Dynamic Transmission Electron Microscopy Research Articles

Dynamic Imaging of Ostwald Ripening by Environmental Scanning Transmission Electron Microscopy

AbstractThe first dynamic atomic resolution environmental scanning transmission electron microscope (ESTEM) study of the nanoparticle sintering of a model Cu system is reported. ESTEM confers the advantage of a Z‐contrast dependence in industrially representative conditions to provide enhanced visibility of sub‐nanometer particles when compared with TEM. The importance of this is demonstrated by the significant enhancement in the Ostwald ripening rate of model Cu nanoparticles in the presence of 3 Pa hydrogen, an effect that is independent of the substrates studied. Temperatures of 400–550 °C are shown to switch the operating regime of the rate‐limiting mechanism. Cu catalysts are used for methanol synthesis and hydrocarbon‐conversion processes for fuel cells, and the importance of observing these catalysts in their working states is demonstrated. Unique ESTEM observations of Ostwald ripening are combined with kinetic models to improve the technical understanding of catalyst deactivation mechanisms.

Organically modified layered zinc phenylphosphonate reinforced stereocomplex-type poly(lactic acid) nanocomposites with highly enhanced mechanical properties and degradability

In this study, stereocomplex-type poly(l-lactide) (SC-PLA)/organo-modified layered zinc phenylphosphonate (m-PPZn) nanocomposites were synthesized and characterized as a new material for green material usages. A long-chain oleylamine was selected to modify layered zinc phenylphosphonate (PPZn). The structural arrangement of the original and oleylamine-modified PPZn was determined using wide-angle X-ray diffraction (WAXD), and m-PPZn exhibited a large interlayer spacing of 30.3 A. The correlation length of PPZn derived using several orders of peak profiles decreased with oleylamine addition, suggesting that the structural arrangement of m-PPZn exhibits less perfect alignment. The mechanical properties, structure, and morphology of the SC-PLA/m-PPZn nanocomposites were characterized with dynamic mechanical analysis, WAXD, and transmission electron microscopy (TEM). Both WAXD and TEM results demonstrate that most of the layered materials of partial delamination are randomly dispersed in the SC-PLA matrix. Mechanical properties of the fabricated 1 wt% SC-PLA/m-PPZn nanocomposites show significant enhancements in the storage modulus when compared to SC-PLA matrix. The biodegradability of SC-PLA/m-PPZn nanocomposites was studied with Trizma buffer solution containing proteinase K. It has been shown that the SC-PLA/m-PPZn nanocomposites exhibit a much higher disintegration rate than that of the SC-PLA matrix.

Preparation and evaluation of hyperbranched p-chloromethyl styrene polymers/montmorillonite clay nanocomposites as dielectric materials

Hyperbranched polymers/montmorillonite clay modified with cetyl trimethyl ammonium bromide (MMT-CTAB) nanocomposites with polystyrene core were prepared by self-condensing vinyl polymerization via atom transfer radical polymerization of p-chloromethyl styrene monomer (CMS) alone or with styrene (St) and methyl methacrylate (MMA) monomers in the presence of MMT-CTAB acting as inimer with the double bond at one end and the alkyl-Cl unit at the other end. Three hyperbranched polymers/MMT-CTAB nanocomposites such as PCMS homopolymer/MMT-CTAB, PCMS-b-PSt copolymer/MMT-CTAB and PCMS-b-PSt-b-PMMA terpolymer/MMT-CTAB were prepared. The prepared hyperbranched polymers/MMT-CTAB nanocomposites were characterized via X-ray diffraction, dynamic mechanical thermal analyses and transmission electron microscopy for further applications as dielectric materials. Accordingly, several parameters were measured including dielectric permittivity (e′), A.C. conductivity (σ) and loss tangent (tan δ) in case of frequency and temperature ranging from 0.1 Hz to 100 kHz and 20–80 °C, respectively.

