Transmission Electron Microscopy Sample Research Articles

Cross-Sectional Transmission Electron Microscopy Sample Preparation of Soldering Joint Using Ultramicrotomy

Many studies have reported the interfacial reaction of Sn-Ag/ electroless nickel immersion gold (ENIG). Various analysis techniques, such as scanning electron microscopy, electron probe microanalyzer, and transmission electron microscopy (TEM), have been used to examine interfacial reaction. Among them, TEM equipped with analytical attachments offers the most complete tool for characterizing the formation of intermetallic compounds (IMCs) at the interface. However, solders are typically soft and ductile, while IMCs tend to be quite hard and brittle, which has limited the level of success in preparing TEM samples. We utilized ultramicrotomy since it might offer a reasonable and relatively quick alternative in this case. Ultramicrotomy has been used for the preparation of TEM specimens from biological materials and extending a range of materials including polymers, coating layer, particles, and even metals (Becker & Bange, 1993; Glanvill, 1995; Howell et al., 1995). TEM sample making to section hard materials by ultramicrotomy are not new. Besides, it has been traditionally considered that the mechanical damage during sectioning by diamond knife might hinder unambiguous specimen characterization. However, this technique also has many advantages such as no ion beam irradiation damage, no chemical mixing, no differential thinning rate and the ease of preparation of many serial sections with large, thin areas of uniform thickness in a relatively short time (Quintana, 1997). The increasing acceptability of ultramicrotomy in materials science is evidenced by a number of recent paper giving results for different hard materials (Hwang & Suganuma, 2003).

TEM Study of the Ionomer/Catalyst Interface and 3D Pore Structure of Catalyst Layer for PEMFC

Proton exchange membrane fuel cells (PEMFCs) are promising energy conversion devices due to their high efficiency, high energy density and low operating temperatures [1]. One of the major obstacles for high performance PEMFCs is that the sluggish oxygen reduction reaction (ORR) and the ORR activity in a membrane electrode assembly (MEA) are dependent of the structure of the ionomer/catalyst interface in catalyst layers. Coverage of the ionomer over the surface of catalyst particles and the thin ionomer film over the catalyst particles, as well as the porosimetry of the catalyst layer are critical factors to be considered in the fabrication of MEAs. Clearly, the determination of ionomer coverage over the surface of the catalyst particles, the morphology of ionomer film over the surface of catalyst particles and porosimetry of catalyst layer of MEAs are of paramount significance for developing high performance and low cost MEAs. Transmission electron microscopy (TEM) is a powerful tool to provide direct observations of the structures. In this work, we present the TEM analysis of MEAs for (1) ionomer coverage over carbon particles, (2) the thickness of ionomer film over carbon particles and (3) the porosimetry of catalyst layer using different TEM techniques. MEAs with different functional groups (which were chemically grafted on the surface of carbon support particles via diazonium reactions) were fabricated using (1) NH3 +- functionalized carbon black (CB) and (2) SO3 - functionalized CB. These two types of MEAs were analyzed in terms of ionomer/catalyst interface and porosimetry. In order to prepare electron transparent TEM samples, different methods were applied, including normal/partial embedding ultra-microtomy and cryo-microtomy. Figure 1 show scanning transmission electron microscopy (STEM) images of catalyst layers (CLs) of two MEAs, as well as energy-dispersive X-ray spectroscopy (EDS) mapping of the same area. Combining these results, it is evident that the fluorine in the NH3 +- functionalized carbon CL is uniformly distributed over the entire region. Meanwhile, the SO3 - functionalized carbon CL (as circled in Figure 1c) shows non-uniform distribution; the F signal is much weaker in some areas than others or even disappeared. These maps indicate that the NH3 +- functionalized carbon CL has better ionomer coverage than that of the SO3 - functionalized carbon CL. On the other hand, the X-ray spectra of both samples are shown in Figure 2. The C/F ratio in NH3 +- functionalized carbon CL is 216 while it is only 16 in SO3 - functionalized carbon CL. Such a large discrepancy in the C/F ratio between two different CLs are mainly due to the CL’s intrinsic property - the ionomer coverage difference - as these two TEM samples were prepared using the same method. As these two MEAs are prepared with the same catalyst support/ionomer ratio, higher C/F signal ratio in NH3 +- functionalized carbon CL indicates more complete coverage and thinner ionomer layer. An overview of catalyst layers in both CLs is shown by the TEM bright-field images in Figure 3. The thickness of catalyst layer made of NH3 +- functionalized CB is approximately 6.3μm, while it is only approximately 1.4 μm of that made of SO3 - functionalized CB. It suggests that the carbon support aggregates are much smaller in the catalyst layer made of NH3 +- functionalized CB, based on the fact that two MEAs are synthesized with same amounts of carbon supports and ionomer. Furthermore, 3D tomography TEM and reconstruction of both MEAs based on focused ion beam (FIB) supports this conclusion. Highly porous catalyst layer of NH3 +- functionalized CB facilitates mass transport for both reactants (H2 and O2) to reach reactive sites and water dissipated out. In summary, TEM characterization shows that NH3 +- functionalized CB catalyst layer has better ionomer coverage, thinner ionomer layer, as well as better porosimetry than SO3 - functionalized CB catalyst layer. In consistency with the TEM characterizations, the NH3 +- functionalized CB MEA provide better electrochemical performance. Reference [1] Kocha, S. S. Principles of MEA preparation. In Handbook of Fuel Cells − Fundamentals, Technology and Applications, ed. 1; Vielstich, W., Lamm, A., Gasteiger, H. A., Eds.; Wiley: Chichester, UK, 2003; Vol. 3, 538 Figure 1

