Microstructure of MmM(5)/Mg multi-layer hydrogen storage films prepared by magnetron sputtering

Multi-layer hydrogen storage thin films with Mg and MmNi3.5(CoAlMn)1.5 (here Mm denotes La-rich mischmetal) as alternative layers were prepared by direct current magnetron sputtering. Transmission electron microscopy investigation shows that the microstructure of the MmNi3.5(CoAlMn)1.5 and Mg layers are significantly different although their deposition conditions are the same. The MmNi3.5(CoAlMn)1.5 layer is composed of two regions: one is an amorphous region approximately 4 nm thick at the bottom of the layer and the other is a nanocrystalline region on top of the amorphous region. The Mg layer is also composed of two regions: one is a randomly orientated nanocrystalline region 50 nm thick at the bottom of the layer and the other is a columnar crystallite region on top of the nanocrystalline region. These Mg columnar crystallites have their [001] directions parallel to the growth direction and the average lateral size of these columnar crystallites is about 100 nm. A growth mechanism of the multi-layer thin films is discussed based on the experiment results.     

The cutting of ultrathin sections with the thickness less than 20 nm from biological specimens embedded in resin blocks

Low voltage electron microscopes working in transmission mode, like LVEM5 (Delong Instruments, Czech Republic) working at accelerating voltage 5 kV or scanning electron microscope working in transmission mode with accelerating voltage below 1 kV, require ultrathin sections with the thickness below 20 nm. Decreasing of the primary electron energy leads to enhancement of image contrast, which is especially useful in the case of biological samples composed of elements with low atomic numbers. As a result treatments with heavy metals, like post‐fixation with osmium tetroxide or ultrathin section staining, can by omitted. The disadvantage is reduced penetration ability of incident electrons influencing the usable thickness of the specimen resulting in the need of ultrathin sections of under 20 nm thickness. In this study we want to answer basic questions concerning the cutting of extremely ultrathin sections: Is it possible routinely and reproducibly to cut extremely thin sections of biological specimens embedded in commonly used resins with contemporary ultramicrotome techniques and under what conditions? Microsc. Res. Tech. 79:512–517, 2016. © 2016 Wiley Periodicals, Inc.     

激光重熔纳米SiC复合陶瓷涂层组织和性能研究

研究了WC／Co-NiCrAl等离子复合陶瓷涂层、激光重熔等离子涂层、激光渗入纳米SiC涂层的组织结构、耐磨性能。结果证明：在所定的工艺参数下，等离子喷涂层组织呈层片状，层间为机械结合界面；经激光重熔后，激光作用区涂层组织细化，孔隙率降低，耐磨性能是原等离子涂层的1．3倍；渗入纳米SiC后，组织进一步细化，孔隙率进一步降低，SiC颗粒仍处于纳米尺度，分布在粗颗粒表面及粗颗粒之间，其耐磨性能是原等离子涂层的2．6倍。     

Contrast and quantitation in uniform regions of thin sections using transmission electron microscopy

A direct approach to quantitative measurements of uniform regions in thin sections is described. Accelerating voltages around 80 kV and objective aperture angles of about 9·3 mrad will provide conditions where contrast is directly proportional to specimen mass thickness. An extensive treatment of electron scattering in Formvar films for wide ranges of electron microscopic operating conditions is summarized in a simple, empirical equation. The extent to which Formvar results may be generalized to other materials, both embedding media and structures within the thin section, is treated. Using these results, precise measurements of local section thickness and of specimen density and/or dry mass of regions which penetrate the entire section thickness are possible, with the accuracy dependent upon irradiation effects and specimen makeup.     

Imaging of fullerene-like structures in CNx thin films by electron microscopy; sample preparation artefacts due to ion-beam milling

