Characteristic Electron Energy Loss Research Articles

Direct Visualization of Homogeneous Chemical Distribution in Functional Polyradical Microspheres.

It is demonstrated that the postfunctionalization of solid polymeric microspheres can generate fully and throughout functionalized materials, contrary to the expectation that core-shell structures are generated. The full functionalization is illustrated on the example of photochemically generated microspheres, which are subsequently transformed into polyradical systems. Given the all-organic nature of the functionalized microspheres, characterization methods with high analytical sensitivity and spatial resolution are pioneered by directly visualizing the inner chemical distribution of the postfunctionalized microspheres based on characteristic electron energy loss signals in transmission electron microscopy (TEM). Specifically, ultrasonic ultramicrotomy is combined successfully with electron energy loss spectroscopy (EELS) and electron spectroscopicimaging (ESI) during TEM. These findings open a key avenue for analyzing all-organic low-contrast soft-matter material structures, while the specifically investigated system concomitantly holds promise as an all-radical solid-state functional material.

Оптические свойства и электронные характеристики празеодима и неодима в конденсированном состоянии

The optical properties of unoxidized surfaces of polycrystalline Pr and Nd films in the spectral range 0.4 - 2.6 μm are studied. Optical constants were measured by Beattie ellipsometric method. Dispersion dependences of the optical conductivity σ, the reflectivity R, imaginary and real parts of the dielectric constant ε1 and ε2, and the function of characteristic electron energy losses Im (ε) -1 were calculated using the obtained optical constants. The paper presents the optical properties of both films and liquid metals studied earlier. The electronic characteristics of praseodymium and neodymium in solid thin-film and liquid states are calculated using the results of measurements in the infrared region of the spectrum using the two-band conductivity model.

The Electronic and Optical Properties of Thin Nanocluster Mo Films for Single-Photon UV Detectors

Results of a study of the electronic structure and optical properties of a novel material based on thin films comprised of Mo nanoclusters obtained by gas-phase magnetron sputtering are presented. The chemical composition of the obtained films immediately after deposition (in situ) and upon exposure to the atmosphere (ex situ) was investigated by X-ray photoelectron spectroscopy. It is shown that exposure to the atmosphere leads to “core–shell” oxidation of the nanoclusters the obtained films are composed of and changes in the valence band. The change in the electronic structure of the obtained films was investigated by spectro-scopy of the characteristic energy losses of electrons. The optical properties of the obtained films were investigated in the wavelength range of 185–800 nm. The possibility of creating thin-film photodetectors based on the obtained Mo nanocluster films for detecting isomeric nuclear transition decay in 229Th nuclei is discussed.

Production of Ablated CeO2 Particles with Nanodispersed Compositional Distribution

A technique for obtaining ablated CeO2 particles of nanodispersed composition has been developed. With the help of transmission electron microscopy and small-angle X-ray scattering diffractometry, it was found that the limiting particle size in a colloidal solution does not exceed 30 nm. It was established by spectroscopy of characteristic electron energy losses that the content of defects in oxygen vacancies increases with decreasing sizes of ablated nanoparticles.

Determination of the Optical Properties and Electrical Characteristics of Solid and Liquid Ytterbium with Ellipsometric Measurements

An ellipsometric method is used to study the optical properties of unoxidized surfaces of polycrystalline ytterbium film in the spectral range of 0.4–2.6 mm. The measured refractive indices and absorption coeffi cient of the film are used to calculate the dispersion dependences of the optical conductivity σ reflectivity R, the imaginary and real parts of the dielectric constant e1 and e2, and the characteristic electron energy loss functions Im(e–1). The infrared measurements are used in a two-band model for the conductivity to calculate the electronic characteristics of ytterbium in the solid and liquid states.

Characteristic energy loss of electrons in Mg with angle resolution

The article discusses electron energy loss of bulk and surface plasmons in solid polycrystalline Mg films. The experimental study of the electrons’ characteristic energy loss is conducted and its results are compared in a wide range of electron incidence angles on the sample (0°–89°), dispersion angles (5°–165°) and electron energies (100–600 eV). Electron wave refraction at the vacuum–solid state interface is considered as one of the factors determining the intensity of surface plasmons.

