Hollow-cone Illumination Research Articles

Schlieren imaging of spatial magnetic fields by hollow-cone illumination

Schlieren imaging of spatial magnetic fields by hollow-cone illumination

Atomic Resolution Imaging of Light Elements in a Crystalline Environment using Dynamic Hollow-Cone Illumination Transmission Electron Microscopy.

Multiple electron scattering and the nonintuitive nature of image formation with coherent radiation complicate the interpretation of conventional transmission electron microscopy images. Precession of the illuminating beam in transmission electron microscopy (TEM) can lead to more robust and interpretable images with some penalty to image contrast, a technique known as dynamic hollow-cone illumination TEM. We demonstrate direct and robust imaging of light and heavy atoms in a crystalline environment with this technique. This method is similar to the annular bright-field technique in scanning transmission electron microscopy, via the principle of reciprocity. Dynamic hollow-cone illumination TEM is challenging in practice due to sensitivity to the misalignment of the precession axis, microscope objective aperture, and crystal zone axis.

Hollow-cone Foucault imaging method

A hollow-cone Foucault (HCF) imaging method using Lorentz microscopy was developed. Hollow-cone illumination was realized by using deflectors above the specimen and an inclined electron beam circulating with respect to the optical axis. The advantage of the HCF method, having the bright and dark-field modes, is that it can simultaneously visualize both magnetic domains and magnetic domain walls under the in-focus condition. Furthermore, schlieren images, obtained under the specific inclination angle of the illumination beam by adjusting the angle between the bright-field and dark-field modes, can qualitatively visualize the electromagnetic fields in spaces around the specimen.

Artifact-free, penetration-adjustable elliptical-mirror-based TIRF microscopy.

Evanescent field distribution in the focal region of the elliptical-mirror-based total-internal-reflection fluorescence (e-TIRF) microscopy is analyzed based on vectorial diffraction theory. The simulation demonstrates that the intensity of an evanescent field generated by elliptical mirror decreases exponentially with the penetration depth, and the polarization characteristic of the evanescent wave in various directions is given. We build up an e-TIRF microscope utilizing a focused hollow-cone illumination with all-direction and large range of incidence. The experiment shows the artifact effect can be well suppressed by using the azimuthal-direction illumination method. In addition, the penetration depth of the evanescent field can be controlled by adjusting the sizes of the aperture and obstruction with a large range.

Elliptical mirror-based TIRF microscopy with shadowless illumination and adjustable penetration depth.

We propose an elliptical mirror-based total-internal-reflection fluorescence (e-TIRF) microscopy with shadowless illumination and adjustable penetration depth. The elliptical mirror is used to produce a hollow-cone illumination with all azimuthal directions and a large range of incident angle, so as to attenuate the potential shadow effects when utilizing a single-direction illumination, such as asymmetries and low contrast. The experiment demonstrates that the e-TIRF method can realize shadowless imaging with symmetric intensity distribution. Meanwhile, the penetration depth of e-TIRF can be theoretically adjusted from 58nm to 250nm by adjusting the size of the aperture or the position of an opaque mask. This method extends the minimum penetration depth, which is useful for high axial resolution.

Phase-contrast Imaging by Annularly Arrayed Detectors in Hollow-cone Illumination STEM

Phase-contrast Imaging by Annularly Arrayed Detectors in Hollow-cone Illumination STEM

Biological Tissues Imaging with Phase-Contrast Scanning Optical Microscopy Using Hollow-Cone Illumination

Biological Tissues Imaging with Phase-Contrast Scanning Optical Microscopy Using Hollow-Cone Illumination

Phase-Contrast Imaging of Biological Tissue Using Dynamic Hollow-Cone Illumination

Phase-Contrast Imaging of Biological Tissue Using Dynamic Hollow-Cone Illumination

