Thin Lamellae Research Articles

Direct measurement of TEM lamella thickness in FIB-SEM.

Transmission electron microscope (TEM) specimen preparation by focused ion beam (FIB) milling requires delicate polishing of a thin window of material during the final stages of the procedure. Over or underpolishing is common and requires extra microscope resources to correct. Despite some methods for lamella thickness measurement being available, the majority of users judge the final polishing step subjectively from scanning electron microscope (SEM) images acquired between milling steps. Here we demonstrate successful thickness determination of thin silicon lamellae using calibrated secondary electron detectors in a FIB-SEM dual-beam chamber. Unlike previous thickness measurement methods it does not require long acquisition times, the use of in-chamber scanning transmission electron microscope (STEM) or energy dispersive x-ray spectroscopy detectors. The calibration aligns a SEM image to an electron energy loss spectroscopy (EELS) map of lamella thickness acquired in a TEM. This calibration reveals the greyscale-thickness dependence of two secondary electron SEM detectors: the through-lens detector (TLD) and the in-chamber electron detector (ICE). It was found that lamella thickness estimation for TLD images is accurate for areas thinner than 0.4 t/λ, whilst ICE images are most accurate for areas thicker than 0.5 t/λ up to 1.1 t/λ. The procedure presented here allows objective lamella thickness determination during the final stages of FIB specimen preparation using conventional imaging modes for common secondary electron detectors. LAY DESCRIPTION: Successful analysis of a material in a transmission electron microscope requires very thin windows of the material to be fabricated. Despite the quality of this analysis relying heavily on the thickness of the window, measuring thickness during window fabrication is not common practice. The authors show that it is possible to measure the thickness of the window directly in a focused-ion-beam chamber with a scanning electron microscope without altering the fabrication procedure, and using electron detectors common to most microscopes.

Methodology for observation of maraging tool steel after 3D printing using FIB and STEM mode

The components of the maraging tool steel produced by 3D printing are further heat-treated after printing. It includes a stress relief annealing and precipitation hardening. During this process precipitates of Ni3Ti and Fe2Mo or Fe7Mo are formed, which significantly contribute to an increase in ultimate tensile strength, hardness, and toughness. To understand the precipitation processes, it is necessary to describe the particles in detail. However, they are very small in size and cannot be examined properly by a light microscope (LM) or by scanning electron microscope (SEM). A possible way to investigate and describe these precipitates is to produce a thin lamella using a focused ion beam (FIB) in the electron microscope chamber, where scanning transmission electron microscopy (STEM) is subsequently used for observation. A lamella was prepared from the DMLS (Direct Metal Laser Sintering) printed part by an ion beam for observation in STEM mode. The experiment took place at the Zeiss AURIGA scanning electron microscope, equipped with an ion gun and also with STEM capabilities for thin samples. The lamella preparation methodology was gradually optimized to achieve sufficient resolution for observation of these very fine microstructures produced by 3D printing.

Influence of the coexistence of thin and thick lamellae on the transformation from crystalline form II to form I in isotactic polybutylene-1

The coexistence of thin and thick lamellae of form II in isotactic polybutylene-1 (PB-1) was obtained by isothermal crystallization at high temperature (100 °C) and subsequent cooling, and then the transformation from coexisted thin and thick lamellae of form II to form I was investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), in-situ wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS), to understand the dependence of lamellar thickness on the transformation from form II to form I. It is seen that the transformation of thick lamellae is always superior to that of thin lamellae. The crystal transformation time is shortened to ∼48 h for the samples with only thick lamellae of form II, which also weakens the retardance of form II to form I transition at late stage. By directly observing the crystalline morphology via POM, we find that crystalline form II formed at higher isothermal temperatures possesses loose and irregular spherulites, which facilitates the transition in contrast with the dense and regular spherulites formed at lower temperatures. Moreover, the large temperature difference during cooling from higher isothermal temperature to room temperature also accelerates the transformation due to increasing internal stress. Our work builds up connections among the crystalline morphology, the lamellar thickness, and the transformation behavior, which may help understand the crystalline transformation from form II to form I in PB-1.

