Dark-field TEM Images Research Articles

Cu-based nano-multilayer film produced by HiPIMS for antimicrobial properties and its application in photodetector

This paper reports on the use of high-power impulse magnetron sputtering to deposit Cu-based nano-multilayer films (CuZrTiAl) on Si wafers and AISI 304 stainless steel. Co-sputtering can be performed using multiple simultaneous targets to decrease the cost of manufacturing alloy targets at industrial scales. Co-sputtering mode allows variations in the power supplied to the various targets to control the intensity of the plasma jets and thereby tailor the composition of the deposited films. Our primary aim in this study was to elucidate the effects of Al target power (from 0.3 to 1.3 kW) on the structure and antibacterial properties of the resulting coatings. Varying the Al target power was shown to alter the chemical composition, layer thickness, and structure. EPMA results revealed that increasing the power from 0.3 to 1.3 kW caused a monotonic increase in Al content from 6.1 to 18.3 at%. Dark-field TEM images revealed that decreasing the period thickness from 8.6 to 4.6 nm caused the ultra-thin film Cu to transform into a single isolated nano-crystal, which facilitated the release of Cu ions to improve antibacterial effects (from 84 % to 99 % for Escherichia coli). This study also demonstrated the recycling of the proposed Cu-based nanoscale multilayer films to fabricate metal-doped ZnO nanowires for use in photodetectors. The photodetector achieved a photocurrent-to-dark-current ratio of 150 when using an LED light source with a wavelength of 365 nm.

An in-situ study of low thermal expansion and internal stress evolution in FeMn alloys

The mechanism of low thermal expansion phenomenon in antiferromagnetic FeMn alloys needs to be revealed. In this work, the evolution of lattice thermal expansion and internal stress in FeMn alloys was investigated by in-situ synchrotron X-ray diffraction during thermal cycling. Preceding the martensitic transformation, the coefficient of lattice thermal expansion (CLTE) decreased and the full width at half maximum (FWHM) of the diffraction peaks broadened abnormally. The evolution of the lattice thermal expansion and the FWHM were both reversible and isotropic. The additional reflection spots around the fundamental diffraction spots in the electron diffraction patterns of austenite and the dispersed nano-scale martensite embryos in austenite observed in the dark field TEM images proves the existence of premartensitic transformation. Similar phenomena were found in FeMn Invar alloy, which indicate that the Invar effect is closely related to the internal stress evolution caused by premartensitic transformation. • In this paper, many abnormal phenomena were observed in the Fe Mn alloys. The lattice thermal expansion behaviors and internal stress evolution in FeMn alloys was investigated by in situ synchrotron X-ray diffraction. The correlation between low thermal expansion property and premartensitic transformation were revealed by comparing the similar abnormal phenomena during Invar effect and the premartensitic transformation. The highlights are as follows: • During the Invar effect of Fe 27Mn alloy and preceding the martensitic transformation of Fe 24Mn alloy, the coefficient of thermal expansion decreased and the FWHM of diffraction peaks of austenite increased abnormally. The evolution of thermal lattice strain and FWHM was reversible and isotropic. • Transmission electron microscopy observations confirmed that there are massive martensite embryos embedded in austenite phase during Invar effect and premartensitic transformation. The existence of martensite embryos caused the abnormal increase of FWHM and may be related to the low thermal expansion behavior of FeMn alloy. • These similar phenomena imply a close relationship between the mechanism of Invar effect and the premartensitic transformation in FeMn alloy. • Our results may help to reveal the relationship between Invar effect and premartensitic transformation in antiferromagnetic Invar alloys, and lead to an in-depth understanding of the mechanism of low expansion property.

