TEM Grids Research Articles

Towards a method for quantitative evaluation of nanoparticle from suspensions via microarray printing and SEM analysis

As part of the development of a library of accurate and efficient methods for measurement of nanoparticle properties, we develop and optimize a method for the efficient analysis of nanoparticle size distribution from suspensions via microprinting and digital analysis of electron microscopy (SEM and TEM) images, with the ultimate aim of automated quantitative concentration analysis (calculated from drop volume). A series of different nanoparticle suspensions (gold, latex, and SiO2 in varying sizes and concentrations) were printed onto TEM grids in a 4 x 4 array in the concentration range 7×108 to 1×1011 nanoparticles/mL and imaged with SEM. Concentrations and printing conditions (temperature, relative humidity) were varied in order to minimize the coffee-ring effect.

(Invited) Synthesis and Characterizations of Various Van Der Waals Hetero-Nanotubes Based on Single-Walled Carbon Nanotubes

We have successfully realized the synthesis of one-dimensional (1D) van der Waals heterostructures with single-walled carbon nanotube (SWCNT) as a template. A typical 1D heterostructure is composed of SWCNT, boron nitride nanotube (BNNT), and molybdenum disulfide nanotube (MoS2NT), coaxially grown by serial chemical vapor deposition (CVD) steps [1]. Isolated SWCNTs, BN-CVD at high temperatures such as 1100 °C from ammonia borane, and MoS2-CVD from MoO3 and Sulfur are original key requirements. Recently, we have achieved the additional CVD growth of carbon nanotubes from ethanol-CVD. We can remove SWCNT from SWCNT@BNNT by gentle oxidation process because BNNT is thermally more stable than SWCNT [2]. By comparing optical properties of BNNT@MoS2NT and SWCNT@BNNT@MoS2NT, we found the strong photoluminescence (PL) from monolayer MoS2NT of BNNT@MoS2NT and the exciton energy transfer between SWCNT and MoS2NT through thin BNNT for SWCNT@BNNT@MoS2NT [2]. We expect to prove the inter-tube excitons from the ultrafast optical spectroscopy [3]. We can realize various hetero-nanotubes in different morphologies such as SWCNT thin film, pillar-suspended SWCNT, chirality separated SWCNT deposited on TEM grid, and bulk SWCNTs grown on zeolite-supported catalysts [4]. Simply with SWCNT@BNNT in a thin film form, the enhanced thermal conductance [5] is very promising for macroscopic applications of heterostructures. Because BNNT coating over SWCNT film will not influence the transparency in the visible range, those films are immediately applicable for a saturable absorber in mode-lock fiber lasers. In order to fabricate a practical electronic or optoelectronics devices, micro-meter long 1D van der Waals heterostructure SWCNT@BNNT@MoS2NT were prepared between Si pillars. After transferring to SiO2 substrates and fabricating metal electrodes, we have examined various device characteristics. The naturally p-doped SWCNT and n-type MoS2NT becomes a radial semiconductor–insulator–semiconductor (S-I-S) heterojunction diode [6]. Optoelectronic and electronic properties of such devices will be discussed.Part of this work was supported by JSPS KAKENHI Grant Numbers JP18H05329, JP20H00220, and by JST, CREST Grant Number JPMJCR20B5, Japan.

Pt/Ag Solid Solution Alloy Nanoparticles in Miscibility Gaps Synthesized by Cosputtering onto Liquid Polymers.

Pt/Ag solid solution alloy nanoparticles (NPs) with mean size below 3 nm were obtained with composition in miscibility gaps by cosputtering onto liquid polyethylene glycol (PEG, MW = 600). Adjusting the sputtering currents from 10 to 50 mA did not influence the particle sizes obviously but caused a substantial difference in the composition and distributions of Pt/Ag NPs. This is different from sputtered Pt/Au NPs where particle size is correlated with composition. For a pair of sputtering currents, the formed Pt/Ag alloy NPs have a range of compositions. The normal distribution with Pt of 60.2 ± 16.2 at % is observed for the Pt/Ag sample with a nominal Pt content of 55.9 at %, whereas Pt-rich (85.1 ± 14.0 at % Pt) and Ag-rich (19.8 ± 12.2 at % Pt) Pt/Ag samples with nominal Pt contents of 90.9 and 11.9 at % contain more pure Pt and pure Ag NPs, respectively. Different from NPs obtained in PEG, the sputtered NPs on TEM grids had more uniform composition for a longer sputtering time along with a significant increase of particle sizes. This reveals that PEG hindered the combination of NPs and clusters, resulting in small particle sizes even for long time sputtering and broader composition distributions. Thus, the samples obtained in PEG have the compositions mainly determined by the random atom combination in the vacuum chamber and possibly in initial landing of atom/clusters on the PEG surface.

