Ultrathin Specimens Research Articles

In situ thermal annealing transmission electron microscopy of irradiation induced Fe nanoparticle precipitation in Fe–Si alloy

The typical experimental conditions inside a transmission electron microscope (TEM), such as ultra-high vacuum, high-energy electron irradiation, and surface effects of ultrathin TEM specimens, can be the origin of unexpected microstructural changes compared with that of bulk material during in situ thermal-annealing experiments. In this paper, we report on the microstructural changes of a Fe–15%Si alloy during in situ TEM annealing, where, in its bulk form, it exhibits an ordering transformation from D03 to B2 at 650 °C. Using a heating-pot type double tilt holder with a proportional–integral–differential control system, we observed the precipitation of α-Fe both at the sample surface and inside the sample. Surface precipitates formed via surface diffusion are markedly large, several tens of nm, whereas precipitates inside the specimen, which are surrounded by Fe-poor regions, reach a maximum size of 20 nm. This unexpected microstructural evolution could be attributed to vacancies on Si sites, which are induced due to high-energy electron irradiation before heating, as well as enhanced thermal diffusion of Fe atoms.

Critical sample aspect ratio and magnetic field dependence for antiskyrmion formation in Mn1.4PtSn single crystals

Mn1.4PtSn is the first material in which antiskyrmions have been observed in ultra-thin single crystalline specimens. While bulk crystals exhibit fractal patterns of purely ferromagnetic domain ordering at room temperature, ultra-thin Mn1.4PtSn lamellae clearly show antiskyrmion lattices with lattice spacings up to several $\mu$m. In the work presented here, we systematically investigate the thickness region from 400 nm to 10 $\mu$m using 100 $\times$ 100 $\mu$m$^2$ -wide Mn1.4PtSn plates, and identify the critical thickness-to-width aspect ratio $\alpha_0 = 0.044$ for the ferromagnetic fractal domain to the non-collinear texture phase transition. Additionally, we also explore these non-collinear magnetic textures below the critical aspect ratio $\alpha_0$ above and below the spin-reorientation transition temperature $T_{SR}$ while applying variable external magnetic fields. What we find is a strong hysteresis for the occurrence of an antiskyrmion lattice, since the antiskyrmions preferentially nucleate by pinching them off from helical stripes in the transition to the field polarized state.

Transmission micro-focus X-ray radiographic measurements towards in-situ tracing capillary imbibition fronts and paths in ultra-thin concrete slices

In the present study, we attempted to trace the imbibition fronts and paths in concrete by controlling specimen dimensions and imbibition liquids in transmission microfocus X-ray radiographic tests. Ultra-thin concrete specimens were specifically prepared for 2D imbibitions. CsCl was used as the agent to enhance X-ray attenuation. SEM/BSE/EDS tests were used to measure the micro morphology and element distributions at local sites. Results show that the designed experiments enable the acquisition of X-ray attenuation images with the enhanced contrast, which helps identify the capillary imbibition paths and fronts in the concrete. Liquid is more likely to penetrate through the interfacial transition zone and highly porous cement paste. CsCl solution also increases the contrast gradient of BSE images. Cs and Cl gradually distribute across the imbibition fronts. The proposed measurements offer a way to instantly, continually and visually probe capillary imbibitions in concrete and other porous materials.

Correctness of determination of energetic materials high temperature decomposition kinetics

The kinetic parameters of high temperature decomposition kinetics are widely used in evaluating the characteristics of thermal explosion, ignition and combustion of energetic materials. At present, the true and correct data on the high temperature kinetics of energetic materials condensed phase reactions are unknown and probably will remain unattainable in the nearest future. This is because of enormous technical difficulties to obtain such information and the absence of proper theoretical approaches for treatment of non-isothermal data. Evidently, with highly exothermic reactions it is impossible to conduct experiments at elevated temperatures using approaches of a low heating rate or isothermal ones. The improvement of characteristics of existing devices for thermal analysis is impeded by both technical complications and difficulties of performing experiments with ultrathin specimens of energetic material to ensure the conditions of uniform heat-up of the bulk of the substance. Based on the results of numerical simulation it is shown in this paper that the approach suggested 50 years ago by A. G. Merzhanov of using ignition delay data for deriving high temperature kinetics was not theoretically justified and can provide only very approximate values for such kinetics. The paper concludes on the today’s relevance of the tasks on elaboration of mathematically justified techniques for determining kinetic parameters of global exothermic condensed-phase reaction, which will be based on the experiments on EMs ignition.

