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Deeply subwavelength phonon-polaritonic crystal made of a van der Waals material
摘要： Photonic crystals (PCs) are periodically patterned dielectrics providing opportunities to shape and slow down the light for processing of optical signals, lasing and spontaneous emission control. Unit cells of conventional PCs are comparable to the wavelength of light and are not suitable for subwavelength scale applications. We engineer a nanoscale hole array in a van der Waals material (h-BN) supporting ultra-confined phonon polaritons (PhPs)—atomic lattice vibrations coupled to electromagnetic fields. Such a hole array represents a polaritonic crystal for mid-infrared frequencies having a unit cell volume of 10??λ?3 (with λ? being the free-space wavelength), where PhPs form ultra-confined Bloch modes with a remarkably flat dispersion band. The latter leads to both angle- and polarization-independent sharp Bragg resonances, as verified by far-field spectroscopy and near-field optical microscopy. Our findings could lead to novel miniaturized angle- and polarization-independent infrared narrow-band couplers, absorbers and thermal emitters based on van der Waals materials and other thin polar materials.
关键词： van der Waals material,near-field microscopy,phonon-polaritonic crystal,mid-infrared,hexagonal boron nitride,Bragg resonance
更新于2025-09-23 15:23:52
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In vivo multiphoton microscopy detects longitudinal metabolic changes associated with delayed skin wound healing
摘要： Chronic wounds are difficult to diagnose and characterize due to a lack of quantitative biomarkers. Label-free multiphoton microscopy has emerged as a useful imaging modality capable of quantifying changes in cellular metabolism using an optical redox ratio of FAD/(NADH+FAD) autofluorescence. However, the utility of an optical redox ratio for long-term in vivo monitoring of tissue metabolism has not been robustly evaluated. In this study, we demonstrate how multiphoton microscopy can be used to monitor changes in the metabolism of individual full-thickness skin wounds in vivo. 3D optical redox ratio maps and NADH fluorescence lifetime images identify differences between diabetic and control mice during the re-epithelialization of wounds. These metabolic changes are associated with a transient increase in keratinocyte proliferation at the wound edge. Our study demonstrates that high-resolution, non-invasive autofluorescence imaging can be performed in vivo and that optical redox ratios can serve as quantitative optical biomarkers of impaired wound healing.
关键词： metabolism,optical redox ratio,autofluorescence,multiphoton microscopy,in vivo imaging,diabetes,FAD,NADH,wound healing
更新于2025-09-23 15:23:52
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Probing shear-induced rearrangements in Fourier space. II. Differential dynamic microscopy
摘要： We discuss in two companion papers how Fourier-space measurements may be coupled to rheological tests in order to elucidate the relationship between mechanical properties and microscopic dynamics in soft matter. In this second companion paper, we focus on Differential Dynamic Microscopy (DDM) under shear. We highlight the analogies and the differences with dynamic light scattering coupled to rheology, providing a theoretical approach and practical guidelines to separate the contributions to DDM arising from the affine and the non-affine part of the microscopic displacement field. We show that in DDM under shear the coherence of the illuminating source plays a key role, determining the effective sample thickness that is probed. Our theoretical analysis is validated by experiments on 2D samples and 3D gels.
关键词： non-affine deformation,shear,soft matter,affine deformation,rheology,Differential Dynamic Microscopy
更新于2025-09-23 15:23:52
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Dislocation bending and stress evolution in Mg-doped GaN films on Si substrates
摘要： P-type doping using Mg is essential for realizing a variety of electronic and optoelectronic III-nitride devices involving hetero-epitaxial thin films that also contain a significant number of dislocations. We report on the effect of Mg incorporation on dislocation and stress evolution during the growth of GaN thin films by using in situ curvature measurements and ex situ transmission electron microscopy. A complete picture involving the interplay between three effects—dopant size effect, dislocation bending, and polarity inversion—is presented. Mg aids dislocation bending, which in turn generates tensile stresses in Mg-doped GaN films. As a result, the compressive stress expected due to the dopant size difference effect can only be discerned clearly in films with dislocation densities below 5 × 10^9 cm^?2. Polarity inversion at doping exceeding 10^19 cm^?3 is associated with a sharp drop in screw dislocation density. A kinetic stress evolution model has been developed to capture dislocation bending and size difference effects, and a match between calculated bending angle from the model and that measured from TEM images is obtained.