Reprint of “Amorphous nickel titanium alloy film: A new choice for cryo electron microscopy sample preparation”

Cryo-electron microscopy (cryoEM) has become one of the most important approach for structural biology. However, barriers are still there for an increased successful rate, a better resolution and improved efficiency from sample preparation, data collection to image processing. CryoEM sample preparation is one of the bottlenecks with many efforts made recently, including the optimization of supporting substrate (e.g. ultra-thin carbon, graphene, pure gold, 2d crystal of streptavidin, and affinity modification), which was aimed to solve air-water interface problem, or reduce beam induced motion (BIM), or change particle distribution in the grid hole. Here, we report another effort of developing a new supporting substrate, the amorphous nickel-titanium alloy (ANTA) film, for cryoEM sample preparation as a layer of holey supporting film covering on TEM grid. Our investigations showed advantages of ANTA film in comparison with conventional carbon film, including much better electron conductivity and trace non-specific interaction with protein. These advantages yield less BIM and significantly improved particle distribution during cryoEM experiment of human apo-ferritn, thus resulting an improved reconstruction resolution from a reduced number of micrographs and particles. Unlike the pure gold film, the usage of the ANTA film is just same with the carbon film, compatible to conventional automatic cryoEM data collection procedure.

Polymer-assisted TEM specimen preparation method for oxidation-sensitive 2D materials

By structural and analytical TEM and scanning electron microscopy experiments we show that atomically-resolved structural characterization of oxidation-sensitive two-dimensional material is strongly hindered when the final step of the preparation process, the transfer to the TEM grid, is performed with a wet etching method involving bases or acids, interacting with the highly reactive sample surface. Here we present an alternative polymer-assisted and mechanical-exfoliation-based sample preparation method and demonstrate it on selected oxidation-sensitive transition metal phosphorus trisulfides and transition metal dichalcogenides. The analysis, obtained from the samples prepared with both of the methods clearly show that oxidation is the origin of discrepancy, the oxidation during the final preparation step is strongly reduced only when the new method is applied, and atomically-resolved structural characterization of the pristine structures is now possible.

Selective Area Growth and Transfer of High Optical Quality MoS2 Layers

AbstractThis study demonstrates that monolayer molybdenum disulfide (MoS2) can be grown on selective areas of a substrate by creating isolated microcavity reactors throughout the substrate in a chemical vapor deposition (CVD) process. The obtained MoS2 in the confined areas can be tuned from isolated triangular domains of few tens of microns to a continuous film with different thicknesses by modulating the growth parameters. In contrast, the growth on the open areas of the substrate leads to an inhomogeneous film. Using the confined‐CVD approach, the area‐selective growth of MoS2 domains and films on arbitrary substrates such as SiO2/Si, sapphire, gold‐patterned SiO2/Si substrates, and SiNx‐membrane‐supported TEM grid is shown. Raman and photoluminescence spectroscopy studies reveal that the confined‐CVD‐derived MoS2 layers have high crystal quality and superior optical performance when compared to mechanically exfoliated flakes. A novel and efficient methodology is further introduced for the selective transfer of the confined‐growth areas to pre‐patterned substrates, therefore allowing multiple use of a single growth sample. Finally, field‐effect transistor devices are made on individual domains and mobilities up to ≈6.8 cm2 V−1 s−1 measured. The confined‐CVD approach and the selective area transfer presented here can be implemented on other transition metal dichalcogenides and 2D materials in general.

