Low-voltage Scanning Electron Microscopy Research Articles

Design and optimization of a conical electrostatic objective lens of a low-voltage scanning electron microscope for surface imaging and analysis in ultra-high-vacuum environment

Low-voltage scanning electron microscopy (LV-SEM) with landing energies below 5 keV has been widely used due to its advantages in mitigating the damage and charging effects to a specimen and enhancing surface information due to small interaction volume of electrons inside a specimen. Additionally, for elemental analysis of the surfaces of bulk specimens with Auger electron spectroscopy (AES) or electron energy loss spectroscopy (EELS), ultra-high-vacuum (UHV) environment is essential to maintain clean surfaces without the absorption of gas molecules during the electron beam irradiation for the acquisition of spectral data. In this study, we propose the optimal design and condition of a conical Electrostatic Objective Lens (EOL) for a UHV LV-SEM to achieve the high spatial resolution and secondary electron (SE) detection efficiency. The EOL is composed of only the three electrodes (retarding, focusing and booster electrodes) and the insulators, which is suitable for maintaining a UHV environment with less out-gassing. The cone angle of the EOL is determined as 60° to integrate a spectrometer in the UHV LV-SEM and in a large size and a higher tilt angle of the sample. Through the optimization with the simulations, the EOL achieves the minimized spherical and chromatic aberration coefficients of 0.05 and 0.03 mm at the sample side, respectively, at the landing energy of 50 eV and the shortest working distance (WD) of 1 mm for high-resolution imaging. In addition, the probe diameter of the optimized EOL is 2.3 nm at 1 keV and 5.7 nm at 50 eV with a WD of 1 mm and a probe current of 10 pA, which are comparable to previously studied compound objective lenses with magnetic and electrostatic lenses. Using a longer WD of 4 mm for analysis, the probe diameter was 5.4 nm at 1 keV and the SE detection efficiency was 83.3 % owing to the separated scintillator detector structure from the booster electrode.These results imply that the optimized EOL has the potential to be applied to a high-performance UHV LV-SEM for the surface imaging and analysis with a simple system configuration.

Migration of binder and conductive agent during drying process of Li-ion battery cathodes

Drying of an electrode film during a wet coating process for Li-ion batteries often leads to a heterogeneous distribution of the binder and conductive agent in the film thickness direction. Because this heterogeneous distribution affects battery performance and durability, understanding and controlling the migration behavior are important. Herein, the distribution of the components (active material/conductive agent/binder) of a cathode is investigated by a novel method and their relationship with the electrode properties is determined. The binder distribution is investigated via two methods: pyrolysis gas chromatography mass spectrometry (Py-GC/MS) analysis of cut electrodes, and low-voltage scanning electron microscopy with energy-dispersive X-ray spectroscopy. In the sample dried at 30 °C, more binder and conductive agent exists in the bottom layer. With increasing drying temperature, the binder and conductive agent migrate from the bottom to the surface because they are transported by capillary-driven convective flow through the pores between the active material particles. Drying at high temperatures causes migration, resulting in reduced adhesion between the electrode film and the current collector, and increases the electrode resistance. The Py-GC/MS method of characterizing the cut electrodes is shown to be a complementary method that can analyze a wider area than cross-sectional observation.

SARS-CoV-2 Impact on Red Blood Cell Morphology.

Severe COVID-19 alters the biochemical and morphological characteristics of blood cells in a wide variety of ways. To date, however, the vast majority of research has been devoted to the study of leukocytes, while erythrocyte morphological changes have received significantly less attention. The aim of this research was to identify erythrocyte morphology abnormalities that occur in COVID-19, compare the number of different poikilocyte types, and measure erythrocyte sizes to provide data on size dispersion. Red blood cells obtained from 6 control donors (800-2200 cells per donor) and 5 COVID-19 patients (800-1900 cells per patient) were examined using low-voltage scanning electron microscopy. We did not discover any forms of erythrocyte morphology abnormalities that would be specific to COVID-19. Among COVID-19 patients, we observed an increase in the number of acanthocytes (p = 0.01) and a decrease in the number of spherocytes (p = 0.03). In addition, our research demonstrates that COVID-19 causes an increase in the median (p = 0.004) and interquartile range (p = 0.009) when assessing erythrocyte size. The limitation of our study is a small number of participants.