Photo-degradation of polyethylene under stress: A successive self-nucleation and annealing (SSA) study

Successive self-nucleation and annealing (SSA) technique based on calorimetry is utilized to reveal the effect of uniaxial tensile stress on the photo-oxidation of high density polyethylene (HDPE). Stress-induced acceleratory and inhibitory effects on HDPE are confirmed by analyzing the newly formed melting peaks at low temperatures and the gradually disappeared melting peaks at high temperatures on the SSA curves. The formation of short chains due to chain scission contributes to both the new higher melting peaks (thick lamellae) and lower melting peaks (thin lamellae) because of high mobility and thermodynamic preference, respectively. Besides, chain crosslinking also gives rise to the formation of low melting peaks due to the decrease in the crystallizable sequence lengths and dynamical constraints. Compared with Fourier Transform Infrared Spectrometry, Scanning Electron Microscopy and Small Angle X-ray Scattering, the SSA technique can more precisely and sensitively reflect the early multi-scale aging behavior of HDPE subjected to stress.

3D interconnected boron- and nitrogen-codoped carbon nanosheets decorated with manganese oxides for high-performance capacitive deionization

The boron- and nitrogen-codoped 3D interconnected carbon nanosheets were synthesized with chitosan hydrogel and boric acid as precursors. The obtained nanosheets were interconnected to form a 3D network with thin lamellae (thickness ∼30 nm) and abundant meso-pores. The successful doping of boron and nitrogen atoms was proved by X-ray photoelectron spectroscopy (XPS). Following the decoration of manganese oxides, the resultant B, N-codoped manganese oxide-containing 3D interconnected carbon nanosheets were highly favorable for ionic transportation and storage. The specific capacitance and desalination amount of the corresponding deionization device reached 249 F g−1 and 20.3 mg g−1, respectively. This nanosheet material exhibited a fast salt adsorption rate and high cycling stability, showing an average salt adsorption rate (ASAR) of 1.5 mg g−1 min−1 and the desalination retention of 90.3% after 50 cycles. B, N-dual doping introduces active sites for ion adsorption and improves the conductivity. In addition, MnO2 deposition contributes to the faradaic pseudocapacitance. This work provides a facile and novel strategy to fabricate 3D carbon nanosheets, by combination of B, N-doping and MnO2 decoration, for highly efficient deionization application.

A New Scandium-Bearing Variety of Tusionite from the Eastern Pamirs (Tajikistan)

A new Sc-bearing variety of tusionite has been found in the Eastern Pamirs, in the near-miarolitic Dorozhny granite pegmatite complex at the Kukurt pegmatite field (left bank of the Kukurt River, 45 km east of the settlement of Murghab, Gorno-Badakhshan Autonomous Oblast, Tajikistan). Miarolitic pegmatites are related to the alpine leucocratic granites of the Shatput intrusive complex and occur in rocks of the Sarydzhilga Formation (PR3?) metamorphosed under amphibolite and epidote–amphibolite facies. Tusionite occurs in association with quartz, K-feldspar, albite, elbaite, Sc-bearing spessartine (up to 0.2 wt % Sc2O3) and accessory fluorapatite, Y-bearing fluorite, Sn-bearing titanite, magnetite, polycrase-(Y), B-rich gadolinite-(Y), ixiolite, manganocolumbite, pyrochlore, chernovite-(Y), cassiterite, varlamoffite, lepidolite, and Hf-rich zircon (up to 17.0 wt % HfO2). Tusionite forms thin lamellae (0.05–0.25 mm) and fanlike aggregates. It is yellow and transparent with a vitreous luster. It has weak pleochroism, No (orange–yellow) > Ne (light yellow). It is a uniaxial negative mineral, no = 1.870(5), ne = 1.760(3). The Raman spectrum has been reported for tusionite for the first time (laser excitation 532 nm); main bands: 228, 305, 379, 466, 661, 733, 750, 942, 1218, and 1458 cm–1. Its X-ray diffraction pattern is similar to tusionite from the Southwestern Pamirs. Hexagonal unit cell parameters: a = 4.772(3), c = 15.28(3) A. Chemical composition (electron microprobe, wt %, average of 14 analyses): 0.06 (0.00–0.31) Ta2O5; 50.28 (49.43–51.03) SnO2; 0.02 (0.00–0.19) TiO2; 1.02 (0.62–1.53) Sc2O3; 0.03 (0.00–0.19) CaO; 0.21 (0.16–0.46) FeO; 24.06 (23.59–24.34) MnO; 24.51 (calc. 23.90) B2O3; total 99.62 (99.08–100.79). The substitution mechanism involving Sc is not clear. Substitution of Sc+3 for Sn+4 with partial replacement of Mn+2 by Mn+3 is possible; however, Sc negatively correlates not only with Sn, but also with (Fe + Mn), which may result from the location of Sc in both octahedral positions with Sn+4 and Mn+2.

