Deflection of an electron beam with a 1.8-MeV energy incident at glancing angles on a dielectric surface

The first results of investigations into the effect of self-deviation of an electron beam with intermediate energy by a dielectric surface, previously discovered by the authors for the interaction of electrons with a glass surface, are presented in the paper. It is shown that optimizing the deflection process and choosing a dielectric target, angles of beam deflection of the order of 5–8° can be obtained and stabilized during subsequent irradiation of the target, which is especially important for applications of this effect to electron-beam optics. Scientific Research Institute of Nuclear Physics at Tomsk Polytechnic University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 12–17, September, 1999.     

Scattering of an unpolarized Bessel beam by spheres

The scattering process of an unpolarized Bessel beam through spherical scatterers is investigated. We derive the analytical solutions of scattered fields of x-and y-polarized Bessel beams using a sphere, after which the dimensionless scattering function for an unpolarized Bessel beam is obtained. The dimensionless scattering function is applicable to spherical scatterers of any size on the beam axis or near it. Through numerical simulations, we demonstrate that extreme points exist in the direction or neighboring direction of the conical angle for spherical scatterers on the beam axis, whereas the existence of extreme points depends on the ratio between the spherical scatterers size and central spot size of the Bessel beam.     

Excitation of microwave by an annular electron beam in a plasma-filled dielectric lined waveguide

An axial relativistic electron beam passing through a slow wave structure is unstable to an electromagnetic perturbation whose phase velocity equals the velocity of the beam. This phenomenon of Cherenkov emission is the basis of all traveling wave tubes. In this paper an excitation of Cherenkov radiation by a thin annular relativistic electron beam in a plasma-filled dielectric-lined waveguide is analysed by use of the self-consistent linear theory. The effect of the thin annular electron beam on the beam-wave interaction is completely described by a jump condition. The dispersion equation and the simultaneous condition of the beam-wave interaction are derived. Finally, the growth rate of the wave is obtained, and the effect of the background plasma density and the electron beam radius on the growth rate of the wave are presented.This work is supported by National Natural Science Foundation of China.     

Hydrocarbon film formed on the surface of a semiconductor irradiated by an electron beam

The rate of formation of a hydrocarbon film on the surface of a sample subjected to the action of an electron beam is studied at room temperature and in cooling a sample to the liquid nitrogen temperature. The thickness and the optical radiation transmission of such films are measured as functions of the electron beam radiation time, the sample temperature, and the level of vacuum. The film thickness is measured with atomic force microscopy. The absorption of the films is determined by comparing the cathodoluminescence intensities from a pure sample surface and from the surface covered with a film. The experimental results can be used to estimate the film formation rate as a function of the sample temperature and the vacuum and to determine the optical radiation absorption at a wavelength of 300, 360, 550, and 665 nm.     

Terahertz surface plasmon excitation over a bismuth thin film by an electron beam

The excitation of terahertz surface plasma wave (SPW) over bismuth thin film-glass structure by a parallel propagating electron beam is studied. The SPW phase velocity is sensitive to the thickness of bismuth film and it is driven via the Cerenkov resonance. The growth rate for terahertz radiation generation by an electron beam is obtained under small signal approximation.     

Polarized light-scattering measurements of dielectric spheres upon a silicon surface

The polarization of light scattered into directions out of the plane of incidence by polystyrene latex spheres upon a silicon substrate was measured for p -polarized incident light. The experimental data show good agreement with theoretical predictions for three sizes of spheres. These results demonstrate that the polarization of light scattered by particles can be used to determine the size of particulate contaminants on silicon wafers. Theoretical models, based on successive degrees of approximation, indicate that the mean distance of a particle from the surface is the primary determinant of the scattered light polarization for small out-of-plane scattering angles.     