A Retrofittable Photoelectron Gun for Low-Voltage Imaging Applications in the Scanning Electron Microscope.

Low-voltage scanning electron microscopy is a powerful tool for examining surface features and imaging beam-sensitive materials. Improving resolution during low-voltage imaging is then an important area of development. Decreasing the effect of chromatic aberration is one solution to improving the resolution and can be achieved by reducing the energy spread of the electron source. Our approach involves retrofitting a light source onto a thermionic lanthanum hexaboride (LaB6) electron gun as a cost-effective low energy-spread photoelectron emitter. The energy spread of the emitter's photoelectrons is theorized to be between 0.11 and 0.38 eV, depending on the photon energy of the ultraviolet (UV) light source. Proof-of-principle images have been recorded using this retrofitted photoelectron gun, and an analysis of its performance is presented.

Imaging mechanism and contrast separation in low-voltage scanning electron microscopy imaging of carbon nanotube arrays on SiO2/Si substrate

Polymer-sorted high-density carbon nanotube (CNT) arrays have shown great potential to extend the silicon-based Moore's law. Imaging the CNT arrays on insulators like SiO2/Si using low-voltage scanning electron microscopy (LVSEM) to acquire array information like the alignment, density, and distribution of residual polymers is necessary. Such a task remains challenging due to the nanoscale CNT body (1–2 nm in diameter), nanoscale tube-to-tube separation (1–10 nm), the broadening of the apparent diameter, and the complex image contrast caused by the insulating substrate and polymer residues. In this study, the imaging mechanism for this system is investigated. Two methods are developed to separate the three dominant contrasts, i.e. topographic contrast, charge contrast, and material contrast, by selecting the take-off angle and energy of the emitted electrons as enabled by changing the working distance or the deceleration voltage. The contrast formation and separation mechanism is further confirmed by the dynamic contrast evolution due to the electron-beam-induced deposition of amorphous carbon. The contrast separation method is further applied to an individual CNT, reducing its apparent diameter from 36 nm to 6 nm. This result hints at the potential for LVSEM to count the density exceeding 150 CNTs/μm of CNT arrays. Finally, a comparative study of LVSEM and transmission electron microscopy confirms the failure of LVSEM to resolve CNTs in a bundle. The results suggest that the density of CNT arrays may be underestimated in reported SEM data. The proposed method can serve as a useful tool for further study and application of arrayed CNTs.

Phase relations in heat treated sodium borosilicate glasses

Sodium borosilicate glasses are processed to porous glasses as well as to Vycor™ type glasses via phase separation and selective leaching. Both materials consist mainly of SiO2. Thermal treatment inducing phase separation is crucial for microstructure development. Sodium borosilicate glasses with molar compositions of 8Na2O.21B2O3.71SiO2 and 8Na2O.28B2O3.64 SiO2 were melted, rapidly cooled and investigated by thermal analysis and scanning electron microscopy. The glasses were thermally treated for 120 h at 630 to 730°C, and then leached, first for 72 h in 0·1 M HCl at 60°C, and subsequently for 4 h in 0·5 M NaOH at 30°C. X-ray fluorescence was applied to characterise the chemical compositions. Microstructure development was first analysed by differential thermal analysis and dilatometry, and the pore structure was characterised by Hg porosimetry and N2 adsorption. Heat treated glasses were then analysed by low voltage scanning electron microscopy, combined in one case with chemical analysis by energy dispersive x-ray analysis. The results are discussed with respect to phase relations. After long term heat treatment, at least three phases exist in two independent metastable two-phase equilibria on different size and time scales.

