Electron Energy Loss Spectroscopy Spectra Research Articles

Templating effect of the substrate on the structure of Cu-phthalocyanine thin film

An experimental study of electronic properties, structure and morphology of Copper-phthalocyanine films deposited onto Al(100) and Au(110), as a function of thickness up to tens of nanometers, is presented. The monolayers grown on these two model substrates are already known to exhibit very different behavior for what concerns both the degree of interaction with the substrate and the formation of long range order; in this experiment, by means of low energy electron scattering and Electron Energy Loss Spectroscopy (EELS), remarkable differences are revealed also in the successive growth. Exploiting the link between the crystal structure and the lineshape of HOMO–LUMO transition in EELS spectrum, two different structural phases are identified, compatible with α and β phases, respectively in the case of the film grown on aluminum and on gold. Besides, the evolution of the specular reflection elastic peak indicates the formation of islands on the gold substrate and a more homogeneous growth on the aluminum one.

Effect of asymmetric morphology on coupling surface plasmon modes and generalized plasmon ruler

Plasmon coupling in aggregated noble metal systems can provide a path to manipulate the optical response purposefully and possesses a wide range of application. Previously, most studies focused on the coupling behavior of Ag–Ag dimers with the same shape. However, plasmon coupling between nanoparticles at different morphologies can provide a new way to modulate optical properties due to broken of symmetry. In this work, we investigate systematically the coupling modes of asymmetric Ag–Ag heterodimers consisting of different morphologies by the boundary element method (BEM). Herein nanoparticles with different surface curvatures (modified by rounding parameter e) are constructed and combined as asymmetric Ag–Ag heterodimers. Simulated electron energy loss spectroscopy (EELS) spectra and eigenmodes are combined to analyze the evolution of coupling modes. The mode energy degeneracy and degeneracy breaking phenomena are found, while the charge states are always not degenerate, for the first time by modulating symmetry of the morphology. It is also found that coupling gap mode G2 can only be excited for Ag–Ag heterodimers with quite small separation distance, and will be greatly influenced by nanogap morphology. The rounded effect can also cause distinct blue shift of bounding dipolar modes. These results provide the possibility to modulate optical response by using different asymmetric dimers effectively. In contrast, optical response of high-order coupling modes is less sensitive to topographic effect than that of low-order coupling modes. Moreover, plasmon ruler for asymmetric Ag–Ag heterodimers is investigated and we demonstrate that a generalized plasmon ruler is applicable to predict the relative shift of coupling dipolar due to change of separation distance.

Structure and electronic states of a graphene double vacancy with an embedded Si dopant.

Silicon represents a common intrinsic impurity in graphene, bonding to either three or four carbon neighbors, respectively, in a single or double carbon vacancy. We investigate the effect of the latter defect (Si-C4) on the structural and electronic properties of graphene using density functional theory. Calculations based both on molecular models and with periodic boundary conditions have been performed. The two-carbon vacancy was constructed from pyrene (pyrene-2C) which was then expanded to circumpyrene-2C. The structural characterization of these cases revealed that the ground state is slightly non-planar, with the bonding carbons displaced from the plane by up to ±0.2 Å. This non-planar structure was confirmed by embedding the defect into a 10 × 8 supercell of graphene, resulting in 0.22 eV lower energy than the previously considered planar structure. Natural bond orbital analysis showed sp3 hybridization at the silicon atom for the non-planar structure and sp2d hybridization for the planar structure. Atomically resolved electron energy loss spectroscopy and corresponding spectrum simulations provide a mixed picture: a flat structure provides a slightly better overall spectrum match, but a small observed pre-peak is only present in the corrugated simulation. Considering the small energy barrier between the two equivalent corrugated conformations, both structures could plausibly exist as a superposition over the experimental time scale of seconds.

Assessing Oxygen Vacancies in Bismuth Oxide through EELS Measurements and DFT Simulations

Pioneering electron energy loss spectroscopy (EELS) measurements of α-Bi2O3 are performed on three samples obtained through different synthesis methods. Experimental low-loss and core-loss EELS spectra are acquired. By combining them with detailed structural characterization and Density Functional Theory (DFT) simulations, we are able to detect and evaluate the presence of oxygen vacancies in the samples. This type of information has not been accessed previously from EELS data in bismuth oxide, because high-resolution EELS spectra or how vacancies reflect in Bi2O3 spectra were unreported. This novel measurement is further validated through comparison with photoluminescence data. Therefore, the technique has the ability to probe oxygen vacancies in Bi2O3 at an unprecedented resolution, which might allow solving material science and technological issues related to this material.

