TEM Specimens Research Articles

Determining the thickness of atomically thin MoS2 and WS2 in the TEM.

Multislice simulations were used to analyze the reliability of annular dark field scanning transmission electron microscopy (ADF-STEM) imaging and selected-area electron diffraction (SAED) for determining the thicknesses of MoS2 and WS2 specimens in the aberration-corrected TEM. Samples of 1 to 4 layers in thickness for both 2H and 1T polymorphs were studied and tilts up to 500mrad off of the [0001] zone axis were considered. All thicknesses including the monolayer showed distortions and intensity variations in their ADF-STEM images and SAED patterns as a result of tilt. Both techniques proved to be applicable to distinguish monolayers from multilayers using tilt. Without tilt, neither technique allows unambiguous thickness determination solely by comparing relative intensities of atomic columns in ADF-STEM images or diffraction patterns oriented along at [0001] zone axis, with the exception of monolayer 2H WS2. However, differentiation is possible using absolute intensities in ADF-STEM images. The analysis of ADF-STEM images and SAED patterns also allows identification of the 2H and 1T polymorphs of MoS2 and WS2.

TEM Specimen Preparation of GaN Thin Films

Cross-sectional TEM observation can be used as an important method in the microstructure investigation of thin films. However, the specimen preparation for cross-sectional TEM observation is generally regarded as a challenging task. In this paper, we discussed the preparation of TEM cross-sectional specimens. An example from GaN thin films grown on Si substrate was discussed correspondingly.

Monitoring of Tempering Behavior in Fe-C-Mn Alloys by Precise Measurement of Electrical Resistivity

Mechanical properties in metallic materials are generally determined by microstructure, which is controlled by thermo-mechanical treatment in addition to its composition. Tempering is the conventional process of heat-treated steel. Therefore, understanding microstructural change during the process is especially important. As is well known, electrical resistivity measurement gives useful information regarding microstructures and lattice defects. In this technique, average information can be obtained from larger volume of specimens than TEM specimens as 108 times. So the purpose of this study was to monitor electrical resistivity changes related to microstructural changes during tempering in Fe-0.19 C-1.5 Mn, Fe-0.35 C-1.5 Mn alloys. Bar shaped specimens were cut from the sheets of steels. The specimens were heat-treated in austenite region and then quenched with ice-water. Then tempering was cumulatively carried out by direct dipping in a nitrate bath held at 423-673 K. Electrical resistivities at 77 K (in liquid nitrogen) and 300 K were measured in each state by a direct current (DC) four-point method. The resistivities abruptly decreased and then gradually decreased by the tempering. First drop and following decreasing of resistivities are corresponding to vanishing vacancies in martensite and precipitation of carbide, respectively. The organized resistivites by Hollomon-Jaffe parameter showed infections during the carbide precipitation. The points must be related to transition of precipitation mode.

Fabrication of high quality plan-view TEM specimens using the focused ion beam

We describe a technique using a focused ion beam instrument to fabricate high quality plan-view specimens for transmission electron microscopy studies. The technique is simple, site-specific and is capable of fabricating multiple large, >100μm2 electron transparent windows within epitaxially grown thin films. A film of La0.67Sr0.33MnO3 is used to demonstrate the technique and its structural and functional properties are surveyed by high resolution imaging, electron spectroscopy, atomic force microscopy and Lorentz electron microscopy. The window is demonstrated to have good thickness uniformity and a low defect density that does not impair the film's Curie temperature. The technique will enable the study of in-plane structural and functional properties of a variety of epitaxial thin film systems.