Cathode-Electrolyte Interphase in Lithium Batteries Revealed by Cryogenic Electron Microscopy

Summary Cathode electrolyte interphase (CEI), the intimate coating layer formed on the positive electrode, has been thought to be critical. However, many aspects of CEI remain unclear. This originates from the lack of effective tools to characterize structural and chemical properties of these sensitive interphases at nanoscale. Here, we develop a protocol to preserve the native state and directly visualize the interface on the positive electrode using cryogenic electron microscopy. We find that under normal operation conditions, there does not exist an intimate coating layer at the single-particle level in carbonate-based electrolyte. However, upon brief external electrical shorting, a solid-electrolyte interphase, which usually forms on anodes, could form on cathodes and be electrochemically converted into a stable, conformal CEI in situ. The conformal CEI helps improve Coulombic efficiency and overall capacity retention of the battery. This generates a different perspective of CEI in commercial carbonate-based electrolytes than previously understood.

An assessment on how different collection methods impact thermal properties, surface functional groups, nanostructure and morphology of diesel particulate matter

Abstract This work assessed the effect of gathering particulate matter from the exhaust of an automotive diesel engine through: a vacuum pump using Teflon filters; a particle trap with stainless-steel wools; a thermophoretic probe with Lacey-carbon TEM grids, and a partial dilution mini tunnel with fiberglass filters, on PM thermal behavior (TGA), chemical functional groups on PM surface (FTIR), and nanostructure (Raman, XRD, HRTEM and TEM). Results showed that for TGA, particulate trap was the most suitable method. The degree of compactness of PM samples gathered with vacuum pump, affected thermogravimetric analysis. The significant uncertainties induced by PM sample preparation from mini tunnel make it unsuitable for TGA. FTIR results revealed that PM samples collected with vacuum pump were the most suitable method to analyze functional groups. PM from particulate trap was passive partially oxidized due to long collection times as evidenced by the 1640 cm−1 wavelength peak. Given that particulate trap method provides a large amount of PM sample, it would be recommendable to shorten enough collection time to avoid PM passive oxidation. Particulate trap and vacuum pump methods showed similar Raman and XRD results. Mini tunnel samples exhibited significantly higher AD3/AG and AD4/AG peaks due to filter fluorescence, which besides induced interference in XRD analysis. Particulate trap samples exhibited a pronounced peak in 2θ = 43° corresponding to stainless-steel contamination. Although it did not affect the lattice parameters from XRD, HRTEM was more suitable for nanostructural characterization. Particles gathered by thermophoretic probe do not require additional post-treatment, making this more suitable for nanostructural and fractal analysis. Results revealed that using a unique collection method may induce significant uncertainties depending on the PM specific property to be analyzed. It was found that a combination of particulate trap and thermophoretic probe methods would be suitable for PM thermal and nanostructural characterization.

Soot Particle Size Distribution, Regulated and Unregulated Emissions of a Diesel Engine Fueled with Palm Oil Biodiesel Blends

In this study, five fuels including pure diesel (B0), pure palm oil biodiesel (B100), and their blends (B10, B20, and B30) were investigated in relation to soot particle distribution and regulated and unregulated emission characteristics in a common rail direct injection (CRDI) diesel engine. The results indicated that CO, hydrocarbon (HC), and particulate matter (PM) regulated emissions were effectively controlled to a very low level by combining the addition of palm oil biodiesel (POB) to diesel with optimized engine operating conditions. Paper filters and TEM grids were used to capture the diesel particles. All the PM primary particles were less than 100 nm in diameter observed by TEM, and the average diameters of the PM primary particles for the biodiesel blends were distributed between 20 and 26 nm. Unregulated emissions such as trace metals including Pb, Mn, and Ba were found in the PM particles, and the xylene, toluene, and benzene unregulated emissions of B100 were reduced by 55.68%, 21.56%, and 18.32%, respectively, compared to those of B0. Therefore, POB is an excellent alternative fuel for diesel engines and has great application potential to solve the current pollution problems of regulated and unregulated emissions.

