Trapping Coefficient Research Articles

Sintering and anisotropy of dimensional changes in uniaxially pressed compacts of stainless steel powders for MIM : H. Kuroki et al. (Hiroshima University, Hiroshima, Japan.) J. Japan Sc. Powder and Powder Metallurgy, Vol 38, No 7, 1991, 844–848. (In Japanese.)

A supported gas discharge sputtering system was used to investigate krypton entrapment in thick films of high rate sputter-deposited glassy metals. Krypton entrapment was studied as a function of the substrate and target voltages for various iron-yttrium, iron-zirconium, iron-silicon, iron-molybdenum, nickel-yttrium and nickel-molybdenum alloys. Continuous substrate bias was used. Krypton contents ⩾ 8 at.% were found in some of the alloys studied, all of which were deposited at rates exceeding 10 nm s-1. The dependence of the ion trapping coefficient on the substrate bias voltage is given for some of the alloys.

Injection moulding of pulverized iron powders : H. Horiguchi et al. (Yoshikawa Kogyo Co. Ltd., Kitakyusyu, Japan.) J. Japan Soc. Powder and Powder Metallurgy, Vol 38, No 7, 1991, 849–853. (In Japanese.)

A supported gas discharge sputtering system was used to investigate krypton entrapment in thick films of high rate sputter-deposited glassy metals. Krypton entrapment was studied as a function of the substrate and target voltages for various iron-yttrium, iron-zirconium, iron-silicon, iron-molybdenum, nickel-yttrium and nickel-molybdenum alloys. Continuous substrate bias was used. Krypton contents ⩾ 8 at.% were found in some of the alloys studied, all of which were deposited at rates exceeding 10 nm s-1. The dependence of the ion trapping coefficient on the substrate bias voltage is given for some of the alloys.

Positron annihilation and the charge states of the phosphorus-vacancy pair in silicon

After electron irradiation two positron lifetimes 250+or-1 and 268+or-3 ps, are observed in phosphorus-doped Si ((P)=3*1016 cm-3) depending on the temperature and the electron fluence. The lifetimes are assigned to the negative and neutral charge states of the phosphorus-vacancy pair (P-V). The longer lifetime at the neutral charge state indicates a larger open volume of the vacancy and implies an outward relaxation of the phosphorus-vacancy pair in the charge-state transition (P-V)- to (P-V)0. A comparison with the theoretical lifetimes yields a breathing-mode relaxation of the nearest-neighbour atoms Delta r/r0 approximately 5.1% (r0 is the Si-Si bond length), or Delta r approximately 0.12 AA. The positron trapping coefficients 2*1016 s-1 at 20 K and 2*1015 s-1 at room temperature at the negatively charged state (P-V)- are estimated. A weakly bound Rydberg-like precursor state is invoked to explain the temperature dependence of positron trapping at the negatively charge centres (P-V)- and V- in Si. The binding energy at the precursor state is 15-30 meV.

Nonexponential picosecond trapping in poly-(N-vinylcarbazole). A theoretical study

A theoretical model for excitation trapping in poly-(N-vinylcarbazole) in the presence of excimer dissociation is presented. We assume a time-dependent trapping coefficient in the form k(t)=b+ct−1/2, which reflects both the diagonal disorder and quasi-one-dimensionality of carbazole hopping sites [Kauffmann et al., J. Chem. Phys. 85, 3566 (1986)]. The equations obtained for monomer and excimer fluorescence decays are given in terms of Laplace transforms. Respective equations for fluorescence decays have been obtained also in the case when excimer formation is time dependent. Equations for monomer and excimer quantum yields are also given.

Implantation and replacement of hydrogen isotopes in 304 stainless steel vacuum wall under RF discharge and RF-DC glow discharge

The saturation and replacement of hydrogen isotopes implanted into a 304 stainless steel vacuum wall at 300 K under RF discharge with and without DC bias potential on an RF antenna have been studied using partial pressure measurements of desorbed isotopes. The energy of ions hitting the wall was estimated to be 30–90 eV from electrostatic probe measurement for RF discharge plasmas. Nearly 90% of the desorbed gas in the isotopic exchange process was HD molecules. The amount of desorbed gas showed a tendency to saturate at a fluence of 2.3 × 10 16 cm −2. The desorption rate can be expressed by an inverse-exponential function with time; a two-component function is normally observed. The time constant of each component is evaluated by introducing an effective trapping coefficient.

