氦离子显微镜对钨中氦行为的实验研究

针对热核聚变面向等离子体钨材料中氦泡形成、演变以及机理研究的需求,克服目前常用离子注入、电子扫描显微镜和透射电子显微镜等离线研究手段存在的不足,提出氦离子显微镜对钨中氦的上述行为原位实时在线研究方法.借助氦离子显微镜的离子注入、显微成像和聚焦离子束纳米加工功能,它可以提供能量为0.5—35 ke V、束流密度可达10~(25) ions/(m~2·s)以上的氦离子束,在该设备上进行钨中氦的注入实验.同时在注入过程,实时在线监测钨中氦泡形成、演变过程以及钨材料表面形貌的变化,原位在线分析钨材料表面氦泡的大小、迁移合并以及其诱发的钨表面和近表面的微观损伤.实验结果表明:氦离子显微镜是研究钨中氦行为演变过程及其微观机理研究的新的研究手段和强有力的实验工具.     

Field-ion microscope observations of helium ion bombardment damage in tungsten

The field-ion microscope has been used in a pilot investigation of the damage caused to tungsten surfaces following bombardment with low-energy helium ions. Such effects could be important because the first wall of a fusion reactor will have to withstand high doses of these particles. The damage observed following bombardment with total doses in the range 10¹³ to 5 × 10¹⁸ ions cm^?2 has been found to be dose dependent. These results have then been related to those derived from studies using more conventional techniques and this has led to the conclusion that the origin of the observed damage lies in the formation of near-surface gas bubbles and surface blisters.     

Electromagnetic radiation of channeling electrons and positrons

General formulae for the spectral and angular distributions of radiation of relativistic channeled particles have been derived. These formulae are valid both for γ-quanta radiation and for radiation in the optical region. The problem of experimental detection of this radiation is discussed.     

Bent crystal channeling of 255 MeV electrons

Charged particles channeled in a bent crystal plane are known to be deflected along the bent plane. Such studies have mainly been performed for high-energy positively-charged particles such as protons, and recently for electrons with energies from 855 MeV to 20.35 GeV. In this work, we present experimental results on the bent crystal channeling of electrons for a lower energy region (255 MeV), where the multiple scattering effect in a crystal is expected to be more dominant. Angular distributions of electrons transmitted through a bent Si crystal have been measured, which are in good agreement with the simulation results.     

Peculiarities of heavy ion channeling

Abstract

Depth distributions of implanted Mg⁺- and Ca⁺-ions and the corresponding radiation damage were studied for different channeling orientations of silicon crystals. The shape of the implantation profiles is discussed by using simple models for dechanneling and energy loss processes. A correlation between dechanneling, damage production and depth distributions of the channeled ions could be observed. This correlation is seen by the maxima shifts in damage and implanted ion distributions between channel and random incidence.     

Inelastic scattering of electrons by helium

Measurements of the angular distribution and total cross section for all inelastic processes in the scattering of intermediate and high energy electrons by helium atoms are analyzed using the first Born approximation.     

Low energy secondary electrons ejected by metastable helium (He) beam: Observation of He spin dependence

Intensity of low energy electrons ejected by a spin polarized metastable helium (He^∗) beam was measured for clean and water-adsorbed Fe surfaces. A definite He^∗ spin dependence was found in the intensity of electrons with energies just above the vacuum level of the sample when an Fe surface was covered with a water multilayer. The He^∗ spin dependence was found to be associated with the He^∗ deexcitation process. The spin dependence is likely to be due to the spin-dependent secondary processes.     

Position-controlled marker formation by helium ion microscope for aligning a TEM tomographic tilt series

We formed nano-dots using a helium ion microscope (HIM) equipped with a gas injection system. Because of position controllability, the nano-dot markers could be placed efficiently on a specimen using the HIM. The sizes of the dots were controlled by changing the beam radiation time. We tried for the first time to form dots on a rod-shaped specimen to use them as markers for aligning a transmission electron microscope tomographic tilt series before reconstructing 3D images.     

