100 keV 10-B + implantation into poly-(di-n-hexyl silane), (PDHSi)

100 keV¹⁰B⁺ ions were implanted into poly-(di-n-hexyl silane) in different directions at a fluence of 1×10¹⁴ cm^-2, and their depth distribution was determined by means of the neutron depth profiling technique. In no case were the projectile ions found to come to rest according to their predicted range profiles. Instead, they are always found to undergo considerable long-range migration. During the irradiation process this motion appears to be radiation-enhanced, and during the subsequent annealing steps one appears to deal with regular thermal diffusion. The implant redistribution is always found to be governed strongly by the self-created damage, insofar as both electronic and nuclear defects in the polymer act as trapping centers. Their population ratio is modified by thermal annealing.The as-implanted redistribution shows a pronounced directional dependence, which essentially is a consequence of the spatial distributions of the electronic and nuclear damage. The changes of the nuclear defect distribution during thermal annealing are studied by a specially developed tomographic method. It is found that boron is preferentially trapped along the irradiation direction, exhibiting quite pronounced prolate (i.e. cigar-like) distributions. This shape is almost unaffected by thermal annealing. PACS 61.80; 66.30; 66.30.L; 87.59.F     

Effect of high doses of N<Superscript>+</Superscript>, N<Superscript>+</Superscript> + Ni<Superscript>+</Superscript>, and Mo<Superscript>+</Superscript> + W<Superscript>+</Superscript> ions on the physicomechanical properties of TiNi

The surface layer of an equiatomic TiNi alloy, which exhibits the shape memory effect in the martensitic state, is modified with high-dose implantation of 65-keV N⁺ ions (the implantation dose is varied from 10¹⁷ to 10¹⁸ ions/cm²). TiNi samples are implanted by N⁺, Ni⁺-N⁺, and Mo⁺-W⁺ ions at a dose of 10¹⁷–10¹⁸ cm⁻² and studied by Rutherford backscattering, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction (glancing geometry), and by measuring the nanohardness and the elastic modulus. A Ni⁺ concentration peak is detected between two maxima in the depth profile of the N⁺ ion concentration. X-ray diffraction (glancing geometry) of TiNi samples implanted by Ni⁺ and N⁺ ions shows the formation of the TiNi (B2), TiN, and Ni₃N phases. In the initial state, the elastic modulus of the samples is E = 56 GPa at a hardness of H = 2.13 ± 0.30 GPa (at a depth of 150 nm). After double implantation by Ni⁺-N⁺ and W⁺-Mo⁺ ions, the hardness of the TiNi samples is ∼2.78 ± 0.95 GPa at a depth of 150 nm and 4.95 ± 2.25 GPa at a depth of 50 nm; the elastic modulus is 59 GPa. Annealing of the samples at 550°C leads to an increase in the hardness to 4.44 ± 1.45 GPa and a sharp increase in the elastic modulus to 236 ± 39 GPa. A correlation between the elemental composition, microstructure, shape memory effect, and mechanical properties of the near-surface layer in TiNi is found.     

Distribution of <Superscript>28</Superscript>Si, <Superscript>29</Superscript>Si,and <Superscript>30</Superscript>Si isotopes under plastic deformation in subsurface layers of Si: B crystals

The redistribution of ²⁸Si, ²⁹Si, and ³⁰Si isotopes in subsurface layers of Si: B single crystals after their plastic deformation has been revealed. It has been found that the distribution profile of ²⁸Si and ²⁹Si isotopes becomes smoother after deformation, whereas the ³⁰Si isotope distribution remains unchanged. A change in the subsurface profile of the ²⁹SiO oxide is observed, which indicates the migration of the ²⁹Si isotope in the composition of oxygen complexes during plastic deformation.     

