Magnetic soft X-ray transmission microscopy

Recent advances in imaging magnetic microstructures on a nanometer length-scale and their temporal evolution on a sub-nanosecond time-scale have been achieved with magnetic transmission X-ray microscopy. With a lateral resolution down to 20 nm, element-specificity, recording in external magnetic fields and stroboscopic pump-and-probe imaging, insights into fundamental mechanisms of the magnetism in thin films and nanopatterned elements are provided which are also relevant in magnetic storage and sensor technologies.     

Broadband transmission masks, gratings and filters for extreme ultraviolet and soft X-ray lithography

Lithography and patterning on a nanometre scale with extreme ultraviolet (EUV) and soft X-ray radiation allow creation of high resolution, high density patterns independent of a substrate type. To realize the full potential of this method, especially for EUV proximity printing and interference lithography, a reliable technology for manufacturing of the transmission masks and gratings should be available. In this paper we present a development of broadband amplitude transmission masks and gratings for extreme ultraviolet and soft X-ray lithography based on free-standing niobium membranes. In comparison with a standard silicon nitride based technology the transmission masks demonstrate high contrast not only for in-band EUV (13.5 nm) radiation but also for wavelengths below Si L-absorption edge (12.4 nm).The masks and filters with free standing areas up to 1000 × 1000 μm² and 100 nm to 300 nm membrane thicknesses are shown. Electron beam structuring of an absorber layer with dense line and dot patterns with sub-50 nm structures is demonstrated. Diffractive and filtering properties of obtained structures are examined with EUV radiation from a gas discharge plasma source.     

毛细管放电软X光激光装置固有预脉冲的消除

本文对毛细管放电产生类氖氩46.9nm激光进行了实验研究。实验中发现毛细管放电装置中布鲁姆林(Blumlein)传输线所产生的固有预脉冲对软X光激光的产生及稳定输出都有十分不利的影响。为了消除这种影响,提出了用外加隔离开关和隔离电容的方法消除固有预脉冲。经过实验验证,确定了隔离开关和隔离电容的最佳位置。结果该方法能够有效隔离固有预脉冲,使整个放电装置达到稳定运行。在此基础上,得到并改善了毛细管放电类氖氩46.9nm激光输出。     

X-ray microanalysis in the transmission electron microscope

The technique of x-ray microanalysis of thin specimens in the transmission electron microscope is well established. Quantitative analyses can be obtained by converting observed x-ray intensity ratios into weight fraction ratios by incorporating suitable correction factors. Flourescence corrections in thin specimens are always significantly less than in bulk specimens and, except where strong characteristic radiation fluorescence enhancement is predicted in the bulk, can be safety ignored. As analysis probes less than 100 Å diameter have become available, the beam spreading has become an important parameter in determining the spatial resolution for analysis. Present developments are directed at improving the quality of the analyses which can be obtained. This requires the generation of high quality correction factors, particularly forZ<13, rapid and accurate methods of determining sample thickness, so that absorption corrections can be made, and the development of reliable procedures for determining the shape of the activated volume in a thin specimen.     

Imaging by using proton-induced quasi-monochromatic X-ray emission

Quasi-monochromatic X-ray emission induced by MeV-proton bombardment onto metallic targets was applied to radiography of small samples. The X-ray energy was adjusted in the range of ≈4–23 keV by changing the target material. The radiograms were recorded on an imaging plate. A small phantom made of Lucite was prepared for the test of photography using a contrast medium (RuCl₃$H₂O; ruthenium chloride). To clearly observe the image of the contrast agent, the photon energy was chosen to be 23.17 keV (Cd Kα) which is slightly above the K-absorption edge of Ru at 22.12 keV. Only the image of the contrast agent was successfully extracted by subtracting the image taken by 21.18-keV X-rays (Pd Kα) from that obtained by the 23.17-keV photons. Also images of a small fish sample were taken using a point-like X-ray source excited by a proton microbeam with a diameter of ≈10 mm. In this experiment, the X-ray energy was adjusted to 4.51 keV (Ti Kα) to obtain a strong attenuation by Ca in the bones. A fine structure of the bones in the thin caudal fin (<100 mm) was highly contrasted by this method. The spatial resolution of the picture was ≈20 mm. Performance of the above technique based on the proton-induced quasi-monochromatic X-ray emission is discussed in comparison to conventional methods.     

