High-resolution Electron Energy Research Articles

Optical properties of InSb derived from reflection electron energy loss spectroscopy spectrum

The energy loss function (ELF) of the narrow bandgap semiconductor, InSb, was derived from the reflection electron energy loss spectroscopy (REELS) spectrum measured at 4 keV incident electron energy in an energy loss range of 1.6–200 eV using a high energy resolution electron spectrometer. The experimental spectrum was analyzed with the reverse Monte Carlo (RMC) method, which integrates the classical trajectory Monte Carlo simulation with the simulated annealing method for optimizing the trial ELF. Subsequently, the complex dielectric function ε(ω), refractive index and extinction coefficient were determined from the obtained ELF in the energy loss (i.e. photon energy) range of 1.6–200 eV. The validity of the obtained data was verified by the f-sum rule, ps-sum rule, inertial sum rule and dc-conductivity sum rule. We found that our calculated data of InSb fulfill the sum rules with very high accuracy; therefore, the use of these calculated optical data in material science and surface analysis is highly recommended for further applications.

Dissociative electron attachment studies of gas-phase acetic acid using a velocity map imaging technique

Advancing instrumentation to explore dissociative electron attachment (DEA) studies allows previously unattainable information to be acquired. Using a newly constructed velocity map imaging spectrometer, we revisited a study on DEA to gas-phase acetic acid. We discuss possible fragmentation channels and compared the corresponding ion yields with previous high electron-energy resolution results. We focus on the channels occurring at higher energies, particularly near 10 eV, and calculate their thermodynamic thresholds. Moreover, we expand previous studies and perform time-sliced imaging near the 10 eV resonance to obtain the kinetic energy distribution of the fragment ions.

Thermal stability and diffusion characteristics of ultrathin amorphous carbon films grown on crystalline and nitrogenated silicon substrates by filtered cathodic vacuum arc deposition

Amorphous carbon (a-C) films are widely used as protective overcoats in many technology sectors, principally due to their excellent thermophysical properties and chemical inertness. The growth and thermal stability of sub-5-nm-thick a-C films synthesized by filtered cathodic vacuum arc on pure (crystalline) and nitrogenated (amorphous) silicon substrate surfaces were investigated in this study. Samples of a-C/Si and a-C/SiNx/Si stacks were thermally annealed for various durations and subsequently characterized by high-resolution transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The TEM images confirmed the continuity and uniformity of the a-C films and the 5-nm-thick SiNx underlayer formed by silicon nitrogenation using radio-frequency sputtering. The EELS analysis of cross-sectional samples revealed the thermal stability of the a-C films and the efficacy of the SiNx underlayer to prevent carbon migration into the silicon substrate, even after prolonged heating. The obtained results provide insight into the important attributes of an underlayer in heated multilayered media for preventing elemental intermixing with the substrate, while preserving the structural stability of the a-C film at the stack surface. An important contribution of this investigation is the establishment of an experimental framework for accurately assessing the thermal stability and elemental diffusion in layered microstructures exposed to elevated temperatures.

Study on double peaks aging strengthening and stress corrosion cracking behaviour of 7075 aluminium alloy

ABSTRACT The aging strengthening effect, stress corrosion cracking (SCC) behaviour and microstructure of 7075 aluminium alloys under double peaks aging treatment have been investigated in this paper. The results show that the hardness and strength of alloys under the second aging peak are equal or slightly higher than those under the first peak. The microstructure analysis demonstrates that the aging strengthening effect of the first peak and second peak mainly depend on fine and intensive GP zones (2–6 nm in size with an inter-particle distance of 4–10 nm) and η’ phase (4–8 nm in size), respectively. Meanwhile, the SCC resistance of specimens under the second aging peak is better than the first peak aging treated ones. Lower Mg and higher Cu segregation on grainboundary induced by second peak aging treatment are considered to be the reason for better SCC behaviour according to high-resolution transmission electron microscopy and energy dispersive spectrometer results.

