Electron Probe Methods Research Articles

Novel low-macroscopic-field emission cathodes for electron probe spectroscopy systems

The current state of electron probe methods [including energy loss spectroscopy of inelastically scattered electrons (EELS)] is considered. The analysis concerning the issues of their application, challenges, and limitations is performed. Particular attention is paid to the fundamental limitations and the means to overcome those during electron probe methods’ subsequent development for the study of composite nanostructured materials. It is emphasized that the emitted electron energy spectrum dispersion (or electron energy distribution function width) is one of the main factors limiting a further increase in EELS energy resolution, although the use of direct detection sensors and monochromators allows one to approach the physical limit of this method. Novel low-macroscopic-field electron emitters are synthesized and investigated. Their properties are analyzed and compared with previously obtained specimens. Both energy and temporal resolutions of an EEL system utilizing the suggested cathodes are estimated. The comparison of its characteristics with the corresponding parameters of classical facilities is performed. The obtained results indicate the possibility to achieving a significant growth in energy and temporal resolutions as well as a decrease in the detection threshold of chemical elements with trace concentrations while maintaining relatively high emission current density values.

Investigation of dielectric parameters of structural nanocomposites based on polyethylene

The dependence of the dielectric constant and specific volume resistance of a structural composite based on (80 wt%) synthetic isoprene rubber and (20 wt%) low density polyethylene on the content of nanosized particles of aluminum fillers, Nalchikin and carbon black in small quantities is shown graphically. Using an electron probe method for studying the microstructure of a structural material, a hydrostatic weighing method based on determining the density of a composite by its double weighing and an electron shadow microscope, this paper presents models and physical mechanisms that lead to extrema in the permittivity and conductivity of composite materials.

Brightness evaluation of pulsed electron gun using negative electron affinity photocathode developed for time-resolved measurement using scanning electron microscope

Temporal changes in carrier relaxations, magnetic switching, and biological structures are known to be in the order of ns. These phenomena can be typically measured by means of an optical-pump & electron-probe method using an electron microscope combined with a pulsed electron source. A photoemission-type pulsed electron gun makes it possible to obtain a short-pulsed electron beam required for high temporal resolution. On the other hand, spatial resolution is restricted by the brightness of the pulsed electron gun used in electron microscopes when a low brightness electron source is used and an irradiation current larger than a certain value is required. Thus, we constructed a prototype pulsed electron gun using a negative electron affinity (NEA) photocathode for time-resolved measurement using a scanning electron microscope (SEM) with high spatiotemporal resolution. In this study, a high-speed detector containing an avalanche photodiode (APD) was used to directly measure waveforms of the pulsed electron beam excited by a rectangular-shape pulsed light with a variable pulse duration in the range of several ns to several μs. The measured waveforms were the same rectangular shape as incident pulsed excitation light. The maximum peak brightness of the pulsed electron beam was 4.2×107 A/m2/sr/V with a pulse duration of 3 ns. This value was larger than that of the continuous electron beam (1.6 × 107 A/m2/sr/V). Furthermore, an SEM image with image sharpness of 6.2 nm was obtained using an SEM equipped with a prototype pulsed electron gun at an acceleration voltage of 3 kV.

Study on effect of chloride ions on corrosion behavior of reinforcing steel in simulated polluted concrete pore solutions by scanning micro-reference electrode technique

• Reinforcing steel passivity was detected by scanning reference electrode technique. • Chloride threshold level for the steel corrosion was determined. • Pitting occurred preferentially at MnS inclusion locations on the steel surface. • Chloride ions were adsorbed preferentially at MnS inclusion locations. Chloride ion (Cl - ) attack is a main reason for localized corrosion of reinforcing steel in concrete. Study on the effect of Cl - on corrosion behavior of the steel is of importance for corrosion protection. In this study, reinforcing steel (Q235 carbon steel) passivity in simulated polluted concrete pore solutions at pH 11.50 with different Cl - concentrations was studied by a scanning micro-reference electrode technique, combined with polarization curve and electrochemical impedance spectroscopy measurements and an electron probe method. The results indicated that the steel remained passive in the solution without Cl - . The steel passivity might be destroyed by the Cl - attack, and the pitting corrosion took place. The chloride threshold level for localized corrosion of the steel in the solution was 0.010 to 0.020 M Cl - . Pitting corrosion occurred preferentially at MnS inclusion locations, and the Cl - was adsorbed at these locations resulting in depassivation of the steel surface.

Measurement of the Thickness Nonuniformity of Nanofilms Using an Electron Probe Method

We propose an electron-probe method for measuring thickness nonuniformity in nanofilms, using the dependence of the ratio of the intensities of the characteristic x-ray film elements on its thickness. The calibration dependence is computed simulating the interaction of electrons with the sample by a Monte-Carlo method.

