摘要:

The classical elastic scattering of parallel and divergent ion beams during their passage between two free atoms is studied. The problems are solved analytically for the momentum approximation and numerically by the computer simulation of ion trajectories. The expressions for the differential cross-sections of two-atomic scattering and the two-atomic focusing energyEfhave been obtained for the inverse power and Born–Mayer potentials. The regularities of two-and one-atom scattering are compared. It has been shown that the characteristics of two-and one-atom scattering are very different in the ion energy rangeE ≲ Ef. The ion beam scattering by crystal surface semichannel is discussed. It has been shown that, in this case, the ions may be consecutively focused by two atomic pairs.

ISSN:0033-7579    

DOI:10.1080/00337577808242081

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The preferential sputtering of a binary alloy is considered using diffusion theory. It is shown that this leads to non-linear-terms in both the bulk diffusion equation and the boundary conditions. The steady-state solution is investigated in detail, and the results indicate that some of the non-linearities are negligible, while others cannot be omitted without appreciable errors. The surface depletion of the more volatile component is much smaller than earlier diffusion studies had suggested.

ISSN:0033-7579    

DOI:10.1080/00337577808242082

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The depth distribution of disorder and the depth integrated disorder produced by ion irradiation of solids is analysed theoretically as a function of increasing ion fluence when disorder saturation processes operate at all depths and the solid surface is continuously uniformly eroded by sputtering. The resulting defining equations are evaluated numerically for a Gaussian approximation to the disorder depth function with parameters appropriate to low, equal and high projectile: substrate mass ratio conditions, for several values of sputtering coefficient and effective atom displacement energy. It is shown that the form, if not the magnitude, of the integrated disorder/projectile fluence function is only weakly dependent upon these parameters. More meaningful comparison with depth resolved disorder functions is, however, possible and such a comparison is made for 100 keV Sb projectiles on a Si substrate.

ISSN:0033-7579    

DOI:10.1080/00337577808242083

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The optical absorption spectra and the epr signals of irradiated anthracene crystals have been measured at 4.2 and 77 K. The optical absorption and the simple Hückel calculations combined with isochronal annealing of the crystals have revealed that 9-, 1-and 2-dibenzocyclohexadienyl radicals are unstable at temperatures higher than 420, 250 and 220 K, respectively. The epr analysis has supported the result of the optical analyses of 9-, 1-and 2-dibenzocyclohexadienyl radicals, and their hyperfine coupling constants are in good agreement with the values calculated. The epr analysis connected with the isochronal annealing has revealed that three phenyl-type radicals are produced in the crystals at low temperature. They have been assigned as 9-, 1-and 2-anthracyl radicals with the line shapes of singlet, doublet and triplet, respectively. Their hyperfine splitting constants are almost in accordance with those obtained in an argon matrix system, and they are unstable at temperatures higher than 130, 200 and 240 K in the order of 9-, 1-and 2-anthracyl radicals. The decay processes of the cyclohexadienyl-and phenyl-type radicals have been discussed in connection with chemical reactions in the crystals. The migration of the radical species in the course of the reactions has been qualitatively confirmed by the microwave power saturation curves of the epr spectra.

ISSN:0033-7579    

DOI:10.1080/00337577808242084

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The kinetic equations of the formation of the F centers (vacancies) and the V4centers (di-interstitials) in KBr are formulated on the basis of the present knowledge of the defect interactions. In order to explain the experimental observations that the vacancy concentration is proportional to the 0.8th power of the irradiation dose and that the formation rate is independent of the dose rate, a model is invoked in which the di-interstitial formation is enhanced in the vicinity of the di-interstitials previously created. It is shown that the solutions of the kinetic equations explain the experimental growth curves and that the present model can account for the nucleation of the cluster of the di-interstitials suggested by Hobbs.

ISSN:0033-7579    

DOI:10.1080/00337577808242085

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

By the presence of dislocations the channels in a single crystal are distorted. The distortion modifies the motion in planar channels, and the extent to which the modified motion influences energy loss spectra of ions transmitted through thin single crystals with screw-dislocations is examined. In the calculation the stopping power model of Robinson1is used, and the motion of the ions in the distorted channels is solved approximately. Within the model used it is concluded that the presence of dislocations will be hard to detect using only energy loss measurements.

ISSN:0033-7579    

DOI:10.1080/00337577808242086

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Backscattering measurements on (111)-oriented CaF2crystals covered with evaporated films of gold or calcium fluoride have been made using 2.0 MeV4He ions and 4.0 MeV protons. Measured angular yield profiles for different layer thicknesses have been compared with calculated profiles obtained from scattered particle distributions due to Sigmund and Winterbon but using different assumptions about the de-channelling process. For gold films the calculated aligned yields and half angles of the angular yield profiles are in good agreement with measurements. For calcium fluoride films good agreement is obtained between the measured and calculated aligned yields if the scattering contribution from the fluorine atoms is treated as a correction to the dominating scattering from the Ca atoms.

ISSN:0033-7579    

DOI:10.1080/00337577808242087

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The formation of radiation defects in n-type GaAs during irradiation with 28-MeV electrons and Co60gamma rays has been studied as a function of the degree of doping and type of dopant. It has been found that irradiation with electrons generates isolated defectsA, Band defect clustersR, while irradiation with Co60gamma rays creates isolated defectsBandC.

ISSN:0033-7579    

DOI:10.1080/00337577808242088

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

We have implanted hydrogen (or deuterium) in magnesium single crystals and used the techniques of nuclear reactions analysis to measure the concentration profiles and the lattice location of the implanted hydrogen. For an implantation at very low temperature (40 K) hydrogen occupies tetrahedral sites. This configuration remains during annealing cycles up to 110 K where hydrogen becomes mobile and is trapped after a few jumps by vacancies. Hydrogen clusters are formed by annealing above 225 K and are subsequently dissolved at a temperature of about 300 K.

ISSN:0033-7579    

DOI:10.1080/00337577808242089

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The fission track technique for detecting235U has been used in conjunction with a mechanical time-of-flight spectrometer in order to measure the energy spectrum in the region 1 eV to 1 keV of material sputtered from a 93% enriched235U foil by 80 keV40Ar+ions. The spectrum was found to exhibit a peak in the region 2–4 eV and to decrease approximately asE–1.77forE≳ 100 eV. The design, construction and resolution of the mechanical spectrometer are discussed and comparisons are made between the data and the predictions of the random collision cascade model of sputtering.

ISSN:0033-7579    

DOI:10.1080/00337577808242090

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor