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The key information about any nanoscale system relates to the orientations and conformations of its parts. Unfortunately, these details are often hidden below the diffraction limit, and elaborate techniques must be used to optically probe them. Here we present imaging of the 3D rotation motion of metal nanorods, restoring the distinct nanorod orientations in the full extent of azimuthal and polar angles. The nanorods imprint their 3D orientation onto the geometric phase and space-variant polarization of the light they scatter. We manipulate the light angular momentum and generate optical vortices that create self-interference images providing the nanorods’ angles via digital processing. After calibration by scanning electron microscopy, we demonstrated time-resolved 3D orientation imaging of sub-100 nm nanorods under Brownian motion (frame rate up to 500 fps). We also succeeded in imaging nanorods as nanoprobes in live-cell imaging and reconstructed their 3D rotational movement during interaction with the cell membrane (100 fps).

Remote visual testing by video cameras is the standard process for inspecting the pressure vessel of nuclear reactors. The inspectors need to find stress corrosion cracking of around several tens of µm wide on a display monitor observed by remote wired cameras in the reactor pressure vessel filled with cooling water. The inside surface of the vessel structure has typically been blasted or grinded during its construction process for smoothing any excess weld metal, and as such, it might contain partly specular areas and partly rough areas. We found that the cracks on such surfaces are hardly distinguished from the boundary of these areas under normal scattered illumination, since the specular area reflects more of the light from the light source outside the path to the camera than the light scattered out by the rough area. To resolve this issue, we propose using two illumination light sources simultaneously, i.e., the bright field illumination and the dark field illumination, to balance the contrast to cracks from both areas. The results of experiments in a simplified condition showed that there was an improvement in the visibility of the cracks using this method.

This study proposes a model that relates the carbon fiber arrangement and orientation in CFRP to the dark-field images captured by X-ray Talbot-Lau interferometer (TLI). X-ray TLI visualizes X-ray ...

Simultaneous application of polarization microscopy and Interphako interference contrast has been used to study the internal structure of algal cells. The interference contrast technique showed fine cell structures (important is the selection of interference colors according to the Mach-Zehnder interferometer setting). In a polarization microscope, the crossed polarization filters together with the first-order quartz compensator mounted turntable showed the maximum birefringence of the individual structures. Material containing green algae was collected in the villages Sýkořice and Zbečno, Protected Landscape Area (PLA) Křivoklátsko. The objects were studied in a Carl Zeiss Jena NfpK laboratory microscope equipped with an In 160 base body with an Interphako In contrast interference module including a Mach-Zehnder interferometer with variable phase contrast, a special condenser with interchangeable aperture plates, a turntable, a Meopta Praha polarizer, a LOMO Sankt Petersburg analyzer, and a quartz compensator with first-order red and the digital camera DSLR Nikon D 70. Green algae of three orders were studied: Siphonocladales, Zygnematales, and Desmidiales. Anisotropic structures were found in all studied representatives of the green algae of the phylum Chlorophyta. Especially their cell walls showed strong birefringence (in all representatives of these orders). On the other hand, a representative of the order Siphonocladales (the genus Cladophora, Cladophoraceae, Ulvophyceae) was rarely found to display weak birefringent granules of storage substances due to the setting of the Mach-Zehnder interferometer and the use of the first-order compensator (interference colors are intensified). In addition, a very weak birefringence of periphyton cells (microbial biofilm) was found. In the study of the second algae of the genus Spirogyra (Zygnemataceae, Zygnematales, Conjugatophyceae), a strongly birefringent connecting wall between algal cells was found in contrast to the weaker birefringence of the peripheral wall. It was the use of Interphako interference contrast together with polarization filters and a first-order quartz compensator that particularly emphasized the central part of the connecting wall. In the study of the twinned Pleurotaenium algae (Desmidiaceae, Desmidiales, Conjugatophyceae), a strongly birefringent wall was found along the periphery of the cell with a nucleus in the middle part (isthmus). In this narrowing in the center of the cell, a sharply delimited birefringent edge of the cell wall is visible, especially when using Interphako interference contrast along with crossed polarization filters and a first-order quartz compensator. In conclusion, Interphako interference contrast provides a high degree of image contrast in a microscope and, if suitably simultaneously complemented by polarization microscopy (including a first-order quartz compensator), it will allow us to infer some of the composition of the investigated structures. However, working with Interphako interference contrast is considerably more difficult (setting Mach-Zehnder interferometer) than using other contrast techniques (positive and negative phase contrast, color contrast, relief contrast, and dark field).

Microscopía electrónica de transmisión/barrido (STEM) ofrece información estructural y química del orden de 0.1 nm de resolución espacial, tal resolución es llevada a cabo mediante el corrector de aberración esférica. En el STEM, un haz de electrones es enfocado y escaneado sobre la muestra, por lo que la imagen es formada midiendo la señal electrónica que surge después de las interacciones electrones-muestra. La señal de los electrones dispersados puede ser empleada para obtener imágenes de campo claro y campo obscuro. El microscopio STEM es un poderoso instrumento para estudiar las propiedades físicas de las nanoestructuras, que requieren de un análisis estructural y químico a nivel atómico. Por lo tanto, STEM es una técnica capaz de identificar la posición de los átomos y las columnas atómicas. En este trabajo, los parámetros instrumentales básicos del microscopio antes de sus aplicaciones fueron evaluados. Además, imágenes experimentales de campo oscuro anular de alto ángulo (HAADF)-STEM y campo claro anular (ABF)-STEM de una muestra de LaAlO3 fueron obtenidas a bajos voltajes de operación y comparadas con imágenes simuladas obtenidas con el método de multicapas. Se encontró que las imágenes simuladas coinciden bien con las imágenes experimentales.