Physical vapor deposited coatings on high Ni content NMC811 Li-ion battery cathode powder

The storage capacity and reliability of Lithium-ion batteries has increased at an amazing rate in the past years. They are operated in millions of electrically powered devices, but still their components are subject to continuous optimization.In this paper we focus on the cathode material of the system, which is based on powders of Nickel-Manganese-Cobalt (NMC) mixed oxides. They store Lithium-ions by intercalation between their oxidic planes. A current trend in the development of these mixed oxides is to increase the Ni content. This would reduce the need for Co, an expensive material mined under hazardous conditions. However, a high Ni content has several drawbacks, like the irreversible occupation of Li sites by Ni, structural phase transformations upon Li removal or surface contaminations caused by the chemical reactivity of Ni.We address the last point by passivating the surface of the powder with a thin layer of inert oxide. Alumina (Al2O3) or Zirconia (ZrO2) with an approximate thickness of 0.2–1.6 nm were deposited by reactive magnetron sputtering on high Ni content NMC 811 powder with an average particle size of approx. 10 μm using a rotating and tumbling powder container. The average thickness and uniformity of the coating could be correlated to the electrical resistance of the powder, which was determined by a custom-built system for powder resistance measurement under variable compression force. These measurements were confirmed by imaging the coatings on selected powder particles using low voltage SEM. Generally, the coatings were found to be uniform on both, individual grains and large ensembles of powder particles. The impact of the coating on the release of Li-ions was checked by Li leaching experiments. The coating reduced the Li release rate by approximately 10 %, which could be tolerated in a battery.

Characterization and quantification of oxidative stress induced particle debris from polypropylene surgical mesh

AbstractExplanted polypropylene (PP) surgical mesh has frequently been reported to show surface alterations, such as cracks and flaking. However, to date the consequence of PP mesh degradation is not clearly understood, particularly its potential to influence the biological host response of surrounding tissues. Of particular concern is a possible host reaction to polypropylene particles released through degradation of surgical mesh in vivo. This concern is driven by previous studies which have postulated that an oxidative stress environment has the potential to etch away particles from the surface of a PP fibers. The release of such particles is of considerable significance as particles in the nano‐ to micro range have been shown to have the capacity to irritate cells and stimulate the immune system. The authors are not aware of any previous studies that have attempted to characterize, quantify or identify any particles released from PP mesh after exposure to an oxidative stress environment. Characterization of the PP mesh, post oxidative stress exposure, including identification of particles was achieved through application of a range of techniques: low voltage‐scanning electron microscopy (LV‐SEM), pyrolysis gas chromatography mass spectrometry (Pyr‐GCMS), nano‐Fourier transform infrared spectroscopy (nano‐FTIR), scattering‐type, scanning near‐field optical microscopy (s‐SNOM), atomic force microscopy (AFM), attenuated total reflectance‐Fourier transform infrared spectroscopy (ATR‐FTIR) and uniaxial tensile testing. The findings of this study indicate that oxidative stress alone is a major factor in the production of PP particle debris. PP debris identified within solution, using Pyr‐GCMS, was shown to be in order of the micron scale.

Characterization in respect to degradation of titanium-coated polypropylene surgical mesh explanted from humans.

Titanium-coated polypropylene (Ti-PP) mesh was introduced in 2002 as a surgical mesh for the treatment of hernias and shortly after for pelvic floor surgery, with the aim of improving biocompatibility when compared to non-titanised/regular PP mesh implants. The application of a titanium coating could also be beneficial to address concerns regarding the exposure of PP in an in vivo environment. Many studies have shown that PP, although it is widely accepted as a stable polymer, is subject to oxidation and degradation, such degradation affects the mechanical behavior, that is, the stiffness and tensile strength of PP mesh. Despite the wide clinical use of Ti-PP surgical meshes, no study has yet investigated the residual material properties post clinical deployment and subsequent explantation. In this study, two explanted Ti-PP mesh samples each having different incorporation durations from two patients were examined. Material analysis conducted within this study includes the following techniques: attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, low voltage - scanning electron microscopy (LV-SEM), backscattered electron (BSE) imaging, energy dispersive X-ray spectroscopy (EDS) and secondary election hyperspectral imaging (SEHI). The hypothesis of this study is that the Ti coating successfully shields the PP mesh from oxidative stress in vivo and thus protects it from degradation. The results of this analysis show for the first time evidence of bulk oxidation, surface degradation, and environmental stress cracking on explanted Ti-PP meshes.

