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Nanoscale Characterization of Surface Plasmon-Coupled Photoluminescence Enhancement in Pseudo Micro Blue LEDs Using Near-Field Scanning Optical Microscopy
摘要： The microcave array with extreme large aspect ratio was fabricated on the p-GaN capping layer followed by Ag nanoparticles preparation. The coupling distance between the dual-wavelength InGaN/GaN multiple quantum wells and the localized surface plasmon resonance was carefully characterized in nanometer scale by scanning near-field optical microscopy. The effects of coupling distance and excitation power on the enhancement of photoluminescence were investigated. The penetration depth was measured in the range of 39–55 nm depending on the excitation density. At low excitation power density, the maximum enhancement of 103 was achieved at the optimum coupling distance of 25 nm. Time-resolved photoluminescence shows that the recombination life time was shortened from 5.86 to 1.47 ns by the introduction of Ag nanoparticle plasmon resonance.
关键词： near-field scanning optical microscopy,micro-LEDs,localization surface plasmon
更新于2025-09-23 15:19:57
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Near-field infrared investigations of an arm-terminated spiral structure with bow-tie probe
摘要： A detailed analysis of micro- and nanoantennas is crucial for enhancing the performance of photodetectors in the mid- and far-infrared (IR) region. In contrast to the rapid progress in IR detectors based on nanodevices, the local nanoscale properties of antennas for the purpose of near-field coupling with these detectors have not been well investigated. In this work, we fabricated and studied a logarithm-spiral (log-spiral) antenna with an arm termination, which was designed as a low-loss, wide-band antenna for highly efficient near-field interaction with nanoscale IR detectors. By using a scattering-type near-field optical microscope (s-SNOM) combined with a highly stable quantum cascade laser, we observed a nanoscale spatial distribution of amplitudes generated via IR illumination on the antenna surface. Experimental and simulated results revealed a clear dependence on IR-light polarization corresponding to the rotationally symmetric structure of the spiral antenna. Furthermore, phase mapping measurements indicated a π reversal of the out-of-plane phase between two adjacent antenna probes regardless of polarization direction, providing a possibility of efficient near-field coupling with nanoscale detectors. These results demonstrate that s-SNOM imaging offers a powerful tool for gaining useful information regarding mutual coupling between optical antennas and nanostructures.
关键词： scanning near-field optical microscopy,optical phase,infrared
更新于2025-09-19 17:15:36
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High-speed imaging and tracking of very small single nanoparticles by contrast enhanced microscopy
摘要： Nanoparticles have been used extensively in biology-related research and many applications require direct visualization of individual nanoparticles by optical microscopy. For long-term and high-speed measurements, scattering-based microscopy is a unique technique because of the stable and indefinite scattering signals. In scattering-based single-particle measurements, large nanoparticles are usually needed in order to generate sufficient signals for detection. However, larger nanoparticles introduce greater mass loading, experience stronger steric hindrance, and are more prone to crosslinking. In this work, we demonstrate coherent brightfield (COBRI) microscopy with enhanced contrast and show its capability of direct visualization of very small nanoparticles in scattering at a high speed. COBRI microscopy allows us to visualize and track single metallic and dielectric nanoparticles, as small as 10 nm, at 1000 frames per second. A quantitative relationship between the linear scattering cross section of the nanoparticle and its COBRI contrast is reported. Using COBRI microscopy, we further demonstrate the tracking of 10 nm gold nanoparticles labeled to lipid molecules in supported bilayer membranes, showing that the small nanoparticles may facilitate single-molecule measurements with reduced perturbation. Furthermore, the identical imaging sensitivities of COBRI and interferometric scattering (iSCAT) is demonstrated at an equal illumination intensity. Finally, future improvements in the speed and sensitivity of scattering-based interference microscopy are discussed.