External feedback assisted reduction of the lasing threshold of a continuous wave random laser in a dye doped polymer film and demonstration of speckle free imaging

The applications of random laser (RL) are still restricted, due to its complexity, high lasing threshold, unstable nature, difficulty in tuning and modulating its light emission characteristics. However, here a low threshold, continuous wave (CW) RL system has been designed in a fluoresecent laser dye (namely DCM) -doped in a polymer film with ZnO micro-cabbages as scatterers. Interestingly, by putting the active medium inside an external feedback (ExFB) system, a narrowed and stable RL emission at ~598 nm is observed with the subsequent reduction of CW lasing threshold (CWITh) by ~2.4 times. The effective cavity length (Leff) has been varied by an ingenious approach to demonstrate the role of Leff over the RL emission characteristics and the experimental results are supported by a theoretical explanation. The statistical fluctuation in the position of generated modes over time and the role of pump volume amplification on the emission characteristics of the developed RL has been studied in detailed. Thus, it is found here that due to the presence of ExFB, reinjection of pump light into scattering-formed cavities has taken place which has led to the generation of stable RL modes with the reduction of CWITh. The temporal coherency of the ExFB based RL light is found to be ~3.2 times less than that of a conventional He–Ne laser light. As a result, we could demonstrate here speckle free imaging with much lowered value of speckle contrast (C) on two different model systems, such as commercially available carbon film-coated TEM grid and cell membrane of Allium cepa. It is expected that this report will open up new possibilities for the development of stable and tunable RLs with other laser dyes for various optoelectronic applications including in bio-imaging.

Atomic-Scale Studies of Overlapping Grain Boundaries between Parallel and Quasi-Parallel Grains in Low-Symmetry Monolayer ReS2

Summary Grain boundaries (GBs) are significant microstructures that dominate properties of polycrystalline two-dimensional (2D) materials. Low-symmetry rhenium disulfide monolayers provide an ideal platform to investigate diverse configurations of GBs and their orientation-dependent characteristics. Here, we utilize the preferential deposition of platinum-based nanoparticles on grain edges to rapidly locate nanoscale-wide overlapping GBs during microscopic-scale observation. Atomic-resolution investigations by aberration-corrected annular dark-field scanning transmission electron microscopy reveal diverse overlapping GBs constructed by parallel grains with transversal displacement. They prefer to align along several primary lattice directions with different interlayer atomic registries. Calculations show that the electronic band structures of overlapping GBs are strongly direction dependent, suggesting their potential in tunable electronic and photonic devices. Incommensurate overlapping GBs formed by quasi-parallel grains with ultrasmall twist angles are also observed. These results unveil the rich polymorphism of GBs and new opportunities to tailor properties of anisotropic 2D materials via GB engineering.

Ligand Incorporation into Protein Microcrystals for MicroED by On-Grid Soaking

A high throughout method for soaking ligands into protein microcrystals on TEM grids is presented. Every crystal on the grid is soaked simultaneously using only standard cryoelectron microscopy vitrification equipment. The method is demonstrated using proteinase K microcrystals soaked with the 5-amino-2,4,6-triodoisophthalic acid (I3C) magic triangle. A soaked microcrystal is milled to a thickness of approximately 200nm using a focused ion beam, and MicroED data are collected. A high-resolution structure of the protein with four ligands at high occupancy is determined. Both the number of ligands bound and their occupancy is higher using on-grid soaking of microcrystals compared with much larger crystals treated similarly and investigated by X-ray crystallography. These results indicate that on-grid soaking ligands into microcrystals results in efficient uptake of ligands into protein microcrystals.

Nanostructural and morphological characteristics of single soot aggregates during low-temperature oxidation

