Studies of relativistic electron scattering at planar alignment in a thin Si crystal

Experiments on 255-MeV electron scattering under (220) planar channeling conditions in a Si crystal were carried out at the linac of the SAGA Light Source. The spatial and angular distributions of electrons penetrating through a 20-μm thick Si crystal at different incident angles with respect to the (220) plane were measured, and features characteristic of the planar alignment were identified. The experimental results were compared with computer simulations, and showed a reasonable agreement. A comparison with doughnut scattering at axial channeling in the same crystal was also performed. It was confirmed that the planar alignment effect is weaker than the axial alignment effect. These studies are important for understanding the basic mechanism of electron scattering and radiation processes in a crystal.     

高电荷态离子与Si(110)晶面碰撞的沟道效应研究

不同电荷态低速离子(Ar^q+,Pb^q+)轰击Si(110)晶面,测量不同入射角情况下的次级粒子的产额. 通过比较溅射产额与入射角的关系,证实沟道效应的存在. 高电荷态离子与Si相互作用产生的沟道效应说明溅射产额主要是由动能碰撞引起的. 在小角入射条件下,高电荷态离子能够增大溅射产额. 当高电荷态离子以40°—50°入射时,存在势能越高溅射产额越大的势能效应. 关键词： 高电荷态离子 溅射 沟道效应     

ABNORMAL ENERGY DEPENDENCE OF AXIAL MINIMUM CHANNELING YIELDS IN GexSi1-x/Si(100) STRAINED

An energy dependence of the axial minimum channeling yield in Ge_xSi_1-x/Si(100) Strained-layer superlattice is observed in the energy range of impinging He⁺ ione from 1.2 to 3.0 MeV. For [100] axial channeling, the measurements ere in agreement with what have been known in a single crystal. However, for [110] axial channeling, it is found that the minimum channeling yields increase markedly with the increase of He⁺ ion energy, which is contrary to the general channeling behaviors in a single crystal. A tentative model is suggested to explain this aberrance.     

Proton channeling studies in thin crystals with a supercollimated beam

Abstract

A supercollimated beam of 4 MeV H^? ions with an angular spread of 1.5 × 10^?3 degrees, a diameter of 25 μ and a current of 10 picoamps was used to study the axial and planar channeling characteristics of single crystal silicon samples ranging in thickness from 0.5 to 1.0 μ. Since the angular spread of the beam is much smaller than most of the gross angular phenomena associated with channeling, it is possible to study the detailed characteristics of both planar and axial channeling with greater precision than before. Preliminary results indicate that this technique will allow a direct study of interatomic or continuum potential distributions and will also be useful for studying nuclear multiple scattering as a function of the tranverse energy of channeled particles relative to atomic rows and planar directions.     

ABNORMAL ENERGY DEPENDENCE OF AXIAL MINIMUM CHANNELING YIELDS IN GexSi1-x/Si(100) STRAINED

An energy dependence of the axial minimum channeling yield in Ge_xSi_1-x/Si(100) Strained-layer superlattice is observed in the energy range of impinging He⁺ ione from 1.2 to 3.0 MeV. For [100] axial channeling, the measurements ere in agreement with what have been known in a single crystal. However, for [110] axial channeling, it is found that the minimum channeling yields increase markedly with the increase of He⁺ ion energy, which is contrary to the general channeling behaviors in a single crystal. A tentative model is suggested to explain this aberrance.     

Carrier removal by implanted IONS in GaAs

Abstract

A model for calculation of the range distribution of energetic ions with taking into account the channeling effect is proposed. The measurement of the depth distributions of boron ions in silicon crystals implanted at 13.6 and 91 MeV revealed significant difference between the measured and the calculated range profiles when the channeling effects have not been included in the calculation. In spite of deminishing the critical angles of channeling with growing ion energy the probability of the capture of ions into the channeling regime is significant in case of high energy implantation even when the incident angles are 7–10° off the main crystallographic directions.     

Relativistic-electron scattering on an atomic string of a crystal at ultrasmall angles of particle incidence on a string

The classical and quantum scattering of fast electrons on an atomic string of a crystal is considered at angles of particle incidence on the string that are much smaller than the critical angle of axial channeling. The investigation was performed within the simplest approximation of the continuous atomic-string potential in the form of a cutoff Coulomb potential. For this case, the azimuthal scattering of particles at an angle exceeding 180° in the plane orthogonal to the string axis is shown to be possible for all impact-parameter values. It is demonstrated that, in particle scattering on a string, an effect can occur that is similar to the Ramsauer-Townsend effect, which consists in a considerable reduction of the total cross section for slow-electron scattering on atoms.     

A qualitative description of the transverse motion of axial channeled particles in thin crystals

The qualitative features of the angular distribution of particles emergent from thin ～ 1μ, uniform single crystals of silicon and germanium for incidence at small angles to axial directions are discussed in terms of the continuum picture of particle channeling. Blocking of axially channeled particles in the transverse plane is demonstrated. Implications and possibilities arising from observation of non-equilibrium of the transverse momentum vector are discussed. The use of the radial spreading of the angular distribution to investigate the average inter-atomic potential distribution in the plane transverse to the axial direction is explored and perturbations due to multiple scattering in surface films or inside the crystal and to beam divergence are qualitatively considered.     

Laser induced single-crystal transition in polycrystalline silicon

Transition to single crystal of polycrystalline Si material underlying a Si crystal substrate of 〈100〉 orientation was obtained via laser irradiation. The changes in the structure were analyzed by reflection high energy electron diffraction and by channeling effect technique using 2.0 MeV He Rutherford scattering. The power density required to induce the transition in a 4500 ? thick polycrystalline layer is about 70 MW/cm² (50ns). The corresponding amorphous to single transition has a threshold of about 45 MW/cm².     