Imaging by using proton-induced quasi-monochromatic X-ray emission

Quasi-monochromatic X-ray emission induced by MeV-proton bombardment onto metallic targets was applied to radiography of small samples. The X-ray energy was adjusted in the range of ≈4–23 keV by changing the target material. The radiograms were recorded on an imaging plate. A small phantom made of Lucite was prepared for the test of photography using a contrast medium (RuCl₃·H₂O; ruthenium chloride). To clearly observe the image of the contrast agent, the photon energy was chosen to be 23.17 keV (Cd Kα) which is slightly above the K-absorption edge of Ru at 22.12 keV. Only the image of the contrast agent was successfully extracted by subtracting the image taken by 21.18-keV X-rays (Pd Kα) from that obtained by the 23.17-keV photons. Also images of a small fish sample were taken using a point-like X-ray source excited by a proton microbeam with a diameter of ≈10 μm. In this experiment, the X-ray energy was adjusted to 4.51 keV (Ti Kα) to obtain a strong attenuation by Ca in the bones. A fine structure of the bones in the thin caudal fin (<100 μm) was highly contrasted by this method. The spatial resolution of the picture was ≈20 μm. Performance of the above technique based on the proton-induced quasi-monochromatic X-ray emission is discussed in comparison to conventional methods.     

X-ray orientation microscopy using topo-tomography and multi-mode diffraction contrast tomography

Polycrystal orientation mapping techniques based on full-field acquisition schemes like X-ray Diffraction Contrast Tomography and certain other variants of 3D X-ray Diffraction or near-field High Energy Diffraction Microscopy enable time efficient mapping of 3D grain microstructures. The spatial resolution obtained with this class of monochromatic beam X-ray diffraction imaging approaches remains typically below the ultimate spatial resolution achievable with X-ray imaging detectors. Introducing a generalised reconstruction framework enabling the combination of acquisitions with different detector pixel size and sample tilt settings provide a pathway towards 3D orientation mapping with a spatial resolution approaching the one of state of the art X-ray imaging detector systems.     

Structure determination of chitosan-stabilized Pt and Pd based bimetallic nanoparticles by X-ray photoelectron spectroscopy and transmission electron microscopy

Chitosan (CTS)-stabilized bimetallic nanoparticles were prepared at room temperature (rt.) in aqueous solution. Palladium (Pd) and platinum (Pt) were selected as the first metals while iron (Fe) and nickel (Ni) functioned as the second metals. In order to obtain the noble metal core-transition metal shell structures, bimetallic nanoparticles were prepared in a two-step process: the preparation of mono noble metallic (Pd or Pt) nanoparticles and the deposition of transition metals (Fe or Ni) on the surface of the monometallic nanoparticles. The structures of the nanoparticles were studied using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The XPS results show that Pd and Pt exist mainly in zero valences. The presence of Fe and Ni in the bimetallic nanoparticles affects the binding energy of Pd and Pt. Moreover, the studies of O 1s spectra indicate the presence of Fe or Ni shells. The analyses of TEM micrographs give the particle size and size distributions while the high-resolution TEM (HRTEM) micrographs show the existence of noble metal core lattices. The results confirm the formation of noble metal core-transition metal shell structures.     

X-ray and transmission electron microscopy structural characterization of multifunctional Perovskite thin films

Different multifunctional (PbTiO₃, Sm_0.6Nd_0.4NiO₃, NdMnO₃) thin films were grown by metalorganic chemical vapor deposition (MOCVD) technique on SrTiO₃ and LaAlO₃ substrates. Transmission electron microscopy (TEM) and X-ray diffraction measurements reveal that almost single crystalline thin films can be epitaxially grown on the top of substrates. The relationship between the crystallographic orientation of the films and those of the substrates were determined by reciprocal space mapping and TEM analyses. PbTi03 thin films appear to be under tensile or compressive strain according to the different mismatch of their cell parameter with those of the substrate. Relaxation mechanism as a function of the film thickness arises from coexistence of different type of domains and size and strain effect are analyzed. SmNiO₃ thin films present diffuse scattering strikes and are less well organized when compared to PbTi0₃ thin films. Different domains are observed as well as an additional parasitic phase close to NiO. Its regular distribution can be associated to reduced transport properties. Preliminary observations on NdMnO₃ thin films shows that an amorphous phase is obtained during MOCVD that can be transformed in a single crystalline film by annealing. The films are under tensile or compressive strain according to the different mismatch of their cell parameter with those of the substrate. Magnetic properties are investigated.     