In this paper the evolution of morphological and nanostructural properties of soot primary particles during low-temperature oxidation with oxygen is presented. Soot primary particles and aggregates from three soot samples with varying morphological and nanostructural initial properties were investigated by high-resolution transmission electron microscopy (HRTEM) at consecutive steps of oxidation. Soot samples were deposited on a TEM grid and then oxidized repetitively. After each oxidation step labelled identical aggregates were scanned and reanalyzed by HRTEM. Size distributions of primary particles and their nanostructure was tracked using an image analysis algorithm. The oxidation conditions (temperature 850 K, O2 concentration 5% by volume) correspond to those of the real application, e.g. for regeneration of particle filters.The tracking of different aggregates revealed that the morphological changes of the primary particles are determined by the predominant oxidation mode, which is governed by the nanostructure of the primary particles. Extended graphene layers favor internal oxidation, while bent, short and reactive layers favor both, external and internal oxidation. In surface oxidation mode, primary particles do not shrink homogeneously, but rather form a blackberry-like cluster of smallest nucleated particles.While a partly expansion of graphene layers is detected in the early stages of oxidation, the number density of graphene layers gradually decreases with increasing oxidation time. Additionally, graphene layers are oxidized by fragmentation until final degradation. Tracking of selected primary particles at different positions within the aggregate brought about that each primary particle is subjected to its own oxidation history. Therefore, each observed and analyzed primary particle possibly exhibits a different oxidation stage at the same oxidation time.

Thermophoretic particle sampling on a TEM grid: A new design for sample preparation with high spatial accuracy

Thermophoretic particle sampling on a TEM grid: A new design for sample preparation with high spatial accuracy

Looking at Silver-Based Nanoparticles in Environmental Water Samples: Repetitive Cloud Point Extraction Bridges Gaps in Electron Microscopy for Naturally Occurring Nanoparticles.

The growing use of silver-based nanoparticles (Ag-b-NPs) in everyday products goes hand in hand with their release into the environment, resulting in ng L-1 traces in natural water bodies. In order to assess their fate, possible transformations and ecotoxicology-essential information to proper risk assessment-particle size, shape, and chemical composition have to be determined. Transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (TEM-EDX) is a powerful tool for determining these particle characteristics, but it requires high particle concentrations in order to produce statistically reliable results. In this study, we will present the extraction of Ag-b-NPs at environmentally relevant concentrations down to 5 ng L-1 from artificial as well as environmental water samples via cloud point extraction on a repetitive basis. The combination with an on-grid centrifugation technique ensures an efficient concentration and deposition of the extracted particles onto the TEM grid for subsequent TEM-EDX measurements. Furthermore, electron microscopy investigations were supplemented by single particle inductively coupled plasma mass spectrometry (sp-ICP-MS) measurements. Ag-b-NPs were successfully visualized and characterized at environmentally relevant concentrations of 5 ng L-1 with TEM-EDX and sp-ICP-MS measurements. Their size, shape, and chemical composition were not affected by the sample preparation.

Electric Field‐Controlled Synthesis and Characterisation of Single Metal–Organic‐Framework (MOF) Nanoparticles

AbstractAchieving control over the size distribution of metal–organic‐framework (MOF) nanoparticles is key to biomedical applications and seeding techniques. Electrochemical control over the nanoparticle synthesis of the MOF, HKUST‐1, is achieved using a nanopipette injection method to locally mix Cu2+ salt precursor and benzene‐1,3,5‐tricarboxylate (BTC3−) ligand reagents, to form MOF nanocrystals, and collect and characterise them on a TEM grid. In situ analysis of the size and translocation frequency of HKUST‐1 nanoparticles is demonstrated, using the nanopipette to detect resistive pulses as nanoparticles form. Complementary modelling of mass transport in the electric field, enables particle size to be estimated and explains the feasibility of particular reaction conditions, including inhibitory effects of excess BTC3−. These new methods should be applicable to a variety of MOFs, and scaling up synthesis possible via arrays of nanoscale reaction centres, for example using nanopore membranes.

Electric Field‐Controlled Synthesis and Characterisation of Single Metal–Organic‐Framework (MOF) Nanoparticles

Achieving control over the size distribution of metal–organic‐framework (MOF) nanoparticles is key to biomedical applications and seeding techniques. Electrochemical control over the nanoparticle synthesis of the MOF, HKUST‐1, is achieved using a nanopipette injection method to locally mix Cu2+ salt precursor and benzene‐1,3,5‐tricarboxylate (BTC3−) ligand reagents, to form MOF nanocrystals, and collect and characterise them on a TEM grid. In situ analysis of the size and translocation frequency of HKUST‐1 nanoparticles is demonstrated, using the nanopipette to detect resistive pulses as nanoparticles form. Complementary modelling of mass transport in the electric field, enables particle size to be estimated and explains the feasibility of particular reaction conditions, including inhibitory effects of excess BTC3−. These new methods should be applicable to a variety of MOFs, and scaling up synthesis possible via arrays of nanoscale reaction centres, for example using nanopore membranes.