Hollow cone illumination for fast TEM, and outrunning damage with electrons

We consider the possibility of imaging individual bioparticles using snapshot diffraction from femotsecond pulses, using a 3 MeV electron beam, based on the recent experimental performance of these coherent beams. Assuming that radiation damage can be outrun using 100 fs pulses (or less), we find that a sufficient number of electrons are scattered per particle only if the beam diameter can be matched to that of the particle (e.g. a virus), about three orders of magnitude smaller than has currently been demonstrated (and limited by space-charge effects). We then propose the use of the hollow-cone illumination mode for fast transmission electron microscope imaging, because it can provide full-field atomic resolution imaging despite the use of the large incoherent annular source required for an efficient photocathode, so that coherent illumination is not needed for high-resolution imaging. Reciprocity arguments are used to compare this full-field mode with data aquisition times and source brightness in scanning transmission electron microscopy.

Direct imaging of structural heterogeneity of the melt-spun Fe85.2Si2B8P4Cu0.8 alloy

A structural heterogeneity of the melt-spun Fe85.2Si2B8P4Cu0.8 alloy has been studied by spherical aberration (Cs) corrected high-resolution transmission electron microscopy. Hollow-cone illumination imaging revealed that the density of coherent scattering regions in the as-quenched Fe85.2Si2B8P4Cu0.8 alloy is much higher than that in the Fe76Si9B10P5 bulk metallic glass. According to the Cs-corrected TEM, crystalline atomic clusters, typically of ∼1 nm in diameter, are densely distributed in an amorphous matrix of Fe85.2Si2B8P4Cu0.8 alloy. Observation of four-fold and six-fold atomic arrangements of these clusters implies existence of Fe clusters with the body centered cubic structure. These Fe clusters must be responsible for the formation of ultrahigh-density α-Fe nanocrystals produced by post-annealing.

Resolving Low-Contrast Microstructure Using Transmitted and Reflected Circular Oblique Lighting (COL)

A little-known illumination method for light microscopy goes by several names, the most prominent being “circular oblique lighting” (COL) and “hollow-cone illumination”. Matthews notes that hollow-cone or annular bright field illumination can give contrast and resolution superior to that obtainable with narrow-pencil illumination and under favorable conditions comparable to that obtained with phase optics. He demonstrates this with photomicrographs of the same unstained epithelial cell from the mouth mounted in saliva, imaged with a 0.65 numerical aperture (NA) 40× objective. Matthews also notes that the dot pattern of Pleurosigmaangulatum can be resolved with a 0.50 NA objective using circular oblique lighting. Leitz previously marketed the Heine illuminator for transmitted annular (hollow cone) illumination. The NA of the Heine condenser's annular illumination can be adjusted to match the phase annuli in phase contrast objectives. The NA can be increased to provide dark field illumination or circular oblique illumination in bright field. The instructions for the Heine condenser call for the annular illumination just falling within the NA of the objective, what Paul James calls COL and Frithjof A. S. Sterrenberg calls extreme annular illumination, “bright field with very rich contrast.” H. J. Dethloff published a more recent article describing the need for the increased contrast of hollow cone bright field to help resolve the striae of pores in the diatom Amplipleurapellucida. This diatom has been the traditional test of the resolution limit of the light microscope; it is considered a low-contrast subject because the visibility of pores in the transparent amorphous silica frustules is determined by the refractive index difference between the mountant and the frustules. The low contrast makes this a challenging, perhaps even unsuitable, test object for resolution. Resolution tests of modern objectives are done with high-contrast but costly patterns of chrome on glass obtained by electron lithography.

Ellipsoidal capillary as condenser for the BESSY full-field x-ray microscope

The BESSY x-ray microscopy group has developed a new full-field x-ray microscope which employs an advanced x-ray optical concept. Traditionally, zone plate based condensers are used in x-ray microscopes providing an energy resolution of only E/ΔE ≤ 500. In addition, this conventional monochromator concept requires a pinhole close to the sample restricting the available space for tomography applications. In our new BESSY microscope, a standard monochromator beam line provides a high energy resolution of up to 10,000 which permits NEXAFS studies. An elliptically shaped mono-capillary is used to form the hollow cone illumination necessary for sample illumination and to match the aperture of the objective. Calculations regarding the performance and accuracies needed are presented and characterizations of capillaries especially made for the BESSY soft x-ray microscope are shown. For the first time, we demonstrate that glass capillaries are well suited as condensers in the soft x-ray energy domain. Their focusing efficiency was measured to be 80% which is about an order of magnitude higher than the diffraction efficiency of zone plate based condensers.