Study of thin film multilayers using X-ray reflectivity and scanning probe microscopy

We have presented new schemes to analyse grazing incidence specular X-ray reflectivity data to obtain structural and chemical information of thin films. Analysis of specular reflectivity data gives information along the depth of the film, whereas, analysis of non-specular data reveals the structural information across the film surface and interfaces. The schemes proposed are based on the Born approximation and the distorted wave born approximation (DWBA). Surface structural parameters such as, height–height correlation and roughness exponent of the film obtained from the analysis of X-ray reflectivity was compared with results obtained from atomic force microscopy     

Three-dimensional imaging of human stem cells using soft X-ray tomography

Three-dimensional imaging of human stem cells using transmission soft X-ray tomography (SXT) is presented for the first time. Major organelle types—nuclei, nucleoli, mitochondria, lysosomes and vesicles—were discriminated at approximately 50 nm spatial resolution without the use of contrast agents, on the basis of measured linear X-ray absorption coefficients and comparison of the size and shape of structures to transmission electron microscopy (TEM) images. In addition, SXT was used to visualize the distribution of a cell surface protein using gold-labelled antibody staining. We present the strengths of SXT, which include excellent spatial resolution (intermediate between that of TEM and light microscopy), the lack of the requirement for fixative or contrast agent that might perturb cellular morphology or produce imaging artefacts, and the ability to produce three-dimensional images of cells without microtome sectioning. Possible applications to studying the differentiation of human stem cells are discussed.     

Characterization of thermally stable W/Ni multilayers by X-rays and cross-sectional transmission electron microscopy

W/Ni multilayer structures (MLS) composed of 5 and 10 bilayers, with composition W(15 Å)/Ni(55 Å), have been deposited on float glass substrate using ion-beam sputtering. X-ray reflectivity and wide-angle X-ray diffraction techniques have been used to study their interface characteristics, such as layer thickness, interface roughness and change in structural parameters. The fabricated MLS were found to be oriented along (111) of Ni having superlattice modulation perpendicular to the film plane. Thermal annealing studies on these multilayers showed that these were stable up to 500 °C. Cross-sectional transmission electron microscopy and selected area electron diffraction studies on as-deposited W/Ni MLS of 10 bilayers revealed well formed interfaces without any correlated roughness. The thicknesses of different layers were found to vary along the film thickness.     

原子力显微镜与X射线光电子能谱对ITO表面改性的研究

采用氧气等离子体(OP)处理对氧化铟锡(ITO)薄膜进行表面改性,通过原子力显微镜(AFM)、X射线光电子能谱(XPS)和四探针等测试手段对薄膜样品进行表征,研究了OP处理对ITO表面性质的影响.实验结果表明OP处理有效去除了ITO表面的污染物,优化了ITO表面的化学组分,降低了ITO表面的粗糙度和方块电阻,改善了ITO的表面形态.与此同时,通过XPS监测研究了OP处理后ITO表面化学组分随老化时间的变化,结果显示经过优化的化学组分随老化时间增加而逐渐退化.另外,以OP处理后经过不同老化时间的ITO样品作为空穴注入电极,制备了有机电致发光器件(OELD),通过测试器件的电压-电流-亮度特性,进一步研究了ITO表面性质对于OELD光电性能的影响.     

Nonlinear light-sheet fluorescence microscopy by photobleaching imprinting

We present a nonlinear light-sheet fluorescence microscopy (LSFM) scheme based on photobleaching imprinting. By measuring photobleaching-induced fluorescence decay, our method simultaneously achieves a large imaging field of view and a thin optical section. Furthermore, the scattered-light-induced background is significantly reduced, considerably improving image contrast. Our method is expected to expand the application field of LSFM into the optical quasi-ballistic regime, enabling studies on non-transparent biological samples.     

