V. Yu. Petukhov

Formation of metal-polymer composites by ion implantation

Abstract Silver nanoparticles have been synthesized by ion implantation at 30 keV into polymethyl-methacrylate at doses from 3.1 × 1015 to 7.5 × 1016 ion cm−2 and a beam current 4 μA cm−2 at room temperature. Transmission electron microscopy was used to determine the structure of the silver-polymer systems obtained. It was observed that in the prepared samples, spherical metal particles with sizes smaller than 12 nm were fabricated. For characterization of the optical response of the composites, transmittance spectroscopy was employed. The formation of the silver nanoparticles leads to an increase of the optical absorption bends at the plasma wavelength in the visible range, where the spectral position of the transmittance minimum depends on the implantation conditions. It was observed that the intensity of the absorption is very weak in spite of the large quantity of silver particles existing in the polymer medium; the factors influencing the optical data are discussed.

Effect of ion current density on the phase composition of ion beam synthesized iron silicides in Si (100)

Abstract Phase composition of Fe+ implanted in Si(100) at elevated temperatures was investigated over a wide range of ion current densities. Phases and texture were determined by glancing angle XRD. Both FeSi and β-FeSi2 phases were observed. The phase composition of the synthesized layers was found to be strongly affected by ion current density. The increase of the ion current density at an implantation temperature of 450°C leads to a rise in relative content of β-FeSi2. This effect is explained by the spreading of the Fe profile. Such changes of the profile are the result of the radiation enhanced diffusion during implantation.

Features of FMR spectra observed in granular films formed by Fe+ implantation into PMMA

Magnetic phase consisting of α-Fe particles arranged in a thin near-surface layer has been synthesized in modified phosphorus-containing polymethylmethacrylate by Fe+ implantation at an energy of 40 keV with a dose of 1.2⊙1017 ion/cm2. The spectrum of magnetic resonance of the obtained samples is a superposition of a wide anisotropic absorption line and a set of reproducible lowintensity noiselike signals registered in a wide range of magnetic field. It has been established that a wide absorption line is due to particle conglomerates (larger than 200 nm), each behaving as a thin ferromagnetic film. Noiselike lines can be explained as resonance signals from separate oblate/prolate nanoparticles (50–200 nm in size) randomly oriented with respect to the irradiated surface. Such complicated nanostructures can be formed at an appropriate combination of properties of a polymer matrix, types of bombarded ions and implantation regimes.

Uniaxial magnetic anisotropy of iron-silicide thin films ion synthesized in an external magnetic field

Fe3Si ferromagnetic thin films are synthesized by iron ion implantation into single-crystal Si(111) and Si(100) wafers. The ion dose dependence of the magnetic properties of the iron-silicide thin films is investigated in detail by the magnetooptical Kerr effect. Magnetically isotropic and anisotropic films are formed, depending on the ion-beam synthesis conditions. The film coercivity increases with implantation dose. According to the results of X-ray analysis, the magnetically isotropic samples with an average crystallite size of 20–30 nm exhibit higher crystlallinity as compared with the magnetically anisotropic films. The results obtained show that the magnetic properties of both the isotropic and anisotropic samples can be described within the random anisotropy model. It is established with increasing ion implantation dose that the magnetocrystalline anisotropy of randomly oriented crystallites compete with the induced uniaxial anisotropy, up to suppression of the latter.

Ferromagnetic resonance investigation of magnetic anisotropy of ion-synthesized iron-silicide thin films

Abstract40 keV iron ions have been implanted into single-crystal silicon wafers at room temperature. As a result, thin iron-silicide films were synthesized in the near-surface region of substrates. Scanning magnetooptical Kerr effect studies showed that some films had the uniaxial magnetic anisotropy. The coercive force determined in the direction of the easy magnetization for films with the magnetic anisotropy increased with the increase in the implantation fluence. However, ferromagnetic samples became isotropic when the dose of the order of 2.6×1017 cm–2 was reached. Ferromagnetic resonance studies showed that the resonance linewidth in isotropic samples increased with the temperature decrease. It was found that the ferromagnetic resonance linewidth for samples with the uniaxial anisotropy was less than that for isotropic ones. The observed behavior of resonance spectra can be explained on the basis of the model taking into account the effect of thermal fluctuations of the resonance line shape in disperse ferromagnets.

