EELS Data Research Articles

Simultaneous Acquisition of 4D and EELS Data by Newly Developed Pixelated STEM Detector

Simultaneous Acquisition of 4D and EELS Data by Newly Developed Pixelated STEM Detector

Simultaneous Acquisition of 4D and EELS Data by Newly Developed Pixelated STEM Detector

Simultaneous Acquisition of 4D and EELS Data by Newly Developed Pixelated STEM Detector

Simultaneous HAADF & EELS Data Acquisition for Relative Quantification of Temperature and Thickness Effects on Thermal Diffuse Scattering in STEM.

Simultaneous HAADF & EELS Data Acquisition for Relative Quantification of Temperature and Thickness Effects on Thermal Diffuse Scattering in STEM.

Electronic structure characterization of TiO2-II with the α-PbO2 structure by electron-energy-loss-spectroscopy and comparison with anatase, brookite, and rutile

TiO2-II is a high pressure form of titania with a density about 2% larger than that of rutile. In contrast to the common polymorphs anatase, brookite and rutile its electronic structure and optical properties are poorly characterized. Here we report on a comparative electron-energy-loss-spectroscopy (EELS) study for which high resolution valence-loss and core-loss EELS data were acquired from nanocrystalline (<75 ​nm sized) titania particles with an energy resolution of about 0.2 ​eV. Electronic structure features revealed from titanium L3,2 and oxygen K electron energy loss near-edge structures show a strong similarity of TiO2-II with both rutile and brookite, which is attributed to similarities in the connectivity of octahedral TiO6 units with neighboring ones. From combined valence-loss EELS and UV-VIS diffuse reflectance spectroscopy data the band gap of TiO2-II was determined to be indirect and with a magnitude of ∼3.18 ​eV, which is very similar to anatase (indirect, ∼3.2 ​eV), and distinctly different from rutile (direct, ∼3.05 ​eV) and brookite (direct, ∼3.45 ​eV).

Correlative study between the local atomic and electronic structures of amorphous carbon materials via 4D-STEM and STEM-EELS

Amorphous materials have been used in a range of electronic and photonic applications, and the need for quantitative analytical techniques on their local structural information is growing. We present a comprehensive analysis of the atomic and electronic structures of an amorphous material, amorphous carbon (a-C), with scanning transmission electron microscopy (STEM)-derived techniques, four-dimensional STEM (4D-STEM), and STEM-electron energy loss spectroscopy (STEM-EELS). Each diffraction pattern of an a-C layer stack acquired via 4D-STEM is transformed into a reduced density function (RDF) and a radial variance profile (RVP) to retrieve the information on the atomic structures. Importantly, a machine-learning approach (preferably cluster analysis) separates distinct features in the EELS and RDF datasets; it also describes the spatial distributions of these features in the scanned regions. Consequently, we showed that the differences in the sp2/sp3 ratio and the involvement of additional elements led to changes in the bond length. Furthermore, we identified the dominant types of medium-range ordering structures (diamond-like or graphite-like nano-crystals) by correlations among the EELS, RDF, and RVP data. The information obtained via STEM-EELS and 4D-STEM can be strongly correlated, leading to the comprehensive characterization of the a-C layer stack for a nanometer-scale area. This process can be used to investigate any amorphous material, thereby yielding comprehensive information regarding the origins of notable properties.

Doping Dependent Magnetic Behavior in MBE Grown GaAs1-xSbx Nanowires

Intrinsic and Te-doped GaAsSb nanowires with diameters ~100–120 nm were grown on a p-type Si(111) substrate by molecular beam epitaxy (MBE). Detailed magnetic, current/voltage and low-energy electron energy loss spectroscopy measurements were performed to investigate the effect of Te-doping. While intrinsic nanowires are diamagnetic over the temperature range 5–300 K, the Te-doped nanowires exhibit ferromagnetic behavior with the easy axis of magnetism perpendicular to the longitudinal axis of the nanowire. The temperature dependence of coercivity was analyzed and shown to be in agreement with a thermal activation model from 50–350 K but reveal more complex behavior in the low temperature regime. The EELS data show that Te doping introduced a high density of states (DOS) in the nanowire above the Fermi level in close proximity to the conduction band. The plausible origin of ferromagnetism in these Te-doped GaAsSb nanowires is discussed on the basis of d0 ferromagnetism, spin ordering of the Te dopants and the surface-state-induced magnetic ordering.