Cleavable magnetic materials from van der Waals layered transition metal halides and chalcogenides

The study of exfoliated 2D magnetic materials is a vibrant and rapidly progressing field and is impacting many areas of condensed matter research including fundamental magnetism, spintronics and optoelectronics, and topological spin and electronic systems. The availability of promising candidate materials has enabled much of the progress in this field. Here, I present my perspective on the development of cleavable magnetic materials with a focus on transition metal halides and chalcogenides and an emphasis on crystal structure and magnetic order. To give proper context for these discussions, brief and incomplete surveys of recent work are included, focusing on specific aspects that I find most useful for guiding work on emerging materials and motivating expansion into other compounds and material families. Several instances of structural changes that can differentiate behaviors of bulk and ultrathin specimens are noted. Probing and understanding potential structural differences present a challenge but also an opportunity for material and device development, if they can be predicted and controlled. It is clear that careful investigations of structure, layer stacking, and defects in materials, how they may relate to the crystal chemistry, and how they may be different in crystals and mono- or few-layer specimens provide invaluable context for understanding the behavior of van der Waals layered magnetic materials.

High Temperature Micromechanical Behavior of a Pt-Modified Nickel Aluminide Bond-Coating and of Its Interdiffusion Zone with the Superalloy Substrate

The micromechanical properties of a $$\beta $$-(Ni,Pt)Al bond-coating was investigated between $$700\,^\circ \hbox {C}$$ and $$1000\,^\circ \hbox {C}$$ using ultrathin freestanding bond-coating specimens. Its brittle-to-ductile transition temperature was close to $$750\,^\circ \hbox {C}$$, with a significant ductility above $$800\,^\circ \hbox {C}$$ (up to 23 pct at $$1000\,^\circ \hbox {C}$$). The tensile strength decreased from 450 MPa at $$750\,^\circ \hbox {C}$$ down to 50 MPa at $$1000\,^\circ \hbox {C}$$. Fractographic observations evidenced the material brittleness at intermediate temperature with large cleaved grains and its ductility above $$750\,^\circ \hbox {C}$$ with important necking of individual grains.

Oxygen/nitrogen-assisted embrittlement of titanium alloys exposed at elevated temperature

Due to high solubility of oxygen and nitrogen in titanium alloys, the influence of the diffusion zone on the macroscopic tensile properties of pre-oxidized annealed Ti-6Al-4V tensile specimens was examined at room temperature. Thin microtensile specimens were prepared with different thicknesses ranging from 100 µm to 500 µm and then exposed at 750°C for durations between 5 and 200h. A dedicated gripping technique was developed in the present study to investigate the brittleness of such pre-oxidized and ultrathin specimens at room temperature. Tensile testing was paired with digital image correlation techniques to assess both macroscopic deformation and full-field strain maps. High temperature pre-oxidation treatments significantly decreased the ductility of the specimen and the tensile strength of the materials (yield strength and ultimate tensile strength). Fractographic examinations revealed typical brittle fracture features in the oxygen/nitrogen-affected diffusion zone in the periphery of the cross-section while the fracture remained ductile in the core of the specimen for most of the specimens. Some specimens fully failed in a brittle manner for “(pre-ox. duration)1/2/thickness” configurations with ratio equal or higher than 0.45 h1/2.µm-1.

Characterizing the back stress of ultra-thin metallic sheet via pre-strain tension/bending process

Abstract The buckling and instability of the ultra-thin sheet metal specimens subjected to compressive loading present an evident difficulty for the investigation of Bauschinger effect by using traditional tensile-compressive loading tests. In that regard, a pre-strain/bending method which is easier to implement was developed to characterize the back stress of ultra-thin metallic sheets. SS 316 L sheet specimens with the thickness of 0.1 mm were first subjected to uniaxial tension for a specific pre-strain. After that, they were bent at different radius levels to achieve different compression conditions. By calculating bending moments based on experiments and constitutive relationship respectively, the back stress which presented the offset stress between the stress-strain curves of loading and reverse loading, could be obtained through iteration according to the equivalence of above two moments. Experimental results indicated that the softening caused by Bauschinger effect led to evident increase of back stress when increasing the pre-strain. By utilizing the experiment and calculation method developed in this study, parameter identification of back stress evolution for ultra-thin metallic sheet can be realized practically and the relationship between the back stress, pre-strain along with reverse plastic strain could be established and analyzed. The presented method was thus proved to be an efficient solution for characterizing the back stress of ultra-thin metallic sheets.

