Model of metal surface erosion under irradiation by high-power pulsed ion beams

The mechanisms of erosion of metal surfaces under the action of submicrosecond (10⁻⁹−10⁻⁶ s) ion beams in the power density range of P = 10⁶−10⁹ W/cm² with a particle energy of 1–2000 keV are considered. It is shown that the collective processes associated with the radiation heating of the surface are of great importance. A model for the erosion is proposed. In accordance with this model, the flow of atoms of the target leaving the surface being irradiated consists of two independent components caused by collisional sputtering and evaporation, respectively. The influence of the irradiation parameters on the erosion coefficient and the ratio between the sputtering and evaporation factors is analyzed.     

Radiation damage of material surfaces under prolonged irradiation with He+ and Ar+ ions with broad energy spectra

The results of studying the redistribution of Be, Al, Ti, Fe, Cu, Zr, Mo, and W atoms incorporated in polycrystalline metal samples under irradiation with He⁺, (He⁺ + Ar⁺), and Ar⁺ ion beams with a broad energy spectrum and an average energy of 10 keV at irradiation doses of 1 × 10²¹ ion/cm² are studied. It is discovered that irradiation at doses exceeding 1 × 10¹⁹ ion/cm² results in local small-crystal formations being produced in a near-surface substrate layer. Their typical dimensions are less than 1–5 μm, and their the density is up to 1–100. They contain incorporated atoms and impurity atoms with a concentration of 0.1–10 at %. Subsequent irradiation at a dose of 1 × 10²⁰ ions/cm² or more leads to disappearance of these formations, mainly because of sputtering processes.     

Multi-element focused ion beams using compact microwave plasma ion source

Focused ion beams (FIB) are widely used for research and applications in nanoscience and technology. We have developed a compact microwave plasma based multi element FIB (MEFIB) system in order to widen the applications and overcome the limitations faced by conventional Liquid Metal Ion Source (LMIS) based FIB systems, that provide primarily Ga ions. The MEFIB source provides high density plasmas (∼1.5 × 10¹¹ cm⁻³) in a compact cross section. Recently the ion energy spread in the plasma meniscus from where the beams are extracted is found to be small (∼5 eV) [1–3]. The beam extraction and focusing are carried out using electrostatic multi electrode assembly. AXCEL INP and SIMION simulation codes are employed for the design of electrostatic Einzel lenses for beam focusing. The beam focal point is measured using a specially designed three slit Faraday cup and the spot size is measured by the micrography of craters formed by the focused ion beams impinging on copper and aluminium substrates. The initial experimental results show a focused beam spot size of ∼ 25 micron which is in good agreement with the simulations. By further reduction of electrode apertures and operating the second Einzel lens at higher potentials, submicron focused ion beams can be expected.     

Influence of ion bombardment on the photoluminescence response of embedded CdS nanoparticles

Semiconductor nanoparticles (CdS) were fabricated by an inexpensive chemical route using polyvinyl alcohol (PVA) as the dielectric host matrix. Nano-CdS in PVA were subjected to ion irradiation (using oxygen, chlorine and gold) in the medium energy range (80–100 MeV) and under fluence variation of 10¹¹–10¹³ ions/cm². The nature of light emission was found to be drastically different in each of the three cases. Photoluminescence spectra of oxygen irradiated samples exhibit band edge emission (2.8 eV) as well as trap related emission (1.76 eV) whereas band edge emission is found to be bleached out for chlorine ion irradiated nano-CdS. The intense broad PL peaks, noticeable in the case of gold ion irradiated samples suggest superposition of the two peaks — namely, band edge emission and trap related emission. Furthermore, in the case of gold ion irradiated nano-CdS, energy shift in the PL spectra reveals variation in size distribution caused by the extra pressure effect of heavy gold ion beams. The mechanism of such a difference as a result of ion irradiation-type and ion-fluence is discussed in detail.     

