Characterization of LiBC by phase-contrast scanning transmission electron microscopy

LiBC was used as a model compound for probing the applicability of phase-contrast (PC) imaging in an aberration-corrected scanning transmission electron microscope (STEM) to visualize lithium distributions. In the LiBC structure, boron and carbon are arranged to hetero graphite layers between which lithium is incorporated. The crystal structure is reflected in the PC-STEM images recorded perpendicular to the layers. The experimental images and their defocus dependence match with multi-slice simulations calculated utilizing the reciprocity principle. The observation that a part of the Li positions is not occupied is likely an effect of the intense electron beam triggering Li displacement.     

Long-term quantitative phase-contrast imaging of living cells by digital holographic microscopy

The dynamic analysis of biological living samples is one of the particular interests in life sciences. An improved digital holographic microscope for long-term quantitative phase-contrast imaging of living cells is presented in this paper. The optical configuration is optimized in the form of a free-space-fiber hybrid system which promotes the flexibility of imaging in complex or semi-enclosed experimental environment. Aberrations compensation is implemented taking into account the additional phase aberration induced by liquid culture medium in long-term observation. The proposed approach is applied to investigate living samples of MC3T3-E1 and MLO-Y4 cells. The experimental results demonstrate its availability in the analysis of cellular changes.     

Unstained viable cell recognition in phase-contrast microscopy

Individual cell recognition is a relevant task to be accomplished when single-ion microbeam irradiations are performed. At INFN-LNL facility cell visualization system is based on a phase-contrast optical microscope, without the use of any cell dye. Unstained cells are seeded in the special designed Petri dish, between two mylar foils, and at present the cell recognition is achieved manually by an expert operator. Nevertheless, this procedure is time consuming and sometimes it could be not practical if the amount of living cells to be irradiated is large. To reduce the time needed to recognize unstained cells on the Petri dish, it has been designed and implemented an automated, parallel algorithm. Overlapping ROIs sliding in steps over the captured grayscale image are firstly pre-classified and potential cell markers for the segmentation are obtained. Segmented objects are additionally classified to categorize cell bodies from other structures considered as sample dirt or background. As a result, cell coordinates are passed to the dedicated CELLView program that controls all the LNL single-ion microbeam irradiation protocol, including the positioning of individual cells in front of the ion beam. Unstained cell recognition system was successfully tested in experimental conditions with two different mylar surfaces. The recognition time and accuracy was acceptable, however, improvements in speed would be useful.     

X射线相衬成像光子筛

基于 Zernike相衬成像原理和光瞳切趾原理,提出一种将相位板和切趾光子筛集成为一个相衬显微物镜的 X射线相衬成像光子筛的设计方法.这种 X射线相衬成像物镜可以实现生物体组织或者其他弱吸收材料的高分辨率和高衬度成像.通过优化光子筛透镜的衍射结构,可以抑制成像系统的点扩展函数的旁瓣和消除高阶衍射焦点,从而提高成像分辨率;另外,将光子筛透镜和变相板合为一体,克服了成像透镜和变相板难以对准的缺陷.以高斯切趾光子筛为例,实验验证了设计方法的可行性. 关键词： X射线显微技术 相衬成像 光瞳切趾 光子筛     

En face imaging of single cell layers by differential phase-contrast optical coherence microscopy

Optical coherence microscopy (OCM) is capable of imaging the backscattering potential of a sample with high transversal and axial resolution. We report on a combination of OCM with a differential phase-contrast technique that permits imaging of the subwavelength optical path differences that occur between a narrow beam probing a sample and its surrounding. This technique allows small transversal refractive-index variations close to a selected interface to be seen. We report on the method and present first images of a test sample and a single cell layer. The cells act as phase objects; imaging the phase properties improves the contrast compared with that of intensity images.     

Quantitative phase-contrast microscopy by a lateral shear approach to digital holographic image reconstruction

Combining the concept of lateral shear interferometry (LSI) within a digital holography microscope, we demonstrate that it is possible to obtain quantitative optical phase measurement in microscopy by a new single-image-processing procedure. Numerical lateral shear of the reconstructed wavefront in the image plane makes it possible to retrieve the derivative of the wavefront and remove the defocus aberration term introduced by the microscope objective. The method is tested to investigate a silicon structure and a mouse cell line.     

Spectral-domain optical coherence phase microscopy for quantitative phase-contrast imaging

We describe a novel microscopy technique for quantitative phase-contrast imaging of a transparent specimen. The technique is based on depth-resolved phase information provided by common path spectral-domain optical coherence tomography and can measure minute phase variations caused by changes in refractive index and thickness inside the specimen. We demonstrate subnanometer level path-length sensitivity and present images obtained on reflection from a known phase object and human epithelial cheek cells.     

Zernike apodized photon sieves for high-resolution phase-contrast x-ray microscopy

We present a type of diffractive lens, Zernike apodized photon sieves (ZAPS), used as the objective for high spatial resolution and high phase-contrast imaging of weakly absorbing materials in x rays. The structure of ZAPS is based on the combination of two concepts: apodized photon sieves and Zernike phase contrast. The ZAPS is a single optic that integrates the appropriate ±π/2 rad phase shift through selective zone placement shifts in an apodized photon sieve. Analysis of the focusing properties of the apodized photon sieve in terms of point-spread function show that the sidelobes have been significantly suppressed at the expense of slightly widening the width of the main lobe. In combination with synchrotron light sources, ZAPS offers new opportunities for high-resolution phase-contrast x-ray microscopy in the physical and life sciences.     