Electron Probe Measurements of Oxide Film Thickness on Silicon Surfaces

An electron probe method for measuring the thickness of oxide films on silicon surfaces is proposed. The measurement range, lateral resolution, and measurement errors are estimated.

Lateral distribution of the energy losses of an electron beam in a substance at normal incidence of charged particles on the sample surface

The results of developing a new universal function describing the lateral distribution of energy losses of an electron beam in a substance are presented for local electron-probe methods, including cathodoluminescence, the method of electron beam induced current (EBIC) in the circuit of a short-circuit diode, and X-ray spectral microanalysis. An analytical expression for the one-dimensional function ?(x) of the distribution of electron energy losses is obtained. It is necessary to calculate the distributions of information signals in the sample surface plane and makes it possible to reliably control the realized spatial resolution of experiments for any materials in a broad range of beam electron energies.

Study of Semiconductor Multilayer Structures by Cathodoluminescence and Electron Probe Microanalysis

Complementary nondestructive electron probe methods were used for characterization of semiconductor multilayer structures. We used cathodoluminescence and electron probe microanalysis for studying laser heterostructures based on GaAs/AlGaAs/InGaAs/GaAs and InGaN/GaN. Our latest investigation showed the possibility of measuring the composition of buried layers and determining the composition of thin nanoscale layers by electron probe microanalysis. Simultaneous use of local cathodoluminescence is very useful for defect study in bulk semiconductors, epilayers, and multilayer heterostructures. This method allows characterization of charge-carrier transport properties and diffusion length in multilayer structures, using the variation of the electron beam energy and calculation of the electron penetration depth.

A Noncontact Electron-Probe Method for Measuring the Diffusion Length and the Lifetime of Minority Charge Carriers in Semiconductors

A Noncontact Electron-Probe Method for Measuring the Diffusion Length and the Lifetime of Minority Charge Carriers in Semiconductors

A Mössbauer effect study of Fe3+ bearing γ-Fe2SiO4

Three synthetic Fe3+ bearing λ-Fe2SiO4 were analyzed using electron probe method, and the Mossbauer spectra of the samples at 298 K, 150 K, and 95 K were measured. Each spectrum at three temperatures is composed of two doublets. These two doublets are assigned to Fe2+ in the octahedral sites and Fe3+ in the tetrahedral sites, respectively. Site occupancies were determined. The results show that Fe3+ and a small amount of Si4+ are in the tetrahedral and octahedral sites, respectively. The average bond lengths of the octahedral and tetrahedral sites were calculated according to the equations primarily given by Hill et al., O’Neill and Navrotsky and modified by the authors. Furthermore, the octahedral and tetrahedral bond lengths were used to calculate cell parameters and oxygen parameters. In addition, Fe3+ line broadening in the Mossbauer spectra of Fe3+ bearing λ-Fe2SiO4 were interpreted by using the next nearest neighbor effects

An investigation of Nb-Ti-Ta alloys and properties of the superconductors based on ternary alloys

The vacuum arc melting technique was used to obtain the ingots of Nb-Ti-Ta alloys with 12.3 and 20.4 wt.% Ta. The microhomogeneity of the alloys was investigated by electron probe method and T/sub c/ of the alloys after homogenization was measured in comparison with that of the binary Nb-47.5wt%Ti alloy. Multifilamentary conductors with filament diameter /spl sim/60 /spl mu/m have been fabricated. The characteristics of the wires which have been produced by the regime with 4 intermediate heat treatments are presented.

The energy spectrum of electrons passing through film targets and some of its applications to electron beam engineering

The problem of analytical description of the energy spectrum of transmitted electrons was solved on the basis of the two-channel model of energy losses: inelastic scattering on valence electrons and inelastic scattering on core electrons of target atoms. Based on the correspondence between the velocity of probable energy losses of each channel and the well known Landau and Thomson-Widdington correlations, the generalized form of the energy losses law is presented which describes the most probable energy losses by kilovolt electrons in films with arbitrary thickness. A semiempirical approach taking into account the straggling of energy losses based on use of the universal function obtained was developed, which characterizes the inelastic discrete losses of each transmitted electron group with energy E. On the basis of these results the analytical description of the energy distribution of transmitted electrons is given for beryllium, aluminium, copper, silver and gold films and correlation is made between the calculated distribution and experimental spectra. Some possibilities of using the results obtained for application to electron probe methods are shown.

Effect of the finite width in the generation region of analytical signals in electron-probe methods of surface analysis

The effect of a finite width in the generation region of analytical signals in Auger-electron spectroscopy and electron-probe X-ray microanalysis is reported. In the first case is part of the high-energy backscattered electrons escaping from solids into vacuum induces secondary electron emission, including Auger electrons. In the second case these electrons induce generation of characteristic X-ray radiation. This results in the appearance of false peaks in the spectra for surfaces containing topographical structures.

