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oe1(光电查) - 科学论文

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出版时间
  • 2018
研究主题
  • light-emitting diode (LED)
  • bulb's replacement
  • lighting parameters at the workplace
  • light sources for household
应用领域
  • Electrical Engineering and Automation
机构单位
  • Poznan University of Technology
  • Central Institute for Labour Protection - National Research Institute
7 条数据
?? 中文（中国） ▾

  • Facilitating Tip-Enhanced Raman Scattering on Dielectric Substrates via Electrical Cutting of Silver Nanowire Probes

    摘要： TERS is a powerful tool for nanoscale optical characterization of surfaces. However, even after 20 years of development, the parameters for optimal TERS tips are still up for debate. As a result, routine measurements on bulk or dielectric substrates remain exceptionally challenging. Herein we help to alleviate this by using electrical cutting to strategically modify silver nanowire TERS probes. Following cutting, the tips present a large, spherical apex and are often nanostructured with numerous nanoparticles, which we argue improve light collection and optical coupling. This doubles TERS signals on a highly-enhancing, gap-mode substrate compared to our standard nanowire tips, whilst maintaining a high reproducibility and resolution. More interestingly, on a dielectric substrate (graphene on SiO2) the tips give ~7x higher signals than our standard tips. Further investigations point to the non-local nature of the enhancement using standard, smooth, TERS probes without gap-mode, making such nanostructuring highly beneficial in these cases.

    关键词： electrical cutting,silver nanowire,TERS,Tip-Enhanced Raman Scattering,nanoscale optical characterization,dielectric substrates

    更新于2025-09-23 15:21:01

  • Surface Characterization of Nanoscale Co-Crystals Enabled through Tip Enhanced Raman Spectroscopy

    摘要： Atomic Force Microscopy coupled with Tip Enhanced Raman Spectroscopy (AFM-TERS) was applied to obtain information about structure and surface composition of single nano co-crystals. For this purpose, a co-crystalline system consisting of 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazatetracyclo-[5.5.0.03,11.05,9]-dodecane (CL-20) and 1,3,5,7-Tetranitro-1,3,5,7-tetrazocane (HMX) in a molar ratio of 2:1 (CL-20/HMX) were chosen. CL-20/HMX nano-plates were prepared by Spray Flash Evaporation. To ensure co-crystallinity and nanostructure, powder X-Ray Diffraction and AFM investigations were performed. Results demonstrate that coherence lengths and particle dimensions are on a similar level though coherence lengths appear shorter than measured particle dimension. According to this fact, defects inside the nano co-crystals are minimized. The co-crystallinity was additionally proven by confocal Raman spectroscopy. Here, marker bands for pristine CL-20 and HMX were chosen which appear in the CL-20/HMX spectrum in an intensity ratio of ~ 2.5:1 (CL-20:HMX). Afterwards surface investigations of single CL-20/HMX nano-plates were performed by AFM-TERS. Due to the surface sensitivity of TERS, these experiments reveal that the ratio of the Raman intensities between CL-20 and HMX inverts at CL-20/HMX nano-plate surfaces. Therefore, it is concluded that nano co-crystal surfaces consist of molecular layers of HMX. A theoretical approximation of the normal coordinates of the investigated marker vibrations supports this conclusion since it can exclude the occurrence of the intensity ratio inversion because of the given orientation between CL-20/HMX nano-plates and the Raman scattering system. Based on this finding, an impact ignition mechanism is proposed.

