TEM Electron Energy Loss Spectroscopy Research Articles

Progress toward Mapping Nanoscale Carrier and Structural Dynamics in Silicon using Ultrafast TEM-Electron Energy-Loss Spectroscopy

Progress toward Mapping Nanoscale Carrier and Structural Dynamics in Silicon using Ultrafast TEM-Electron Energy-Loss Spectroscopy

Development of a CaCO3 Precipitation Method Using a Peptide and Microwaves Generated by a Magnetron

Microwave applications, such as microwave ovens and mobile phones, are ubiquitous and indispensable in modern society. As the utilization of microwave technology is becoming more widespread, the effects of microwaves on living organisms and physiological processes have received increased attention. This study aimed to investigate the effects of microwaves on calcium carbonate biomineralization as a model biochemical process. A magnetron oscillator was used to generate 2450 MHz microwaves because magnetrons are relatively inexpensive and widespread. We conducted transmission electron microscopy (TEM), atomic force microscopy (AFM), TEM-electron energy-loss spectroscopy (EELS), dynamic light scattering (DLS), and high-performance liquid chromatography (HPLC) measurements to analyze the calcium carbonate precipitates. Our findings showed the formation of string-like precipitates of calcium carbonate upon microwave irradiation from one direction, similar to those obtained using a semiconductor oscillator, as reported previously. This implied that the distribution of the frequency had little effect on the morphology. Furthermore, spherical precipitates were obtained upon microwave irradiation from two directions, indicating that the morphology could be controlled by varying the direction of microwave irradiation. Magnetrons are versatile and also used in large-scale production; thus, this method has potential in medical and industrial applications.

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.

Novel dry deposition of LiNbO3 or Li2ZrO3 on LiNi0.6Co0.2Mn0.2O2 for high performance all-solid-state lithium batteries

LiNbO3 (50–100 nm) and Li2ZrO3 (30–60 nm) nanoparticles are a suitable electrode-coating agent because they can suppress direct contact with the sulfide-based solid electrolyte, decrease contact loss, and eliminate the space-charge layer. The LiNbO3 and Li2ZrO3 nanoparticles were coated on LiNi0.6Co0.2Mn0.2O2 (NCM) cathode material by a ResonantAcoustic® Mixer (LabRAM II) for all-solid-state lithium batteries (ASSLBs) and their improved electrochemical properties were assessed. ASSLBs using LiNbO3 and Li2ZrO3-coated NCM material showed higher capacity than did bare NCM cathode material. X-ray diffraction patterns showed no deviation on diffraction patterns and lattice parameters on cathode materials after the coating. Field-emission scanning electron microscopy and transmission electron microscopy images obtained with electron dispersive spectroscopy mapping confirmed homogeneous coating with a uniformly thick LiNbO3 or Li2ZrO3 layer of around 50–200 nm. X-ray photoelectron spectroscopy showed that the surface of NCM had two different O1s peaks and an Nb-O peak, and displayed the Ni, Co, Mn 2p, and Nb 3d peaks. Electrochemical studies on bare NCM and LiNbO3 and Li2ZrO3-coated NCM materials using electrochemical impedance spectroscopy elucidated the galvanostatic cycle performances by assembling an all-solid-state cells with c-rate performances. Notably, the 3 wt% LiNbO3-coated NCM exhibited capacity retention of 84% at a current density of 15 mA/g during 20 cycles, whereas the bare NCM exhibited a capacity retention of only 16.1%. In addition, we used X-ray photoelectron spectroscopy and TEM-electron energy-loss spectroscopy to measure the cathode composites after 20 cycles. The 3 wt% LiNbO3 and Li2ZrO3-coated NCM composite showed an improved interface and lowered side reaction.