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.     

Channeling and RHEED analyses of Pb-implantation in silicon

Si 〈111〉 single crystals implanted with 40 keV Pb⁺ have been analyzed by channeling and reflection high-energy electron diffraction (RHEED) techniques. A suitable use of both techniques gives information on the thickness of the damaged regions. In particular, 60 KV electron impinging at ～0.3° and 1° with respect to the crystal surface give information on 40 Å and 100 Å thick Si layers, respectively. The low dose implanted region grow epitaxially onto the underlaying Si single crystal substrate. High dose implantation will not allow recrystallization for annealing temperature up to 900°.     

Spin-flip probability for 7.6 MeV neutrons scattered inelastically (Q = −2.23 MeV) by a sulfur target

The spin-flip probability for 7.6 MeV (ΔE = 0.250 MeV) neutrons scattered inelastically (Q = ?2.23 MeV) from naturally occuring sulfur has been measured at scattering angles between 40° and 160° using a γ-correlated neutron time-of-flight method. The scattering by the natural sulfur target was assumed to be characteristic of ³²S. The results of the measurement were compared with an incoherent sum of statistical compound-nucleus (CN) and direct-interaction (DI) contributions. The DI contributions were obtained using either a DWBA calculation or the coupled-channel (CC) formalism. Neither combination of CN plus DI contributions reproduced the experimental spin-flip probability angular distribution which was peaked near 110° with a maximum value of 0.33 ± 0.08.     

The Ar(p, d)Ar reaction

The ³He spin analysing power of hydrogen (protons) has been measured at a c.m. energy of 20 MeV at 14 c.m. angles from 40° to 160°. The measurement of ³He target polarization was calibrated by measuring the ³He spin analysing power of ⁴He at an energy and angle where it was ?1.00. The proton-³He differential elastic scattering cross section is also reported at a c.m. energy of 20.0 MeV for 36 c.m. angles from 20° to 170°.     

A channeled ion energy loss study of the surfactant-mediated growth of Ge on Si(100)

Scattered ion energy distribution for the system Sb/Ge/Si(100) are studied using transmission ion channeling. One monolayer (ML) of Sb was deposited on the clean Si(100) surface prior to deposition of one ML of Ge at 350°C. Experimental energy distributions for the <100>, {110}, and “random” directions are compared with simulated energy distributions obtained by overlapping trial absorbate positions (relative to bulk positions) with ion positions in the channel at the beam-exit surface. Ion positions and energies are calculated via a Monte Carlo simulation of channeling that incorporates a model for channeled ion energy loss. We find that the energy distributions clearly show that the surfactant, Sb, moves to the surface upon Ge deposition at 350°C. Further, our results are consistent with the sites recently reported by Grant et al. [Surf. Sci. 316 (1994) L1088], for Sb deposited on Ge/Si(100), namely, tilted Sb dimers on Ge asymmetrically displaced from bulk sites.     

Features of the formation of radiation spectra at (111) planar channeling of relativistic electrons in a Si crystal

The spectral intensity of (111) channeling radiation from electrons is numerically calculated at the energy varying from 100 to 900 MeV and different electron incidence angles relative to the (111) planes in thin Si crystals. The calculation results show that the channeling radiation’s spectra have a more complicated structure, and the total channeling radiation’s yield is several times larger than that at (100) or (110) channeling.     

Quasi-free scattering of pions on 3, 4He

Differential cross sections for ^{3, 4}He(π, π') are presented for angles of 60° and 120° at 200 MeV and 120° at 295 MeV. The momentum spectra for the scattered pions are dominated by a peak attributed to quasi-free scattering from individual nucleons. There are significant differences between the scattering on ³He and ⁴He as well as between the scattering of π⁺ and π^? on ³He. The data are compared to a simple model incorporating the free π+N scattering amplitudes. Modifications for the structure and dynamics of the target nucleus are discussed.     

Precompound emission in the reaction 65Cu(p,xn) and the nucleon-nucleon scattering mechanism

The reaction ⁶⁵Cu(p, xn) has been studied with E_p = 26.7 MeV for angles 3° ? θ ? 177°0. Whereas the angle-integrated spectrum can be explained by a semiclassical preequilibrium model, the nucleon-nucleon scattering approach fails for the preequilibrium neutron emission at far backward angles. The failure is shown to be due to principal shortcomings. In contrast, the quantummechanical statistical multistep calculations give good agreement with the main contribution for residual energies U < 9 MeV coming from the SMDE component.     

Determination of the step distance on a crystal surface by surface channeling

The scattering of grazingly incident ions on a crystal surface under axial surface channeling conditions is sensitive to consecutive upward surface steps. The comparison of the experimentally observed scattering yield with computer simulations provides a sensitive method to determine the mean terrace width of the upward steps in a region of about 30 to 300 atomic distances. Applying this method, we have found that the mean terrace width of an electropolished NiFe (110) surface is 75 atomic distances along the [11?0] lattice direction.     

(100) and (110) SiSiO2 interface studies by MeV ion backscattering

Thin oxide layers on (110) and (100) Si have been studied by ion scattering experiments in a channeling grazing exit angle geometry. Oxides are found to be stoichiometric SiO₂ to within 10 Å of the (100) substrate surface, and 7 Å of the (110). The transition interface region between single crystal Si and the SiO₂ layer is abrupt and is characterized by approximately one to two monolayers of Si which is out of registration with the substrate lattice for the (110) case. The possibility of a layer of O-deficient oxide is also explored.