Selective and reversible surface complexation of aqueous palladium(II) by polycarboxylate (pyromellitic acid) functionalized hybrid aerogel sorbent

The recovery of palladium compounds from aqueous solutions containing other metal salts is a challenging task of environmental technology. One solution is the development of selective sorbents by the appropriate design of surface functionality. For this purpose, a mesoporous, polycarboxylate (pyromellitic acid monoamide) functionalized silica-gelatin aerogel was prepared by the sol-gel method and supercritical drying. It is characterized using low voltage scanning electron microscopy (LV-SEM), N2-sorption porosimetry, small angle neutron scattering (SANS), infrared spectroscopy (FT-IR), solid-state nuclear magnetic resonance spectroscopy (ssNMR) and X-ray photoelectron spectroscopy (XPS). Its aqueous phase Zeta potential was investigated as a function of pH. The aerogel has excellent selectivity for binding Pd(II) around pH = 2.0 in the simultaneous presence of Pt(II), Pt(IV) and six other metal ions with a very high sorption capacity of 369 mg g−1 at pH = 2.3. The quantitative recovery of Pd(II) and the regeneration of the sorbent is possible using 5 mM methionine. The mechanism of binding is the reversible surface complexation of Pd(II) via the O-atoms of the adjacent carboxylate groups of the aerogel, as shown by XPS. This high stability coordination mode accounts for the excellent selectivity of the sorbent, and prevents the reduction of Pd(II).

Role of landing energy in e-beam metrology of thin photoresist for high-numerical aperture extreme ultraviolet lithography

BackgroundLithography advancements require to resist layer thickness reduction, essential to cope with the low depth of focus (DOF) characteristic of high numerical aperture extreme ultraviolet lithography (HNA EUVL). However, such a requirement poses serious challenges in terms of resist process metrology and characterization, as patterns in thin resist suffer from low contrast, which may affect the performance of the edge detection algorithms used for image analysis, ultimately impacting metrology.AimInvestigate e-beam imaging using low landing energy (LE) settings as a possible way to address the thin resist film metrology issues.ApproachA low-voltage aberration-corrected SEM developed at Carl Zeiss is to image three thin resist thicknesses and two different underlayers, at various LE and number of frames. All images are analyzed using MetroLER software, to extract the parameters of interest [mean critical dimension (CD), line width roughness (LWR), and linescan signal-to-noise ratio (SNR)] in a consistent way.ResultsThe results indicate that mean CD and LWR are affected by the measurement conditions, as expected. Imaging through LE unravels two opposing regimes in the mean CD estimate, the first in which the mean CD increases due to charging and the second in which the mean CD decreases due to shrinkage. Additionally, the trend between LE and linescan SNR varies depending on the stack.ConclusionWe demonstrated the ability of low-voltage aberration-corrected SEM to perform thin-resist metrology with good flexibility and acceptable performance. The LE proved to be an important knob for metrology of thin resist.

Functionalizing aerogels with tetraazamacrocyclic copper(II) complexes: Nanoenzymes with superoxide dismutase activity

