Surface modification of polycrystalline oxides (V<Subscript>2</Subscript>O<Subscript>5</Subscript>, MoO<Subscript>3</Subscript>, and WO<Subscript>3</Subscript>) irradiated with high-power ion beams

The influence of a high-power ion beam on polycrystalline oxides (V₂O₅, MoO₃, and WO₃) is investigated. Oxide irradiation with ion beams with current densities of greater than ～30 A/cm² is established to initiate changes in the color of irradiated layers and lead to surface-layer particle melting. It is demonstrated that a distinctive feature of the interaction between a high-power ion beam and V₂O₅ is the formation of surface nanosheets and nanowires whose characteristic cross-sectional size and thickness are ～1 μm and up to ～40 nm, respectively. The nanosheets are generated near emerging surface cracks if the beam current density is ～100 A/cm². Possible mechanisms of surface nanostructures formation under the action of pulsed ion beams are discussed.     

H+5团簇离子及其中性团簇产物H3和H4

报道了H⁺₅的实验结果.分析讨论了H⁺₅的 形成和分解途径.根据理论分析，以稳定的H⁺₃为核心与一个或多个氢分子结合可能形成稳定的H^{+_n氢团簇离子.另一方面，在高频离子源中, 有发生H+₃与H₂反应的条件.实 验中，从高频离子源引出的离子束被静电加速器加速，然后用9 关键词： +}₅团簇离子')" href="#">H⁺₅团簇离子 3中性团簇')" href="#">H₃中性团簇 4中性团簇')" href="#">H_{4中性团簇}     

Ion induced secondary electron emission from single crystal surfaces

Yields of ion impact induced electrons from very pure Ni(110) and Ni(111) surfaces have been measured. In several tilt planes the angle of incidence of a 5 keV H⁺, H⁺₂ or H⁺₃ ion beam is varied from perpendicular to grazing incidence. Below = 75° the yield increases as sec but shows characteristic depressions when the beam is incident along crystallographically low indexed lattice directions. This is explained by kinetic electron emission with respect to the projectile transparency of the crystal lattice.     

Improvement of corrosion resistance of carbon steel using chemical vapor deposition from Cr(CO)6 with an ArF excimer laser

Corrosion resistance of carbon steel coated with thin film deposited from Cr(CO)₆ using an ArF excimer laser (193 nm) has been evaluated by an electrochemical method as a function of laser beam intensity. The carbon steel coated with the film formed at higher beam intensity shows higher corrosion resistance. Microstructure, composition, and thickness of the films have also been investigated. SEM micrographs show that the films consist of small grains which decrease in size with increasing beam intensity. Auger electron spectroscopy (AES) combined with Ar⁺ beam sputtering reveals that the films deposited at higher beam intensity give higher chromium content, and that the thickness at a fixed total irradiation energy increases up to the intensity of 10 MW cm^–2, falling above this intensity. In addition, the change of film thickness by addition of buffer gases (Ar, CO, and H₂O) has been investigated. The thickness is 10 times smaller under the addition of H₂O, and twice smaller under the addition of Ar or CO than without the addition of gases. A deposition mechanism based on photolysis of Cr(CO)₆ in the gas phase is proposed related to the experimental data after the discussion of several possible mechanisms.     

Modification of polycrystalline SnO2 and ZnO under the action of a high-power ion beam of nanosecond duration

The modification of polycrystalline oxides (SnO₂ and ZnO) under the action of a nanosecond high-power ion beam (HPIB) with current densities of 50–150 A/cm², which is accompanied by melting of initial particles of the surface layer, is investigated. It is established that submicron-sized particles of tetragonal SnO whose average size is 210 nm are formed on the SnO₂ surface irradiated by an ion beam with a current density of 150 A/cm². These particles have pronounced crystallographic faceting. When ZnO is irradiated by HPIBs with different current densities, a thin Zn film is formed in the sintered surface layer. Possible mechanisms of the observed conversions are discussed.     

Using polyatomic primary ions to probe an amino acid and a nucleic base in water ice

In this study on pure water ice, we show that protonated water species [H₂O]_nH⁺ are more prevalent than (H₂O)_n⁺ ions after bombardment by Au⁺ monoatomic and Au₃⁺ and C₆₀⁺ polyatomic projectiles. This data also reveals significant differences in water cluster yields under bombardment by these three projectiles. The amino acid alanine and the nucleic base adenine in solution have been studied and have been shown to have an effect on the water cluster ion yields observed using an Au₃⁺ ion beam.     

The formation of an intense secondary pulsed molecular beam and obtaining accelerated molecules and radicals in it

A method for obtaining an intense secondary pulsed molecular beam is described. The kinetic energy of molecules in the beam can be controlled by vibrational excitation of the molecules in the source under high-power IR laser radiation. A compression shock (shock wave) is used as a source of secondary beams. The shock wave is formed in interaction between an intense pulsed supersonic molecular beam (or flow) and a solid surface. The characteristics of the secondary beam were studied. Its intensity and the degree of gas cooling in it were comparable with the corresponding characteristics of the unperturbed primary beam. Vibrational excitation of molecules in the shock wave and subsequent vibrational-translational relaxation, which occurs when a gas is expanded in a vacuum, allow the kinetic energy of molecules in the secondary beam to be substantially increased. Intense [≥10²⁰ molecules/(sr s)] beams of SF₆ and CF₃I molecules with kinetic energies approximately equal to 1.5 and 1.2 eV, respectively, were generated in the absence of carrier gases, and SF₆ molecular beams with kinetic energies approximately equal to 2.5 and 2.7 eV with He (SF₆/He=1/10) and H₂ (SF₆/H₂=1/10) as carrier gases, respectively, were obtained. The spectral and energy characteristics of acceleration of SF₆ molecules in the secondary beams were studied. The optimal conditions were found for obtaining high-energy molecules. The possibility of accelerating radicals in secondary molecular beams was demonstrated.     

The influence of discharge parameters on the generation of ions H<Subscript>3</Subscript><Superscript>+</Superscript> in the source based on reflective discharge with hollow cathode

For hydrogen ions source based on reflective discharge with hollow cathode the investigations of the effect of discharge current and gas pressure on the component composition of the ion beam have been performed. It has been shown that the optimization of the discharge parameters makes it possible to achieve up to 70% triatomic hydrogen ions H₃ ⁺ in the beam.     

Circular ion diode with self-magnetic insulation

The results of a study of the generation of a gigawatt-level pulsed ion beam formed by a diode with an explosive-emission potential electrode in self-magnetic insulation mode are presented. The experiments have been performed on the TEMP-4M ion accelerator operating in double-pulse formation mode: the first pulse is negative polarity (300–500 ns, 100–150 kV) and the second is positive (150 ns, 250–300 kV). The ion current density is 20–40 A/cm²; the beam consists of protons and carbon ions. To increase the efficiency of the ion current generation, a circular geometry diode is proposed. It is shown that with the new design, the plasma is effectively formed over the entire working surface of the graphite potential electrode. During ion beam generation, magnetic insulation of the electrons is achieved over the entire length of the diode (B/B _cr ≥ 3). Because of the high drift velocity, the transit time of electrons in the anode-cathode gap is 3–5 ns, whilst the transit time of C⁺ carbon ions exceeds 8 ns. This indicates low efficiency self-magnetic insulation for this geometry of diode. At the same time, it has been observed experimentally that during ion current generation (the second pulse), the electron component of the total current is suppressed by a factor of 4–5. A new mechanism of limiting the electron emission, which explains the decrease in the electron component of the total current in the circular diode with self-magnetic insulation, is proposed.     

Structure and magnetic properties of a new single-molecule magnet [Mn11Fe1O12 (CH3COO)16(H2O)4].2CH3COOH.4H2O

A new single-molecule magnet [Mn₁₁Fe₁O₁₂ (CH₃COO)₁₆(H₂O)₄]?2CH₃COOH?4H₂O (Mn₁₁Fe₁) has been synthesized.The structure has been studied by the single crystal x-ray diffraction. The difference of Jahn--Teller distortion between Fe³⁺ and Mn³⁺ ion reveals that Fe³⁺ ion substitutes for Mn³⁺ ion on the Mn(3) sites in the Mn₁₂ skeleton. The temperature dependence of the magnetization gives a blocking temperature T_B=1.9K for Mn₁₁Fe₁. Based on the magnetization process analysis of the crystal at T=2K, we suggest that Mn₁₁Fe₁ has the ground state with a total spin S= 11/2.     