Choice of operating voltage for a transmission electron microscope

An accelerating voltage of 100-300kV remains a good choice for the majority of TEM or STEM specimens, avoiding the expense of high-voltage microscopy but providing the possibility of atomic resolution even in the absence of lens-aberration correction. For specimens thicker than a few tens of nm, the image intensity and scattering contrast are likely to be higher than at lower voltage, as is the visibility of ionization edges below 1000eV (as required for EELS elemental analysis). In thick (>100nm) specimens, higher voltage ensures less beam broadening and better spatial resolution for STEM imaging and EDX spectroscopy. Low-voltage (e.g. 30kV) TEM or STEM is attractive for a very thin (e.g. 10nm) specimen, as it provides higher scattering contrast and fewer problems for valence-excitation EELS. Specimens that are immune to radiolysis suffer knock-on damage at high current densities, and this form of radiation damage can be reduced or avoided by choosing a low accelerating voltage. Low-voltage STEM with an aberration-corrected objective lens (together with a high-angle dark-field detector and/or EELS) offers atomic resolution and elemental identification from very thin specimens. Conventional TEM can provide atomic resolution in low-voltage phase-contrast images but requires correction of chromatic aberration and preferably an electron-beam monochromator. Many non-conducting (e.g. organic) specimens damage easily by radiolysis and radiation damage then determines the TEM image resolution. For bright-field scattering contrast, low kV can provide slightly better dose-limited resolution if the specimen is very thin (a few nm) but considerably better resolution is possible from a thicker specimen, for which higher kV is required. Use of a phase plate in a conventional TEM offers the most dose-efficient way of achieving atomic resolution from beam-sensitive specimens.

TEM Characterization of the Microstructure of Hot-Hydrostatically Extruded 93W-4.9Ni-2.1Fe Alloy

The microscopic analysis of 93W-4.9Ni-2.1Fe (wt. %) tungsten heavy alloy by hot-hydrostatic extrusion with severe plastic deformation strengthening were experimentally investigated mainly by transmission electron microscopy. Due to the profound differences in hardness of the tungsten particles and the NiFeW matrix a special TEM specimen preparation method had to be employed.It was shown that the microstructure of the as-extruded alloy was characterized by elongated tungsten particles with refinement cellular sub-structures consisting of high-density dislocations embedded in a binding Ni-Fe-W matrix phase with fine dynamically re-crystallized grains.

A Study of Fracture Mechanisms in RAFM Steel in the Ductile to Brittle Transition Temperature Regime

The fracture behaviour of a Reduced Activation Ferritic Martensitic Steel (RAFM) has been studied within the Ductile to Brittle Transition Temperature (DBTT) regime. The DBTT has been determined by ASTM E 1921 based reference temperature approach under dynamic loading condition. The dynamic reference temperature (T0dy) was found to be − 33.8°C. The fracture mechanism has been studied by extracting TEM specimens precisely at the crack initiation sites using focused ion beam (FIB) technique in a high resolution dual beam scanning electron microscope. Detailed analytical TEM studies revealed that the morphology of carbides play a crucial role in the initiation of a crack. The larger ellipsoidal carbides, which were found to be Cr-rich, have been found to be responsible for dislocation piles ups. The shorter edge of these ellipsoidal carbides are areas of high stress concentration and were found to initiate cracks by decohesion of the particle-matrix interface. On the contrary, the iron rich carbides have been found to be smaller, more spherical, and thus less effective in blocking dislocation movement and therefore formation of pile ups. The results, which reveal an important mechanism towards crack initiation in ferritic-martensitic steels, will be presented in detail.

Cleavage Fracture Initiation at M–A Constituents in Intercritically Coarse-Grained Heat-Affected Zone of a HSLA Steel

Local brittle zones, i.e., martensite–austenite (M–A) islands, are formed within the coarse-grained heat-affected zone (CGHAZ) and the intercritically reheated CGHAZ (ICCGHAZ) during welding of many HSLA steels. In the current study, the M–A constituents in the microstructure of simulated ICCGHAZ of an API X80 pipeline steel were investigated using transmission electron microscopy and scanning electron microscopy. The focused ion beam technique was applied to make TEM specimens of M–A constituents that were located in the initiation sites of cleavage cracks. The main purpose of the study was to identify crack-initiation sites of cleavage fracture in ICCGHAZ and to prove the presence of M–A constituents in such initiation sites. Twinned martensite was detected in all local brittle zones that were investigated in the current study, demonstrating that they are M–A constituents. It was also demonstrated that the fracture initiation occurred preferentially at M–A constituents by a debonding mechanism rather than cracking of the M–A constituents.

Intraoperative Ultrasound-Guidance in Neurosurgery

ince the first recorded use of the “ultrasonoscope” for localizing subcortical intracerebral neoplasms in postmorS tem specimens in 1950 (4), technological advances in ultrasound have seen a transformation from poor-quality, A-mode wave forms to superb-quality, real-time images in 2 (2D) and 3 (3D) dimensions. As a result, intraoperative ultrasonography (IOUS) has undergone remarkable development, particularly in the last 2 decades.