Mapping the layer count of few-layer hexagonal boron nitride at high lateral spatial resolutions

Layer count control and uniformity of two dimensional (2D) layered materials are critical to the investigation of their properties and to their electronic device applications, but methods to map 2D material layer count at nanometer-level lateral spatial resolutions have been lacking. Here, we demonstrate a method based on two complementary techniques widely available in transmission electron microscopes (TEMs) to map the layer count of multilayer hexagonal boron nitride (h-BN) films. The mass-thickness contrast in high-angle annular dark-field (HAADF) imaging in the scanning transmission electron microscope (STEM) mode allows for thickness determination in atomically clean regions with high spatial resolution (sub-nanometer), but is limited by surface contamination. To complement, another technique based on the boron K ionization edge in the electron energy loss spectroscopy spectrum (EELS) of h-BN is developed to quantify the layer count so that surface contamination does not cause an overestimate, albeit at a lower spatial resolution (nanometers). The two techniques agree remarkably well in atomically clean regions with discrepancies within ±1 layer. For the first time, the layer count uniformity on the scale of nanometers is quantified for a 2D material. The methodology is applicable to layer count mapping of other 2D layered materials, paving the way toward the synthesis of multilayer 2D materials with homogeneous layer count.

Investigation of Deuterium Implantation into Beryllium Sample by Electron Energy Loss Spectroscopy

Quantitative analysis of hydrogen isotopes in first wall as well as in construction materials of future fusion devices plays a crucial role to understand the evolution of those materials under operation conditions. A quantitative understanding of hydrogen in materials is also an important issue for storing energy as well as for fuel cells. A combination of Electron Energy Loss Spectroscopy (EELS) and Elastic Peak Electron Spectroscopy (EPES) is presented in this study to tackle these problems of modern material research for energy production and storage. Accurate inelastic scattering background subtraction is a key part of the presented quantitative measurement of the Be/D ratio. The differential inelastic scattering cross-section is determined by the fitting procedure. The fitting procedure is based on the iterative solution of the direct problem and minimization of the residual between computed and measured spectra. This study also takes into account the difference in electron energy loss laws for surface and bulk. The inelastic scattering cross-sections for different doses of deuterium ions in beryllium substrate (5.5·1021 m−2 and 2.01·1022 m−2) were defined in a two-layered model. The analysis is carried out for the EELS spectra. Relative concentration of D atoms is defined.

UHV AFM based colloidal probe studies of adhesive properties of VAlN hard coatings

Abstract The adhesion of polystyrene (PS) on V0.27Al0.29N0.44 and the related influence of the oxidation states of both surfaces was investigated using X-Ray Photoelectron Spectroscopy (XPS) and Colloidal Force Spectroscopy (CFS) in Ultra-High Vacuum (UHV). Complementary, the intimate relation between the adhesion force, the chemical structure and surface polarizability was investigated by XPS valence band spectroscopy and the calculation of non-retarded Hamaker coefficients using Lifshitz theory based on optical data as derived from Reflection Electron Energy Loss Spectroscopy (REELS) spectra. The combined electron and force spectroscopic analysis of the interaction forces disclosed quantitatively the separation of the adhesion force in van der Waals and Lewis acid-base contributions. Further, the surface polarizability of VAlN was shown to be unaffected by oxygen incorporation due to the formation of an only gradually oxidized surface comprising a range of vanadium oxidation states. In contrast, the adhesion force analysis revealed additional Lewis acid-base interactions between the oxidized and non-oxidized VAlN surfaces and carboxyl groups present in the surface of PS after an oxidative oxygen beam treatment.