Structural characterization of ELO-GaN film on mask-stripe patterned GaAs (0 0 1) substrate grown by metalorganic vapor phase epitaxy

GaN films were epitaxial laterally overgrown on the [110]-stripe-patterned GaAs (001) substrate by MOVPE. AlGaN intermediate layers and low-temperature GaN buffer layer were inserted in order to prevent structural defects. The epitaxial lateral overgrowth of GaN results in a trapezoidal shape with flat facets. Structural phases and defects distribution were studied by TEM. Selective-area diffraction pattern indicates the mixed phase of GaN and a high density of stacking faults at nucleation. However, with the deposition of dielectric SiNx masks, a lateral overgrowth resulted in nearly free of defects, and the cubic phase transformed into hexagonal despite a cubic template. Moreover, dark-field TEM images were used to demonstrate the structural phase transformation.

Illuminating Invisible Grain Boundaries in Coalesced Single-Orientation WS2 Monolayer Films.

Engineering atomic-scale defects is crucial for realizing wafer-scale, single-crystalline transition metal dichalcogenide monolayers for electronic devices. However, connecting atomic-scale defects to larger morphologies poses a significant challenge. Using electron microscopy and ReaxFF reactive force field-based molecular dynamics simulations, we provide insights into WS2 crystal growth mechanisms, providing a direct link between synthetic conditions and microstructure. Dark-field TEM imaging of coalesced monolayer WS2 films illuminates defect arrays that atomic-resolution STEM imaging identifies as translational grain boundaries. Electron diffraction and high-resolution imaging reveal that the films have nearly a single orientation with imperfectly stitched domains that tilt out-of-plane when released from the substrate. Imaging and ReaxFF simulations uncover two types of translational mismatch, and we discuss their origin related to relatively fast growth rates. Statistical analysis of >1300 facets demonstrates that microstructural features are constructed from nanometer-scale building blocks, describing the system across sub-Ångstrom to multimicrometer length scales.

Resolving atomic-scale phase transformation and oxygen loss mechanism in ultrahigh-nickel layered cathodes for cobalt-free lithium-ion batteries

Summary Doped LiNiO2 has recently become one of the most promising cathode materials for its high specific energy, long cycle life, and reduced cobalt content. Despite this, the degradation mechanism of LiNiO2 and its derivatives still remains elusive. Here, by combining in situ electron microscopy and first-principles calculations, we elucidate the atomic-level chemomechanical degradation pathway of LiNiO2-derived cathodes. We uncover that the O1 phase formed at high voltages acts as a preferential site for rock-salt transformation via a two-step pathway involving cation mixing and shear along (003) planes. Moreover, electron tomography reveals that planar cracks nucleated simultaneously from particle interior and surface propagate along the [100] direction on (003) planes, accompanied by concurrent structural degradation in a discrete manner. Our results provide an in-depth understanding of the degradation mechanism of LiNiO2-derived cathodes, pointing out the concept that suppressing the O1 phase and oxygen loss is key to stabilizing LiNiO2 for developing next-generation high-energy cathode materials.

Microstructural characterization of Mg-SiC nanocomposite synthesized by high energy ball milling

High-energy ball milling is successfully used to produce magnesium matrix nanocomposites reinforced with SiC nanoparticles. Changes in morphology and microstructural features of the milled powders were characterized in order to highlight advantages of the mechanical milling process and evaluate the role of the SiC nanoparticles. It was observed that with increasing volume fraction of SiC nanoparticles, a finer nanocomposite powder with more uniform particle size distribution is obtained. A homogeneous distribution of SiC nanoparticles, even up to 10% volume fraction, in magnesium matrix after 25 h milling was confirmed by elemental mapping and TEM results. The analysis of the XRD patterns accompanied by dark-field TEM images revealed that magnesium crystallites refine to fine nanocrystalline sizes after the mechanical milling. The results showed that the crystallite size of the magnesium matrix reduced with increasing SiC nanoparticle content in addition to the induced lattice strain.

