Background formation in SIMS analysis of hydrogen,carbon, nitrogen and oxygen in silicon

The (background) intensities of H^-, C^-, SiN^- and O^- secondary ions emitted from Si due to 10 keV Cs⁺ bombardment have been measured under ultrahigh vacuum conditions as a function of the beam current and the rastered area. Adsorption during beam-off periods has also been investigated. The results suggest that the sticking coefficients for carbon and nitrogen-carrying residual gas molecules are significantly enhanced by simultaneous ion bombardment whereas only a negligible beam-induced enhancement effect is seen with hydrogen and oxygen-carrying species. At low currents the background intensities of H^- and O^- become independent of the beam current. This reduces the effectiveness of the electronic gating technique commonly employed in raster scanning depth profiling. At a base pressure of 1×10⁻⁸ Pa and an erosion rate of 1 nm/s, the background intensities observed in depth profiling of H, C, N and O in Si correspond to bulk concentrations of 1×10¹⁸, 2×10¹⁷, 8×10¹⁵ and 1×10¹⁸ atoms/cm³, respectively.     

Imaging of submicron objects with the light microscope

Using conventional optics coupled with image processing, several submicron objects have been studied with light microscopy. These include polystyrene beads (88, 264 and 557 nm), frustules from the diatom Pleurosigma angulatum and the T-4 bacteriophage, either attached to its host, Escherichia coli, or free in the medium. The best results were obtained from dark-field and phase contrast optics. Digital image processing with the use of colour look-up tables in real time greatly promoted precise focusing of the objects. Selective discrimination of image histogram grey values allowed for selection of a sharp contour boundary, thus more effectively delimiting the submicron objects. User interactive scaling of the diffraction limited boundaries greatly improved discrimination of the objects. While Abbe limits have not been surpassed by these techniques, the greater ‘apparent resolution’ could be attributable to a ‘better recognition’ of the submicron objects examined. Equivalence of images of polystyrene beads and bacteriophages was demonstrated with light and electron microscopy of the same field.     

液氮发动机配气装置的原理与实验研究

液氮发动机的供气能力决定着它的工作效率,为了提供液氮发动机工作所需要的充足、稳定的高压气体,设计了一种应用于液氮发动机的配气装置,该装置由液氮存储设备、低温泵、换热器及配气筒组成,该装置将低温液氮通过换热器汽化成高压氮气,提供液氮发动机的正常工作所需的高压气体.对配气装置的原理和热力过程进行研究,并通过实验对换热器性能进行测验和分析,通过实验研究发现该装置供气稳定,出口压力和进出口压力差都能满足液氮发动机正常的工作需要.     

Imaging in the far-red with electronic light microscopy: Requirements and limitations

The acquisition of simultaneous dual confocal images with red and far-red light has both advantages (e.g. lower autofluorescence) and limitations. An understanding of these requisites is necessary to acquire high-quality images and to avoid the misinterpretation of experimental data. The poor detection of far-red light mandates a high optical transfer efficiency for the system, thus the transmittance of the objective lens and its axial and lateral chromatic aberration in the far-red are important factors for consideration. This technical note is an attempt to ‘demystify’ the process of filter set design for confocal microscopy by discussing the considerations that went into the construction of a filter set for use with the reagents cyanine 3.18 (Cy3) and cyanine 5.18 (Cy5), and thus to encourage users to look beyond the multi-purpose designs available commercially. The 568-nm laser line exciting Cy3 is at its emission maximum, which limits the collectable Cy3 fluorescence. High-transmission optical filters with sharp band pass cutoffs are thus desirable for maximum light throughput. Light path mirror efficiency rapidly degrades above 700 nm, but the loss of this portion of the Cy5 emission spectrum is acceptable since the fluorophore is very bright, and these very long wavelengths are also likely to introduce aberration. While resolution is decreased with far-red light, there is also greater penetration and less scattering, and it is thus possible to obtain high-quality images from deeper within the specimen. Although only one make and model of confocal microscope (the Bio-Rad MRC–600) is considered, similar considerations pertain to the design of filter sets for any confocal microscope that accommodates user-installed filters.     