    关键词： surface characterization,CL-20/HMX,AFM-TERS,Raman spectroscopy,nano co-crystals

    更新于2025-09-23 15:19:57

  • Study of the Molecular Bending in Azobenzene Self-Assembled Monolayers Observed by Tip-Enhanced Raman Spectroscopy in Scanning Tunneling Mode

    摘要： Tip-enhanced Raman Spectroscopy (TERS) is capable of amplifying the extremely weak Raman response of azobenzene self-assembled monolayers (SAMs), thus allowing for the chemical characterization of the sample surface at the nanoscale. Recently, we introduced a physical model describing the TERS intensity of azobenzene SAMs probed in a scanning tunneling mode configuration (STM-TERS), that takes into account the molecular bending induced by the high electric field inside the tunneling junction. The model predicts quite well the experimental variation in the TERS intensity of a hexil azobenzene SAM (AzoC6) on gold polycrystalline film (111) with changing the electric field in the gap between the tip and the substrate. Nevertheless, a disagreement between the model and the experiment has been observed while studying, in the same conditions, the TERS intensity of undecyl azobenzene (AzoC11) SAM formed by molecules featuring an alkyl chain nearly two times longer with respect to the previous case. In this work we extend the molecular bending model through considering an additional bending mechanism due to the mechanical interaction between the tip and the SAM, occurring when the tip-to-sample distance is shorter than the molecular length. The extended model is able to describe well the TERS intensity behavior with changing either the bias voltage or the tip-to-sample distance for both AzoC6 and AzoC11. Eventually, we determine quantitatively the difference in elastic properties of the two molecules physically accounting for the difference in the TERS intensity behavior of the two SAMs.

    关键词： STM-TERS,self-assembled monolayers,SAMs,Tip-enhanced Raman Spectroscopy,TERS,molecular bending,azobenzene

    更新于2025-09-19 17:13:59

  • Direct molecular-level near-field plasmon and temperature assessment in a single plasmonic hotspot

    摘要： Tip-enhanced Raman spectroscopy (TERS) is currently widely recognized as an essential but still emergent technique for exploring the nanoscale. However, our lack of comprehension of crucial parameters still limits its potential as a user-friendly analytical tool. The tip’s surface plasmon resonance, heating due to near-field temperature rise, and spatial resolution are undoubtedly three challenging experimental parameters to unravel. However, they are also the most fundamentally relevant parameters to explore, because they ultimately influence the state of the investigated molecule and consequently the probed signal. Here we propose a straightforward and purely experimental method to access quantitative information of the plasmon resonance and near-field temperature experienced exclusively by the molecules directly contributing to the TERS signal. The detailed near-field optical response, both at the molecular level and as a function of time, is evaluated using standard TERS experimental equipment by simultaneously probing the Stokes and anti-Stokes spectral intensities. Self-assembled 16-mercaptohexadodecanoic acid monolayers covalently bond to an ultra-flat gold surface were used as a demonstrator. Observation of blinking lines in the spectra also provides crucial information on the lateral resolution and indication of atomic-scale thermally induced morphological changes of the tip during the experiment. This study provides access to unprecedented molecular-level information on physical parameters that crucially affect experiments under TERS conditions. The study thereby improves the usability of TERS in day-to-day operation. The obtained information is of central importance for any experimental plasmonic investigation and for the application of TERS in the field of nanoscale thermometry.

    关键词： surface plasmon resonance,nanoscale thermometry,Tip-enhanced Raman spectroscopy (TERS),spatial resolution,near-field temperature rise

    更新于2025-09-19 17:13:59

  • A Comparative Investigation of Plasmonic Properties between Tunable Nanoobjects and Metallized Nanoprobes for Optical Spectroscopy

    摘要： In order to evaluate the optical efficiency of tip-based probes for future tip-enhanced optical spectroscopy applications, we have developed an experimental setup based on the coupling of an achromatic inverted microscope equipped with a total internal reflection objective and an atomic force microscopy (AFM) head. This spectroscopic tool has been validated using individual nanofabricated antennas (gold nanodisks/nanocones) on a glass substrate, which act as nanoresonators based on localized surface plasmons. Spectrally tunable transverse electric and magnetic plasmonic resonances are identified and are in excellent agreement with numerical calculations performed as a function of the nano-antenna geometry and size. We have investigated a series of state-of-the-art gold-coated AFM probes, which are commonly used for tip-enhanced (Raman spectroscopy) optical experiments. Their scattering spectrum consists of resonances depending on the tip sharpness or granularity superimposed on a broad emission spectrum due to semi-infinite metal layer acting as a non-resonant antenna. From the comparison between the plasmonic response of both types of optical antennas, a new generation of probes for tip-enhanced optical spectroscopy is proposed, in which single plasmonic nano-antennas are engineered at the apex of a non-metallic AFM tip. As from numerical simulation results, such tips would ensure a spectral tunability as a function of the material, size, and geometry, together with expected high enhancement factors. Such features would allow the design of spectrally tunable surface enhanced Raman spectroscopy substrates, and should be a reliable and efficient alternative to tips commonly used in tip-enhanced optical spectroscopy experiments such as tip-enhanced Raman spectroscopy.