Fabrication of high aspect ratio AFM probes with different materials inspired by TEM “lift-out” method

The most commonly used materials in all commercially available high-aspect-ratio (HAR) nanowire's (NW) tips are made of silicon and carbon nanotube which limit their applications in other types of atomic force microscopy (AFM), such as conducting AFM and magnetic force microscope. Therefore, a simple process inspired by cross-sectional transmission electron microscopy sample preparation method was used to demonstrate the feasibility of fabricating HAR AFM probes, which can easily define the tilt angle of the NW tip with respect to the direction that is normal to the axis of the cantilever to which it is attached by simply tilting the sample stage where the cantilever is placed. This is very important as it enables precise control of the inclination angle of the NW tip and allows the tip to be made perpendicular to the probed surface for scanning with different AFM mounts. Two different tips were fabricated, one attached parallel and the other attached at an angle of 13° with respect to the normal of the cantilever axis. These tips were used to profile the topography of a silicon nanopillar array. Only the probe attached at an angle of 13° allowed mapping of the topography between nanopillars. This is the first successful demonstration of an HAR AFM tip being used to map the topography of a nanopillar array. In addition, the authors also demonstrated that this method can be extended to fabricate HAR AFM tips of different materials such as copper with a slightly modified approach.

Structure and magnetic properties of Zr–Mn substituted strontium hexaferrite Sr(Zr,Mn) x Fe12−2x O19 nanoparticles synthesized by sol–gel auto-combustion method

In this research, nano-sized powders of Zr–Mn substituted strontium hexaferrite (Sr(Zr,Mn) x Fe12−2x O19 (x = 0, 2, 2.5, 3)) were synthesized by sol–gel auto-combustion route using subsequent heat treatment. The samples were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), Mössbauer spectroscopy and vibration sample magnetometer (VSM) techniques. XRD and Mössbauer spectroscopy results revealed formation of Sr(Zr,Mn) x Fe12−2x O19 accompanied with Mn δ Fe2−δ O4 lateral phase in the samples. Also, FTIR and XRD results demonstrated presence of SrO impurity phase. FESEM micrographs show particle size reduction and presence of two distinct powder morphologies with different brightness levels with Zr4+ and Mn2+ substitutions which approves existence of lateral phases in the substituted samples. TEM micrographs show nanometric particles with sizes smaller than 100 nm with high crystallinity. Mössbauer results showed that at low level of substitution, Zr4+ ions prefer to occupy both 4f1 and 2b however, at higher level of substitution, they prefer exclusively 4f1 site. While, Mn2+ ions distributed approximately equally between 12k and 2a sites. The presence of nonmagnetic Zr4+ cation leads to decrease in exchange interaction, especially at 12k and 2a sites. VSM results showed decrement of coercivity force ( i H c ) from 5593.60 to 3282.46 Oe and maximum magnetization from 62.60 to 46.15 emu g−1, respectively, by increment of Zr–Mn substitution values. Variations in maximum magnetization magnitude have been explained on the basis of occupation of the substituted cations at different iron sites.