关键词： Mg doping,stress evolution,dislocation bending,in situ curvature measurements,transmission electron microscopy,polarity inversion,GaN
更新于2025-09-23 15:23:52
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Photoswitching FRET to monitor protein–protein interactions
摘要： FRET is a powerful approach to study the interactions of fluorescent molecules, and numerous methods have been developed to measure FRET in cells. Here, we present a method based on a donor molecule's photoswitching properties, which are slower in the presence vs. the absence of an acceptor. The technique, photoswitching FRET (psFRET), is similar to an established but underutilized method called photobleaching FRET (pbFRET), with the major difference being that the molecules are switched 'off' rather than photobleached. The psFRET technique has some of the FRET imaging advantages normally attributed to fluorescence lifetime imaging microscopy (FLIM), such as monitoring only donor fluorescence. However, it can be performed on a conventional widefield microscope, requires less illumination light to photoswitch off than photobleaching, and can be photoswitched 'on' again to repeat the experiment. We present data testing the validity of the psFRET approach to quantify FRET in cells and demonstrate its use in imaging protein–protein interactions and fluorescent protein-based biosensors.
关键词： FRET,imaging,microscopy,photoswitchable,fluorescence
更新于2025-09-23 15:23:52
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Silver Nanostructures on Graphene Oxide as the Substrate for Surface-Enhanced Raman Scattering (SERS)
摘要： Nanosized surface-enhanced Raman scattering (SERS) substrates fabricated by the controlled growth of metal nanostructures on water-dispersed two-dimensional nanomaterials can open a new avenue for SERS analysis of liquid samples in biological fields. In this work, regular and uniform Ag nanostructures were grown on the surface of graphene oxide (GO) through a microwave-assisted hydrothermal method. Polyamidoamine (PAMAM) dendrimers were assembled on the surface of GO to form GO/PAMAM templates for growing Ag nanostructures, which are primarily comprised of Ag dimers and trimers. The prepared Ag/GO nanocomposites are highly dispersed and stable in aqueous solution and may be used as substrates for enhanced Raman detection of rhodamine 6 G (R6G) in aqueous solution. This special substrate provides high-performance SERS and suppresses R6G fluorescence in aqueous solution and is promising as a nanosized material for the enhanced Raman detection of liquid samples in biological diagnostics.
关键词： graphene oxide (GO),Surface-enhanced Raman scattering (SERS),polyamidoamine (PAMAM) dendrimers,transmission electron microscopy (TEM),Fourier transform infrared (FTIR) spectroscopy,rhodamine 6G (R6G)
更新于2025-09-23 15:23:52
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Esters of 4-nitrocinnamic acids and 4-halogene-4’-hydroxyazobenzenes – synthesis, mesogenic and optical studies
摘要： Six new compounds were synthesized that have no alkyl chains in their structure: 4-nitrocinnonates of 4-hydroxyazobenzene, 4-nitro-4'-hydroxyazobenzene, 4-fluoro-4'-hydroxyazobenzene, 4-chloro-4'-hydroxyazobenzene, 4-bromo-4'-hydroxyazobenzene, and 4-iodo-4'-hydroxyazobenzene. Using the polarizing microscopy and differential scanning calorimetry, enthalpies and temperatures of phase transitions were determined. All investigated compounds have an enantiotropic nematic phase. These compounds proved to be extremely thermally stable. Thermal decomposition was observed in temperatures above 300°C. Investigated compounds contain two different chromophore groups (i.e. azo and ethene moieties), which influenced the complex trans–cis isomerization processes of both groups (three time-separated processes were observed). It was shown that the presence of the ethene group significantly shifts the π-π* band towards higher energies. The substituent polarity in the azo group also affected the energy of this absorption band. A weak luminescence effect was observed in the 4-nitrocinnonates of 4-hydroxyazobenzene compound.