Study of structural and electronic environments of hydrogenated amorphous silicon carbonitride (a-SiCN:H) films deposited by hot wire chemical vapor deposition

Hydrogenated amorphous silicon carbon nitride (a-SiCN:H) thin films were deposited by hot wire chemical vapor deposition (HWCVD) using SiH₄, CH₄, NH₃ and H₂ as precursors. The effects of the H₂ dilution on structural and chemical bonding of a-SiCN:H has been investigated by Raman and X-ray photoelectron spectroscopy (XPS). Increasing the H₂ flow rate in the precursor gas more carbon is introduced into the a-SiCN:H network resulting in decrease of silicon content in the film from 41 at.% to 28.8 at.% and sp² carbon cluster increases when H₂ flow rate is increased from 0 to 20 sccm.     

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.     

Understanding the mechanism of DNA deactivation in ion therapy of cancer cells: hydrogen peroxide action*

Changes in the medium of biological cells under ion beam irradiation has been considered as a possible cause of cell function disruption in the living body. The interaction of hydrogen peroxide, a long-lived molecular product of water radiolysis, with active sites of DNA macromolecule was studied, and the formation of stable DNA-peroxide complexes was considered. The phosphate groups of the macromolecule backbone were picked out among the atomic groups of DNA double helix as a probable target for interaction with hydrogen peroxide molecules. Complexes consisting of combinations including: the DNA phosphate group, H₂O₂ and H₂O molecules, and Na⁺ counterion, were considered. The counterions have been taken into consideration insofar as under the natural conditions they neutralise DNA sugar-phosphate backbone. The energy of the complexes have been determined by considering the electrostatic and the Van der Waals interactions within the framework of atom-atom potential functions. As a result, the stability of various configurations of molecular complexes was estimated. It was shown that DNA phosphate groups and counterions can form stable complexes with hydrogen peroxide molecules, which are as stable as the complexes with water molecules. It has been demonstrated that the formation of stable complexes of H₂O₂-Na⁺-PO₄ ^- may be detected experimentally by observing specific vibrations in the low-frequency Raman spectra. The interaction of H₂O₂ molecule with phosphate group of the double helix backbone can disrupt DNA biological function and induce the deactivation of the cell genetic apparatus. Thus, the production of hydrogen peroxide molecules in the nucleus of living cells can be considered as an additional mechanism by which high-energy ion beams destroy tumour cells during ion beam therapy.     

MeV氢微团簇离子与固体介质的电荷交换

利用静电加速器提供的0.6—1.8MeV的H⁺，H⁺₂，H⁺₃离子，轰击不同厚度的碳膜，分别测量这些离子通过碳膜后各种产物的产额. 得到了不同能量的H⁺通过碳膜后中性原子H和负离子H^-的产额随入射质子速度的变化关系；分别得到能量为1.2MeV,1.8MeV的H⁺₂，H⁺₃团簇离子通过不同厚度碳膜的透射产额及其与团簇离子在碳膜中驻留时间的关系；对结果进行了理论分析与讨论. 关键词： 团簇离子 电荷交换     

Anomalous carbon nuclei

Results are presented from a bubble chamber experiment to search for anomalous mean free path (MFP) phenomena for secondary multicharged fragments (Z _f =5 and 6) of a¹²C beam at 4.2 GeV/c per nucleon. A total of 50,000 primary interactions of carbon with propane (C₃H₈) were treated. Approximately 6,000 beam fragments with charges Z _f =5 and 6 were analyzed in detail to search for an anomalous decrease of MFP. The anomaly is observed only for secondary carbon nuclei. The experiment has been performed at the Laboratory of High Energies, JINR.     

