Atomic-resolution electron energy loss spectroscopy imaging in aberration corrected scanning transmission electron microscopy

The "delocalization" of inelastic scattering is an important issue for the ultimate spatial resolution of innershell spectroscopy in the electron microscope. It is demonstrated in a nonlocal model for electron energy loss spectroscopy (EELS) that delocalization of scanning transmission electron microscopy (STEM) images for single, isolated atoms is primarily determined by the width of the probe, even for light atoms. We present experimental data and theoretical simulations for Ti L-shell EELS in a [100] SrTiO3 crystal showing that, in this case, delocalization is not significantly increased by dynamical propagation. Issues relating to the use of aberration correctors in the STEM geometry are discussed.     

Unoccupied electron states in low-energy electron total-current and transmission spectroscopy of molybdenum disulfide

A theoretical interpretation of the fine structure in the low-energy electron total-current spectra and low-energy electron transmission spectra measured along the normal to the (0001)MoS₂ single-crystal surface is proposed. The calculations took into account the energy dependence of band level broadening and the electronic structure of the high final unoccupied states (above the vacuum level E_vac), which become occupied by electrons entering a solid. A comparison with the available experimental and theoretical data is performed. The effects of the bulk band structure are shown to play a dominant role in the formation of the spectra (the extrema in the spectra identify the energy position of critical points, such as the band edges or the points of extremal curvature of the dispersion branches). The proposed method makes it possible to separate the bulk effects in spectra from surface effects, this approach can be used to advantage in monitoring the state of a surface in the course of its treatment.     

Practical spatial resolution of electron energy loss spectroscopy in aberration corrected scanning transmission electron microscopy

The resolution of electron energy loss spectroscopy (EELS) is limited by delocalization of inelastic electron scattering rather than probe size in an aberration corrected scanning transmission electron microscope (STEM). In this study, we present an experimental quantification of EELS spatial resolution using chemically modulated 2×(LaMnO(3))/2×(SrTiO(3)) and 2×(SrVO(3))/2×(SrTiO(3)) superlattices by measuring the full width at half maxima (FWHM) of integrated Ti M(2,3), Ti L(2,3), V L(2,3), Mn L(2,3), La N(4,5), La N(2,3) La M(4,5) and Sr L(3) edges over the superlattices. The EELS signals recorded using large collection angles are peaked at atomic columns. The FWHM of the EELS profile, obtained by curve-fitting, reveals a systematic trend with the energy loss for the Ti, V, and Mn edges. However, the experimental FWHM of the Sr and La edges deviates significantly from the observed experimental tendency.     

Spatial resolution of transmission electron spectroscopy for the study of ordered materials

The structure of barium-rich oxides of the Ba-Bi-O system was studied with the transmission electron spectroscopy (TEM) and electron diffraction techniques. The results show that TEM cannot reveal the presence of an ordered state in a material composed of irregular intergrown crystallites, if their sizes are less than several nanometers.     

2D atomic mapping of oxidation states in transition metal oxides by scanning transmission electron microscopy and electron energy-loss spectroscopy

Using a combination of high-angle annular dark-field scanning transmission electron microscopy and atomically resolved electron energy-loss spectroscopy in an aberration-corrected transmission electron microscope we demonstrate the possibility of 2D atom by atom valence mapping in the mixed valence compound Mn3O4. The Mn L(2,3) energy-loss near-edge structures from Mn2+ and Mn3+ cation sites are similar to those of MnO and Mn2O3 references. Comparison with simulations shows that even though a local interpretation is valid here, intermixing of the inelastic signal plays a significant role. This type of experiment should be applicable to challenging topics in materials science, such as the investigation of charge ordering or single atom column oxidation states in, e.g., dislocations.     