Modernized setup for studying the interaction of ions with energies to 40 keV with the surface

A modernized setup for studying the ion-surface interaction is briefly described. The main ion channel implemented on the “Large MEPhI mass monochromator” with an ion energy range of 1–40 keV makes it possible to obtain ion beams with (EM/Z) ≤ 4000 keV × a.m.u. Operation with intermediate-energy hydrogen ions allows obtaining information on the thickness of layers of atoms with masses differing from substrate atoms, by analyzing energy spectra of protons scattered from two- or three-layer targets. The use of new digital power units and relevant control programs also allows automation of the ion beam control and makes it possible to perform ion-beam experiments using preliminarily developed irradiation programs.     

Effects of irradiation parameters on metal surface erosion by pulsed ion beams

Potential application of high-power ion beams of submicrosecond and microsecond durations with the initial particle energy from 50 to 1000 keV and power density 10⁷–10⁹ W/cm² to ensure metal surface erosion are investigated. Evaporation is treated as a major erosion mechanism and the erosion coefficient is taken as an efficiency indicator. Dependences of the erosion coefficients of several metals on beam parameters obtained via calculations using a technique based on the solution of thermal conductivity equation with phase transitions are presented. The ion species, their initial energy, current pulse duration and power density are used as the beam parameters controlling the result of irradiation. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 49–54, August, 2007.     

Experimental and theoretical determination of the stopping power of ZrO<Subscript>2</Subscript> films for protons and <Emphasis Type="Italic">α</Emphasis>-particles

We report the results of an experimental-theoretical study on the stopping power of ZrO₂ films for swift H and He ion beams. The experiments, using the Rutherford Backscattering technique, were done for protons with incident energies in the range 200–1500 keV and for α-particle beams with energies in the range 160–3000 keV. The theoretical calculations were done in the framework of the dielectric formalism using the MELF-GOS model to account for the ZrO₂ target electronic response. It is shown that for both ion beams, the agreement between theory and experiment is quite remarkable.     

Formation of silicon carbide and diamond nanoparticles in the surface layer of a silicon target during short-pulse carbon ion implantation

Synthesis of silicon carbide and diamond nanoparticles is studied during short-pulse implantation of carbon ions and protons into a silicon target. The experiments are carried out using a TEMP source of pulsed powerful ion beams based on a magnetically insulated diode with radial magnetic field B _r . The beam parameters are as follows: the ion energy is 300 keV, the pulse duration is 80 ns, the beam consists of carbon ions and protons, and the ion current density is 30 A/cm². Single-crystal silicon wafers serve as a target. SiC nanoparticles and nanodiamonds form in the surface layer of silicon subjected to more than 100 pulses. The average coherent domain sizes in the SiC particles and nanodiamonds are 12–16 and 8–9 nm, respectively.     

Simulation of Ion Paths in the Target Material for the Injection Complex of the BELA Facility

To realize the simulation experiments with the use of two ion beams at the injection complex of the BELA accelerator (Based on ECR ion source Linear Accelerator), it is necessary to determine the energy and irradiation angle of the beam of light ions which will be implanted into the region of radiation damage induced by heavy-ion beam. The depth of light-ion implantation is determined by the energy and kind of particles initiating the damage, as well as by their incidence angle. It is supposed that the incidence direction of heavy ions will coincide with the normal to the specimen surface. In our work, the necessary implantation zone for the iron ion beam with an energy of 3.2 MeV is located at depths of 300–800 nm. The simulation of the hydrogen and helium ion paths in the material of the iron target in the energy range from 150 to 600 keV at the angle to the normal from 0° to 65° is performed. The range of energies and irradiation angles for the hydrogen and helium ions are determined for the implantation into the radiation-induced defect-formation zone.     

Formation of wide-aperture electron beams in electron accelerators with explosive emission cathodes

The problems concerning the formation of electron beams of microsecond duration, electron energy 500–600 keV, and current density up to 20–30 A/cm² with a rectangular cross section of area 0.1–1 m² in high-current electron accelerators with explosive emission cathodes are considered. The designs of vacuum diodes capable of producing such beams to be used in high-power lasers and for ionization of gas in large volumes are presented. Institute of High-Current Electronics, Siberian Division of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 87–91, April, 2000.     