    关键词： Optical Spectroscopy,Plasmonics,TERS,Nano-antennas,AFM

    更新于2025-09-12 10:27:22

  • Reference Module in Materials Science and Materials Engineering || Tip-Enhanced Raman Microscopy: Instrumentation, Techniques and Applications in Practice

    摘要： The idea of optical microscopy is to use a set of lenses to magnify the object to see. Scientists changed the idea of this conventional optical microscopy since the scanning probe microscope (SPM) came out in 1980s. Inouye and Kawata proposed to use a sharp metal probe to create an optical image [1]. They scanned the metal tip on a sample surface while recording the optical near-field signals scattered by the tip [1,2]. The spatial resolution is not determined by the numerical aperture (N.A.) of the objective lens but by the tip radius that is typically a few tens of nanometers. The use of a metal tip provides not only high spatial resolution but also an enhancement of optical signals as a result of excitation of surface plasmons at the sharp metal tip. With the tip-enhancement effect, it becomes possible to detect even a very weak optical signal scattered from an extremely tiny volume. One such process is Raman scattering. The application of tip-enhancement to Raman spectroscopy was reported in the year of 2000 by three independent groups led by Kawata, Zenobi, and Anderson, respectively [3–6]. Using TERS, distribution of molecules [7–11] and electronic [12] and chemical properties within nanoscale materials [13–18] have been successfully visualized through Raman signatures with a nanoscale spatial resolution. There are a number of review articles for TERS microscopy and spectroscopy available in literatures [14,19–22]. During the past 20 years, the development of TERS has been mostly driven by research labs having research-grade apparatus operated by skillful researchers. The situation has been changing in the recent years, some companies have started to sell commercial products of TERS microscopes in the market. However, in order to realize TERS microscope as an analytical tool for the routine use of research and industry, challenges in TERS probes, reproducibility issues remain such as stable implementation of atomic force microscopes (AFMs), and peripheral operational techniques.

    关键词： Raman spectroscopy,nanoscale imaging,plasmonic enhancement,Tip-Enhanced Raman Microscopy,TERS

    更新于2025-09-10 09:29:36

  • Imaging the Optical Fields of Functionalized Silver Nanowires through Molecular TERS

    摘要： We image 4-mercaptobenzonitrile-functionalized silver nanowires (~20 nm diameter) through tip-enhanced Raman scattering (TERS). The enhanced local optical field-molecular interactions that govern the recorded hyperspectral TERS images are dissected through hybrid finite-difference time-domain-density functional theory simulations. Our forward simulations illustrate that the recorded spatio-spectral profiles of the chemically functionalized nanowires may be reproduced by accounting for the interaction between orientationally averaged molecular polarizability derivative tensors and enhanced incident/scattered local fields polarized along the tip axis. In effect, we directly map the enhanced optical fields of the nanowire in real space through TERS. The simultaneously recorded atomic force microscopy (AFM) images allow a direct comparison between our attainable spatial resolution in topographic (13 nm) and TERS (5 nm) imaging measurements performed under ambient conditions. Overall, our described protocol enables local electric-field imaging with few nm precision through molecular TERS, and it is therefore generally applicable to a variety of plasmonic nano-structures.

    关键词： silver nanowires,TERS,nanoscale imaging,optical fields,tip-enhanced Raman scattering

    更新于2025-09-09 09:28:46