Direction Of Primary Beam Research Articles

Study of alignment and orientation in alkali ion-inert gas atom collisions with the polarized photon-quasi-coincidence technique

The alignment and the orientation of the electron charge cloud of the Li(2 2P), Na(3 2P)-state excited in 2.6 keV Li +, Na +-inert gas collisions is studied with the quasi-coincidence technique of Wittmann and Andrä. A polarization analysis of the photons emitted in the subsequent ( 2 P → 2 S) transitions has been carried out. The present experiment breaks rotational symmetry with respect to the primary beam direction, but possesses no full planar symmetry. Thus a direct experimental derivation of amplitudes for the capture process is not feasible. For Li + −He the characteristics of the quasi-coincidence technique could be studied in detail because experimental data obtained with the photon-scattered atom coincidence technique and theoretical studies are available. The results for Li + −He are consistent with the available results which showed that the well established 2pσ-2pπ rotational coupling is responsible for the first step in the capture process. The results support the prediction of the theory that the linear polarization P 2 changes its sign between 2.0 and 6.0 keV. The results for Li-Ar and Kr suggest that rotational coupling at small internuclear distances (similarly as for LiHe) is the dominant mechanism for capture with alkali atom excitation.

Angular distributions of very low energy recoil ions

We present the first measurements of the angular distribution of recoil ions near 90 ° with respect to the incident projectile direction. Beams of 22.5 and 33 MeV chlorine ions (incident charge states q = 4,5,8) have been used as “hammer” beams incident on Ne atoms. We do not confirm the long standing assumption that these recoil ions are ejected preferentially at angles very near 90 ° with respect to the primary beam direction, although they do have energies typically less than 5 eV. Recoil ions ejected around 90 ° have an energy distribution appreciably wider than those ejected at either larger or smaller angles.

Analytical determination of the exact primary beam direction from Kikuchi patterns

An exact analytical solution for the beam direction is derived using two indexed Kikuchi line pairs. The method allows for a rapid analysis of Kikuchi patterns.

Kikuchi Patterns due to Plasmon and Phonon Excitations

The intensity profiles of Kikuchi patterns are calculated for the Si(220) reflection at 75 keV. The patterns due to plasmon and phonon excitations are treated separately. The discussion is concerned only with the special case of the primary-beam direction satisfying exactly the Bragg condition for the reflection (220). The patterns due to plasmon excitation are strongly affected by the anomalous absorption, and they have many subsidiary maxima because of their coherent part. On the other hand, patterns due to phonon excitation are not affected by anomalous absorption, and they have no subsidiary maxima because of their vanishingly small coherent part. These results agree with the experimental results of Meyer-Ehmsen and Siems.

Energy distributions of charged and neutral hydrogen atoms backscattered from metal surfaces bombarded with 5 to 18 keV protons

Polycrystalline targets of Be, V, Nb, Mo and Ta have been bombarded with protons with primary energies in the range from 5 to 18 keV. The energy distributions of the charged and the neural particles backscattered at 135° with respect to the primary beam direction have been measured between 200 eV and 18 keV. The energy distribution of the neutrals has a pronounced maximum between 0.5 and 1 keV whose position does not depend on the primary energy or the target material, or the angle of emergence of the scattered particles. The energy distribution of the charged particles shows a less pronounced maximum between 1 and 1.5 keV. Only slight differences in the shape of the energy distributions have been observed for different target materials. The fractional number of charged backscattered particles increases from ≈; 3% at 300 eV to ≈; 40% at 18 keV.

Some angular| dependences of the ion-electron emission coefficient

Abstract In the cases when primary ion beam direction is aligned with close-packed planes the dependences of the reduced coefficient of ion-electron emission on various angles has been studied. It was found that there are such ranges of azimuthal angle and angle of incidence of primary ion beam within which the reduced coefficient is determined mainly by the angle between the primary ion beam and close-packed plane only.

Accommodation coefficients for low-energy ions on metal surfaces

Abstract The interaction of low-energy ions (E = 3 to 100 eV) with the surface of a solid cannot be treated in terms of gas dynamics. The scattering of particles at an energy of E o > 20 eV may be explained in terms of binary collisions with the atoms of the target. The validity of the single collision model with free surface atoms for medium energies from 10 to 100 eV and even down to 1 eV was confirmed on the basis of both experimental and computational data. This paper describes experimental studies of the secondary ion emission from the (100) and (110) faces of a Mo single crystal and both experimental and theoretical studies of alkaline ion accommodation coefficient on polycrystalline Mo within the energy range E = 3 to 50 eV with a varying direction of the primary ion beam from normal to the glancing angle of incidence (ρ = 0 to 75°). On the basis of the retarding potential method using a spherical condenser whose central electrode was the target, we measured the energy distribution of secondary ion...

A Versatile Molecular Beam Scattering Apparatus Utilizing Electron Bombardment Detection

A versatile crossed molecular beam apparatus has been designed, fabricated, and tested. The instrument consists of a large cylindrical stainless steel ``scattering chamber'' which contains differentially pumped nozzle-skimmer and detector chambers. The crossed beams intersect at the cylinder axis. The detector assembly can be rotated about the scattering center from −43 to +133° with respect to the primary beam direction. The scattered intensity is measured using a modified Weiss electron bombardment ionizer with quadrupole mass filter. Over-all detection efficiency of the system for a thermal argon beam is 0.25%. Background discrimination is effected by means of double modulation (synchronous chopping of both crossed beams with beat frequency lock-in detection). The apparatus has been employed in studies of the rainbow scattering of Ar by various gases.

Electron Diffraction Studies of Cuprous Oxide

Etched surfaces of single crystals of cuprous oxide produce electron diffraction patterns consisting of spots and Kikuchi lines. In some cases lines are observed corresponding to all of the most widely spaced planes of copper atoms which are so situated as to be able to give reflections on the photographic plate. An example is given, however, of a diffraction pattern from which lines due to the most widely spaced plane of atoms, (111), are missing when this plane lies parallel to the primary beam direction; the lines appear when the crystal is rotated to destroy this parallelism. The existence of Kikuchi line patterns indicates that the surfaces of etched cuprous oxide single crystals are relatively smooth. When spot patterns also appear they show anomalies which seem attributable to refraction, thus confirming the conclusion regarding smoothness. An example is given of an array of spots made up of three distinct patterns which are displaced with respect to each other and with respect to the primary beam position. Polycrystalline surfaces made up of rather large crystals produce patterns of spots which are often drawn out into streaks lying approximately parallel to the plane of incidence. This effect, which is attributable to refraction and is a proof of smoothness of the surface, is most pronounced after etching in nitric acid. It is rarely, or never, found after etching in a mixture of hydrogen peroxide and ammonium hydroxide. Nitric acid etch produces upon the surface of a single crystal of cuprous oxide, or upon a polycrystalline surface made up of rather large crystals, crystals of some new compound which are cubic with cell edge 8.35A. These are sharply oriented with one or another of the most important planes parallel to the gross surface plane of the oxide. The sharpness of this orientation is proof of the flatness of the underlying oxide surface upon which the crystals are formed. This new 8.35A structure is produced by potassium cyanide etch as well as nitric acid, but never by sulphuric acid nor by ammonium hydroxide.