Internal energy distribution of sputtered sulfur molecules

Bombarding targets of CS₂ and sulfur with keV Ar⁺ ions induces among other species the sputtering of S₂ molecules. We measured the internal energy (vibration and rotation) of these sputtered molecules with a laser induced fluorescence technique. The results show a Boltzmann behaviour for both the vibrational and rotational distributions. A vibrational temperature T_vib = 1500 K and a rotational temperature T_rot = 300 K is obtained for both target materials. The results are compared with different ejection mechanisms, where a molecule on the surface receives one (single collision) or two (double collision) momentum transfers from the solid. Two classical models are able to explain part of the experimentally observed internal energy distribution: a Monte Carlo calculation of the double collision model, and a single collision model assuming a sudden momentum transfer to the molecule as a whole, which yields an analytical expression (via a relation between the internal and kinetic energy). If we assume that some additional rotational cooling, due to time dependent relaxation effects, occurs during the ejection from the surface, the experimental results can be reasonably interpreted within the proposed sputtering models.     

Momentum and recoil-flux anisotropies in collision-cascades: Influence on sputtered particle angular distributions

The anisotropy in the spatial distributions of recoil-flux and recoil-momentum have been studied by Monte Carlo simulation for the specific case of amorphous germanium bombarded with Ar⁺ ions. For all the energies investigated, (1.25 to 320 keV) both the recoil-flux and momentum-flux distributions are strongly backwards directed at the surface, becoming forwards directed at greater depths. Further the angular distributions are (relatively) insensitive to the choice of interatomic potential. The calculations show that the backwards-directedness of sputtered particle angular distributions may be completely explained by the anisotropy in the recoil flux. It is also demonstrated that the adoption of more realistic surface models, than the usual infinite target approximation does not lead to significant changes in the angular distribution of recoil-, momentum- and sputtered particle-fluxes.     

Energy and angular distributions of sputtered particles: A comparison between analytical theory and computer simulation results

Sputtering from a collision cascade, initiated by ion bombardment of a random medium, is investigated via a numerical solution scheme of the linear Boltzmann equation (BEST). Energy and angular distributions are calculated for several commonly used interaction cross sections. The results are in good agreement with available analytical solutions. In particular, recently obtained analytical results for the half space energy and angular distributions are confirmed and extended to more general cross sections.

A comparison with results obtained by the simulation code TRIM is undertaken. TRIM's energy distributions can be reproduced. It is however essential not only to use the same interaction potential but also to introduce the same cut off in the cross section as TRIM employs. TRIM'S angular distributions deviate from the BEST results. The origin of these deviations is discussed.     

Energy distributions of neutral atoms sputtered by very low energy heavy ions

Polycrystalline Cu was sputtered by normally incident, very low energy Ar⁺ ions (E₀ = 40–1000 eV). The kinetic energy (E) distributions of the neutral Cu atoms sputtered normally from the Cu surface were measured, using secondary neutral mass spectrometry. For values of E₀ above approximately 600 eV, the observed energy distributions agreed closely with the Thompson-Sigmund theory. For values of E₀ less than about 600 eV the distributions fell off faster than predicted by the Thompson-Sigmund theory, and the peak value of the distribution shifted to somewhat lower energies. Both these effects were exaggerated as E₀ was further lowered. The average kinetic energy of the sputtered neutral Cu atoms increased with increasing E₀. The rate of this increase was less at higher values of E₀.     

The angular distribution of sputtered silver atoms

Angular distributions of sputtered atoms have been determined for a Ag target under bombardment with 20 and 30 keV ²⁰Ne⁺, ⁴⁰Ar⁺, ⁸⁴Kr⁺ and ¹³²Xe⁺ ions both at normal and oblique angles of incidence. At normal ion incidence the distribution is symmet with respect to the target normal, while at oblique ion incidence the distribution is asymmetric in the plane containing the ion beam and the surface normal and symmetric in the transverse plane. Scanning electron microscopy of the sputtered surface shows the development of a high density array of cones in the bombarded area. The results are discussed from the viewpoint of sputtering from a very rough surface.     