Microstructural and Compositional Analysis of Strontium-Doped Lead Zirconate Titanate Thin Films on Gold-Coated Silicon Substrates

This article discusses the results of transmission electron microscopy (TEM)-based characterization of strontium-doped lead zirconate titanate (PSZT) thin films. The thin films were deposited by radio frequency magnetron sputtering at 300 degrees C on gold-coated silicon substrates, which used a 15 nm titanium adhesion layer between the 150 nm thick gold film and (100) silicon. The TEM analysis was carried out using a combination of high-resolution imaging, energy filtered imaging, energy dispersive X-ray (EDX) analysis, and hollow cone illumination. At the interface between the PSZT films and gold, an amorphous silicon-rich layer (about 4 nm thick) was observed, with the film composition remaining uniform otherwise. The films were found to be polycrystalline with a columnar structure perpendicular to the substrate. Interdiffusion between the bottom metal layers and silicon was observed and was confirmed using secondary ion mass spectrometry. This occurs due to the temperature of deposition (300 degrees C) being close to the eutectic point of gold and silicon (363 degrees C). The diffused regions in silicon were composed primarily of gold (analyzed by EDX) and were bounded by (111) silicon planes, highlighted by the triangular diffused regions observed in the two-dimensional TEM image.

Ellipsoidal and parabolic glass capillaries as condensers for x-ray microscopes

Single-bounce ellipsoidal and paraboloidal glass capillary focusing optics have been fabricated for use as condenser lenses for both synchrotron and tabletop x-ray microscopes in the x-ray energy range of 2.5-18 keV. The condenser numerical apertures (NAs) of these devices are designed to match the NA of x-ray zone plate objectives, which gives them a great advantage over zone plate condensers in laboratory microscopes. The fabricated condensers have slope errors as low as 20 murad rms. These capillaries provide a uniform hollow-cone illumination with almost full focusing efficiency, which is much higher than what is available with zone plate condensers. Sub-50 nm resolution at 8 keV x-ray energy was achieved by utilizing this high-efficiency condenser in a laboratory microscope based on a rotating anode generator.

Novel wavelength-resolved fluorescence detection for a high-throughput capillary electrophoresis system under a diascopic configuration

This paper presents a novel method regarding a wavelength-resolved fluorescence detection scheme for high-throughput analysis of bio-samples in a micro-CE chip. Instead of using the conventional laser-induced fluorescence (LIF) microscope equipped with delicate spatial filters and complex control systems, this study adopts a hollow cone illumination generated using a dark-field condenser for exciting fluorescence in the microchannel and an ultraviolet–visible–near–infrared (UV–Vis–NIR) spectrometer for detecting the emission signals. Experimental results show that the proposed system is feasible for simultaneously detecting a mixed sample composed of Atto 610, Rhodamine B and fluorescein isothiocyanate (FITC) fluorescent dyes in a single test run. Furthermore, a mixed bio-sample composed of two mixed 16-mer single-stranded DNAs labeled with Cy3 and FITC fluorescent dyes is also successfully detected with the proposed system. The measured limit of detection (LOD) for detecting FITC of the proposed system can be as low as 5.4 × 10 −6 M (S/N = 3). This proposed detection method has shown its potential on RNA identification and DNA sequencing applications.