Mapping thermal conductivity across bamboo cell walls with scanning thermal microscopy

Scanning thermal microscopy is a powerful tool for investigating biological materials and structures like bamboo and its cell walls. Alongside nanoscale topographical information, the technique reveals local variations in thermal conductivity of this elegant natural material. We observe that at the tissue scale, fibre cells in the scattered vascular tissue would offer preferential pathways for heat transport due to their higher conductivities in both anatomical directions, in comparison to parenchymatic cells in ground tissue. In addition, the transverse orientation offers more resistance to heat flow. Furthermore, we observe each fibre cell to compose of up to ten layers, with alternating thick and thin lamellae in the secondary wall. Notably, we find the thin lamellae to have relatively lower conductivity than the thick lamellae in the fibre direction. This is due to the distinct orientation of cellulose microfibrils within the cell wall layers, and that cellulose microfibrils are highly anisotropic and have higher conductivity along their lengths. Microfibrils in the thick lamellae are oriented almost parallel to the fibre cell axis, while microfibrils in the thin lamellae are oriented almost perpendicular to the cell axis. Bamboo grasses have evolved to rapidly deposit this combination of thick and thin layers, like a polymer composite laminate or cross-laminated timber, for combination of axial and transverse stiffness and strength. However, this architecture is found to have interesting implications on thermal transport in bamboo, which is relevant for the application of engineered bamboo in buildings. We further conclude that scanning thermal microscopy may be a useful technique in plant science research, including for phenotyping studies.

Magnetization signals in μm-thin lamellae of highly oriented pyrolytic graphite: a field-dependent study

The recent discovery of superconductive features in HOPG has attracted much interest. However, further investigations are needed in order to clearly elucidate the magnetization properties of these materials. In this letter we investigated the structural and magnetic characteristics of μm thin lamellae extracted from inner/central regions of HOPG (grade B, θmisfit-tilt ∼ 0.8°) by using exfoliation-methods. Unusual magnetic signals were detected in the lamellae extracted from inner-central-regions by SQUID-magnetometry. Instead ferromagnetic signals were detected on the HOPG surface layers. The field dependent characteristics of these signals were investigated. ZFC and FC measurements of superficial and inner lamellae of the HOPG sample revealed significantly different signals which may imply the existence of multiple magnetic components within the whole HOPG structure.

Origin of the double melting peaks of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) with a high HV content as revealed by in situ synchrotron WAXD/SAXS analyses

ABSTRACTWe here reported the dual melting behaviors with a large temperature difference more than 50 °C without discernible recrystallization endothermic peak in isomorphous poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (P(HB‐co‐HV)) with a high HV content of 36.2 mol %, and the structure evolution upon heating was monitored by in situ synchrotron wide‐angle X‐ray diffraction/small‐angle X‐ray scattering (WAXD/SAXS) to unveil the essence of such double endothermic phenomena. It illustrated that the thinner lamellae with the larger unit cell and the thicker crystals having the smaller unit cell were melted around the first low and second high melting ranges, respectively. By analyzing in situ WAXD/SAXS data, and then coupling the features of melting behavior, the evolution of the parameters of both crystal unit cell and lamellar crystals, we proposed that the thinner unstable lamellae possess a uniform structure with HV units total inclusion, and the thicker stable lamellae reflect the sandwich structure with HV units partial inclusion. It further affirmed that the thicker sandwich and thinner uniform lamellae formed during the cooling and subsequent isothermal crystallization processes, respectively. These findings fully verify that it is the change of structure of lamellae rather than the melting/recrystallization that is responsible for double melting peaks of isomorphous P(HB‐co‐36.2%HV), and enhance our understanding upon multiple endothermic behaviors of polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1453–1461

