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Close Up and Far Out : Seeing the World Differently
\"An illustrated picture book of early scientists Antonie van Leeuwenhoek and Galileo Galilei, who used similar observation tools but saw the world very differently, their discoveries leading to innovations in both microscopes and telescopes.\" -- Provided by publisher.
BOOK
On-chip nanophotonic topological rainbow
The era of Big Data requires nanophotonic chips to have large information processing capacity. Multiple frequency on-chip nanophotonic devices are highly desirable for density integration, but such devices are more susceptible to structural imperfection because of their nano-scale. Topological photonics provides a robust platform for next-generation nanophotonic chips. Here we give an experimental report of an on-chip nanophotonic topological rainbow realized by employing a translational deformation freedom as a synthetic dimension. The topological rainbow can separate, slow, and trap topological photonic states of different frequencies into different positions. A homemade scattering scanning near-field optical microscope with high resolution is introduced to directly measure the topological rainbow effect of the silicon-based photonic chip. The topological rainbow based on synthetic dimension have no restrictions for optical lattice types, symmetries, materials, wavelength band, and is easy for on-chip integration. This work builds a bridge between silicon chip technologies and topological photonics.
Here the authors provide the experimental observation of a topological rainbow in a silicon-based nanophotonic chip. The system is robust against disorders allows to separate and trap topological photonic states of different wavelength into different positions.
Journal Article
Nano-spectroscopy of excitons in atomically thin transition metal dichalcogenides
Excitons play a dominant role in the optoelectronic properties of atomically thin van der Waals (vdW) semiconductors. These excitons are amenable to on-demand engineering with diverse control knobs, including dielectric screening, interlayer hybridization, and moiré potentials. However, external stimuli frequently yield heterogeneous excitonic responses at the nano- and meso-scales, making their spatial characterization with conventional diffraction-limited optics a formidable task. Here, we use a scattering-type scanning near-field optical microscope (s-SNOM) to acquire exciton spectra in atomically thin transition metal dichalcogenide microcrystals with previously unattainable 20 nm resolution. Our nano-optical data revealed material- and stacking-dependent exciton spectra of MoSe
2
, WSe
2
, and their heterostructures. Furthermore, we extracted the complex dielectric function of these prototypical vdW semiconductors. s-SNOM hyperspectral images uncovered how the dielectric screening modifies excitons at length scales as short as few nanometers. This work paves the way towards understanding and manipulation of excitons in atomically thin layers at the nanoscale.
Excitons play an important role in the optical properties of 2D semiconductors, but their spatial characterization is usually constrained by the diffraction limit. Here, the authors report near-field optical spectroscopy of 2D transition metal dichalcogenides with 20 nm resolution, revealing their spatially dependent excitonic spectra and complex dielectric function.
Journal Article
Experimental investigation on mechanical behaviors of Nanan granite after thermal treatment under conventional triaxial compression
Understanding the mechanical behaviors of granite after high temperature exposure and under confining stress conditions is an important issue in deep rock engineering projects such as the mining of deep underground solid mineral resources, deep geothermal energy exploitation and deep nuclear waste repositories. In this research, conventional triaxial compression experiments were conducted on Nanan granite after thermal treatment from 200 °C to 600 °C. Based on the experimental results, the influences of pressure and temperature on the deformation and strength characteristics were analysed. The physico-mechanical change mechanisms of the heat-treated granite were revealed by optical microscopy. The test results show that under 600 °C, granite volume increases by 4.11%, whereas the mass and density decrease by 0.28% and 4.21%, respectively. Average values of triaxial compressive strength and elastic modulus, cohesion and internal friction angle all reduce with temperature, decreasing rapidly by 54.99%, 39.81%, 49.39% and 27.51% from 500 to 600 °C, respectively. Granite specimens are less brittle and have higher ductility and plasticity as the temperature increases. However, confining pressure improves the mechanical properties of granite. Optical microscope images show that microcracks in granite specimens are generated and extend gradually with temperature, causing the deterioration of the physico-mechanical behaviors of heat-treated granite.
Journal Article
Terahertz near-field imaging of graphene disks
Due to the weak power of Terahertz sources, metal tips are often used to enhance the signal intensity of the Terahertz scattering scanning near-field optical microscope (THz s-SNOM). However, while enhancing the near-field, metal tips also affect the field distribution on the sample surface. In this paper, a home-built 97.8GHz sub-Terahertz near-field imaging system was used to image graphene disks with dozens of microns in diameter. It was found that the field distribution was significantly different from that without the tip, and was related to the incident direction of the terahertz wave.
Journal Article
Recent progress and challenges on two-dimensional material photodetectors from the perspective of advanced characterization technologies
Atomically thin two-dimensional (2D) materials exhibit enormous potential in photodetectors because of novel and extraordinary properties, such as passivated surfaces, tunable bandgaps, and high mobility. High-performance photodetectors based on 2D materials have been fabricated for broadband, position, polarization-sensitive detection, and large-area array imaging. However, the current performance of 2D material photodetectors is not outstanding enough, including response speed, detectivity, and so forth. The way to further promote the development of 2D material photodetectors and their corresponding practical applications is still a tremendous challenge. In this article, these issues of 2D material photodetectors are analyzed and expected to be solved by combining micro-nano characterization technologies. The inherent physical properties of 2D materials and photodetectors can be accurately characterized by Raman spectroscopy, transmission electron microscopy (TEM), and scattering scanning near-field optical microscope (s-SNOM). In particular, the precise probe of lattice defects, doping concentration, and near-field light absorption characteristics can promote the researches of low-noise and high-responsivity photodetectors. Scanning photocurrent microscope (SPCM) can show the overall spatial distribution of photocurrent and analyze the mechanism of photocurrent. Photoluminescence (PL) spectroscopy and Kelvin probe force microscope (KPFM) can characterize the material bandgap, work function distribution and interlayer coupling characteristics, making it possible to design high-performance photodetectors through energy band engineering. These advanced characterization techniques cover the entire process from material growth, to device preparation, and to performance analysis, and systematically reveal the development status of 2D material photodetectors. Finally, the prospects and challenges are discussed to promote the application of 2D material photodetectors.