Quantum theory of interstitial diffusion in crystals

A quantum theory of diffusion is proposed based on the following premises. The impurity state is taken in the form of a wave packet constructed out of its Bloch states in the host lattice, and its time evolution is studied including its interaction with the host-lattice phonons. It is shown that a correspondence can be established between the classical diffusion equation and the time evolution of the probability density arising out of the impurity wave packet. The diffusion and trapping coefficients DT and gamma T are related to the imaginary part of the energy shift of the impurity caused by its interaction with phonons. The detailed calculations are based on second-order perturbation theory for the energy shift, the Debye model for the host lattice and the effective-mass approximation for the impurity band. At low temperatures DT is found to be proportional to T32/, and at high temperatures the Arrhenius formula of Vineyard (1957) is obtained. The estimated migration energies for mu + diffusion in BCC metals agree reasonably with the experimental values. The conditions for non-existence of gamma T are also discussed.

高周波放電および直流グロー放電下のステンレス鋼真空壁における水素同位体交換脱離

The saturation and replacement of hydrogen isotopes implanted into 304 stainless steel vacuum wall at 300 K under RF discharge and RF-DC glow discharge has been studied from partial pressure measurements of desorbed isotopes. The bombarding ion flux on the wall are 12×1013 ions/cm2·s. The energy of H2+ or D2+ ion is determined by acceleration with space potential produced in discharge plasma, and is about 40 eV for RF discharge and 300 eV for RF-DC glow discharge. The hydrogen and deuterium saturation concentrations in the wall surface are 4.2×1015 and 1.3×1016 molecules/cm2 for ion bombardment of 40 eV and 300 eV, respectively. Nearly 90% of desorbed gas in isotopic exchange process is HD molecule. The desorption rate is expressed by inverse-exponential function with time. The time constant is proportional to isotope concentration and inversely proportional to bombarding ion flux.Experimental results show that the local mixing model (LMM) is still valid for such ion implantation in lower energy region less than 1 keV. But LMM must be corrected for explanation of the isotope exchange process under plasma ion bombardment at 40 eV. Two-component inverse-exponential functions are observed in the replacement. The function of component 2 is explained by adopting an effective trapping coefficient, although another function of component 1 can be described by LMM.

Selective removal of low density lipoprotein by plasmapheresis in familial hypercholesterolemia.

Plasma lipoproteins were selectively removed from familial hypercholesterolemic patients by using two types of plasmapheresis: double-membrane filtration and selective adsorption of very low density lipoproteins (VLDL) and low density lipoproteins (LDL). In both techniques, plasma was separated from blood cells by using hollow-fiber filters, and 100% of the VLDL and LDL was recovered in the filtrate. In double-membrane filtration, the second hollow-fiber filter trapped 84% of LDL + VLDL, 48% of high density lipoprotein (HDL), 24% of albumin, and 46% of the remaining plasma protein. By treating 3 liters of plasma from a patient weighing 60 kg, 60% of the LDL and 30% to 40% of the HDL were removed as a result of an exponential decay of each component with the respective trapping coefficients. When dextran sulfate-cellulose was used as a LDL sorbent, there was only loss of LDL and VLDL, and no loss of any other major plasma component or of HDL. The sorbent column (400 ml) was saturated with 7.5 g of LDL cholesterol by treatment with 3.5 liters of plasma; the maximum reduction of LDL cholesterol was thus about 300 mg/dl for the patient weighing 60 kg. No serious side effects were observed during the long-term trials (19 to 27 months for four patients on double-membrane filtration and 10 months for the two patients on dextran sulfate-cellulose treatment.

Trapping and reflection coefficients for deuterium in graphite at oblique incidence

Trapping and particle reflection coefficients for 0.4–10keVD on graphite have been measured for angles of incidence 0≦α≦85° by determining the areal density of implanted D as a function of the implanted fluence. The experimental data are compared to computer calculations with the TRIM-program. The agreement between measurement and calculation is good.

Trapping and reflection coefficients for3He in Ni at oblique incidence

The areal density and the depth distribution of3He trapped in Ni as a function of the bombarding fiuence was measured in the energy range of 1–25 keV and at angles of incidence between 0 and 85° using nuclear reaction analysis. At fluences below saturation a linear relation is found between the areal density and the fiuence. From its slope the trapping and reflection coefficients can be determined.

