Field Hot Spots Research Articles

Optimizing electrode structure of carbon nanotube gas sensors for sensitivity improvement based on electric field enhancement effect of fractal geometry

With the rapid development of carbon nanotubes gas sensor, the sensitivity of the sensing response is becoming more and more demanding. Different from the traditional studies on gas-sensitive materials, this paper combines the microscopic dimensional effects and physical properties of fractal geometry theory from the structure and morphology of sensor devices. The electrode structures of carbon nanotubes gas sensor is designed and optimized by Hilbert–Piano curve. Simulation experiments demonstrate that the electric field intensity and hot spot distribution of the fractal electrode are superior to those of the traditional interdigital electrode. Moreover, a novel chemiresistive gas sensor is fabricated combining the characteristics of carbon nanotubes and fractal geometry, and a test with exposure to nitric oxide showed that the sensors with fractal electrode structures improved the gas sensing sensitivity over sensors with traditional geometrical structures. It provides a new idea for the exploration of gas sensing technology.

Preparation of gold core and silver shell substrate with inositol hexaphosphate inner gap for Raman detection of trace Penicillin G

The abuse of Penicillin G (PG) in the feeds of livestock resulted in health risk for human being via the food chain. It is urged to develop the rapid and sensitive method for monitoring PG residue in food products. In this work, silver shell was formed on the core gold nanoparticles protected with inositol hexaphosphate (IP6), designated as Ag@IP6@AuNPs, which is used as surface enhanced Raman scattering (SERS) substrate. Thanks to the presence of IP6 between silver shell and core gold, Ag@IP6@AuNPs show high storage stability. The great surface plasmon resonance of hot spot field generated in the molecular gap between core-shell extends to nanoparticle surface results in synergistic enhancement of Raman scattering effect. Ag@IP6@AuNPs-based SERS assay is employed to successfully detect trace PG residue in milk with a wide linear quantitative range from 10−5 to 10-11 mol/L and the limit of detection at 10-12 mol/L. The sensitivity of such Raman protocol meets the requirement for the maximum residue limit (MRL, 4 μg/kg or 1.2 × 10−8 mol/L) of PG in milk products set by the European Union. Additionally, the detection recoveries in the range from 92.18 % to 101.4 % mean the acceptable robustness of such SERS method. The proposed SERS method could be advanced to realize the on-field determination of PG in milk for guarantee of food safety.

The NV metamaterial: Tunable quantum hyperbolic metamaterial using nitrogen vacancy centers in diamond

We show that nitrogen-vacancy (NV) centers in diamond can produce a unique quantum hyperbolic metamaterial. We demonstrate that a hyperbolic dispersion relation in diamond with NV centers can be engineered and dynamically tuned by applying a magnetic field at 20 K. This quantum hyperbolic metamaterial with a tunable window for the negative refraction allows for the construction of a superlens beyond the diffraction limit. In addition to subwavelength imaging, this NV metamaterial can be used in spontaneous emission enhancement, heat transport, and acoustics, analog cosmology, and lifetime engineering. Therefore, our proposal interlinks the two hotspot fields, i.e., NV centers and metamaterials.

Driver Fatigue Detection Based on Facial Key Points and LSTM

In recent years, fatigue driving has been a serious threat to the traffic safety, which makes the research of fatigue detection a hotspot field. Research on fatigue recognition has a great significance to improve the traffic safety. However, the existing fatigue detection methods still have room for improvement in detection accuracy and efficiency. In order to detect whether the driver has fatigue driving, this paper proposes a fatigue state recognition algorithm. The method first uses MTCNN (multitask convolutional neural network) to detect human face, and then DLIB (an open-source software library) is used to locate facial key points to extract the fatigue feature vector of each frame. The fatigue feature vectors of multiple frames are spliced into a temporal feature sequence and sent to the LSTM (long short-term memory) network to obtain a final fatigue feature value. Experiments show that compared with other methods, the fatigue state recognition algorithm proposed in this paper has achieved better results in accuracy. The average accuracy of the proposed method in detecting key points of the face is as high as 93%, and the running time is less than half of the ordinary DLIB method.