Contrast,resolution, pixelation,dynamic range and signal-to-noise ratio: fundamental limits to resolution in fluorescence light microscopy

In a perfect optical system numerical aperture and wavelength determine resolution. In a real optical system, however, the number of photons collected from a specimen determines the contrast and this limits the resolution. Contrast is affected by the number of picture elements per unit area, the number of photons and the aberrations present in every optical system. The concept of contrast vs. distance functions is used to compare the resolution achievable in confocal and wide-field fluorescence microscopes and the effect of a further reduction of the observable volume. In conclusio: (a) real optical systems will never be able to achieve the theoretical resolution, (b) wide-field fluorescence microscopy will often provide a better resolution than confocal fluorescence microscopy, (c) decreasing the observed volume does not necessarily increase the resolution and (d) using multiple fluorophores can improve the accuracy with which distances are measured. Some numbers for typical situations are provided.     

Detection of reactive oxygen and reactive nitrogen species in skeletal muscle.

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are usually identified with pathological states and mediators of cellular injury. However, over the last decade ROS and RNS have been identified in skeletal muscle under physiological conditions. Detection of ROS and RNS production by skeletal muscle cells is fundamental to the problem of differentiating between physiological and pathological levels. The goal of this paper is to review the techniques that have been used to detect ROS and RNS in skeletal muscle. Electron spin resonance, fluorescent assays, cyotchrome c reduction, chemiluminescence, hydroxylation of salicylate, and nitration of phenylalanine are some of the assay systems that have been used thus far. A large body of evidence now indicates that ROS and RNS are continually produced by many different skeletal muscle types studied in vivo, in situ, and in vitro. Under resting conditions, ROS and RNS are detectable in both intracellular and extracellular compartments. Production increases during both non-fatiguing and fatiguing muscle contractions. In the absence of disease, the individual molecular species detected in skeletal muscle include parent radicals for the ROS and RNS cascades: superoxide anions and nitric oxide. Both are generated at rates estimated to range from pmol-to-nmol/mg muscle/minute. Evidence indicates that hydrogen peroxide, hydroxyl radicals, and peroxynitrite are also present under physiological conditions. However, the molecular species that mediate specific biological effects remains largely undetermined, as do the sources of ROS and RNS within muscle fibers. Eventual delineation of the mechanisms whereby ROS and RNS regulate cellular function will hinge on our understanding of the production and distribution of ROS and RNS within skeletal muscle.     

一次进样分析氧气中碳、硫化物和质量数丰度值与比值

建立了一次进样分析氧气中的碳、硫化物信号和质量数丰度值与比值的方法,并可获知单位氧气内不同质量数的分子、原子分布16 O≈0.56%;17 O≈0.15%;32 O2≈87.16%;33 O2≈11.05%;34 O2≈0.47%;35 O2≈0.06%;48 O2≈0.03%。     

Optical microscopy with improved resolution using two-beam interference of low-coherence light

In recent years, high-resolution microscopy using structured illumination has been practically applied for fluorescent bio-imaging. However, there is a large amount of speckle noise in reflected- and scattered-light images, because structured illumination is typically generated by laser-beam interference. Hence, this high-resolution imaging technique cannot be effectively used in industrial applications. In this study, we attempted to generate structured illumination using two-beam interference of low-coherence light for high-resolution and low-speckle imaging. First, we constructed an optical system consisting of a Michelson interferometer configured in such a manner that it achieved zero optical path-length difference and allowed the interference fringes to be manipulated. Then, we confirmed that the generated structured illumination width corresponded to the coherence length of the light source. As a final result of the resolution improvement experiment, the narrow sample pitch of 0.4 μm was successfully resolved beyond the diffraction limit of 0.74 μm with relatively less speckle noise.     

The microanalysis of light elements using transmitted energy loss electrons.