Effect of Specimen Preparation Method on Transmission Electron Microscope Investigation in a Bulk Metallic Glass

In this paper, high resolution transmission electron microscopy (HRTEM) has been used to observe a Zr41.25Ti13.75Ni10Cu12.5Be22.5 (at. %) bulk metallic glass (BMG) prepared from different methods, i.e. ion milling and electropolishing. The ion thinning brings out the white bulb pattern on the specimen surface and induces localized temperature increasing. The electropolishing does not influence microstructure of the amorphous phase. A new preparation technique of grinding method is introduced. For BMG, the electropolishing and grinding are the better method for TEM specimen preparation as compared with the ion thinning.

Light‐Induced Reduction of Cuprous Oxide in an Environmental Transmission Electron Microscope

AbstractPhotocatalysts for solar fuel production are subject to intensive investigation as they constitute one viable route for solar energy harvesting. Cuprous oxide (Cu2O) is a working photocatalyst for hydrogen evolution but it photocorrodes upon light illumination in an aqueous environment. Environmental transmission electron microscopy (ETEM) makes it possible to obtain insight into the local structure, composition and reactivity of catalysts in their working environment, which is of fundamental interest for sustainable energy research and is essential for further material optimization. Herein, photoreduction of Cu2O is studied in situ using a dedicated TEM specimen holder for light illumination.

Characterization of an amorphous carbon film covering a Mo grid during in situ heating TEM study

In the present study, we investigated the behavior of an amorphous carbon film covering a Mo grid at high temperature. It was found that metastable nanosized particles were formed on the carbon film at 400 °C. They finally became nanosized α-Mo 2 C crystals with an average size of 3.5 nm at 700 °C. Moreover, modification of the amorphous carbon support film was observed. High-resolution TEM images showed that the carbon film was transformed to irregular and disordered lamellar structures at 300 °C and to short-range ordered and crystallized structures at 700 °C. Based on these experimental results, we suggest selecting suitable metal grids and support films for the TEM specimen preparation and performing a chemical analysis of nanostructure materials in in situ heating experiment. Finally, it is expected that these results will be helpful for the appropriate experimental designs for the in situ TEM studies. ► Amorphous carbon film covering a Mo grid was investigated by the in situ TEM technique. ► Unexpected nanosized α-Mo 2 C crystals were formed at 700 °C. ► The amorphous carbon film was transformed into the crystalline phase during the in situ heating process.

Electron microscope verification of prebreakdown-inducing α-FeSi2 needles in multicrystalline silicon solar cells

It had been shown already earlier by X-ray microanalysis that, in positions of defect-induced junction breakdown in industrial multicrystalline (mc) silicon solar cells, iron-containing precipitates may exist. However, the nature of these precipitates was unknown so far. Here, in such positions, scanning transmission electron microscopy was performed after defect-controlled focused ion beam preparation. First of all, the defect site was localized by microscopic reverse-bias electroluminescence imaging. The high accuracy of following FIB target preparation (<0.1 μm necessary) was obtained by both, electron beam-induced current imaging and secondary electron material contrast observation during the slice-by-slice milling of the TEM specimen. By nano-beam electron diffraction (NBED) and energy dispersive spectroscopy, the iron-containing precipitates were identified as α-type FeSi2 needles, about 30 nm in diameter and several μm in length. The FeSi2 needles show preferential orientation relationships to the silicon matrix and are located in terraced large-angle grain boundaries. Elaborate nano-beam electron diffraction investigation of the FeSi2 revealed orientation relationships of the precipitate to the silicon, which confirm earlier investigations on monocrystalline material. A model explaining the defect-induced breakdown mechanism due to rod-like α-FeSi2 precipitates is presented.