Vacuum Field Photonic Trap for Excitons

AbstractThe spectral and spatial dependence of the resonant Lamb shift of an exciton inside a photonic vacuum field landscape is considered to predict an optical dipole potential generated via virtual photons quantum fluctuations. This trapping potential can be exploited for exciton self‐positioning in electric field hotspots at the nanoscale in view of quantum electrodynamics effects. By non Hermitian decomposition of the electromagnetic Green tensor in terms of quasi normal modes, the resonant part of the Lamb shift is expressed as Fano profile strictly interlinked to the Purcell enhancement of the exciton radiative lifetime. This approach explains how to tailor the depth of the vacuum photonic potential in several possible scenarios.

Anapole-assisted giant electric field enhancement for surface-enhanced coherent anti-Stokes Raman spectroscopy

The coherent anti-Stokes Raman spectroscopy (CARS) techniques are recognized for their ability to detect and identify vibrational coherent processes down to the single-molecular levels. Plasmonic oligomers supporting full-range Fano-like line profiles in their scattering spectrum are one of the most promising class of substrates in the context of surface-enhanced (SE) CARS application. In this work, an engineered assembly of metallic disk-shaped nanoparticles providing two Fano-like resonance modes is presented as a highly-efficient design of SECARS substrate. We show that the scattering dips corresponding to the double-Fano spectral line shapes are originated from the mutual interaction of electric and toroidal dipole moments, leading to the so-called non-trivial first- and second-order anapole states. The anapole modes, especially the higher-order ones, can result in huge near-field enhancement due to their light-trapping capability into the so-called “hot spots”. In addition, independent spectral tunability of the second Fano line shape is exhibited by modulating the gap distance of the corner particles. This feature is closely related to the electric current loop associated with the corner particles in the second-order anapole state and provides a simple design procedure of an optimum SECARS substrate, where the electric field hot spots corresponding to three involved wavelengths, i.e., anti-Stokes, pump, and Stokes, are localized at the same spatial position. These findings yield valuable insight into the plasmonic substrate design for SECARS applications as well as for other nonlinear optical processes, such as four-wave mixing and multi-photon surface spectroscopy.

The effect of gain-assisted silica separate layer on the plasmonic local field enhancement of Ag-Si-Ag coaxial-cable type silver nanotube

The plasmonic local electric field enhancement characters of gain-assisted coaxial-cable type Ag-Si-Ag nanotube have been investigated computationally. The calculation results based on quasi-static analysis indicate that the three surface plasmon resonance (SPR) hybridization modes depend on the gain medium of the silica separate layer in different ways. The SPR band from antisymmetric coupling between bonding tube plasmon mode and the wire plasmon mode (denoted as peak3) is mostly sensitive to the gain assist, and the greatest local field enhancement factor of 104 could be achieved with a critical gain coefficient. The physical mechanism has been attributed to the appearance of the local field hot spot in silica separate layer, in which the gain medium has been dropt. The critical gain coefficient could be tuned by altering the geometry factors of the nanostructure. It has been found that the thickness of the middle silica nanolayer with gain medium greatly affect the critical gain coefficient. For peak3, the maximum plasmonic field enhancement could be easily achieved with a small gain coefficient and within a slight change region. Whereas for SPR band from the symmetric coupling between the bonding tube plasmon mode and the wire plasmon mode (denoted as peak2), the local field hot spot appears in the inner Ag nanowire without gain medium. Thus the maximum plasmonic field enhancement could only be achieved with a large gain coefficient when the middle nanolayer with gain medium has a thin thickness.

