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Despite the considerable research interest in InGaN‐based microdisk lasers, owing to their unique circular geometry distinct from vertical cavity surface‐emitting lasers (VCSEL) or edge‐emitting lasers, commercial products remain scant due to deficient performance under electrical injection. This study proposes an innovative method integrating a thin‐film configuration with a metallic undercut, significantly augmenting optical confinement, overlap factor, and thus lasing performance. This approach results in a diminished lasing threshold from 1500 to 670 Wcm−2 and a record high quality (Q) factor of 10100 under electrical injection. Strain relaxation in the metallic undercut, identified via scanning near‐field optical microscopy (SNOM), beneficially mitigates the Quantum Confined Stark Effect (QCSE), boosting the internal quantum efficiency of the laser. Furthermore, a beneficial blue‐shift in the emission spectrum aligns with the lasing peak, strengthening the Q factor. A tactfully implemented recessed top contact enables electrical injection lasing without optical performance compromise. The study provides invaluable insights for future microdisk laser technology advancements, potentially leading to specialized functionalities, including quantum optics, thereby opening new avenues for research and applications in this field. [ABSTRACT FROM AUTHOR]

This review paper presents an overview of the optical characterization techniques for Indium Gallium Nitride (InGaN) quantum well (QW) structures at a nanoscale. The two major techniques are reviewed—Electron Microscopy‐Cathodoluminescence (EM‐CL) and Scanning Near‐field Optical Microscopy (SNOM). It elucidates the critical role these methodologies play in revealing the complex properties of InGaN QWs, including their structural characteristics, optical properties, carrier dynamics, and the effects of defects and doping. The review highlights key findings from a variety of studies, demonstrating how EM‐CL and SNOM have contributed to the understanding of these micro‐/nano‐ structures and their potential applications in high‐efficiency optoelectronic devices. [ABSTRACT FROM AUTHOR]

Light propagation in Photonic integrated circuits (PICs), which can nowadays involve complex systems of light-guiding structures, is measured with different approaches(Nuzhdin et al., 2020, Lončar et al., 2002, Hopman et al., 2007, Morichetti et al., 2014, Sapienza et al., 2012, Vesseur et al., 2007). An interferometric polarization-sensitive measurement of the evanescent fields of these structures provides insight in the performance of the circuit detects possible malfunction with sub-wavelength precision(Engelen et al., 2007, Gersen et al., 2005, Barwick et al., 2009). We demonstrate a Near-field scanning optical microscopy (NSOM) measurement on coupled ring resonators that shows how the guided modes evolve as they propagate across the optical chip. Analysis of the measurements provides information about intensity distribution of the two polarization components (TE and TM) and their spatial confinement. The data validates our methodology and opens new possibilities for analysis of signal propagation in prototyping and optimization of integrated optical systems. Direct observation of polarization state of the guided modes allows for clear understanding of mode conversion in coupling systems.

Silver nanoparticles on a glass substrate are experimentally investigated by aperture scanning near-field optical microscopy (a-SNOM). To understand the experimental results, finite-element-method simulations are performed building a theoretical model of the a-SNOM geometry. We systematically vary parameters like aperture size, aluminum-coating thickness, tip cone angle, and tip-surface distance and discuss their influence on the near-field enhancement. All these investigations are performed comparatively for constant-height and constant-gap scanning modes. In the end, we establish a reliable and stable optical model for simulating a-SNOM measurements, which is capable of reproducing trends observed in experimental data. [ABSTRACT FROM AUTHOR]

Optical nanoantennas demonstrate the ability to confine and enhance electromagnetic fields. This ability makes nanoantennas essential tools for highresolution microscopy. The nanoantenna resonance and response can be tuned by changing their size, shape, and material as well as adjusting the probing conditions, e.g. excitation wavelength. In this paper we simulated the propagation and interaction of visible light with computer generated models of butterfly nanoantenna arrays using the finite-difference time-domain (FDTD) method. The simulations were used to understand and predict the experimental results obtained with scanning nearfield microscopy (SNOM) on commercially available samples. Simulation parameters are chosen carefully to reflect the measurement conditions. [ABSTRACT FROM AUTHOR]

