Transmission Electron Microscopy Thin Foils Research Articles

In situtransmission electron microscopy study of the thermally induced formation of δ′-ZrO in pure Zr and Zr-based alloy

This study reportsin situobservations of the formation of the δ′-ZrO phase, occurring during the annealing of transmission electron microscopy (TEM) thin foils of both pure Zr and a Zr–Sn–Nb–Mo alloy at 973 K in a transmission electron microsope. The lattice parameters of δ′-ZrO were measured and determined to be similar to those of the ω-Zr phase. The orientation relationship between the δ′-ZrO and α-Zr phases has been identified as either {(11 \overline{2}0)}_{\rm ZrO}//{(0002)}_{\alpha} and {[0002]}_{\rm ZrO}//{[11 \overline{2}0]}_{\alpha} or {(\overline{1}011)}_{\rm ZrO}//{(0002)}_{\alpha} and {[01{\overline 1}1]_{{\rm{ZrO}}}}//{[11{\overline 2}0]_\alpha} depending on the orientation of the α grain relative to the TEM thin-foil normal. The nucleation and growth of δ′-ZrO were dynamically observed. This study suggests a new and convenient way to study oxidation mechanisms in Zr alloys and provides a deeper understanding of the properties of the newly reported δ′-ZrO. Since δ′-ZrO has a Zr sublattice which is identical to that of ω-Zr, the orientation relationships between the α and δ′-ZrO phases may also shed light on the orientation relations existing between α- and ω-Zr, and hence α- and ω-Ti.

Cross section TEM characterization of high-energy-Xe-irradiated U-Mo

U-Mo alloys irradiated with 84 MeV Xe ions to various doses were characterized with transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) techniques. The TEM thin foils were prepared perpendicular to the irradiated surface to allow a direct observation of the entire region modified by ions. Therefore, depth-selective microstructural information was revealed. Varied irradiation-induced phenomena such as gas bubble formation, phase reversal, and recrystallization were observed at different ion penetration depths in U-Mo.

Spark plasma sintering mechanisms at the necks between TiAl powder particles

In order to precise the role of the electric current involved in the spark plasma sintering (SPS) technique on the microscopic mechanisms occurring at the necks between TiAl powder particles during densification, transmission electron microscopy thin foils have been extracted at the necks on interrupted states, for the first time, by focused ion beam. Microscopic plasticity mechanisms and recovery-recrystallization phenomena have been identified. The densification rate, which has been shown in this study to occur by deformation of the powder particles at a deformation rate of 10−3 s−1, can be accounted for by these phenomena. In particular, no specific effect, as signs of electric arcs, plasma or local overheating for example, induced by the SPS current, have been detected.

A New Marking Technique for the Site-Specific Target in Focused Ion Beam-Based Transmission Electron Microscopy Thin Foil Preparation

A New Marking Technique for the Site-Specific Target in Focused Ion Beam-Based Transmission Electron Microscopy Thin Foil Preparation

Focused Ion Beam Milling Technique for Plan-View TEM Sampling of DRAM Capacitor

As the semiconductor device feature size becomes smaller, the aspect ratio of DRAM capacitor gets higher. The higher the height of capacitor, the more storage node bent. Therefore, we adopt the Mechanically Enhanced Storage node for virtually unlimited Height (MESH) [1] process to prevent storage node’s bending nowadays. Nevertheless, the bending failure still exists, and thus we need to make a sample for physical failure analysis (PFA). Normally PFA needs a site specific transmission electron microscopy (TEM) sample which is vertically cross-sectioned by using focused ion beam (FIB) , but sometimes a plan-view TEM sample is also required to clarify the exact cause of failure. Figure 1-(a) shows the vertical TEM result of two bits failure caused by DRAM storage node’s bending. In the conventional plan-view TEM sampling process, the target height for plan-view TEM sampling is marked with ‘l’ shape marker [2] after realizing the height of node bridge as shown in figure 1-(b). It is important to know the end point during FIB milling [3]. And then, the top (red area) and bottom (yellow area) parts are removed to get the plan-view TEM sample. Figure 1-(c) is a TEM image after this plan-view TEM sampling process. The nodes do not stand in a line as you see in figure 1-(c). The nodes seem to move during the 3rd step milling (mill a bottom part) because of the void between nodes. The node may fall off a TEM thin foil sample in the worst case. In order to overcome this problem, we add a carbon deposition step right after the 2nd step of the top part milling as shown in figure 2-(a). As a result, we are able to get a plan-view TEM image where the nodes stand in a line as shown in figure 2-(b). Four major steps are, Step 1 : ‘1’ shape marking at the target height Step 2 : milling a top part of capacitor Step 3 : carbon deposition to fill the space between nodes Step 4 : milling a bottom part of capacitor We adopted this modified milling method to the TEM sampling of a real failure case and obtained a PFA result of a 2 bit failure using plan-view TEM image as shown in figure 2-(c). The new modified milling method turned out to be very effective and can be adopted in a mass production.