Using the near field optical trapping effect of a dielectric metasurface to improve SERS enhancement for virus detection

In this paper, we report the effect of optical trapping on the enhancement factor for Raman spectroscopy, using a dielectric metasurface. It was found that a higher enhancement factor (up to 275%) can be obtained in a substrate immersed in water, where particles are freee to move, compared to a dried substrate, where the particles (radius r=9 nm, refractive index n=1.58) are fixed on the surface. The highest enhancement is obtained at low concentrations because, this case, the particles are trapped preferentially in the regions of highest electric field (hotspots). For high concentrations, it was observed that the hotspots become saturated with particles and that additional particles are forced to occupy regions of lower field. The dielectric metasurface offers low optical absorption compared to conventional gold substrates. This aspect can be important for temperature-sensitive applications. The method shows potential for applications in crystal nucleation, where high solute supersaturation can be achieved near the high-field regions of the metasurface. The high sensitivity for SERS (surface-enhanced Raman spectroscopy) at low analyte concentrations makes the proposed method highly promising for detection of small biological particles, such as proteins or viruses.

Manipulating the surface-enhanced Raman spectroscopy (SERS) activity and plasmon-driven catalytic efficiency by the control of Ag NP/graphene layers under optical excitation

Abstract Highly efficient plasmon-driven catalysis and excellent surface-enhanced Raman spectroscopy (SERS) performance are proportional to the square of the local electromagnetic field (hot spot). However, a proven way to realize the enhancement in intensity and density of “hot spot” still needs to be investigated. Here, we report on multilayered Ag nanoparticle (Ag NP)/graphene coupled to an underlying Cu film system (MAgNP-CuF) which can be used as an effective SERS substrates realizing ultra-sensitive detection for toxic molecules and in situ monitoring the plasmon-driven reaction for p-nitrothiophenol (PNTP) to p,p′-dimercaptobenzene (DMAB) conversion. The mechanism of ultra-sensitive SERS response and catalytic reaction is investigated via Ag NP/graphene layer-dependent experiments combined with theoretical simulations. The research found that the intensity and density of “hot spot” can be effectively manipulated by the number of plasmonic layers, and the bottom Cu film could also reflect the scattered and excitation beam and would further enhance the Raman signals. Moreover, the MAgNP-CuF exhibits outstanding performance in stability and reproducibility. We believe that this concept of multilayered plasmonic structures would be widely used not only in the field of SERS but also in the wider research in photocatalysis.

Coherent Networks of Si Nanocrystals: Tunable Collective Resonances with Narrow Spectral Widths

The ultralong coherent networks of Si nanocrystals (NCs) via lattice‐enhanced dipole–dipole coupling and the formation of disordered arrays of phase‐correlated field hotspots are studied. Such arrays occur in structures consisting of Si NCs randomly positioned inside long strips that are periodically repeated. The theoretical results predict the formation of all‐dielectric coherent networks of Si NCs, formed via in‐phase coupling of the resonances generated by diffraction of light. Such networks are extended along the lengths of the strips while supporting high field enhancement associated with the phase‐correlated chains of field hotspots between the nanocrystals. It is shown that these phenomena occur at the wavelengths where the Rayleigh anomaly condition is satisfied. Under this condition the electric field is squeezed between two field‐impenetrable regions, causing efficient concentration of electromagnetic energy along the disordered arrays of Si NCs in each strip. The results show that these arrays act as coherently assembled units that are efficiently coupled with the lattice modes, forming highly tunable collective resonances with spectral widths less than 5 nm. These results pave the way for all‐dielectric‐tunable optical filters with very small losses and near‐perfect reflectivity and laser systems based on Si NCs.

Exploring Research Trends and Building a Multidisciplinary Framework Related to Brownfield: A Visual Analysis Using CiteSpace

Brownfield has become one of the critical issues in modern cities. Over the past few decades, a considerable number of papers on brownfield research have been published. This study reviewed 773 documents themed with “brownfield” in the Web of Science core database between 1980 and 2020 and used the CiteSpace software to sort out the spatial and temporal distribution, knowledge groups, subject structures and hotspot fields, and evolutionary trends of global brownfield research. The analysis focuses on distribution of lead authors and their institutions, high-frequency categories and keywords, high influential journals, author contribution, and evolutionary trends based on coword analysis, coauthor analysis, cocitation analysis, and cluster analysis of documents. On the basis of the aforementioned keywords, clusters, and citation bursts analysis, this paper establishes a multidisciplinary framework for brownfield research, suggesting the main research directions for the future development, which provides theoretical support and practical guidance for the research direction of future brownfield research.