Stoßdissoziation von H 2 + - und D 2 + -Ionen

The angular and energy distribution of protons produced by collision-induced dissociations of H ₂ ⁺ ions with energies of 10 and 20 keV were measured in a parabola spectrograph. From these measurements the velocity distribution of the protons in the center of mass system of the H ₂ ⁺ ion can be calculated. This gives information about the type, the abundance, and the anisotropy of the processes involved. The most frequent transitions leading to dissociations are the excitation of the 2pσ_u state, the ionisation of the H ₂ ⁺ ion, the transition into the vibrational continuum, and the electron capture into the 1³ σ _u ⁺ state of the hydrogen. It is shown that the cross section for an electronic transition depends on the velocity of the ion, the distance of the nuclei in the ion, the angle between the internuclear axis and the direction of the primary ion beam, and the excitation energy of the target. The fraction of protons produced by vibrational excitation increases with increasing atomic number of the target. Concerning electronic transitions D ₂ ⁺ ions equal H ₂ ⁺ ions of the same velocity.     

Carbon-13 Isotopic Species of H2C3, H2C4, and H2C5: High-Resolution Rotational Spectra

The microwave rotational spectra of the carbon-13 isotopic species of H₂C₃, H₂C₄, and H₂C₅ have been observed in a pulsed supersonic molecular beam by Fourier transform microwave spectroscopy. At high resolution all of the rotational lines exhibit hyperfine structure produced by the magnetic interaction between the nuclear spin of ¹³C and the overall rotation of the molecule. The component of the nuclear spin-rotation tensor along the a-inertial axis is large for most isotopic species, especially at the carbene carbon; at this position C_aa is two to three times larger than at other substituted positions along the chain. In contrast to both H₂C₃ and H₂C₃, in H₂C₄C_aa exhibits a pronounced alternation along the carbon chain backbone. Following detection of the five carbon-13 isotopic species and D₂C₅, an experimental structure (r₀) has been determined to high accuracy for H₂C₅.     

Formation of por-Si/SnOx nanocomposite by high-power ion beams of nanosecond duration

Layers of por-Si/SnO _x nanocomposite formed by high-power ion beam irradiation with nanosecond duration have been studied. The results of structural and elemental analyses of these layers are presented. The high sensitivity of this nanocomposite to low NO₂ concentrations at room temperature has been revealed.     

Infrared multiple-photon dissociation of ion-molecules in a beam

First experiments on the infrared multiple-photon dissociation with ion molecules in beams have been carried out. A mass selected beam of SF⁺₅ parent ions is crossed with a focused pulsed CO₂ laser beam. Using mass spectroscopy for the detection, fragmentation into SF⁺₄ and SF⁺₃ has been observed. The relative yield and power dependence have been measured. Features of the MPD of ions in beams are discussed.     

Hydration-induced conformational changes in protonated 2,4-pentanedione in the gas phase

Starting with H⁺[CH₃C(O)CH₂C(O)CH₃] (denoted H⁺PD), the protonated diketone-water clusters H⁺PD(H₂O) _n (n = 1–3) have been characterized by density functional theory calculations in combination with vibrational predissociation spectroscopy to explore the conformational changes of a protonated bifunctional ion solvated by water in the gas phase. Theoretical calculations for H⁺PD revealed that the ion contains an intramolecular hydrogen bond (IHB), with two oxygen atoms bridged by the extra proton in an O—H⁺ … O form. Attachment of one water molecule to it readily ruptures this IHB, replacing the H⁺ by the H₃O⁺ moiety. Further replacement of the IHB by two water molecules occurs at n = 2 and the ?C(O)CH₂C(O)- chain is fully opened (or unfolded) after transfer of the extra proton to the water trimer at n = 3. To verify the computational findings, infrared spectroscopic measurements were performed using a vibrational predissociation ion trap spectrometer to identify cluster isomers from the signatures of hydrogen bonded and non-hydrogen bonded OH stretching spectra of H⁺PD(H₂O)_2,3 produced in a corona discharge supersonic expansion. Besides open form isomers, evidence for the formation of water-bridged structures has been found for H⁺PD(H₂O)₃ at an estimated temperature of 200 K. A detailed illustration of the unfolding steps as well as the energy profiles for the evolution of a two-water bridge isomer from the protonated H⁺PD monomer are analysed pictorially (including both stable intermediates and transition states) in the present investigation.