Effect of Spatial Dispersion on Plasmon Resonance in Silver Nanoparticles

Using the modified discrete sources method, the problem of calculating plasmon spectra of the characteristic energy loss of electrons during the interaction with silver nanoparticles from 2 to 8 nm in size is solved. The calculated spectra are compared with the experimental data confirming the significant spatial dispersion effect. The importance of the consideration of this factor when analyzing the properties of plasmonic nanoparticles for applications in biosensorics and biomedicine is discussed.

The Effect of the Ion Assistance Energy on the Electrical Resistivity of Carbon Films Prepared by Pulsed Plasma Deposition in a Nitrogen Atmosphere

Thin carbon films prepared by pulsed plasma ion-assisted deposition of graphite in an atmosphere of a mixture of argon and nitrogen are studied. The results of characteristic electron energy loss spectroscopy and electron diffraction indicate the increase in the graphite component with increasing ion assistance energy. The use of ion assistance during the film deposition makes it possible to control their resistivity by changing it from 105 to 102 Ω cm.

Optical Properties of Gadolinium in the Condensed State

The optical properties of gadolinium in liquid and solid states have been studied. The optical constants are measured by the Beatty ellipsometry method in the range of 0.48–2.6 μm. The dispersion dependences of light conductivity σ, reflectivity R, the imaginary and real parts of dielectric permittivity e1 and e2, and the function Im(e)-1 of the characteristic electron energy losses are calculated from the measured values of the refractive index and the absorption coefficient. The electronic characteristics of gadolinium in solid and liquid states are calculated on the basis of a two-band conductivity model with measurement results in the infrared spectral region.

Fundamental Optical Functions and Fine-Structure Parameters of Strontium–Selenide Crystal Transition Bands in the 0–40 eV Range

The spectral complex of fundamental optical functions of strontium-selenide (SrSe) crystal in the range 0–40 eV was determined. Spectra of the imaginary parts of three functions [transverse dielectric permittivity e2(E) and longitudinal volume –Im e–1 and surface –Im (1 + e)–1 characteristic electron energy losses] of SrSe crystal were deconvoluted into 36 elementary bands. Energies of maxima Ei, half-widths Hi, amplitudes Ii, areas Si, and oscillator strengths fi were determined for every band of the three spectra. The main spectral features of the optical functions and 36 elementary bands of SrSe in the range 3–35 eV due to excitons and transverse and longitudinal interband transitions were established. The calculations were based on experimental reflectance spectra and used the Kramers–Kronig integral relations, a modified combined Argand diagram method, and a number of computer programs.

Quantum Well on the n-GaAs Surface Irradiated by Argon Ions

The density of states of the valence band of a p-GaAs layer formed on an n-GaAs surface owing to the bombardment by 2500-eV Ar+ ions has been studied by photoelectron spectroscopy. A number of peaks have been detected in the spectrum of the edge of the valence band in the binding energy range EV < 1.2eV. Their number and energy positions correspond to the quantum confinement levels calculated for a hole quantum well on the surface with the width about the ion penetration depth Rp = 3.6nm. Electronic transitions from these levels to the bottom of the conduction band have been revealed in the spectrum of characteristic energy losses of electrons reflected from the surface. Thus, it has been shown that the action of the argon ion beam on n-GaAs results in the formation of a quantum well on the surface.

The use of AES and EELS for complex analysis of two-dimensional coatings and their growth process

Additional possibilities for complex analysis of two-dimensional coatings (thickness <1nm or <10ML) grown by physical vapor deposition (PVD) on a single-crystal silicon substrate under two deposition regimes have been revealed: 1) low-temperature (at a low beam temperature) and 2) high-temperature (at an elevated temperature of the beam), respectively. Coatings, including those in the form of pure metal and a silicide mixture, and their interface with the substrate have been analyzed by Auger electron spectroscopy (AES) and characteristic electron energy loss spectroscopy (EELS). A technology of the deposition from a ribboned source has been developed to ensure both deposition regimes. The conventional uses of AES are limited to the characterization of elemental composition, electron energy structure and coating thickness. For EELS, the conventional uses are the determination of phase types (valence electron density) and phase formation stages. The simultaneous use of the two methods and the choice of equal (and minimal) probing depths, ~ 2.5nm (primary electron energy 300eV), provided new possibilities for studying subnanometric two-dimensional coatings, in particular, for comparison of coating composition and density. The chosen probing depth also made it possible to characterize the interface between the coating and the substrate. At the same time, the use of similar probing depths made allowed using the thickness of the coating obtained from AES data for analyzing EELS data. In addition, other possibilities have been considered, i.e., the use of the following dependences: a) the energy of the plasmon satellite of the Auger peak vs the thickness of the coating for analyzing changes in the electron density in the near-interface layer of silicon; b) the attenuation of the Auger signal generated by marker atoms at the interface between the coating and the substrate for localizing the adsorption sites of the deposited atoms; c) the intensity and energy of the loss peaks in the EELS as a function of the primary electron energy for depth profiling of coating compositions. The use of two depth attenuation functions for two probing depths has enabled a quantitative Auger analysis of binary coatings. These advantages have provided the possibility of a more complete characterization of two-dimensional coatings and their interfaces with substrates, as well as the coating formation processes. In particular, it has for the first time become possible to identify the wetting nanophase layer of metals on silicon substrates, to investigate the process of its formation and to show how its composition depends on vapor-phase physical deposition modes.