The copper(II) complexes of 1,4,7,10-tetraazacyclododecane (cyclen) and 1,4,8,11- tetraazacyclotetradecane (cyclam) were covalently immobilized in mesoporous silica aerogels by the sol–gel method using functionalized silica precursors. The modified macrocyclic precursors are characterized by mass spectrometry (MS) and solution phase nuclear magnetic resonance (NMR) spectroscopy. The supercritically dried aerogels are characterized using low voltage scanning electron microscopy (LV-SEM), N2-sorption porosimetry, infrared spectroscopy (FT-IR), electron paramagnetic resonance spectroscopy (EPR) and contrast variation small angle neutron scattering (SANS). The suspended aerogel particles act as nanoenzymes, because they have significant SOD activities, dramatically higher than the corresponding dissolved Cu(II) complexes. The most important factors responsible for the altered reactivities due to the covalent immobilization of the complexes were elucidated based on the compiled results of the characterization methods. These are: i) the formation of new chemical environments and Cu(II) coordination modes; ii) the effective separation of the active Cu(II) centers in the aerogels; and iii) the confinement effect operative in the nanoporous network. As a perspective, the present functionalized aerogel microparticles can be developed into passive targeting antioxidant pharmaceutical agents administered locally or subcutaneously.

A Novel Monochromator with Offset Cylindrical Lenses and Its Application to a Low-Voltage Scanning Electron Microscope.

Low-voltage scanning electron microscopes (LV-SEMs) are widely used in nanoscience. However, image resolution for SEMs is restricted by chromatic aberration due to energy spread of the electron beam at low acceleration voltage. This study introduces a new monochromator (MC) with offset cylindrical lenses (CLs) as one solution for LV-SEMs. The MC optics, with highly excited CLs in offset layouts, has advantageous high performance and simple experimental setup, making it suitable for field emission LV-SEMs. In a preliminary evaluation, our MC reduced the energy spread from 770 to 67 meV. The MC was integrated into a commercial SEM equipped with an out-lens (a conventional objective lens without immersion magnetic or retarding electric fields) and an Everhart–Thornley detector. Comparing SEM images under two conditions with the MC turned on or off, the spatial resolution was improved by 58% at 0.5 and 1 keV. The filtering effect of the MC decreased the probe current with a ratio (i.e., transmittance) of 5.7%, which was consistent with estimations based on measured energy spreads. To the best of our knowledge, this is the first report on an effective MC with higher-energy resolution than 100 meV and the results offer encouraging prospects for LV-SEM technology.

The Design of a Reflection Electron Energy Loss Spectrometer Attachment for Low Voltage Scanning Electron Microscopy

This paper presents the design of a reflection electron energy spectrometer (REELS) attachment for low voltage scanning electron microscopy (LVSEM) applications. The design is made by carrying out a scattered electron trajectory ray paths simulation. The spectrometer attachment is small enough to fit on the specimen stage of an SEM, and aims to acquire nanoscale spatially resolved REELS information. It uses a retarding field electrostatic toroidal sector energy analyzer design, which is able to lower the kinetic energies of elastically backscattered electrons to pass energies of 10 eV or less. For the capture of 1 keV BSEs emitted in the polar angular range between 40 to 50°, direct ray-tracing simulations predict that the spectrometer attachment will have an energy resolution of around 0.4 eV at a pass energy of 10 eV, and 0.2 eV at a pass energy of 5 eV. This predicted performance will make it a suitable REELS attachment for SEMs that use field emission electron sources.

Impact of order of catalytic ethylene and propylene polymerization on nanometer scale isotactic polypropylene‐polyethylene blend morphology in nascent heterophasic granules revealed by low voltage scanning electron microscopy and scanning transmission electron microscopy