Energy distributions of atoms sputtered from polycrystalline surfaces

A new formula is presented for the energy and angular distributions of atoms ejected from polycrystalline solids due to keV particle bombardment. The formula predicts that the peak position in the energy distribution decreases with increasing polar angle from the surface normal. It also predicts that the angular distribution is ∼cos θ for low energy particles and is ∼cos²θ as the energy of the particles increases.     

运用GEANT3模拟分析闪烁光纤辐照特性与光纤直径及射线入射角之关系

利用ＧＥＡＮＴ３系统模拟计算、分析了γ射线在闪烁光纤中的能量沉积与光纤直径的产主射线能量沉积的角分布特性。     

Neutron elastic scattering angular distribution in the resolved and unresolved resonance regions

We derive a simple relationship between observed total cross sections and elastic scattering angular distributions for neutron-induced reactions in the fast energy range by combining resonance theory and the optical model (OM). This relationship enables us to estimate the anisotropy in the scattering angular distribution when experimental total cross-section data are available. We apply this method to the angular distributions of ⁵⁸Ni and ⁵⁶Fe and compare with the evaluated values which are based on the experimental data. We also explore the method with ⁹⁰Zr for which the multi-level Breit-Wigner resonance parameters are given.     

CuAu合金溅射原子角分布的实验研究

荷能离子轰击固体复合材料表面时某种成分的择优发射现象,是人们很感兴趣的研究课题。这是因为,择优发射机制至今尚不清楚。同时,很多现代表面分析设备,诸如俄歇电子     

Ar离子轰击Ag靶的溅射角分布

本文描述了用溅射粒子捕集器和Rutherford背散射分析测定溅射粒子角分布的实验方法。给出了100keV Ar~+在入射角分别为0°、30°、50°和80°时轰击Ag靶的溅射角分布。角分布偏离余弦形状,有前倾趋势。溅射产额随入射角增大而迅速增加。由50keV Ar~+垂直入射Ag的溅射角分布计算出的总溅射产额为16.8±2.4~(atoms)/Ar~+。实验结果与理论值进行了比较,并作了定性分析。     

An impulsive collision model for the vibrational and rotational excitation of sputtered molecules

An impulsive collision model describing the vibrational, rotational and translational energy of sputtered diatomic molecules is presented. A pre-existing molecule at the surface undergoes a single collision with a subsurface particle and is consequently ejected from the solid. Repulsive potential interactions and an impulsive approximation of the collision determine energy transfer to both atoms of the molecule and thus the partition over internal and kinetic motion. Model calculations of the vibrational, rotational and kinetic energy distributions yield a good agreement with recent experimental data of sputtered diatomic sulfur molecules. Almost all of the qualitative features are reproduced by the model calculations.     

Angle and energy distributions of fission neutrons

Using the statistical model of the nucleus the angle distribution of fission neutrons is determined taking into account the anisotropy in the angle distribution of the fission fragments. The latter quantity is approximated by a simple expression of the form 1 + kcos² .It is assumed that the neutrons are emitted isotropically in the coordinate system in which the fragment is at rest.Using U²³⁸, a calculation is carried out to determine the values of P — the ratio of the intensity of fission neutrons emitted in the direction of the incident neutrons to that of neutrons emitted perpendicularly to the incident beam — at various energy values of the primary and secondary neutrons (in the region from 1 to 10 Mev). The mean value of P in fission in U²³⁸ by neutrons characteristic of a fission spectrum is found to be approximately 1.13. The energy spectra for fission neutrons at various primary-neutron energies are also obtained. The method of calculation can also be employed in investigations of the anisotropy of neutrons produced in fission of other nuclei.In conculations the authors wish to thank V. K. Sauleva for setting up the prograsm for the electronic computer.