The use of AES and EELS for complex analysis of two-dimensional coatings and their growth process

Additional possibilities for complex analysis of two-dimensional coatings (thickness &lt;1 nm or &lt;10 ML) grown by physical vapor deposition (PVD) on a single-crystal silicon substrate under two deposition regimes are revealed: 1) low-temperature (at low beam temperature) and 2) high-temperature (at an elevated temperature of the beam), respectively. Coatings, including in the form of pure metal and a silicide mixture, and their interface with the substrate were analyzed by Auger electron spectroscopy (AES) and characteristic electron energy loss spectroscopy (EELS). To ensure both deposition regimes, a technology of the deposition from the ribboned source was developed. The traditional use of AES is limited to determining the composition of the elements, the energy electronic structure, and the thickness of the coating. And EELS — the types of phases (the density of valence electrons) and the stages of their formation. The simultaneous use of both methods and the choice of equal (and minimal) probing depths, ~ 2.5 nm (primary electron energy 300 eV), provided new possibilities for studying subnanometric two-dimensional coatings, in particular, — for comparison of the composition of coatings and their density. The chosen probing depth made it possible to characterize also interface between coating and substrate. At the same time, the same probing depth made it possible to use the thickness of the coating obtained from the AES data to analyze the data of the EELS. In addition, other possibilities are considered. This is the use of dependencies: a) the energy of the plasmon satellite of Auger peak, depending on the thickness of the coating, for analyzing changes in the electron density in the near-interface layer of silicon; B) attenuation of the Auger signal generated by marker atoms at the interface between the coating and the substrate to localize the places of adsorption of deposited atoms; and c) the intensity and energy of the loss peaks in the EELS in dependence on the primary-electron energy for profiling the composition of coatings over the depth. The use of two attenuation functions for two depths of probing provided a quantitative Auger analysis of binary coatings. All this made it possible to characterize more fully both the two-dimensional coatings themselves and the interface layer of the substrate, as well as the processes of their formation. And, in particular, this made it possible to identify for the first time the wetting nanophase layer of metal on a silicon substrate, to investigate the process of its formation and to show how its composition depends on the modes of vapor-phase physical deposition.

Study of the Optical Properties of Barium Selenide Crystals. II. Elementary Transition Bands and Their Fundamental Parameters

The spectral dependences of the imaginary parts of the dielectric permittivity e2(E), bulk (–Im e–1) and surface (–Im (1 + e)–1) characteristic electron energy losses for a barium selenide crystal are decomposed into 34 elementary bands in the 3–5.5 eV region at 2 K and in the 5.5–26 eV region at 77 K by an improved combined Argand diagram method. For each band in the three types of spectra, we determined the energy maxima Ei, the half-widths Hi, the amplitudes Ii, the areas Si, and the oscillator strengths fi. The parameter fi is calculated using a modification of the familiar formula for the effective number of valence electrons neff (E). We have established the main features of the 34 elementary bands of barium selenide in the 3–26 eV region, due to excitons and transverse and longitudinal interband transitions.

Optical Properties and Electronic Structure of CaO

Spectra of 11 optical functions of CaO in the ranges 6.5–7.2 eV at 2 K and 0–60 eV at 77 K were determined. A total of 14 maxima and shoulders of excitons and interband transitions were found including two distinct exciton structures at 6.9 and 11.4 eV and volume and surface plasmon maxima at ~38.3 and 33.2 eV, respectively. Their principal features and general trends were established. Variable formation efficiencies of spectra of the dielectric permittivity and characteristic electron-energy losses in different spectral ranges were analyzed. The calculations used known experimental reflectance spectra and computer programs based on the Kramers–Kronig correlations and analytical formulae for the relationship between optical functions.