The relationship between transient and steady-state photoconductivity in amorphous semiconductors

Dispersive transport experiments in a-Si:H and a-As 2Se 3 have shown that current resulting from excess carriers is limited by multiple trapping in an exponential density of states. In this paper, the relationship between steady-state photoconductivity and the transient phenomena is explored. Because of the exponential density of states, the well-known G γ dependence is expected for steady state, where G is the excitation density. The power γ is related to the dispersion parameter, α, by γ = (1 + α) −1. It is predicted that, in the approach to steady state, the current rises as t α . When the recombination coefficient, b r, is much greater than the trapping coefficient b t, the current is predicted to exceed the steady-state value by a factor, which depends on b r b t and α, before settling down to the steady level. The time of the maximum and the time to reach steady state are predicted to vary as G − γ . After reaching steady state, when the excitation is turned off the current is predicted to decay as t − α for the same amount of time as is required to reach steady state when the light is turned on. After this time, the current is predicted to decay as t −1. A number of important parameters characterizing transport and recombination in a multiple trapping system can be obtained from the approach to and decay from steady state.

Application of the McNabb-Foster trapping equations to the diffusion of oxygen in dilute niobium alloys

The McNabb-Foster equations, solved using a finite difference approach, have been applied to the data reported earlier by Lauf and Altstetter for the diffusion of oxygen in dilute niobium alloys. It was assumed that the substitutional alloy atoms acted as traps for the oxygen. Ratios of the release coefficient to the trapping coefficient,p/k, were calculated at various temperatures by computer-assisted curve fitting. Trapping energies obtained from plots ofp/k vs 1/T agree fairly well with those reported earlier using the Oriani model, but differ somewhat from those obtained using a recent model proposed by McLellan. The merits and limitations of the models with respect to the treatment of experimental data are discussed. Initial fractional trap occupancies were also calculated for these alloys and plotted against 1/T, and the results are also discussed.

Krypton entrapment in continuous-biased sputter-deposited glassy metals

A supported gas discharge sputtering system was used to investigate krypton entrapment in thick films of high rate sputter-deposited glassy metals. Krypton entrapment was studied as a function of the substrate and target voltages for various iron-yttrium, iron-zirconium, iron-silicon, iron-molybdenum, nickel-yttrium and nickel-molybdenum alloys. Continuous substrate bias was used. Krypton contents ⩾ 8 at.% were found in some of the alloys studied, all of which were deposited at rates exceeding 10 nm s -1. The dependence of the ion trapping coefficient on the substrate bias voltage is given for some of the alloys.

A simple model describing hydrogen re-cycling in fusion experiments and its influence on discharge behaviour

A model first used to describe hydrogen isotope trapping and replacement in the wall of pinch discharges is extended to tokamak discharges including pulsed gas inlet. It calculates the trapped-particle density in the walls versus time as a function of trapping coefficient, replacement cross-section, geometrical factors, particle confinement time and cold-gas influx. The solutions are used to describe the development of the average electron density and yield criteria for the conditions under which the plasma density falls or rises during a discharge. The model also allows a distinction between plasma/limiter and plasma/first-wall interaction. A comparison with measurements from tokamak discharges is made.

Temperature dependence of trapping and depth profiles of 6 to 15 kev deuterium in carbon

Depth profiles of 30 keV D + 2 and 20 keV D + 2 implanted into edge and basal-oriented pyrolytic graphite have been measured by means of the D( 3He,α)H nuclear reaction in the temperature range of 300 to 800 K. At room temperature deuterium concentrations up to 30 at.% are found in a surface layer corresponding to the range of the ions. The measured depth profiles do not fully agree either with calculated range profiles or with the damage profiles, but are determined by the two together. At higher temperatures the deuterium concentrations decrease and the profiles broaden. At room temperature the amount of trapped deuterium increases linearly with dose below 10 18 deuterons/cm 2. The trapping coefficient is roughly 60%. At 5 × 10 18 deuterons/cm 2 the amount of trapped deuterium in the probed layer (~4000 Å) reaches saturation and the trapping coefficient becomes zero. The saturation value decreases with increasing temperature and increases with increasing energy.

Trapping coefficients of energetic hydrogen (0.3–8 keV) in Ti at high doses

The trapping coefficient for hydrogen in Ti has been measured in the energy range from 300 eV to 8 keV and was compared with the trapping coefficient of Zr. In accordance with theory the trapping coefficient for Ti is higher than for Zr in the investigated energy range. The values for both materials fairly agree with computer calculations. Deviation has been found for Ti below 1 keV and for Zr below 1.5 keV. Room temperature irradiation produced swelling in the Ti target, most probably due to hydride formation.