关键词： nematic,luminescence,Azobenzenes,trans–cis isomerization,polarizing microscopy,DSC calorimetry
更新于2025-09-23 15:23:52
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Optical thickness identification of few-layer MoS <sub/>2</sub> deposited by chemical vapor deposition
摘要： The physical and optoelectronic properties of MoS2 are closely related to their thickness. Few-layer molybdenum disulfide (MoS2) has been intensively studied for its potential applications. In this work, monolayer and few-layer MoS2 nanosheets with large size and high crystallization quality were successfully prepared by chemical vapor deposition (CVD). Then, the layer number of CVD-grown MoS2 nanosheets were identified for the first time by extracting the R channel contrast of the optical image of the sample with ImageJ software. Compared with Raman spectra and PL spectra, this method can identify the layer number of CVD-grown MoS2 nanosheets efficiently and accurately, which provides a simple and feasible method for the study of the layer number of CVD-grown MoS2 nanosheets and can help us exploiting their applications in the future.
关键词： Thickness identification,chemical vapor deposition,MoS2,optical microscopy,Raman spectroscopy
更新于2025-09-23 15:23:52
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Preliminary Clinical Microneurosurgical Experience With the 4K3-Dimensional Microvideoscope (ORBEYE) System for Microneurological Surgery: Observation Study
摘要： BACKGROUND: The exoscope has been reported as a novel neurosurgical instrumentation in clinical practice. OBJECTIVE: To investigate the possibility that ORBEYE (OE), a novel instrument that excludes eyepiece lenses and allows for microsurgery by observation of the 4K3D monitor, could replace microscopes. METHODS: We report 22 clinical cases by 5 experienced neurosurgeons and the comparative results of training 10 residents. An observation study with questionnaire survey was conducted on usability. Twelve items including image quality, eyestrain, and function of the arm were evaluated. RESULTS: The following 22 clinical procedures were conducted: surgery for intracranial hemorrhage (n = 2) and brain tumor (n = 8), laminectomy (n = 3), aneurysm clipping (n = 3), vascular anastomosis (n = 2), carotid endarterectomy (n = 2), and nerve decompression (n = 1). No complications were observed. The fluorescent study, including indocyanine-green and 5-aminolevunic acid, allowed for clear depiction on the 4K monitor. The surgeon could operate in a comfortable posture. Similar to the microscope, it was possible to change the optical and viewing axes with the OE, but the OE was switched to the microscope or endoscope in hematoma removal and pituitary surgery. Residents judged that eyestrain was strong (P = .0096). Experienced neurosurgeons acting as assistants judged that the scope arm’s range of movement was narrow (P = .0204). Sixty percent of residents judged that the OE was superior to the microscope. CONCLUSION: Although based on limited experience, it was not possible to substitute the microscope with the OE in all operations; however, the OE surpasses the microscope in terms of ergonomic features.
关键词： Microsurgery,Fluorescence,Microscopy,Endoscope
更新于2025-09-23 15:23:52
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Self-trapping and ordering of heavy holes in the wide band-gap semiconductor
摘要： Scanning tunneling microscopy (STM) has been utilized for imaging and manipulation of self-trapped holes on the surface of the wide band-gap semiconductor β-Ga2O3. A positively charged surface layer comprised of localized holes with 1013 cm?2 density has been observed for n-doped samples. We show that the surface layer can be populated by hole pumping from the STM tip. A transition between the glassy phase and ordered striped phase of self-trapped holes has also been observed. Our analysis indicates that the saturated two-dimensional density of self-trapped holes may be determined by balance of self-trapping and Coulomb repulsion energies.
关键词： β-Ga2O3,scanning tunneling microscopy,self-trapping,heavy holes,charge ordering,Wigner-Mott regime
更新于2025-09-23 15:23:52