Short-pulse ECR: A source of multiply charged ions

Extensive investigation is now under way in CERN (European Organization for Nuclear Research) in the framework of the Beta Beam project with the aim of gaining insight into neutrino oscillations. It is suggested that the decay of ⁶He nuclei produce neutrino beams accelerated to an energy on the order of 100 GeV/nucleon. To this end, it is necessary to generate short-pulse (30–100 μs) beams of multiply charged ions of this isotope. Conventional ECR-based ion sources seem to be inappropriate for this purpose, since the plasma density grows slowly (for more than a millisecond) in this case compared with the desired pulse duration. A design concept of a short-pulse ECR-based source of multiply charged ions is proposed. In experiments with pumping at frequencies of 37.5 and 75.0 GHz, pulses as short as ∼50 μs were obtained. Good agreement between theory and experiments is demonstrated.     

Construction and study of a magnetoactive plasma ion source

The interaction of intense electron beams with plasmas in a nonuniform magnetic field is studied for the purpose of obtaining a magnetoactive plasma ion source. The resulting experimental data are used to trace the dynamics of the changes in the basic parameters of the source, both during the stage where it interacts with the beam and in the cooling stage. It is found that the charged particles are contained for a long time and that the efficiency of energy transfer from the beam to the source is high. This source is intended to be used for shaping and accelerating multiampere ion beams. Zh. Tekh. Fiz. 69, 44–47 (April 1999)     

Effect of the electron beam and ion flux parameters on the rate of plasma nitriding of an austenitic stainless steel

The method of nitriding of metals in an electron beam plasma is used to change the current density and energy of nitrogen ions by varying the electron beam parameters (5–20 A, 60–500 eV). An electron beam is generated by an electron source based on a self-heated hollow cathode discharge. Stainless steel 12Kh18N10T is saturated by nitrogen at 500°C for 1 h. The microhardness is measured on transverse polished sections to obtain the dependences of the nitrided layer thickness on the ion current density (1.6–6.2 mA/cm²), the ion energy (100–300 eV), and the nitrogen-argon mixture pressure (1–10 Pa). The layer thickness decreases by 4–5 μm when the ion energy increases by 100 V and increases from 19 to 33 μm when the ion current density increases. The pressure dependence of the layer thickness has a maximum. These results are in conflict with the conclusions of the theory of the limitation of the layer thickness by ion sputtering, and the effective diffusion coefficient significantly exceeds the well-known reported data.     

Magnet design and beam dynamics in computed fields for the DC-350 cyclotron

The DC-350 is an isochronous cyclotron designed in the Flerov Laboratory of Nuclear Reaction (FLNR). It is intended for accelerating ions with a mass-to-charge ratio A/Z within an interval of 5–10 and with an energy of 3–12 MeV/u at the extraction radius. These ion beams will be used in nuclear and applied physics experiments. The paper describes the results of a 3D magnet simulation. The cyclotron magnet and IM90 analiziting-bend magnet of the axial injection channel are studied here. The influence of correction coils on the cyclotron magnet is calculated. All magnet fields were calculated by MERMAID 3D code [1]. The text was submitted by the authors in English.     

Physical foundations for high-temperature electron-beam modification of ceramics

We consider the phenomenon of radiation-accelerated high-temperature mass transfer (RAHTMT) in heterogeneous ion structures under the influence of powerful electron beams. We present a theoretical basis for a surface-recombination mechanism for RAHTMT. The basis for the mechanism is the notion of volume-inhomogeneous dissipation of radiation energy in heterogeneous structures and thermal-diffusion stimulation of mass transfer. We show that high-temperature radiation annealing is an efficient technological method for obtaining ceramics with different and unique properties. Methods of radiation modification have been used to obtain corundum—zircon ceramics with world-class properties. Tomsk Polytechnic University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 176–192, November, 1996.     