Investigating carbonization and graphitization using electron energy loss spectroscopy (EELS) in the transmission electron microscope (TEM)

Electron energy loss spectroscopy (EELS) in the transmission electron microscope (TEM) is explored as a useful characterization technique in the study of carbonization and graphitization of organic precursors. A model series of carbon materials was prepared from highly graphitizable petroleum pitch heat treated in the range 200–2730°C. Initial characterization was performed using the established techniques of X-ray diffraction (XRD), He pycnometry, TEM, electron diffraction and high-resolution lattice imaging (HREM). EELS in the TEM was then examined. Two routes are presented to quantify the change in the proportion of sp ² type hybridization accompanying the heat treatment as the material transforms to the graphitic state. Both routes suggest an initial relative sp ² content of ～70%, rapidly increasing to ～90% during mesophase development and carbonization, and then slowly increasing to 100% during graphitization. The peak position of the bulk valence plasmon (π?+?σ) is shown to be an excellent measure of the degree of graphitic character, and its fundamental dependence upon sample density (ρ) is confirmed. The appearance and definition of features within the core loss region representing the density of unoccupied σ* states are demonstrated to be an excellent measure of the extent of order. Finally, a method is established by which to extract the C–C bond length from core loss EELS spectra with an accuracy of ±0.1?pm. This method suggests an average bond length of 1.44?Å in samples with low heat treatment temperatures, decreasing to the theoretical length of 1.42?Å as both the heteroatom content and proportion of non-sp ²-type hybridized carbon atoms decrease.     

Mechanisms of charging in electron spectroscopy

From the use of physical arguments based on classical electrostatics and elementary solid state physics, the role of the various parameters involved in the charging mechanisms of insulating materials is analysed in detail when these insulating specimens are investigated by surface analytical techniques (mainly XPS and e⁻AES). The role of the sub-surface composition and structure is outlined and the strong correlations between charging effects and some radiation damage effects are pointed out. Some strategies are also deduced to minimise these effects.     

Detection limits in Auger electron spectroscopy

The sources of background noise in Auger electron microanalysis are analyzed in order to evaluate the minimum detectable concentration x_m and the minimum number of detectable atoms y_m that can be reached. The best choices of operating conditions (the energy E₀, intensity I₀, and spot size d₀ of the incident electron beam, and the duration of the experiment t_e) are deduced for bulk and thin film analysis. The main results are: (i) The choice of E₀ is not very stringent, at least when E₀ ? 5E_i(A), where E_i(A) is the ionization energy, (ii) For a given electron dose received by the sample, x_m is improved by the use of the largest incident spot size while y_m is improved by the use of the finest spot size. The results also hold for other microanalytical techniques such as electron energy loss spectroscopy or electron probe microanalysis. (iii) Chemical identification of a single atom will be possible on samples able to tolerate very large electron doses by using incident electron beams 10 nm or less in diameter. The expected performance of a coincidence technique first suggested by Wittry is also discussed.     

The secondary-electron background problem in electron excited auger electron spectroscopy

Dynamic background subtraction is used to demonstrate that the recently suggested spline-polynomial scheme for characterizing the secondary electron background neglects an important aspect of the Auger feature. As a consequence of this neglect, area measurements using the spline approximation are difficult to relate to the true Auger current.     

Some examples of the application of Mössbauer spectroscopy and transmission electron microscopy to micas

I discuss the weaknesses and strengths of Mössbauer spectroscopy and transmission electron microscopy and present the potential of combining them using experimental weathering of biotite as an example. A natural biotite was treated in acid at room temperature and the reaction products were removed by a continuous flow of an external eluent that was in contact with the mineral suspension through a dialysis membrane. The fractionation of Mg/Fe into the fluid was determined by wet chemical analysis, the state of Fe in the solid was monitored by Mössbauer spectroscopy, and the structural changes were characterized by transmission electron microscopy. Weathering is controlled primarily by pH, the type of acid used, and K selectivity of the solid. Once equilibrium has been reached, further weathering does not affect the oxidation state of iron. The tetrahedral layer collapses during the last phase of weathering leaving an amorphous phase rich in Si and Al. Moreover, transmission electron microscopy shows that weathering is a discontinuous processes resulting in quasi-periodic texture. The periodicity is controlled by the concentration of the K in solution.     