High efficiency core-loss EELS analyzing from the viewpoint of chemometrics

Electron energy–loss spectroscopy (EELS) equipped on a modern scanning transmission electron microscope is a powerful high resolution elemental analysis technique. However, the conventional method of extracting elemental information quantitatively from EELS spectra is non-trivial. In this article we tried to interpret EELS data from the viewpoint of chemometrics. An EELS spectrum image collected from a vicinal SiC/SiO2 interface was employed as an example. By analyzing the EELS data with sophisticated chemometrics methods, chemical components and elemental ratios of C/Si and O/Si across the interface were derived. Compared with conventional EELS analysis, the chemometrics methods gave more reliable and accurate results with higher calculation efficiency. The chemometrics analysis confirmed that the transition from SiC to SiO2 was chemically sharp, and the transition layer in the vicinal interface was a linear combination of SiC and SiO2. Chemometrics analysis can be a fast and robust complementary method for EELS analysis.

Green Aromatics from Catalytic Fast Pyrolysis of Fast Growing Meranti Biomass

The study on catalytic pyrolysis decomposition of Shorea leprosula wood biomass to form aromatic compounds in fast pyrolysis was performed by pyrolytic-gas chromatography/mass spectroscopy (Py-GC/MS) and transmission electron microscope (TEM) - electron energy-loss spectroscopy (EELS) to analyze the chemical compound and solid residue microstructure. Py-GC/MS and TEM-EELS analysis showed that the fast pyrolysis increased the decomposition of hardwood, in which in the presence of ZSM-5 catalyst, the liquid products from wood decomposition was then diffused into the pore of ZSM-5 catalyst to form aromatics including benzene, toluene, styrene, naphthalenes and indanes. The carbonaceous solid compounds or cokes were not deposited on the surface of pores of ZSM-5 catalyst in the fast pyrolysis, as shown by the EELS spectrum that exhibited no detection of any solid carbonaceous compound in the solid residue.

Structures of Boron Loaded Turbostratic Graphene with Enhanced Performance in Solid Acid Fuel Cell

Solid acid fuel cells (SAFC) working at intermediate temperature (250°C) have many advantages compared to the lower temperature proton exchange membrane fuel cell (PEMFC), such as increased catalyst activity and are more resistant to CO poisoning.1, 2 The state-of-the-art cathode is comprised of porous protonic conductor coated by Pt.3, 4 There are two major roles of Pt in the cathode: (1) the oxygen reduction reaction (ORR) catalyst and (2) the electron conductor. To maintain a highly electron conductive network, a high fraction of Pt has to be loaded in ‘conventional’ SAFC electrodes. However, to generate wider application, the cost of the cathode must be reduced significantly. The function of Pt as electron conductor can be replaced by the catalyst support to achieve this reduction in loading. The catalyst support must have high electron conductivity, corrosion-resistance and high surface area. The carbon nanostructures are the common catalyst supports used in the fuel cells. In our previous studies, we demonstrated that multi-wall carbon nanotubes are much more stable during fuel cell testing compared to the single wall carbon structures.5 Indeed, pure single layer or few-layer carbon supports are well known to be particularly vulnerable to corrosion in the present of water. However, previous research showed that substitutional boron can lower the electron density of the reactive carbon, leading to a reduction in the rate of O2 chemisorption.6 Meanwhile, very small amounts of boron (~1%) have been demonstrated to enhance the conductivity of the single carbon structure.7In our recent studies, we synthesize the pure single wall carbon, carbon structures in hydrogen gas and with boron loading. Surprisingly, the boron loading induces the growth of few-layer graphenes (FLGs), which exhibit much better corrosion resistance than the single wall carbon and carbon synthesized in hydrogen gas which consists of multi-wall and single-wall carbon structure. In this research, we focus on the structural investigation of those FLGs. Characterization of the FLGs are performed by high resolution transmission electron microscopy (HRTEM) imaging, monochromated electron energy-loss spectroscopy (EELS), nano-beam electron diffraction (NBED), aberration corrected scanning transmission electron microscopy (STEM) imaging, X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), Raman spectroscopy and X-ray diffraction (XRD). Representative STEM images in a low and high magnification are shown in Figure 1 (a)-(b). A significantly structure deviation compared to pure graphene/graphite is evident due to 1-3% boron loading. Those results indicate the few-layer graphene does not stack in a normal graphitic way in the c direction. The EELS, XPS and NMR show complicated electronic states of the boron in the carbon, implying boron does not have to be in the substitutional site. For example, Figure 1(c) show a representative EELS spectrum taken from a FLG. The featureless boron K-edge looks like to be taken from amorphous boron instead of substitutional boron. This result is also supported by the NBED and XRD, showing a non-flat features of the FLGs. Finally, we used the density functional theory (DFT) to explain the excellent oxygen resistance of FLG with this unique structure. Acknowledgments This work is supported by ARPA-E via cooperative agreement DE-AR0000499. The synthesis science is supported by BES-MSED. We thank JIAM and CNMS for microscopy use. Reference 1. K. Ishiyama, F. Kosaka, I. Shimada, Y. Oshima and J. Otomo, Journal of Power Sources, 2013, 225, 141-149. 2. A. B. Papandrew, R. W. Atkinson Iii, R. R. Unocic and T. A. Zawodzinski, Journal of Materials Chemistry A, 2015, 3, 3984-3987. 3. A. B. Papandrew, C. R. I. Chisholm, R. A. Elgammal, M. M. Özer and S. K. Zecevic, Chemistry of Materials, 2011, 23, 1659-1667. 4. A. B. Papandrew, C. R. I. Chisholm, S. K. Zecevic, G. M. Veith and T. A. Zawodzinski, Journal of The Electrochemical Society, 2013, 160, F175-F182. 5. A. B. Papandrew, R. A. Elgammal, M. Tian, W. D. Tennyson, C. M. Rouleau, A. A. Puretzky, G. M. Veith, D. B. Geohegan and T. A. Zawodzinski, Journal of Power Sources, 2017, 337, 145-151. 6. B. Yuan, W. Xing, Y. Hu, X. Mu, J. Wang, Q. Tai, G. Li, L. Liu, K. M. Liew and Y. Hu, Carbon, 2016, 101, 152-158. 7. M. Harada, T. Inagaki, S. Bandow and S. Iijima, Carbon, 2008, 46, 766-772. Figure 1