Application of mechanical scanning to ion implantation

Abstract

Atomic depth profiles from Be-implanted Si have been examined as a function of implant fluence and annealing, and the results have been correlated with theoretically calculated implantation induced damage profiles. The Be atomic depth profiles were obtained by secondary ion mass spectrometry (SIMS) techniques from samples implanted at 300 keV to fluences ranging from 2 × 10¹² to 10¹⁵ cm^?2. Subsequent to annealing at 600°C for 30 min, the Be SIMS profiles exhibited anomalous redistribution effects. The Be profiles obtained from the annealed samples had the same general features as the depth distribution of implant energy deposited into damage, based on Brice's¹ calculations. The correlation of the SIMS atomic profiles and the theoretical damage profiles indicated that Be “decorates” the implantation induced damage regions while redistributing during the annealing process.     

Micro-Raman spectroscopic investigation of NiSi films formed on BF<Subscript>2</Subscript><Superscript>+</Superscript>-, B<Superscript>+</Superscript>- and non-implanted (100)Si substrates

The micro-Raman spectroscopic technique was used to investigate vibrational properties of NiSi thin films formed on three different (100)Si substrates: non-implanted, 20 keV BF₂⁺-implanted, and 20 keV B⁺-implanted. Raman measurements were also performed on NiSi powder to identify various phonon modes associated with different selection rules of group theory. It was found that the Raman peaks for NiSi thin films formed on the BF₂⁺-implanted substrate were broader and shifted to lower frequencies compared to those for films formed on the other substrates. The broadening of the Raman peaks for these films, which also exhibit much improved thermal stability, is attributed to the small grains that probably result from the segregation of fluorine to grain boundaries and interfaces. It is further proposed that grain boundary segregation influences the stress in the silicide film, resulting in shifts in phonon peak positions. PACS 78.30.Am; 74.25.Kc; 68.35.Dv; 68.55.Ln; 66.30.Jt     

Influence of Cr<Superscript>+</Superscript> ion implantation and pulsed ion-beam annealing on the formation and optical properties of Si/CrSi<Subscript>2</Subscript>/Si(111) heterostructures

The effect of pulsed ion-beam annealing on the surface morphology, structure, and composition of single-crystal Si(111) wafers implanted by chromium ions with a dose varying from 6 × 10¹⁵ to 6 × 10¹⁶ cm⁻² and on subsequent growth of silicon is investigated for the first time. It is found that pulsed ion-beam annealing causes chromium atom redistribution in the surface layer of the silicon and precipitation of the polycrystalline chromium disilicide (CrSi₂) phase. It is shown that the ultrahigh-vacuum cleaning of the silicon wafers at 850°C upon implantation and pulsed ion-beam annealing provides an atomically clean surface with a developed relief. The growth of silicon by molecular beam epitaxy generates oriented 3D silicon islands, which coalesce at a layer thickness of 100 nm and an implantation dose of 10¹⁶ cm⁻². At higher implantation doses, the silicon layer grows polycrystalline. As follows from Raman scattering data and optical reflectance spectroscopy data, semiconducting CrSi₂ precipitates arise inside the silicon substrate, which diffuse toward its surface during growth.     

Diffusion study of <Superscript>18</Superscript>O implanted into α-Ti using the nuclear resonance technique

The diffusion of ¹⁸O in α-Tiwas studied in the 623–873 K temperature range by using the ion implantation and nuclear resonance techniques. The measurements show that the diffusion coefficients follow an Arrhenius behavior with diffusion parameters D₀=(2±1)10^-7 m² s^-1 and Q=(±) 16950kJ/mol, values typical of interstitial diffusion mechanism. A comparison of the present and previous results is also done. PACS 66.30.Jt; 85.40.Ry     

Surface characteristics of V-Ga alloys after irradiation by Ar<Superscript>+</Superscript> and N<Superscript>+</Superscript> ions

V-5Ga-6Cr and V-5Ga-0.05Ce vanadium alloys irradiated by Ar⁺ and N⁺ ions with energies of 20 keV have been investigated. Irradiation by Ar⁺ and N⁺ ions leads to strengthening of the surface layers of samples. Their thicknesses exceed the projectile ranges of these ions (16.4 and 32.8 nm, respectively) in vanadium by more than two orders of magnitude. The experimentally determined penetration depth of argon ions is less that 70 nm. The sample side irradiated by Ar⁺ ions has a predominant orientation of crystallites in the (100) and (211) planes, while the unirradiated sample has a (110) surface. The lattice parameter of the irradiated sample does not differ from that of the initial sample. Possible mechanisms by which modified deep layers are formed during ion bombardment are discussed.     