Electron spectroscopy of iron disilicide

We have reported on the results of a complex investigation of iron disilicide FeSi2 using characteristic electron energy loss spectroscopy, inelastic electron scattering cross section spectroscopy, and X-ray photoelectron spectroscopy. It has been shown that the main peak in the spectra of inelastic electron scattering for FeSi2 is a superposition of two unresolved peaks, viz., surface and bulk plasmons. An analysis of the fine structure of the spectra of inelastic electron scattering cross section by their decomposition into Lorentzlike Tougaard peaks has made it possible to quantitatively estimate the contributions of individual energy loss processes to the resulting spectrum and determine their origin and energy.

Comparative analysis of characteristic electron energy loss spectra and inelastic scattering cross-section spectra of Fe

The inelastic electron scattering cross section spectra of Fe have been calculated based on experimental spectra of characteristic reflection electron energy loss as dependences of the product of the inelastic mean free path by the differential inelastic electron scattering cross section on the electron energy loss. It has been shown that the inelastic electron scattering cross-section spectra have certain advantages over the electron energy loss spectra in the analysis of the interaction of electrons with substance. The peaks of energy loss in the spectra of characteristic electron energy loss and inelastic electron scattering cross sections have been determined from the integral and differential spectra. It has been shown that the energy of the bulk plasmon is practically independent of the energy of primary electrons in the characteristic electron energy loss spectra and monotonically increases with increasing energy of primary electrons in the inelastic electron scattering cross-section spectra. The variation in the maximum energy of the inelastic electron scattering cross-section spectra is caused by the redistribution of intensities over the peaks of losses due to various excitations. The inelastic electron scattering cross-section spectra have been analyzed using the decomposition of the spectra into peaks of the energy loss. This method has been used for the quantitative estimation of the contributions from different energy loss processes to the inelastic electron scattering cross-section spectra of Fe and for the determination of the nature of the energy loss peaks.

Polarized spectral complexes of optical functions of monovalent mercury iodide

Spectral complexes of optical functions of monovalent mercury iodide Hg2I2 were determined for E ⊥ c and E || c polarizations in the range from 2 to 5.5 eV at 4.2 K. The permittivity and characteristic electron energy loss spectra were expanded in simple components with the determination of their main parameters, including the energy of the maximum and the oscillator strength. The calculations were performed based on known reflectance spectra. Computer programs based on Kramers–Kronig relations and the improved parameter-free method of Argand diagrams were used.

Studies of structural-phase state of medical titanium alloys by contemporary methods of analytical electron microscopy

An example of original studies of titanium alloys for medical applications is used to discuss methodical features of analysis of the structural-phase state of metal materials with usage of contemporary methods of analytical scanning and transmission (including high-resolution) electron microscopy. Methods of X-ray energy dispersion spectroscopy and spectroscopy of characteristic electron energy loss are described and discussed. The possibilities of these methods for local (nanometer range) measurement of concentrations of alloying elements, including light ones (carbon), are shown. An example of focused ionic beam for study of grain boundary gliding in nanostructured pure titanium at room temperature is considered.

Channelling contrast analysis of lattice images: Conditions for probe-insensitive STEM

Quantitative analysis of lattice resolved images generated by scanning transmission electron microscopy (STEM) requires specification of probe characteristics, such as defocus, aberration and source distribution. In this paper we show that knowledge of such characteristics is unnecessary for quantitative interpretation, if the signal is integrated over a unit cell. Such a condition, whether the result of experimental setup or post-processing of lattice resolved images, reduces the intensity distribution to that of channelling contrast, where the signal for plane wave incidence is averaged over the angular range of the probe, and the result is independent of the probe characteristics. We use a Bloch wave model to show analytically how this applies to all forms of STEM imaging, such as that formed by annular dark field or backscatter detection, as well as characteristic X-ray fluorescence or electron energy loss. As a specific example, we consider how the signal from an annular dark field detector can be used to determine specimen thickness via a transfer curve for the zone axis and scattering geometries employed. This method has advantages over matching lattice images with calculations since these are sensitive to probe coherence and aberration, and saturation of the on-column intensity is approached more rapidly.