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16 pages, 65520 KiB

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Surface- and Tip-Enhanced Raman Scattering by CdSe Nanocrystals on Plasmonic Substrates

by Ilya A. Milekhin, Alexander G. Milekhin and Dietrich R. T. Zahn

Nanomaterials 2022, 12(13), 2197; https://doi.org/10.3390/nano12132197 - 26 Jun 2022

Cited by 8 | Viewed by 2894

This work presents an overview of the latest results and new data on the optical response from spherical CdSe nanocrystals (NCs) obtained using surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS). SERS is based on the enhancement of the phonon response from nanoobjects such as molecules or inorganic nanostructures placed on metal nanostructured substrates with a localized surface plasmon resonance (LSPR). A drastic SERS enhancement for optical phonons in semiconductor nanostructures can be achieved by a proper choice of the plasmonic substrate, for which the LSPR energy coincides with the laser excitation energy. The resonant enhancement of the optical response makes it possible to detect mono- and submonolayer coatings of CdSe NCs. The combination of Raman scattering with atomic force microscopy (AFM) using a metallized probe represents the basis of TERS from semiconductor nanostructures and makes it possible to investigate their phonon properties with nanoscale spatial resolution. Gap-mode TERS provides further enhancement of Raman scattering by optical phonon modes of CdSe NCs with nanometer spatial resolution due to the highly localized electric field in the gap between the metal AFM tip and a plasmonic substrate and opens new pathways for the optical characterization of single semiconductor nanostructures and for revealing details of their phonon spectrum at the nanometer scale. Full article

(This article belongs to the Special Issue New Achievements in Nanostructured and Low Dimensional Materials and Systems)

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10 pages, 3058 KiB

Open AccessArticle

Revealing the Hemispherical Shielding Effect of SiO₂@Ag Composite Nanospheres to Improve the Surface Enhanced Raman Scattering Performance

by Fengyan Wang, Daxue Du, Shan Liu, Linna Wang, Tifeng Jiao, Zhaopeng Xu and Haiyan Wang

Nanomaterials 2021, 11(9), 2209; https://doi.org/10.3390/nano11092209 - 27 Aug 2021

Cited by 11 | Viewed by 3076

Abstract

Many studies widely used SiO₂@Ag composite nanospheres for surface enhanced Raman scattering (SERS), which mainly contributes to electromagnetic enhancement. In addition to experiments, previous simulations mostly adopted a two-dimensional model in SERS research, resulting in the three-dimensional information being folded and masked. In this paper, we adopted the three-dimensional model to simulate the electric field distribution of SiO₂@Ag composite nanospheres. It is found that when the Ag nanoparticles are distributed densely on the surface of SiO₂ nanospheres, light cannot pass through the upper hemisphere due to the local surface plasmon resonance (LSPR) of the Ag nanoparticles, resulting in the upper hemisphere shielding effect; and if there are no Ag nanoparticles distributed densely on the surface of SiO₂ nanospheres, the strong LSPR cannot be formed, so the incident light will be guided downward through the whispering gallery mode of the spherical structure. At the same time, we designed relevant experiments to synthesize SiO₂@Ag composite nanosphere as SERS substrate and used Rhodamine 6G as a probe molecule to study its SERS performance. This design achieved a significant SERS effect, and is very consistent with our simulation results. Full article

(This article belongs to the Special Issue Polymer Based Nanocomposites: Experiment, Theory and Simulations)

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11 pages, 5133 KiB

Open AccessArticle

Quantitative Investigation of Surface Charge Distribution and Point Probing Characteristics of Spherical Scattering Electrical Field Probe for Precision Measurement of Miniature Internal Structures with High Aspect Ratios

by Xingyuan Bian, Junning Cui, Yesheng Lu, Yamin Zhao, Zhongyi Cheng and Jiubin Tan

Appl. Sci. 2020, 10(15), 5268; https://doi.org/10.3390/app10155268 - 30 Jul 2020

Cited by 2 | Viewed by 2448

Abstract

For precision measurement of miniature internal structures with high aspect ratios, a spherical scattering electrical field probe (SSEP) is proposed based on charge signal detection. The characteristics and laws governing surface charge distribution on the probing ball of the SSEP are analyzed, with the spherical scattering electrical field modeled using a 3D seven-point finite difference method. The model is validated with finite element simulation by comparing with the analysis results of typical situations, in which probing balls of different diameters are used to probe a grounded plane with a probing gap of 0.3 μm. Results obtained with the proposed model and finite element method (FEM) simulation indicate that 31% of the total surface charge on a ϕ1 mm probing ball concentrates in an area that occupies 1% of the total probing ball surface. Moreover, this surface charge concentration remains unchanged when the surface being measured varies in geometry, or when the probing gap varies in sensing range. Based on this, the SSEP has realized approximate point probing capability with a virtual “needle” of electrical effect. Together with its non-contact sensing characteristics and 3D isotropy, it can, therefore, be concluded that the SSEP has great potential to be an ideal solution for precision measurement of miniature internal structures with high aspect ratios. Full article

(This article belongs to the Special Issue Manufacturing Metrology)

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14 pages, 8552 KiB

Open AccessArticle

Ultraprecision Diameter Measurement of Small Holes with Large Depth-To-Diameter Ratios Based on Spherical Scattering Electrical-Field Probing

by Xingyuan Bian, Junning Cui, Yesheng Lu and Jiubin Tan

Appl. Sci. 2019, 9(2), 242; https://doi.org/10.3390/app9020242 - 10 Jan 2019

Cited by 19 | Viewed by 5351

Abstract

In order to solve the difficulty of precision measurement of small hole diameters with large depth-to-diameter ratios, a new measurement method based on spherical scattering electrical-field probing (SSEP) was developed. A spherical scattering electrical field with identical sensing characteristics in arbitrary spatial directions was formed to convert the micro gap between the probing-ball and the part being measured into an electrical signal. 3D non-contact probing, nanometer resolution, and approximate point probing—which are key properties for high measurement precision and large measurable depth-to-diameter ratios—were achieved. A specially designed hole diameter measuring machine (HDMM) was developed, and key techniques, including laser interferometry for macro displacement measurement of the probe, multi-degree-of-freedom adjustment of hole attitude, and measurement process planning, are described. Experiments were carried out using the HDMM and a probing sensor with a ϕ3-mm probing ball and a 150-mm-long stylus to verify the performance of the probing sensor and the measuring machine. The experimental results indicate that the resolution of the probing sensor was as small as 1 nm, and the expanded uncertainty of measurement result was 0.2 μm (k = 2) when a ϕ20-mm ring gauge standard was measured. Full article

(This article belongs to the Special Issue Precision Dimensional Measurements)

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