High-intensity Si cluster ion emission from a silicon target bombarded with large Ar cluster ions

Secondary ions emitted from Si targets were measured with a quadrupole mass spectrometer under large Ar cluster and monomer ion bombardment. Incident ion beams with energies from 7.5 to 25 keV were used and the mean size of the Ar cluster ion was about 1000 atoms/cluster. Si_n⁺ ions with n values up to n = 8 were detected under Ar cluster ion bombardment, whereas Si cluster ions were scarcely detected under Ar monomer ion bombardment. These cluster ion yields showed the power law dependence on the cluster size.     

SIMS of silicon bombarded with Sb m + cluster ions

The emission of Si _n ⁺ (n = 1–11) cluster ions and Si _n X _m ⁺ (X stands for B or Sb) polyatomic ions when bombarding a single silicon crystal with Sb _m ⁺ (m = 1–4) cluster ions with energies E ₀ = 3–12 keV is studied. Considerable nonadditive enhancement of the yield of Si _n ⁺ cluster ions and most polyatomic ions is observed when the number of atoms in the bombarding cluster ions is increased. The sensitivity enhancement factor for detecting boron impurities is as high as 50 when the cluster-SIMS-molecule technique is applied.     

Secondary ion emission from Si bombarded with large Ar cluster ions under UHV conditions

Si was bombarded with size-selected 40 keV Ar cluster ions and positive secondary ions were measured using the time-of-flight technique under high and ultra-high vacuum (HV and UHV respectively) conditions. Si⁺ ions were main species detected under the incidence of 40 keV Ar cluster ions, and the yields of Si cluster ions such as Si₄⁺ were also extremely high under both conditions. On the other hand, oxidized secondary ions such as SiO⁺ were detected with high intensity only under the HV condition. The yield ratios of oxidized ions decreased in UHV to less than 1% of their values in HV. The effect of residual gas pressure on Si cluster ion yields is relatively low compared to oxidized ions, and the UHV condition is required to obtain accurate secondary ion yields.     

Continuous electron energy spectra ejected from solid carbon targets bombarded with light and heavy ions

Energy distributions of electrons were measured under an observation angle of 42.3° by bombarding thin carbon foils with protons of 0.5 to 2.5 MeV and with Neon of 10 MeV energies. Comparison of the experimental results with binary-encounter-approximation calculations, taking into account the electron energy loss in the solid, show that the spectra from proton bombardment can be described by this model.     

Surface properties of germanium bombarded by nitrogen ions

Results are given for ions of energy 1800 eV. Measurements have been made of the rate of surface recombination and of the surface conductivity for specimens of specific resistance 10 and 40 ohmcm. The results are interpreted in terms of donor level production, in agreement with earlier work. Trapping curves derived from the surface conductivity are used to deduce the position of the donor levels relative to the middle of the forbidden band.     

Sputter yields in diamond bombarded by ultra low energy ions

Artificial diamond is an ideal material for high power, high voltage electronic devices, and for engineering use in extreme environments. Diamond process development requires parallel development in characterization techniques such as ultra low energy SIMS (uleSIMS), especially in the ability to depth profile for impurities and dopants at high depth resolution.As a contribution to the background knowledge required, we have measured the sputter yields of single crystal high pressure high temperature (HPHT) diamond using O₂⁺, Cs⁺ and Ar⁺ primary ions in the energy range 300 eV to 2 keV. We compare these with yields for silicon and GaAs. We show that the erosion rates with oxygen are ∼10 times what would be expected from ballistic processes and essentially energy independent in the measured range. This result agrees with the anomalously high sputter yield observed in the ion etching context. Conversely, positive ion yields for elements such as boron are very low in comparison with silicon. This points to a reactive ion etching process liberating CO or CO₂ rather than sputtering as the principal erosion process.This is both problematic and beneficial for SIMS analysis. Oxygen can be used to reach buried structures in diamond efficiently, and the effects of the near-normal incidence beam are planarizing as they are in silicon. Conversely, since positive ion yields are low, alternative probes or strategies must be found for high sensitivity profiling of electropositive elements.     

Secondary-ion emission from silicon bombarded with atomic and molecular noble-gas ions

The emission of Si⁺ from a clean silicon surface has been studied for bombardment with various atomic and molecular noble gas ions at energies between 1.5 and 30 keV. It was found that the degree of ionization of Si⁺ depends strongly (l?inearly) on the projectile energy but only weakly on the projectile mass. These results suggest that the degree of ionization is heavily affected by the (dynamic) perturbation of the bulk properties of the bombarded area which increases with increasing nuclear energy deposition.     

Emission of radiation by charged particles reflected from solid surfaces

It is predicted that charged particles reflected from solid surfaces could emit radiation due to the change in their direction of motion upon reflection. The theoretical spectrum of this radiation is obtained for specular reflection. The general concept of ‘transition radiation’ is reconsidered to include this new effect which is found to dominate for low-energy, non-penetrating electrons and for high-energy electrons at grazing incidence.     

Emission of circularly polarized recombination radiation from p-doped GaAsP bombarded with longitudinally polarized electrons

We report measurements of circularly polarized recombination radiation from a GaAs_0.6P_0.4 crystal bombarded with longitudinally spin polarized electrons of 10 eV energy. Qualitatively, this process can be considered as the inverse of the photoemission utilized in GaAs and GaAsP polarized-electron sources. The measured degree of circular polarization is 0.29%±0.06% if the crystal is cooled with liquid nitrogen and the incident electrons are 15%±3% polarized.     