Auger Electron Spectroscopy, Electron Energy Loss Spectroscopy, UV Photoelectron Spectroscopy, and Photoluminescence Characterization of In2O3 Associated to the Theoretical Calculations Based on the Generalized Gradient Approximation and Modified Becke Johnson

The indium oxide In2O3 is among the transparent conducting oxides (TCO) appropriate for solar cells and optoelectronics. The physical properties are based on the electron distribution on the core levels and in the valence band of material. The knowledge of the electron distribution on the different states is fundamental to predict the possibilities of electron transitions. In this respect, we adopt calculations based on the generalized gradient approximation (GGA) and modified Becke Johnson (mBJ) to show the electron state density. We associate to the numerical simulation the experimental analysis techniques auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), and UV photoelectron spectroscopy (UPS) of great sensitivity to characterize the material surfaces. The analysis technique AES is used for proving the chemical composition of the In2O3 compound through the In-M45N45N45 and O-KLL signals. The energy loss peak at 16.3 eV on the EELS spectra is related to plasmons. The energy lo...

Characterization of carbon nanostructures in Al and Ag covetic alloys

Electrocharging assisted process is a method for the incorporation of carbon in molten metals under high electric current which results in the formation of networks of carbon nanostructures inside the metal matrix, and gives the new material improved mechanical, electrical and thermal properties. Alloys produced with this method are called covetics. In our previous works, different characterization techniques such X-ray photoelectron spectroscopy (XPS), Raman, X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) confirmed the presence of sp2 crystalline graphene nanoribbons and sheets in Ag and Al-covetic samples. Here, we report on detailed Raman mapping and characterization of Al-6061, Al-7075 and Ag covetics to further investigate the fraction of sp2/sp3 bonding, strain, defects, degree of oxidation, and crystalline sizes of the graphene nanoribbons. Gradual changes of strain are observed in regions with sp2 bonding and some degree of amorphous carbon is revealed by Raman scattering. Different degrees of oxidation of the carbon nanostructures with mostly sp2 bonding are evident by EELS spectrum imaging. Atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) also reveal the presence of graphene ribbons and sheets with different lengths and conductivity.