AbstractNew heterophasic granules comprised of two high molecular weight semi‐crystalline components ‐ polyethylene (PE) and isotactic polypropylene (iPP) ‐ are prepared from a MgCl2 supported Zeigler‐Natta catalyst. The impact of order of monomer addition on granule morphology and extent of mixing of PE and iPP in these monomer‐to‐polymer scenarios are examined. In one polymerization propylene is followed by ethylene (iPP‐PE; 1), and in the second ethylene is followed by propylene (PE‐iPP; 2). Detailed morphological assessments were carried out on RuO4 stained sections of the nascent granules of these heterophasic products using low voltage scanning electron microscopy (LVSEM) and scanning transmission electron microscopy (STEM). In these side‐by‐side granule morphology comparisons, LVSEM, which has not been used for granule examinations, has proved to be invaluable, typically providing insights into phase morphology that STEM does not. Both polymerizations 1 and 2 result in intimate mixing of PE and iPP on the tens to hundreds of nanometer scale. However, morphological outcomes for 1 and 2 are markedly different. In the case of 1, comprising 31 wt% iPP and 69 wt% of PE (the second‐grown phase), a reticulated mesh network of PE is readily observed coursing through much of the first produced iPP globular and sub‐globular matrix. The PE fibrils that comprise this network are remarkably uniform in diameter; approximately 100–150 nm. This aspect of the morphology is consistent with a PE sheath encapsulating both iPP globules and sub‐globules commonly found in iPP homopolymer granules made with MgCl2 catalysts. This morphology is similar to that of the most extensively studied heterophasic granules, classic iPP‐ethylene‐propylene rubber (EPR) impact copolymer (ICP), where the second grown EPR fills in space between and around the iPP globules and sub‐globules. Thus, the dominant morphology of 1 is consistent with the often‐called pore‐filling model. Using the same catalyst and arriving at a similar global composition (65 wt% PE and 35 wt% iPP), sample 2 is produced through the reverse order of monomer addition. The dominant morphology for 2 cannot be explained by the pore‐filling model. Instead, LVSEM most clearly shows that the second grown iPP phase, is finely dispersed throughout the PE matrix (not outside it) as irregularly shaped inclusions that are nominally 100 to 400 nm in diameter, so the dominant morphology in 2 is consistent with the proposed but not previously observed core‐shell model. The STEM results for 2 also reveal the presence of primitive PE spherulites and organized PE lamellae in the granules; structures not found in 1 and apparently not reported before in polyethylene homopolymer granules. These structures form likely from heat released during ethylene polymerization in the first step in 2. In LVSEM, the PE and iPP phases provide different amplitude contrast (grayscale) that is useful for calibration. In the LVSEM images of both samples 1 and 2, non‐binary strong grayscale gradients are observed in many regions in the micrographs. These suggest, but do not yet prove, fine dispersion of some PE in the first formed iPP (1) as well as a fine dispersion, perhaps on the ~10 nm scale, of some iPP in the first formed PE (2). So even granules of 1 appear to have some hybrid quality; primarily pore‐filling, with some core‐shell result as well. Finally, in STEM images of both 1 and 2 well‐formed, long PE lamella provide occasional marked contrast (especially at boundaries) with nascent iPP, which exists in a microparacrystalline state (short, poorly formed crystals). Regardless of the morphological complexity, the exceedingly fine mixing of the two semi‐crystalline phases accomplished during dilation of the granules to accommodate each second produced crystallizable polymer offers the potential for utility of these heterophasic granules in materials design (grafting and cross‐coupling, for example).

Direct visualization of highly resistive areas in GaN by means of low-voltage scanning electron microscopy

The damage-induced voltage alteration (DIVA) contrast mechanism in scanning electron microscope (SEM) at low electron energy has been presented as a fast and convenient method of direct visualization of increased resistivity induced by energetic ions irradiation in gallium nitride (GaN). Epitaxially grown GaN layers on sapphire covered with a metallic masks with etched windows were subjected to He2+ irradiations at 600 keV energy. The resulting two-dimensional damage profiles at the samples cross-sections were imaged at SEM at different e-beam currents and scan speeds. The gradual development of image contrast was observed with the increase of cumulative charge deposited by electron beam irradiation, to finally reach the saturation level of the contrast related to the local resistivity of the ion-irradiated part of GaN.The presented method allows one to directly visualize the ion-irradiated zone even for the lowest resistivity changes resulting from ion damage, i.e. all levels of insulation build-up in GaN upon irradiation with ions. Taking into account that it is not possible to apply the etch-stop technique by wet chemistry to GaN, it makes the presented technique the only available method of visualization of highly resistant and insulating regions in GaN-based electronic devices.Main aim of the presented work is to get a deeper insight into a DIVA contrast in GaN with the special emphasize to discuss the role of rastering speed and electron beam current, i.e. details of charge build-up ion the sample surface.

