Optical and electron energy loss experiments in ionic CrBr3 crystals

Electron energy loss spectra of ZnSe using linear response theory

Reflectance data are presented for Si, Ge, GaP, GaAs, InAs, and InSb in the range of photon energies between 1.5 and 25 eV. The real and imaginary parts of the dielectric constant and the function describing the energy loss of fast electrons traversing the materials are deduced from the Kramers-Kronig relations. The results can be described in terms of interband transitions and plasma oscillations. A theory based on the frequency-dependent dielectric constant in the random phase approximation is presented and used to analyze these data above 12 eV, where the oscillator strengths coupling the valence and conduction bands are practically exhausted. The theory predicts and the experiments confirm essentially free electron-like behavior before the onset of $d$-band excitations and a plasma frequency modified from that of free electrons due to oscillator strength coupling between valence and $d$ bands and $d$-band screening effects. These complications are absent in Si. The energy loss functions obtained from optical and characteristic energy loss experiments are also found to be in good agreement. Arguments for interpreting structure in the reflectance curves above 16 eV in terms of $d$-band excitations are given.

Structural, electronic and vibrational properties of GexCy (x+y=2–5) nanoclusters: A B3LYP-DFT study

Dispersion relations for the energy loss rate are derived for anisotropic materials; they are a nontrivial extension of the usual Kramers-Kronig expression. It is shown for the case of uniaxial crystals that these formulae allow a determination of the longitudinal dielectric tensor from electron energy-loss experiments. The connection between the dielectric tensor so obtained and the optical constants is examined and their equivalence is established in the long-wavelength limit.

ELS and XPS study of Pd/PdO methane oxidation catalysts

Smart acquisition EELS

We present first principles calculations of the electronic, structural and optical properties of the cubic perovskite CsSrF3 by using the full potential linearized augmented plane wave (FP-LAPW) plus local orbitals method with generalized gradient approximation (GGA) in the frame work of density functional theory. The calculated lattice constant is in a good agreement with the experimental result. The electronic band structure shows that the fundamental band gap is wide and direct at Γ point. The contribution of the different bands was analyzed from the total and partial density of states curves. The charge density plots show strong ionic bonding in Cs-F, ionic and weak covalent bonding between Sr and F. The calculated optical spectra viz., the dielectric function, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss, are presented for the energy range of 0–30 eV.

The structural and optoelectronic properties of cubic perovskite RbPbF3 are calculated using all electrons full potential linearized augmented plane wave (FP-LAPW) method. The calculated lattice constant is in good agreement with the experimental result. The calculated band structure shows a direct band gap of 3⋅07 eV. The contribution of different bands is analysed from the total and partial density of state curves. We identified hybridization of Pb s, Pb p states with F p states in the valence bonding region. Calculations of the optical spectra, viz., the dielectric function, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss are performed for the energy range of 0–30 eV. Based on the direct bandgap, as well as other optical properties of the compound, it is predicted that this material is useful for vacuum-ultraviolet-transparent (VUV-transparent) applications.

We have developed a theory of electron energy loss spectra (EELS) for reflection geometry that includes the electromagnetic retardation effect. This theory analytically reduces to the standard EELS result when \(\frac{\omega}{c}\) is much smaller than | k ∥ | , where ω and k ∥ are the frequency and the wavevector parallel to the sample surface, respectively, of an elementary excitation created in the scattering process. As a concrete example we calculate the energy loss probability for a Au sample including the electromagnetic retardation effect.

A kinetic Monte Carlo (KMC) simulation tool for modeling the pattern formation process in photoresist materials for extreme ultraviolet (photon energy 92 eV) nanolithography is presented. The availability of such a tool should support the progress toward novel materials and experimental procedures that lead to an improved pattern resolution. The molecular-scale simulations describe the process in a stochastic and mechanistic manner and include the excitation of high-energy electrons upon light absorption, the creation of a charged-particle cloud, electron-induced chemical degradation of the photoresist molecules, the resulting bond formation between neighboring degraded molecules, and a chemical development step after which a pattern of the remaining non-dissolved molecules is obtained. The method is applied to the application-relevant class of Sn-oxocore photoresist materials and uses their known electronic structure and optical electron energy loss function. The validity of the approach is tested by comparing measured and simulated total electron yield spectra and photoelectron spectra. A demonstration of the method is given by calculating the dose and pitch dependent average shape and stochastic variability (line edge roughness) of line patterns that are obtained for rectangular and sine-wave illumination, assuming various scenarios that determine how molecular-scale degradation will lead to bond creation. We show how from these simulations the ultimate pattern resolution can be deduced. The findings are analyzed systematically using results of KMC simulations that reveal the size of the cloud of degraded molecules around a point of absorption (blur length) and that further reveal the sensitivity to uniform illumination (contrast curves), and using percolation theory. We find that KMC modeling captures the consequences of the strong gradients in the density of degraded molecules and of the stochasticity of the patterning process that simplified models do not include, leading to a significantly improved view of the final pattern quality.