Elucidating the Origin of Oxide Ion Blocking Effect at GDC/Srzr(Y)O3/YSZ Heterointerfaces

Solid oxide fuel cells (SOFCs) have attracted significant attention over recent years due to their promising use as source of clean and efficient power generation. Towards the goal of enhancing the efficiency of these devices, it is important to eludicate the mechanisms governing fundamental electrochemical processes, specifically incorporation and transport of oxygen species across heterostructures. Degradation of cell performance has been attributed to the formation of SrZrO3 (SZ), especially along the GDC/YSZ interface, resulting from cation interdiffusion across LSCF/GDC/YSZ heterostructures. In this study, using a combination of isotope oxygen tracer and secondary ion mass spectroscopy (SIMS) depth profiling, we examined oxide ion transport in dense SZ and Y-doped SrZrO3 (SZY) thin films in conjunction with other oxide materials in a multilayered heterostructure, viz., GDC/SZ(Y)/YSZ. The GDC/SZ(Y) multilayers were prepared on (100) YSZ single crystal substrates using pulsed laser deposition; X-ray diffraction results confirmed that the SZ and SZY films were highly oriented along (h00). SIMS depth profile measurements after isotope exchange revealed that ionic transport is drastically inhibited at the SZ(Y)/YSZ interface, indicating the existence of an oxide ion barrier which blocks ionic flow. A similar behavior was also observed at the GDC/SZ interface; however, this was not observed for GDC/SZY. To elucidate the mechanism for the oxide ion blocking effect, we performed detailed microstructural analyses of the interfaces using transmission electron microscopy (TEM) and spatially resolved electron energy loss spectroscopy (EELS) technique. TEM results showed that the GDC/SZ(Y) and SZ(Y)/YSZ interfaces are atomically sharp and devoid of any secondary phases. The SZ film also appears to contain a high density of microstructural defects such as stacking faults which extend across its thickness. Furthermore, evident changes in the O K-edge EELS spectra measured across the heterostructures suggest the possible existence of oxygen disorder in the YSZ region adjacent to the SZ(Y)/YSZ interface. This may indicate a possible link between oxygen disorder, which can effectively break the oxygen diffusion pathways, and blocking of oxide ion transport across the SZ(Y)/YSZ interface.

Transmission electron microscopy of carbon-coated and iron-doped titania nanoparticles

We present a study on the properties of iron (Fe)-doped and carbon (C)-coated titania (TiO2) nanoparticles (NPs) which has been compiled by using x-ray diffraction (XRD), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS). These TiO2 NPs were prepared by using the flame synthesis method. This method allows the simultaneous C coating and Fe doping of TiO2 NPs. XRD investigations revealed that the phase of the prepared NPs was anatase TiO2. Conventional TEM analysis showed that the average size of the TiO2 NPs was about 65 nm and that the NPs were uniformly coated with the element C. Furthermore, from the x-ray energy dispersive spectrometry analysis, it was found that about 8 at.% Fe was present in the synthesized samples. High-resolution TEM (HRTEM) revealed the graphitized carbon structure of the layer surrounding the prepared TiO2 NPs. HRTEM analysis further revealed that the NPs possessed the crystalline structure of anatase titania. Energy-filtered TEM (EFTEM) analysis showed the C coating and Fe doping of the NPs. The ratio of L3 and L2 peaks for the Ti-L23 and Fe-L23 edges present in the core loss electron energy loss spectroscopy (EELS) revealed a +4 oxidation state for the Ti and a +3 oxidation state for the Fe. These EELS results were further confirmed with XPS analysis. The electronic properties of the samples were investigated by applying Kramers–Kronig analysis to the low-loss EELS spectra acquired from the prepared NPs. The presented results showed that the band gap energy of the TiO2 NPs decreased from an original value of 3.2 eV to about 2.2 eV, which is quite close to the ideal band gap energy of 1.65 eV for photocatalysis semiconductors. The observed decrease in band gap energy of the TiO2 NPs was attributed to the presence of Fe atoms at the lattice sites of the anatase TiO2 lattice. In short, C-coated and Fe-doped TiO2 NPs were synthesized with a rather cost-effective and comparatively easily scalable method. The presented analysis enables us to predict the excellent efficiency of these NPs for solar-cell and photo-catalysis applications.