Multiband light emission and nanoscale chemical analyses of carbonized fumed silica

Fumed silica with a specific area of 295 m2/g was carbonized by successive phenyltrimethoxysilane treatments followed by annealing in inert atmosphere up to 650 °C. Emission, excitation, kinetics, and photo-induced bleaching effects were investigated by steady state and time-resolved photoluminescence spectroscopies. The local chemistry was also studied by infrared transmission spectroscopy. Strong ultraviolet and visible photoluminescence was observed in the samples after the chemical treatments/modifications and thermal annealing. It has been shown that ultraviolet photoluminescence in chemically modified fumed silica is associated with phenyl groups, while near ultraviolet and visible emission in annealed samples originated from inorganic pyrolytic carbon precipitates dispersed in the silica host matrix. Two types of emission bands were identified as a function of the annealing temperature: one is in the near UV and the other is in the visible range. Based on the emission/excitation analysis of these two bands, as well as on correlations with the synthesis conditions, a structural-energy concept of light-emitting centers has been proposed. According to this model, the light-emitting centers are associated with carbon clusters that can be bonded or adsorbed on the silica surface. This has been validated by a detailed (S)TEM-electron energy-loss spectroscopy study, confirming the inhomogeneous distribution of nanoscale carbon precipitates at the surface of the silica nanoparticles. These carbon precipitates are mostly amorphous although they possess some degree of graphitization and local order. Finally, the fraction of sp2 carbon in these nanoclusters has been estimated to be close to 80%.

Epitaxial corundum-VTiO3 thin films grown on c-cut sapphire

Corundum structured VTiO3 has been grown as epitaxial films on c-cut sapphire by laser molecular beam epitaxy. The properties of the film were characterized by reflection high energy electron diffraction, X-ray diffraction, transmission electron microscopy (TEM), and photoemission spectroscopy. All the structural probes clearly indicate the corundum structure of the film. X-ray photoemission spectroscopy (XPS) indicates that V is in a 3+ charge state implying that Ti also should adopt a 3+ charge state in order for the corundum structure to form. However, the Ti-2p XPS, while clearly broadened to the lower binding energy side compared to TiO2, also exhibits a pronounced Ti4+ component. Similarly TEM-electron energy loss spectroscopy indicates a mixture of Ti3+ and Ti4+. This is tentatively assigned to a combination of final state effects in XPS measurements and existence of excess (interstitial) oxygen. The valence band spectra show occupation of 3d metal states that resemble more closely those of Ti2O3 than for V2O3, suggesting that mostly the a1g molecular states are occupied.

Boron-rich inclusions and boron distribution in HPHT polycrystalline superconducting diamond

Polycrystalline boron-doped superconducting diamond, synthesized at high pressure and high temperature (HPHT) via a reaction of a single piece of crystalline boron with monolithic graphite, has been investigated by analytical transmission electron microscopy. The local boron distribution and boron environment have been studied by a combination of (scanning) transmission electron microscopy ((S)TEM) and spatially resolved electron energy-loss spectroscopy (EELS). High resolution TEM imaging and EELS elemental mapping have established, for the first time, the presence of largely crystalline diamond–diamond grain boundaries within the material and have evidenced the presence of substitutional boron dopants within individual diamond grains. Confirmation of the presence of substitutional B dopants has been obtained through comparison of acquired boron K-edge EELS fine structures with known references. This confirmation is important to understand the origin of superconductivity in polycrystalline B-doped diamond. In addition to the substitutional boron doping, boron-rich inclusions and triple-points, both amorphous and crystalline, with chemical compositions close to boron carbide B4C, are evidenced.