A system for monitoring the ion current in the ILU-3 implanter

The design of a small device for detecting charged particles and a system for monitoring the ion-beam current are described. The system contains several sensors for ion-current measurements, thus increasing the information content and making it possible to visualize the processes of implantation and monitoring of the ion-beam parameters, and allows adjustment of the ion-bombardment regimes directly during implantation.

Investigation of metabolic changes in blood and tissue of mice γ-irradiated with sublethal doses by direct observation of EPR signals from Hb-NO complexes

The metabolic changes in probes of blood and tissue (spleen, liver and kidney) of mice under total γ-irradiation with the doses varied in the interval of 1–10 Gy at the dose rate of 0.073 Gy/min were studied in the early postirradiation period by ex vivo electron paramagnetic resonance (EPR). It was established that the impact with the lower dose rate leads to more intensive nitric monoxide biosynthesis in comparison with higher dose rates. In the early postirradiation period (from 2 up to 6 h), irradiation with doses higher than 2 Gy brings about an increase of the NO concentration and, hence, the appearance of nitrosyl complexes which were registered directly by EPR in blood and spleen. The observed line is identified as the signal from α-(Fe2+-NO)2β(Fe3+)2 or α-(Fe2+-NO) α(Fe2+)β(Fe3+)2 complexes since the methemoglobin concentration also increases in comparison with the control level. The concentration of Hb-NO complexes in blood and spleen depends on the dose and individual radiosensitivity of the organism. Therefore, the intensity of the Hb-NO signal may serve as a criterion of the radiation injury level during the first hours after the irradiation. 30 h after the impact, the Hb-NO complexes were no longer detected. For the first day, the concentration of Fe3+-transferrin in blood increases with the dose and time passed after the irradiation. The intensity of the EPR signal from Fe3+-transferrin in blood may also serve as a measure of the radiation injury level.

Ion-Beam Synthesis of Ferromagnetic Films by the Implantation of Co+ Ions into Silicon

Thin ferromagnetic films of cobalt silicide are synthesized by implanting Co+ ions into single-crystal silicon plates under an external magnetic field. Scanning magnetopolarimetry shows that the samples implanted at a dose greater than 2 × 1017 cm–2 have uniaxial magnetic anisotropy. Based on the dose dependence of the anisotropy field and the experiment on switching the direction of the easy magnetization axes, it is concluded that the induced magnetic anisotropy in the resulting films is due to the directional atomic pair ordering. The absence of the effect of external mechanical stress created during implantation on the magnetic properties of cobalt-silicide films is revealed.

Change in the sign of the Kerr effect in ion-beam-synthesized Fe3Si films

Ion-beam-synthesized Fe3Si thin films are studied using the magneto-optical Kerr effect, ferromagnetic resonance, electron diffraction, and Auger spectroscopy. A change in the direction of rotation of the plane-polarized light as a function of film-synthesis conditions is discovered when the meridional Kerr effect is recorded. It is shown that the observed effect is related to the presence of thin interference films with different thicknesses on the surfaces of the magnetic layers.

A high-temperature unit for the ion collector of the ИЛУ-3 accelerator

The design of the multiposition high-temperature unit for the ion collector of the ИЛУ-3 accelerator with an operating range up to 1000°C is described. The unit is intended to sequentially implant up to four samples at a stabilized temperature without devacuumization of the accelerator chamber. The temperature of the target was calculated in the process of implantation with consideration for the contact and radiation heat exchanges. The effect of implantation conditions and modes on the equilibrium target temperature is shown.