关键词： nanoparticles,scattering,iSCAT,COBRI,tracking,optical microscopy
更新于2025-09-19 17:15:36
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Optical microscopy unveils rapid, reversible electrochemical oxidation and reduction of graphene
摘要： We unveil the reaction dynamics of monolayer graphene in electrochemical oxidation and reduction processes through interference reflection optical microscopy. At 300-nanometer spatial resolution and 200-millisecond temporal resolution, we reveal rapid electrochemical oxidation of graphene, as well as its efficient electrochemical reduction back to the unoxidized state. We identify 1.4 V (vs. Ag/AgCl) as the onset voltage for oxidation, and show that the process is driven by free radicals generated in the electrolysis of water and so fully suppressible by a radical-trapping molecule. Moreover, we find the oxidation process to be spatially heterogeneous at the nanoscale, defect- and history-dependent, and characterized by a self-limiting effect unique to the two-dimensional system. We further demonstrate that electrochemical reduction rapidly reverses the oxidized graphene back to the unoxidized state in a controlled manner, and find strong dependency of reduction speed on the reduction voltage and pH, from which we conclude a one-to-one relationship between protons and electrons in the reduction process. Besides elucidating the electrochemical reaction mechanisms of graphene, our results point to new pathways to the controlled generation and fine-tuning of graphene derivatives through electrochemistry.
关键词： Graphene,reversible reduction,electrochemistry,oxidation,optical microscopy
更新于2025-09-19 17:15:36
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Near-field infrared microscopy of nanometer-sized nickel clusters inside single-walled carbon nanotubes
摘要： Nickel nanoclusters grown inside single-walled carbon nanotubes (SWCNT) were studied by infrared scattering-type scanning near-field optical microscopy (s-SNOM). The metal clusters give high local contrast enhancement in near-field phase maps caused by the excitation of free charge carriers. The experimental results are supported by calculations using the finite dipole model, approximating the clusters with elliptical nanoparticles. Compared to magnetic force microscopy, s-SNOM appears much more sensitive to detect metal clusters inside carbon nanotubes. We estimate that these clusters contain fewer than 700 Ni atoms.
关键词： s-SNOM,infrared scattering-type scanning near-field optical microscopy,magnetic force microscopy,single-walled carbon nanotubes,Nickel nanoclusters
更新于2025-09-16 10:30:52
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Directed Emission from Self‐Assembled Microhelices
摘要： Bottom-up assembly can organize simple building blocks into complex architectures for light manipulation. The optical properties of self-assembled polycrystalline barium carbonate/silica double helices are studied using fluorescent Fourier and Mueller matrix microscopy. Helices doped with fluorescein direct light emission along the long axis of the structure. Furthermore, light transmission measured normal and parallel to the long axis exhibits twist sense-specific circular retardance and waveguiding, respectively, although the measurements suffer from depolarization. The helices thus integrate highly directional emission with enantiomorph-specific polarization. This optical response emerges from the arrangement of nanoscopic mineral crystallites in the microscopic helix, and demonstrates how bottom-up assembly can achieve ordering across multiple length scales to form complex functional materials.
关键词： bioinspired materials,optical microscopy,hierarchical structures,polarimetry,self-assembly
更新于2025-09-12 10:27:22
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Skin and subcutaneous fat morphology alterations under the LED or laser treatment in rats in vivo
摘要： The main objective of this work is to quantify the dynamic/photothermal treatment by using visible LED and NIR laser irradiation through the skin of subcutaneous fat in vivo followed up by tissue sampling and histology. The optical method may provide reduction of regional or site-specific accumulations of abdominal or subcutaneous adipose tissue precisely and least-invasively by inducing cell apoptosis and controlled necrosis of fat tissue. As photo-dynamic/photothermal adipose tissue sensitizers Brilliant Green (BG) or Indocyanine Green (ICG) dyes were injected subcutaneously in rats. The CW LED device (625 nm) or CW diode laser (808 nm) were used as light sources, respectively. Biopsies of skin together with subcutaneous tissues were taken for histology. The combined action BG-staining and LED-irradiation (BG + LED) or ICG-staining and NIR-laser irradiation (ICG + NIR) causes pronounced signs of damage of adipose tissue characterized by a strong stretching, thinning, folding and undulating of cell membranes and appearance of necrotic areas. As a posttreatment after 14 days only connective tissue was observed at the site of necrotic areas. The data obtained are important for safe light treatment of site-specific fat accumulations, including cellulite. This work provides a basis for the development of fat lipolysis technologies and to move them to clinical applications.