It is well known that the energy loss spectra of fast electrons transmitted through thin specimens may he employed to analyze the material through which they have passed. Therefore, in principle, electrons can be used in a similar manner as one uses UV light to probe the chemical compositions of a specimen. The distinct advantage, of course, is the potential capability of utilizing the electron microscope for identifying compounds with microscopic spatial resolution (see, for example, Ref. 1). In biological membranes, for example, there thus exists the possibility of distinguishing proteins, phospholipids, cholesterol and carbohydrates on the basis of their electron energy loss spectra. This could be of value in delineating the twodimensional molecular architecture of membranes. We have therefore undertaken a program to determine the extent to which energy loss electrons can be useful in the scanning transmission electron microscopy of membranes.

Plasmon energy losses experienced by fast electrons passing through a thin specimen are readily measured using electron energy loss spectroscopy. We describe a simple model of the shape and energy of the single scattering distribution plasmon peak, which relates the energy loss spectrum to the material parameters of average band gap ${\overline{E}}_{g}$, lattice parameter $a$, core ion dielectric constant ${\ensuremath{\epsilon}}_{c}$, and plasmon lifetime $\ensuremath{\tau}$. This model is used to interpret maps of plasmon energy and full width at half maximum taken from an $\mathrm{In}\mathrm{As}∕{\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ quantum dot-in-well structure. We find that the bulk plasmon peak shifts are mainly determined by the strain in the structure, which may provide a new means of mapping strain on the nanoscale. The regions of maximum plasmon peak width appear to correspond to regions of high strain gradient. It is possible to separate the effects of plasmon lifetime from the other factors, leaving a parameter which is a combination of ${\overline{E}}_{g}$, $a$, and ${\ensuremath{\epsilon}}_{c}$. We have been able to map this parameter with a spatial resolution of a few nm.

At present transmission electron energy loss spectrum (EELS) analysis is only carried out in dedicated research instruments such as transmission electron microscopes (TEMs) or scanning transmission electron microscopes. This article presents a new design of second-order geometric aberration corrected EELS spectrometer attachment using split plates, which enables conventional scanning electron microscopes (SEMs) to provide TEM-like EELS spectra. Correction to a third-order dominant geometric aberration pattern has been achieved, which indicates that most of the second-order geometric aberration component is eliminated. This second-order aberration corrected spectrometer attachment design can enable SEMs to provide transmission EELS spectrums.

We report on first-principles calculations of electron energy-loss (EEL) spectra for bulk group-III nitrides and of spatially resolved EEL spectra for a variety of edge and screw dislocations in GaN. The theoretical bulk low-loss EEL spectra, in the 0--10 eV range, are in good agreement with recent experimental data. We find gap states associated with undecorated full-core dislocations that lead to absorption below the bulk onset energy in low-loss EEL spectroscopy. It is also found that the electrostatic potential at N atoms in the vicinity of an edge dislocation varies by an order of a volt and casts doubt on any simple interpretation of core-loss spectroscopy.

<p indent="0mm">Synchrotron radiation and transmission electron microscopy (TEM) technologies are important characterization methods of materials and are widely used in the frontier research fields of physics, chemistry, materials, environment, and energy. Both methods exploit the interaction of photons and electrons with materials, including the scattering and absorption of photons in the material and the diffraction and energy loss of electrons. Through these techniques, various specific characterization methods have evolved. In the density functional theory (DFT) which is based on quantum mechanics, the eigenfunction can be related to the charge density obtained from the synchrotron radiation X-rays diffraction and electron diffraction in TEMs, and the eigenvalue corresponds to the energy level or band structure obtained from the photoelectron emission spectra/absorption spectra of synchrotron radiation and the electron energy loss spectra of TEM. With these corresponding relations, the two techniques and theoretical calculations can verify and/or complement each other, providing detailed analyses of the structure and electronic information of materials. This article reviews the progress of synchrotron radiation and transmission electron microscopy technologies and their applications to typical material characterization. The article emphasizes how the spatial and temporal resolutions of both technologies have advanced through nanotechnology and quantum mechanics developments. Such cutting-edge technology will promote the discovery of new functional materials.