Theoretical study of charge-exchange and excitation processes in collisions of He<Superscript>+</Superscript> ions with C<Superscript>5+</Superscript>, N<Superscript>6+</Superscript>, and O<Superscript>7+</Superscript> hydrogen-like ions

Data on the cross sections for single-electron charge exchange and excitation in collisions of He⁺ ions with C⁵⁺, N⁶⁺, and O⁷⁺ ions in the He⁺ ion energy range of 0.2–3.0 MeV are obtained for the first time. The cross sections for the single-electron charge transfer into the singlet and triplet 1snl states of C⁴⁺, N⁵⁺, and O⁶⁺ (2≤n≤5) ions and for the 1s → 2p _{0, ±1} electronic excitation of He⁺(1s) ions are calculated. The calculations were performed by solving close-coupling equations on the basis of ten two-electron quasi-molecular states.     

Study of the Involvement of <Superscript>8</Superscript>Be and <Superscript>9</Superscript>B Nuclei in the Dissociation of Relativistic <Superscript>10</Superscript>C, <Superscript>10</Superscript>B,and <Superscript>12</Superscript>C Nuclei

The results obtained by estimating the contribution of 8Be and 9B nuclei to the coherent dissociation of ¹⁰C, ¹⁰B, and ¹²C relativistic nuclei in nuclear track emulsions (“white” stars) are presented. The selection of white stars accompanied by 9B leads to a distinct peak appearing in the distribution of the excitation energy of 2α2p ensembles and having a maximum at 4.1 ± 0.3 MeV. A 8Be nucleus manifests itself in the coherent-dissociation reaction ¹⁰B → ²He + H with a probability of (25 ± 5)%, (14 ± 3)% of it being due to 9B decays. The ratio of the branching fractions of the ⁹B + n and ⁹Be + p mirror channels is estimated at 6 ± 1. An analysis of the relativistic dissociation of ¹²C nuclei in a nuclear track emulsion revealed nine 3α events corresponding to the Hoyle state.     

Stark structure of the spectrum and decay kinetics of the Er<Superscript>3+</Superscript> photoluminescence in pseudoamorphous <Emphasis Type="Italic">a</Emphasis>-nc-GaN films

Amorphous films containing nanocrystalline inclusions, a-nc-GaN, were codoped with Er in the course of magnetron sputtering. Intense intracenter emission of Er³⁺ ions in the wavelength region λ=1510–1550 nm was obtained only after multistage annealing at temperatures of 650–770°C. The intracenter emission was excited indirectly through electron-hole pair generation in the a-nc-GaN matrix by a pulsed nitrogen laser. Subsequent recombination via a number of localized states in the band gap transferred the excitation energy to the Er³⁺ ions. Measurements of photoluminescence (PL) spectra carried out with time resolution in various annealing stages at different temperatures in the range 77–500 K and in the course of decay permitted us to establish the Stark nature of the PL spectrum and to reveal the dynamic and nonequilibrium character of redistribution of the intracenter emission energy among the Stark modes in the course of the excitation pulse relaxation. The information thus obtained was used to interpret the dominant hot-mode contribution and the complex decay kinetics.     