Amorphous nickel titanium alloy film: A new choice for cryo electron microscopy sample preparation

Cryo-electron microscopy (cryoEM) has become one of the most important approach for structural biology. However, barriers are still there for an increased successful rate, a better resolution and improved efficiency from sample preparation, data collection to image processing. CryoEM sample preparation is one of the bottlenecks with many efforts made recently, including the optimization of supporting substrate (e.g. ultra-thin carbon, graphene, pure gold, 2d crystal of streptavidin, and affinity modification), which was aimed to solve air-water interface problem, or reduce beam induced motion (BIM), or change particle distribution in the grid hole. Here, we report another effort of developing a new supporting substrate, the amorphous nickel-titanium alloy (ANTA) film, for cryoEM sample preparation as a layer of holey supporting film covering on TEM grid. Our investigations showed advantages of ANTA film in comparison with conventional carbon film, including much better electron conductivity and trace non-specific interaction with protein. These advantages yield less BIM and significantly improved particle distribution during cryoEM experiment of human apo-ferritn, thus resulting an improved reconstruction resolution from a reduced number of micrographs and particles. Unlike the pure gold film, the usage of the ANTA film is just same with the carbon film, compatible to conventional automatic cryoEM data collection procedure.

Chemical kinetics for operando electron microscopy of catalysts: 3D modeling of gas and temperature distributions during catalytic reactions

In situ environmental transmission electron microscopy (ETEM) is a powerful tool for observing structural modifications taking place in heterogeneous catalysts under reaction conditions. However, to strengthen the link between catalyst structure and functionality, an operando measurement must be performed in which reaction kinetics and catalyst structure are simultaneously determined. To determine chemical kinetics for gas-phase catalysis, it is necessary to develop a reliable chemical engineering model to describe catalysis as well as heat and mass transport processes within the ETEM cell. Here, we establish a finite element model to determine the gas and temperature profiles during catalysis in an open-cell operando ETEM experiment. The model is applied to a SiO2-supported Ru catalyst performing CO oxidation. Good agreement is achieved between simulated compositions and those measured experimentally across a temperature range of 25 – 350 °C. In general, for lower conversions, the simulations show that the temperature and gas are relatively homogeneous within the hot zone of the TEM holder where the catalyst is located. The uniformity of gas and temperature indicates that the ETEM reactor system behavior approximates that of a continuously stirred tank reactor (CSTR). The large degree of gas-phase uniformity also allows one to estimate the catalytic conversion of reactants in the cell to within 10% using electron energy-loss spectroscopy. Moreover, the findings indicate that for reactant conversions below 35%, one can reliably evaluate the steady-state reaction rate of catalyst nanoparticles that are imaged on the TEM grid.

Analysis of Electron Transparent Beam-Sensitive Samples Using Scanning Electron Microscopy Coupled With Energy-Dispersive X-ray Spectroscopy.

Scanning electron microscopy, coupled with energy-dispersive X-ray spectroscopy (EDS), is a powerful tool used in many scientific fields. It can provide nanoscale images, allowing size and morphology measurements, as well as provide information on the spatial distribution of elements in a sample. This study compares the capabilities of a traditional EDS detector with a recently developed annular EDS detector when analyzing electron transparent and beam-sensitive NaCl particles on a TEM grid. The optimal settings for single particle analysis are identified in order to minimize beam damage and optimize sample throughput via the choice of acceleration voltage, EDS acquisition time, and quantification model. Here, a linear combination of two models is used to bridge results for particle sizes, which are neither bulk nor sufficiently thin to assume electron transparent. Additionally, we show that the increased count rate obtainable with the annular detector enables mapping as a viable analysis strategy compared with feature detection methods, which only scan segmented regions. Finally, we discuss advantages and disadvantages of the two analysis strategies.