Tunable terahertz radiation from arbitrary profile dielectric grating coated with graphene excited by an electron beam

In this paper, the enhanced terahertz radiation transformed from surface plasmon polaritons, excited by a uniformly moving electron bunch, in a structure consisting of a monolayer graphene supported on a dielectric grating with arbitrary profile is investigated. The results show that the grating profile has significant influence on the dispersion curves and radiation characteristics including radiation frequency and intensity. The dependence of dispersion and radiation characteristics on the grating shape for both the symmetric and asymmetric gratings is studied in detail. Moreover, we find that, for an asymmetric grating with certain profile, there exist two different diffraction types, and one of the two types can provide higher radiation intensity comparing to the other one. These results will definitely facilitate the practical application in developing a room-temperature, tunable, coherent and miniature terahertz radiation source.     

Features of surface acoustic wave propagation in lithium niobate damaged by an electron beam

The propagation of surface acoustic waves (SAWs) in a thin-film aluminum waveguide of Δv/v type fabricated on a 128° Y-X LiNbO₃ plate by lift-off lithography and direct writing by a 20-keV electron beamis studied experimentally. The temperature dependence of the phase of the signal passed through an SAW delayline exhibits steps and hysteresis. The line consists of such a waveguide and two interdigital transducers with acenter frequency of 486 MHz and is exposed to a nitrogen flow. The vapors of water-containing analytes introduced into the nitrogen flow cause anomalous phase changes. These changes are of opposite sign and more thanone order of magnitude greater than the phase changes observed under similar conditions in specimens fabricated by optical lithography. It is concluded that these phenomena offer possibilities for designing SAW humidity sensors with a low threshold of sensitivity.     

Effect of electron drift and emission on the surface potential of an irradiated dielectric

A mathematical model is proposed for the steady-state charging of dielectrics with an open surface under bombardment with a nonpenetrating electron beam. The model is based on inclusion of the emission and drift mechanisms of the leakage of charge injected into the dielectric. Charge transfer through the unirradiated layer of dielectric adjacent to the grounded substrate is assumed to occur in a space-charge-limited current mode. As a result of this the strength in the unirradiated layer is of sufficient strength to make a certain contribution to the surface potential of the dielectric. The steady-state surface potential on the electron-beam parameters and the characteristics of the sample are studied by analyzing the proposed model. We consider the irradiation conditions under which one of the charge-leakage mechanisms dominates.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 5–10, November, 1990.     

Characterization of dielectric spheres by spiral imaging

We study the spiral spectra scattered off transparent dielectric spheres when probed by different Laguerre-Gaussian light beams, carrying nested topological wavefront dislocations. We show that such scattering data may be employed to determine geometrical properties of the spheres, such as their position. The technique is a generalization of standard Mie scattering, and it can be extended to study and to characterize nanospheres.     

Influence of an external magnetic field on the threshold of multipactor onset on a dielectric surface

In this paper, we propose a theoretical model of the initial stage of development of a one-sided secondary-emission (multipactor) discharge on a dielectric surface. Consideration is based on a statistical method supported by an exact analytical solution for the transit-time distribution function of secondary electrons. The general integral equation allowing us to determine the stationary emission-phase distribution functions and the threshold of multiplicator onset in the presence of an external magnetic field is formulated. It is shown that the presence of an external magnetic field can significantly change the conditions of multipactor onset. It is found that the discharge-zone boundaries calculated within the framework of a statistical model are in qualitative agreement with the results obtained by the Monte-Carlo method. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 2, pp. 118–133, February 2007.     

Silicon dioxide modification by an electron beam

The overheating temperature of a microvolume of silicon dioxide produced by bombardment by a high specific-power electron beam has been estimated. Calculations showed that the maximum temperature to which a microvolume of silicon dioxide is overheated can be as high as 1200°C for an electron beam current of 100 nA. The variation in the cathodoluminescence characteristics of amorphous silica with different contents of hydroxyl groups was studied for various electron beam specific-power levels. The impact of a high specific-power electron beam was shown to create additional lattice defects up to the formation of silicon clusters.     