Cluster structure in amorphous Ti-Ni-Cu alloys subjected to high-pressure torsion deformation

The features of the internal structure's evolution of melt-spun (MS) amorphous Ti50Ni25Cu25 alloy samples subjected to high-pressure torsion (HPT) at 20 and 150 °C were revealed by TEM and STEM – in the planar direction and the cross-sectional direction of the HPT-processed disc-shaped samples.In STEM HAADF observations in the planar direction, areas with brightness contrast with a size of 20 nm are revealed. We assume them to be “amorphous nanoclusters”. In dark-field TEM images, in many areas nanocrystals (with sizes about 5 nm) are revealed, resulting from strain-induced nanocrystallization. In STEM HAADF images, there can be seen nanoclusters (with sizes about 20 nm) separated by bright boundaries. Groups of shear bands (SBs) are revealed on the cross-sectional directions on lamellae cut from the HPT-processed samples. Nanocrystals form directly in the shear bands as a result of strain-induced nanocrystallization. Amorphous nanoclusters are also observed in the amorphous phase surrounding the SBs. Formation of the amorphous nanocluster in the areas surrounding the shear bands has been discovered for the first time. Atomic force microscopy (AFM) was used to study the surface morphology of foils prepared by ion polishing from the initial amorphous ribbons and HPT-processed samples. A hollows-like surface morphology in the HPT-processed state is revealed by AFM, which is reflected as nanocluster contrast in TEM images. The hollows-like surface morphology could be explained by the specifics of etching processes in the HPT-processed state. Brittle fracture of melt-spun Ti50Ni25Cu25 in the as-cast state and after HPT processing is determined during tensile tests. However, observable changes in the fracture surfaces correspond to an increased local ductility in samples subjected to HPT, in comparison with the initial state.

Morphology of Spherulites in Rapidly Solidified Ni3Ge Droplets

The congruently melting, single phase, L12 intermetallic β-Ni3Ge has been subject to rapid solidification via drop-tube processing. Four different cooling rates are used in this process, at very low cooling rates (≥850 μm diameter particles, ≥700 K s−1) and slightly higher cooling rates (850–500 μm diameter particles, 700–1386 K s−1) the dominant solidification morphology, revealed after etching, is that of isolated spherulites in an otherwise featureless matrix. At higher cooling rates, (500–300 μm diameter particles, 1386–2790 K s−1 and (300–212 μm diameter particles, 2790–4600 K s−1) mixed spherulite and dendritic morphologies are observed. Indeed, at the higher cooling rate dendrites with side-branches composed of numerous small spherulites are observed. Selected area diffraction analysis in the TEM indicate that the formation of spherulites is due to an order-disorder transformation. Dark-field TEM imaging has confirmed that the spherulites appear to consist of lamellae of the ordered phase, with disordered material in the space between the lamellae. The lamellar width within a given spherulite is constant, but the width is a function of cooling rate, with higher cooling rates giving finer lamellae. As such, there are many parallels with spherulite growth in polymers.

Investigation of Pristine Li1.2Ni0.13Mn0.56Co0.13O2 By Advanced TEM

Layered Li-transition metal (TM) oxides are very promising materials for new Li ion battery cathodes. Compounds with an increased content of Li and Mn are particularly interesting because they exhibit a high capacity of 200-300 mAhg-1 even after an initial drop in capacity during the first charging cycle.[1] The structure of such compounds and their capacity degradation over multiple cycles is not fully understood due to the complexity of the crystallographic phases, the ambiguities in the diffraction data and the presence of additional phases. The investigated compound Li1.2Ni0.13Mn0.56Co0.13O2 is derived from LiNi0.33Mn0.33Co0.33O2, (NMC). Due to the higher capacity of the Li-rich compound, it will be referred to as high energy NMC (HENMC).[2] The chemical formula of HENMC can be rewritten as Li2MnO3 · LiNi0.33Mn0.33Co0.33O2 which implies that this compound is a mixture of trigonal NMC and monoclinic Li2MnO3. In NMC, there are two different cation layers which are exclusively occupied by Li and TM respectively. In Li2MnO3 one third of the TM sites are occupied by Li. HENMC must be either a phase mixture with distinct domains of the two oxides or a solid solution of the two, with “Li rich” positions in the TM layers and an overall reduced, monoclinic symmetry (Figure 1).[3] The exact nature of HENMC and similar materials is crucial to understand the de-lithiation processes during charging cycles. The layered structure and its relation to other phases was investigated with a combination of electron diffraction in bright-field and scanning modes with high resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning TEM (HAADF-STEM) imaging. Due to the high structural similarity of NMC and Li2MnO3, all lattice distances which can be found for NMC can also be found for Li2MnO3; as seen in the respective electron diffraction patterns (Figure 2). HAADF-STEM imaging reveals the presence of Li-rich positions in the TM layers as indicated by a lower intensity of the related atom columns (Figure 3). Due to the stacking faults of the TM layers, the interpretation of contrast in any other orientation becomes by far less intuitive as we will demonstrate. A LiTM2O4 spinel phase is found on the surface quite frequently. Its relation to the bulk phase was derived from high resolution images. STEM-EELS revealed the presence of surface reduction due to oxygen depletion in HENMC. This work thus provides structural information about the synthesized material in its pristine state to facilitate understanding the changes the material undergoes during the (de-)lithiation segments of electrochemical cycling. Further investigations on such effects are currently being carried out and will be discussed. [1] B. L. Ellis, K. T. Lee, L. F. Nazar, Chem. Mater. 2010, 22, 691-714. [2] C. S. Johnson, N. Li, C. Lefief, J. T. Vaughey, M. M. Thackeray, Chem. Mater. 2008, 20, 6095-6106. [3] H. Yu, H. Zhou, J. Phys. Chem. Lett. 2013, 4, 1268−1280. Figure 1