The Focused Ion Beam-SEM as a Critical Tool For Nano-scale Characterization of Highly Radioactive Nuclear Fuels

There are unique challenges associated with conducting nanometer and atomic level materials characterization on highly irradiated and/or radiologically contaminated nuclear reactor fuels and structural materials, where contact handling is not feasible with the high levels of ionizing radiation emitted. Historically, particularly for irradiated nuclear fuel, samples could only be prepared remotely in heavily shielded facilities that precluded the fine contact work needed to prepare usable, let alone high quality, transmission electron microscopy thin foils and atom probe tomography (APT) tips. Thus, most published data on irradiated fuels detail micron level characterization (optical and SEM) and little information is available on nanometer and atomic level structure and chemistry.

Oxidation of Co- and Ce-nanocoated FeCr steels: A microstructural investigation

The effect of novel Co and Ce nanocoatings on oxidation behaviour and chromium volatilization from a commercial Fe–22Cr steel (Sanergy HT) developed for solid oxide fuel cell interconnect applications is investigated. Three different coatings (10nm Ce, 640nm Co and 10nm Ce+640nm Co) are studied. Uncoated and nanocoated samples are exposed isothermally at 850°C in the air with 3% H2O for 168h. The detailed microstructure of the different coatings is investigated. The surface morphology and microstructure of the oxide scales are characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray analysis (EDX). Cross-section TEM thin foils are prepared by using a combined FIB/SEM (focused ion beam/scanning electron microscope) instrument. A 640nm cobalt coating strongly inhibits Cr volatilization but has only minor effects on oxidation rate. In contrast, a 10nm Ce coating decreases the oxidation rate but has no significant effects on chromium volatilization. Combining the two coatings, i.e., applying a 640nm Co coating on top of the 10nm Ce, effectively reduces Cr evaporation and slows down the rate of alloy oxidation.

Study of defect evolution by TEM with in situ ion irradiation and coordinated modeling

The paper describes a novel transmission electron microscopy (TEM) experiment with in situ ion irradiation designed to improve and validate a computer model. TEM thin foils of molybdenum were irradiated in situ by 1 MeV Kr ions up to ∼0.045 displacements per atom (dpa) at 80°C at three dose rates −5 × 10−6, 5 × 10−5, and 5 × 10−4 dpa/s – at the Argonne IVEM-Tandem Facility. The low-dose experiments produced visible defect structure in dislocation loops, allowing accurate, quantitative measurements of defect number density and size distribution. Weak beam dark-field plane-view images were used to obtain defect density and size distribution as functions of foil thickness, dose, and dose rate. Diffraction contrast electron tomography was performed to image defect clusters through the foil thickness and measure their depth distribution. A spatially dependent cluster dynamic model was developed explicitly to model the damage by 1 MeV Kr ion irradiation in an Mo thin foil with temporal and spatial dependence of defect distribution. The set of quantitative data of visible defects was used to improve and validate the computer model. It was shown that the thin foil thickness is an important variable in determining the defect distribution. This additional spatial dimension allowed direct comparison between the model and experiments of defect structures. The defect loss to the surfaces in an irradiated thin foil was modeled successfully. TEM with in situ ion irradiation of Mo thin foils was also explicitly designed to compare with neutron irradiation data of the identical material that will be used to validate the model developed for thin foils.

