Comparison of theoretical and experimental 3He desorption behaviour of titanium tritide films

Helium-3 formed by tritium radioactive decay from tritide layer desorbs at room temperature slowly in a first step, more strongly afterwards. A helium-3 desorption model has been established, based on the positions of He-3 atom and trapping sites in the γ tritide lattice, CaF₂ type, supposed in a perfect state. Theoretical desorption curves as a function of time or helium concentration in the layer has been computed, for metal tritide or deutero-tritide layers. Experimental curves, for a wide tritium concentration range, are given here in the case of titanium layers. They show good agreement with theoretical curves for appropriate parameter values, up to a helium/titanium atomic ratio of 0.25 to 0.30. For higher helium concentrations, rapid helium desorption can be explained by gas bubble growth and percolation, and mechanical degradation of the layer: at this stage, the theoretical model does not apply.     

ESR of residual defects in silicon from recoil implantation of oxygen in Si/SiO2 systems

In ionic crystals or other insulators with partial ionic binding, the ion-target interaction differs from that of neutral atoms due to different electronic distributions and overall electrical charges Consequently, the nuclear stopping power and defect production by recoiling atoms will deviate from standard values, obtained from e g Moliere-potentials In the present paper, realistic potentials between projectile ion and target ion are determined by the free electron gas model of overlapping Hartree-Fock-Slater or Lenz-Jensen ions (and neutral atoms for comparison) With the new potentials, the transferred energies T and the range of interaction is determined for either damage production (T>E_d) and for nuclear stopping (T>hω> for bound ions) In addition the excitation of optical phonons is taken into account which are excited by the transient electrical field of the charged projectile     

Ion implantation effects in glasses

Abstract

Ion implantation can be used to introduce network damage and to alter the chemical composition in glasses. Structural changes can be inferred from IR measurements near 1000 cm^?1 and by optical absorption near 2150 Å. Implantation-induced damage decreases the implanted volume in fused silica with consequent changes in the refractive index, the near-surface hardness, and the tensile surface stress. Prior work in these areas is reviewed. Implantation into alkali silicate glasses depletes the alkali content in the implanted region. These changes allow preferential surface crystallization in Li₂O-2SiO₂ glasses. Crystallization of amorphous SiO2 can be induced by implantation of Li. Insight into the crystallization process is obtained by following the associated ion movement by elastic recoil detection (ERD) and optical techniques. Implantation of 20keV H shows that saturation of implanted H-sites in fused silica occurs at about 2.2 × 10²¹ H/cm³ in agreement with free volume estimates of the maximum number of available interstitial sites. Details of H and D interactions in fused silica were studied as a function of fluence and temperature. Results are of interest in studies of corrosion in glasses considered for nuclear waste encapsulation and for components in fusion reactors.

IV Summary     

Low-energy antimony implantation in silicon

Abstract

Antimony is known to be a donor in silicon, Low-energy implantations of Sb in Si produce very shallow profiles which have many device applications. Gibbons et al. ¹ calulated the projected ranges of Sb ion-implanted in Si, using the LSS (Lindhard, Scharff, and Schiott) method. Oetzmann et al. ² measured projected ranges and range straggling for several heavy ions in Si, Al, and Ge, using high-resolution backscattering; in the energy region of interest to us, e = 10^?2 to 10^?1, their results were about 30% higher than those reported by Gibbons et al. In the study reported here, we implanted 5 × 10¹⁴ Sb/cm² in Si at 5–60 keV, measured the resulting depth distribution by secondary ion mass spectrometry, and checked the measurements by backscattering. Our results showed the experimental projected ranges to be about halfway between those reported in the earlier studies. The discrepancies between theoretical calculations and experimental results are due not to the electronic stopping cross section, which is negligible in the range of interest here, but to the nuclear stopping power. Using a modified nuclear scattering potential given by Wilson et al.,³ we calculated the projected range distribution according to the method described by Winterbon.⁴ Our results are in very good agreement with the experimental measurements.     

Chemical and catalytic effects of ion implantation

Energetic particles are used for inducing chemical reactions as well as for modifying the properties of materials with regard to their bulk and surface chemical behavior. The effects are partly caused by radiation damage or phase intermixing, partly by the chemical properties of the individual bombarding particles. In this contribution a survey of relevant applications of these techniques is presented:

1) Chemical reactions of implanted and recoil atoms and their use for syntheses, doping and labeling of compounds.

2) The formation of thin films by decomposing chemical compounds with ion beams.

3) Catalytic effects on substrates treated by sputtering or ion implantation. Recent results with nonmetallic substrates are reviewed. Mainly hydrogenation reactions at a solid/gas interface or redox reactions at an electrified solid/liquid interface are mentioned.

The present status and future prospects of these kinds of investigations will be discussed.     

用两带Ginzburg-Landau理论分析两带超导体Lu2Fe3Si5的表面临界磁场

用两带Ginzburg-Landau(GL)理论分析了Lu₂Fe₃Si₅的表面临界磁场,当超导体的表面与任一主晶面重合,且外磁场平行于超导体的表面时,比值H_c3/H_c2(H_C2是Lu₂Fe₃Si₅的上临界磁场)强烈依赖于温度. 当超导体的表面是bc平面,且 关键词： 两带超导体 GL理论 2Fe₃Si₅')" href="#">Lu₂Fe₃Si₅ 表面临界磁场     

Harmonic Force Fields and Mean Amplitudes For Gallium And Indium Trihalide Monomers

Harmonic force fields (in-plane) for gallium and indium trihalides are developed from complete or incomplete experimental assignments of vibrational frequencies. The missing frequencies are predicted from the calculations Mean amplitudes of vibration are calculated.     

On the mechanism of the interaction between oxygen and close-packed single-crystal aluminum surfaces

Using periodic first principles simulations we investigate the interaction of oxygen molecules with both regular Al(111) and Al(001) surfaces as well as a stepped Al(111) substrate. The limitation of this approach is the use of thin metallic slabs with a limited range for their coverage by adsorbed oxygen. The advantage is the detailed modeling that is possible at an atomic level. On the regular Al(111) surface, we have been able to follow the oxidation process from the approach of O₂ molecules to the surface, through the chemisorption and absorption of O atoms, up to the formation of first Al₂O₃ formula units. An energetically feasible mechanism for the formation of these Al₂O₃ ‘molecules’ is proposed but their aggregation to Al₂O₃ growth nuclei can only be surmised. On the Al(001) surface, absorption of oxygen atoms occurs more readily without any restrictions on the density of their surface overlayer, in agreement with the failure to observe a distinct chemisorption stage for O on Al(001) experimentally. The stepped Al(111) surface contains both {111} and {001} microfacets: the latter are obviously preferred for penetration of the oxygen adatoms into the subsurface space of the substrate. Before considering the O/Al interfaces the computational method is tested thoroughly by simulations on bulk Al and close-packed aluminum surfaces.     

Preparation and luminescent characteristic of Li3NbO4 nanophosphor

Synthesis and luminescence properties of Li₃NbO₄ oxides by the sol-gel process were investigated. The products were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy and absorption spectra. The PL spectra excited at 247 nm have a broad and strong blue emission band maximum at 376 nm, corresponding to the self-activated luminescence of the niobate octahedra group [NbO₆]⁷⁻. The optical absorption spectra of the samples sintered at temperatures of 600 and 700 °C exhibited the band-gap energies of 4.0 and 4.08 eV.     

Ab-initio density functional theory study of a WO3 NH3-sensing mechanism

WO 3 bulk and various surfaces are studied by an ab-initio density functional theory technique.The band structures and electronic density states of WO 3 bulk are investigated.The surface energies of different WO 3 surfaces are compared and then the (002) surface with minimum energy is computed for its NH 3 sensing mechanism which explains the results in the experiments.Three adsorption sites are considered.According to the comparisons of the energy and the charge change between before and after adsorption in the optimal adsorption site O 1c,the NH 3 sensing mechanism is obtained.     

Effects of RE2O3 (RE = Tm, Sc, Yb) addition on the superconducting properties of ErBa2Cu3Oy

We investigated the effects of added Tm₂O₃, Sc₂O₃, and Yb₂O₃ on the superconducting properties of sintered Er123 samples. Tm₂O₃ addition caused the least T_c degradation, exhibiting a T_c above 90 K even for 17 vol% addition. Samples with added Sc₂O₃ maintained a T_c at above 90 K up to an addition of 7.2 vol%, while Yb₂O₃-containing samples showed a monotonic decrease in T_c with increased vol% of added Yb₂O₃. Tm₂O₃-containing samples exhibited a slight increase in J_c(0.1 T)/J_c(0) and had constant J_c values even for 17 vol% addition. XRD and SEM results indicate that the Tm₂O₃ is very stable in the superconducting matrix.     

A model for the transition in the oxidation of zirconium-base alloys

At a weight gain of approximately 20 to 30 mg/dm² during the oxidation of zirconium-base alloys at reactor operating temperatures the oxidation rate accelerates. This is the so-called transition. A mechanistic model has been developed to describe the transition based on the growth and interconnection of small pores along the oxide-metal interface. Once the pores interconnect, coolant can reach the oxide-metal interface and oxidation accelerates. The model has been programmed and incorporated into the previously reported oxidation model. Good agreement has been obtained between the model predictions and experimental data.     

Group Classification of Biological Tissues by Infrared Spectroscopy

Infrared spectra of rat tissues, RNA tumor virus (Rauschler) and pure RNA and DNA are examined by the technique of frustrated multiple internal reflection (FMIR). An attempt has been made to characterize biologically important tissue components on the basis of infrared spectral analysis and published literature on the subject.

Under the conditions described, rat tissues may be grouped according to their infrared spectra. The spectral differences in vivo between normal and N-nitroso-dimethylamine (DMN)-injected rat liver have been presented to show the usefulness of the FMIR technique for rapid detection of induced changes in the tissue composition.     

Creation of nanoparticles and luminescence in Al2O3 crystal by Zn ion implantation

Single crystal α-Al₂O₃ wafers were implanted with 45 keV Zn ions up to a fluence of 1×10¹⁷ ions/cm², and were then subjected to furnace annealing in oxygen atmosphere at different temperatures. Various techniques have been applied to study the creation of nanoparticles (NPs), defects and their thermal evolutions, as well as their effects on optical properties of Al₂O₃. Our results clearly show that Zn NPs have been synthesized in the as-implanted sample and they begin to be oxidized at 500 °C. Two broad photoluminescence bands appear in the Zn ion-implanted samples and their intensities depend on the annealing temperatures. The results have been interpreted in view of creation of the defects and NPs, Zn atoms diffusion as well as their thermal evolution during annealing.     

Assessment of damage ranges by measurements of the refractive index in ion implanted LiNbO3 and LiTaO3

Ion implantation in LiNbO₃ and LiTaO₃ produces radiation damage by nuclear collisions. The amorphisation of the lattice reduces the refractive index of the material. In the case of fast ion bombardment with helium this damage layer is buried below the surface. The refractive index profile which then exists is suitable for an optical waveguide on the surface which supports several modes. Analysis of the refractive index profile yields the damage distribution in the crystal and this in turn can be compared with theoretical estimates of the damage production and ion ranges.

Our analyses show that in the high energy range from 0.5 to 2.0 MeV the depth of the damage is predominantly controlled by the electronic stopping.     

Kinetics of hydrazinium nitrate decomposition in nitric acid solutions under the effect of power ultrasound

The effect of ultrasound (f = 20 kHz) on the decomposition of hydrazinium nitrate was investigated in a nitric acid medium. The kinetics of N2H5+ decomposition and initial HN3 formation increase in a linear manner with the HNO3 concentration (from 1 to 6 M) and with the ultrasonic intensity (from 0.5 to 3.1 W cm-2). Both rates were equal to that of HNO2 formation in the absence of N2H5+, indicating that the N2H5+ decomposition mechanism is the same as observed without ultrasound between HNO2 and N2H5+. The variation of the steady-state HN3 concentration with the HNO3 concentration and the ultrasonic intensity suggests the existence of a nonexplosive HN3 thermal decomposition mechanism in the cavitation bubble under the effect of ultrasound. It was also observed at ultrasonic intensities exceeding 3.5 W cm-2 that the decomposition of HN3 led to the accumulation of NH4+ in solution.     

On the origin of the 2.2-2.3 eV photoluminescence from chemically etched germanium

The photoluminescence (PL) at ∼2.2-2.3 eV from Ge-based nanocrystalline materials is described in the literature as nanocrystal size-independent. We have observed visible luminescence from two different types of stain-etched Ge samples, one prepared after Sendova-Vassileva et al. (Thin Solid Films 255 (1995) 282) in a solution of H₂O₂:HF at 50:1 volume ratio, and the other in a solution of HF:H₃PO₄:H₂O₂ at 34:17:1 volume ratio. Energy dispersive X-ray analysis (EDX), Raman and FTIR spectroscopy, and the near edge X-ray absorption structure (XANES), indicate that the chemically etched Ge layers of the former type of samples are composed of non-stoichometric Ge oxides, i.e. GeO_x (0<x<2), and free from any Ge nanoconstructions. It is also suggested from XANES that the latter type of chemically etched Ge samples comprise 8-9 nm nanocrystals of Ge, surface-covered with mainly oxygen. Photoluminescence occurred at ∼2.3 eV for all samples. The PL behavior of the latter type of chemically etched Ge on annealing in different chemical environments (air or H) allowed us to conclude that the PL from these materials, as well as that from those Ge-based nanocrystalline materials reported in the literature, is from GeO_xs.     

Structure and electronic structure of S-doped graphitic C3N4 investigated by density functional theory

The structures of the heptazine-based graphitic C3N4 and the S-doped graphitic C3N4 are investigated by using the density functional theory with a semi-empirical dispersion correction for the weak long-range interaction between layers.The corrugated structure is found to be energetically favorable for both the pure and the S-doped graphitic C3N4.The S doptant is prone to substitute the N atom bonded with only two nearest C atoms.The band structure calculation reveals that this kind of S doping causes a favorable red shift of the light absorption threshold and can improve the electroconductibility and the photocatalytic activity of the graphitic C3N4.     

A comparative study of electronic structure and magnetic properties of SrCrO3 and SrMoO3

A comparative study of electronic structure and magnetic properties of SrCrO₃ and SrMoO₃ has been carried out using FPLAPW method with density-functional theory. The calculated results suggest that both compounds are nonmagnetic (NM) metal in cubic structures at room temperature, and they exhibit very similar band structure and electronic properties except more extend Mo 4d orbitals than Cr 3d electronic states. However, the electronic structure and magnetic properties exhibit remarkable differences between them in the low temperature phases. SrCrO₃ is with a C-AFM ground state with magnetic moment of 1.18μ_B/Cr in the tetragonal structure, while SrMoO₃ is with a NM ground state in the orthorhombic structure. It is assumed that the extend 4d orbitals may be the reason which results in NM solution at low temperature phase of SrMoO₃.     

A Study on the Rheological and Magnetic Properties of Polymer-Bonded Magnets Using Polycarbonate as the Bonding Material

The effect of three metal oxides on the magnetic properties of polymer bonded magnets (PBMs) was studied. The three PBMs, using polycarbonate (PC) as binder and 5 wt% of Fe₃O₄, Fe₂O₃, or CuO nanoparticles, were prepared by melt extrusion in a twin screw extruder followed by compression molding. Transmission electron microscopic (TEM) images showed a better dispersion for the PC/Fe₃O₄ nanocomposite compared with that of the other nanocomposites. The dynamic intersection frequency (ω_c), which is related to the crossing of the G′ and G^″ curves, showed that there was more homogeneity in the PC/Fe₃O₄ and PC/Fe₂O₃ nanocomposites. The curves of saturation magnetization for the three nanocomposites showed that there was a relationship between the magnetic properties and the homogeneity of the nanoparticles studied by rheometry. Because the magnetic strength of PC/Fe₃O₄ was greater than that of the other nanocomposites, it was concluded that not only the intrinsic magnetic property of the filler was an important factor to increase the magnetic property, but also the homogeneity of the filler within the matrix had an important role.