Ultra-thin occlusal veneers bonded to enamel and made of ceramic or hybrid materials exhibit load-bearing capacities not different from conventional restorations

ObjectivesThe objective of this study was to test whether or not the load-bearing capacity of occlusal veneers bonded to enamel and made of ceramic or hybrid materials does differ from those of porcelain-fused-to-metal or lithium disilicate glass ceramic crowns. Material and methodsIn 80 human molars occlusal enamel was removed without extending into the dentin in order to mimic substance defects caused by attrition. The restorations were digitally designed at a standardized thickness of either 0.5 mm or 1.0 mm. For each thickness, 4 test groups were formed each including a different restorative material: “0.5-ZIR”: 0.5 mm thick zirconia (Vita YZ HT); “1.0-ZIR”: 1.0 mm thick zirconia (Vita YZ HT); “0.5-LDC”: 0.5 mm thick lithium disilicate ceramic (IPS e.max Press); “1.0-LDC”: 1.0 mm thick lithium disilicate ceramic (IPS e.max Press); “0.5-HYC”: 0.5 mm thick PICN (Vita Enamic); “1.0-HYC”: 1.0 mm thick PICN (Vita Enamic); “0.5-COC”: 0.5 mm thick tooth shaded resin composite (Lava Ultimate) and “1.0-COC”: 1.0 mm thick tooth shaded resin composite (Lava ultimate). Each group consists of 10 specimens. Two additional groups of 10 specimens each were used as controls and exhibited conventional crown preparations. In one group the crowns were made of lithium-disilicate ceramic (“CLD”: IPS e.max CAD) and the other group consisted of porcelain-fused to metal crowns (“PFM”). All restorations were cemented onto the prepared teeth following the manufacturer's instruction of the corresponding luting cement. Subsequently, they were thermo-mechanically aged and then loaded until fracture. Load-bearing capacities (Fmax) between the groups were compared applying the Kruskal-Wallis test (p < 0.05) and pairwise group comparisons using the Dunn's method. ResultsMedian values (and quartiles) for the load-bearing capacity amounted to (Fmax) 2′407 (1′670; 2′490) N for the CLD group and to 2′033 (1′869; 2′445) N for the PFM group. For the 0.5 mm thick restorations Fmax reached the highest median value in group 0.5-HYC 2′390 (1′355; 2′490) N, followed by 0.5-COC 2′200 (1′217; 2′492) N and 0.5-LDC 1′692 (1′324; 2′355) N. No results were obtained for group 0.5-ZIR due to the impracticability to fabricate ultra-thin specimens. The distribution of the values for the 1.0 mm thick restorations was 2′489 (2′426; 2′491) N for 1.0-COC, 2′299 (2′156; 2′490) N for 1.0-ZIR, 2′124 (1′245; 2′491) N for 1.0-HYC, and 1′537 (1′245; 1′783) N for 1.0-LDC. The differences of the medians between the test and the control groups did not reach statistical significance for the 0.5 mm thick specimens (KW: p = 0.6952 and p = 0.6986). Within the groups exhibiting 1.0 mm thickness, however, significant different medians were found: 1.0-LDC < 1.0-ZIR and 1.0-LDC < 1.0-COC (KW: p < 0.0209). ConclusionsRegarding their maximum load-bearing capacity, minimally invasive occlusal veneers made of ceramic and hybrid materials can be applied to correct occlusal tooth wear and thus replace conventional crown restorations.

Micromechanical testing of ultrathin layered material specimens at elevated temperature

The mechanical characterisation of ultrathin specimens at very high temperature is challenging in terms of specimen preparation and mechanical testing under ‘inert’ atmospheres. An experimental procedure for the local characterisation of mechanical and thermal properties at elevated temperature is presented. Various common ‘inert’ atmospheres were investigated up to 1373 K in order to identify the most efficient environmental conditions to prevent surface reactivity and degradation of specimens. A NiCoCrAlYTa-coated monocrystalline Ni-based superalloy was used to exemplify the capabilities of the technique because of its high surface reactivity at very high temperature, i.e. oxidation and sublimation. Purified overpressured argon atmosphere combined with oxygen getters was found to be particularly suitable for the study of alumina-forming alloys at elevated temperature.

Ultrathin porous pavement made with high viscosity asphalt rubber binder: A better acoustic absorption?

This work presents a non-destructive technique applied to ultrathin porous asphalt pavements that allows us to characterize their internal structure. Comparison between acoustic absorption data from experimental tests with an impedance tube and analytical simulation leads to an optimization of intrinsic parameters, such as tortuosity, airflow resistivity and porosity. The studied ultrathin specimens are of a high air void content porous mixture made with conventional polymer modified bituminous binder and high viscosity rubber binder. It has been found that one of the studied mixtures presents less air void content than specified by the manufacturer, and thus absorbs less noise as foreseen. Finally, in this case it appears that using a high viscosity asphalt rubber binder has no influence on maximum acoustic absorption but on the frequency of appearance of this maximum, tortuosity and airflow resistivity.

Evidence of High‐Temperature Strain Heterogeneities in a Nickel‐Based Single‐Crystal Superalloy

The creep behavior of a single crystal superalloy is investigated at the dendritic scale. The chemical segregation in the dendritic structure is correlated to strain heterogeneities after creep experiments on ultrathin specimens. It is shown that primary dendrite axes have a strengthening effect.

Ultrathin specimen preparation by a low-energy Ar-ion milling method

The low-energy Ar-ion milling method was used to prepare ultrathin specimens for transmission electron microscope observation. The samples were thinned initially by a usual focused ion beam technique or typical Ar-ion milling with a high energy of 2-10 keV and were thinned additionally by an Ar-ion beam with an energy less than 1 keV, typically 500-900 eV. This low-energy ion beam was scanned over the specimen, and secondary electrons induced by the ion beam could be detected to form secondary electron images with a resolution of a few micrometre. Because a desired area can be selected and thinned by the low-energy ion beam, redeposition or cross contamination from irradiation of a metal grid that supports the sample can be prevented. It was shown that the low-energy Ar-ion beam thins a surface amorphous damage layer preferentially and effectively rather than a crystal specimen. Images from ultrathin specimens of two different materials revealed a detailed structure.

Sub-diffraction Limit Localization of Proteins in Volumetric Space Using Bayesian Restoration of Fluorescence Images from Ultrathin Specimens

Photon diffraction limits the resolution of conventional light microscopy at the lateral focal plane to 0.61λ/NA (λ = wavelength of light, NA = numerical aperture of the objective) and at the axial plane to 1.4nλ/NA2 (n = refractive index of the imaging medium, 1.51 for oil immersion), which with visible wavelengths and a 1.4NA oil immersion objective is ∼220 nm and ∼600 nm in the lateral plane and axial plane respectively. This volumetric resolution is too large for the proper localization of protein clustering in subcellular structures. Here we combine the newly developed proteomic imaging technique, Array Tomography (AT), with its native 50–100 nm axial resolution achieved by physical sectioning of resin embedded tissue, and a 2D maximum likelihood deconvolution method, based on Bayes' rule, which significantly improves the resolution of protein puncta in the lateral plane to allow accurate and fast computational segmentation and analysis of labeled proteins. The physical sectioning of AT allows tissue specimens to be imaged at the physical optimum of modern high NA plan-apochormatic objectives. This translates to images that have little out of focus light, minimal aberrations and wave-front distortions. Thus, AT is able to provide images with truly invariant point spread functions (PSF), a property critical for accurate deconvolution. We show that AT with deconvolution increases the volumetric analytical fidelity of protein localization by significantly improving the modulation of high spatial frequencies up to and potentially beyond the spatial frequency cut-off of the objective. Moreover, we are able to achieve this improvement with no noticeable introduction of noise or artifacts and arrive at object segmentation and localization accuracies on par with image volumes captured using commercial implementations of super-resolution microscopes.

Low-Cost, Atmospheric-Pressure Scanning Transmission Electron Microscopy

Solid materials in subambient gaseous environments have been imaged using in situ transmission electron microscopy (TEM), for example to study dynamic effects: carbon nanotube growth, nanoparticle changes during redox reactions, and phase transitions in nanoscale systems. In these studies the vacuum level in the specimen region of the electron microscope was increased to pressures of up to 10 mbar using pump-limiting apertures that separated the specimen region from the rest of the high-vacuum electron column, but it has not been possible to achieve the higher pressures that are desirable for catalysis research. TEM imaging at atmospheric pressure and at elevated temperature was achieved with 0.2-nm resolution by enclosing a gaseous environment several micrometers thick between ultra-thin, electron transparent silicon nitride windows. Although Ångström-level resolution in situ TEM has been demonstrated with aberration-corrected systems, the key difficulty with TEM imaging is its dependence on phase contrast, which requires ultra-thin specimens, limiting the choice of experiments.