Fischer–Tropsch synthesis: Iron-based catalysts supported on nitrogen-doped carbon nanotubes synthesized by post-doping

A new approach was developed to prepare nitrogen-doped carbon nanotubes (N-CNTs) by a post-doping method at 700–900°C. In this technique acetonitrile is passed over pre-synthesized CNTs in a CVD tube so that N (and C) deposit on the CNT surface. Our results showed that no significant change in the morphologies between CNT and the synthesized N-CNTs at temperatures up to 800°C were observed. This indicates that N-CNTs produced by in-situ (contains a bamboo structure) and post-doping procedures (hollow tube) have different morphologies. When the post-doping temperature was increased to ≥850°C, spherical carbon was formed on the N-CNTs. The N-CNT yield and nitrogen content in the N-CNTs increased almost linearly with increasing post-doping temperature, whereas the surface areas of the N-CNTs decreased with increasing temperature due to tube cavity shrinkage and the deposition of spherical carbon. Raman spectroscopy data showed a decreased ID/IG ratio up to 850°C, suggesting a change in the graphitic structures with temperature. TEM-electron energy loss spectroscopy (TEM-EELS) mapping and XPS showed that the nitrogen atoms were homogeneously dispersed on the N-CNTs and they were pyridinic N atoms, quaternary N atoms and N atoms from pyridinic oxide. Fe catalysts supported on both CNTs and N-CNTs (containing 1.75% nitrogen) functionalized under both mild and harsh acid conditions were prepared in order to investigate the effect of the doped-nitrogen atoms on the performance of the Fe catalysts in Fischer–Tropsch synthesis (FTS). It was found that the incorporation of nitrogen atoms into CNTs did not significantly change the Fe oxide particle sizes. The Fe/CNT and Fe/N-CNT catalysts prepared under a mild pretreatment had large Fe oxide particles, while the Fe/CNT and Fe/N-CNT catalysts pretreated using harsh conditions presented small iron oxide particles. For Fe catalysts supported on CNT and N-CNT pretreated at mild or harsh conditions, the Fe/N-CNT catalysts are less reducible than the corresponding Fe/CNT catalysts due to the incorporation of nitrogen atoms. The interactions between iron oxides and carbon supports significantly affected the FTS performance: the Fe/N-CNT catalysts have superior FTS activity than Fe/CNT catalysts, irrespective of whether they were pretreated at mild or harsh condition. Furthermore, the pretreatment conditions affected the FTS activity of both Fe/CNT and Fe/N-CNT catalysts and the Fe catalysts pretreated at harsh conditions presented an improved FTS activity over the iron catalysts pretreated at mild conditions.

The effect of substrate temperature on the etching properties and the etched surfaces of magnetic tunnel junction materials in a CH3OH inductively coupled plasma system

The etching characteristics of the magnetic films (PtMn, CoFe) and hard mask materials (W, Ta) forming a magnetic tunnel junction (MTJ) stack in a CH3OH inductively coupled plasma (ICP) system were investigated. We examined the etch rates of the metal films as a function of substrate temperature, and assessed the microstructures of the etched surfaces using high resolution transmission electron microscopy (HR-TEM). We also analyzed the surface states using X-ray photoelectron spectroscopy (XPS) and TEM electron energy loss spectroscopy (TEM-EELS). The PtMn and CoFe etch rates increased as the temperature increased, whereas the etch rates of W and Ta decreased slightly. Therefore the etch selectivity increased linearly with increasing substrate temperature. The CH3OH plasma formed nonvolatile etching byproducts with the magnetic films and hard mask metals. In the case of PtMn and CoFe, the surface composition of the etching byproducts changed with increasing temperature; the relative concentration of pure metal compared with metal oxide or carbide increased as the substrate temperature rose. The etch rate was determined by the sputtering yield of the materials formed on the etched surface; accordingly the etch rates of those magnetic films would increase due to the higher sputtering yield of pure metal.

Effect of the capping on the local Mn oxidation state in buried (001) and (110) SrTiO3/La2/3Ca1/3MnO3 interfaces

The electronic stability of (001) and (110) surfaces of La2/3Ca1/3MnO3 (LCMO) capped with nanometric SrTiO3 (STO) layers in epitaxial heterostructures is addressed by (S)TEM electron energy loss spectroscopy. It is found that growth of STO on (001)LCMO promotes a significant electron doping of LCMO that extends a few nanometers deep into the film. In contrast, (110)LCMO appears to be electronically more robust and no electronic reordering has been observed. These results are in clear correlation with the distinct magnetic properties observed in those interfaces and illustrate that complex chemical phenomena take place at interfaces among multivalent oxides.