The microstructure of CN(x) thin films, deposited by reactive magnetron sputtering, was investigated by transmission electron microscopy (TEM) at 200kV in plan-view and cross-sectional samples. Imaging artefacts arise in high-resolution TEM due to overlap of nm-sized fullerene-like features for specimen thickness above 5nm. The thinnest and apparently artefact-free areas were obtained at the fracture edges of plan-view specimens floated-off from NaCl substrates. Cross-sectional samples were prepared by ion-beam milling at low energy to minimize sample preparation artefacts. The depth of the ion-bombardment-induced surface amorphization was determined by TEM cross sections of ion-milled fullerene-like CN(x) surfaces. The thickness of the damaged surface layer at 5 degrees grazing incidence was 13 and 10nm at 3 and 0.8keV, respectively, which is approximately three times larger than that observed on Si prepared under the same conditions. The shallowest damage depth, observed for 0.25keV, was less than 1nm. Chemical changes due to N loss and graphitization were also observed by X-ray photoelectron spectroscopy. As a consequence of chemical effects, sputtering rates of CN(x) films were similar to that of Si, which enables relatively fast ion-milling procedure compared to carbon compounds. No electron beam damage of fullerene-like CN(x) was observed at 200kV.     

Subject index to volume 10

The scanning transmission electron microscope with a field emission electron source operated at 100 kV allows X-ray microanalysis using electron probes as small as 1 to 2 nm. Measurements of the probe in a Vacuum Generators HB-501 STEM show that spherical aberration in the objective lens controls the probe size and shape at beam convergence half-angles of 10 mrad and greater typically used for X-ray microanalysis. A virtual objective aperture eliminates X-ray contributions from the probe-forming system, but must be aligned exactly to avoid asymmetrical broadening of the probe by spherical aberration. It is estimated that 5 nm X-ray spatial resolution can be achieved in low to medium atomic number materials. Even at this resolution however, probe broadening in the specimen controls the resolution; the main limitation is one of specimen preparation and a knowledge of the final specimen thickness. Determination of composition profiles near voids, dislocations and other individual defects in thin foils also requires a knowledge of the defect depth position and deconvolution of the probe and composition profiles.     

Rationale for the application of thin,continuous metal films in high magnification electron microscopy

Various metal films of different thicknesses were deposited on to a particle test specimen and their effects on topographic contrast generation and specimen preservation were determined. Tobacco mosaic virus adsorbed on to thin carbon supports or silicon chips was imaged in TEM or high resolution SE-I SEM at a magnification of 350,000×. Tantalum films of 1–2 nm (average mass) thickness produced best contrasts and prevented volume loss of the particles from electron beam damage. Excessively thick films of 5–10 nm thickness blanketed fine structures and caused severe volume losses. Discontinuous 2 nm thick films of gold or platinum decorated the surfaces, caused a loss in topographic contrasts and induced very high volume losses. Thin continuous metal films were necessary to generate high topographic contrast and to prevent volume loss from beam damage by providing sufficient mechanical stability for small topographic features and increased thermal conductivity of the specimen surface.     

A determination of thickness and surface relief in reembedded sections of an epoxy- and a melamine-resin containing ferritin as size standard

Chemical and physical data of two electron microscopic embedding media (the non-polar epoxy resin Epon 812 and the polar melamine resin Nanoplast FB 101) suggest that less kinetic energy must be applied for cutting a section from a Nanoplast block than from an Epon block of the same hardness and that, consequently, the cutting qualities of Nanoplast are better. To test this hypothesis, normal and extremely thin sections of Epon- and Nanoplast-embedded horse spleen ferritin micropellets were reembedded and resectioned for a determination of thickness and surface roughness. The ease with which extremely thin sections can be cut from the Nanoplast resin (8 nm versus 15 nm in Epon) and the smooth surface of these sections support the hypothesis that the cutting quality of an embedding material is determined primarily by its energy balance, i.e. by the kinetic energy which must be introduced for sectioning and the bonding energy which is released exothermically from a polymer while being sectioned.     

High-resolution scanning electron microscopy study of sputtered nanolaminated Ti/TiN multilayers

This work presents the morphologic and structural study of nanolaminated Ti/TiN multilayers using high-resolution scanning electron microscopy (HR-SEM), coupled to x-ray reflectometry (XRR). The multilayers have been deposited by reactive rf-sputtering on silicon substrates. For large period thickness (lambda=40 nm, 10 periods), in XRR, the low number of interfaces makes the interference less structured. An experimental pattern with broad and weakly intense Braggs peaks is obtained, but is difficult to simulate. On the other hand, HR-SEM observation of cross sections gives excellent pictures of the multilayer, so that precise measurements of the thickness can be achieved: a 42 nm thick period is observed, formed with 17 nm of Ti and with 25 nm of TiN. For small (Ti+TiN) period thickness (lambda=2.5 nm, 120 periods), the XRR pattern exhibits intense and narrow Bragg peaks: the number of interfaces is sufficient to structure the interference and an intense signal is obtained. The best fit of simulation is obtained for a 2.6 nm thin period, made of 0.9 nm of Ti and 1.7 nm of TiN. No laminated structure has been observed by cross-section HR-SEM observation because its resolution (around 2 nm at 10 kV) is larger than the layer thickness in a period. High-resolution SEM and XRR are thus two complementary techniques for the routine characterization of multilayers.     