Surface, Subsurface, and Bulk Oxygen Vacancies Quantified by Decoupling and Deconvolution of the Defect Structure of Redox-Active Nanoceria.

Oxygen vacancy concentrations are critical to the redox/photocatalytic performance of nanoceria, but their direct analysis is problematic under controlled atmospheres but essentially impossible under aqueous conditions. The present work provides three novel approaches to analyze these data from XPS data for the three main morphologies of nanoceria synthesized under aqueous conditions and tested using in vacuo analytical conditions. First, the total oxygen vacancy concentrations are decoupled quantitatively into surface-filled, subsurface-unfilled, and bulk values. Second, the relative surface areas are calculated for all exposed crystallographic planes. Third, XPS and redox performance data are deconvoluted according to the relative surface areas of these planes. Correlations based on two independent empirical results from volumetric surface XPS, combined with sequential deep XPS and independent EELS data, confirm that these approaches provide quantitative determinations of the different oxygen vacancy concentrations. Critically, the redox/photocatalytic performance depends not on the total oxygen vacancy concentration but on the concentration of the active sites on each plane in the form of subsurface-unfilled oxygen vacancies. This is verified by the pH-dependent performance, which can be increased significantly by exposing these vacancies to the surroundings. These approaches have significance to the design and engineering of semiconducting materials exposed to the environment.

Small-moment paramagnetism and extensive twinning in the topochemically reduced phase Sr2ReLiO5.5.

Reaction of the cation-ordered double perovskite Sr2ReLiO6 with dilute hydrogen at 475 °C leads to the topochemical deintercalation of oxide ions from the host lattice and the formation of a phase of composition Sr2ReLiO5.5, as confirmed by thermogravimetric and EELS data. A combination of neutron and electron diffraction data reveals the reduction process converts the -Sr2O2-ReLiO4-Sr2O2-ReLiO4- stacking sequence of the parent phase into a -Sr2O2-ReLiO3-Sr2O2-ReLiO4-, partially anion-vacant ordered sequence. Furthermore a combination of electron diffraction and imaging reveals Sr2ReLiO5.5 exhibits extensive twinning - a feature which can be attributed to the large, anisotropic volume expansion of the material on reduction. Magnetisation data reveal a strongly reduced moment of μeff = 0.505μB for the d1 Re6+ centres in the phase, suggesting there remains a large orbital component to the magnetism of the rhenium centres, despite their location in low symmetry coordination environments.

Ondrej Krivanek's early scientific research

In 1806, Humphrey Davey said that "nothing promotes the advancement of science so much as a new instrument". This paper reviews some of the lesser-known achievements of Ondrej's early career, and reminds us of the level of performance of instruments in those days, in order to appreciate how great has been the progress in instrumentation, much of it due to Ondrej and his leadership, since then. Some new results in the field of EELS are described, including extraction of the time-dependence of the dielectric response (with better time resolution than an X-ray free electron laser (XFEL)) from Nion EELS data. An approximation for atomic-resolution imaging which includes multiple scattering effects is given for biological samples, for use with aberration-corrected instruments when these become needed at the higher beam energies required to preserve the projection approximation, on which the 3D merging of single-particle cryo-EM images is based. We also discuss the requirements for out-running radiation damage using pulsed electron beams, a worthy final challenge for OLK.

Transition radiation in EELS and cathodoluminescence

The excitation probability of transition radiation is measured for varying beam energies in a transmission electron microscope once using optical spectrometry of the emitted light and second using electron energy loss spectrometry. In both cases similar results are found being in good agreement with theory. The knowledge about this probability enables us to judge whether or not transition radiation has to be considered in EELS and CL data interpretation. Additionally it is shown that the emission of transition radiation happens at the sample surfaces only, when the electron passes the vacuum/sample interface and thus feeling the change of its dielectric environment. We demonstrate that in the case of aluminum the influence of transition radiation on the low loss EELS spectrum is only minor and conclude that it might be negligible for many other materials.