Erosion of the GaAs target under irradiation by a high-power pulsed ion beam

The results of examination of the GaAs-target erosion under irradiation by a high-power pulsed ion beam are reported. In the experiments, use was made of a high-power pulsed ion source with the following parameters: ion energy — 250 keV, target current density — 350 A/cm², pulse duration — 80 ns, target energy density — up to 7 J/cm². The target erosion coefficient and its dependence on the number of successive pulses are measured. It is found that the surface roughness parameter is increased with the number of successive beam pulses. A regular structure of surface relief is observed to form in the case where the number of pulses > 20–40. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 66–70, January, 2007.     

Sputtering of tungsten, tungsten oxide, and tungsten-carbon mixed layers by deuterium ions in the threshold energy region

An original experimental method is developed for determining the sputtering coefficients of electrically conducting materials during bombardment by light gas ions at threshold energies. This information is very valuable in both purely scientific and practical terms. The basis of the method is a special field-ion-microscopic analysis regime. The procedure for measuring the sputtering coefficients includes cleaning the surface by field desorption and evaporation, with the subsequent work on an atomically clean and atomically smooth surface. The method permits identification of single vacancies on the irradiated surface, i.e., it is possible to count individual sputtered atoms. The method is tested on commercially pure tungsten, tungsten oxide, and a W-C mixed layer on tungsten under deuterium ion bombardment. The energy dependences of the sputtering coefficients of these materials for sputtering by deuterium ions at energies of 10–500 eV are obtained and analyzed. An important relationship between the energy threshold for sputtering and the conditions for oxidation of tungsten is found. The energy threshold for sputtering of an oxidized tungsten surface is 65 eV. The energy threshold for sputtering of the W-C mixed layer is almost equal to the corresponding value for pure tungsten. Zh. Tekh. Fiz. 69, 137–142 (September 1999)     

Reflection and Absorption of Conical and Bessel Light Beams by Cylindrical Objects

The problem of reflection and refraction of a conical beam at the boundary of an object of cylindrical shape is solved analytically. The amplitude and energy coefficients of reflection for a field of variable polarization are calculated. The light energy absorption in a cylindrical object and its distribution over the cross section are investigated. The advantage of using conical beams of light for probing cylindrically shaped objects, including biological ones, is shown. Presented at the 5th International Scientific-Technical Conference “Quantum Electronics,” November 22–25, 2004, Minsk, Belarus. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 664–669, September–October, 2005.     

Investigation of the role of the projectile-target orientation angles on the evaporation residue production

The measured yield of evaporation residues in reactions with massive nuclei have been well reproduced by using the partial fusion and quasifission cross sections obtained in the dinuclear-system model. The influence of the orientation angles of the projectile- and target-nucleus symmetry axes relative to the beam direction on the production of the evaporation residues is investigated for the ⁴⁸Ca + ¹⁵⁴Sm reaction as a function of the beam energy. At the low beam energies only the orientation angles close to αP = 30° (projectile) and αP = 0°–15° (target) can contribute to the formation of evaporation residues. At large beam energies (about E _c.m. = 140–180 MeV) the collisions at all values of orientation angles αP and α _T of reactants can contribute to the evaporation residue cross section which ranges between 10–100 mb, while at E _c.m. > 185 MeV the evaporation residue cross section ranges between 0.1–1 mb because the fission barrier for the compound nucleus decreases by increasing its excitation energy and angular momentum.     

Longitudinal dynamics of <Superscript>197</Superscript>Au<Superscript>32+</Superscript> and <Superscript>197</Superscript>Au<Superscript>79+</Superscript> ions in NICA injection chain

The main objective of the NICA project developed at the Joint Institute for Nuclear Research (JINR) is to conduct experimental studies with colliding heavy ion beams in an energy range of 1–4.5 GeV/nucleonucleon with luminosity on the level of 1 × 10²⁷ cm⁻² s⁻¹. In this paper the operation regime of the collider injection chain providing the bunch with experimentally desirable parameters at the output of the Nuclotron is considered for gold ions as an example.