Structure analysis of sputter-coated and ion-beam sputter-coated films: a comparative study

Gold, platinum and tungsten films were deposited by low energy input (7 mA, 450 V), or high deposition rate (80 mA, 1500 V), diode sputter coating and by ion beam sputter coating. Film structures on Formvar coated grids and on the surface of coated erythrocytes, resin embedded, sectioned, and recorded at high magnification in a TEM were compared using computer-assisted measurements and analysis of film thickness and grain size. The average grain size of the thinnest gold and platinum films was relatively independent of the mode or rate of deposition but as the film thickness increased, significant differences in grain size and film structure were observed. Thick platinum or gold films deposited by low energy input sputter coating contained large grain size and electron transparent cracks; however, more even films with narrower cracks but larger grain size were produced at high deposition rates. Ion beam sputter coated gold had relatively large grain size in 10 nm thick films, but beyond this thickness the grains coalesced to form a continuous film. Platinum films deposited by ion beam sputter coating were even and free of electron transparent cracks and had a very small grain size (1–2 nm), which was relatively independent of the film thickness. Tungsten deposition either by low energy input or ion beam sputter coating resulted in fine grained even films which were free of electron transparent cracks. Such films remained granular in substructure and had a grain size of about 1 nm which was relatively independent of film thickness. Tungsten films produced at high deposition rates were of poorer quality. We conclude that thick diode sputter coated platinum and gold films are best deposited at high deposition rates provided the specimens are not heat sensitive, the improvement in film structure being more significant than the slight increase in grain size. Thick diode or ion beam sputter coated gold films should be suitable for low resolution SEM, and thin discontinuous gold films for medium resolution SEM. Diode sputter coated platinum should be suitable for medium resolution SEM and ion beam sputter coated platinum for medium and some high resolution SEM. 1–5 nm thick tungsten films, deposited by low energy input or ion beam sputter coating should be suitable for high resolution SEM, particularly where contrast is of less importance than resolution.     

张力切削法制造超薄钢带的研究

本工作研究了张力切削法制造超薄钢带时所获得的连续切屑带。其扫描电镜的表面形貌与传统的金属切削加工获得的切屑的情况基本相同：呈剪切前沿-层结构。但层宽对切削深度的变化规律在小的切削深度时与传统的金属切削加工时的规律相反。微观应变和显微硬度对切削深度的曲线以及层宽对切削深度的曲线的形状相似,发现三曲线在同一切削深度的坐标处出现极小值。合适的张应力可使超薄钢带切削成形时的形变量降低,形变较为均匀,有助于超薄钢带的成形。张应力可能是通过改变切削时的剪切角起作用的。     

Recent developments in analytical electron microscopy

Recent years have seen the way in which the analytical electron microscope has been applied to problems involving thin specimens in metallurgy, mineralogy and many branches of biology. The limits of sensitivity have been explored and its potential usefulness in these fields investigated. Problems concerning the interaction of electrons with the specimen are discussed in relation to the correct choice of operating conditions and specimen preparation. In biological work, frozen sections provide new information about subcellular elemental localization of mobile electrolytes, while analysis of tissue prepared by conventional means is used to detect physiological levels of some naturally occurring elements. Examination of mineral dispersions provides analysis of particles just 10 nm thick, visible only in transmission electron microscopy, and further work with thin metal foils confirms the value of high resolution transmission imaging as a complementary facility to micro-analysis. Work has been done to investigate the possibilities of improving sensitivities both by changing operational parameters and instrumental design, and the value of quantitation in thin specimen analysis explored.     