脉冲离子束作用下靶面次级电子的抑制

论述了离子束作用下固体表面次级电子产生的机制,介绍了特种真空器件中次级电子抑制的各种方法及其优缺点,提出了脉冲离子束作用下靶面次级电子抑制的自偏势法和曲面靶法等设计思路,并在实验上进行了初步验证。实验结果表明,自偏势电压大于80 V后,次级电子得到很好的抑制。在相同束流情况下,曲面靶较平面靶的次级电子产额少。利用实验结果进行估算得到了近似的次级电子产额约为0.67,比文献中的结果(0.58)偏大。对实验中自偏势法抑制反峰电子电流的效果进行了分析和讨论,结果表明：自偏势法不但能够有效抑制离子打靶产生的次级电子,还能抑制由功率源不稳定带来的入射反峰电子流。     

Linear polarization of channeling radiation from axially channeled electrons

Abstract

The degree of polarization of channeling radiation emitted by axially channeled electrons has been calculated using the many-beam method. The polarization was found to be substantial, and to increase monotonically with the channeling angle. The many-beam results are compared with those obtained from the single-string approximation and are found to be significantly different.     

脉冲离子束作用下靶面次级电子的抑制

论述了离子束作用下固体表面次级电子产生的机制,介绍了特种真空器件中次级电子抑制的各种方法及其优缺点,提出了脉冲离子束作用下靶面次级电子抑制的自偏势法和曲面靶法等设计思路,并在实验上进行了初步验证。实验结果表明,自偏势电压大于80 V后,次级电子得到很好的抑制。在相同束流情况下,曲面靶较平面靶的次级电子产额少。利用实验结果进行估算得到了近似的次级电子产额约为0.67,比文献中的结果(0.58)偏大。对实验中自偏势法抑制反峰电子电流的效果进行了分析和讨论,结果表明:自偏势法不但能够有效抑制离子打靶产生的次级电子,还能抑制由功率源不稳定带来的入射反峰电子流。     

KeV channeling effects in the Mott scattering of electrons and positrons

High-energy scattering experiments mandate a point-like charge on the electron. However, the spectroscopic properties of the electron suggest an overall Compton-sized geometry. Adopting the model of a Compton-sized electron or positron that has a equatorial point charge, we use detailed computer calculations of classical Coulomb scattering off atomic nuclei to delineate the boundaries of a narrow energy window, in the KeV range, in which finite-size effects should be observable. Some experimental evidence for these finite-size effects can be found in the published literature.1. This work was performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.2. The impact parameters shown in Fig. 1 were obtained by numerical integration of point-particle trajectories, with relativistic effects and nuclear screening included.3. When rotational and recoil effects are set equal to zero, the calculated large-positron elastic differential cross sections are accurately point-like at all incident energies.4. The calculations shown here required more than 10,000 hours of computer time on a network of seven Sun SPARC 1 and SPARC 2 computers.     

Volume capture of ultrarelativistic electrons in the axial channeling regime

Using computer simulation the volume capture effect of ultrarelativistic electrons in the axial channeling regime in crystals is investigated. The thickness, temperature and orientational dependences of the beam fraction captured in the channeling regime in the volume of the crystal are obtained.     

Axial bloch wave channeling of 15 MeV electrons in silicon

Experimental transmission profiles of 15 MeV electrons in silicon [111] have been measured. They show a fine structure which is not reproduced by a classical calculation. On the basis of the dynamical theory of diffraction a 331-beam calculation has been performed to interpret the experimental curves.     

Elastic scattering of electrons by helium and neon atoms

Summary  Partial and total cross-sections of electrons scattering by helium and neon atoms are calculated at eleven values of incident energy ranging from 0.1 a.u. to 1.1 a.u. The calculations are carried out via model potential (describing the electron target interaction). The iterative Green’s function partial-wave expansion technique was used. The comparison between our results and those obtained by other authors show significant agreement and supports our simple model scattering process.     

Surface channeling of protons and electrons on reflection by a single crystal

Computer modeling is used to investigate the reflection of 0.67-MeV protons and 1-MeV electrons by the (110) face of an Au single crystal for angles of divergence < _cr of the incident beam with the direction 110 lying in the surface. The angular distributions and reflection coefficients of protons and electrons are compared. Several maxima are found in the angular distributions. In additon to the specular-reflection maximum at = there is a maximum at > for protons and a maximum at < for electrons. The maxima in the angular distributions are attributed to multiple scattering at atomic chains of the crystal surface. An analytic approximation of the reflection coefficient for protons K_cor() is given. The great contribution to the reflected flux from particles channeled in the surface layer allows it to be used for structural analysis of crystal surfaces.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 85–90, March, 1979.