Dislocation structures in nanoindented ductile metals—a transmission electron microscopy direct observation

Several attempts have been made over recent years to understand indentation size effect (ISE). The theoretical models, based essentially on strain gradient plasticity theories, such as the Nix–Gao model, predict that ISE is caused by an increase in the density of dislocations as the indentation size decreases. Molecular dynamics simulation results tend to confirm this fact, but the truth is that very few experimental studies exist on the direct observation of how dislocations are generated and accommodated in the vicinity of nanoindentations. In this study, using a Ni transmission electron microscopy thin foil as model material, we show that when the material is submitted to atomic force microscopy-based nanoindentation a high dislocation density zone is generated at the centre of the indented region, and that prismatic loop and helical dislocations are emitted sidewards from the central region of the nanoindentation along the ⟨1 1 0⟩ directions. Moreover, we show that the dislocation array formed during the nanoindentation process is far from the ideal model proposed by Nix and Gao, based on load axi-centred dislocation loops. With this study we aim at contributing to a better comprehension of ISE mechanisms in ductile metals.

Combining FIB milling and conventional Argon ion milling techniques to prepare high‐quality site‐specific TEM samples for quantitative EELS analysis of oxygen in molten iron

This paper reports a procedure to combine the focused ion beam micro-sampling method with conventional Ar-milling to prepare high-quality site-specific transmission electron microscopy cross-section samples. The advantage is to enable chemical and structural evaluations of oxygen dissolved in a molten iron sample to be made after quenching and recovery from high-pressure experiments in a laser-heated diamond anvil cell. The evaluations were performed by using electron energy-loss spectroscopy and high-resolution transmission electron microscopy. The high signal to noise ratios of electron energy-loss spectroscopy core-loss spectra from the transmission electron microscopy thin foil, re-thinned down to 40 nm in thickness by conventional Argon ion milling, provided us with oxygen quantitative analyses of the quenched molten iron phase. In addition, we could obtain lattice-fringe images using high-resolution transmission electron microscopy. The electron energy-loss spectroscopy analysis of oxygen in Fe(0.94)O has been carried out with a relative accuracy of 2%, using an analytical procedure proposed for foils thinner than 80 nm. Oxygen K-edge energy-loss near-edge structure also allows us to identify the specific phase that results from quenching and its electronic structure by the technique of fingerprinting of the spectrum with reference spectra in the Fe-O system.

A methodology suitable for TEM local measurements of carbon concentration in retained austenite

Carbon concentration in retained austenite grains is of great importance determining the mechanical properties of hot-rolled TRansformation Induced Plasticity steels. Among the different techniques available to measure such concentrations, Kikuchi lines obtained in Transmission Electron Microscopy provide a relatively easy and accurate method. The major problem however is to be able to locate an austenitic grain in the observed Transmission Electron Microscopy thin foil. Focused Ion Beam in combination with Scanning Electron Microscopy was used to successfully prepare a thin foil for Transmission Electron Microscopy and carbon concentration measurements from a 700 nm retained austenite grain.

Scanning electron microscopy imaging of dislocations in bulk materials, using electron channeling contrast

The imaging and characterization of dislocations is commonly carried out by thin foil transmission electron microscopy (TEM) using diffraction contrast imaging. However, the thin foil approach is limited by difficult sample preparation, thin foil artifacts, relatively small viewable areas, and constraints on carrying out in situ studies. Electron channeling imaging of electron channeling contrast imaging (ECCI) offers an alternative approach for imaging crystalline defects, including dislocations. Because ECCI is carried out with field emission gun scanning electron microscope (FEG-SEM) using bulk specimens, many of the limitations of TEM thin foil analysis are overcome. This paper outlines the development of electron channeling patterns and channeling imaging to the current state of the art. The experimental parameters and set up necessary to carry out routine channeling imaging are reviewed. A number of examples that illustrate some of the advantages of ECCI over thin foil TEM are presented along with a discussion of some of the limitations on carrying out channeling contrast analysis of defect structures.

PREPARATION OF TEM THIN FOIL CONTAINING POWDER PARTICLE BY ELECTRODEPOSITION METHOD

A practical technique to prepare transmission electron microscopy (TEM) thin foil containing powder particle was described and the data for the codeposition of two type particles with copper in the electroplating were presented. By depositing the particles which were distributed in CuSO 4 electrolyte on cathode together with Cu 2+ in electrodeposition bath, composite coating with suitable thickness could be formed. The thin coating was separated from the substrate and cut into a disc with diameter of 3mm for electropolishing. When the Cu matrix was thinned during electropolishing, the particles contained in the coating plate were also thinned to meet the suitable thickness for TEM observation. Various experimental results revealed that during electrodepositing the current density, pH-value of electrolyte and stirring mode all have significant effects on the distribution of particles in composite coating and the surface quality of the composite coating. The proper parameters used during electrodepositing to prepare TEM thin foil containing powder particle were discussed.