Herein we investigate the character of the near-field emission of a two- (2D) and novel three-dimensional (3D) probe geometries fabricated using 3D direct laser writing lithography. Near-field scans in x–y and y–z planes were measured both before and after the deposition of hyperbolic dispersion metamaterial (HMM) to further verify the directional propagation of the high wave-vector components present in the vicinity of the structures. Additional computational and theoretical characterization forewent the actual experimental measurements, showing a promising performance, particularly for the 3D Fresnel zone plate (FZP). Overall, the experimental data documents a subwavelength resolution with a significant signal enhancement in the focal spot of the 3D FZP and highly subwavelength depth of focus.

Single-crystalline lead halide perovskite nanowires are emerging as promising one-dimensional blocks for nanoscience and nanotechnology, and extensive studies of nano-lasers and nano-photodetectors have been reported. However, as perfect confined structures, their optical waveguide performances have not been widely paid attention to up to now. Here, we report on the such issue on single-crystalline CsPbBr3 nanowires and quantify it by near-field optical response mappings. The waveguide is verified as total internal reflection mode at the visible band (532 nm), and its far-field end-facet coupling efficiency of 89.6% and propagation loss as low as 5.9 dB/mm are measured from the nanowire with cross-sectional geometry of ∼600 nm × 300 nm. No evident bending loss exists in naturally curved nanowires, while it usually emerges in artificial-bended ones due to the wrinkled surfaces. Naturally welded nanowire networks show significant advantages in integrated waveguides over the artificial assembled ones, due to the coupled photons at the space-confined end-facet segments. Roughened surface reasoned by lattice degradation is detrimental to propagation loss, but it provides leaked channels for waveguide coupling on nanowire surface. This work studies the optical waveguide performance of perovskite nanowires with different geometries and goes a step further for integrated nanophotonics. [ABSTRACT FROM AUTHOR]

We present a new methodology that enables studies of the molecular structure of graphene-liquid interfaces with nanoscale spatial resolution. It is based on Fourier transform infrared nanospectroscopy (nano-FTIR), where the infrared (IR) field is plasmonically enhanced near the tip apex of an atomic force microscope (AFM). The graphene seals a liquid electrolyte reservoir while acting also as a working electrode. The photon transparency of graphene enables IR spectroscopy studies of its interface with liquids, including water, propylene carbonate, and aqueous ammonium sulfate electrolyte solutions. We illustrate the method by comparing IR spectra obtained by nano-FTIR and attenuated total reflection (which has a detection depth of a few microns) demonstrating that the nano-FTIR method makes it possible to determine changes in speciation and ion concentration in the electric double and diffuse layers as a function of bias.

We demonstrate the formation of the near field with non-trivial phase distribution using surface plasmon interference devices, and experimental quantitative imaging of that phase with near-field phase microscopy. The phase distribution formed with a single device can be controlled by the polarization of the external illumination and the area of the device assigned to the object wave. A comparison of the experimental data to a numerical electromagnetic model and an analytical model assigns the origin of the near-field phase to the out-of-plane electric component of surface plasmon polaritons, and also verifies the predictive power of the models. We demonstrate a formation of near-field plane waves with different propagation directions on a single device, or even simultaneously at distinct areas of a single device. Our findings open the way to the imaging and tomography of phase objects in the near field.

The inherent crystal anisotropy of hexagonal boron nitride (hBN) provides the ability to support hyperbolic phonon polaritons, that is, polaritons that can propagate with very large wave vectors within the material volume, thereby enabling optical confinement to exceedingly small dimensions. Indeed, previous research has shown that nanometer-scale truncated nanocone hBN cavities, with deep subdiffractional dimensions, support three-dimensionally confined optical modes in the mid-infrared. Because of optical selection rules, only a few of the many theoretically predicted modes have been observed experimentally via far-field reflection and scattering-type scanning near-field optical microscopy (s-SNOM). The photothermal induced resonance (PTIR) technique probes optical and vibrational resonances overcoming weak far-field emission by leveraging an atomic force microscope (AFM) probe to transduce local sample expansion caused by light absorption. Here we show that PTIR enables the direct observation of previously unobserved, dark hyperbolic modes of hBN nanostructures. Leveraging these optical modes and their wide range of angular and radial momenta could provide a new degree of control over the electromagnetic near-field concentration, polarization in nanophotonic applications.