Nanoscale Concentration Quantification of Pharmaceutical Actives in Amorphous Polymer Matrices by Electron Energy-Loss Spectroscopy

We demonstrated the use of electron energy-loss spectroscopy (EELS) to evaluate the composition of phenytoin:hydroxypropyl methylcellulose acetate succinate (HPMCAS) spin-coated solid dispersions (SDs). To overcome the inability of bright-field and high-angle annular dark-field TEM imaging to distinguish between glassy drug and polymer, we used the π-π* transition peak in the EELS spectrum to detect phenytoin within the HPMCAS matrix of the SD. The concentration of phenytoin within SDs of 10, 25, and 50 wt % drug loading was quantified by a multiple least-squares analysis. Evaluating the concentration of 50 different regions in each SD, we determined that phenytoin and HPMCAS are intimately mixed at a length scale of 200 nm, even for drug loadings up to 50 wt %. At length scales below 100 nm, the variance of the measured phenytoin concentration increases; we speculate that this increase is due to statistical fluctuations in local concentration and chemical changes induced by electron irradiation. We also performed EELS analysis of an annealed 25 wt % phenytoin SD and showed that the technique can resolve concentration differences between regions that are less than 50 nm apart. Our findings indicate that EELS is a useful tool for quantifying, with high accuracy and sub-100 nm spatial resolution, the composition of many pharmaceutical and soft matter systems.

Cytotoxicity, intracellular localization and exocytosis of citrate capped and PEG functionalized gold nanoparticles in human hepatocyte and kidney cells.

Surface-modified gold nanoparticles (AuNPs) are nanomaterials that hold promise in drug delivery applications. In this study, the cytotoxicity, uptake, intracellular localization, and the exocytosis of citrate-stabilized (Cit-AuNP) and polyethylene glycol (PEG)-modified gold nanoparticles with the carboxyl (COOH) terminal functional group were assessed in human embryonic kidney (HEK 293) and the human caucasian hepatocytes carcinoma (Hep G2) cell systems, representing two major accumulation sites for AuNPs. The zeta (ζ)-potential measurements confirmed the negative surface charge of the AuNPs in water and in cell growth medium. The transmission electron microscopy confirmed the size and morphology of the AuNPs. Both types of AuNPs were shown to induce cytotoxic effects in cells. The Hep G2 cells were more sensitive cell type, with the COOH-PEG-AuNPs inducing the highest toxicity at higher concentrations. Dark field microscopy and TEM images revealed that the AuNPs were internalized in cells, mostly as agglomerates. TEM micrographs further revealed that the AuNPs were confined as agglomerates inside vesicle-like compartments, likely to be endosomal and lysosomal structures as well as in the cytosol, mostly as individual particles. The AuNPs were shown to remain in cellular compartments for up to 3weeks, but thereafter, clearance of the gold nanoparticles from the cells by exocytosis was evident. The results presented in this study may therefore give an indication on the fate of AuNPs on long-term exposure to cells and may also assist in safety evaluation of AuNPs.