The use of transmitted energy loss electrons is shown to hold considerable promise for the elemental analysis of light elements. In this technique, those electrons which have lost energy in exciting characteristic inner shell atomic levels are detected rather than X-rays resulting from the decay of the excited levels. The advantages of this technique are (1) a large fraction (0.1-1) of the information-carrying energy loss electrons can be detected, and (2) for each excited level, one energy loss electron is produced independent of the fluorescent yield. Thus the technique potentially offers higher sensitivity than X-ray analysis. We have begun a program to evaluate this technique both theoretically and experimentally for electron probe devices. First, we have developed the necessary theoretical framework to make predictions concerning relevant quantities of elemental analysis such as the minimum detectable mass (MDM) and mimimum detectable mass fraction (MMF). The results of these calculations for thin specimens indicate a potential reduction in the MDM by up to three orders of magnitude and in the MMF by up to 500 through the use of transmitted energy loss electrons rather than X-rays; the advantages over X-ray detection being greater for lower atomic number. Second, we have begun experimental measurements to verify our predictions. These experiments were performed in a field emission scanning microscope with known limitations in collection efficiency, but the results indicate the validity of the basic assumptions and also aid in the design of an instrument which can fully exploit this technique. The experimental results obtained indicate the ease of detection of characteristic K-shell energy levels in elements as light as lithium and indicate the mass detectability of less than 10(-18)g.     

纳米分辨微小光斑光强分布检测系统设计

介绍了现有的微小光斑测量技术,针对纳米分辨率检测精度要求,对纳米分辨微小光斑光强分布检测技术进行深入研究,设计和构建了具有纳米分辨的微小光斑光强分布检测系统。利用该检测系统进行了低数值孔径弱聚焦下所形成的微光场光强分布检测实验,得到较好的光强分布图。实验结果表明,该检测系统具有可靠性高、稳定性好、便于操作等优点。     

Precise measurement of the resolution in light microscopy using Fourier transform

The resolution power of light microscope has been accurately measured (+/-5%) by Fourier transform of various object images and further evaluation of the highest spatial frequency in Fourier spectrum. Any unknown shape plane object with a shape feature's size smaller than the resolution to be measured was shown to provide a reliable resolution test. This simple method gives a direct measurement of the resolution power as defined by Abbe [Archiv. F. Mikroskopische Anat. 9, 413 (1873)]. The results have been justified by comparison to a standard resolution measurement by using calibrated periodic line patterns. Notably, the approach is applicable in super-resolution light microscopy (transmission, reflection, and fluorescence), where calibrated resolution targets do not occur. It was conveniently implemented by using a compact disk as a test object and free IMAGEJ imaging software.     

Energy resolution of silicon surface-barrier detectors for oxygen and sulphur ions

A group of 9 silicon surface-barrier detectors, 4 manufactured by ORTEC and 5 fabricated by the first author and his students. has been tested for their energy resolutions with oxygen ions of 36.750 and 50 MeV energy and sulphur ions of 51.086 MeV energy from the University of Pittsburgh Van de Graaff accelerator. Six of the detectors had previously been tested with oxygen ions of 25 and 50 MeV energy at Pittsburgh, and those results are compared with the present ones. It is now possible to conclude that the energy resolution of the best detectors is independent of oxygen ion energy between 36.750 and 50 MeV and is about 100 keV (fwhm). When tested with sulphur ions, 4 of the detectors showed anomalous effects, including peaks and smudges both below and above the main peak. Some of these could be eliminated by varying the reverse bias voltage across the detector, others could not. In particular, the ORTEC detector 40, used in the previous work as the standard detector presently available, did not show a single peak at any bias. It is an excellent detector for oxygen ions, but is not useful for sulphur ions. The energy resolution of the best detectors for 51.086 MeV sulphur ions is under 300 keV (fwhm).     

Application of light collecting probe with high spatial resolution to spark-ignited spherical spray flames

A light collecting probe named Multi-color Integrated Cassegrain Receiving Optics (MICRO) is applied to spark-ignited spherical spray flames to obtain the flame propagation speed in freely falling droplet suspension produced by an ultrasonic atomizer. Two MICRO probes are used to monitor time-series signals of OH chemiluminescence from two different locations in the flame. By detecting the arrival time difference of the propagating flame front, the flame propagation speed is calculated with a two-point delay-time method. In addition, time-series images of OH chemiluminescence are simultaneously obtained by a high-speed digital CCD camera to ensure the validity of the two-point delay-time method by the MICRO system. Furthermore, the relationship between the spray properties measured by phase Doppler anemometer (PDA) and the flame propagation speed are discussed with three different experimental conditions by changing the fuel injection rate. It was confirmed that the two-point delay-time method with two MICRO probes is useful and convenient to obtain the flame propagation speed and that the flame propagation speed depends on the spray properties.     