Crystallographic analysis of thin specimens

Electron backscattering diffraction (EBSD) is commonly used on bulk samples for crystallographic material characterization. In this work, the technique was applied on transmission electron microscopy (TEM)-type thin specimens, prepared with a focused ion beam. Orientation maps were successfully collected on specimens made of a Cu₃Au copper–gold alloy. As compared to EBSD analysis on a bulk specimen, an improved pattern quality and a high spatial resolution (well below 10 nm) were obtained. Furthermore, a clear improvement of the signal-to-noise ratio with decreasing sample thickness was observed.     

Choosing the appropriate section thickness in the melamine embedding technique

When biological materials are infiltrated by a water-soluble melamine resin and hardened, they become as hard as glass. This is a prerequisite for extreme thin-sectioning. In this paper, the structural information from unsupported transparent thin sections of beef liver catalase, calf thymus DNA, horse spleen ferritin, insect muscle and rat microtubules is compared to that of normal thin sections. While ferritin molecules (12 nm diameter), microtubule subunits (8 nm long axis) and catalase crystals (8 nm subunit diameter) appear to become mechanically damaged in a 10 nm section (as measured by resectioning), DNA-molecules (3 nm diameter) are satisfactorily preserved during sectioning. Remarkably, for electron phase contrast imaging of unstained cross-sectioned insect muscle, a minimum section thickness of about 30–40 nm is required.     

Texture of cellulose microfibrils of root hair cell walls of Arabidopsis thaliana, Medicago truncatula, and Vicia sativa

Cellulose is the most abundant biopolymer on earth, and has qualities that make it suitable for biofuel. There are new tools for the visualisation of the cellulose synthase complexes in living cells, but those do not show their product, the cellulose microfibrils (CMFs). In this study we report the characteristics of cell wall textures, i.e. the architectures of the CMFs in the wall, of root hairs of Arabidopsis thaliana, Medicago truncatula and Vicia sativa and compare the different techniques we used to study them. Root hairs of these species have a random primary cell wall deposited at the root hair tip, which covers the outside of the growing and fully grown hair. The secondary wall starts between 10 (Arabidopsis) and 40 (Vicia) μm from the hair tip and the CMFs make a small angle, Z as well as S direction, with the long axis of the root hair. CMFs are 3-4 nm wide in thin sections, indicating that single cellulose synthase complexes make them. Thin sections after extraction of cell wall matrix, leaving only the CMFs, reveal the type of wall texture and the orientation and width of CMFs, but CMF density within a lamella cannot be quantified, and CMF length is always underestimated by this technique. Field emission scanning electron microscopy and surface preparations for transmission electron microscopy reveal the type of wall texture and the orientation of individual CMFs. Only when the orientation of CMFs in subsequent deposited lamellae is different, their density per lamella can be determined. It is impossible to measure CMF length with any of the EM techniques.     

Combining Ar ion milling with FIB lift-out techniques to prepare high quality site-specific TEM samples

Focused ion beam (FIB) techniques can prepare site‐specific transmission electron microscopy (TEM) cross‐section samples very quickly but they suffer from beam damage by the high energy Ga⁺ ion beam. An amorphous layer about 20–30 nm thick on each side of the TEM lamella and the supporting carbon film makes FIB‐prepared samples inferior to the traditional Ar⁺ thinned samples for some investigations such as high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). We have developed techniques to combine broad argon ion milling with focused ion beam lift‐out methods to prepare high‐quality site‐specific TEM cross‐section samples. Site‐specific TEM cross‐sections were prepared by FIB and lifted out using a Narishige micromanipulator onto a half copper‐grid coated with carbon film. Pt deposition by FIB was used to bond the lamellae to the Cu grid, then the coating carbon film was removed and the sample on the bare Cu grid was polished by the usual broad beam Ar⁺ milling. By doing so, the thickness of the surface amorphous layers is reduced substantially and the sample quality for TEM observation is as good as the traditional Ar⁺ milled samples.     