TEM thin foil preparation for ceramic composites with multilayered matrix

A method for preparing thin foils for transmission electron microscopy (TEM) has been developed in the field of ceramic matrix composites (CMC). These composites belong to the last generation. They are developed for high temperature applications in oxidative environment (1350 °C). They possess a self-healing capability. Their design is based on a multilayered matrix. A refinement of the regular ion-milling technique was necessary to thin the samples and to proceed to a full observation of the inner matrix of the composite by TEM. In a regular CMC, the matrix is homogeneous and thereafter it has not to be fully inspected from the fiber to the surface. This sampling technique unable to thin the complete sequence of the different layers in the vicinity of large pores where the ion-milling technique is known to be very difficult. High resolution TEM as well as electron energy loss spectroscopy can be managed anywhere in the core sequence of the matrix.

Transmission electron microscopic study of early stage γ 1 (Ag 2Hg 3) and β 1 (Ag-Hg) phases : Technical note

Incomplete reaction, residual free mercury, and high volatility of mercury are often major causes of the discrepancy in chemical composition of γ 1 measured by different methods. The high mercury volatility also proves to be a major difficulty in transmission electron microscopy (TEM) study of high mercury materials. Provided in this report is a preparation method for TEM thin foils that can largely eliminate the mercury loss problem. The results show that the lattice constant of early stage γ 1 crystals is 10.05 Δ with a chemical composition of Ag 41.08Hg 58.92 (or Ag 2Hg 2.87). The chemical composition data shows that little or no mercury is lost during specimen preparation. The lattice parameters, a and c, of β 1 crystals are 3.01 and 4.88 Δ, respectively with a chemical composition of Ag 1.1Hg 0.94. It seems that the present specimen preparation method allows for accurate TEM microanalysis of high mercury amalgam phases such as γ 1 and β 1, which has been extremely difficult to do in the past.

Carbon-carbon thin foil preparation techniques and problems

In spite of the many conventional transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) studies on carbon fibers, mesophase, and other carbonaceous materials, little TEM work on carbon-carbon (C/C) composites has been reported. This unfortunate lack of important knowledge on the detailed microstructure, especially on the various types of interfaces in C/C, has left a gap of knowledge in relating manufacturing parameters to the properties of C/C composites. This paper discusses one reason for the limited TEM work on C/C which involves the difficulties in preparing thin, clean, mechanically intact TEM thin foils, which is particularly important for interface analysis.

Mechanical damage introduced into aluminum monocrystals during TEM thin-foil preparation

The mechanical damage that is introduced into annealed aluminum by the various steps used in the preparation of thin foils for transmission electron microscopy (TEM) is discussed. These steps are: (1) preparation of 3-mm discs by mechanical punching; (2) preparation of 3-mm discs by spark-cutting; and (3) intermediate thinning by hand-grinding discs to thicknesses of 500, 375, 300, or 200 ..mu..m. Often these steps precede the final electrochemical jet-thinning used to obtain perforated TEM foils. The mechanical damage produced by these steps was evaluated by comparing, in the TEM, thin foils utilizing one of these steps with other thin foils of annealed (undamaged) aluminum. Damage was manifested by an increased dislocation density. The mechanical punching was performed on a device machined at the Lawrence Livermore National Laboratory that was very similar to smaller, commercially available punches. The spark-cutting was performed on a Metal Research LTD Servomet at a setting of 6 using a tubular brass cutting tool. Jet-thinning was done on a Struers Tenupol 2 using an electrolyte of 469 mL methyl alcohol, 25 mL H/sub 2/SO/sub 4/ and 6 mL HF at 265 K. Thinning was performed at 25 V. The aluminum (99.999% pure) was provided by Highways Internationalmore » as plate (1 x 100 x 100 mm). The plate was annealed at 723 K for 20 min in vacuum. The resulting average grain size was about 4 mm. Therefore, the discs that were punched, spark-cut, and ground were smaller than the typical grain or monocrystal.« less