601 砥粒除去加工によるTEM薄膜試料の作製法の検討(OS7-1 材料と加工(ローテクの中のハイテク(1),OS7 材料と加工(ローテクの中のハイテク)

601 砥粒除去加工によるTEM薄膜試料の作製法の検討(OS7-1 材料と加工(ローテクの中のハイテク(1),OS7 材料と加工(ローテクの中のハイテク)

Preparation methods for TEM specimens of Bismuth Telluride and Related Thermoelectric Alloys

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Substructure in the columnar crystals of the Ti0.45O0.20N0.35 oxynitride thin film

In situ oxygen doping modifies both the morphology and texture of the TiN films. It has been found that beyond 15 at% oxygen doping the columnar morphology is preserved however the <111> texture is changed to the <002>. The detailed structure analysis of the Ti0.45O0.20N0.35 oxynitride films prepared by reactive unbalanced magnetron sputtering (UBMS) in an argon/nitrogen/oxygen mixture atmosphere discovered a substructure in the bulk of the TiN(O) single crystal columns. In the cross sectional transmission electron microscopy (X-TEM) images the substructure is showing up in form of fibre-like morphology parallel to the axis of the columnar crystals and in a honeycomb-like supernetwork in the cross section of the single crystal columns in the plane view TEM specimens. The fibre-like substructure proceeds to the film surface and manifests itself in the morphology of the dome-shaped surface areas of the single crystal columns as revealed by atomic force microscopy analysis.

Electron backscatter diffraction (EBSD) analyses of phyllosilicates in petrographic thin sections

Applications of electron backscatter diffraction (EBSD) to obtain crystallographic information of minerals in petrographic thin sections in mineralogy and petrology are increasing. However, platy phyllosilicates that mostly appear with their silicate layers terminated by the surface in the thin sections generally do not show sharp EBSD patterns in spite of gentle mechanical polishing. TEM examination indicated that this is due to crystal bending of phyllosilicates from the surface to a few micrometers in depth, caused by the polishing process. Ion beam etching commonly used to prepare TEM specimens was found to be applicable to remove the surface region with crystal bending. As a result, clear and sharp EBSD patterns were acquired from the phyllosilicates (micas, chlorite, etc.) in petrographic thin sections, by which their crystal orientations and polytypes were unambiguously determined.

Effects of small specimen tilt and probe convergence angle on ADF-STEM image contrast of Si0.8Ge0.2 epitaxial strained layers on (100) Si

The effects of specimen tilt and probe convergence angle on annular dark field (ADF) image contrast of Si(0.8)Ge(0.2) heteroepitaxial strained layers on (100) Si were investigated in a 200 kV scanning transmission electron microscope (STEM) for a TEM specimen thickness of 195 nm. With 0.5 degrees of specimen tilt away from the exact <011> zone-axis orientation, the signal-to-noise level of atomic columns was significantly reduced for both Si(0.8)Ge(0.2) and Si in high resolution ADF-STEM lattice images. When the specimen was tilted 0.5 degrees around the <011> axis, or the STEM probe convergence semiangle was reduced from 14.3 to 3.6 mrad, the ADF-STEM image intensity profiles across the Si(0.8)Ge(0.2) and Si layers changed significantly as compared to those obtained at the exact <011> zone axis orientation, and no longer reflected the composition changes occurring across the layer structure. Multislice image simulation results revealed that the misfit strain between the Si(0.8)Ge(0.2) and Si layers, and strain relaxation near the surface of the TEM specimen, were responsible for the observed changes in image intensity.

FIBによるその場電顕観察用試料の作製と材料科学への応用&lt;br/&gt;&amp;mdash;FIBとガラスマニピュレータによるTEM試料作製&amp;mdash;

FIBによるその場電顕観察用試料の作製と材料科学への応用&lt;br/&gt;&amp;mdash;FIBとガラスマニピュレータによるTEM試料作製&amp;mdash;

The fourth SINQ Target Irradiation Program, STIP-IV

The 4th SINQ Target Irradiation Program (STIP-IV) was performed in 2004 and 2005. More than 1000 specimens from about 40 kinds of materials were irradiated up to 27dpa and 2300appm He in the temperature range of 80–550°C. The majority of specimens were irradiated in helium gas environment. Some specimens were irradiated in contact with lead and lead–bismuth eutectic. Neutron radiography inspections on specimen and target rods were performed before and after irradiation, which revealed some interesting features of the target rods with thermal couples. Neutronic calculations were performed using the proton distribution profile obtained by γ-mapping on the beam window of the AlMg3 target container after irradiation. Irradiation parameters of the specimens such as proton and neutron spectra and fluxes, heat deposition, irradiation dose in terms of displacement damage (dpa), helium and hydrogen concentrations were calculated. Most of the specimens were retrieved. But, more than 360 tensile and TEM specimens were lost due to a leak in a specimen rod occurred during irradiation.