Investigation by ellipsometry of the damage in GaAs bombarded with low-energy Ar ions

The crystalline-amorphous transition in GaAs induced by Ar ions (energy 1–3 keV) has been investigated using single-wavelength ellipsometry. The experiments have been performed in-situ at room temperature. Ion damage straggling, amorphization threshold and critical energy density have been derived by means of a simple analytical model for the growth of the amorphous layer. This model is discussed and the corresponding calculations are found to be in satisfactory agreement with experimental data.     

Frozen methanol bombarded by energetic particles: Relevance to solid state astrochemistry

Methanol is an important precursor of many complex prebiotic species and is found abundantly, in solid phase, in several astrophysical environments, such as comets and protostars. These environments are, in general, subjected to some form of ionizing particles as cosmic rays, solar wind particles and/or photons. To simulate physico chemical effects of cosmic rays on methanol and to investigate in particular its fragmentation and cluster emission from the solid phase, condensed methanol at 55 K was bombarded with ∼65 MeV heavy ions constituted by ²⁵²Cf fission fragments. Mass spectra of positive desorbed ions were obtained using a time-of-flight Plasma Desorption Mass Spectrometry (PDMS-TOF), giving information on the fragmentation pattern and abundance of the ionic species released from the frozen sample surface. Since and CH₃O⁺ are the most abundant species detected, the hydrogenation and de-hydrogenation of methanol result to be the predominant ionic processes in the methanol surface. Furthermore, the hydrogenation yields emission of the (CH₃OH)_nCH₃ cluster series, while the CH₃O⁺ species does not attach to methanol molecules. The production of other cluster ion series, some of them with mass/charge up to 300 u/e was also analyzed by PDMS.     

Distributions of ions in a cluster plasma created by a laser pulse

Energy and charge distributions of ions are calculated for a cluster beam irradiated by a high-power ultrashort laser pulse. It is shown that the self-consistent field of a cluster ionized by the laser beam strongly affects the characteristics of the ion distributions obtained after the cluster explodes. The mean concentration of atoms bound into clusters in a beam, the cluster size distribution, and the focal-spot diameter are found to have a weak effect on both energy and charge distributions of the ions, whereas the energy spectrum of the produced ions is determined by the mean cluster size.     

Sputtering yields of PMMA films bombarded by keV C60 ions

A quartz crystal microbalance (QCM) has been used to determine total-mass sputtering yields of PMMA films by 1-16 keV C₆₀^+,2+ ion beams. Quantitative sputtering yields for PMMA are presented as mass loss per incident ion Y_m. Mass-lost rate QCM data show that a 13 keV C₆₀ cluster leads to emission equivalent to 800 PMMA molecules per ion. The power law obtained for the increase in sputtering yield with primary ion energy is in good agreement those predicted by “thermal spike” regime and MD models, when crater sizes are used to estimate sputtering.     

Radiation from silver films bombarded by low-energy electrons

Emission spectra from Ag films irradiated by low energy electrons (20–1500 eV) have been measured, and the results compared with theory. For relatively smooth films, two peaks in the spectra are resolved. One at 3.73 eV, the volume plasmon energy, is attributed to transition radiation and/or bremsstrahlung. The second, at about 3.60 eV, is very sensitive to surface roughness in both position and magnitude and is produced by roughness-coupled radiation from surface plasmons. For rough films, the roughness-coupled radiation dominates the emission. In addition to spectral shapes, the polarization of the radiation and its intensity as a function of electron energy were measured. The experimental results are compared with new calculations of roughness-coupled emission which account for most of our observations. They indicate that high wavevector roughness components play the dominant role in the emission process.     

Experimental investigation of the energy distribution of sputtered excited target atoms bombarded by medium-energy ions

In this paper we experimentally investigate the parameter dependence of a model energy distribution of excited potassium atoms, knocked out by bombarding a KCl monocrystal with normally incident Ar⁺ ions, on the ion energy and the partial oxygen pressure in the chamber. On the basis of the obtained results a model of the energy distribution is proposed that corresponds to the kinetic formation mechanism for the excited atoms during the sputtering of the target.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 9–12, March, 1985.     

Short-laser-pulse-driven emission of energetic ions into a solid target from a surface layer spalled by a laser prepulse

An efficient emission of picosecond bunches of energetic protons and carbon ions from a thin layer spalled from a organic solid by a laser prepulse is demonstrated numerically. We combine the molecular dynamics technique and multi-component collisional particle-in-cell method with plasma ionization to simulate the laser spallation and ejection of a thin (∼20–30 nm) solid layer from an organic target and its further interaction with an intense femtosecond laser pulse. In spite of its small thickness, a layer produced by laser spallation efficiently absorbs ultrashort laser pulses with the generation of hot electrons that convert their energy to ion energy. The efficiency of the conversion of the laser energy to ions can be as high as 20%, and 10% to MeV ions. A transient electrostatic field created between the layer and surface of the target is up to 10 GV/cm. Received: 13 March 2001 / Accepted: 20 March 2001 / Published online: 20 June 2001     

Neutralization of mass-selected cluster ions by charge transfer reactions

Mass-separated beams of clusters with a single, well-defined number of atoms or molecules are indispensable for studies of cluster properties. This paper presents a technique with the potential to generate such a beam which contains neutral clusters of one size only. For this purpose mass-selected cluster ions have been neutralized by charge transfer reactions in metal and sulphur vapors. Relative charge exchange cross sections were measured for different cluster sizes. They reveal pronounced variations of the electronic structure of these particles. Thus, the study of charge transfer processes is introduced as a method to probe the positions of electronic energy levels in neutral clusters.