Investigation of early growth of calcium hydroxide crystals in cement solution by soft X-ray transmission microscopy

The early growth of calcium hydroxide (CH) crystals in cement solution is investigated by soft X-ray transmission microscopy imaging. A quantitative analysis of the successively recorded images of the hydration process enabled to evaluate the supersaturation ratio of solution, growth rates, both kinetic and diffusion coefficients, and concentrations of solute molecules at and {0001} facets of the CH crystals. It is concluded that the difference in obtained concentrations of solute molecules at these facets may be associated with solubility anisotropy of crystallographic facets of the CH. The interfacial energy of the CH nuclei in aqueous solution is evaluated to be 0.114 J/m² that by an order of magnitude is smaller than the average free surface energy of this phase. The proposed theoretical approach is universal and, in potential, may be applied to any precipitating phase in a supersaturated solution.     

Damage mode tensile testing of thin gold films on polyimide substrates by X-ray diffraction and atomic force microscopy

In situ tensile testing has been performed on thin gold film, 320 nm thick, deposited on polyimide substrates. During the tensile testing, strain/stress measurements have been carried out by X-ray diffraction using the d-sin²ψ method. The X-ray stress analysis suggests crack formation in the films for stresses greater than 670 MPa. The surface of the deformed specimen observed by atomic force microscopy (AFM) exhibits both cracks and two types of straight-sided buckling patterns lying perpendicular to the tensile axis. These buckling patterns can have a symmetrical or asymmetrical shape. The evolution of these two kinds of buckling structures under tensile stress has been observed in situ by AFM and compared to X-ray stress data. The results indicate that symmetrical straight-sided buckling patterns are induced by the compressive stress during unloading, whereas the asymmetrical result from the delamination of the film during the tensile deformation.     

Atomic force microscopy and X-ray photoelectron spectroscopy evaluation of adhesion and nanostructure of thin Cr films

Chromium (Cr) thin films were deposited on float glass using electron beam (e-beam) physical vapor deposition and radio frequency (RF) magnetron sputtering techniques. Surface morphology of these Cr films was studied using atomic force microscopy (AFM). The e-beam deposited Cr films consisted of isolated surface mounds while in RF sputtered samples, these mounds combined to form larger islands. Lower surface adhesive properties were observed for e-beam deposited films, as determined from AFM force-distance curves, presumably due to the nanostructural differences. Similar amounts of adsorbed atmospheric carbonaceous contaminants and water vapor were detected on samples deposited using both methods with e-beam deposited samples having additional carbide species, as determined by X-ray photoelectron spectroscopy data. The dominant crystallographic plane in both e-beam deposited and RF sputtered Cr thin films was (110) of body-centered cubic Cr metal structure as determined from X-ray diffraction data. Weak (211) reflection was also observed in RF sputtered samples and was attributed to a different thin Cr film condensation and growth mechanism which resulted in nanostructural differences between films deposited using two different methods.     

On the determination of dopant-concentration profiles by grazing emission X-ray fluorescence spectroscopy using the maximum-entropy method

The determination of concentration profiles of impurities in silicon from angle scans of emitted x-ray fluorescence intensities using the maximum-entropy method is studied. Existence and convergence properties of the maxium- entropy method are discussed. The application of the maximum-entropy method to Grazing emission X-Ray Fluorescence Spectromety is compared with an analytical method. It is found that, provided noise levels are sufficiently low, concentration profiles can be reconstructed without using a priori knowledge.     

Scanning transmission electron microscopy (STEM)-transmission electron microscopy (TEM) analysis of nitrogen ion implanted austenitic 302 stainless steel

The microstructure of nitrogen implanted AISI 302 austenitic stainless steel and the effect of long-term room temperature ageing on it have been studied. Samples were implanted in 1992 with 2.5×10²¹ N₂⁺ m⁻² at 130 keV. The characteristics of the implanted layer and the depth profile have been investigated by scanning transmission electron microscope combined with energy dispersive X-ray spectrometry. Electron diffraction patterns recorded in the implanted layer using transmission electron microscopy confirm the formation of CrN along with the presence of Cr₂N. The identification of phases by glancing angle X-ray diffraction also indicates the formation of Cr₂N and nitrogen solid solutions. The effects of ageing on the microstructure are observed to be small.