Dust to dust: Evidence for the formation of “primary” hematite dust in banded iron formations via oxidation of iron silicate nanoparticles

Conventional models for the deposition of banded iron formations (BIFs) envisage the oxidation of upwelled ferrous iron and the precipitation of ferric oxide/hydroxide particles in surface waters that settled to form laterally extensive layers of iron-rich sediment. A fundamental tenet of this model is that fine-grained hematite (so-called dusty hematite) in least-altered BIFs represents the dehydration product of original oxide/hydroxide precipitates. However, this premise has never been proven. We have investigated the origin of the earliest-formed iron oxides in chert in well-preserved BIFs of the 2.63–2.45 billion-year-old Hamersley Group, Australia. We find that laminated chert in BIFs show progressive stages of in situ alteration from gray–green chert, containing iron-silicate nanoparticles, to red chert with abundant hematite dust. Analysis of textures by transmission electron microscopy of samples from the transition zone between gray–green and red chert reveals that dusty hematite formed after partial dissolution of iron-silicate nanoparticles by the precipitation of iron oxides in resulting cavities. These observations suggest that hematite dust is not a relict of an original seawater precipitate but the end-product of post-depositional oxidation. Our observations are consistent with paleomagnetic results from the Hamersley Group, which record two major phases of magnetic remanence carried by hematite that post-date deposition by more than 200 million years. Our results may provide an alternative explanation for the origin of jasper in BIFs deposited before the start of the Great Oxidation Event about 2.4 billion years ago. If correct, it follows that hematite dust is not a reliable proxy for paleoenvironmental conditions or biological processes in early Precambrian seawater. Furthermore, our results suggest that the primary iron precipitate in BIFs was iron-silicate mud that was silicified at or just below the sediment–water interface, a hypothesis that requires neither dissolved oxygen nor photosynthetic life, but was an inorganic, chemical process, reflecting anoxic oceans enriched in iron and silica.

Transmission Electron Microscopy Specimen Preparation of Delicate Materials Using Tripod Polisher

Transmission electron microscopy (TEM) is a powerful tool for analyzing a broad range of materials and provides localized information about the microstructure. However, the analysis results are strongly influenced by the quality of the thin foil specimen. Sample preparation for TEM analysis requires considerable skill, especially when the area of interest is small or the material of interest is difficult to thin because of its high hardness and its mechanical instability when thinned. This article selectively reviews recent advances in TEM sample preparation techniques using a tripod polisher. In particular, it introduces two typical types (fl at type and wedge type) of TEM sample preparation and the benefits and drawbacks of each method; finally, a method of making better samples for TEM analysis is suggested.

Morphological degradation of human hair cuticle due to simulated sunlight irradiation and washing

Morphological changes in hair surface are undesirable, since they cause shine loss, roughness increase and split ends. These effects occur more frequently in the cuticle, which is the outermost layer of the hair strand, and thus the most exposed to the environmental damages. Sunlight irradiation contributes significantly to these morphological alterations, which motivates the investigation of this effect on hair degradation. In this work, the influence of irradiation and hand-washing steps on the morphology of pigmented and non-pigmented hair cuticle was investigated using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). To simulate daily conditions, where hair is hand-washed and light exposed, samples of dark brown and gray hair underwent three different conditions: 1) irradiation with a mercury lamp for up to 600h; 2) irradiation with the mercury lamp combined with washes with a sodium lauryl sulphate solution; and 3) only washing. A new preparation procedure was applied for TEM samples to minimize natural variations among different hair strands: a single hair strand was cut into two neighbouring halves and only one of them underwent irradiation and washing. The non-exposed half was used as a control, so that the real effects caused by the controlled irradiation and washing procedures could be highlighted in samples that had very similar morphologies initially. More than 25images/sample were analysed using FESEM (total of 300 images) and ca. 150images/sample were obtained with TEM (total of 900 images). The results presented herein show that the endocuticle and the cell membrane complex (CMC) are the cuticle structures more degraded by irradiation. Photodegradation alone results in fracturing, cavities (Ø≈20–200nm) and cuticle cell lifting, while the washing steps were able to remove cuticle cells (≈1–2 cells removed after 60 washes). Finally, the combined action of irradiation and washing caused the most severe damages, resulting in a more pronounced cuticle extraction (≈1–4 cuticle cells after a 600h irradiation and a 60 times washing). This irradiation dose corresponds to ca. 2months of sunlight exposure (considering 5h/day) in Campinas-SP, Brazil, during the day period of maximum irradiation intensity. The combined action of irradiation and washing can be explained by the creation of fragile photodegraded spots in the endocuticle and in the CMC, where the mechanical stress associated to the washing steps are more prone to induce rupture.