Sensitivity of thermo-electric power measurements to α–α′ phase separation in Cr-rich oxide dispersion strengthened steels

The sensitivity of thermo-electric power (TEP) measurement to detect the undesired α–α′ phase separation occurring in Cr-rich oxide dispersion strengthened steels was investigated. TEP values were found to increase with time of exposure to 475 °C—the maximum temperature of the miscibility gap in Fe–Cr alloys. Exposure to 650 °C did not induce any changes in the TEP value. By examining the bend contours in dark-field TEM images, α′ precipitates were evidenced in aged PM2000. Using the Fe–XCr–YAl model alloys and X-ray photoelectron spectroscopy, the changes in TEP were traced back to the depletion of Cr from the matrix, caused by the formation of the Cr-rich α′ phase. By quantifying the effect of Cr content on the TEP value of model alloys, it was estimated that following 1000 h of aging, the Cr concentration in the α matrix of PM2000 alloy was reduced from 20 to ~13.5 at.%.

Influences of two-step growth and off-angle Ge substrate on crystalline quality of GaAs buffer layers grown by MOVPE

GaAs buffer layers were grown on off-angle Ge substrates with a two-step growth process by metalorganic vapor phase epitaxy in order to prepare a high quality buffer layer for the InGaAsN p–i–n solar-cell structure. In our contribution, we present results from the optimized two-step growth of GaAs buffer layers, namely with a low-temperature step at 470°C and a high-temperature step at 580°C, combined with the use of Ge substrates misoriented by 4° and 6° towards [110]. HRXRD results showed that by using the off-angle substrates, the FWHM of (004) rocking curves was decreased to 6.7sec, which is about 4 times the FWHM of the GaAs commercial substrate. A decreased FWHM indicates a narrower distribution of crystal orientation. Furthermore, a smooth surface with a RMS roughness of 0.7nm was clearly observed by AFM. Cross-sectional dark-field TEM images showed the GaAs buffer layer with 20–30nm diamond-shaped anti-phase domains (APDs) at the GaAs/Ge interface, followed by APDs-free GaAs regions on the 6° off-angle Ge substrate. However, anti-phase boundaries were generated along the [001] direction for the buffer layer on the on-axis substrate. Our results demonstrated that the use of 6° off-angle Ge substrate and a two-step growth process allow the suppression of APDs in the GaAs buffer layer.

Palladium assisted hetroepitaxial growth of an InAs nanowire by molecular beam epitaxy

The palladium (Pd) assisted epitaxial growth of technologically important InAs nanowires grown on GaAs{111}B substrates using molecular beam epitaxy is reported. The grown free-standing InAs nanowires adapted a vapor–liquid–solid growth mechanism. The impacts of the catalyst particle density, growth temperature and input V/III precursor ratio have been investigated to identify better growth conditions for getting high-density non-<111>-orientated InAs nanowires. We assert here that two kind of nanowires are observed, one having a pure zinc-blende crystalline structure free of stacking faults, and the other with a defect-free wurtzite crystalline structure. However, few of them have defect imperfections too. The L- and Y-shaped nanowires confirm similar surface free energies for possible <110> growth directions. These unusual growth directions are attributed to the effect of the catalyst material as well as the surface-induced strain at the interface between the grown nanowires with substrates. The structural features of the grown nanowires are studied by employing scanning and transmission electron microscopic techniques. The obtained TEM results confirm that the nanowire catalyst interface is not a straightforward zinc-blende structured nanowire. Energy dispersive x-ray (EDX) analysis reveals that the tip of the grown nanowires with the chemical composition of Pd and In have a nearly 50:50 ratio, while the nanowire body did not have any catalyst traces other than the composition of InAs for both type of nanowires. The obtained high angle annular dark field (HAADF) TEM image for both types of nanowires along with the intensity profile provided evidence for cubic as well as hexagonal facets.