Thearticledealswith the comparative application of optical and raster microscopy for non-metallic objects and non-conducting surfaces. It is noted that this issue is not covered much in the special literature. There are practically no publications that compare and describe photos of the structure of materials obtained using fundamentally different microscopes, in particular, metallographic and raster. The causes of image distortion in a raster electron microscope in the study of dielectrics are considered. Comparative images of the oxidized surface, fabrics and natural leather obtained using raster and optical microscopy are presented. The advantages of optical microscopy in the study of non-conducting surfaces are shown.

We developed an instrument that allows us to measure dynamic light scattering from soft materials on solid substrates by avoiding strong background due to the reflection light from substrates. In the instrument, samples on substrates are illuminated by evanescent-light field and the resultant scattered light from the samples is collected with a dark-field optical configuration by employing a high numerical aperture microscope objective. We applied the instrument to measure the dynamic properties of supported lipid bilayers (SLBs), which have been widely utilized in industries as functional materials such as biosensors. From the time course of the scattered light from the SLBs, the power spectrum with the broad peak ranging from 10 to 20 kHz is observed. The use of the microscope objectives enables us to apply the instrument to future light scattering imaging for dynamic properties of soft materials supported on various substrates by combining with conventional microscope systems.

The flow-inducing effect of the bobbin-tool features (tri-flat pin and scrolled shoulder) were replicated by a simple analogue model for aluminium welds by layered plasticine samples. Flow patterns of the weld zone were clarified by a typical stereomicroscopy instrument assisted by dark-field/bright-field illumination. The effects of the pin features, specifically threads and flats in centre of bond zone and scrolled shoulder in sides of stirred zone, were identified. This study shows that internal flow features for BFSW welds is transferable from the friction stir welding process to the functional metal forming processes such where the shearing can extensively affect the microstructure. The similarity between the flow pattern of the provided aluminium samples and the plasticine analogue can validate the accuracy of the flow model presented in this work.

Dark-field microscopy is a standard imaging technique widely employed in biology that provides high image contrast for a broad range of unstained specimens1. Unlike bright-field microscopy, it accentuates high spatial frequencies and can therefore be used to emphasize and resolve small features. However, the use of dark-field microscopy for reliable analysis of blood cells, bacteria, algae and other marine organisms often requires specialized, bulky microscope systems, as well as expensive additional components, such as dark-field-compatible objectives or condensers2,3. Here, we propose to simplify and downsize dark-field microscopy equipment by generating the high-angle illumination cone required for dark-field microscopy directly within the sample substrate. We introduce a luminescent photonic substrate with a controlled angular emission profile and demonstrate its ability to generate high-contrast dark-field images of micrometre-sized living organisms using standard optical microscopy equipment. This new type of substrate forms the basis for miniaturized lab-on-chip dark-field imaging devices that are compatible with simple and compact light microscopes. A luminescent photonic substrate with a controlled angular emission profile is introduced and its ability to generate high-contrast dark-field images of micrometre-sized living organisms is demonstrated using standard optical microscopy equipment.

In this study, size-selected platinum (Pt) nanoclusters were imaged with aberration-corrected scanning transmission electron microscopy in high-angle annular dark field (HAADF) mode. For image analysis, a relatively simple macro program was developed by making the use of existing ImageJ plug-ins. The macro allows effectively for assessing criterions chosen for intensity threshold and filter blurring factors. It can extract the integrated HAADF intensity, peak intensity and projected area of the clusters. Here, the effects of magnification and objective lens defocus on nanocluster measurement were investigated. It was found that the integrated HAADF intensity of Pt clusters is a more robust sample descriptor than the peak intensity and the projected area. The macro program developed is freely available. LAY DESCRIPTION: Measuring precisely the size of nanoclusters plays an important role in the investigation of nanocluster-based material systems. Aberration-corrected scanning transmission electron microscopy (STEM) is one of the most powerful tools to extract the size of clusters directly from their images. In this study, we developed a macro program based on existing ImageJ plug-ins, allowing easy-assessment of criterions chosen for image intensity threshold and filter blurring factors. It can be used to extract the integrated intensity, peak intensity, and projected area of the clusters for size determination. Using the program, we investigated the effects of magnification and objective lens defocus on measurements performed on size-selected platinum (Pt) nanoclusters, and found that the integrated intensity of Pt clusters is a more robust sample descriptor than the peak intensity and the projected area. The macro developed allows a rapid assessment of factors affecting the accuracy with which size information can be obtained from clusters.

This chapter elucidates the general introduction of light, perception of colour, mechanism of image formation in the eye, basic principles of light microscope and components of light microscope along with guidelines of handling of the microscope. The spherical lens of the microscope may have several optical faults or aberrations. Image distortion occurs due to these various optical aberrations. The common aberrations include chromatic aberration, spherical aberration, astigmatism and curvature of field. This chapter highlights the causes of these aberrations and their solutions. In addition various other microscopes have also been discussed in this chapter.

Microstructures are widely used in the manufacture of functional surfaces. An optical-based in-process and non-invasive method is preferred for the depth measurement of the fine microgroove structure. A dark-field method is proposed using the features of polarization based on the waveguide theory. According to the numerical simulation based on the FDTD method and Fourier optics, the proposed method allows depth measurement for fine microgroove having an aperture size of less than several hundred nanometers with an aspect ratio (width/depth) of larger than one, even under the far-field measurement.

