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An optical test to unveil twisting of birefringent crystals in spherulites
摘要： Helical conformations and structures are frequently observed in materials. The presence of helices at points of the unit cell of a crystal, on a larger size scale in the crystalline lattice or even in the microscopic structure of crystals, affects the chemico-physical properties of a solid and, hence, also interactions with light. Here, attention has been drawn to the geometrical properties of helices produced by a hypothetical torque of a transparent crystal, and optical properties of twisted crystals easily observed by a polarizing microscope have been discussed. Radially grown spherulites are obtained by most substances crystallized from melt. The circular optical arrangement of behaviour of larger dimensions of spherulites, allows investigations otherwise hardly feasible on separate crystals. According to the torsional analysis of elongated bodies and the birefringence theory, information on the existence of helically shaped crystals can be deduced, as hereinafter explained, from the microscopic appearance and birefringence pattern of spherulites. Indeed, twisting decreases the birefringence throughout an elongated crystal and, therefore, also the birefringence of spherulites formed by twisted radial crystals is reduced.
关键词： optical microscopy,microstructure,helical deformation,birefringence,crystals,banding
更新于2025-10-24 16:38:51
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Controlling the Dynamics and Optical Binding of Nanoparticle Homodimers with Transverse Phase Gradients
摘要： While transverse phase gradients enable studies of driven nonequilibrium phenomena in optical trapping, the behavior of electrodynamically interacting particles in a transverse phase gradient has not been explored in detail. In this Letter we study electrodynamically interacting pairs of identical nanoparticles (homodimers) in transverse phase gradients. We establish that the net driving force on homodimers is modulated by a separation-dependent interference effect for small phase gradients. By contrast, large phase gradients break the symmetry of the interaction between particles and profoundly change the electrodynamic interparticle energy landscape. Our findings are particularly important for understanding multiparticle dynamics during the self-assembly and rearrangement of optical matter.
关键词： nonequilibrium,optical trapping,optical microscopy
更新于2025-09-23 15:23:52
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Automated quantification of immunomagnetic beads and leukemia cells from optical microscope images
摘要： Quanti?cation of tumor cells is crucial for early detection and monitoring the progress of cancer. Several methods have been developed for detecting tumor cells. However, automated quanti?cation of cells in the presence of immunomagnetic beads has not been studied. In this study, we developed computer vision based algorithms to quantify the leukemia cells captured and separated by micron size immunomagnetic beads. Color, size based object identi?cation and machine learning based methods were implemented to quantify targets in the images recorded by a bright ?eld microscope. Images acquired by a 40× or a 20× objective were analyzed, the immunomagnetic beads were detected with an error rate of 0.0171 and 0.0384 respectively. Our results reveal that the proposed method attains 91.6% precision for the 40× objective and 79.7% for the 20× objective. This algorithm has the potential to be the signal readout mechanism of a biochip for cell detection.
关键词： Leukemia cells,Immunomagnetic beads,Support vector machines,Bright-?eld optical microscopy,Image-processing,Machine learning
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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Applications of nanostructures in wide-field, label-free super resolution microscopy
摘要： Super resolution imaging capable of resolving details beyond the diffraction limit is highly desired in many scientific and application fields, including bio-medicine, nanomaterial science, and opto-electronic integration. Up to now, many different methods have been proposed, among which wide-field, label-free super resolution microscopy is indispensable due to its good applicability to diverse sample types, large field of view (FOV), and high imaging speed. In recent years, nanostructures have made a crucial contribution to the wide-field, label-free subdiffraction microscopy, with various working mechanisms and configuration designs. This review summarizes the recent applications of the nanostructures in the wide-field, label-free super resolution microscopy, with the emphasis on the designs of hyperlens with hyperbolic dispersion, microsphere with “nano-jets”, and nanowire ring illumination microscopy based on spatial frequency shift effect. The bottlenecks of the current techniques and possible solutions are also discussed.
关键词： spatial resolution,nanowire,metamaterials,optical microscopy
更新于2025-09-23 15:23:52
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Effects of temporary fogging and defogging in plastic scintillators
摘要： Recent studies have shown that under certain environmental conditions, plastic scintillators which are used in a variety of applications in outdoor environments develop defects called "fogging", resulting in a reduced useful lifetime and increased maintenance cost. Applications of plastic scintillators include scanning recycled steel going into a processing plant, personnel portals to scan employees, and scanning cargo and cars crossing borders of many countries. In this report, fogging was studied in conventional PVT and PS-based plastic scintillators, both field aged and freshly cast. A new fogging-resistant PVT-based formulation developed by scientists at Lawrence Livermore National Laboratory (LLNL) was tested as well. We used accelerated aging experiments via temperature and humidity cycling in controlled laboratory conditions to create observable temporary fogging defects in small samples (≤1 in3). Photoluminescence and optical transmission studies were used to evaluate the effect of the fogging. The time evolution of the induced temporary fogging formation and defogging (i.e. fading of defects in ambient conditions over time) were recorded using optical microscopy, time-lapse photography, and gravimetric analysis.