NbC Precipitation and Deformation of SS 347H Crept at 850°C

Niobium stabilized 347H stainless steel is a candidate alloy for fuel cladding of Generation IV Supercritical Water-Cooled Reactors (SCWR). The creep properties and microstructural evolution of SS 347H are vitally important for the proposed SCWR challenging design conditions. The high temperature mechanical properties and phase stability of stainless steels is linked to formation, dissolution and coarsening of precipitates [1]. In solution annealed and aged condition, type 347 stainless steel forms NbC precipitates which stabilise the steel against grain boundary precipitation of M23C6 to reduce sensitizati knowledge, microstructural investigation on crept specimens at 850°C is not available. In this study precipitation and deformation behaviours of a commercial SS 347H plate (17%Cr, 9%Ni, 0.36%Nb, 0.04%C) in the as received, aged at 850°C for 1244h (i.e., TEM sample taken from the head of creep specimen) and the creep conditions were examined using the FEI TEM -ray detection technology operating at 200kV. In Fig 1(A) typical NbC precipitates within the matrix in the as received condition are shown. Figure 1(B) is an HRTEM image of one of these precipitates that appears to be coherent with the matrix. An overlay of Nb EDX map on a high angle annular dark field (HAADF) image of this sample is shown in Fig 1(C), highlighting uniformly distributed precipitates. In the aged condition, Fig 2 presents a series of micrographs showing distribution of the NbC precipitates within the matrix and also at grain boundaries. In the crept sample, Fig. 3(A) is a STEM-HAADF image with CBED inset representing [011] zone axis and Fig. 3(B) shows the corresponding EDX elemental map highlighting the NbC precipitates of the crept specimen. These precipitates were found to be aligned towards slip direction (Fig. 3(B)). The slip lines visible in Fig 3(A) were analysed in HRTEM image of Fig 3(C), where the inset is the corresponding fast Fourier transform (FFT). From the FFT pattern the ( 11 1) spot was used to form the masked inversed FFT shown in Fig 3(D), illustrating the effect of slip in ( 11 1) planes. Figure 3(E) is a dark field TEM image formed using (1 11 ) reflection of a cubic NbC precipitate circled in Fig 3(B). Figures 3(F) and (G) compare the deformation in the matrix of the aged and the crept samples. In the high resolution STEM images, Moire fringes magnify the effect of defects within the matrix, and are indicative of the deformation. Arrows point to the image of the dislocations in Moire fringes and illustrate severe deformation in the crept sample as opposed to the aged sample. Figure 3(G) also implies that the NbC precipitate (circled in 3(B)) is oriented towards slip lines of creep deformation. In all samples larger NbC precipitates were also found in grain boundaries. It is interesting to note that no sigma, Z-phase (CrNbN) or M23C6 precipitates were observed in the aged specimens. Based on published data presence of the sigma phase in the aging regime we used is expected [3]. This study shows that NbC precipitates were oriented towards slip direction during creep at 850°C and can hinder the slip process. Study of longer creep test specimens is underway.

Ion-beam synthesis and characterization of narrow-gap A3B5 nanocrystals in Si: Effect of implantation and annealing regimes

The process of InAs and GaSb nanoprecipitates creation in Si matrix using high-fluence ion implantation of species from groups V and III followed by thermal treatment has been investigated. We have studied in detail a complex system of defects and nanocrystals in implanted layers, have compared a damage level for both systems, evaluated the influence of implantation and annealing regimes on a size of A3B5 nanocrystals and on a defect distribution in implanted layers. The crystalline nature of precipitates was identified by observing Moiré fringe patterns in TEM images, the Moiré period showing a tendency to increase with increasing size of inclusion. A “glowing” effect was observed at the nanocrystal/Si interfaces in the dark-field TEM images of the implanted and annealed samples, this being ascribed to the presence of misfit dislocation networks at the InAs/Si and GaSb/Si interfaces generated as a result of strain relaxation in the highly mismatched A3B5/Si systems. Also we compared our results on structural characterization of “A3B5 nanocrystals–Si matrix” systems with other papers.