New Methods for the Study and Fabrication of Nano-Structured Materials Using FIB SEM

Techniques for characterisation and methods for fabrication at the nanoscale are becoming more powerful, giving new insights into the spatial relationships between nanostructures and greater control over their development. A case in point is the application of state-of-the-art focused ion beam technology (FIB), in combination with high-performance scanning electron microscopy (SEM), to generate cross-sections into bulk material and create a sequential image series. These two-dimensional images can then be correlated and rendered into a three-dimensional representation. In addition, site-specific, ultra-thin lamellar specimens can be made for observation in the transmission electron microscope (TEM) or scanning transmission electron microscope (STEM), with the further advantage that FIB cutting through hard-soft interfaces poses fewer difficulties compared to ultramicrotomy. Another big impact of FIB SEM on nanotechnology is the ability to use either ions or electrons to perform advanced nanolithography, via etching or chemical vapour deposition. In all cases, numerous parameters must be considered in order to achieve high quality results, particularly where stringent critical dimensions are required or when dealing with challenges such as electrically insulating and/or soft materials. We have developed strategies to address these issues, enabling results across a wide range of nanotechnology applications.

Millimeter-Wave Measurement of Complex Permittivity by Perturbation Method Using Open Resonator

This paper explains how better accuracy can be achieved in measurements of the complex permittivity (relative dielectric constant epsivr ' and dielectric loss tangent tan delta) of thin films having a thickness in the range of 10-100 mum. Specimens to be measured using a conventional open-resonator method need to have a thickness that is an integral multiple of a half wavelength, so specimens thinner than this half wavelength cannot be measured with an open resonator. However, the use of the perturbation method made it possible to obtain values of complex permittivity of ultrathin specimens of materials such as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), and PTFE including glass fiber used for printed circuit boards identical to those obtained for thick specimens.

835 ステンレス鋼 SUS304 極薄板材の疲労特性におよぼす TiN 被覆の影響

835 ステンレス鋼 SUS304 極薄板材の疲労特性におよぼす TiN 被覆の影響

Suppressed localization of a major autolysin on Staphylococcus aureus treated with tetracycline.

Surface localization of a major autolysin (atl gene product, ATL) on Staphylococcus aureus treated with tetracycline (TC, 4MIC: 1.56 microg ml(-1)) was examined using the protein A-gold labelling method. No labelling was noted on the surface of the next septal region, but it was observed on the previous septal region. In contrast, on untreated cells the gold particles were found not only along the septal surface, but also on the next septal region. These findings agree with those obtained from both ultrathin and whole-mount specimens, indicating that TC inhibits the localization of ATL in the next septal region. They further support the suggestion that ATL localization on the cell surface is closely associated with the cell cycle. When S. aureus was treated with otherwise lytic concentrations of penicillin G (PCG, 4MIC: 0.02 microg ml(-1)) in the presence of TC, the distribution of the label on the cell surface was found to be very similar to that on the TC-treated organisms. This suggests that the inhibitory effect of TC on PCG-induced lysis was not due to complete loss of ATL on the cell surface but instead to inhibition of ATL localization in the next septal region.

Cryo-TEM Imaging the Flow-Induced Transition from Vesicles to Threadlike Micelles

Transition of vesicles to micelles induced by flow of dilute aqueous cetyltrimethylammonium chloride (CTAC)/sodium 3-methylsalicylate (CH3Sal-) dispersion was directly imaged by rapidly vitrifying small ultrathin specimens after varying periods of postflow on-the-grid relaxation, and then examining them by cryogenic-temperature transmission electron microscopy (cryo-TEM). Vesicles prevail in quiescent equimolar 5 mM dispersions of CTAC and NaCH3Sal at equilibrium. When the dispersions are deformed and strained by rapid drainage of the excess from the specimens, the vesicles transform into an entangled network of threadlike micelles. The micelles revert to vesicles with time after drainage flow ceases. Intermediate structures during the transition were also captured by cryo-TEM. We hypothesize that the straining actions of flow disrupt vesicles, distort the distribution of, or strip, the counterions around vesicle fragments, shift the binding and dissociation equilibrium of counterions, alter the local pre...