Dynamic Transmission Electron Microscope Study on the Crystallization of Ion-Bombarded Amorphous Germanium Thin Films

The structure-properties relationships of amorphous group IV semiconductors such as germanium (a-Ge) have attracted wide research interests over the past decades. The materials have great technological significance thanks to a plethora of applications, and understandings of their structural properties provide key scientific insights for those with similar covalently bounded networks. Pulsed laser induced crystallization is a common method to evolve the nanostructure in a-Ge. In this study, we report the correlations between the differences in the nanostructure of a-Ge thin films created by ion bombardment, and the laser crystallization kinetics measured using dynamic transmission electron microscope (DTEM).

Understanding Nanoscale Battery Processes By Operando (Scanning) Transmission Electron Microscopy

Many processes in materials science, chemistry and biology take place in a liquid environment – such as the synthesis of nanoparticles, biological cellular functions and the operation of Li-ion/next generation batteries. In these cases, the overall process/function of the system is a result of a series of complicated transients, where a change in the order, magnitude or location of any of the individual steps can lead to a radically different result. Understanding and subsequently controlling the final system outcome can therefore be greatly aided by the ability to directly observe these fundamental transient processes as and where they happen. Aberration corrected (scanning) transmission electron microscopy ((S)TEM) has the spatial resolution (typically < 0.1 nm) to directly visualize the atomic scale structural and chemical variations taking place in materials. Historically, such high resolution microscopy has been used to analyze materials before and after a process takes place to infer the dynamics of what happened in between. While there are still great advances that can be made with such analyses (at the very least in providing benchmark structures for nanoscale systems), a major breakthrough in recent years has been the design and implementation of in-situ gas and liquid stages that allow (S)TEM images to be obtained while the transient processes are actually taking place. For battery systems in particular, this means that we can now observe structural and chemical variations that occur in and around the interfaces between the electrodes and a liquid electrolyte during the charge/discharge process.Here we will discuss the implementation of an operando electrochemical stage within the (S)TEM that has been configured to form a “Li battery” (the same general configuration can be used for Li-ion, Li-air and Li-S batteries, as well as for any other novel battery architecture). One of the first experiments that has been performed is a quantification of the electrochemical processes that occur at the anode during charge/discharge cycling. Of particular importance for these observations is the identification of an image contrast reversal that originates from solid Li being less dense than the surrounding liquid electrolyte and electrode surface. This contrast allows Li to be identified from Li containing compounds that make up the solid-electrolyte interphase (SEI) layer. By correlating images showing the sequence of Li electrodeposition and the evolution of the SEI layer with simultaneously acquired cyclic voltammograms (CV), electrodeposition and electrolyte breakdown processes can be quantified directly on the nanoscale. In addition, changes in the morphology of the Li deposits (dendrites) obtained by introducing additives into the electrolyte can also be readily quantified from these (S)TEM observations.The experimental conditions needed to obtain these results (including identifying and eliminating the electron beam effect) will be discussed in detail. Preliminary results from Li-air, Li-S and Mg battery systems will be presented to highlight the development of stage technologies for future electrochemical experiments. In addition, the potential for microsecond time resolution experiments in the newly developed dynamic transmission electron microscope (DTEM) and the implementation of Compressive Sensing (CS) methods to identify the initial stages of SEI/dendrite formation will be explored.

Curing and thermo-mechanical studies of a modified thermosetting clearcoat containing OH-functional POSS nanocages

Abstract This paper attempts to study the chemical, thermo-mechanical and rheological properties of an acrylic/melamine clearcoat modified with a polyhedral oligomeric silsesquioxane (POSS) macromolecule. OH-functional groups of the linear acrylic resin were stoichiometrically substituted with those of the POSS. This modification resulted in a drop in viscosity compared with the pristine sample, mainly because of the globular compact structure of the modifier. This lowered the chain entanglements and provided more mobile functional groups during curing. FTIR spectroscopy, dynamic mechanical thermal analysis (DMTA) and transmission electron microscopy (TEM) techniques were utilized to study the resultant clearcoats. It was illustrated that reduced viscosity facilitated curing reactions and lead to a more efficient and more extensive curing degree, leading to an enhanced cross-linking density in presence of the POSS nanostructure. It was also illustrated that compatibility of POSS and acrylic/melamine lead to a molecular-scale dispersion of POSS nanostructures within the matrix.