Structural studies of Y2O3 dispersoids during mechanical milling and annealing in a Fe-15 Y2O3 model ODS alloy

The Fe-15wt% Y2O3 model Oxide Disperson Strengthened (ODS) alloy powder was prepared by mechanical milling in an inert atmosphere using high energy planetary ball mill. The present paper deals with the study on structural changes of nano-crystalline yttria dispersoids in Fe matrix during mechanical milling for various durations and subsequent annealing. The crystallinity of Y2O3 in the milled powder was studied by X-ray diffraction (XRD) technique which showed that the intensity of diffraction peaks of Y2O3 gradually disappeared with increase in milling time. Dark field TEM imaging of the milled powder showed that both Fe and Y2O3 particles were refined to few nanometers during milling. Electron diffraction analysis showed polycrystalline rings for Fe and broad rings with a few spots corresponding to the (411) plane of Y2O3 after 10h of milling time. The yttria diffraction peaks became broad and diffuse with increasing milling time. Subsequent annealing of the 60h milled powder at 1273K for 1h results in recrystallization of Y2O3 and growth of Fe crystallites.

The use of a central beam stop for contrast enhancement in TEM imaging

Dark field TEM imaging using a stop of the central beam (DF-000) is reported. It is shown that a strong enhancement in the contrast can be obtained for graphene as example of weak phase object and endocytic multivescilar body as example of an unstained biological sample. No charging or significant contamination of the central beam stop is observed. For graphene, a resolution beyond 1Å(-1) was easily obtained. DF-000 imaging can be considered as a good and easy to use alternative of a phase plate.

Structural characterization of He ion microscope platinum deposition and sub-surface silicon damage

In this paper we studied helium ion beam induced deposition (HIBID) of Pt on a silicon wafer using the recently commercialized helium ion microscope (HIM) at 25 kV and low beam currents. The motivation of this work was to understand the impact of light, inert helium ions on deposition rate and structure purity, with some implications on the usefulness of HIM nano-machining for circuit modification. Two Pt-rich deposits with sub-micron dimensions were grown with HIBID at different ion beam currents. The pillar and substrate structure were studied using bright and dark field TEM images. The authors analyzed metal purity profile of the HIBID deposit on height using energy dispersive x-ray spectroscopy. The maximum Pt content measured reached 41%, which is the highest measured metal content of a HIBID-grown structure. TEM studies of the sub-surface damage to the Si shows more damage below the deposit grown at a higher beam current. The differences in amorphization layer thickness between the two different beam currents are discussed. A comparison to Pt deposition by Ga FIB and electron beam induced deposition is provided, along with conclusions regarding the usage of HIBID technology for circuit modification.

In situ study of heavy ion induced radiation damage in NF616 (P92) alloy

NF616 is a nominal 9Cr ferritic–martensitic steel that is amongst the primary candidates for cladding and duct applications in the Sodium-Cooled Fast Reactor, one of the Generation IV nuclear energy systems. In this study, an in situ investigation of the microstructure evolution in NF616 under heavy ion irradiation has been conducted. NF616 was irradiated to 8.4dpa at 50K and to 7.6dpa at 473K with 1MeV Kr ions. Nano-sized defects first appeared as white dots in dark-field TEM images and their areal density increased until saturation (∼6dpa). Dynamic observations at 50K and 473K showed appearance and disappearance of TEM-visible defect clusters under irradiation that continued above saturation dose. Quantitative analysis showed no significant change in the average size (∼3–4nm) and distribution of defect clusters with increasing dose at 50K and 473K. These results indicate a cascade-driven process of microstructure evolution under irradiation in these alloys that involves both the formation of TEM-visible defect clusters by various degrees of cascade overlap and cascade induced defect cluster elimination. According to this mechanism, saturation of defect cluster density is reached when the rate of defect cluster formation by overlap is equal to the rate of cluster elimination during irradiation.