Soft-core Interaction for the <Superscript>4,6</Superscript>He + <Superscript>64</Superscript>Zn Fusion Reactions

In this paper, the cross section of the ⁴He + ⁶⁴Zn and ⁶He + ⁶⁴Zn reactions, at bombarding energies above and below the fusion barrier, has been investigated. Soft-core nucleon-nucleon interaction and the Monte Carlo method have been employed for studying the nuclear potential of the projectile-target system. One adjustable parameter has been chosen in this study. This parameter can change the depth of the soft-core potential. It has to be adjusted so that the calculated elastic scattering and fusion cross sections are in acceptable agreement with experimental data. Our results indicate that an increase in energy decreases the depth parameter of the soft-core nucleon-nucleon potential obtained from careful analysis the ⁴He + ⁶⁴Zn and ⁶He + ⁶⁴Zn reactions. Likewise, by comparing the results obtained from both reactions, one can observe that the calculated depth parameter for the reaction related to ⁶He is larger than that for ⁴He at the same energy, in particular at the sub-barrier energies. We try to explain this behavior.     

One-neutron stripping reactions of <Superscript>11</Superscript>Be and <Superscript>19</Superscript>C on light target

We have calculated the one-neutron absorption cross-section and the longitudinal momentum distribution of the core fragment coming out from the breakup of ¹¹Be and ¹⁹C on ⁹Be target at 63 MeV/A and 88 MeV/A beam energies respectively. The reaction mechanism is treated within the framework of the eikonal approximation. The effective range of the nuclear interaction between the core and the valence neutron within the projectile has been determined by comparing the predicted stripping cross-section with the recently measured one. The effective range for ¹⁹C has been found to be smaller than that for ¹¹Be. It qualitatively indicates that ¹⁹C is slightly more halo than ¹¹Be. The smaller width, predicted as well as measured, of the LMD of ¹⁸C than ¹⁰Be also strengthens this fact. The experimental data concerning the LMD of core fragments have been well represented.      

Effect of local cationic environment on the valence state of <Superscript>119</Superscript>Sn probe atoms on the surface of antiferromagnet MnTiO<Subscript>3</Subscript> with ilmenite structure

Annealing in argon of MnTiO₃ impregnated with a SnCl₄ solution leads to the distribution of Sn⁴⁺ ions over sites with different cationic environments in the surface layers of crystallites. The chemical behavior of Sn⁴⁺ ions emerging on the surface upon subsequent annealing in hydrogen depends on the tendency of the neighboring cations to retain the octahedral coordination by O^2? anions. The absence of spin polarization of the Sn²⁺ cations formed on the surface shows that their specific valence state is stabilized by the nearby Ti⁴⁺ cations.     

Hydrogen-enhanced recrystallization in N<Superscript>+</Superscript>-implanted GaAs

The hydrogen-enhanced recrystallization during thermal annealing in N⁺-implanted GaAs has been studied by combinatorial implantation process. Raman spectroscopy was used to study the crystallization properties of a set of hydrogenated cells on the N⁺-implanted GaAs wafer. A whole competitive process between H⁺ implantation-induced damage and recovery in the regrowth process of amorphous GaAs was observed within the proton dose region of 1.6×10¹⁵ to 1.1×10¹⁷ cm^-2. In H⁺ dose region of 2.1×10¹⁶ to 5.4×10¹⁶ cm^-2, H-enhanced recovery of crystal dominates the regrowth process. The crystal quality is better than that of unhydrogenated cell of N⁺-implanted GaAs in the H⁺ dose range from 4.7×10¹⁶ to 8.1×10¹⁶ cm^-2. It is suggested that the vacancy supersaturation produced during hydrogen irradiation is dominantly responsible for the enhancement of thermal regrowth in the N⁺-implanted GaAs. Both the crystallization and amorphization process are clearly observed in different proton implantation dose regions. PACS 61.72.Vv; 63.20.Dj; 81.05.Ea     

<Superscript>17</Superscript>O and<Superscript>23</Superscript>Na nuclear quadrupole double resonance of sodium formate and sodium acetate

The¹⁷O and²³Na nuclear quadrupole resonance spectra of powdered sodium formate and sodium acetate have been determined at room temperature by proton-¹⁷O and proton-²³Na double resonance. All¹⁷O sites have been found to be chemically equivalent. The nonzero value of the asymmetry parameter of the electric field gradient tensor at the¹⁷O site shows that the electron density distribution is not cylindrically symmetric around the C−O bond axis.     