Non-isothermal curing kinetics and physical properties of MMT-reinforced unsaturated polyester (UP) resins

Cure behavior of unsaturated polyester (UP)/montmorillonite (MMT)/methyl ethyl ketone peroxide (MEKP)/cobalt octoate intercalated nanocomposites with various MMT loadings was investigated by dynamic differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). UP/MMT nanocomposites were prepared by sequential mixing. Non-isothermal DSC curves were obtained by applying heating rates ranging from 5 to 20°C/min. They presented two exothermic peaks, which should correspond to two independent cure reactions. The effective activation energy Ea, was determined by applying both the Kissinger’s and Starink’s methods. The results showed slightly higher activation energy for nanocomposites, except for UP/10-MMT. It was found that the dependence of Ea on α is complex. All the systems in this study fitted Sesták–Berggren (SB) model in overall reaction controlled kinetics and the corresponding model parameters, n, m, A were obtained, but it was insufficient in depicting the complex reaction kinetics. Transmission electron microscopy data support the formation of a partially delaminated nanocomposite material. UP and nanocomposites showed similar behavior on thermal stability.

Properties of epoxy and unsaturated polyester nanocomposites with polycation modified montmorillonites

Polyesters (P) based on N-alkyldiethanolamines (alkyl being octyl, ODEA; dodecyl, DDEA; or hexadecyl, HDEA) and succinic acid anhydride were synthesized and transferred to polyester hydrochlorides (P-HCl) by the addition of HCl. They were used for modification of mineral montmorillonite (Mt). It was assumed that one part of the P-HCl molecule exchanged sodium cations from the interlayer spaces, while the other part was subsequently unprotonated with water. This part of the macromolecule should be better miscible with polymers of similar polarity, such as unsaturated polyesters (UP) and epoxides (E), than quaternary ammonium salts. Molar ratio Mt:P:HCl was 1:3:3 or 1:3:1.5 in accordance with Mt cation exchange capacity. The d-values of Mt, modified with polyesters P-ODEA, P-DDEA and P-HDEA, were 1.80nm, 3.65nm, and 4.12nm, respectively, and they were independent of HCl ratio.Unsaturated polyester and epoxy resin nanocomposites with 1%, 3%, and 5% of modified Mt were prepared and characterized by dynamic mechanical analysis (DMA), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The storage modulus increases with the increasing Mt content, and it decreases with the length of alkyl side chain in modifying polyester, indicating a plasticizing effect of the long alkyl chain, which is supported also by the decrease of glass transition temperatures. The thermal stability of the clay polymer nanocomposites (CPN) is the same as that of the neat resin for unsaturated polyester and deteriorates for epoxy nanocomposites.

Styrene/Isoprene/Styrene Thermoplastic Elastomer Prepared by Anionic Bulk Polymerization in a Twin-Screw Extruder

Abstract In this study, a styrene/isoprene/styrene (SIS) triblock copolymer was synthesized in an intermeshing, co-rotating, twin-screw extruder. N-butyl lithium was used as the initiator. The styrene and isoprene monomer as well as 1,2-dibromoethane were sequentially added into the extruder. The weight content of isoprene in this copolymer was above 60%. Gel permeation chromatography (GPC) results showed that the polystyrene in the copolymer chains was mainly comprised of only one long block. Dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM) showed that the polystyrene phase transferred from larger numbers of small microdomains to a continuous aggregation after the coupling reaction. As a result, the tensile stress and ultimate elongation was significantly improved, similar to the commercial product. Traditionally, SIS has only been synthesized by solution polymerization. The present work offers the capacity to synthesize it with very little or no solvent. This method fits the environmentally friendly trend.