Photonic metasurfaces offer exceptional control over light at the nanoscale, facilitating applications spanning from biosensing, and nonlinear optics to photocatalysis. Many metasurfaces, especially resonant ones, rely on periodicity for the collective mode to form, which makes them subject to the influences of finite size effects, defects, and edge effects, which have considerable negative impact at the application level. These aspects are especially important for quasi-bound state in the continuum (BIC) metasurfaces, for which the collective mode is highly sensitive to perturbations due to high-quality factors and strong near-field enhancement. Here, the mode formation in quasi-BIC metasurfaces on the individual resonator level using scattering scanning near-field optical microscopy (s-SNOM) in combination with a new image processing technique, is quantitatively investigated. It is found that the quasi-BIC mode is formed at a minimum size of 10 × 10-unit cells much smaller than expected from far-field measurements. Furthermore, it is shown that the coupling direction of the resonators, defects and edge states have pronounced influence on the quasi-BIC mode. This study serves as a link between the far-field and near-field responses of metasurfaces, offering crucial insights for optimizing spatial footprint and active area, holding promise for augmenting applications such as catalysis and biospectroscopy., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

In this study, we theoretically and experimentally investigate the propagation of a second-order cylindrical vector beam through an aluminum lens which forms a tight focus at the distance of the wavelength. Simulation by the finite-difference time-domain method and the Richards–Wolf formulae produces light field distributions which coincide with experimental measurements provided with scanning near-field optical microscopy. We demonstrate that a pyramidal metallized cantilever with a hole is more sensitive to the transversal component of intensity than to the full intensity or to the Umov–Poynting vector in areas of reverse energy flow. [ABSTRACT FROM AUTHOR]

We theoretically study the broadband near-field optical spectrum of twisted bilayer graphene (TBG) at various twist angles near the magic angle using two different models. The spectrum at low Fermi energy is characterized by a series of peaks that are almost at the same energies as the peaks in the far-field optical conductivity of TBG. When the Fermi energy is near a van Hove singularity, an additional strong peak appears at finite energy in the near-field spectrum, which has no counterpart in the optical conductivity. Based on a detailed calculation of the plasmon dispersion, we show that these spectroscopic features are associated with interband and intraband plasmons, which can provide critical information about the local band structure and plasmonic excitations in TBG. The near-field peaks evolve systematically with the twist angle, so they can serve as fingerprints for identifying the spatial dependent twist angle in TBG samples. Our findings pave the way for future experimental studies of the novel optical properties of TBG in the nanoscale. [ABSTRACT FROM AUTHOR]

ABC-stacked trilayer graphene has exhibited a variety of correlated phenomena owing to its relatively flat bands and gate-tunable bandgap. However, convenient methods are still lacking for identifying ABC graphene with nanometer-scale resolution. Here we demonstrate that the scanning near-field optical microscope working in ambient conditions can provide quick recognition of ABC trilayer graphene with no ambiguity and excellent resolution (∼20 nm). The recognition is based on the difference in their near-field infrared (IR) responses between the ABA and ABC trilayers. We show that in most frequencies, the response of the ABC trilayer is weaker than the ABA trilayer. However, near the graphene phonon frequency (∼1585 cm ^−1 ), ABC’s response increases dramatically when gated and exhibits a narrow and sharp Fano-shape resonant line, whereas the ABA trilayer is largely featherless. Consequently, the IR contrast between ABC and ABA becomes reversed and can even be striking (ABC/ABA ∼ 3) near the graphene phonon frequency. The observed near-field IR features can serve as a golden rule to quickly distinguish ABA and ABC trilayers with no ambiguity, which could largely advance the exploration of correlation physics in ABC-stacked trilayer graphene.