Capacity-Fading Mechanisms of LiNiO2-Based Lithium-Ion Batteries: II. Diagnostic Analysis by Electron Microscopy and Spectroscopy

We used a suite of transmission electron microscopy (TEM) and associated electron spectroscopy methods to examine the local structure and changes in the electronic structure of positive electrode material. We found a scattered rock-salt phase near grain surfaces and grain boundaries, where turned to , deduced from relative intensity ratios and fine structures of the white-line peaks of the transition metals. The spatial distribution of the degraded phase throughout the secondary particle was found using a scanning TEM-electron energy loss spectroscopy spectral imaging technique and multivariate analysis. The degradation process and its relationship to the surface reactions with electrolytes is discussed based on the spatial-distribution map of the degraded phases.

Determination of Inelastic Mean Free Path by Electron Energy-Loss Spectroscopy in TEM: A Model Study Using Si and Ge

ABSTRACTAlthough the inelastic mean free path for Si and Ge have been measured previously, reported experimental values for silicon range from 121 nm to 160 nm for 200 keV and a large collection angle. A key factor responsible for this uncertainty is the lack of an accurate measurement of the specimen thickness at the point at which the EELS spectra are obtained. In this research, we have evaluated a systematic methodology for determination of the specimen thickness. In the thickness measurement based on converging beam electron diffraction, CBED, instead of the classic “trial and error” straight-line-fitting method to either the maxima or minima, a non-linear least square fitting of the theoretical diffraction profile to the energy filtered two-beam CBED is used. The low-loss EELS spectrum is also obtained from the same location. The inelastic mean free path was determined using the measured thickness and EELS data. Furthermore, attempt is also made to obtain the dielectric function from the low-loss spectrum. The established method will be extended to other materials and the results will be compared with numerical simulations.

Energy-filtered TEM imaging and EELS study of ODS particles and Argon-filled cavities in ferritic–martensitic steels

Oxide-dispersion-strengthened (ODS) ferritic–martensitic steels with yttrium oxide (Y 2O 3) have been produced by mechanical alloying and hot isostatic pressing for use as advanced material in fusion power reactors. Argon gas, usually widely used as inert gas during mechanical alloying, was surprisingly detected in the nanodispersion-strengthened materials. Energy-filtered transmission electron microscopy (EFTEM) and electron energy loss spectroscopy (EELS) led to the following results: (i) chemical composition of ODS particles, (ii) voids with typical diameters of 1–6 nm are formed in the matrix, (iii) these voids are filled with Ar gas, and (iv) the high-density nanosized ODS particles serve as trapping centers for the Ar bubbles. The Ar L 3,2 energy loss edge at 245 eV as well as the absorption features of the ODS particle elements were identified in the EELS spectrum. The energy resolution in the EEL spectrum of about 1.0 eV allows to identify the electronic structure of the ODS particles.

分析電子顕微鏡 ＥＥＬＳを中心として

The principle of electron energy loss spectroscopy (EELS) is discussed based on the dielectric function of solid specimen. Electron energy loss spectra in low (<50eV) and high energy loss regions (>50eV) are analysed for graphite and explained by its electronic band structure. Limitations of the spatial resolution and the detectable mass concentration by EELS in TEM are discussed from the point of view of local chemical analysis. The mapping techniques and images formed by characteristic energy losses of each element contained within the specimen are shown for some examples. In addition to EELS in TEM, other examples of EELS in SEM are shown for surface analysis of bulk specimen.

Formations of rhombohedral boron nitride, as revealed by TEM-electron energy loss spectroscopy

Formations of rhombohedral boron nitride, as revealed by TEM-electron energy loss spectroscopy