Dynamic ambient HetNet for hybrid data communication and transmission in IoT networks

In this manuscript, the Dynamic ambient HetNet for hybrid data communication and transmission in IoT networks is proposed. The lodging of colossal devices and their linkages in and beyond 5th generations (5G) has obtained a great deal of studies from academia and business. In the macro hotspot field, the uses of emerging Device-to-device (D2D), Light Fidelity (LiFi), Unmanned Aerial Vehicle (UAV) and Drones can’t simply cross the paths of transient network support prerequisites. Environmental interaction is an optional way to efficiently reduce this problem through the provision of urgent connections among limited-power servers. In addition, the effectiveness of transmission relies on parameters and range from factors like signal form, Radio frequency (RF) origin and the atmosphere, i.e. indoor or outdoor. The proposed Dynamic Ambient HetNet architecture both indoors and outdoors, where a source node is connected to the target node via radio frequency-powered relays to increases network coverage and enhance the efficiency of mobile devices either within the macro hot spot region or during the disaster area like hurricanes. This method can exploit the Wireless interweave down-convert up-convert protocol with energy-collection capacity for simultaneous information and power transfer. During the propagation from the origin node, radio frequency-powered relay can monitor hybrid data broadcasts, owing to its full duplex features. The efficiency assessment in MATLAB demonstrates the traditional models for radio frequency relay in hybrid communication. Moreover, we endow with the challenges in relation to the ambient backscatter communication network. The experimental results proved that the proposed method is better in terms of power factor and throughput gives 90%, ratio for the uplink and down link in terms of cell load has obtained 75%, and packet throughput in terms of speed has the value of 93%.

Tailoring lab-on-fiber SERS optrodes towards biological targets of different sizes

• Three different types of SERS substrates were fabricated by nanosphere lithography. • Performances were compared against different bio-targets (molecule, protein, cell). • A readout system for SERS optrode operation, via optical fiber, was optimized. In this paper, we studied the influence of the geometrical configuration of surface-enhanced Raman scattering (SERS)-active self-assembling gold nanostructures on the interaction with biological targets of different sizes, aiming at large-scope SERS lab-on-fiber optrodes composed of highly efficient SERS substrates integrated onto optical fibre tips. By using nanosphere lithography, we fabricated three types of highly ordered and reproducible SERS-active substrates. To correlate the SERS response to the steric hindrance of the biological target, we experimentally analysed and compared the SERS spectra of three representative biological probes, i.e., ultralow-molecular-weight molecules of biphenyl-4-thiol (BPT, small molecule, 186.27 Da), bovine serum albumin (BSA, medium molecule, 66.5 kDa) and red blood cells (RBCs, diameter <10 μm, complex target). All SERS-active substrates provided the Raman fingerprint of the biological targets, but the SERS intensity was dependent on the substrate geometry and its specific steric interfacing with biological targets. A full three-dimensional numerical analysis was carried out by means of the finite element method to gain insight into the electric field distribution and hot spot distribution of the fabricated structures. By correlating the electric field distribution with the SERS response, we conclude that the most efficient target-based architectures feature not only “intense” but also “accessible” hot spots. Finally, we optimized a Raman readout system for SERS optrode operation with efficient illumination and collection via an optical fibre.

Lithography-free disordered metal–insulator–metal nanoantennas for colorimetric sensing

The colorimetric detection of bio-agent targets has attracted considerable attention in nanosensor designs. This platform provides an easy to use, real-time, and rapid sensing approach, as the color change can be easily distinguished by the naked eye. In this Letter, we propose a large scale compatible fabrication route to realize colorimetric optical nanosensors with a novel configuration. For this purpose, we design and fabricate a tightly packed disordered arrangement of Fabry-Perot based metal-insulator-metal nanoantennas with a resonance frequency at visible light wavelengths. In this design, the adsorbed bio-agent changes the effective refractive index of the cavity, and this causes a shift in the resonance wavelength. The experimental data show that the proposed design can have sensitivity values >70nm/refractive index unit. Unlike other optical sensing schemes that rely mainly on hot spot formation and field enhancement, this design has a large active area with relatively uniform patterns that make it a promising approach for low-level and reliable bio-detection.