Plasmons have received intensive attention owing to their significant spectrum shift in environmental sensing. Experimentally, the same spectral shifts may be caused by different combinations of structural parameters of a plasmonic nanoparticle. This multi-parameter problem cannot be solved by just a single feature analysis, but requires using the full scattering spectrum containing all features of the parameters. In this Letter, a deep learning method for solving multi-parameter problems is proposed based on the layer refractive index ( n ) and layer thickness ( d ) sensing of different nanorods and nanospheres. The full scattering spectrum can be theoretically simulated, precisely predicted using a well-trained deep learning method, and experimentally obtained using a homemade dark-field microscope. An error analysis of the simulation and experimental results indicates that this method is a potential way to determine n and d and further solve multi-parameter in plasmon sensing.

In this work, we investigate mushroom type phase-change material (PCM) memory cells based on Ge2Sb2Te5. We use low-angle annular dark field (LAADF) STEM imaging and energy dispersive X-ray spectroscopy (EDX) to study changes in microstructure and elemental distributions in the PCM cells before and after SET and RESET conditions. We describe the microscope settings required to reveal the amorphous dome in the RESET state and present an application example involving the failure analysis of a PCM test array made with devices fabricated at IBM’s Albany AI Hardware Research Center.

Extending 0.33NA EUV single patterning to pitch 28nm will enable metal layers cost-efficiency and significantly shorter process flow for N2 node. At the same time, EUV single patterning becomes very challenging in terms of stochastic defectivity and process window. In this paper, the lithographic performance of the M1 layer of an imec N3 (foundry N2 equivalent) random logic layout is evaluated by means of source mask optimization on these three mask candidates: a standard binary Ta-based absorber mask, a high extinction (high-k) absorber mask and a low-n attenuated phase-shift mask. The impact of mask tonality (bright field vs. dark field) and insertion of sub-resolution assist features on pattern fidelity and process window is evaluated.

X-ray computed micro-tomography typically involves a trade-off between sample size and resolution, complicating the study at a micrometer scale of representative volumes of materials with broad feature size distributions (e.g. natural stones). X-ray dark-field tomography exploits scattering to probe sub-resolution features, promising to overcome this trade-off. In this work, we present a quantification method for sub-resolution feature sizes using dark-field tomograms obtained by tuning the autocorrelation length of a Talbot grating interferometer. Alumina particles with different nominal pore sizes (50 nm and 150 nm) were mixed and imaged at the TOMCAT beamline of the SLS synchrotron (PSI) at eighteen correlation lengths, covering the pore size range. The different particles cannot be distinguished by traditional absorption µCT due to their very similar density and the pores being unresolved at typical image resolutions. Nevertheless, by exploiting the scattering behavior of the samples, the proposed analysis method allowed to quantify the nominal pore sizes of individual particles. The robustness of this quantification was proven by reproducing the experiment with solid samples of alumina, and alumina particles that were kept separated. Our findings demonstrate the possibility to calibrate dark-field image analysis to quantify sub-resolution feature sizes, allowing multi-scale analyses of heterogeneous materials without subsampling., Scientific Reports, 11 (1), ISSN:2045-2322

Electron microscopy (EM) is the most versatile tool for the study of matter at scales ranging from subatomic to visible. The high vacuum environment and the charged irradiation require careful stabilization of many specimens of interest. Biological samples are particularly sensitive due to their composition of light elements suspended in an aqueous medium. Early investigators developed techniques of embedding and staining with heavy metal salts for contrast enhancement. Indeed, the Nobel Prize in 1974 recognized Claude, de Duve, and Palade for establishment of the field of cell biology, largely due to their developments in separation and preservation of cellular components for electron microscopy. A decade later, cryogenic fixation was introduced. Vitrification of the water avoids the need for dehydration and provides an ideal matrix in which the organic macromolecules are suspended; the specimen represents a native state, suddenly frozen in time at temperatures below -150 °C. The low temperature maintains a low vapor pressure for the electron microscope, and the amorphous nature of the medium avoids diffraction contrast from crystalline ice. Such samples are extremely delicate, however, and cryo-EM imaging is a race for information in the face of ongoing damage by electron irradiation. Through this journey, cryo-EM enhanced the resolution scale from membranes to molecules and most recently to atoms. Cryo-EM pioneers, Dubochet, Frank, and Henderson, were awarded the Nobel Prize in 2017 for high resolution structure determination of biological macromolecules.A relatively untapped feature of cryo-EM is its preservation of composition. Nothing is added and nothing removed. Analytical spectroscopies based on electron energy loss or X-ray emission can be applied, but the very small interaction cross sections conflict with the weak exposures required to preserve sample integrity. To what extent can we interpret quantitatively the pixel intensities in images themselves? Conventional cryo-transmission electron microscopy (TEM) is limited in this respect, due to the strong dependence of the contrast transfer on defocus and the absence of contrast at low spatial frequencies.Inspiration comes largely from a different modality for cryo-tomography, using soft X-rays. Contrast depends on the difference in atomic absorption between carbon and oxygen in a region of the spectrum between their core level ionization energies, the so-called water window. Three dimensional (3D) reconstruction provides a map of the local X-ray absorption coefficient. The quantitative contrast enables the visualization of organic materials without stain and measurement of their concentration quantitatively. We asked, what aspects of the quantitative contrast might be transferred to cryo-electron microscopy?Compositional contrast is accessible in scanning transmission EM (STEM) via incoherent elastic scattering, which is sensitive to the atomic number Z. STEM can be regarded as a high energy, low angle diffraction measurement performed pixel by pixel with a weakly convergent beam. When coherent diffraction effects are absent, that is, in amorphous materials, a dark field signal measures quantitatively the flux scattered from the specimen integrated over the detector area. Learning to interpret these signals will open a new dimension in cryo-EM. This Account describes our efforts so far to introduce STEM for cryo-EM and tomography of biological specimens. We conclude with some thoughts on further developments.