Hydrophobin-stabilized dispersions of PVDF nanoparticles in water

In this study, aqueous dispersions of partially crystalline PVDF nanoparticles (NPs) were obtained employing hydrophobin (HFB), an amphiphilic film-forming protein able to film hydrophobic surfaces. Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM) analysis of PVDF-HFBII aqueous dispersions confirmed the HPBII ability to film PVDF hydrophobic NPs. Freeze-dried PVDF-HFBII bio-nanocomposites were shown to be effectively re-dispersible in water. An aqueous dispersion of PVDF NPs may have an impact on the applications of this polymer in the perspective of the development of environmentally friendly coating methods.

Time-Resolved Nanosecond Imaging of Nanoscale Condensed Phase Reaction

The reaction between metallic fuel and oxygen carriers produced by the laser heating of aluminum and copper oxide (CuO) nanoparticles (NPs) was investigated (NPs) using movie mode dynamic transmission electron microscopy (MM-DTEM), which enables multiframe imaging with nanometer spatial and nanosecond temporal resolution. Nanothermite materials heated in situ at ∼1011 K/s showed significant morphological changes on time scales of 1–5 μs. The resulting structures were typically phase-separated into adjoining spheroids. Further analysis with energy dispersive spectroscopy (EDS) and selected area electron diffraction (SAED) was used to determine the extent of reaction. Bulk scale reaction experiments using temperature jump wire heating (∼105K/s) revealed that both the reaction products and general processes were comparable to the reactions driven by the DTEM laser heating. These results indicate that condensed phase and interfacial reactions are fast and dominant mechanisms in nanothermite combustion.

Movie-mode dynamic electron microscopy

Abstract

A novel system for measurement of the transverse electron momentum distribution from photocathodes.

The transverse momentum of electrons produced by a photocathode contributes significantly to the performance of several different types of accelerator-based light sources, such as Free Electron Lasers, as well as systems designed for ultrafast electron diffraction and dynamic transmission electron microscopy. Minimization of the transverse emittance from photocathodes is the subject of intensive research, and therefore measurement of this parameter is of great importance. Here, we describe a simple system that offers real time measurements of transverse emittance and can be easily integrated into the photocathode fabrication process.

有机粘土/聚醚砜/环氧树脂杂化纳米复合材料的制备和性能*

分别用溶剂法和熔融法成功制备了有机粘土/聚醚砜/环氧树脂杂化纳米复合材料,对其拉伸性能、断裂韧性、热性能和微观结构进行了研究。结果表明:两种杂化纳米复合材料的拉伸强度可达75 MPa以上,模量可达3.0 GPa以上,断裂韧性可达1.1 MPam1/2以上。观察到了聚醚砜和有机粘土对环氧树脂的协同增韧现象。聚醚砜/环氧树脂基体具有半互穿网络结构,有机粘土片层呈有序剥离形态。用溶剂法制备的杂化纳米复合材料样本的玻璃化转变温度(Tg)在170℃以上,用熔融法制备的样本的Tg在180℃以上。

Temperature-driven disorder–order transitions in 2D copper-intercalated MoO3 revealed using dynamic transmission electron microscopy

We demonstrate two different classes of disorder–order phase transitions in two-dimensional layered nanomaterial MoO3 intercalated with ∼9–15 atomic percent zero-valent copper using conventional in situ electron diffraction and dynamic transmission electron microscopy. Heating to ∼325 °C on a time scale of minutes produces a superlattice consistent with the formation of a charge density wave stabilized by nanometer-scale ordering of the copper intercalant. Unlike conventional purely electronic charge-density-wave states which form, reform, and disappear on picosecond scales as the temperature is changed, once it forms the observed structure in Cu–MoO3 is stable indefinitely over a very large temperature range (30 °C to the decomposition temperature of 450 °C). Nanosecond-scale heating to ∼380–400 °C produced a completely different structure, replacing the disordered as-fabricated Cu–MoO3 with a much more crystallographically ordered metastable state that, according to a precession electron diffraction reconstruction, resembles the original MoO3 lattice apart from an asymmetric distortion that appears to expand parts of the van der Waals gaps to accommodate the copper intercalant. Control experiments in Cu-free material exhibited neither transformation, thus it appears the copper is a necessary part of the phase dynamics. This work shows how the combination of high-density metal atom intercalation and heat treatment over a wide range of time scales can produce nanomaterials of high crystalline quality in unique structural states that cannot be accessed through other methods.