Optical oscillation modes of plasmon particles observed in direct space by phase-contrast near-field microscopy

Light distributions near resonant metal nanoparticles are recorded by a scattering-type scanning near-field optical microscope (s-SNOM), for the first time with a sub-particle-size resolution (<10 nm) and with simultaneous amplitude and phase contrast. The images depict the optical oscillation patterns of single plasmon particles. Examples are presented of particles excited in dominantly dipolar and quadrupolar modes, and also of closely spaced particles sustaining a gap mode. The gap mode can provide enhanced optical fields in nanometric spots for non-linear and single-molecule spectroscopy applications. Received: 20 June 2001 / Revised version: 3 August 2001 / Published online: 19 September 2001     

Quantitative phase-contrast imaging of cells with phase-sensitive optical coherence microscopy

We describe a method for en face phase-contrast imaging of cells with a fiber-based differential phase-contrast optical coherence microscopy system. Recorded en face images are quantitative phase-contrast maps of cells due to spatial variation of the refractive index and (or) thickness of various cellular components. Quantitative phase-contrast images of human epithelial cheek cells obtained with the fiber-based differential phase-contrast optical coherence microscopy system are presented.     

Work function of single-walled carbon nanotubes determined by field emission microscopy

The field emission characteristics of a single micro-bundle of single-walled carbon nanotubes (SWCNTs) were investigated using field emission microscopy (FEM). Fowler–Nordheim plots revealed that the work function of the SWCNTs was reduced with increasing heating temperature, and reached a minimum value around 1000 °C, assuming that the β factor was constant during the heating process. Field emission patterns also demonstrated fine structures that were believed to be images of the cap of a SWCNT, which was in a clean state. The radius of the SWCNT micro-bundle was measured by transmission electron microscopy (TEM), and the β factor was calculated using two empirical formulae. Then, the work function of the SWCNT was determined from the slope, K, of its Fowler–Nordheim plot. The work function values were Φ₁=4.76 eV and Φ₂=4.88 eV, respectively. Received: 26 October 2001 / Revised version: 19 February 2002 / Published online: 6 June 2002     

Domain structures of phospholipid monolayer Langmuir-Blodgett films determined by atomic force microscopy

Atomic Force Microscopy (AFM) has been used to show the formation of solid-phase domains from fluid-phase domains on compression of DiPalmitoyl-PhosphatidylCholine (DPPC) monolayer Langmuir-Blodgett (LB) films. The chiral structures on the solid substrates were observed for the first time. By applying the friction force technique, we were able to distinguish the different regions of LB films according to their elastic properties. The influence of rates of compression on the domain shape as well as the microstructure within the domain were also studied.     

Dynamic and quantitative phase-contrast imaging of living cells under simulated zero gravity by digital holographic microscopy and superconducting magnet

The experiment of dynamic and quantitative phase-contrast imaging of living cells in simulated zero gravity environment were performed by using digital holographic microscopy (DHM) combined with a superconducting magnet (SM). The SM with large gradient high magnetic field was used to simulate zero gravity by levitating biological living samples. The proposed DHM system provided highly efficient and versatile means for dynamically and quantitatively phase-contrast imaging MC3T3-E1 cells. To our knowledge, the phase images of living cells undergoing modifications and division under simulated zero gravity were firstly obtained by using DHM-SM prototype.     

Chemical composition and surface morphology of anodic alumina determined by electron microscopy and thermogravimetry

The results of the investigation of anodic aluminà (AA) by atomic force microscopy and differential thermal analysis depending on the electrolyte composition and anodization current density are presented. It has been revealed that the concentration of impurities in the form of electrolyte anions and hydration water the AA formed in a combined electrolyte is three times lower than the AA obtained in oxalate electrolyte. The roughness of the outer surfaces of the analyzed specimens is half that of the oxide obtained in a combined electrolyte. The correlation between the composition of the electrolyte, current density, and morphological parameters has been revealed.     

Medium range order of bulk metallic glasses determined by variable resolution fluctuation electron microscopy

Variable resolution fluctuation electron microscopy (FEM) experiments are implemented with hollow-cone dark-field transmission electron microscopy. Medium range order lengths of zirconium and iron based bulk metallic glasses and amorphous silicon nitride are determined from the FEM results. It shows that maximum normalized intensity variances of FEM images occur when their nominal resolution approaches the correlation length Λ of the amorphous materials. Additionally, differences in the length and magnitude of medium range order are compared between metallic and covalent bond amorphous materials.     

Electronic effect of doped oxygen atoms in Bi2201 superconductors determined by scanning tunneling microscopy

Oxygen dopants are essential for tuning the electronic properties of the cuprate superconductors Bi_2Sr_2Ca_(n-1)Cu_nO_(2n+4+δ).Here,we study an optimally doped Bi_2Sr_(2-x)La_xCuO_(6+δ)and an overdoped Bi_(2-y)Pb_ySr_2CuO_(6+δ)by scanning tunneling microscopy and spectroscopy(STM/STS).Based on the characteristic features of local STS,three forms of oxygen dopants are identified:interstitial oxygen atoms on the SrO layers,oxygen vacancies on the SrO layers,and interstitial oxygen atoms on the BiO layers.In both samples,the first form dominates the number of oxygen dopants.From the extracted spatial distribution of the oxygen dopants,we calculate the dopant concentrations and estimate the average hole carrier density.The magnitudes of the electronic pseudogap state in both samples are inhomogeneously distributed in space.The statistical analysis on the spatial distributions of the oxygen dopants and the pseudogap magnitude demonstrates that the doped oxygen atoms on the SrO layers tend to suppress the nearby pseudogap magnitude.