Peri-tumoral Lymphovascular density by antipodoplanin antibody D2-40, as a predictor of nodal metastasis in oral squamous cell carcinoma

BACKGROUND:&#x0D; The involvement of regional lymph nodes by cancer is a major determinant of prognosis in oral squamous cell carcinoma (OSCC) and is a significant predictor of patient survival. Peri-tumoral lymphangiogenesis is being studied as an important tool in predicting neck lymph node metastasis. Podoplanin, a transmembrane glycoprotein is expressed on lymphatic vessel endothelium and considered as a marker of lymphangiogenesis. The high podoplanin expression has been associated with invasion, progression, and metastasis of oral cancer. D2-40, an anti-podoplanin monoclonal antibody, is a specific marker of lymphatic endothelial cells. The present study was designed to investigate the peritumoral lymphovascular density (PT-LVD) by evaluating D2-40 expression and its potential utility in predicting lymph node metastasis in OSCC.&#x0D; METHODS: Seventy-two patients with OSCC were enrolled (36 with early and 36 with advanced-stage tumors). Differential expression of peritumoral lymphovascular density (PT-LVD) was evaluated using D2-40 expression by immunohistochemistry (IHC). Expression was categorized as low and high, derived from the mean of a number of vessels per 10 high power fields in hot-spots. Statistical methods were employed to correlate expression with age, gender, tumor site, stage, and neck lymph node involvement. &#x0D; RESULTS: We observed a significant association between peritumoral lymphovascular density (PT-LVD) with clinical neck lymph node status (p=0.001) and tumor stage (p=0.033). There was no significant correlation of D2-40 expression with age, gender, tumor site, T stage, and tumor differentiation.&#x0D; CONCLUSION: PT-LVD is a positive predictor of neck lymph node metastasis. It has translational potential, along with other clinical parameters for decision making in the treatment of the neck in oral cancer.

Broadband Field Enhancement and Giant Nonlinear Effects in Terminated Unidirectional Plasmonic Waveguides

Unidirectional wave propagation in nonreciprocal structures enables exciting opportunities to control and enhance wave-matter interactions in extreme ways. Within this context, here we investigate the possibility of using terminated unidirectional plasmonic waveguides to enhance typically weak nonlinear effects by orders of magnitude. We theoretically demonstrate remarkable levels of electric field enhancement and confinement (field hot spots) when the unidirectional waveguiding structure is terminated with a suitable boundary that fully stops the one-way mode. Such a large field enhancement, originating from a nonresonant effect, is fundamentally different from the narrow-band field concentration effects in resonant plasmonic structures. Instead, it is analogous to the broadband response of plasmonic tapers, but without the need for any adiabatic impedance matching. We show that this effect can indeed lead to a substantial boosting of nonlinear light-matter interactions, exemplified by an improvement of several orders of magnitude in the third-harmonic-generation efficiency, which is of large significance for several applications. More broadly, our findings show the potential of extreme nonreciprocal configurations for enhanced wave-matter interactions.

Raman enhancement properties of a high uniformity PS microsphere-Ag nanoparticle substrate

A structured SERS substrate with high uniformity and sensitivity was fabricated orderly by hydrophilizing the monocrystalline silicon substrate, self-assembling a layer of dense polystyrene (PS) microsphere array on the silicon, and depositing a layer (5 nm, 10 nm, 20 nm, 30 nm or 50 nm) of silver film. Rhodamine 6G (R6G) was used as a probe to characterize the performance of Raman enhancement. Experimental results show that our sample with deposition of a 5 nm silver film (PS-Ag-5) can obtain a large number of spatially distributed local electromagnetic field hot spots, with an enhancement factor of over 108, which is several orders of magnitude higher than that of other samples. The sensitivity of PS-Ag-5 to the concentration of probe molecules and the optical enhancement effect of PS microspheres were also analyzed. This novel structured substrate can achieve considerable uniformity, and the calculated relative standard deviation (RSD) of the characteristic peak at 1650 cm-1 is approximately 8%.

