E. N. Evstaf’eva

Mechanisms of charging of insulators under irradiation with medium-energy electron beams

The electron emission and charge characteristics of a large number of massive insulators are investigated qualitatively and quantitatively. It is demonstrated that irradiation of insulators with a medium-energy continuous electron beam leads to a decrease in the equilibrium energy of incident electrons (the second critical energy) as compared to the theoretical value. The equilibrium state of charging to saturation is attained for times from several seconds to several hundred seconds depending on the irradiation current density, the electron energy, and the insulator material. The mechanisms of charging are explained in the framework of the model according to which irradiation is accompanied by the formation of a charged double layer that consists of a positively charged layer (with the thickness equal to the escape depth of secondary electrons) and a negatively charged layer (with the thickness equal to the penetration depth of primary electrons).

Complex investigations of effects of charging a polymer resist (PMMA) during electron lithography

Results of the measurement of the surface charging potential for PMMA films of various thicknesses under the effect of irradiation by electron beams of various energies are presented. The corresponding energy ranges of primary electrons are given for the cases of both positive and negative charging of the dielectrics. It is shown that two individual critical electron energies exist for each thickness of the PMMA resist, at which the resist is not charged. These energies can be recommended for low-voltage and high-voltage electron nanolithography with minimal errors in beam positioning. The experiments showed a very high value of the critical breakdown voltage of the PMMA film of about 107 V/cm.

Methodological aspects of the electron-beam investigation of dielectric target charging

The basic characteristics of dielectric target charging with (2–30)-keV electron beams were investigated using the example of a typical insulator, Al2O3. A new hypothetical scenario of dielectric charging, based on the reduction of secondary-electron current due to the formation of polarized excitons in the positive layer of a charged target, is proposed on the basis of modeling calculations and the experimental data.

An explanation of certain contradictions in the treatment of the charging dynamics of dielectric targets under the effect of electron irradiation

Explanations of contradictory results in some studies of the temporal characteristics of charging dielectric targets via the electron irradiation effect are given. Disagreement is caused by the difference in the times of the appearance of a quasi-equilibrium state of two main parameters of charging, namely, the complete coefficient of secondary electron emission and the surface electrostatic potential.

Some kinetic aspects of the charging of dielectric targets by a (1–50)-keV electron beam

The electron-emission characteristics of dielectrics irradiated with electron beams with a current density of about 10−5 A cm−2 have been experimentally investigated. An ambiguous relationship between the secondary electron-emission properties, the charged-surface potential, and the positive and negative charges accumulated in the surface region of dielectric targets is demonstrated. The character and values of various experimentally observed time charging constants, inconsistent with a number of theoretical models and estimates, are qualitatively explained.

Magnetic ordering in nickel ferrite-chromite NiFeCrO4 below the compensation temperature

The behavior of the magnetoresistance of nickel ferrite-chromite NiFeCrO4 is studied at temperatures in the vicinity of the compensation temperature. A model of magnetic ordering in this compound is proposed. It is established that, at T = 0 K, the sublattice B is responsible for magnetic ordering.

X-ray microanalysis of uranium dioxide particles by using low electron beam energy

The elemental analysis results of the various size uranium dioxide fragments, performed with a scanning electron microscope (SEM) equipped by X-ray energy dispersive analyzer (INCA x-act, “Oxford Instruments”, Great Britain), are presented. The elemental composition calculation was carried out applying the pre-installed program based on the XPP matrix correction algorithm. It is shown that for the bulky UO2 samples, measured with the varied accelerating voltage in range of 6–20 kV, the uranium concentrations slightly differ (relative uncertainties doesn’t exceed ±2%). The composition of uranium dioxide particles sized up to 0.5 μm can be defined using beam energy of 6 keV with typical for bulky sample accuracy.

Characteristics of dielectric film charging, depending on their thickness upon electron irradiation

Basic principles of charging dielectric films on conducting substrates upon irradiation with electrons of average energy are considered. A ratio associating the equilibrium charging potential and the mean thickness of the dielectric film is calculated. The analytical expression is in good agreement with experimental results over a wide range of energies for electrons irradiating the target.

Charging potential of dielectrics and insulated conductors as a function of the angle of incidence of an electron beam

The cardinal characteristics of the charging of dielectric and ungrounded metal targets within radiation by medium-energy electrons (0.5–10 keV) have been studied theoretically and experimentally as a function of the angle of incidence of the electron beam. The coefficients of electron emissions and the second critical energy of primary (radiating) electrons, E2C, have been determined as a function of the angle of incidence α when the targets are not being charged.

Mössbauer study of copper ferrite diluted by Ga3+ and Al3+ ions

Mössbauer spectra of the CuGaxAl2xFe2 − 3xO4 system (x = 0.1, 0.2, 0.3, 0.4, 0.5) have been studied at a temperature of 295 K. The results obtained are compared with Mössbauer data for the CuGaxAlxFe2−2xO4 system. It is established that the hyperfine magnetic fields HB (for octahedral sites) and HA (for tetrahedral sites) for ferrites in both systems with ferrimagnetic ordering decrease linearly depending on the total number of nonmagnetic ions in octahedral and tetrahedral sites of the two systems.