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

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

Lithium Transport of Fast Battery Cycles in a LiMn2O4 Cathode Imaged By Operando Eels

Lithium ion batteries are required to be fast-chargeable. However, it has been reported that fast charge causes low reversible capacity and fast degradation of electrode materials [1]. Recently, in-situ observation of lithium ion batteries has been reported that phase transformation behaviour of cathode materials changed depending on charge rate. In-situ XRD studies showed that meta-stable phase appeared during fast charge, but not during slow charge in LiFePO4 cathode [2]. Our previous in-situ TEM studies on LiMn2O4 cathode showed that during fast charge-discharge two-phase reaction continued to the voltage range of solid-solution reaction [3]. Also, it was imaged that Li-excess tetragonal phase appeared at the interface between cathode and electrolyte during early stage of 4 V range [4]. These results suggest the different lithium transport mechanism of fast charge from that of slow charge. However, XRD and TEM methods monitor the structural change, not lithium ion itself. Direct Li imaging method would be very helpful to reveal the lithium transport behaviour during fast charge. Electron energy loss spectroscopy (EELS) is one of most suitable methods to detect lithium ion itself because Li-K edge peak due to the existence of lithium ions can be detected. Furthermore, recent quantitative analysis of EELS can visualize the lithium concentration change simply [5]. In this study, we performed operando EELS mapping for understanding the lithium transport by using our developed nano battery, which consists of LiMn2O4 nanowire cathode, ionic liquid electrolyte and Li4Ti5O12 anode. The nano battery was charged or discharged in TEM during operando EELS observation as loaded in our homemade in-situ TEM sample holder. Charge-discharge was performed by cyclic voltammetry of which scan speed was 0.55mV/s. EELS spectrum was recorded by Gatan Tridiem ER spectrometer (Gatan, Inc.) in aberration corrected TEM, R005 [6] which is equipped with cold field emission gun. The acceleration voltage was 200kV and the convergent semi-angle of electron probe was 23 mrad. The entrance aperture size was 60 mrad and the energy dispersion of 0.2eV/ch was used. The full width half maximum of zero loss peak was 1 eV. The pixel size of EELS images was around 9 x 9 nm2. The electron probe current was less than 5 pA in order to suppress electron beam damage. The dwell time per pixel was 0.2 s and the probe size was adjusted to pixel size. During fast battery cycles, we found that lithium concentration changed with time delay with the cell current change in both of charge and discharge. Furthermore, the lithium concentration was imaged to change from the area far from the cathode/electrolyte interface. The observed lithium concentration change cannot be explained by conventional diffusion model, but the lithium drift model that lithium moves due to electric potential gradient inside cathode caused by high charge rate. In addition, after the first battery cycle lithium concentration changed only slightly around the range of x~1 in LixMn2O4 near the interface. It is attributed that solid electrolyte interface formation at high voltage after charge makes the chemical potential changed locally as an interface effect. We believe that these findings open the new way to understand the phase transformation under non-equilibrium state such fast charge as well as the new strategy to design fast chargeable batteries. [1] S.S. Choi, H.S. Lim, J. Power Sources 2002, 111, 130-136. [2] H. Liu, F. C. Strobridge, O. J. Borkiewicz, K. M. Wiaderek, K. W. Chapman, P. J. Chupas, C. P. Grey, Science 2014, 344, 1252817 [3] S. Lee, Y. Oshima, E. Hosono, H. Zhou, K. Kim, H. M. Chang, R. Kanno, K. Takayanagi, ACS Nano, 2015, 9, 626 [4] S. Lee, Y. Oshima, E. Hosono, H. Zhou, K. Kim, H. M. Chang, R. Kanno, K. Takayanagi, J. Phys. Chem. C 2013, 117, 24236 [5] N. Taguchi, T. Akita, H. Sakaebe, K. Tatsumi, Z. Ogumi, J. Electrochem. Soc. 2013, 160, A2293 [6] H. Sawada, Y. Tanishiro, N. Ohashi, T. Tomita, F. Hosokawa, T. Kaneyama, Y. Kondo, K. Takayanagi, J. Electron. Microsc. 2009, 58, 357