Surface-Enhanced Raman Scattering Based on Au-DNA-Ag Plasmonic Nanoparticles

The dependence of the Surface-Enhanced Raman Scattering (SERS) by gold and silver nanoparticles on their shape is examined using the organic dye, as a probe molecule. SERS has been explored extensively for applications in sensing and imaging, but the design and optimization of efficient substrates are still challenging. In order to understand and optimize the SERS process in nanoparticles, gold and silver Nanospheres and their composition as gold-DNA-silver nanoparticle were synthesized and characterized according to their average size, zeta potential and UV/visible absorption. In fact, in this research, an asymmetric new plasmonic nano-particle is proposed and designed as gold-DNA-silver and is compared to gold, silver, gold-DNA-gold, and silver-DNA-silver nanoparticles. With the help of this new nanoparticle, we design and recommend a Raman booster so that the effect of Raman is improved noticeably. It will be shown that using the proposed asymmetric nano-particle of gold-DNA-silver, the absorbance, and intensity of Raman booster is improved noticeably. In suspensions of equal nano-particle and dye concentration, the SERS effect increases as gold- DNA-silver, clearly indicating that control over the number of local field hotspots can optimize the SERS efficiency. Notably, it is demonstrated that the SERS intensity per nanoparticle scales with the magnitude of the SPR absorbance at the excitation wavelength (785 nm), providing a clear guide to optimization of the process experimentally.

Superconducting Compound Hg0.8Sb0.2Ba2Ca2Cu3O8+δ Compared with Hg0.8Sb0.2Ba2Ca1Cu2O6+δ to Evaluate Transition Temperature

The high temperature superconductor’s compounds are one of the hot spot field of science, due to their applications in industries. Hg0.8Sb0.2Ba2Ca2Cu3O8+δ and Hg0.8Sb0.2Ba2Ca1Cu2O6+δ, were manufactured using a doable-step of solid state reaction method. The samples were sintered at 800 ° C. The transition temperatures Tc are found from electrically resistively by using four probe techniques. The resistivity become zero when the transition temperature Tc(offset) have 131 and 119 K, and the onset temperature Tc(onset) have 139 K for Hg0.8Sb0.2Ba2Ca2Cu3O8+δ and 132 K for Hg0.8Sb0.2Ba2Ca1Cu2O6+δ. Analysis of X-ray diffraction showed a tetragonal structure with lattice parameters changes for all samples.

Bibliometric and Visualization Analysis of Human Coronaviruses: Prospects and Implications for COVID-19 Research.

Human coronaviruses, which can cause a range of infectious diseases, have been studied for nearly 60 years. The field has gained renewed interest from researchers around the world due to the COVID-19 outbreak in late 2019. Despite a large amount of research, little is known about the knowledge structure and developing trends of this topic. Here, we apply bibliometric analysis along with visualization tools to analyze 15,207 publications related to human coronavirus from the Scopus database, using indicators on publication and citation, journal, country or territory, affiliation and international cooperation, author, and keyword co-occurrence cluster. The results show that research on human coronavirus is dominated by SARS-CoV. Although there have been many publications, only 626 publications (4.1% of total) have more than 100 citations. The top 20 journals with most publications account for 20.6% of total publications and 41% of total citations. In addition to the United States and some European countries, many Asian and African countries are involved in this research, with China holding an important position in this area. Leading researchers from various fields of human coronavirus research are listed to facilitate collaboration and promote effective disease prevention and control. The keywords co-occurrence analysis reveals that the research focus on virology, public health, drugs and other hotspot fields, and uncovers changes in the direction of coronavirus research. The research map on human coronavirus obtained by our analysis are expected to help researchers to efficiently and effectively explore COVID-19.