Single atom spectroscopy: Decreased scattering delocalization at high energy losses, effects of atomic movement and X-ray fluorescence yield

Single atom localization and identification is crucial in understanding effects which depend on the specific local environment of atoms. In advanced nanometer scale materials, the characteristics of individual atoms may play an important role. Here, we describe spectroscopic experiments (electron energy loss spectroscopy, EELS, and Energy Dispersed X-ray spectroscopy, EDX) using a low voltage transmission electron microscope designed towards single atom analysis. For EELS, we discuss the advantages of using lower primary electron energy (30keV and 60keV) and higher energy losses (above 800eV). The effect of atomic movement is considered. Finally, we discuss the possibility of using atomically resolved EELS and EDX data to measure the fluorescence yield for X-ray emission.

Probing the active sites for water–gas shift over Pt/molybdenum carbide using multi-walled carbon nanotubes

Pt/Mo2C is known to have water–gas shift (WGS) rate per total mole of Pt that is higher than on any oxide-supported Pt catalyst. The difficulties for the characterization of Pt/Mo2C were overcome by preparing the carbide using Multi-Walled Carbon Nanotubes (MWCNT), which showed the expected kinetics. X-ray absorption spectroscopy confirmed formation of alloy with Mo and STEM–EELS data confirmed the elemental composition of Pt particles as Pt–Mo for a series of Pt/Mo2C/MWCNT catalysts. A linear correlation is obtained between the WGS rate per gram at 120°C and the area covered by Pt–Mo alloy nanoparticles on Mo2C, estimated using STEM images. Pt is shown to preferentially bind to the Mo2C domains. The kinetic data in tandem with the characterization techniques suggest that the active sites are formed by Pt–Mo alloy nanoparticles in contact with Mo2C, not by the formation of the alloy. The water activation on Mo2C is suggested to be the cause for the higher WGS rate over Pt/Mo2C.

Inversion of STEM EELS Data to Obtain Site Occupancy and Near Edge Structure

Inversion of STEM EELS Data to Obtain Site Occupancy and Near Edge Structure

New Approach to Analysis of Noisy EELS Data

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Synthesis of 4H-SrMnO3.0 Nanoparticles from a Molecular Precursor and Their Topotactic Reduction Pathway Identified at Atomic Scale

Stoichiometric 4H-SrMnO3.0 nanoparticles have been synthesized from thermal decomposition of a new molecular heterometallic precursor [SrMn(edta)(H2O)5]·3/2H2O whose crystal structure has been solved by single crystal X-ray diffraction. From this precursor, highly homogeneous 4H-SrMnO3.0 nanoparticles, with average particle size of 70 nm, are obtained. The agglomeration of these nanoparticles maintains the sheet-assembling morphology of the metal–organic compound. Local structural information, provided by atomically resolved microscopy techniques, shows that 4H-SrMnO3.0 nanoparticles exhibit the same general structural features as the bulk material, although structural disorder, due to edge dislocations, is observed. The nanometric particle size enables a topotactic reduction process at low temperature stabilizing a metastable 4H-SrMnO2.82 phase. The oxygen deficiency is accommodated through extra cubic layers breaking the ...chch... 4H-sequence. These defect areas are Mn3+ rich, as evidenced by high energy resolution EELS data. Magnetic characterization of nano-SrMnO3.0 shows significant variations with respect to the bulk material. Besides the dominant antiferromagnetic interactions, a weak ferromagnetic contribution as well as exchange bias and a glassy-like component are present. After the reduction process, the stabilization of Mn3+ in the 4H-structure gives rise to magnetic anomalies in the 40–60 K temperature range. The origin of such magnetic features is discussed.