Dark-field microscopy is known to offer both high resolution and direct visualization of thin samples. However, its performance and optimization on thick samples is under-explored and so far, only meso-scale information from whole organisms has been demonstrated. In this work, we carefully investigate the difference between trans- and epi-illumination configurations. Our findings suggest that the epi-illumination configuration is superior in both contrast and fidelity compared to trans-illumination, while having the added advantage of experimental simplicity and an "open top" for experimental intervention. Guided by the theoretical analysis, we constructed an epi-illumination dark-field microscope with measured lateral and axial resolutions of 260 nm and 520 nm, respectively. Subcellular structures in whole organisms were directly visualized without the need for image reconstruction, and further confirmed via simultaneous fluorescence imaging. With an imaging speed of 20 to 50 fps, we visualize fast dynamic processes such as cell division and pharyngeal pumping in Caenorhabditis elegans.

The dark-field signal measures the small-angle scattering strength and provides complementary diagnostic information. This is of particular interest for lung imaging due to the pronounced small-angle scatter from the alveolar microstructure. However, most dark-field imaging techniques are relatively complex, dose-inefficient, and require sophisticated optics and highly coherent X-ray sources. Speckle-based imaging promises to overcome these limitations due to its simple and versatile setup, only requiring the addition of a random phase modulator to conventional X-ray equipment. We investigated quantitatively the influence of sample structure, setup geometry, and source energy on the dark-field signal in speckle-based X-ray imaging with wave-optics simulations for ensembles of micro-spheres. We show that the dark-field signal is accurately predicted via a model originally derived for grating interferometry when using the mean frequency of the speckle pattern power spectral density as the characteristic speckle size. The size directly reflects the correlation length of the diffuser surface and did not change with energy or propagation distance within the near-field. The dark-field signal had a distinct dependence on sample structure and setup geometry but was also affected by beam hardening-induced modifications of the visibility spectrum. This study quantitatively demonstrates the behavior of the dark-field signal in speckle-based X-ray imaging.

We present results on colors of metal disk arrays viewed under a darkfield microscope and show that the darkfield colors can be manipulated independently of the brightfield colors. We investigate the appearance of colors as disks are clustered to form a new array with double the pitch and a basis of four disks. These structures of aluminum disks on aluminum oxide on aluminum have resonances in the visible spectrum, so by arranging them in small tight clusters, a coupled plasmon resonant mode is produced at shorter wavelengths. This feature causes a reflectance minimum and leads to an increase in the gamut of darkfield colors produced. These colors are tuned by changing the size of the disk and the inter-disk gap within the clusters. Interestingly, the intensities of the reflectance peaks also demonstrate good agreement with the Fourier series coefficients for square waves. Polarization-tunable colors are also demonstrated by designing rectangular arrays that have dissimilar periods along the two orthogonal axes of the array, and a four-level security tag is fabricated that encodes images for viewing under brightfield, darkfield (both x and y polarization), and infrared illumination.

We demonstrate a simple single grating beam modulation technique, which enables the use of a highly intense neutron beam for differential phase and dark-field contrast imaging and thus spatially resolved structural correlation measurements in full analogy to interferometric methods. In contrast to these interferometric approaches our method is intrinsically achromatic and provides unprecedented flexibility in the choice of experimental parameters. In particular the method enables straight forward application of quantitative dark-field contrast imaging in time-of-flight mode at pulsed neutron sources. Utilizing merely a macroscopic absorption mask unparalleled length scales become accessible. We present results of quantitative dark-field contrast imaging combining microstructural small angle scattering analyses with real space imaging for a variety of materials.

We introduce the application of a symmetric Talbot-Lau neutron grating interferometer which provides a significantly extended autocorrelation length range essential for quantitative dark-field contrast imaging. The highly efficient set-up overcomes the limitation of the conventional Talbot-Lau technique to a severely limited micrometer range as well as the limitation of the other advanced dark-field imaging techniques in the nanometer regime. The novel set-up enables efficient and continuous dark-field contrast imaging providing quantitative small-angle neutron scattering information for structures in a regime from some tens of nanometers to several tens of micrometers. The quantitative analysis enabled in and by such an extended range is demonstrated through application to reference sample systems of the diluted polystyrene particle in aqueous solutions. Here we additionally demonstrate and successfully discuss the correction for incoherent scattering. This correction results to be necessary to achieve meaningful quantitative structural results. Furthermore, we present the measurements, data modelling and analysis of the two distinct kinds of cohesive powders enabled by the novel approach, revealing the significant structural differences of their fractal nature.

We propose a process technology that can be applied to a variety of applications by machining existing lenses to create an optical system required for research by modifying commercial glass optical systems. A 1-in. hole was created in an LF5 glass lens by drilling, followed by spiral grinding, and finally, precision spiral grinding. In addition, cracking and chipping were analyzed according to the processing process and optimized process conditions. We fabricated an achromatic doublet lens with a diameter of 50.8 mm, focal fa of 75 mm and fba of 65.7 mm, under optimized processing conditions. The processed lenses were determined by measuring the surface geometry of the lenses using ASI, and the lenses were inspected internally using OCT and dark field measurements to verify the internal sectional cracks and chipping of the lenses. The results confirm that there are no problems with the use of the hole in the existing glass lens as an optics. In addition, the manufactured lens will be available as an integrated optical system that can combine lenses with mirrors or detectors to create small systems and multi-axial views.