Effect of novel cryogenic treatment in the corrosion behaviour, microstructure analysis and electrochemical properties of Al 6101 closed-cell foam

ABSTRACT The corrosion behaviour of the closed-cell aluminium foam made of Al 6101 alloy in different heat regimes such as heat treatment (HT), cryogenic treatment (CT) and cryogenic heat treatment (CHT) are investigated in this research work. The Electrochemical Impedance Spectroscopy (EIS) and DC polarisation are the techniques employed in this research work. The microstructure, surface morphology and composition of the treated foam samples are evaluated using a high-resolution Scanning Electron Microscope (SEM) and Energy Dispersive Analysis of X-rays (EDAX). The polarisation and electrochemical impedance measurements of the CT and HT foam samples reveal appealing results in the corrosion resistance when comparing with untreated foam sample. From the SEM images, it is evident that the deep cryogenic treatment changes the morphology of Al 6101 foam and the formation of the Guinier-Preston (GP) zone increases the density of dislocation.

Calibration and Performance of the CMS Electromagnetic Calorimeter in LHC Run2

Many physics analyses using the Compact Muon Solenoid (CMS) detector at the LHC require accurate, high resolution electron and photon energy measurements. Excellent energy resolution is crucial for studies of Higgs boson decays with electromagnetic particles in the final state, as well as searches for very high mass resonances decaying to energetic photons or electrons. The CMS electromagnetic calorimeter (ECAL) is a fundamental instrument for these analyses and its energy resolution is crucial for the Higgs boson mass measurement. Recently the energy response of the calorimeter has been precisely calibrated exploiting the full Run2 data, aiming at a legacy reprocessing of the data. A dedicated calibration of each detector channel has been performed with physics events exploiting electrons from W and Z boson decays, photons from π0 and η decays, and from the azimuthally symmetric energy distribution of minimum bias events. This talk presents the calibration strategies that have been implemented and the excellent performance achieved by the CMS ECAL with the ultimate calibration of Run2 data, in terms of energy scale stability and energy resolution.

DECONTAMINATION OF PESTICIDE RESIDUES IN WATER SAMPLES USING COPPER AND ZINC CO-DOPED TITANIA NANOCATALYST

Copper and Zinc co-doped titania nano photocatalyst (Cu-Zn-TiO2 NPC) was fabricated and characterized using room temperature X-ray diffraction (XRD), field emission electron microscopy (FESEM) with high-resolution transmission electron microscopy (HRTEM) and energy dispersion X-ray (EDX). X-ray diffraction studies of the Cu2+-Zn2+/TiO2 show the presence of anatase phase TiO2 and in the sample prepared from 0.05, 0.10, 0.15 and 0.20 mmol have also shown the presence of anatase phase only. The photocatalytic efficiency of the synthesized catalysts was investigated by the photocatalytic degradation of aqueous bispyribac sodium under sun light irradiation, and it was found that the Cu and Zn co-doped TiO2 catalysts has better photocatalytic activity. It can be also showed that with the addition of dopants to titania hinders the growth of nanoparticles. This can be attributed of the fact that there is a more efficient electron-hole creation in Cu and Zn co-doped TiO2 in sunlight, contrary to un-doped TiO2 which can be excited only in UV irradiation. Photocatalytic studies of bispyribac sodium at various conditions such as acidic, basic and neutral reveals that the activity is enormously increased with co-doped TiO2 is proved to be effective for photocatalysis of bispyribac sodium and is more effective in basic medium.

Surface plasmon resonances in a branched silver nanorod

The properties of surface plasmon-polariton (SPP) resonance modes were investigated in a branched silver nanorod consisting of two nanorods using high energy resolution electron energy-loss spectroscopy (EELS) combined with scanning transmission electron microscopy. The experimental EELS maps of the SPP excitation showed a specific distribution depending on the resonance mode. The analytical formulas of the EELS signal and the resonance conditions for SPP resonance in the branched nanorod were derived by expanding the method reported for a one-dimensional straight resonator, and these were applied to interpret the experimental results. The SPP resonance in the branched nanorod can be attributed to Fabry-Perot type resonance that propagates in any of the three different resonance paths. It was also demonstrated that the modes of SPP resonance are changed by the position of the crossing point in the branched structure, which indicates that the combination of the lengths of the respective branches can be used to control the propagation path and the resonance energy of SPP waves in branched structures.