Structure and magnetic properties of 4H-SrMnO3-δ(δ=0.0 and 0.18) nanoparticles synthesized by thermal decomposition of appropriate precursor

ABSTRACTStoichiometric 4H-SrMnO3.0 nanoparticles have been successfully synthesized for the first time from thermal decomposition of a new heterometallic precursor [SrMn(edta)(H2O)5]·3/2H2O. From this precursor, highly homogeneous 4H-SrMnO3.0 nanoparticles with average particle size 70 nm are obtained. Local structural information, provided by atomically-resolved microscopy techniques, shows that 4H-SrMnO3.0 nanoparticles exhibit the same general structural features than the bulk material, although structural disorder, due to edge-dislocations, is observed. The nanometric size of particles enables a topotactic reduction process at low temperature stabilizing a metastable 4H-SrMnO2.82 phase. The oxygen deficiency is accommodated through extra cubic layers breaking the …hchc… 4H-sequence. These defect areas are Mn3+ rich as evidenced by high energy resolution EELS data. Magnetic characterization of nano-4H-SrMnO3-δ shows significant variations with respect to the bulk material.

Effective Defect Control in TiN Metal Hard Mask Cu/Low-k Dual Damascene Process

Metallic hard masks (MHM) are routinely employed in Cu/low k dual damascene (DD) etching, but can create defectivity problem. N2 plasma post-etch treatment (N2PET) based on high substrate temperature has been developed to provide effective TiFx residue reduction and MHM defect prevention without low k damage and productivity concerns. Strong gains in surface de-fluorination with substrate temperature and N2PET time was determined. SLIC, XPS, SEM data show 90% reduction of F residue on TiN and no defects on pattern at optimized N2PET. AES and EELS data show that “TiFx” defects are actually TiOx crystals covered by TiFx residue catalyzing the crystal growth. N2PET de-fluorination and defect growth are in focus of this study. An alternative approach in preventing defect growth by surface passivation in CF4/C4F8 etch chemistry was also studied. Both methods, N2PET cleaning and surface passivation, provide effective defect control in TiN MHM Cu/low-k DD etch process.

Direct Atomic Observation in Powdered 4H-Ba0.8Sr0.2Mn0.4Fe0.6O2.7

A new hexagonal polytype in the BaMn1-xFexO3-δ system has been stabilized. Powdered Ba0.8Sr0.2MnIV0.4FeIII0.6O2.70 crystallizes in the 4H hexagonal polytype (space group P63/mmc) according to X-ray diffraction. HAADF images and chemical maps with atomic resolution have been obtained by combining Cs-corrected electron microscopy and EELS spectroscopy. The structure is formed by dimers of face-sharing octahedra linked by corners. EELS data show a random distribution of the transition metals ions identified by Fe and Mn-L2,3 chemical maps. A systematic difference in contrast observed in the O–K signal mapping suggests that anion deficiency is randomly located along the hexagonal layers in agreement with ND data. The magnetic structure consists of ferromagnetic sheets with the magnetic moments aligned along the x-axis and coupled antiferromagnetically along the c-axis.

Controlled oxidation of mono-Si and Si3N4 under irradiation of composite ion beams at room temperature

Composite 1keV ion beam irradiation was used to oxidise the mono-Si and Si3N4 wafers at room temperature. It was shown the formation of ∼50nm amorphous SiO2 layer at the top of the wafer. XTEM EELS data proved the high quality of radiation-induced silicon oxide. In bouth cases, at the beginning of irradiation we have demonstrated the preferable oxidation of inner layers at the irradiation-induced maximun vacancy production depth.

Excitation spectrum of TTF-TCNQ: a finite temperature calculation

AbstractIn this paper we study the excitation spectrum of the organic conductor tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) using finite temperature calculations. The effect of electronelectron interaction is considered within the random phase approximation (RPA). Our results show the temperature dependent plasmon and dipolar mode corresponding qualitatively to the modes obtained previously using zero temperature formalism assigned to the observed excitations at 10 meV and 0.75 eV. These modes have an essential influence on the energy-loss function. The obtained results are in good qualitative agreement with the optical and EELS data of TTF-TCNQ.