In vitro drug release and biological evaluation of biomimetic polymeric micelles self-assembled from amphiphilic deoxycholic acid–phosphorylcholine–chitosan conjugate

Novel biomimetic amphiphilic chitosan derivative, deoxycholic acid–phosphorylcholine–chitosan conjugate (DCA–PCCs) was synthesized based on the combination of Atherton–Todd reaction for coupling phosphorylcholine (PC) and carbodiimide coupling reaction for linking deoxycholic acid (DCA) to chitosan. The chemical structure of DCA–PCCs was characterized by 1H and 31P nuclear magnetic resonance (NMR). The self-assembly of DCA–PCCs in water was analyzed by fluorescence measurements, dynamic laser light-scattering (DLS), zeta potential and transmission electron microscopy (TEM) technologies. The results confirmed that the amphiphilic DCA–PCCs can self-assemble to form nanosized spherical micelles with biomimetic PC shell. In vitro biological evaluation revealed that DCA–PCCs micelles had low toxicity against NIH/3T3 mouse embryonic fibroblasts as well as good hemocompatibility. Using quercetin as a hydrophobic model drug, drug loading and release study suggested that biomimetic DCA–PCCs micelles could be used as a promising nanocarrier avoiding unfavorable biological response for hydrophobic drug delivery applications.

In situ investigation of explosive crystallization in a-Ge: Experimental determination of the interface response function using dynamic transmission electron microscopy

The crystallization of amorphous semiconductors is a strongly exothermic process. Once initiated the release of latent heat can be sufficient to drive a self-sustaining crystallization front through the material in a manner that has been described as explosive. Here, we perform a quantitative in situ study of explosive crystallization in amorphous germanium using dynamic transmission electron microscopy. Direct observations of the speed of the explosive crystallization front as it evolves along a laser-imprinted temperature gradient are used to experimentally determine the complete interface response function (i.e., the temperature-dependent front propagation speed) for this process, which reaches a peak of 16 m/s. Fitting to the Frenkel-Wilson kinetic law demonstrates that the diffusivity of the material locally/immediately in advance of the explosive crystallization front is inconsistent with those of a liquid phase. This result suggests a modification to the liquid-mediated mechanism commonly used to describe this process that replaces the phase change at the leading amorphous-liquid interface with a change in bonding character (from covalent to metallic) occurring in the hot amorphous material.

Capturing Dynamics of Pulsed Laser Induced Melting and Rapid Solidification in Aluminum Polycrystals with Nanoscale Temporal Resolution In-situ TEM