Identification and Formation Mechanism of a New Interstitial Defect Found in Ion Implanted Silicon

For 40 years, extended defects are found in silicon after ion implantation and annealing. Widely studied for shallow implantation, thermal evolution of these defects follow the same path in the particular case of a Si layer transferred by Smart Cut™ technology.Being extrinsic or intrinsic precipitates, these defects are formed under supersaturated condition and grow by interchanging interstitials, or vacancies, during annealing. All along their growth, the precipitates rearrange them-selves to transform into a more stable structure.A transferred Si layer needs a combination of very high-temperature annealing in neutral and oxidizing atmospheres to thin and smooth the fractured surface. Despite these treatments, irregular topography has been detected on the extremely smooth surface. Studying them in detail, we have found a new type of interstitial-type crystalline defects, extremely stable, that we have named “tent-like” defects in reference to their shape. The presence of such structures was a surprise as it is generally believed that the high-temperature treatment following fracture was sufficient to dissolve all the precipitates initially present in the transferred Si layer.It is the goal of this work to report the characteristics, formation mechanism and origin of these structures. From that, we infer, and then experimentally confirm the process conditions promoting or hampering their formation.For this work, 300 nm-thick Si layers were transferred by using H+ and other species, wafer bonding and thermal initiation of the fracture. Afterwards, the transferred layers were subjected to different annealing steps, oxidizing or not, then annealed at temperatures up to 1200°C under Ar atmosphere.Figure 1a is a typical Scanning Electron Microscopy (SEM) image of one of these structures. Such images were obtained using a low voltage SEM with the ability to image mono-atomic steps separating flat (001) terraces all over the surface of a 300 mm wafer. Step bunching imaged on the right of the defect, as contour lines, reveals some “erosion” around the rectangular shape, at the origin of a shallow hole which was initially detected. In general, these structures are elongated along one of the two in-plane <110> directions (Fig. 1a). Their length increases during oxidizing annealing whereas their width stays almost constant. Since silicon oxidation results in the injection of Si interstitials into the underlying crystal, this growth suggests they are extrinsic defects i.e., contain excess Si atoms.Figure 1b is a HREM image of such a defect, cut in its body part, as shown in Fig. 1a. Two intersecting {111} stacking faults (SF) define a V-shape defect (Fig. 1b). Figure 1c shows the geometric phase distributions around the structure obtained by Dark Field Electron Holography (DFEH) for g= 004, g=111 and g=-1-11. From such images (no phase jump for g=004 and mirror symmetry between g=111 and g=-1-11), the Burgers vector of the dislocation, seen edge-on at the SFs intersection, is found to be 1/6[-1-10], i.e. that of a stair-rod Lomer-Cottrell dislocation. This finding suggests that the tent-like defect probably results from the dissociation of straight dislocation segments, each following a path such as 1/3<-1-11>=1/6<-1-10>+1/6<-1-12>.Based on these experimental data, we propose a scenario describing the formation of such structures. At the beginning an interstitial loop (Frank or perfect) was buried in the matrix. Such loops are known to form in ion implanted silicon annealed at high enough temperature. During oxidation, such a loop can grow up to, or may be cut by, the SiO2/Si interface. It then forms a half-loop. Based on energetic criteria, we show that such a half-loop tends to elongate and becomes segmented. During high-temperature annealing, the dislocation lines dissociate: a 2D defect transforms into a 3D “obtuse wedge elongated defect” bound by four {111} SFs and five segments of stair-rod Lomer-Cottrell dislocations. This dissociation is similar to the one describing the formation of tetrahedral defects from triangular Frank dislocation loops.In summary, we have found a new type of extended defects in Si, of interstitial character, which may appear as a result of the precipitation of silicon interstitials. This defect has not been identified before as the conditions for its formation are quite stringent. Beyond the process conditions under which they have been observed at first, the mechanisms which lead to their formation requires that a highly I-supersaturated region is initially located very close to a free surface (possibly an interface) where a half-dislocation loop can form and then dissociate, a condition rarely found in real cases with the notable exception of layers transferred by the Smart Cut™ process. Figure 1