High capital expenditures associated with manufacturing thin silicon wafers make it difficult for the industry to scale up and prevent novel technologies from entering the market. Thin wafers fail largely due to breakage during solar cell processing and handling. One of the root causes for breakage is sub-mm edge cracks in the silicon wafer, and these cracks cannot be reliably detected by most commercially-available crack detection tools. In this work, we first investigate the correlation between wafer thickness and critical crack length, and explain the importance of detecting sub-500-μm edge cracks as the wafer thickness is reduced. Secondly, we extend our previous work of micro-crack detection to demonstrate an edge illumination technique using a near-infrared laser to image edge cracks less than 500 μm in length in multicrystalline silicon. Thirdly, we investigate two fundamental edge illumination mechanisms based on dark-field imaging; namely, direct and vicinal illumination. We will then compare these methods to a state-of-the-art rear illumination method. The advantages and disadvantages of both illumination methods are presented and provide an in-depth analysis of light-crack interaction. In particular, we find that the robustness of vicinal illumination is due to diffuse reflectance. The diffuse reflectance has less dependence on crack configurations, while direct illumination has more dependence on the crack configurations because it utilizes specular reflectance. Our results show that our proposed prototype can detect sub-mm edge cracks in multicrystalline silicon wafers, which is an important step in enabling thin silicon wafer manufacturing.

Assessing tissues’ inhomogeneous optical properties is helpful for diagnosis, but high-cost measurement and experimental setups limit its development, data collecting and applications. In this paper, a portable microscope is proposed to assess the inhomogeneous optical properties of the sample. In the single LED illumination mode, accurate quantitative phase (QP) map can be recovered from 5 intensity images captured at different axial positions. Then based on the scattering-phase theorem and statistical dispersion relation (SDR), the inhomogeneous optical properties of the sample can be quantitatively assessed from these QP maps. In the incoherent dark field illumination mode, strong scattering structures can be observed easily without post processing. An improved resolution comparing with bright field imaging and qualitative optical properties would be obtained. In contrast to DHM and SLIM, our setup is cost-effective, use-flexible, and with a small amount of data acquisition, thus having the potential to promote the development of assessing tissues’ inhomogeneous optical properties, especially in resource-limited areas.

The detection of bulk micro-defects in Czochralski-grown silicon (Si) 〈100〉 wafers has significant importance in wafer quality control. Light Scattering Tomography (LST) is an industry standard technique for this purpose. This optical non-contact metrology requires destructive sample preparation: Samples have to be cleaved into half. One particular feature of the method is a dark field detection arrangement, which is achieved by separating the light detection part (microscope unit) from the illumination. Illumination is applied to the front surface of the sample, and the light scattered off of the defects is collected via the cleaved surface. The technique requires the perpendicularity of the cleaved surface to the front surface, which is fulfilled for Si(100) wafers. However, the nominally cleaved surface for Si(111) wafers is not perpendicular to the front surface but has an angle of 70.5°. This significant difference in cleavage results in the fact that Si(111) wafers cannot be measured by standard LST systems. Fortunately, the standard LST system can be modified by tilting the detection part under a proper angle allowing the measurements of Si(111) samples. In this article, we present this new technique in detail, showing the design and measurement capability of the new system. The measurement results are validated by a direct comparison to standard LST measurements on the same samples after proper sample preparation.

Background and Objectives: Cataract is still the leading cause of blindness. Its development is well researched for UV radiation. Modern light sources like LEDs and displays tend to emit blue light. The effect of blue light on the retina is called blue light hazard and is studied extensively. However, its impact on the lens is not investigated so far. Aim: Investigation of the impact of the blue visible light in porcine lens compared to UVA and UVB radiation. Materials and Methods: In this ex-vivo experiment, porcine lenses are irradiated with a dosage of 6 kJ/cm2 at wavelengths of 311 nm (UVB), 370 nm (UVA), and 460 nm (blue light). Lens transmission measurements before and after irradiation give insight into the impact of the radiation. Furthermore, dark field images are taken from every lens before and after irradiation. Cataract development is illustrated by histogram linearization as well as faults coloring of recorded dark field images. By segmenting the lens in the background’s original image, the lens condition before and after irradiation could be compared. Results: All lenses irradiated with a 6 kJ/cm2 reveal cataract development for radiation with 311 nm, 370 nm, and 460 nm. Both evaluations reveal that the 460 nm irradiation causes the most cataract. Conclusion: All investigated irradiation sources cause cataracts in porcine lenses—even blue visible light.

We present the computational technique for automatic numerical refocusing in coherent lensless Gabor microscopy (digital in-line holographic microscopy). It is based on the adaptive filtering of the recorded on-axis Gabor hologram to eliminate its incoherent background term and extract interference fringes determined by the light scattered on the sample. Numerical propagation of such filtered hologram, based on the angular spectrum method, yields the computationally generated dark-field imaging realized in amplitude channel of the complex propagated f ield. As the focus metric we calculate the variance of the dark-field gradient - it attains maximum value in the focal planes for all types of objects (phase, amplitude and mixed phase-amplitude). Demonstrated autofocusing technique is positively validated using experimental data exhibiting significant variation of the confluence for double focal plane scenarios (two closely located sample planes filled with microbeads). Described technique compares favorably with other well-established automatic numerical refocusing methods (e.g., based on the high-pass filtered complex amplitude and edge sparsity) mainly in terms of higher axial resolution and better robustness to hologram low signal-to-noise ratio and object non-uniformity.