Electron energy loss spectroscopy of excitons in two-dimensional-semiconductors as a function of temperature

We have explored the benefits of performing monochromated Electron Energy Loss Spectroscopy (EELS) in samples at cryogenic temperatures. As an example, we have observed the excitonic absorption peaks in single layer Transition Metal Dichalcogenides. These peaks appear separated by small energies due to spin orbit coupling. We have been able to distinguish the split for MoS2 below 300 K and for MoSe2 below 220 K. However, the distinction between peaks is only clear at 150 K. We have measured the change in absorption threshold between 150 K and 770 K for MoS2 and MoSe2. We discuss the effect of carbon and ice contamination in EELS spectra. The increased spectral resolution available made possible with modern monochromators in electron microscopes will require the development of stable sample holders which reaches temperatures far below that of liquid nitrogen.

XPS and EELS characterization of Mn2SiO4, MnSiO3 and MnAl2O4

X-ray Photoelectron Spectroscopy (XPS) and Electron Energy Loss Spectroscopy (EELS) are strong candidate techniques for characterizing steel surfaces and substrate-coating interfaces when investigating the selective oxidation and reactive wetting of advanced high strength steels (AHSS) during the continuous galvanizing process. However, unambiguous identification of ternary oxides such as Mn2SiO4, MnSiO3, and MnAl2O4 by XPS or EELS, which can play a significant role in substrate reactive wetting, is difficult due to the lack of fully characterized standards in the literature. To resolve this issue, samples of Mn2SiO4, MnSiO3 and MnAl2O4 were synthesized and characterized by XPS and EELS. The unique features of the XPS and EELS spectra for the Mn2SiO4, MnSiO3 and MnAl2O4 standards were successfully derived, thereby allowing investigators to fully differentiate and identify these oxides at the surface and subsurface of Mn, Si and Al alloyed AHSS using these techniques.

Automated background subtraction technique for electron energy-loss spectroscopy and application to semiconductor heterostructures.

Electron energy-loss spectroscopy (EELS) has become a standard tool for identification and sometimes also quantification of elements in materials science. This is important for understanding the chemical and/or structural composition of processed materials. In EELS, the background is often modelled using an inverse power-law function. Core-loss ionization edges are superimposed on top of the dominating background, making it difficult to quantify their intensities. The inverse power-law has to be modelled for each pre-edge region of the ionization edges in the spectrum individually rather than for the entire spectrum. To achieve this, the prerequisite is that one knows all core losses possibly present. The aim of this study is to automatically detect core-loss edges, model the background and extract quantitative elemental maps and profiles of EELS, based on several EELS spectrum images (EELS SI) without any prior knowledge of the material. The algorithm provides elemental maps and concentration profiles by making smart decisions in selecting pre-edge regions and integration ranges. The results of the quantification for a semiconductor thin film heterostructure show high chemical sensitivity, reasonable group III/V intensity ratios but also quantification issues when narrow integration windows are used without deconvolution.

Quasinormal mode theory and modelling of electron energy loss spectroscopy for plasmonic nanostructures

Understanding light–matter interactions using localized surface plasmons (LSPs) is of fundamental interest in classical and quantum plasmonics and has a wide range of applications. In order to understand the spatial properties of LSPs, electron energy loss spectroscopy (EELS) is a common and powerful method of spatially resolving the extreme localized fields that can be obtained with metal resonators. However, modelling EELS for general shaped resonators presents a major challenge in computational electrodynamics, requiring the full photon Green function as a function of two space points and frequency. Here we present an intuitive and computationally simple method for computing EELS maps of plasmonic resonators using a quasinormal mode (QNM) expansion technique. By separating the contribution of the QNM and the bulk material, we give closed-form analytical formulas for the plasmonic QNM contribution to the EELS maps. We exemplify our technique for a split ring resonator, a gold nanorod, and a nanorod dimer structure. The method is accurate, intuitive, and gives orders of magnitude improvements over direct dipole simulations that numerically solve the full 3D Maxwell equations. We also show how the same QNM Green function can be used to obtain the Purcell factor (and projected local density of optical states) from quantum dipole emitters or two level atoms, and we demonstrate how the spectral features differ in general to the EELS spectrum.