Non-octahedral-like dislocation glides in aluminum induced by athermal effect of electric pulse

Abstract

Preparation and characterization of magnetic fluorescent microspheres for delivery of kaempferol

This study focused on the preparation and characterization of magnetic fluorescent microspheres (MFMs) for delivery of kaempferol. Magnetic microspheres were prepared by miniemulsion polymerization in the presence of Fe3O4 ferrofluids and kaempferol, and then, the microspheres were modified with amino-functionalized graphene quantum dots through chemically bonding. The properties of as-obtained MFMs were characterized by Fourier-transform infrared spectrum, transmission electron microscopy, thermogravimetric analysis and vibration sample magnetometry and X-ray fluorescence spectrometry. It was found that the superparamagnetic microspheres had ultrafine size (below 120 nm), high saturation magnetization of 32.48 emu/g, and significant fluorescence. Then, MFMs were used as a carrier to delivery of kaempferol, and the results indicated that they had a favourable release property for kaempferol. Finally, by incorporating the MFMs with Hela cells, they could efficiently induce inhibitory effect on Hela cells.

FEI Helios NanoLab 400S FIB-SEM

The FEI Helios NanoLab400S FIB-SEM is one of the world's most advanced DualBeamTM focused ion beam (FIB) platforms for transmission electron microscopy (TEM) sample preparation, scanning electron microscopy (SEM) imaging and analysis in semiconductor failure analysis, process development and process control. The FEI Helios NanoLab400S FIB-SEM combines an ElstarTM electron column for high-resolution and high-contrast imaging with a high-performance SidewinderM ion column for fast and precise cross sectioning. The FEI Helios NanoLab M 400S is optimised for high throughput high-resolution S/TEM sample preparation, SEM imaging and energy dispersive X-ray analysis. Its exclusive FlipStageTM and in situ STEM detector can flip from sample preparation to STEM imaging in seconds without breaking vacuum or exposing the sample to the environment. Platinum gas chemistry is the preferred metal deposition when a high deposition rate and precision of the deposition are required. Carbon deposition can be chosen as well. The system additionally allows for spatially resolved compositional analysis using the attached EDAX Genesis XM 4i X-ray microanalysis system.

FEI Helios NanoLab 460F1 FIB-SEM

The FEI Helios NanoLab 460F1 is a highly advanced dual beam FIB-SEM platform for imaging and analytical measurements, transmission electron microscopy (TEM) sample and atom probe (AP) needle preparation, process development and process control. For these purposes, the FEI Helios NanoLab 460F1 combines an ElstarTM UC technology electron column for high-resolution and high material contrast imaging with the high-performance TomahawkTM ion column for fast and precise sample preparation. The FEI Helios NanoLab 460F1 is additionally equipped with the MultiChemTM gas delivery system, an EasyLiftTM nanomanipulator, a cooling trap, an inert gas transfer (IGT) holder loadlock, a quick loader, a FlipStage 3TM, an EDX-System and an STEM III detector. This instrument is one of the few dual beam systems which combine an IGT holder loadlock with a FlipStage 3+TM EasyLiftTM nanomanipulator. Typical examples of use and technical specifications for the instrument are given below.