Analysis of <Superscript>8</Superscript>B Proton Halo Nucleus Scattered from <Superscript>12</Superscript>C and <Superscript>58</Superscript>Ni at Different Energies

Angular distributions in the elastic scattering of ⁸B from ¹²C and ⁵⁸Ni targets at different energies have been analyzed in the framework of the double-folding (DF) optical model. The real central part of the nuclear optical potential is obtained by folding the M3Y effective interaction with the cluster density distribution of the ⁸B nucleus. The experimental angular distributions have been successfully reproduced. This confirms the validity of the cluster structure of the ⁸B nucleus.     

Nuclear level densities in <Superscript>47</Superscript>V, <Superscript>48</Superscript>V, <Superscript>49</Superscript>V, <Superscript>53</Superscript>Mn,and <Superscript>54</Superscript>Mn from neutron evaporation spectra

The spectra of neutrons from the (p, n) reactions on ⁴⁷Ti, ⁴⁸Ti, ⁴⁹Ti, ⁵³Cr, and ⁵⁴Cr nuclei were measured in the proton-energy range 7–11 MeV. The measurements were performed with the aid of a fast-neutron spectrometer by the time-of-flight method over the base of the EGP-15 tandem accelerator of the Institute for Physics and Power Engineering (IPPE, Obninsk). Owing to a high resolution and a high stability of the time-of-flight spectrometer used, low-lying discrete levels could be identified reliably along with a continuum section of neutron spectra. An analysis of measured data was performed within the statistical equilibrium and preequilibrium models of nuclear reactions. The relevant calculations were performed by using the exact formalism of Hauser-Feshbach statistical theory supplemented with the generalized model of a superfluid nucleus, the back-shifted Fermi gas model, and the Gilbert-Cameron composite formula for the nuclear level density. The nuclear level densities for ⁴⁷V, ⁴⁸V, ⁴⁹V, ⁵³Mn, and ⁵⁴Mn were determined along with their energy dependences and model parameters. The results are discussed together with available experimental data and recommendations of model systematics.     

Fragmentation of <Superscript>7</Superscript>Li relativistic nuclei on a proton into the <Superscript>3</Superscript>H + <Superscript>4</Superscript>He channel

In a track nuclear photoemulsion exposed to a beam of ⁷Li nuclei accelerated to a momentum of 3 GeV/c per nucleon at the synchrophasotron of the Joint Institute for Nuclear Research (JINR, Dubna), 13 events in which ⁷Li nuclei interacting with protons break up into ³H and ⁴He fragments were detected among 3730 inelastic-interaction events. For this fragmentation channel, the cross section was found to be 8 ± 2 mb. The average value of the fragment total transverse momentum was 214 ± 5 MeV/c. This value exceeds markedly the average value of the transverse-momentum transfer in the coherent dissociation of ⁷Li nuclei on track-emulsion nuclei (166±5MeV/c). The recoil-proton transverse momentum was on average 98% of the total proton momentum. The longitudinal-momentum distribution of protons was characterized by a variance of 16 MeV/c and a mean value of 37 ± 2MeV/c.     

Photodynamic processes in CaF<Subscript>2</Subscript> crystals activated by Ce<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript> ions

The photochemical properties of CaF₂ crystals activated by Ce³⁺ and Yb³⁺ ions are studied. A model of the photodynamic processes induced by pumping UV or VUV radiation in active media is suggested and experimentally verified. This model explains both the presence of color centers of electronic and hole nature in crystals activated by cerium and the mechanism of suppressing of solarization processes after additional activation of the samples by Yb³⁺ ions. The cross sections of the processes of free-carrier capture by various ytterbium impurity centers are estimated. These impurity centers are established to be effective centers of recombination of free carriers of both signs.