Trapping coefficients of energetic hydrogen (0.3–8 keV) in Ti at high doses

The trapping coefficient for hydrogen in Ti has been measured in the energy range from 300 eV to 8 keV and was compared with the trapping coefficient of Zr. In accordance with theory the trapping coefficient for Ti is higher than for Zr in the investigated energy range. The values for both materials fairly agree with computer calculations. Deviation has been found for Ti below 1 keV and for Zr below 1.5 keV. Room temperature irradiation produced swelling in the Ti target, most probably due to hydride formation. Le coefficient de piégeage de l'hydrogène par le titane a été mesuré dans l'intervalle d'énergie de 300 eV à 8 keV et a été comparé au coefficient de piégeage par le zirconium. En accord avec la théorie, le coefficient de piégeage pour Ti est plus élevé que pour Zr dans le domaine d'énergies étudié. Les valeurs pour les deux matériaux sont en bon accord avec celles calculées par ordinateur. L'écart entre valeurs calculées et expérimentales est inférieur à 1 keV pour Ti et à 1,5 keV pour Zr. L'irradiation à la température ambiante produisait un gonflement dans la cible de titane en raison, très probablement, de la formation d'hydrure. Der Einschlusskoeffizient für Wasserstoff in Ti wurde im Energiebereich von 300 bis 8000 eV gemessen und mit dem Einschlusskoeffizienten in Zr verglichen. In Übereinstimmung mit der Theorie is der Einschlusskoeffizient im untersuchten Energiebereich in Ti höher als in Zr. Die Werte für beide Materialien stimmen gut mit Computersimulationen überein. Abweichungen wurden für Ti unter 1 keV, für Zr unter 1,5 keV gefunden. Wasserstoffbeschuss von Ti bei Raumtemperatur verursachte ein Schwellen des Materials im Bereich des Beschussflecks, wahrscheinlich hervorgerufen durch Hydridbildung.

Backscattering, trapping and post-bombardment thermal release of 100 eV to 2 keV D 2+ ions at a Mo surface

D 2 + ions in the energy range 100 eV to 2 keV have been injected into polycrystalline [preferred (100) orientation Me] at 250 K. Measurements of total backscattering yield and ion trapping coefficient were studied as functions of ion energy and fluence. Post-bombardment gas evolution was also recorded during linear rate of rise tempering and the rates of gas release monitored mass spectrometrically to determine evolution kinetics and activation energies. The measured total backscattering yields were significantly lower than theoretical calculations based upon a randomised atomic target array but agreed more closely with estimates based upon binary scattering from a simulated single crystal. Activation energies for D 2 evolution suggest that D is trapped atomically in the Mo and recombines within the bulk or after diffusion to the surface.

Erfassungskoeffizient des Aerosols AgJ durch einen fallenden Wassertropfen

The author first derives the coefficient of trapping of the aerosol by a water droplet. Having determined the velocity field of the medium in the neighbourhood of the droplet and solved the equation of motion of the aerosol, he determined the critical Stokes number, Stk = 5/6, beginning with which the aerosol is trapped by inertia. The next section deals with the experiment. Using the apparatus, located at the observatory of the Institute of the Physics of the Atmosphere in Hradec Kralove, the author carried out experiments which proved that there existed a critical Stokes number and also that it was possible, given sufficiently small values of St, to adopt with sufficient accuracy the trapping coefficient as ɛ = (2.5 ± 0.3) a/r, where a is the radius of the aerosol particle and r is the radius of the droplet.

Surface Studies of Sintered and Single Crystal UO2 by Low Energy Ion Bombardment

The desorption spectroscopy of trapped gas by low energy ion bombardment in sintered and single crystal UO2, enables us to estimate the threshold energy for entrapment, the trapping coefficient and its variation with both ion energy and implantation temperature and the activation energy for desorption. By comparing the desorption spectra from sintered and single crystal UO2 the surface effects are clearly illustrated for sinters and practically nonexistent in single crystals. The same conclusion could be drawn from fractional gas release experiments. From the entrapment studies of nobles gas ions in UO2, information on gas dissolution, diffusion and bubble formation processes could be derived. Recrystallization of near surface layers and gas bubble production induced by energetic ion bombardment at high doses, observed by TEM, have shown to be closely related to gas release stages.