A novel approach to the characterization of thin oxide layers

A novel approach to the characterization of thin coatings or surface layers by means of the ASTAR hardware attached to the transmission electron microscope (TEM) and the dedicated software, used for orientation and phase map analyses, was applied to examine the Sanicro 25 steel after 500h of oxidation in water vapor at 700°C. Phase composition and grain orientation maps as well as texture analysis of thin (i.e. with a thickness of below 1µm) oxide layers were performed using a new TEM technique similar to electron backscatter diffraction in the scanning electron microscope. The spatial resolution of this technique was sufficient for the imaging of nm-sized grains and a full characterization of the thin oxide scale. The acquired results were verified using data obtained by means of conventional selected area electron diffraction (TEM-SAED), energy-dispersive X-ray spectroscopy and texture analyses using X-ray diffraction techniques. It should be noted that high-quality TEM samples are required for such investigations.

Making the practically impossible "Merely difficult"--Cryogenic FIB lift-out for "Damage free" soft matter imaging.

The preparation of thinned lamellae from bulk samples for transmission electron microscopy (TEM) analysis has been possible in the focussed ion beam scanning electron microscope (FIB-SEM) for over 20 years via the in situ lift-out method. Lift-out offers a fast and site specific preparation method for TEM analysis, typically in the field of materials science. More recently it has been applied to a low-water content biological sample (Rubino 2012). This work presents the successful lift-out of high-water content lamellae, under cryogenic conditions (cryo-FIB lift-out) and using a nanomanipulator retaining its full range of motion, which are advances on the work previously done by Rubino (2012). Strategies are explored for maintaining cryogenic conditions, grid attachment using cryo-condensation of water and protection of the lamella when transferring to the TEM.

Visible-light photocatalytic oxidation of CO over plasmonic Au/TiO2: Unusual features of oxygen plasma activation

To seek an efficient activation of plasmonic Au/TiO2 photocatalysts, atmospheric-pressure cold plasmas of oxygen (OP) and argon (ArP) were employed to activate the Au/TiO2 coating samples on glass substrate and compared with the conventionally calcination. The activated samples were evaluated in a continuous-flow photocatalytic oxidation (PCO) reactor under visible light (λ>420nm) for CO removal from synthetic air and characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy, CO chemisorption and electron paramagnetic resonance (EPR). Although Au nanoparticles (NPs) of the three activation samples averaged at around 4nm by TEM, the OP and ArP samples exhibited the highest and lowest PCO activity, respectively. An unusual feature of oxygen plasma activation is high content of surface oxygen, which favors superoxide (O2−) formation by accepting hot electron generated from absorption of visible light through local surface plasmon resonance (LSPR) of Au NPs. The OP sample has the lowest metallic Au content but its cationic Au can be rapidly reduced to form numerous low-coordinated metallic Au around the interface between Au NPs and TiO2 support in the induction period, which is another unusual feature of oxygen plasma activation.

Direct investigation of (sub-) surface preparation artifacts in GaAs based materials by FIB sectioning

The introduction of preparation artifacts is almost inevitable when producing samples for (scanning) transmission electron microscopy ((S)TEM). These artifacts can be divided in extrinsic artifacts like damage processes and intrinsic artifacts caused by the deviations from the volume strain state in thin elastically strained material systems. The reduction and estimation of those effects is of great importance for the quantitative analysis of (S)TEM images. Thus, optimized ion beam preparation conditions are investigated for high quality samples. Therefore, the surface topology is investigated directly with atomic force microscopy (AFM) on the actual TEM samples. Additionally, the sectioning of those samples by a focused ion beam (FIB) is used to investigate the damage depth profile directly in the TEM. The AFM measurements show good quantitative agreement of sample height modulation due to strain relaxation to finite elements simulations. Strong indications of (sub-) surface damage by ion beams are observed. Their influence on high angle annular dark field (HAADF) imaging is estimated with focus on thickness determination by absolute intensity methods. Data consolidation of AFM and TEM measurements reveals a 3.5nm surface amorphization, negligible surface roughness on the scale of angstroms and a sub-surface damage profile in the range of up to 8.0nm in crystalline gallium arsenide (GaAs) and GaAs-based ternary alloys. A correction scheme for thickness evaluation of absolute HAADF intensities is proposed and applied for GaAs based materials.