Specimen thickness dependence of hydrogen evolution during cryo‐transmission electron microscopy of hydrated soft materials

The evolution of hydrogen from many hydrated cryo‐preserved soft materials under electron irradiation in the transmission electron microscope can be observed at doses of the order of 1000 e nm^?2 and above. Such hydrogen causes artefacts in conventional transmission electron microscope or scanning transmission electron microscopy (STEM) imaging as well as in analyses by electron energy‐loss spectroscopy. Here we show that the evolution of hydrogen depends on specimen thickness. Using wedge‐shaped specimens of frozen‐hydrated Nafion, a perfluorinated ionomer, saturated with the organic solvent DMMP together with both thin and thick sections of frozen‐hydrated porcine skin, we show that there is a thickness below which hydrogen evolution is not detected either by bubble observation in transmission electron microscope image mode or by spectroscopic analysis in STEM electron energy‐loss spectroscopy mode. We suggest that this effect is due to the diffusion of hydrogen, whose diffusivity remains significant even at liquid nitrogen temperature over the length scales and time scales relevant to transmission electron microscopy analysis of thin specimens. In short, we speculate that sufficient hydrogen can diffuse to the specimen surface in thin sections so that concentrations are too low for bubbling or for spectroscopic detection. Significantly, this finding indicates that higher electron doses can be used during the imaging of radiation‐sensitive hydrated soft materials and, consequently, higher spatial resolution can be achieved, if sufficiently thin specimens are used in order to avoid the evolution of hydrogen‐based artefacts.     

Study on the effect of DIC deformation sensor on mechanical property of substrate

The thin epoxy film with micro-scale speckle pattern as a digital image correlation (DIC) deformation sensor has been fabricated or transferred on the surface of sample in the previous study. When the thickness of the film cannot be ignored, it may have an influence on the validity of measurement results. And thus, the influence of the thin epoxy film on mechanical properties of substrates should be investigated. In this study, the mechanical behavior of thin film itself and surface strain of composite structure of thin film and substrate were measured using micro digital image correlation (MDIC) method. And theoretical and simulative results were also analyzed. From the comparison analysis of theoretical, simulative and experimental results, it is concluded that when the ratios of Young’s modulus and thickness between the film and substrate are smaller than 13 and 0.5 respectively, the influence from the thin film can be ignored, and thin epoxy film as DIC sensor can be used to measure the deformation of substrate.     

Three-dimensional distributions of elements in biological samples by energy-filtered electron tomography

By combining electron tomography with energy-filtered electron microscopy, we have shown the feasibility of determining the three-dimensional distributions of phosphorus in biological specimens. Thin sections of the nematode, Caenorhabditis elegans were prepared by high-pressure freezing, freeze-substitution and plastic embedding. Images were recorded at energy losses above and below the phosphorus L2,3 edge using a post-column imaging filter operating at a beam energy of 120 keV. The unstained specimens exhibited minimal contrast in bright-field images. After it was determined that the specimen was sufficiently thin to allow two-window ratio imaging of phosphorus, pairs of pre-edge and post-edge images were acquired in series over a tilt range of +/-55 degrees at 5 degrees increments for two orthogonal tilt axes. The projected phosphorus distributions were aligned using the pre-edge images that contained inelastic contrast from colloidal gold particles deposited on the specimen surface. A reconstruction and surface rendering of the phosphorus distribution clearly revealed features 15-20 nm in diameter, which were identified as ribosomes distributed along the stacked membranes of endoplasmic reticulum and in the cytoplasm. The sensitivity of the technique was estimated at < 35 phosphorus atoms per voxel based on the known total ribosomal phosphorus content of approximately 7000 atoms. Although a high electron dose of approximately 10(7)e/nm2 was required to record two-axis tilt series, specimens were sufficiently stable to allow image alignment and tomographic reconstruction.     

Ultramicrotomy of nanocrystalline materials

The methodology and one of the first attempts to produce transmission electron microscopic (TEM) specimens of nanocrystalline metals, alloys and ceramics by ultramicrotomy are presented. Samples of the pure elements Co, Pd; alloys of Y-12 at.% Fe, Al-7 at.% Ag and W-30 at.% Ga; and ZnO ceramic, were found to section successfully to varying degrees. Advantages of sections prepared through ultramicrotomy over ion beam methods include extensive electron-transparent regions of uniform thickness and absence of ion beam damage. Typical artefacts were observed (knife marks, tearing, pull-out, shear lamellae, section curling, and anodic dissolution) but did not impede TEM analysis significantly. A potentially important effect observed was that of a texture development upon sectioning of the Co and Pd samples. It is thought that this unusual phenomenon results from the extremely fine scale of the microstructure and the purity of the Co and Pd samples, and may be enhanced by frictional heating effects and the state of the knife edge. © 1995 Government of Canada.

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