Probing structures of nanomaterials using advanced electron microscopy methods, including aberration-corrected electron microscopy at the Angstrom scale

Structural and compositional studies of nanomaterials of technological importance have been carried out using advanced electron microscopy methods, including aberration-corrected transmission electron microscopy (AC-TEM), AC-high angle annular dark field scanning TEM (AC-HAADF-STEM), AC-energy filtered TEM, electron-stimulated energy dispersive spectroscopy in the AC-(S)TEM and high-resolution TEM (HRTEM) with scanning tunneling microscopy (STM) holder. The AC-EM data reveal improvements in resolution and minimization in image delocalization. A JEOL 2200FS double-AC field emission gun TEM/STEM operating at 200 kV in the Nanocentre at the University of York has been used to image single metal atoms on crystalline supports in catalysts, grain boundaries in nanotwinned metals, and nanostructures of tetrapods. Joule heating studies using HRTEM integrated with an STM holder reveal in situ crystallization and edge reconstruction in graphene. Real-time in situ AC-HAADF-STEM studies at elevated temperatures are described. Dynamic in-column energy filtering in an AC environment provides an integral new approach to perform dynamic in situ studies with aberration correction. The new results presented here open up striking new opportunities for atomic scale studies of nanomaterials and indicate future development directions.     

星载成像光谱仪杂散光测量与修正

分析了星载成像光谱仪杂散光的来源和危害,研究了杂散光对此类光谱仪光谱测量精度的影响.介绍了用点扩散函数描述成像光谱仪杂散光的原理,推导了杂散光影响矩阵和杂散光修正矩阵的求解,给出了杂散光测量和修正的具体方案,并对测量和修正精度进行了分析.实验表明,基于点扩散函数的矩阵法可实现成像光谱仪杂散光的测量和修正.像元中心波长入...     

Imaging streptavidin 2D crystals on biotinylated lipid monolayers at high resolution with the atomic force microscope

Streptavidin crystals were grown on biotinylated lipid monolayers at an air/water interface and transferred onto highly oriented pyrolytic graphite (HOPG). These arrays could be imaged to a resolution below 1 nm using the atomic force microscope. The surface topographs obtained were compared with negative-stain electron microscopy images and the atomic model as determined by X-ray crystallography. The streptavidin tetramer (60 kDa) exposes two free biotin-binding sites to the buffer solution, while two are occupied by linkage to the lipid monolayer. Therefore, the streptavidin 2D crystals can be used as nanoscale matrices for binding biotinylated compounds. Furthermore, this HOPG-based preparation method provides a general novel approach to study the structure of protein arrays assembled on lipid monolayers with the AFM.     

硅中氧、碳的二次离子质谱(SIMS)分析

本文采用相对灵敏度因子法,对硅中氧、碳含量的SIMS定量分析方法进行研究。通过对样品进行预溅射的方法,氧、碳的的检测限分别可达到6.0e16atoms/cm~3、2.0e16atoms/cm~3。     

ELNES for boron, carbon, and nitrogen K-edges with different chemical environments in layered materials studied by density functional theory

Electron energy-loss near-edge fine structures (ELNES) were calculated for graphene, doped graphene, a hexagonal BN monolayer, and a hexagonal BC₂N layer using an ab initio pseudopotential plane wave method including the core-hole effect. Spectral features that can be used to distinguish different chemical environments are identified. The spectral features are closely related to the atomic species and arrangement. The connection between chemical environments and fine structures is discussed.     

TruSpec CN元素分析仪测定土壤中碳氮方法研究

采用美国Leco公司TruSpec CN元素分析仪对土壤中碳氮含量进行测定并对土壤的分析方法进行优化,确定了最佳取样装置、最小分析时间、燃烧时间和最佳称样量。实验结果表明,碳氮的线性范围分别为0．632～24．647mg（R〉0．999）和0．0601～5．754mg（R〉0．999）,检出限（3S／N）分别为0．0022和0．0032mg。土壤样品碳氮的回收率分别为99．2％～100．9％和98．2％～99．2%,测得5种土壤碳氮的相对标准偏差（RSD）为0．997％～2．143％和0．214％～3．115％。该方法操作简便快速、灵敏度高,具有较好的精密度和准确度,可准确可靠地用于土壤碳氮含量的测定。