Magnetically confined electron beam system for high resolution electron transmission-beam experiments.

A novel experimental setup has been implemented to provide accurate electron scattering cross sections from molecules at low and intermediate impact energies (1-300 eV) by measuring the attenuation of a magnetically confined linear electron beam from a molecular target. High-resolution electron energy is achieved through confinement in a magnetic gas trap where electrons are cooled by successive collisions with N2. Additionally, we developed and present a method to correct systematic errors arising from energy and angular resolution limitations. The accuracy of the entire measurement procedure is validated by comparing the N2 total scattering cross section in the considered energy range with benchmark values available in the literature.

Electron irradiation effects on lithium peroxide

In this study, electron irradiation effects on lithium peroxide (Li2O2), which is an important discharge product of Li–air (or Li–O2) batteries, were investigated using selected-area electron diffraction (SAED) and high-energy resolution electron energy-loss spectroscopy (EELS). The results obtained show that Li2O2 to Li2O transformation occurs with 80 and 300 keV incident electrons under high electron dose rates at 20 and −183 °C. The Li2O2 to Li2O transformation rate for 300 keV was 1/5 of that for 80 keV with the irradiation taking place at −183 °C. We also present a series of the EELS spectra that can be used as a criterion to judge the molar ratio of Li2O to Li2O2 in the general systems where Li2O2 and Li2O coexist.

Dielectric Properties of Photo-Luminescent CdSe/CdS Mono-Shell and CdSe/CdS/ZnS Multi-Shell Nanocrystals Studied by TEM-EELS

Semiconductor nanocrystals (NCs) of CdSe/CdS (core/shell) mono-shell and CdSe/CdS/ZnS (core/shell/shell) multi-shell having bright and stable luminescence were investigated using high energy-resolution electron energy-loss spectroscopy (EELS) based on transmission electron microscopy to evaluate their dielectric properties in the visible light energy region. EELS spectra of the mono-shell and multi-shell NCs showed two-step structures attributed to interband transitions near band gaps of individual CdSe core and CdS shell. EELS simulations based on the classical dielectric theory revealed that the two-step structures were results of dielectric response from CdSe core and CdS shell. The intensity profiles of the two-step structures depend on a thickness of CdS shells and mono/multi-shell structures of NCs. Besides, the quantum confinement effect was observed in the spectra of mono- and multi-shell NCs, where onset energy of the CdSe core was larger than that of bulk CdSe. The EELS spectra of multi-shell NCs, however, did not present an evident onset due to a bandgap of ZnS outer-shell suggesting defects or amorphous state in ZnS outer-shell. Such dielectric properties of NCs obtained from EELS analysis could provide valuable information to evaluate the crystallinity of individual core and shells in NCs.

Electron energy loss spectroscopy with parallel readout of energy and momentum.

We introduce a high energy resolution electron source that matches the requirements for parallel readout of energy and momentum of modern hemispherical electron energy analyzers. The system is designed as an add-on device to typical photoemission chambers. Due to the multiplex gain, a complete phonon dispersion of a Cu(111) surface was measured in 7 min with 4 meV energy resolution.

High energy resolution electron beam spectrometer in the MeV range

Two electron spectrometers have been developed for the characterisation of scintillating counters with MeV range electrons. These spectrometers offer a monoenergetic electron beam ranging from 0.4 to 1.8 MeV with an energy resolution (FWHM) of 1.0 ± 0.2% at 1 MeV and a linearity better than 2%. The transverse profile of the beams consists of a typical 3.0 mm Gaussian width. These electron beams can automatically scan surfaces up to 60 × 200 cm2 in 1 mm increments. They have been used in the calorimeter module development for the SuperNEMO experiment.