Fluorine in sarcolite: additional history and new chemical data

AbstractThe historical background leading to the discovery of sarcolite by Thomson is reviewed. Many mineralogical reference works quote Thompson (1807) but no paper on sarcolite by Thomson has been found; also the spelling of Thomson is incorrect on numerous occasions. The history of sarcolite from its original discovery is reviewed. Chemically, sarcolite is inadequately characterized in spite of a structural study by Giuseppetti et al. (1977). All known chemical analyses are collated and discussed. Two new analyses, using a combination of gravimetric, colorimetric, atomic absorption, and electron probe methods, are presented which show sarcolite to contain 2 wt. % flourine. The presence of this element in sarcolite was reported in 1860 but no quantitative data given; the new determinations cast some doubt over certain aspects of the sarcolite structure.Measured densities of sarcolite range from 2.93 to 2.96 (mean 2.95) gm/cm3; the tetragonal unit cell of a 12.32 and c 15.48 Å leads to a calculated density of 2.925 gm/cm3 using the empirical formula. Empirically sarcolite may be expressed as:Na1.38Ca6.0(Ca0.37,K0.13,Fe0.08,Sr0.07,Mg0.05)Σ0.70 Al3.90Si6.02P0.54O26.20F1.06C0.06and ideallyNa2Ca12(Ca,K,Fe,Sr,Mg)2Al8Si12(P,Si)O52F2and suggests 27 (oxygen and fluorine) atoms in the quarter unit cell.Details are given of the mineralogical assemblage, optical properties, infra-red and thermal behaviour of sarcolite which, after 176 years, is still known from only one locality—Monte Somma.

Synthesis of minerals in the Cu — Fe — Bi — S system under hydrothermal condition and their phase relations

Chalcopyrite, bornite, nukundamite, intermediate solid solution, wittichenite, emplectite, cuprobismutite, and phases CuBi₃S₅ (E), Cu₈Bi₈S₁₉ (Y) and Cu₈.₄Fe₁.₂Bi₁₀.₈S₂₂ (Z) in the system Cu — Fe — Bi — S were synthesized by a temperature gradient transport method using gold tubing under hydrothermal conditions at 300 °C and 420 °C. 5m NH₄Cl aqueous solution was used as solvent and various sulfides produced by evacuated glass tube method were employed as nutrient materials. The minerals synthesized were either a single crystal or aggregates. They were identified by ore microscope and Gandolfi or Guinier camera, and electron probe methods. According to these data, bornite and wittichenite contain 13.9 weight percent bismuth at 420 °C and 1.0 weight percent iron at 300 °C, respectively, while chalcopyrite has a very small amount, less than 0.1 weight percent, of bismuth. Emplectite and cuprobismutite have the compositions of CuBiS₂ and Cu₁₀B₁₂S₂₃, respectively, and occur as a stable phase at 300 °C and at 420 °C, respectively. A four component phase, Z, was found at 300 °C and 420 °C. It is prismatic form (monoclinic) and has a = 17.483 Å, b = 3.902 Å, c = 12.869 Å and β = 108.11° cell parameters. The stable assemblages formed at 300 °C were as follows : chalcopyrite + bornite + wittichenite + nukundamite, chalcopyrite + wittichenite + nukundamite + phase Z, wittichenite + emplectite + phase Z + phase Y, wittichenite + nukundamite + phase Z + phase Y, chalcopyrite + nukundamite + phase Z + phase Y, chalcopyrite + phase E + phase Z + phase Y, emplectite + phase E + phase Z + phase Y, intermediate solid solution + pyrrhotite + bismuthinite + Bi etc. The chalcopyrite˗wittichenite assemblage which is often found in natural ore occurs at 300 °C, but it disappears at 420 °C because the assemblages of bornite˗nukundamite˗phase Z and bornite˗nukundamite˗cuprobismutite become stable.

Application of a network method for nondispersive electron probe x ray analysis of thin films

The network scheme of pulse-height analysis proposed by Mitra and Hall in 1971 can be used in a modified form for the nondispersive analysis of thin films in accord with the electron probe method introduced by Marshall in 1967. The general scheme for n-element analysis and the calibration procedure for the network are presented in this paper. The advantages of the network method for the nondispersive analysis of thick specimens exist equally for the analysis of thin films and the proposed scheme is therefore widely applicable in the field of electron microscopy.A three-channel network apparatus described by Mitra has been used to analyse a Permalloy thin film in order to demonstrate the validity of the new analytical procedure.

Electron probe methods of X-ray microanalysis

The use of an electron probe to produce a point source of X-rays permits chemical analysis, by X-ray absorption or fluorescence spectroscopy, of regions down to 1 to 10 μ in diameter. For the study of surfaces, the emission method, in which the probe excites the specimen itself, is more suitable; this gives a resolving power of about 1 μ and a detection sensitivity of 10-14 g. By means of a scanning technique, an image of the surface can be formed with a selected emission line, so that the distribution of a particular element is presented visually. The three methods are described with typical applications and are shown to be in many respects complementary.