Deformation of lamellar FCC-B2 nanostructures containing Kurdjumov-Sachs interfaces: Relation between interfacial structure and plasticity

Dual-phase lamellar microstructures containing alternating regions of plastically soft and hard phases are known to produce alloys with exceptional combination of strength and ductility. Here, by coupling high-resolution transmission electron microscopy and molecular dynamics (MD) simulations, we have investigated the deformation mechanisms prevalent in lamellar microstructures with soft fcc and harder bcc-ordered intermetallic B2 whose interfaces follow the Kurdjumov-Sachs (KS) orientation relationship. We have identified two key structural features at such an fcc/B2 KS interface. The mating KS-fcc (111) interfacial plane contains periodically arranged 1/6<112>fcc predominantly screw partial dislocations that are separated by extended dislocation “core-overlap” regions. The KS interface also contained steps and ledges with several steps exhibiting fcc-B2 lattice continuity between the {111}fcc and {011}B2. The effects of such interfaces on the uniaxial deformation of fcc-B2 multicrystal nanostructures, as a function of lamellae thickness, were studied using MD simulations. We observed that the screw-like interfacial partials facilitated the KS interfacial sliding and strain accumulation at the interphase interfaces, and reduced the yield strength of the composite material compared to a pure-fcc reference material. Deformation character depends on lamellae thickness. Thin B2 lamellae (~4 Å) sheared via twinning to drastically lowered flow stress such that the flow-strength was comparable to the pure fcc constituent phase. In contrast, thicker B2 lamellae (~12 Å) sheared via a slip-transfer mechanism, which allowed the fcc-B2 composite to maintain its flow-strength. Thus, the atomic structure of fcc/B2 KS interfaces was directly linked to dominant operative plastic deformation mechanisms.

Mind the gap: Micro-expansion joints drastically decrease the bending of FIB-milled cryo-lamellae

Cryo-focused ion beam (FIB)-milling of biological samples can be used to generate thin electron-transparent slices from cells grown or deposited on EM grids. These so called cryo-lamellae allow high-resolution structural studies of the natural cellular environment by in situ cryo-electron tomography. However, the cryo-lamella workflow is a low-throughput technique and can easily be hindered by technical issues like the bending of the lamellae during the final cryo-FIB-milling steps. The severity of lamella bending seems to correlate with crinkling of the EM grid support film at cryogenic temperatures, which could generate tensions that may be transferred onto the thin lamella, leading to its bending and breakage. To protect the lamellae from such forces, we milled “micro-expansion joints” alongside the lamellae, creating gaps in the support that can act as physical buffers to safely absorb material motion. We demonstrate that the presence of micro-expansion joints drastically decreases bending of lamellae milled from eukaryotic cells grown and frozen on EM grids. Furthermore, we show that this adaptation does not create additional instabilities that could impede subsequent parts of the cryo-lamella workflow, as we obtained high-quality Volta phase plate tomograms revealing macromolecules in their natural structural context. The minimal additional effort required to implement micro-expansion joints in the cryo-FIB-milling workflow makes them a straightforward solution against cryo-lamella bending to increase the throughput of in situ structural biology studies.

Tracking of the Growth Interface during PVT-Growth of SiC Boules Using a X-Ray Computed Tomography Setup

A crystal comprising various polytype switches was analyzed in detail. A very flat temperature profile together with an on axis seed are used to increase the probability for the nucleation of foreign polytypes during growth. Formation of foreign polytype occurred from thin lamella propagating from the edge of the main facet to the crystal rim as well as from 2D nucleation. The evolution of the crystal surface during the growth time is visualized using in-situ X-Ray computed tomography. Two concurrent growth centers are identified in the beginning of the growth process. Nucleation and lateral growth of foreign polytypes in the main facet area can be traced during the growth process.