The unprecedented spatiotemporal resolution offered by the dynamic transmission electron microscope (DTEM) facilitates unique studies of irreversible transitions in condensed matter [1]. In prior work we utilized the DTEM for single-shot nano-second temporal resolution bright field imaging and diffraction studies of rapid solidification (RS) in Al, Cu, Ag and Al-Cu alloy thin films [2-5]. Recent upgrades to the DTEM instrument enable single-pump/multiple-image-acquisition experiments (image series), which hold prospect to greatly reduce quantitative uncertainties in measurements, e.g. transformation front velocity, during RS, and increase by about one order of magnitude the data density obtained from direct observations of the dynamics of the irreversible transformation processes [6]. Here we report and discuss first results of in-situ TEM investigations of the dynamics of pulsed-laser induced melting and RS in Al thin films performed with the upgraded DTEM. Thin Al films, 80nm-160nm thick, were deposited by e-beam evaporation on square windowed TEM grids with 50 nm thick amorphous Si3N4 membranes and melted with a single 15 ns, 1064 nm laser pulse, defining time t0 (Fig. 1). Image series comprised of nine frames have been acquired with preselected 20ns exposures per frame and 0.2s time steps between frames and also for 50ns exposures and inter-frame time steps of 2s. The resulting image series spanning at least ~1.8s (e.g. Fig. 1) and up to ~20.4s have been acquired for systematically varied pre-delay times, t, in the range of -0.2s to 40μs. Dynamics of the morphological and structural changes in the nano-crystalline Al thin films and the kinetics during the pulsed laser induced sequences of melting and subsequent RS have been determined from direct observations. Bright field imaging showed (e.g. Fig. 2) that the laser pulse induced irreversible transformation involves the preferential melting along grain boundaries and development of a ‘mushy’ two-phase region during the melting sequence. Subsequently solidification initiates with a transformation interface that is rough on the scale of the adjacent crystalline grains. Driven by the thermal gradient the solidification interface transitions to a planar morphology, which supports growth of columnar crystals to the center of the melt pool. Effects from the Si frame support of the TEM transparent square windows, which represents a heat sink, on the solidification velocity measurements in the DTEM have been studied systematically. Kinetic details of the Al thin film melting and the solidification sequences under the driven conditions are analyzed quantitatively and discussed. Post-mortem TEM analysis have been performed to evaluate crystallographic details of the directional solidified Al grains relative to the original film.

Combining nanocalorimetry and dynamic transmission electron microscopy for in situ characterization of materials processes under rapid heating and cooling.

Nanocalorimetry is a chip-based thermal analysis technique capable of analyzing endothermic and exothermic reactions at very high heating and cooling rates. Here, we couple a nanocalorimeter with an extremely fast in situ microstructural characterization tool to identify the physical origin of rapid enthalpic signals. More specifically, we describe the development of a system to enable in situ nanocalorimetry experiments in the dynamic transmission electron microscope (DTEM), a time-resolved TEM capable of generating images and electron diffraction patterns with exposure times of 30 ns-500 ns. The full experimental system consists of a modified nanocalorimeter sensor, a custom-built in situ nanocalorimetry holder, a data acquisition system, and the DTEM itself, and is capable of thermodynamic and microstructural characterization of reactions over a range of heating rates (10(2) K/s-10(5) K/s) accessible by conventional (DC) nanocalorimetry. To establish its ability to capture synchronized calorimetric and microstructural data during rapid transformations, this work describes measurements on the melting of an aluminum thin film. We were able to identify the phase transformation in both the nanocalorimetry traces and in electron diffraction patterns taken by the DTEM. Potential applications for the newly developed system are described and future system improvements are discussed.

The preliminary evaluation on cholesterol-modified pullulan as a drug nanocarrier

To further develop cholesterol-modified pullulan self-aggregated nanoparticles (CHSPNs) as a drug nanocarrier, CHSP was synthesized and characterized. Its cholesterol degree determined by 1H NMR was 5.2 cholesterol groups per hundred glucose units. CHSPNs were prepared in aqueous media and characterized by dynamic laser light-scattering (DLS), zeta potential and transmission electron microscopy (TEM). These nanoparticles were almost spherical in shape, and the zeta potentials of CHSPNs were near zero in aqueous media. CHSPNs can be stable at least 2 months with no significant size and zeta potential changes. Single dose toxicity test in mice was investigated for the safety evaluation of CHSPNs as a drug nanocarrier, and the result showed CHSPNs were well tolerated at the dose of 200 mg/kg in mice. Epirubicin (EPI)-loaded CHSPNs (EPI-CHSPNs) were prepared and the in vivo pharmacokinetics and biodistribution were studied. Compared with the EPI solution, EPI-CHSPNs have exhibited higher plasma drug concentration, longer half-life time (t1/2) and the larger area under-the-curve (AUC). Moreover, the drug level of EPI-CHSPNs increased in liver and decreased in heart. The results indicated that CHSPNs were stable, safe and may be a promising drug delivery carrier.