Self-assembly of CdSe quantum dots and colloidal titanium dioxide on copolymer microspheres (PS) for CdSe/PS and TiO2/CdSe/PS sub-microspheres with yolk–shell structure

Semiconductor nanocrystals serve as the building blocks for designing next generation solar cells, chemical/biological sensors, and metal chalcogenides (e.g., CdS, CdSe, PbS, and PbSe) are particularly useful for harnessing size-dependent optical and electronic properties in nanostructures. In this paper, relying on the interaction including van der Waals forces and hydrogen bond, CdSe/PS sub-microspheres composite and TiO2/CdSe/PS sub-microspheres with yolk–shell structure were prepared via self-assembly of CdSe quantum dots and colloidal titanium dioxide on modified PS surface. The morphology, structure and composition obtained products were investigated by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and energy disperse X-ray spectroscopy (EDX). Transmission electron microscopy (TEM) investigations show the CdSe quantum dots and colloidal titanate were assembled on the surface of PS sub-microspheres. CdSe QD-polymer sub-microspheres composites in which the QDs retain their original emission efficiency can be obtained. TiO2/CdSe/PS sub-microspheres with yolk–shell structure can improve the efficiency of charge separation.

Electronic structures of three-dimensional C60 polymers studied by high-energy-resolution electron energy-loss spectroscopy based on transmission electron microscopy

Electronic structures of two three-dimensional (3D) C60 polymers, which are Immm (3D C60-Immm) and Fcc (3D C60-Fcc) crystal symmetry, were investigated by high energy-resolution electron energy-loss spectroscopy based on transmission electron microscopy. Dielectric functions of 3D C60-Immm and 3D C60-Fcc were derived from valence electron excitation spectra by Kramers–Kronig analysis. The K-shell excitation spectrum of 3D C60-Immm specimen showed a step-like structure at the onset, which might correspond to Fermi edge. Therefore, metallic property of 3D C60-Immm could be confirmed. On the other hand, Fermi edge could not be observed for 3D C60-Fcc, suggesting to be a semiconductor.

Observing interference effect in binary (e, 2e) of molecules

We present investigations on the two-center and multi-center interference effects of molecules in binary (e, 2e) experiments. The high energy resolution electron momentum spectroscopy (EMS) measurements on H2 are reported with final vibrational states resolved. The experimental momentum profiles for ionization transitions to the individual final vibrational states of the ion are obtained. The measured and calculated vibrational ratios of the cross sections deviate from Franck-Condon principle, which can be ascribed to the Young-type two-center interference. Furthermore, with the help of our latest version of EMS spectrometer which has considerably higher sensitivity and much wider momentum range from 0 to 8 a.u., we are able to extend our observations to multi-center interference effect in high symmetry molecules like NF3 and CF4 with several oscillation periods included.

Quantitative analysis of the energy distributions of electrons backscattered elastically from polyethylene

We present results of theoretical and experimental studies of the spectra of electrons backscattered elastically from polyethylene in the primary energy range between 1 and 5keV. The experiments were performed using a high energy resolution electron spectroscopy. The theoretical interpretation is based on a Monte Carlo simulation of the recoil and Doppler effects. The separation between the carbon and hydrogen peak in the energy distributions is shown as a function of the primary electron energy. The simulations give many partial distributions separately, depending on the number of elastic scatterings (single, and multiple scatterings of different types). We show our results for intensity ratios, peak shifts and broadenings. We also present detailed analytical calculations for the main parameters of a single scattering. Finally, we present a qualitative comparison with the experimental data. We find our resulting energy distribution of elastically scattered electrons to be in good agreement with our measurements.

Preparation and exchange bias effects of Bi0.8Ba0.2FeO3/La0.7Sr0.3MnO3 heterostructures

Bi0.8Ba0.2FeO3/La0.7Sr0.3MnO3 multiferroic heterostructures are successfully synthesized on single crystal LaAlO3(100) substrates by pulsed laser deposition via adjusting the parameters of laser energy, laser frequency, substrate temperature, oxygen pressure, distance between substrate and target, etc. The pure phase with perovskite structure is confirmed by the X-ray diffraction measurements. Using high-resolution transmission electron microscopy and energy dispersive X-Ray spectroscopy, we find that all the layers show preferential (00l) orientation, suggesting the epitaxial growth of the multilayered structure. Isothermal (7 K) M-H curves measured on sample after cooling the sample down to lower than ± 1 T fields reveal a shift in M-H loop. The strong temperature dependence of HEB is likely to be directly related to an electronic orbital reconstruction at the interface and complex interplay between orbital and spin degrees of freedom.