Interpreting electron transmission spectroscopy and negative ion mass spectrometry data using a spherical potential well model

Experimental data obtained using electron transmission spectroscopy and negative ion mass spectrometry based on resonance electron capture are interpreted within the framework of a spherical potential well model in application to a series of chloro-and bromoalkane molecules. Allowance for the scattering of a single partial p-wave of the incoming electron makes possible (i) reproduction of the ratio of a resonance peak width to the electron energy observed in the electron transmission spectra and (ii) establishment of a relation between the total cross section of electron scattering on a molecule and the dissociative electron attachment cross section. The proposed model offers a radical simplification of the approach developed previously based on the Fashbach-Fano resonance theory.     

高对比度透射光谱中碰撞增强的Hanle共振

在高对比度透射光谱中观察到线宽18mG(FWHM)钠原子基态中碰撞增强的Hanle共振.此共振的线宽仍表现出Dicke变窄效应,但信号的强度却随着缓冲气体压强急剧地增加.     

Investigation of nanoparticulate silicon as printed layers using scanning electron microscopy,transmission electron microscopy,X‐ray absorption spectroscopy and X‐ray photoelectron spectroscopy

The presence of native oxide on the surface of silicon nanoparticles is known to inhibit charge transport on the surfaces. Scanning electron microscopy (SEM) studies reveal that the particles in the printed silicon network have a wide range of sizes and shapes. High‐resolution transmission electron microscopy reveals that the particle surfaces have mainly the (111)‐ and (100)‐oriented planes which stabilizes against further oxidation of the particles. X‐ray absorption spectroscopy (XANES) and X‐ray photoelectron spectroscopy (XPS) measurements at the O 1s‐edge have been utilized to study the oxidation and local atomic structure of printed layers of silicon nanoparticles which were milled for different times. XANES results reveal the presence of the +4 (SiO₂) oxidation state which tends towards the +2 (SiO) state for higher milling times. Si 2p XPS results indicate that the surfaces of the silicon nanoparticles in the printed layers are only partially oxidized and that all three sub‐oxide, +1 (Si₂O), +2 (SiO) and +3 (Si₂O₃), states are present. The analysis of the change in the sub‐oxide peaks of the silicon nanoparticles shows the dominance of the +4 state only for lower milling times.     

Continuous X-ray-induced Auger electron spectroscopy

Bremsstrahlung emission from a tungsten anode has been used, for the first time, to obtain X-ray-induced Auger electron spectra (CXAES) in a conventional X-ray photoelectron spectrometer. Auger KLL signal and background intensities obtained from a silicon—aluminium sample have been compared with those obtained un der the same experimental conditions but using a standard aluminium anode. For such an aluminium anode, the respective contributions of the bremsstrahlung and the characteristic radiation to the C_KVV intensity have also been established.     

Conversion electron spectroscopy at IGISOL

Conversion elecron spectroscopy has been an important part of the nuclear spectrocopy research at the Department of Physics of the University of Jyväskylä since the commissioning of the first cyclotron in the mid 1970s. At the IGISOL facility a specialiced conversion electron spectrometer ELLI was developed in the late 1980s. The first results with ELLI were obtained using the beams from the old MC-20 cyclotron to study newly discovered isotopes of refractory fission products. In the present K130 cyclotron laboratory ELLI has been utilized in many decay-spectroscopy experiments both neutron-deficient and neutron-rich side of the valley of stability. In the early 2000s the new JYFLTRAP ion trap system overthrew ELLI from its permanent place in the IGISOL beamline. Conversion electron spectroscopy has continued with the new Penning trap that has been used in in-trap electron spectroscopy tests and post-trap electron spectroscopy is foreseen.