Field Emission Tip Array Fabrication Utilizing Geometrical Hindrance in the Oxidation of Si

Both the surface‐enhanced Raman spectroscopy (SERS) and coherent anti‐Stokes Raman spectroscopy (CARS) are widely used methods in the bio‐sensing field for improving the intensity of Raman scattering process. By combining the mechanisms of CARS (coherence and nonlinear process) and SERS (plasmon resonance), a multiplicative enhancement can be achieved through surface‐enhanced CARS (SECARS). Besides sensitivity, high specificity with wide spectral bandwidth is also preferred for bio‐sensing techniques but not well developed in SECARS setups reported in the literature. In this work, a broadband SECARS setup with high sensitivity and high spectral resolution is presented. Rhodamine 6G dye molecules and several biomolecules are used as the model system to benchmark the functionality of the SECARS system in terms of its sensitivity, the lowest detectable concentration, and the spectral resolution. Our setup rendered single‐molecule sensitivity with spectral resolution of <35 cm−1. More than 102 times stronger signal‐to‐noise ratio compared with that of SERS is observed with the detection limit being 10−9 m. Different from the SECARS systems in the literature, our setup employs a unique graphene‐Au pyramids hybrid platform. The graphene in this structure provides additional SERS enhancement and a bio‐compatible surface. This powerful technique could be instrumental in furthering the understanding of various chemical and biological processes. Copyright © 2017 John Wiley & Sons, Ltd.

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Broadband surface‐enhanced coherent anti‐Stokes Raman spectroscopy with high spectral resolution

Yan

Liu

Xia

et al. 2017

J Raman Spectroscopy

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Silicon tip sharpening based on thermal oxidation technology

Zhang

Yang

et al. 2016

Microsyst Technol

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Silicon tips are conventionally fabricated by isotropic etching followed by oxidation sharpening at temperatures below 1050 °C, based on the reduced oxidation rate at the step edge due to high compressive stress around the edge (Marcus and Sheng 1982). However, the effects of the oxidation temperature on the tip profile have been far from studied yet. This work investigated in detail the optimized oxidation temperature to fabricate sharp tips with high aspect ratio. The results indicated that a trade-off between aspect ratio and the tip diameter should be taken into account when choosing the oxidation temperature. Sharp silicon tip with a diameter of 6.3 nm was fabricated. Figure 1 described the fabrication process of the silicon tips. First, A 300 nm thick oxide was thermally grown on 4-inch (100) silicon wafer substrate as the mask. The lithography was performed to define the tip apex, and the pattern was transferred to the thermal oxide by reactive ion etching (RIE). Then silicon etching was followed by isotropic dry etching using RIE to get the silicon posts. After isotropically etching Si to a depth of 6 um, a neck was formed about 1 micron below the mask, located at the thinnest part of the silicon post, as illustrated in Fig. 1d. Silicon necks with widths between 97 and 330 nm were produced by changing the mask sizes. The oxide mask was removed by buffered hydrofluoric (BHF) acid solution and the silicon posts or "pre-tips" were formed. Figure 3a-c shows the SEM photographs of the fabricated silicon posts. Experimental arrangementsFour groups of silicon post samples were prepared and thermal oxidation were performed at temperatures of 900, 950, 1000, and 1050 °C, respectively. Low temperature oxidation has been studied to sharpen silicon tips (Umimoto Abstract Thermal oxidation at low temperatures (below 1050 °C) is widely used in the microfabrication of sharp silicon tips. However, the influences of the oxidation temperature on morphology of the tips have not been investigated in detail. This work systematically studied the dependence of tip profile on the oxidation temperature. Thermal oxidation were performed in four groups at 900, 950, 1000 and 1050 °C. The results show that a trade-off between the tip aspect ratio and diameter should be taken into account when choosing the oxidation temperature. The optimized oxidation temperature to make tips with small apex, high aspect ratio, and smooth surface is around 1000 °C. The tip with a diameter of 6.3 nm was realized through oxidation at 1000 °C.

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Preparation, microstructure characterisation and corrosion behaviour of directionally grown TaSi2 fibre arrays with sharp tip fabricated by selective wet etching

Yang

Zhang

et al. 2013

Corrosion Science

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Field Emission Tip Array Fabrication Utilizing Geometrical Hindrance in the Oxidation of Si

Cited by 12 publications

References 25 publications

Broadband surface‐enhanced coherent anti‐Stokes Raman spectroscopy with high spectral resolution

Broadband surface‐enhanced coherent anti‐Stokes Raman spectroscopy with high spectral resolution

Silicon tip sharpening based on thermal oxidation technology

Preparation, microstructure characterisation and corrosion behaviour of directionally grown TaSi2 fibre arrays with sharp tip fabricated by selective wet etching

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