In the past decade neutron dark-field contrast imaging has developed from a qualitative tool depicting microstructural inhomogeneities in bulk samples on a macroscopic scale of tens to hundreds of micrometers to a quantitative spatial resolved small-angle scattering instrument. While the direct macroscopic image resolution around tens of micrometers remains untouched microscopic structures have become assessable quantitatively from the nanometer to the micrometer range. Although it was found that magnetic structures provide remarkable contrast we could only recently introduce polarized neutron grating interferometric imaging. Here we present a polarized and polarization analyzed dark-field contrast method for spatially resolved small-angle scattering studies of magnetic microstructures. It is demonstrated how a polarization analyzer added to a polarized neutron grating interferometer does not disturb the interferometric measurements but allows to separate and measure spin-flip and non-spin-flip small-angle scattering and thus also the potential for a distinction of nuclear and different magnetic contributions in the analyzed small-angle scattering.

In light transmission microscopy, axial scanning does not directly provide tomographic reconstruction of specimen. Phase deconvolution microscopy can convert a raw intensity image stack into a refractive index tomogram, the intrinsic sample contrast which can be exploited for quantitative morphological analysis. However, this technique is limited by reconstruction artifacts due to unoptimized optical conditions, which leads to a sparse and non-uniform optical transfer function. Here, we propose an optimization method based on simulated annealing to systematically obtain optimal illumination schemes that enable artifact-free deconvolution. The proposed method showed precise tomographic reconstruction of unlabeled biological samples.

Single particle tracking has found broad applications in the life and physical sciences, enabling the observation and characterization of nano- and microscopic motion. Fluorescence-based approaches are ideally suited for high-background environments, such as tracking lipids or proteins in or on cells, due to superior background rejection. Scattering-based detection is preferable when localization precision and imaging speed are paramount due to the in principle infinite photon budget. Here, we show that micromirror-based total internal reflection dark field microscopy enables background suppression previously only reported for interferometric scattering microscopy, resulting in nanometer localization precision at 6 μs exposure time for 20 nm gold nanoparticles with a 25 × 25 μm2 field of view. We demonstrate the capabilities of our implementation by characterizing sub-nanometer deterministic flows of 20 nm gold nanoparticles at liquid–liquid interfaces. Our results approach the optimal combination of background suppression, localization precision, and temporal resolution achievable with pure scattering-based imaging and tracking of nanoparticles at interfaces., ACS Photonics, 8 (10), ISSN:2330-4022

As the impact of defects on yield has become significant for advanced process technology nodes, it is imperative to shrink the defect inspection dimension. In this work, mask design method for un-patterned dark field defect inspection system is proposed to reduce the haze signals caused by wafer roughness. The mask is designed according to the bidirectional reflectance distribution function. The effect of the mask is verified by the scattering model we have developed based on the tools which NIST provided. The mask is designed to block part of the strong haze signals, which effectively improves the accuracy of defect inspection.

The optical quality of intraocular lenses (IOLs) of different materials that have been implanted from 16 to 44 years in human eyes was studied. The IOLs were explanted due to other causes than loss of transparency. The scattered light from the IOLs was assessed in two angular regimes by using dark field images (for wide angles) and the optical integration method (for narrower angles). No evident differences were found in the scattering intensities processed from the dark images. The explanted lenses presented slightly increased amounts of straylight between 1 and 5.1° when compared to a reference new unused lens.

We evaluated the printability of patterns relevant for Logic Metal at P28nm (L/S and T2T) on wafer using EUV single expose. We compare illumination sources with and without fading correction as well as Bright field / Dark field mask tonalities and NTD MOR / PTD CAR resist. In simulations, Bright field (BF) imaging gives better image quality than Dark field (DF) at small pitch/CD. It also enables smaller T2T. To avoid tone inversion (assuming dual damascene processing), BF imaging requires the use of a NTD resist. On wafer, exposure latitudes increase for a BF/NTD choice, concurrent with simulations, even after correcting out SEM shrinkage. Also, T2T CD is reduced. In terms of illumination, we compare dipole sources to fading corrected sources. As fading correction, we have both induced aberrations (Z6-corrected dipole) and monopoles. As expected, a fading correction significantly reduces best focus differences of L/S through pitch and T2T. Moreover, the Z6-corrected dipole is optimal to print small T2T with better uniformity. Finally, we observe that PTD and NTD MOR resist utilize the same aerial image differently. NTD resist can leverage pupil shapes with high exposure latitude, but low depth of focus, better than PTD resist. Fading correction via induced aberrations naturally produces such sources. In summary, the preferred option is a Z6-corrected dipole for best focus alignment and sharp T2T, together with BF imaging to allow higher L/S exposure latitudes and small T2T. Combining this choice with NTD MOR resist avoids tone inversion and leverages the illumination source optimally.