The Influence of Holding Time on the Microstructure and Mechanical Properties of a 58CrMnSiNiMo Wear‐Resistant Cast Steel during Diffusion Annealing

The microstructure and mechanical properties of a 58CrMnSiNiMo wear‐resistant cast steel with or without diffusion annealing heat treatment are investigated. The results reveal a microstructural inhomogeneity and variation in the chemical composition of the steel without diffusion annealing, and the microstructural inhomogeneity is characterized by a dislocation substructure in the lath martensite and a twin substructure in the lenticular martensite. After diffusion annealing, the inhomogeneity is effectively reduced, and some complicated lath orientations are produced. With an increase in the diffusion annealing holding time, the average spacing of the martensite laths increases by 54.48%, with a value of 0.79 μm. After diffusion annealing, the second‐phase precipitates, mainly identified as M7C3 and M23C6 carbides, accelerate the division/formation of packet boundaries, block boundaries, and lath boundaries, and pin the packet boundaries and block boundaries. The diffusion annealing process significantly improves the ultimate tensile strength and toughness of the experimental steel from 1775 MPa and 44 J cm−2 to a maximum of 2029 MPa and 143.1 J cm−2, respectively. After diffusion annealing, an increase in the toughness is attributed to high density dislocations in the martensite laths as well as thin lamellae of retained austenite between or around the corners of these laths.

Structural characterization and ab-initio resolution of natural occurring zaccariniite (RhNiAs) by means of Precession Electron Diffraction

The crystal structure of naturally occurring zaccariniite from Loma Peguera (Republica Dominicana) has been studied in Transmission Electron Microscopy (TEM) with variable angle Precession Electron Diffraction (PED) techniques: 0.7° Precession Electron Diffraction Tomography (Precession EDT) for unit cell and Laue class sorting, 0.5° Scanning Precession Diffraction (SPED) for crystal orientation mapping and grain alignment, and high symmetry zone axis 1.2° to 2.2° Zone Axis High Angle Precession Electron Diffraction (ZA high angle PED) for Space Group assessment and supercell information gathering. The natural sample has been prepared into an electron thin lamella by means of Focused Ion Beam (FIB). The analysis of the data has yielded tetragonal cell parameters of 3.86, 3.86, 6.77 Å and space group of P4/nmm for the basic structure, and its constituent atom positions for Ni, As and Rh were determined as well by ab-initio structure resolution method in accordance to the elemental composition of the natural zaccariniite obtained with Energy Dispersive X-ray (EDX) and High Magnification Electron Microscopy (HMEM) analysis. A modulation of the crystal basic structure of 3 by 1 in the basal plane has been reported for the first time on natural occurring zaccariniite.

Interface Analysis of Spark Plasma Sintered Carbon Nanotube Reinforced Ti6Al4V

This study investigated the dispersion and interface reactions in a multi-walled carbon nanotube (MWCNTs) reinforced Ti6Al4V composite consolidated by the spark plasma sintering technique. The 1 wt.% MWCNTs were dispersed in Ti6Al4V by high-energy ball milling, and the milled composite powder was consolidated at 1000°C. The other parameters adopted during the sintering process were applied pressure (50 MPa), heating rate (100°C/min) and 5 min holding time, respectively. Thin lamellae from the synthesized bulk Ti6Al4V/1 wt.% MWCNT composite were prepared and characterized by transmission Kikuchi diffraction (TKD), scanning electron microscopy and high-resolution scanning transmission electron microscopy. Large agglomerations of MWCNTs in the order of 50–100 µm were distributed in the composite, and the TKD analysis on the sample retrieved from the MWCNT/Ti6Al4V interface had a polycrystalline layer of titanium carbide formed between the Ti6Al4V matrix particles and the MWCNT clusters.

