. It has been demonstrated that the frequencies of surface optical phonon modes of the studied nanostructures are in good agreement with the theoretical values obtained from calculations performed within the effective dielectric function model.
Journal of Nanoscience and Nanotechnology, 2016
Ordered arrays of Au-nanorod-tips protruding from an anodic aluminum oxide (AAO) template are reported as reproducible and active surface-enhanced Raman scattering (SERS) substrates. The Au-nanorods were grown in the nanochannels of the AAO template by use of alternative current electrodeposition, then the template was strengthened using a polymer, and finally the template bottom side was selectively etched to expose the Au-nanorod tips. By controlling the thinning of the AAO-porewalls, the inter-nanorod-gaps were tuned to ∼5 nm, forming dense and uniform nanogap induced "hot spots" among the adjacent Au-nanorod tips. As a result, the electromagnetic field of the Au-nanorod-tip arrays was uniformly enhanced, and demonstrated high SERS sensitivity with good signal reproducibility. The Au-nanorod-tips have the potential to be used in SERS-based applications in order to rapidly detect trace pollutants in the environment.
Au-covered hollow urchin-like ZnO nanostructures for surface-enhanced Raman scattering sensing
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Electrochemical Growth of Gold Nanostructures for Surface-Enhanced Raman Scattering
The Journal of Physical Chemistry C, 2011
We demonstrate a facile fabrication of gold nanostructures including Au nanoplates (NPs), Au nanothorns (NTs), and Au nanowires (NWs) on indium tin oxide substrates via electrochemical growth. A simple two-electrode electrochemical deposition system was applied for the fabrication process. Dense Au nanostructures were grown directly on an Au seeding layer on the substrate. After 48 h, the Au NPs were 2-5 μm in width and 150-200 nm in thickness. The Au NTs were 1-3 μm in height, 300-500 nm in bottom side width, and 20 nm at the apex. The Au NWs were 30-80 nm in diameter and about 20 μm in length. The entire process was template-free and economical. We investigated the correlation between surface plasmon resonance (SPR) and surface enhanced scattering (SERS) effects of the Au nanostructures with different excitation wavelengths. By using the SPR absorption maxima of the nanostructures as the excitation wavelengths for SERS, the highest SERS enhancements were achieved. SERS effects of the Au NWs were investigated further. We discovered that the length and the density of the Au NWs affected the SERS performance significantly. The result is rationalized by the amount of "hot spot" generated at the crossing of the Au NWs. With the Au NWs, Rhodamine 6G can be detected at a concentration as low as 10-9 M.
Plasmonic dimer antennas for surface enhanced Raman scattering
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Electron beam induced deposition (EBID) has recently been developed into a method to directly write optically active three-dimensional nanostructures. For this purpose a metal-organic precursor gas (here dimethyl-gold(III)-acetylacetonate) is introduced into the vacuum chamber of a scanning electron microscope where it is cracked by the focused electron beam. Upon cracking the aforementioned precursor gas, 3D deposits are realized, consisting of gold nanocrystals embedded in a carbonaceous matrix. The carbon content in the deposits hinders direct plasmonic applications. However, it is possible to activate the deposited nanostructures for plasmonics by coating the EBID structures with a continuous silver layer of a few nanometers thickness. Within this silver layer collective motions of the free electron gas can be excited. In this way, EBID structures with their intriguing precision at the nanoscale have been arranged in arrays of free-standing dimer antenna structures with nanometer sized gaps between the antennas that face each other with an angle of 90 •. These dimer antenna ensembles can constitute a reproducibly manufacturable substrate for exploiting the surface enhanced Raman effect (SERS). The achieved SERS enhancement factors are of the order of 10 4 for the incident laser light polarized along the dimer axes. To prove the signal enhancement in a Raman experiment we used the dye methyl violet as a robust test molecule. In future applications the thickness of such a silver layer on the dimer antennas can easily be varied for tuning the plasmonic resonances of the SERS substrate to match the resonance structure of the analytes to be detected.