Aberration Correction Based on Focus Modulation Transmission Electron Microscopy and its Applications

Three techniques of wave field reconstruction using focus modulation transmission electron microscopy are reviewed based on a fundamental concept of three-dimensional optical transfer properties. These techniques use a set of through-focus images for the processing and enable not only correction of spherical aberration but also separate imaging of the phase and amplitude components of the sample. Defocus-image modulation processing enables real-time correction of spherical aberration by combining techniques such as high-speed control of focus and high-speed image processing. Three-dimensional Fourier filtering enables correction of all Seidel aberrations including spherical aberration and higher-order aberrations with high signal-to-noise ratios. Dynamic hollow-cone illumination combined with image processing using Fourier filtering has the possibility of reducing the degradation of spatial resolution caused by chromatic aberration. Experimental data obtained by these methods are presented describing the inherent characteristics of the respective methods.

Synthetic incoherence for electron microscopy

Tomographic studies of submicrometer samples in materials science using electron microscopy have been inhibited by diffraction effects. In the present work, we describe a practical method for ameliorating these effects. First, we find an analytic expression for the mutual coherence function for hollow-cone illumination. Then, we use this analytic expression to propose a Gaussian weighting of hollow-cone illumination, which we name tapered solid-cone illumination, and present an analytic expression for its mutual coherence function. Finally, we investigate numerically an n-ring approximation to tapered solid-cone illumination. The results suggest a method for removing diffraction effects and hence enabling tomography.

Wave field restoration using focal-depth extension techniques under dynamic hollow-cone illumination

Wave field restoration has been achieved based on focal-depth extension under dynamic hollow-cone illumination using an optical microscope. Two kinds of focal-depth extension techniques, such as moving focus averaging and an objective annular aperture, were compared and their effectiveness for transmission electron microscopy applications is discussed. Both techniques enabled resolution enhancement at the same level and effectively obtained aberration-free phase and amplitude images separately by canceling out the rotationally invariant component of system wave aberrations, such as spherical aberration. The influence of nonlinear interference on image contrast was confirmed as significant by using a figure 8 shaped spatial frequency filter.

Direct electron crystallographic determination of zeolite zonal structures

The prospect for improving the success of ab initio zeolite structure investigations with electron diffraction data is evaluated. First of all, the quality of intensities obtained by precession electron diffraction at small hollow cone illumination angles is evaluated for seven representative materials: ITQ-1, ITQ-7, ITQ-29, ZSM-5, ZSM-10, mordenite, and MCM-68. It is clear that, for most examples, an appreciable fraction of a secondary scattering perturbation is removed by precession at small angles. In one case, ZSM-10, it can also be argued that precession diffraction produces a dramatically improved ‘kinematical’ data set. There seems to no real support for application of a Lorentz correction to these data and there is no reason to expect for any of these samples that a two-beam dynamical scattering relationship between structure factor amplitude and observed intensity should be valid. Removal of secondary scattering by the precession mode appears to facilitate ab initio structure analysis. Most zeolite structures investigated could be solved by maximum entropy and likelihood phasing via error-correcting codes when precession data were used. Examples include the projected structure of mordenite that could not be determined from selected area data alone. One anomaly is the case of ZSM-5, where the best structure determination in projection is made from selected area diffraction data. In a control study, the zonal structure of SSZ-48 could be determined from selected area diffraction data by either maximum entropy and likelihood or traditional direct methods. While the maximum entropy and likelihood approach enjoys some advantages over traditional direct methods (non-dependence on predicted phase invariant sums), some effort must be made to improve the figures of merit used to identify potential structure solutions.

30 nm resolution x-ray imaging at 8keV using third order diffraction of a zone plate lens objective in a transmission microscope

A hard x-ray transmission microscope with 30nm spatial resolution has been developed employing the third diffraction order of a zone plate objective. The microscope utilizes a capillary type condenser with suitable surface figure to generate a hollow cone illumination which is matched in illumination range to the numerical aperture of the third order diffraction of a zone plate with an outmost zone width of 50nm. Using a test sample of a 150nm thick gold spoke pattern with finest half-pitch of 30nm, the authors obtained x-ray images with 30nm resolution at 8keV x-ray energy.