Journal Article
Near-Field Imaging of Hybrid Surface Plasmon-Phonon Polaritons on n-GaN Semiconductor
Near-field imaging of the hybrid surface plasmon-phonon polaritons on the n-GaN semiconductor was performed using a scattering scanning near-field optical microscope at the selected frequencies of 920 cm−1 and 570 cm−1. The experimental measurements and numerical modeling data were in good agreement, revealing the large propagation distances on the n-GaN semiconductor and other insights which could be obtained by analyzing the dispersion characteristics of hybrid polaritons. In particular, the decay lengths of polaritons at the excitation frequency of 920 cm−1 were measured to be up to 25 and 30 µm in experiment and theory, respectively. In the case of excitation at the frequency of 570 cm−1, the surface plasmon-phonon polaritons’ decay distances were 25 µm and 105 µm, respectively, noting the limitations of the near-field optical microscope setups used. Dispersion characteristics of the resonant frequency and the damping rate of hybrid polaritons were numerically modeled and compared with the analytical calculations, validating the need for further experiment improvements. The launch conditions for the near-field observation of extraordinary coherence of the surface plasmon-phonon polaritons were also discussed.
Journal Article
An optical microscope algorithm with precise focusing strategy and migration strategy with application in 3D path planning
The optical microscope algorithm (OMA) has garnered significant attention due to its clear mechanism and effectiveness in solving various optimization problems. However, the approach demonstrates vulnerabilities to premature convergence and local solution attraction, particularly in complex, high-dimensional problem spaces. Therefore, this paper proposes OMA with a precise focusing strategy and migration strategy (PMOMA). Firstly, a multi-fusion strategy will be proposed to enhance the initial population quality. Secondly, an introduction of the precise focusing strategy enhances the exploration ability of the algorithm and accelerates convergence speed. Finally, introducing a migration strategy prevents the algorithm from falling into local optima, resulting in improved solution accuracy. To evaluate PMOMA’s performance, we compare it with 9 other algorithms in CEC 2017 benchmark functions, Virtual Library of Simulation Experiments, and NLtoolbox. Additionally, PMOMA was implemented for solving engineering applications and 3D path planning to further validate its effectiveness. Overall, PMOMA demonstrated superiority in both numerical benchmarks and practical experiments.
Journal Article
A liquid crystal–based biosensor for sensitive detection of tumor necrosis factor-alpha
Tumor necrosis factor-alpha (TNF-α) is a cytokine secreted by the macrophages and Th1 cells of the immune system in response to inflammation. Given its significance as a biomarker with elevated levels in physiological fluids in various conditions, there is an increasing demand for a simple and accurate TNF-α detection strategy. In this article, we present a liquid crystal (LC)–based biosensor developed for sensitive TNF-α detection. The biosensor operates as follows: TNF-α and detection antibodies (DAbs) form complexes during preincubation. These complexes then bind with the surface-immobilized capture antibodies (CAbs), facilitating the antigen–antibody reaction between the CAbs and the TNF-α/DAb complexes. This target recognition interaction alters the surface topography, disrupting the vertical orientation of LCs produced by dimethyloctadecyl[3-(trimethoxysilyl)-propyl]ammonium chloride. The orientational change in the LCs can be easily visualized with a polarized optical microscope, resulting in brighter images as TNF-α levels rise. Our results demonstrated a linear range of 5.00–500 pg/mL, with a limit of detection and limit of quantification being 1.08 and 3.56 pg/mL, respectively. Recovery experiments on diluted saliva samples produced reasonable results, with TNF-α recoveries ranging from 97.1% ± 2.58% to 107% ± 5.95%.
Graphical Abstract
Journal Article
Nanoscale resolved mapping of the dipole emission of hBN color centers with a scattering-type scanning near-field optical microscope
Color centers in hexagonal boron nitride (hBN) are promising candidates as quantum light sources for future technologies. In this work, we utilize a scattering-type near-field optical microscope (s-SNOM) to study the photoluminescence (PL) emission characteristics of such quantum emitters in metalorganic vapor phase epitaxy grown hBN. On the one hand, we demonstrate direct near-field optical excitation and emission through interaction with the nanofocus of the tip resulting in a subdiffraction limited tip-enhanced PL hotspot. On the other hand, we show that indirect excitation and emission via scattering from the tip significantly increases the recorded PL intensity. This demonstrates that the tip-assisted PL (TAPL) process efficiently guides the generated light to the detector. We apply the TAPL method to map the in-plane dipole orientations of the hBN color centers on the nanoscale. This work promotes the widely available s-SNOM approach to applications in the quantum domain including characterization and optical control.
Journal Article