We have used the MET5 exposure system using “dark field” lithography, where a small σ=0.1 source is wholly contained in the 30% Central Obscuration of the 0.5NA mirror optics. One goal of this paper is to quantify and explain the superior image contrast of dark field lithography over normal dipole imagery. We demonstrate that almost ideal grating images can be obtained over the pitch range from 15 to 25nm. With the x-polarized source, gratings with Horizontal lines (TE polarized) have the best image contrast, while Vertical lines (TM polarized) have lesser contrast, showing less contrast as pitch decreases. By comparing lines of different orientation, the impact of polarization on lithography can be assessed. At the 16nm pitch, the experimental data showed roughly 20% improvement of the LWR metric for TE over TM. Besides the image contrast, we also calculate the effective contrast Ceff by folding in a Gaussian resist blur. These calculations highlight the need to find resist processes with small blur, e.g. with σ < 3nm. Exposure latitude scales with Ceff, as does LWR, LCDU and stochastic defect levels. Therefore optimization of Ceff, at the small pitches needed for production, is of high importance. We have also looked at dense arrays of bright spots produced with dark field imaging, which can produce either dense contact holes or dense pillars depending on the resist process tone. Our experimental results used a negative tone Metal Oxide resist process to print pillar arrays with pitches of 22, 24 and 26nm. Our experiments, and most of our simulations, were done with a standard EUV mask using a Ta-based absorber. Additional simulations explored the use of alternative absorber materials which can increase the dark field image intensity. For example, 25nm thick Ru absorber can more than double the image intensity relative to Ta absorber. The MET5 dark field litho imaging method is well-suited for testing resist processes in advance of the high NA tool availability. Both dense line gratings and dense hole/pillar array images can be imaged with good image contrast. However, pure dark field imaging is not capable of producing all the patterns needed for production, such as the larger pitch structures needed for overlay and alignment marks. On the other hand, there is a kind of “partial” dark field imagery that is very promising for production imaging with the high NA tool. Allowing Source Mask Optimization (SMO) software to include source points within the obscured part of the pupil, i.e. “dark field source points”, implements this capability in a very natural way and seems attractive for High Volume Manufacturing (HMV) applications with the high NA tool in the near future.

Significance We demonstrate an approach to generate a new type of X-ray imaging mode, which is called omnidirectional X-ray differential phase imaging. The proposed method enables us to detect the subtle phase changes in all directions of the imaging plane, which complements conventional X-ray imaging methods with information that they cannot provide. Importantly, the omnidirectional dark-field images can also be simultaneously retrieved for studying a wide range of complicated samples, particularly strongly ordered systems. The extracted information will not only provide insights into the microarchitecture of materials, but also enrich our understanding the macroscopic behavior. The presented technique could potentially open up numerous practical imaging applications in both biomedical research and materials science., Ever since the discovery of X-rays, tremendous efforts have been made to develop new imaging techniques for unlocking the hidden secrets of our world and enriching our understanding of it. X-ray differential phase contrast imaging, which measures the gradient of a sample’s phase shift, can reveal more detail in a weakly absorbing sample than conventional absorption contrast. However, normally only the gradient’s component in two mutually orthogonal directions is measurable. In this article, omnidirectional differential phase images, which record the gradient of phase shifts in all directions of the imaging plane, are efficiently generated by scanning an easily obtainable, randomly structured modulator along a spiral path. The retrieved amplitude and main orientation images for differential phase yield more information than the existing imaging methods. Importantly, the omnidirectional dark-field images can be simultaneously extracted to study strongly ordered scattering structures. The proposed method can open up new possibilities for studying a wide range of complicated samples composed of both heavy, strongly scattering atoms and light, weakly scattering atoms.

X-ray phase imaging has found limited clinical use due to requirements on x-ray coherence that may not be easily translated to clinical practice. Instead, this work employs a conventional source to create structured illumination with a simple wire mesh. The system has been employed to produce high contrast absorption images with simultaneous differential phase contrast images. In previous work we have demonstrated accurate quantitative phase extraction. In this work, we have incorporated the dark field information to successfully reveal additional structure in low contrast objects.

Context. One of the key challenges facing direct exoplanet imaging is the continuous maintenance of the region of high contrast within which light from the exoplanet can be detected above the stellar noise. In high-contrast imaging systems, the dominant source of aberrations is the residual wavefront error that arises due to non-common path aberrations (NCPA) to which the primary adaptive optics (AO) system is inherently blind. Slow variations in the NCPA generate quasi-static speckles in the post-AO corrected coronagraphic image resulting in the degradation of the high-contrast dark hole created by the coronagraph. Aims. In this paper, we demonstrate spatial linear dark field control (LDFC) with an asymmetric pupil vector apodizing phase plate (APvAPP) coronagraph as a method to sense time-varying NCPA using the science image as a secondary wavefront sensor (WFS) running behind the primary AO system. By using the science image as a WFS, the NCPA to which the primary AO system is blind can be measured with high sensitivity and corrected, thereby suppressing the quasi-static speckles which corrupt the high contrast within the dark hole. Methods. On the Subaru Coronagraphic Extreme Adaptive Optics instrument (SCExAO), one of the coronagraphic modes is an APvAPP which generates two PSFs, each with a 180° D-shaped dark hole with approximately 10−4 contrast at λ = 1550 nm. The APvAPP was utilized to first remove the instrumental NCPA in the system and increase the high contrast within the dark holes. Spatial LDFC was then operated in closed-loop to maintain this high contrast in the presence of a temporally-correlated, evolving phase aberration with a root-mean-square wavefront error of 80 nm. In the tests shown here, an internal laser source was used, and the deformable mirror was used both to introduce random phase aberrations into the system and to then correct them with LDFC in closed-loop operation. Results. The results presented here demonstrate the ability of the APvAPP combined with spatial LDFC to sense aberrations in the high amplitude regime (∼80 nm). With LDFC operating in closed-loop, the dark hole is returned to its initial contrast and then maintained in the presence of a temporally-evolving phase aberration. We calculated the contrast in 1 λ/D spatial frequency bins in both open-loop and closed-loop operation, and compared the measured contrast in these two cases. This comparison shows that with LDFC operating in closed-loop, there is a factor of ∼3x improvement (approximately a half magnitude) in contrast across the full dark hole extent from 2−10 λ/D. This improvement is maintained over the full duration (10 000 iterations) of the injected temporally-correlated, evolving phase aberration. Conclusions. This work marks the first deployment of spatial LDFC on an active high-contrast imaging instrument. Our SCExAO testbed results show that the combination of the APvAPP with LDFC provides a powerful new focal plane wavefront sensing technique by which high-contrast imaging systems can maintain high contrast during long observations. This conclusion is further supported by a noise analysis of LDFC’s performance with the APvAPP in simulation.