High energy-resolution electron energy-loss spectroscopy study of the dielectric properties of multi-shell nanoparticles.

Nanoparticles, which have multi-shell structure, are expected to be stable and high efficient for the light-emitting devices. The efficiency of luminescence is considered to be affected by the multi-shell structure. In order to understand the mechanism of high efficiency luminescence, it is necessary to evaluate the multi-shell structure and dielectric properties from each particle. High energy-resolution electron energy-loss spectroscopy (HR-EELS) based on TEM is a powerful tool for this purpose. By comparing between the experimental and the simulated results, it is possible to evaluate the effect of the size and physical property of each shell material on the dielectric properties of multi-shell nanoparticles. In this study, simulations of EELS spectra of multi-shell nanoparticle (core: CdSe, inner shell: CdS, outer shell: ZnS) and mono-shell nanoparticle (core: CdSe, shell: CdS) were conducted by the dielectric continuum theory[1].Figure1 shows calculated EELS spectra of multi and mono shell nanoparticles. The spectra are calculated from dielectric functions of single CdSe, CdS and ZnS crystals, which were experimentally derived from HR-EELS spectra by using Kramers-Kronig analysis. The radius of 6.9 nm for the nanoparticle in the simulation corresponds to the average size of actual synthesized nanoparticles. Energy positions of arrows in the inset correspond to band gap energies of CdSe, CdS and ZnS[2]. In the spectrum of multi-shell nanoparticle, the intensity corresponding to interband transition near band gap of CdSe is suppressed comparing with that of the mono shell nanoparticle. This result indicates that ZnS outer shell affects the intensity profile of EELS spectrum near band gap. This effect should be sensitive for the thickness of the shells. Thus, there is a possibility that the effect of size and thickness of each core and shell on dielectric properties of multi-shell nanoparticles could be evaluated by using HR-EELS technique.jmicro;63/suppl_1/i18/DFU039F1F1DFU039F1Fig. 1.Calculated EELS spectra.

Optical properties of Group X-XII intermetallic compounds studied by HR-EELS.

Electronic structure of d orbital states in transition metals is a key factor for their physical properties and chemical functions. Copper and intermetallic compound PdZn have good catalysis function for the methanol steam reforming reaction. Tsai et al. showed that from results of XPS measurements the d electronic structure of PdZn was similar with that of copper, and the catalysis function should be related to the d electron states [1]. This similarity of d electronic states leads to another view point of the mechanism for coloring the intermetallic compounds. It is well-known that the characteristic red color of copper is caused by interband transition from the d electrons. Therefore, PdZn and Group X-XII intermetallic compounds are expected to be colored and the optical properties should depend on the d electronic states. In this study, the relations between optical properties and d electron states of Group X-XII intermetallic compounds were investigated by using high energy-resolution electron energy-loss spectroscopy (HR-EELS) based on transmission electron microscopy (TEM). From the relation between optical properties and d electronic states, the mechanism of colored intermetallic compounds will be discussed.Figure shows the optical reflectivity of NiZn, PdZn and PtZn, which were derived from EELS spectra by Kramers-Kronig analysis. Intensity drops (arrows) of the reflectivity were observed in visible energy region. These are caused by the interband transitions from d electronic states. The energy positions of the reflectivity drops have tendency of shifting to higher energy side with increasing atomic number of Group X elements (Ni → Pd → Pt). This indicates that the transition energies of d electrons become larger with the atomic number of the elements. First principle calculations (WIEN2k) confirmed that the interband transitions of d electronic states were excitations from bonding d states to hybrid states of anti-bonding s, p, and d states of Group X elements. The bonding anti-bonding energy split increase with the atomic numbers because of increasing crossover of wave function. This implies the intermetallic compounds should be colored and the color should be changed gradually depending on the atomic number of Group X elements.