关键词： Accelerated aging,Optical microscopy,Scintillator,Gamma detection
更新于2025-09-23 15:22:29
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Quasi-1D TiS <sub/>3</sub> Nanoribbons: Mechanical Exfoliation and Thickness-Dependent Raman Spectroscopy
摘要： Quasi-one-dimensional (quasi-1D) materials enjoy growing interest due to their unusual physical properties and promise for miniature electronic devices. However, the mechanical exfoliation of quasi-1D materials into thin flakes and nanoribbons received considerably less attention from researchers than the exfoliation of conventional layered crystals. In this study, we investigated the micromechanical exfoliation of representative quasi-1D crystals, TiS3 whiskers, and demonstrate that they typically split into narrow nanoribbons with very smooth, straight edges and clear signatures of 1D TiS3 chains. Theoretical calculations show that the energies required for breaking weak interactions between the two-dimensional (2D) layers and between 1D chains within the layers are comparable and, in turn, are considerably lower than those required for breaking the covalent bonds within the chains. We also emulated macroscopic exfoliation experiments on the nanoscale by applying a local shear force to TiS3 crystals in different crystallographic directions using a tip of an atomic force microscopy (AFM) probe. In the AFM experiments, it was possible to slide the 2D TiS3 layers relative to each other as well as to remove selected 1D chains from the layers. We systematically studied the exfoliated TiS3 crystals by Raman spectroscopy and identified the Raman peaks whose spectral positions were most dependent on the crystals’ thickness. These results could be used to distinguish between TiS3 crystals with thickness ranging from one to about seven monolayers. The conclusions established in this study for the exfoliated TiS3 crystals can be extended to a variety of transition metal trichalcogenide materials as well as other quasi-1D crystals. The possibility of exfoliation of TiS3 into narrow (few-nm wide) crystals with smooth edges could be important for the future realization of miniature device channels with reduced edge scattering of charge carriers.
关键词： transition metal trichalcogenides,quasi-one-dimensional materials,scanning near-field optical microscopy,Raman spectroscopy,mechanical exfoliation
更新于2025-09-23 15:21:21
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[Ceramic Engineering and Science Proceedings] Advanced Processing and Manufacturing Technologies for Nanostructured and Multifunctional Materials (A Collection of Papers Presented at the 38th International Conference on Advanced Ceramics and Composites January 27-31, 2014 Daytona Beach, Florida) || Advanced Measurements of Indentation Fracture Resistance of Alumina by the Powerful Optical Microscopy for Small Ceramic Products
摘要： A round robin on indentation fracture resistance, KIFR of two types of alumina with different purity was conducted by thirteen laboratories in order to confirm the reliability of the IF method using powerful optical microscopy. Our new approach employed both an objective lens of 40x or 50x and a traveling stage to reduce the measuring error of crack lengths. The standard deviations of KIFR reported for the two samples indented at 98 N were 0.3 and 0.2 MPa m1/2 for mean KIFR of 4.3 and 3.6 MPa m1/2, respectively, indicating good matching between different laboratories. The grand averages of KIFR for both samples from all participants were only 0.4 MPa m1/2 higher than those of KIFR re-measured by the authors using the returned samples, which demonstrated a little room for improvement of the new technique. The results in this study together with the previous two round robins for SiC and Si3N4 ceramics revealed that the reliability of the IF method has reached a sufficient level since the reproducibility of KIFR for the three major ceramics was verified reasonable.
关键词： KIFR,alumina,indentation fracture resistance,optical microscopy,round robin
更新于2025-09-23 15:21:01
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Direct mineralogical imaging of economic ore and rock samples with multi-modal nonlinear optical microscopy
摘要： Multi-modal nonlinear optical (NLO) microscopy, including stimulated Raman scattering (SRS) and second harmonic generation (SHG), was used to directly image mineralogical features of economic ore and rock samples. In SRS/SHG imaging, ore samples generally require minimal preparation and may be rapidly imaged, even in their wet state. 3D structural details, at submicron resolution, are revealed tens of microns deep within samples. Standard mineral imaging based on scanning electron microscopy (SEM), with elemental analysis via energy dispersive X-Ray spectroscopy, was used to independently validate the mineral composition of the samples. Spatially-resolved SRS from dominant Raman-resonant bands precisely maps the locations of specific minerals contained within the samples. SHG imaging reveals locally non-centrosymmetric structures, such as quartz grains. Competing absorption and nonlinear scattering processes, however, can reduce contrast in SRS imaging. Importantly, the correlation between standard electron microscopy and multi-modal NLO optical microscopy shows that the latter offers rapid image contrast based on the mineral content of the sample.
关键词： mineralogical imaging,second harmonic generation,stimulated Raman scattering,rock samples,nonlinear optical microscopy,economic ore
更新于2025-09-23 15:21:01
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Dielectric and electro-optic properties of cybotactic nematic phase in hydrogen-bonded liquid crystals
摘要： The new compounds 4-decyloxy-2-fluorobenzoic acid and 4-dodecyloxy-2-fluorobenzoic acid display hydrogen-bonded liquid crystals (HBLC) of smectic and nematic phases. Their phase behavior established using polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) consistently occurs as the sequence upon cooling: Isotropic liquid – Nematic – SmC – crystalline solid. The dielectric study in the nematic phase shows a single relaxation process at low frequency characteristic of a cybotactic nematic phase. The optical properties of the nematic phase show a decrease of birefringence as alkyl chain length increases in the high-temperature part of the nematic domain, which reveals a decrease of order parameter for longer chains.
关键词： Polarized optical microscopy,Dielectric spectroscopy,Nematic,Hydrogen-bonded liquid crystal
更新于2025-09-23 15:19:57