In this study, we theoretically and experimentally investigate the propagation of a second-order cylindrical vector beam through an aluminum lens which forms a tight focus at the distance of the wavelength. Simulation by the finite-difference time-domain method and the Richards–Wolf formulae produces light field distributions which coincide with experimental measurements provided with scanning near-field optical microscopy. We demonstrate that a pyramidal metallized cantilever with a hole is more sensitive to the transversal component of intensity than to the full intensity or to the Umov–Poynting vector in areas of reverse energy flow.

Using e-beam lithography, a 16-sector spiral metalens was fabricated in an amorphous silicon, capable of converting linearly polarized incident light into an azimuthally polarized optical vortex. When illuminated by a 633-nm linearly polarized laser beam, the metalens generated a near-surface subwavelength focal spot equal to 0.75 of the incident wavelength at full-width of half-maximum intensity. The focusing performance of the spiral metalens was numerically shown to be sensitive to the deviation of the factual microrelief from the calculated height. For the designed microrelief height, a circularly polarized incident beam was focused into a bright ring with a reverse energy flow occurring at its center. For the microrelief height other than the designed one, the energy backflow effect did not occur.

In this paper, we introduce a new aperture-type near-field scanning optical microscopy (NSOM) imaging concept that relies on specially designed large-area (e.g., >200 nm x 200 nm) aperture geometries having sharp corners. Unlike in conventional NSOM, the spatial resolution of this near-field imaging modality is not determined by the size of the aperture, but rather by the sharpness of the corners of the large aperture. This approach significantly improves the light throughput of the near-field probe and, hence, increases the SNR. Here, we discuss the basic concepts of this near-field microscopy approach and illustrate both theoretically and experimentally how an array of detectors can be utilized to further improve the SNR of the near-field image. The results of this work are particularly relevant for imaging of biological samples at a spatial resolution of quality.

The photonic spin Hall effect, referring to the spatial separation of photons with opposite spins due to spin-orbit interactions, has enabled potential for various spin-sensitive applications and devices. Here, using scattering-type near-field scanning optical microscopy, we observe spin-orbit interactions introduced by a subwavelength semiring antenna integrated in a plasmonic circuit. Clear evidence of unidirectional excitation of surface plasmon polaritons is obtained by direct comparison of the amplitude- and phase-resolved near-field maps of the plasmonic nanocircuit under excitation with photons of opposite spin states coupled to a plasmonic nanoantenna. We present details of the antenna design and experimental methods to investigate the spatial variation of complex electromagnetic fields in a spin-sensitive plasmonic circuit. The reported findings offer valuable insights into the generation, characterization, and application of the photonic spin Hall effect in photonic integrated circuits for future and emerging spin-selective nanophotonic systems.

Basic and translational research in reproductive medicine can provide new insights with the application of scanning probe microscopies, such as atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM). These microscopies, which provide images with spatial resolution well beyond the optical resolution limit, enable users to achieve detailed descriptions of cell topography, inner cellular structure organization, and arrangements of single or cluster membrane proteins. A peculiar characteristic of AFM operating in force spectroscopy mode is its inherent ability to measure the interaction forces between single proteins or cells, and to quantify the mechanical properties (i.e., elasticity, viscoelasticity, and viscosity) of cells and tissues. The knowledge of the cell ultrastructure, the macromolecule organization, the protein dynamics, the investigation of biological interaction forces, and the quantification of biomechanical features can be essential clues for identifying the molecular mechanisms that govern responses in living cells. This review highlights the main findings achieved by the use of AFM and SNOM in assisted reproductive research, such as the description of gamete morphology; the quantification of mechanical properties of gametes; the role of forces in embryo development; the significance of investigating single-molecule interaction forces; the characterization of disorders of the reproductive system; and the visualization of molecular organization. New perspectives of analysis opened up by applying these techniques and the translational impacts on reproductive medicine are discussed.