Evaluation of Ionomer Distribution on Electrocatalysts for Polymer Electrolyte Fuel Cells by Use of a Low Acceleration Voltage Scanning Electron Microscope

The qualitative evaluation of the dispersion of prefluorosulfonic ionomer (PFSI) with different ionomer/carbon mixing ratios (I/C) using electron microscopy was carried out without the use of a stain treatment. Both low acceleration voltage transmission electron microscopy (LAV-TEM) and ultralow acceleration voltage scanning electron microscopy with a retarding method (ULV-SEM) use a characteristically low acceleration voltage, which allows the selective examination of the sensitive ionomer morphology. The high-performance charge-coupled device enables one to obtain high contrast ionomer images without the use of lead or cesium staining, which could otherwise result in morphological changes during these pre-treatments. The electrochemically active surface area of the polymer electrolyte fuel cell using Pt/GCB increased with increasing PFSI content and saturated at an ionomer/carbon weight ratio (I/C) of 1.2, where full coverage of the ionomer was detected by LAV-TEM. The ULV-SEM images showed the obvious occlusion of the primary and secondary pores of the Pt/GCB catalyst layers above I/C = 1.2. The nitrogen gas adsorption measurement, carried out by use of quenched solid-density-functional theory analysis, also supported the occlusion of the primary and secondary pores of the Pt/GCB catalyst layers above I/C = 1.2.

False Morphology of Aerogels Caused by Gold Coating for SEM Imaging.

The imaging of non-conducting materials by scanning electron microscopy (SEM) is most often performed after depositing few nanometers thick conductive layers on the samples. It is shown in this work, that even a 5 nm thick sputtered gold layer can dramatically alter the morphology and the surface structure of many different types of aerogels. Silica, polyimide, polyamide, calcium-alginate and cellulose aerogels were imaged in their pristine forms and after gold sputtering utilizing low voltage scanning electron microscopy (LVSEM) in order to reduce charging effects. The morphological features seen in the SEM images of the pristine samples are in excellent agreement with the structural parameters of the aerogels measured by nitrogen adsorption-desorption porosimetry. In contrast, the morphologies of the sputter coated samples are significantly distorted and feature nanostructured gold. These findings point out that extra care should be taken in order to ensure that gold sputtering does not cause morphological artifacts. Otherwise, the application of low voltage scanning electron microscopy even yields high resolution images of pristine non-conducting aerogels.

Understanding Surface Modifications Induced via Argon Plasma Treatment through Secondary Electron Hyperspectral Imaging.

Understanding the effects that sterilization methods have on the surface of a biomaterial is a prerequisite for clinical deployment. Sterilization causes alterations in a material's surface chemistry and surface structures that can result in significant changes to its cellular response. Here we compare surfaces resulting from the application of the industry standard autoclave sterilisation to that of surfaces resulting from the use of low‐pressure Argon glow discharge within a novel gas permeable packaging method in order to explore a potential new biomaterial sterilisation method. Material surfaces are assessed by applying secondary electron hyperspectral imaging (SEHI). SEHI is a novel low‐voltage scanning electron microscopy based characterization technique that, in addition to capturing topographical images, also provides nanoscale resolution chemical maps by utilizing the energy distribution of emitted secondary electrons. Here, SEHI maps are exploited to assess the lateral distributions of diverse functional groups that are effected by the sterilization treatments. This information combined with a range of conventional surface analysis techniques and a cellular metabolic activity assay reveals persuasive reasons as to why low‐pressure argon glow discharge should be considered for further optimization as a potential terminal sterilization method for PGS‐M, a functionalized form of poly(glycerol sebacate) (PGS).