关键词： visible light,laser,optical microscopy,fat morphology,skin,subcutaneous adipose tissue,photodynamic and photothermal treatment,LED,Brilliant Green,NIR,Indocyanine Green (ICG)
更新于2025-09-11 14:15:04
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Near‐field analysis of discrete bowtie plasmonic nanoantennas
摘要： A discrete antenna is a discretized version of a traditional antenna design which enhances the antenna properties (such as field intensity, multi-band, compact size, and low sidelobe levels) of its traditional counterpart. In this work, a classical bowtie antenna is discretized using circular elements of different sizes. Numerical simulations and near-field optical scanning microscopy are performed on classical and discrete bowtie antennas in the infrared. Simulations show that discrete antennas have an increased bandwidth and an increased number of electric-field hot-spots and near-field measurements confirm the increment of hotspots. These characteristics make discrete antennas potentially useful in applications where an extended region of localized electric field enhancements is of interest.
关键词： discrete bowtie,scanning-scattering near-field optical microscopy,plasmonic nanoantenna
更新于2025-09-11 14:15:04
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Correlated Materials Characterization via Multimodal Chemical and Functional Imaging
摘要： Multimodal chemical imaging simultaneously offers high resolution chemical and physical information with nanoscale, and in select cases atomic resolution. By coupling modalities that collect physical and chemical information, we can address scientific problems in biological systems, battery and fuel cell research, catalysis, pharmaceuticals, photovoltaics, medicine and many others. The combined systems enable local correlation of material properties with chemical makeup, making fundamental questions in how chemistry and structure drive functionality approachable. In this review we present recent progress and offer a perspective for chemical imaging used to characterize a variety of samples by a number of platforms. Specifically, we present cases in infrared and Raman spectroscopies combined with scanning probe microscopy; optical microscopy and mass spectrometry; nonlinear optical microscopy; and finally, ion, electron and probe microscopies with mass spectrometry. We also discuss the challenges associated with the use of data originated by the combinatorial hardware, analysis, and machine learning as well as processing tools necessary for interpretation of multidimensional data acquired from multimodal studies.
关键词： raman spectroscopy,ion microscopy,nonlinear optical microscopy,mass spectrometry,electron microscopy,infrared spectroscopy,chemical imaging,scanning probe microscopy,data analytics,optical microscopy
更新于2025-09-10 09:29:36
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In-Plane Optical Anisotropy of Low-Symmetry 2D GeSe
摘要： As a new member of 2D materials, GeSe has attracted considerable attention recently due to its fascinating in-plane anisotropic vibrational, electrical, and optical properties originating from the low-symmetry crystal structure. Among these anisotropic properties, the anisotropic optical property, as a new degree of freedom to manipulate optoelectronic properties in 2D materials, is of great importance for practical applications. However, the fundamental understanding of the optical anisotropy of GeSe is still under exploration, severely restricting its utility in polarization-sensitive optical systems. Here, a systematic study about the in-plane optical anisotropy of GeSe is reported, including its anisotropic optical absorption, reflection, extinction, and refraction. The anisotropic band structure of GeSe is experimentally observed for the first time through angle-resolved photoemission spectroscopy, explaining the origin of the optical anisotropy. The anisotropic reflection and refraction of GeSe are further directly visualized through the angle-dependent optical contrast of GeSe flakes by azimuth-dependent reflectance difference microscopy and polarization-resolved optical microscopy, respectively. Finally, GeSe-based photodetectors exhibit a polarization-sensitive photoresponsivity due to the intrinsic linear dichroism. This study provides fundamental information for the optical anisotropy of GeSe, forcefully stimulating the exploration of novel GeSe-based optical and optoelectronic applications.
关键词： polarization-resolved optical microscopy,azimuth-dependent reflectance difference microscopy,birefringence,angle-resolved photoemission spectroscopy,germanium monoselenide
更新于2025-09-10 09:29:36