Flash electropolishing of TEM lamellas of irradiated tungsten

The study in the transmission electron microscopy (TEM) of the irradiation-induced microstructure of tungsten, a material promising for its applications at high temperatures in harsh radiation environments, is rendered difficult by the high level of radioactivity. To circumvent this problem, it is nowadays a routine to reduce the TEM sample size with the focused ion beam (FIB) technique. In this way, one extracts an electron transparent thin lamella that is only a few microns in size. However, FIB induces additional radiation damage in the surface layer, which has to be removed by the so-called flash polishing technique in order to detect the initial damage structure in an irradiated sample. In this study, we evaluate the technique of flash electropolishing in an aqueous solution of NaOH as a method to remove this surface damage from tungsten lamella samples. The conditions of flash electropolishing are optimized as a function of temperature, voltage, FIB grid and weld material. Anisotropic etching dependence on the crystallographic direction was evaluated, with the highest polishing resistance in the region between (5 2 1) and (1 1 0).

A sustainable self-reproducing liposome consisting of a synthetic phospholipid.

A novel phosphoric membrane lipid (phospholipid) bearing an oleyl group as one of the hydrophobic chains formed a liposome with a thin lamella in water. Since the anionic membrane of pre-existing liposomes acted as a catalytic surface in phosphate buffer, membrane lipids could be generated from their precursor in an autocatalytic manner without the inclusion of catalytic amphiphiles in the liposome. The morphological changes of this anionic liposome were monitored both by flow cytometry and optical microscopy, and it was found that the liposomes deformed into a budding shape, followed by division, after the addition of a membrane precursor. Hence, this anionic monocomponent liposome could be regarded as a sustainable self-reproducing system. This liposome was also able to provide a reaction cavity for enzymatic reactions, such as DNA amplification by a polymerase chain reaction.

Numerical study of binary droplets collision in the main collision regimes

Direct numerical simulation of binary droplets collision is done using a conservative level-set method. The Navier-Stokes and level-set equations are solved using a finite-volume method on collocated grids. A novel lamella stabilization approach is introduced to numerically resolve the thin lamella film appeared during a broad range of collision regimes. This direction-independent method proves to be numerically efficient and accurate compared with experimental data. When the droplets collide, the fluid between them is pushed outward, leaving a thin gas layer bounded by the surface of two droplets. This layer progressively gets thinner and depending on the collision regime, may rupture resulting in coalescence of the droplets or may linger resulting in bouncing-off the droplets. Embedded ghost-nodes layer makes it possible to mimic both bouncing and coalescence phenomena of the droplets collision. The numerical tools introduced are validated and verified against different experimental results for a wide range of collision regimes. A very good agreement is observed between the results of this paper and experimental data available in the literature. A detailed study of the energy budget for different shares of kinetic and dissipation energies inside of the droplet and matrix, in addition to the surface tension energy for studied cases, is provided. Supplementary quantitative values of viscous dissipation rate inside of the matrix and droplet, and also the radial expansion of the droplet are presented as well.

Using focus ion beam to prepare crystal lamella for electron diffraction

Electron diffraction provides a powerful tool to solve the structures of small protein crystals. However, strong interactions between the electrons and the materials limit the application of the electron crystallographic method on large protein crystals with micrometer or larger sizes. Here, we used the focused ion beam (FIB) equipped on the scanning electron microscope (SEM) to mill a large crystal to thin lamella. The influences of the milling on the crystal lamella were observed and investigated, including radiation damage on the crystal surface during the FIB imaging, deformation of the thin crystal lamella, and variation in the diffraction intensities under electron radiation. These observations provide important information to optimize the FIB milling, and hence is important to obtain high-quality crystal samples for routine structure determination of protein crystals using the electron cryo-microscope.

Analysis of glued-laminated timber structure during five years of outdoor operation

The influence of variable climatic conditions on the strength of a glued-laminated arched timber structure after five years of outdoor operation was examined. The aim of the investigation was to determine the tensile and shear strength perpendicular to grains of samples as well as the global bending and shear strength, and to compare them with corresponding design values. It was concluded that the shear strength significantly decreased after five years compared with measurements following fabrication. The shear strength of the arched structure with a load did not reach values computed by Eurocode5 (EC5) standards, but instead showed a significant decrease. This phenomenon may provide a reason for the delamination failures often experienced in built structures. This research aimed to investigate the differences in strength of glued-laminated structures when thin and thick lamellae were used in manufacture, and to suggest ways forward.