The nitrogen-doped, n-type 4H-SiC with 6 μm thick epitaxial layer was irradiated at the perpendicular incidence and room temperature by 167 MeV Xe+26 ions to a fluence of 5 × 1012 cm−2. The Monte Carlo simulation code, Stopping and Range of Ions in Matter (SRIM) was used to simulate the Xe26+ ions irradiated in SiC. The Rutherford backscattering spectrometry (RBS) analysis with 3.5 MeV He++ ions which have a projected range of ~9 μm in SiC (SRIM prediction) did not detect implanted Xe. Raman spectroscopy and imaging depth profiles clearly showed three distinct parts of the swift heavy ion (SHI)-irradiated 4H-SiC, i.e. 5.6 μm irradiated epitaxial layer, 6.9 μm damaged irradiated layer and non-irradiated 4H-SiC bulk. Raman spectroscopy showed new broad bands of crystalline Si Si and distorted Si C in the damaged irradiated layer. The new Si Si bands were attributed to the ordering in the Si Si homonuclear bonds without crystal amorphization. The scanning near-field optical microscopy (SNOM) results of the SHI-irradiated 4H-SiC sample displayed a very low signal counts (transmission) compared to the virgin sample, and this difference in the optical absorption could be correlated with the defects energy levels created within the bandgap of the sample upon irradiation. • The n-type 4H-SiC with an epitaxial layer was irradiated by 167 MeV Xe ions. • Three distinct layers of the irradiated sample were demonstrated, including the thicknesses. • SNOM showed an increase in the optical absorption of the irradiated sample. [ABSTRACT FROM AUTHOR]

A scanning near-field fluorescence microscopy for in situ test is demonstrated in this letter. The scanning near-field fluorescence microscopy can be applied to commercial environmental scanning electron microscopy (ESEM) without changing the ESEM performance. The designed scanning near-field fluorescence microscopy combines the advantage of the ESEM and scanning near-field optical microscopy (SNOM). The CdSe/ZnS quantum dot samples are prepared to verify system performance. The system offers fluorescence image and topography image simultaneously with a high depth and high resolution, thus permitting further ingredient and functional research. The topography image spatial resolution and the fluorescence image spatial resolution are below 130 nm and 115 nm, respectively, with a tip aperture of ~100 nm. The image range reaches $300\,\,\times \,\,300\,\,\mu \text{m}$ by virtue of the micromanipulators and image stitching technology. [ABSTRACT FROM AUTHOR]

Purpose: Penetrating abdominal injuries caused by stabbing or firearms are rare in Germany, thus there is lack of descriptive studies. The management of hemodynamically stable patients is still under dispute. The aim of this study is to review and improve our management of penetrating abdominal injuries. Methods: We retrospectively reviewed a 10-year period from the Trauma Registry of our level I trauma center. The data of all patients regarding demographics, clinical and outcome parameters were examined. Further, charts were reviewed for FAST and CT results and correlated with intraoperative findings. Results: A total of 115 patients with penetrating abdominal trauma (87.8% men) were analyzed. In 69 patients, the injuries were caused by interpersonal violence and included 88 stab and 4 firearm wounds. 8 patients (6.9%) were in a state of shock at presentation. 52 patients (44.8%) suffered additional extraabdominal injuries. 38 patients were managed non-operatively, while almost two-thirds of all patients underwent surgical treatment. Hereof, 20 laparoscopies and 3 laparotomies were nontherapeutic. There were two missed injuries, but no patient experienced morbidity or mortality related to delay in treatment. 106 (92.2%) FAST and 91 (79.3%) CT scans were performed. Sensitivity and specificity of FAST were 59.4 and 94.2%, while those of CT were 93.2 and 85.1%, respectively. Conclusion: In hemodynamically stable patients presenting with penetrating abdominal trauma, CT is indicated and the majority of injuries can be managed conservatively. If surgical treatment is required, diagnostic laparoscopy for stable patients is feasible to avoid nontherapeutic laparotomy. [ABSTRACT FROM AUTHOR]