Strain maps extracted from atomic resolution images have the ultimate spatial resolution, but have a field of view limited by the sampling necessary to resolve atomic lattices. This has typically confined strain maps to dimensions less than ∼100 nanometers. To extend the field of view beyond this limit, we apply a modified geometric phase analysis to undersampled images of atomic lattices (i.e. with a pixel size too large to resolve atomic lattices). To reduce the effects of environmental and instrumental instabilities, the images were obtained by aligning series of rapid annular dark field scanning transmission electron microscopy acquisitions. We demonstrate that for undersampled images, a geometric phase analysis can still be performed on aliased frequencies and, as long as the appropriate scaling matrix is applied, provide accurate atomic displacement measurements at large scale. Experimental challenges related to the increased effects of scanning errors as the magnification is lowered are examined. Although such errors are found to significantly reduce geometric phase signals, it was still possible to produce strain maps for arrays of up to sixteen 20nm-technology transistors, corresponding to a field of view exceeding one micrometer.

In any characterization method, the resolution, the precision and the accuracy are the usual metrics of the interest for the analyst. In the following chapter, the performance of the STEM Moire GPA (SMG) strain characterization technique is assessed. The accuracy is first judged by comparing the STEM Moire GPA method applied on a simple stack grown by molecular beam epitaxy with the Dark Field Electron Holography technique. Then, the same experimental results are confronted to mechanical simulations modeling the strain relaxation from a thin foil. The study unveils the importance to consider the depth of field for a proper interpretation of the STEM Moire GPA accuracy. Subsequently, the application of the Geometrical Phase Analysis (GPA) method on a STEM Moire hologram is theoretically detailed evaluating the resolution and the sensitivity of STEM Moire GPA strain maps. Overall, the STEM Moire GPA method reveals to be comparable with other strain characterization technique using the GPA process, and can be seen as the direct extension of the classic HR-STEM GPA technique by simply increasing the field of view. Finally, specific theoretical and practical limits of the STEM Moire GPA technique are presented setting the scope of application of the strain characterization method and potential paths for development.

We present a method to calibrate and correct lens aberrations in dark-field Digital Holographic Microscope (df-DHM). In this method a gold nanoparticle is used to measure the point-spread function (PSF) of the df-DHM.

Dual-energy imaging is a clinically well-established technique that offers several advantages over conventional X-ray imaging. By performing measurements with two distinct X-ray spectra, differences in energy-dependent attenuation are exploited to obtain material-specific information. This information is used in various imaging applications to improve clinical diagnosis. In recent years, grating-based X-ray dark-field imaging has received increasing attention in the imaging community. The X-ray dark-field signal originates from ultra small-angle scattering within an object and thus provides information about the microstructure far below the spatial resolution of the imaging system. This property has led to a number of promising future imaging applications that are currently being investigated. However, different microstructures can hardly be distinguished with current X-ray dark-field imaging techniques, since the detected dark-field signal only represents the total amount of ultra small-angle scattering. To overcome these limitations, we present a novel concept called dual-energy X-ray dark-field material decomposition, which transfers the basic material decomposition approach from attenuation-based dual-energy imaging to the dark-field imaging modality. We develop a physical model and algorithms for dual-energy dark-field material decomposition and evaluate the proposed concept in experimental measurements. Our results suggest that by sampling the energy-dependent dark-field signal with two different X-ray spectra, a decomposition into two different microstructured materials is possible. Similar to dual-energy imaging, the additional microstructure-specific information could be useful for clinical diagnosis.

One interest of Scanning Transmission Electron Microscopy (STEM) Moire interferometry is to increase the field of view of the electron micrograph mapping the structural properties of the material analyzed. The field of view extension is based on undersampling the features present in the sample and can be done without loss of information following the Moire sampling recovery theorem. The Moire sampling recovery theorem indeed enables the missing information between the undersampled Moire fringes to be completed reconstructing an oversampled version of the STEM Moire hologram. As STEM Moire interferometry carries all the structural properties of the sample, dedicated characterization methods can be furthermore developed. In the following chapter, the characterization of strain in STEM Moire interferometry is explored. As the phase from the Geometrical Phase Analysis (GPA) method is not distorted by the sampling process, the approach using the GPA method directly on the STEM Moire hologram is favored. From the theoretical description, a novel strain characterization technique, called STEM Moire GPA (SMG), is first presented. The application of SMG and its practical aspects are subsequently detailed on a simple case of study. SMG reveals to be an easy and efficient method mapping the 2D strain field over large field of views up to several microns and is complementary to both Dark Field Electron Holography and Nano Beam Precession Electron Diffraction techniques.

X-ray phase contrast imaging is a rapidly evolving field, covering a range of different imaging methods. Its integration in the daily medical imaging routines, however, has proven to be difficult, despite encouraging results. In addition to the phase information, small angle X-ray scattering information is accessible through the so called dark field signal. The dark field signal holds great potential for lung imaging applications due to its ability to detect sub-pixel structures. Edge illumination, an incoherent form of phase contrast imaging, is particularly promising due to its low coherence requirements. A remaining issue in conventional edge illumination phase contrast imaging, however, is the absorption of photons by the detector mask, as these photons contribute to the dose but not to the image. In this work, we explore the dark field potential of a setup without detector mask for lung imaging through Monte Carlo simulations. In order to approximate the irregular shape of alveoli, surface roughness is taken into account.