Mesoporous and Al-rich MFI crystals assembled with aligned nanorods in the absence of organic templates

Mesoporous zeolites have been paid much attention recently due to their excellent mass transfer and high activity for bulky molecules as well as unique shape selectivity, but their syntheses usually require the presence of organic templates. Here, we report organotemplate-free synthesis of mesoporous and Al-rich MFI zeolite in the presence of the zeolite seeds (MFI-SDS). The MFI-SDS crystals are assembled with rod-like nanocrystals having almost the same aligned direction, confirmed by the sample transmission electron microscopy (TEM). The space between nanocrystals forms the mesoporosity in the sample, supported by N2 sorption isotherms. 27Al MAS NMR spectroscopy and ICP analysis show that the MFI-SDS has abundant tetrahedral Al species in the zeolite framework, giving the Si/Al ratio at 9.5. Catalytic tests in cumene cracking show that the MFI-SDS exhibits higher catalytic activities and longer catalyst life than conventional ZSM-5 zeolites synthesized in the absence (ZSM-5-OTF) or presence of organic template, TPA+ (ZSM-5-TPA). The excellent catalytic performance should be assigned to the combined contribution of the presence of both mesoporosity and rich tetrahedral Al species in the MFI-SDS. These features would be critically important for industrial applications of MFI zeolite catalysts in the future.

Edge-melting: nanoscale key-mechanism to explain nanoparticle formation from heated TEM grids

In this study, we examine at both experimental and fundamental levels, the experimental evidence of nanoparticle formation in transmission electron microscopy (TEM) metal grids annealed at temperatures lower than the melting point of the corresponding metal bulk material. Our experimental investigation considers the most thermally unstable TEM grids (i.e. Cu-grids) and inspects the possible sources and mechanisms of contamination of thin films, conventionally deposited on carbon-coated Cu-grids. The investigations are supported by morphological–compositional analyses performed in different regions of the TEM sample. Then, a general model is formulated and discussed in order to explain the grid thermal instability, based on the critical role of edge-melting (i.e. melting initiated at edges and corners of the grid bars), the enhanced rate of evaporation from a liquid surface and the polycristallinity of the grid bars. Hence, we totally disregard conventional arguments such as bulk evaporation and metal vapor pressure and, in order to emphasize and clarify the alternative point of view of our model, we also overview the nano-scale melting phenomenology relevant to our discussion and survey the discrepancies reported in the literature.

Virus Isolation and Preparation of Sucrose-Banded Chikungunya Virus Samples for Transmission Electron Microscopy.

Virus isolation and purification is an invaluable technique in virology to detect and characterize viruses. This chapter describes a large-scale Chikungunya virus (CHIKV) propagation and purification methods by using discontinuous sucrose gradient, and sample preparation for transmission electron microscopy. Sucrose-banding yields large quantities of high-titer (10(10) pfu/ml) CHIKV stocks. Such stocks are stable for years when stored at -70 °C.

Complex surface structure of (110) terminated strontium titanate nanododecahedra.

The surface structure of (110) faceted strontium titanate nanoparticles synthesized via solvothermal method has been resolved using high-resolution electron microscopy (HREM). We demonstrate that the surface is a titania-rich structure containing tetrahedrally coordinated TiO4 units similar to the family of (n × 1) reconstructions observed on (110) surfaces of bulk crystalline strontium titanate. When compared with prior results for (001) terminated strontium titanate single crystals made with traditional transmission electron microscopy (TEM) sample preparation techniques, the results demonstrate that many models for oxide nanoparticles need to be revisited. This work serves as a reminder that attention must be paid to the surface of nanoparticles. Even with a simple perovskite as the starting point the end result can be very complex. As more materials are synthesized on the nanoscale, this will become increasingly important to take into consideration.

Direct observation of morphological evolution of a catalyst during carbon nanotube forest growth: new insights into growth and growth termination.

In this study, we develop a new methodology for transmission electron microscopy (TEM) analysis that enables us to directly investigate the interface between carbon nanotube (CNT) arrays and the catalyst and support layers for CNT forest growth without any damage induced by a post-growth TEM sample preparation. Using this methodology, we perform in situ and ex situ TEM investigations on the evolution of the morphology of the catalyst particles and observe the catalyst particles to climb up through CNT arrays during CNT forest growth. We speculate that the lifted catalysts significantly affect the growth and growth termination of CNT forests along with Ostwald ripening and sub-surface diffusion. Thus, we propose a modified growth termination model which better explains various phenomena related to the growth and growth termination of CNT forests.