L. A. Baranova

Charged particle energy analyzer based on a modified cylindrical mirror

A modified design of an electrostatic energy analyzer of the cylindrical mirror type is suggested. The outer electrode of the modified analyzer consists of three cylinders with equal radii and different potentials. The electron-optical properties of the analyzer are numerically simulated, and it is demonstrated that it may offer a much higher focusing quality than a conventional cylindrical mirror. Optimal design and operating conditions are found for which the spherical aberration decreases fivefold compared with the conventional mirror.

Electron spectrograph with a hyperbolic electrostatic field

The electron-optical properties of an energy analyzer representing a parallel-plate capacitor with a linear distribution of the potential on the upper plate are studied. It is shown that first-order focusing conditions in this analyzer do not depend on the particle energy and the linear dispersion is proportional to the square root of the energy. Such an analyzer can simultaneously record an electron spectrum in a wide energy range, that is, operate as a spectrograph. Double focusing conditions in a box-type analyzer are found, which allows the relative aperture of the spectrograph to be raised several-fold.

Study of aberration correction in two types of electrostatic lenses

A detailed comparative study is carried out of chromatic and spherical aberration in a crossed lens and in a lens formed by four cylindrical electrodes, the two inner ones of which are cut into four symmetrical longitudinal sections. The study was performed by numerical modeling. The possibility of simultaneous correction of both types of aberration in a linear image is demonstrated. A comparison is made with an equivalent axisymmetric lens.

Computer simulation of hexapole aberration correctors

The use of hexapole electron-optical elements to correct the spherical aberrations of the objective lenses of a low-voltage scanning electron microscope is investigated. Compared with the conventional quadrupole-octupole correctors, hexapole systems are simpler in design, easier to tune, and less sensitive to manufacturing imperfections and power supply instabilities. Two configurations of hexapole correctors, RHRHR and HRRH (where R and H stand for round lens and hexapole component, respectively), are considered. Both configurations considerably suppress the spherical aberration of the electron microscope objective lens but cannot correct chromatic aberrations. The second configuration possesses important advantages over the first one: it is mechanically and electrically simpler and also is easier to tune. In addition, as follows from our investigation, the hexapole electrode voltages in the second configuration are lower, the correction accuracy is higher, and the sensitivity to mechanical defects is lower. However, the chromatic aberration in the second configuration is somewhat larger.

Improved cylindrical mirror energy analyzer

A study has been carried out of the electron-optical properties of improved design of the cylindrical mirror energy analyzer. Both external and internal electrodes of the analyzer are divided into three isolated parts, whereby the potentials on the individual parts can be regulated independently from each other. In symmetric operating mode at identical potentials on the side parts of the electrodes, a significant increase has been obtained in resolving power and light-gathering power of the analyzer compared to the standard design of the cylindrical mirror. In asymmetric operating mode, which is implemented in a linear potential distribution on the external electrode, the conditions have been found under which the linear dispersion of the analyzer increases several times.

Cylindrical mirror energy analyzer with the input of charged particles through end-surface diaphragm

Computer simulation is used to study electron-optical properties of a cylindrical mirror analyzer with the input of charged particles through the end-surface diaphragm. Regimes with double crossing of the optical axis (two-stage analyzer) are considered to increase the linear dispersion. The external electrode of the electron-optical system under study can be divided into several insulated parts with independently controlled potentials. Such an approach allows the second-order tuning of focusing and wide-range variation in the dispersion. Optimal working regimes make it possible to increase the linear dispersion by a factor of 3–4 in comparison with the one-stage regime.

Conical Mirror Energy-Analyzer

Electron optical properties of an axisymmetric mirror energy-analyzer are studied. The internal electrode represents a cylinder, and the external electrode is formed by two identical cones with common bases. It is shown that the relative aperture and resolution of such an analyzer are significantly greater than the corresponding parameters of a conventional cylindrical mirror. The internal electrode is made of three cylinders with different diameters, and the potentials of the cylinders are identical. Such a structure is used to further improve electron optical characteristics of the conical analyzer. At a relatively small beam angle, the resolution of the conical analyzer is two times greater than the resolution of the cylindrical mirror, and the difference of the resolutions amounts to an order of magnitude when the beam angle increases.

Submicron source of free electrons

An original way of fabricating multitip microemitters based on the track membrane technology is suggested. Reproducibility of the geometrical parameters of microemitters with a tip diameter of 20–40 nm is achieved. For such tip diameters, the field emission mode sets in at a potential difference of 100–300 V. With these emitters used in diode and triode structures, the speed may be as high as ∼10−12 s. In experimental micro-emitters, a tip density of ∼106 cm−2 is reached. According to calculations, this value may provide technically reasonable field-emission currents. The suggested method of creating multitip microemitters is fairly simple, so that samples several tens of square centimeters in area can be obtained under laboratory conditions. Using special equipment, multitip microemitter arrays several hundred square meters in area can be fabricated.

Charged particle energy analyzer based on a modified cylindrical mirror in the ring-axis focusing mode

The electron-optical properties of systems with a modified structure of the energy analyzer in the form of a cylindrical mirror proposed earlier are investigated. The analyzer operating mode in which the source of charged particles is in the inner cylinder and the detector is on the cylinder axis (ring-axis focusing) is considered. It is shown using numerical simulation that the modified structure ensures higher focusing quality as compared to the traditional cylindrical mirror. The optimal structure and voltage supply are determined for which spherical aberration is five times smaller than with a conventional cylindrical mirror.

Dissociation of alkane ionized molecules

The subject of investigation is the fragmentation of variously charged molecular ions arising in col-lisions of several kiloelectronvolt H+, He2+, and Ar6+ ions with molecules of the simplest alkanes (from methane to butane). Using the method of time-of-flight mass spectrometry, the formation cross sections of dissociation-induced fragment ions are measured. The dissociation takes place when an incident ion captures an electron from a methane, ethane, or propane molecule. The role of additional ionization of the molecule, which accompanies the electron capture by the incident ion, is elucidated. The kinetic energy spectrum for protons resulting from the fragmentation of multiply charged alkane ions is determined. The most plausible kinetic energies of protons depending on the degree of ionization and molecule size fall into the range 1–25 eV. It is shown that, when the molecule loses several electrons, the kinetic energies of protons are governed by Coulomb interaction between all fragment ions and are determined by their flying apart from the relative spatial arrangement of corresponding atoms in a parent molecule.