The surface plasmon resonance of dewetted Au structures on TiO2 substrate using physical vapor deposition and post-annealing is investigated. In this work, we employ an aperture-probe scanning near-field optical microscope (SNOM) to study the plasmonic properties of dewetted Au structures and the influence of the size, shape, and interdistance of the dewetted structures on their plasmonic behavior. This investigation is corroborated by numerical calculations performed using finite-difference time-domain (FDTD) and atomic force microscopy (AFM) to provide a realistic and direct comparison with SNOM experiments. The near-field images obtained by both experiments and simulations reveal surface plasmon resonance around Au structures which are correlated to the broadband activity in the visible light region observed by UV-Vis spectrophotometry and photoluminescence. In addition, near-field enhancement is associated with the external quantum efficiency (EQE), which shows a multi-peak response after 570 nm due higher-order modes of plasmon resonance. This broadband improvement in the visible region obtained by controlled dewetting has potential use in large-scale solar energy applications.Graphical Abstract [ABSTRACT FROM AUTHOR]

This article provides a careful comparison between the electric and mechanical excitation of a tuning fork for shear force feedback in scanning probe microscopy, an analysis not found in present literature. A setup is designed and demonstrated for robust signal and noise measurements at comparable levels of physical movement of the probe. Two different signal amplification methods, combined with two excitation ways provide three possible configurations. For each method a quantitative analysis, supported by analytical elaboration and numerical simulations, is provided. Finally, it is shown that in practical circumstances electric excitation followed by detection with a transimpedance amplifier provides the best result. • Shear force feedback provides height feedback in scanning probe microscopy. • Quartz tuning forks outfitted with sharp probe suit purpose of shear force detection. • Sub-micrometer movement of a tuning fork induces interaction between tip and sample. • Possible tuning fork excitation and signal detection methods impact measurement. [ABSTRACT FROM AUTHOR]

Silver nanoparticles on a glass substrate are experimentally investigated by aperture scanning near-field optical microscopy (a-SNOM). To understand the experimental results, finite-element-method simulations are performed building a theoretical model of the a-SNOM geometry. We systematically vary parameters like aperture size, aluminum-coating thickness, tip cone angle, and tip-surface distance and discuss their influence on the near-field enhancement. All these investigations are performed comparatively for constant-height and constant-gap scanning modes. In the end, we establish a reliable and stable optical model for simulating a-SNOM measurements, which is capable of reproducing trends observed in experimental data., (Creative Commons Attribution license.)

Recent advances in nanotechnology have opened a lot of new possibilities for nanomaterials application in wide variety of industrial, pharmaceutical, medicinal and environmental applications. This review aims to description of various Fourier Transform Infrared (FTIR)-based spectroscopic techniques suitable to characterize (i) different types of nanomaterials and (ii) various macroscopic samples at their nanoscale. In the introductory section, nanomaterials are classified according to their crucial properties, i.e. chemical composition, size and surface morphology. Application of traditional FTIR techniques, such as Attenuated Total Reflection (ATR), Diffuse Reflection (DRIFT) and infrared micro (spectro)scopy, for characterization of nanomaterials and nanostructures is compared with novel optical nanoscopic techniques derived from scanning probe microscopy which enable to overcome the diffraction limit and to characterize nanomaterials at molecular scale. [ABSTRACT FROM AUTHOR]

The paper reviews our recent achievements in developing a multimode scanning near-field optical microscopy (SNOM) technique. The multimode SNOM apparatus allows us to simultaneously measure spatial variations of photoluminescence spectra in the illumination and illumination-collection modes, their transients and sample surface morphology. The potential of this technique has been demonstrated on a polar InGaN epitaxial layer and nonpolar InGaN/GaN quantum wells. SNOM measurements have allowed revealing a number of phenomena, such as the band potential fluctuations and their correlation to the surface morphology, spatial nonuniformity of the radiative and nonradiative lifetimes, as well as the extended band nature of localized states. The combination of different modes enabled measurements of the ambipolar carrier diffusion and its anisotropy. [ABSTRACT FROM AUTHOR]