Cherenkov terahertz radiation from Dirac semimetals surface plasmon polaritons excited by an electron beam

We demonstrate a physical mechanism for terahertz(THz) generation from surface plasmon polaritons(SPPs). In a structure with a bulk Dirac semimetals(BDSs) film deposited on a dielectric substrate, the energy of the asymmetric SPP mode can be significantly enhanced to cross the light line of the substrate due to the SPP-coupling between the interfaces of the film. Therefore, the SPPs can be immediately transformed into Cherenkov radiation without removing the wavevector mismatch. Additionally, the symmetric SPP mode can also be dramatically lifted to cross the substrate light line when a buffer layer with low permittivity relative to the substrate is introduced. In this case, dual-frequency THz radiation from the two SPP modes can be generated simultaneously. The radiation intensity is significantly enhanced by over two orders due to the field enhancement of the SPPs. The radiation frequency can be tuned in the THz frequency regime by adjusting the beam energy and the chemical potential of the BDSs. Our results could find potential applications in developing room temperature, tunable, coherent, and intense THz radiation sources to cover the entire THz band.     

Recording of domains by an electron beam on the surface of +Z cuts of lithium niobate

Using an electron beam, spontaneous polarization on the surface of +Z cuts of lithium niobate crystals of various compositions is switched. Domains 100–200 nm in size are formed in a thin surface layer, with the thickness dependent on the primary-electron energy. The sizes of segments, on which submicron domains are formed, exceed the sizes of the irradiation region. The distributions of domains on the surface in crystals of various compositions are different and depend on the method of moving the electron beam and irradiation conditions. The results are discussed in the context of notions on the charging of dielectric materials by the electron beam. It is assumed that the spontaneous polarization in the surface layer of +Z cuts of lithium niobates is switched by the field of a double layer of charges formed as a result of the charging process near the surface.     

Polarization effects of electron current settling when the cerenkov radiation is excited by a nonrelativistic electron beam in an open dielectric resonator

We study the effect of electron current settling of a strip nonrelativistic electron beam (EB) on the Cerenkov radiation (CR) in a metal-dielectric channel formed by the metal surface and the surface of a rectangular open dielectric resonator having isotropic properties and operated at millimeter wavelengths (3.6–5.8 mm). The choice of this channel was substantiated by theoretical studies of the CR energy density. We experimentally examined several effects, including the neutralization of the dielectric surface dipole charge by electrons, the accumulation of electron charge at the dielectric surface, and the influence of the electron charge on the EB and CR. Conclusions are drawn on the prospects of using short pulses of EB and special metal-dielectric diffraction gratings for the excitation of CR. Institute of Radioengineering and Electronics, Ukrainian National Academy of Sciences, Kharkov, Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 4, pp. 491–505, April, 1997.     

Angle-resolved elastic peak electron spectroscopy: Role of surface excitations

We analyze the possibility of determining the surface excitation parameter (SEP) from the dependence of the elastic backscattering signal intensity on the emission angle. It has been found that the shape of this dependence is reasonably well described by the theoretical model implemented in a typical Monte Carlo simulation strategy. As shown recently, the mean percentage deviation between the experimental angular dependence and the theoretical dependence is equal to 8.82% at 200 eV, 6.28% at 500 eV and 4.69% at 1000 eV. In the theoretical model used, the surface energy losses were ignored. Close inspection of the deviations between theory and experiments indicates systematic trends that can be ascribed to the surface energy losses. We found here that taking into the account the surface energy losses further improves the agreement between theory and experiment. The total mean percentage deviation, equal to 6.65%, decreases to 5.59% if the mathematical form of the Chen formula for SEP is used, or to 5.16% if the Oswald expression is used. The material dependent coefficients in the expression of SEP derived from the emission angle dependence of the elastic peak intensity differ from these coefficients resulting from other methods. We conclude that the determination of SEP from shape of the angular dependence requires the experimental data of high quality, and the reliable theoretical model describing elastic electron backscattering.     

Plasma instabilities excited by an azimuthal electron beam

The paper describes the effect of the finite temperature T of an azimuthal electron beam on plasma stability. Only instabilities for which the longitudinal macroscopic velocity of the beam is of no importance are discussed. It is shown that at the limit of applicability the weak and strong inhomogeneity approximations give the same results.