摘要:

The effects of segregation on the preferred sputtering of alloy surfaces have been analyzed. The top layer of the surface is regarded as behaving differently from the layers beneath the second layer: segregation and dissolution rate constants between the top and second layers are included in the kinetic equations explicitly. It is shown that the fundamental kinetic equations are of a form similar to that developed by Ho, Webb, Carter and Collins, even though the coefficients of the equations are different. The time-dependent solution of the kinetic equations shows that the segregation rate constant plays an important role in the build-up of the steady state. Similarly to the previous result, the altered layer is shown to have a thickness of the diffusion constant divided by the velocity of the recession of the surface. The steady-state compositions at the top and second layers relative to the bulk composition were found to be a function of three parameters: the surface enrichment factor, the diffusion constant divided by the velocity, and the ratio of the yields of atomic removal from the top layer, a correction factor being needed in a particular boundary condition. The existing experimental data on Cu-Ni, Cu-Au and some other alloys are surveyed critically in terms of the results of the theoretical calculation.

ISSN:0033-7579    

DOI:10.1080/00337578408216461

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A new method of approximation is described, which can be used to obtain energy eigen values in a simplified manner. The result of the new approximation has been tested against an exactly calculated eigen value and has been found to be identical with it. For the potentialV(X) = (KX2/2) + λX4, the energy eigen values calculated by the new approximation method have been compared with the exact results (or 20 orders of perturbation theory) and the agreement was found to be satisfactory. As a practical application of this new approximation, it has been applied to calculate the characteristics of the radiation emitted from relativistic positrons channeled between the major planes in single crystal silicon. The sharp peaks of the emission spectrum in the keV region is predicted correctly.

ISSN:0033-7579    

DOI:10.1080/00337578408216462

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The angular dependence of light-ion sputtering has been investigated in the direct knock-out model. Simple expressions for the angle of incidence at the maximum yield and the angle of preferential emission are derived, and agreement between theory and experiment is very good.

ISSN:0033-7579    

DOI:10.1080/00337578408216463

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

We have measured sputtering yields of H2O films with 19F ions at bombarding energies from 1.6 to 25 MeV. The sputtering yield was found to be very sensitive to the incident charge state of the beam, and insensitive to the thickness of the ice film for thicknesses ranging from approximately 20 to 80×l016H2O/cm2. The yield was independent of the target substrate temperature from 10 to 60 K and independent of the F beam current density from < 1 to approximately 5.5 particle nanoamps/mm2. There are several models proposed to explain enhanced sputtering of dielectrics; we have discussed their relevance to our data.

ISSN:0033-7579    

DOI:10.1080/00337578408216464

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Excitation functions on molybdenum isotopes and a theoretical evaluation of helium accumulation in natural molybdenum for proton irradiation in the 15–30 MeV energy region have been obtained. It has been shown that 19–22 MeV protons are the most suitable for simulation of helium accumulation processes and atom displacement formation taking place when natural molybdenum is irradiated by neutrons with a CTR spectrum and neutrons with 14 MeV energy.

ISSN:0033-7579    

DOI:10.1080/00337578408216465

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Small-angle specular reflection of 10-30 keV Ar+ ions from (001) and (011)Cu faces has been experimentally studied. The half-widths of reflected ion spatial distributions have been found to decrease nonmonotonically as the primary ion glancing angle decreases. For the (001) Cu face in the studied range of glancing angles (3–16°) a local decrease of spatial distribution half-width has been observed in two narrow transient regions. Angular positions of these regions have been found to correspond to some fixed values of transverse energy. A “large”-angle transient region is associated with the glancing angle at which favourable conditions for ion-focusing in surface semichanncls take place. The relationship of low-angle peculiarities in spatial distributions, energy spectra and azimuthal dependences of the reflected ion intensity to near-surface channeling is discussed.

ISSN:0033-7579    

DOI:10.1080/00337578408216466

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The theory of ionization of atomic particles channeled by an interplanar crystal potential is developed. Taking account of nuclei thermal vibrations the effect of the diminution of electron loss probability of an ion by elastic interaction with the lattice atoms during channeling as well as in a crystal with random orientation is investigated.

ISSN:0033-7579    

DOI:10.1080/00337578408216467

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Zero-energy density effect in stopping power of carbon has been studied. A modified Drude dielectric function was used to describe the interaction of incident electrons with the valence band of graphite, glassy carbon and diamond. The Hartree-Fock generalized oscillator strength was employed to evaluate the stopping power of gaseous carbon. Results were analyzed with respect to density, structure and phase.

ISSN:0033-7579    

DOI:10.1080/00337578408216468

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Sputtering processes can be classified by considering the time-scale. Thus, if an incident particle hits at t = 0, one can recognize, for 10minus;15⩽t⩽ 10−14s,prompt collisionalprocesses involving direct (or nearly direct) particle-target interactions. The yield is often expressible as a simple integral of a differential cross section. These are followed, for 10−14⩽t⩽10−13to 10−12s, byslow collisionalprocesses due to the internal flux of target atoms in the cascade intersecting the surface. The yield for sputtered atoms is given by a relation (that of Sigmund) which is conceptually similar to that for the flux of perfect gas atoms against a surface and which can be restated very directly in these terms. An important feature, as is shown in simple derivations, is that the high-energy limit of the sputtered flux is predicted to have the formfluxœE0-2 for atoms butfluxœE0-4.5 for diatomic molecules, provided the molecules are formed by recombination.Eois the sputtered particle energy. For 10−13to 10−12⩽t⩽10−11to 10−10s, one has what may be calledprompt thermalprocesses. The yield is given ideally by ∫ ∫p(2πmkT)−1/22πydydt, wherepis the equilibrium vapor pressure (whether vapor is present or not); the flux is proportional toE0exp(-Eo/kT). The evidence for thermal sputtering is reviewed in particular detail in view of the controversial nature of the process.Slow thermalprocesses, which occur fort⩾10−11to 10−10s, include the vaporization of metal from halides or oxides after it accumulates due to electronic sputtering of halogen or oxygen.Electronicsputtering, which may be either fast or slow (t⩽or⩾10−11to 10−10s), comes about in events such as interatomic Auger decay or the assumed diffusion of halogen or oxygen interstitials, i.e. H centers, to the surface, with resultant vaporization or expulsion of halogen or oxygen. Finally,exfoliationalsputtering, due to the rupture of gas-filled cavities, sets in at very high doses of light inert-gas atoms. There are thus six fairly distinct sputtering processes, any one of which is found to be important for particular systems or particular experiments.

ISSN:0033-7579    

DOI:10.1080/00337578408216469

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor