Ion Emission Yield Research Articles

Ion-induced electron and hydrogen ions emission of lead-bismuth silicate glass by ToF

A micro-channel Plate (MCP) is a continuous photo-electron multiplier, which has been widely used in the field of particle detectors and low-light night vision imaging devices. The electrons produced by particles collision from the incident end of MCP constitute the useful signal, while the electrons and negative ions produced by collision of ions formed by ionizing gas molecules are considered noise. To reduce the noise from ion collisions, it is important to identify the electron and negative ion emissions caused by collision of unexpected ion. In this paper, the electron and hydrogen ion emissions caused by 1.5MeV Au2+ were analyzed for the cases of acid-etched, alkali-etched, and hydrogen reduced lead-bismuth silicate glass (LBSG). The Time of Flight (ToF) method was used to detect the electron and hydrogen ion emission yields of LBSG. Hydrogen reduction significantly increases the yield of ion-induced electron and negative ions, and the alkali treatment gets the higher yield compared to acid treatment. It is proved that the ToF method is feasible to detect the ion-induced negative particles emission and would be more effectively if the accumulation of positive charges is avoided. The results are valuable not only for noise analysis and manufacturing parameters optimization of low-noise and high-gain MCP, but also as a reference for preparation of new-type micro-channels and investigation on the electron emission properties of glass for space.

Charging of dielectrics under ion irradiation

We present an experimental study of charging of dielectrics and ferroelectrics under Ar+ ion beam irradiation. Complex measurements of ion emission yield, accumulated charges and a surface charging potential have been carried out. It has been found an effective charging of dielectrics to high positive potentials closed to the potential of an ion gun. The experimental data show that the ion emission coefficient from charged dielectrics may differ significantly from the one from uncharged dielectrics and conductive samples. The specific features of ion charging of ferroelectrics are interpreted by taking into account the polarization switching of ferroelectric crystals.

Effects of anode geometry on forward wide-angle neon ion emissions in 3.5 kJ plasma focus device by novel mega-size panorama polycarbonate image detectors

Forward wide-angle neon ion emissions in a 3.5 kJ plasma focus device (PFD) were studied using 5 different anode top geometries; hollow-end cylinder, solid triangle, solid hemisphere, hollow-end cone and flat-end cone. Position-sensitive mega-size panorama polycarbonate ion image detectors (MS-PCID) developed by dual-cell circular mega-size electrochemical etching (MS-ECE) systems were applied for processesing wide-angle neon ion images on MS-PCIDs exposed on the PFD cylinder top base under a single pinch shot. The images can be simply observed, analyzed and relatively quantified in terms of ion emission angular distributions even by the unaided eyes. By analysis of the forward neon ion emission images, the ion emission yields, ion emission angular distributions, iso-fluence ion contours and solid angles of ion emissions in 4π PFD space were determined. The neon ion emission yields on the PFD cylinder top base are in an increasing order ~2.1×109, ~2.2 ×109, ~2.8×109, ~2.9×109, and ~3.5×109 neon ions/shot for the 5 stated anode top geometries respectively. The panorama neon ion images as diagnosed even by the unaided eyes demonstrate the lowest and highest ion yields from the hollow-end cylinder and flat-end cone anode tops respectively. Relative dynamic qualitative neon ion spectrometry was made by the unaided eyes demonstrating relative neon ion energy as they appear. The study also demonstrates the unique power of the MS-PCID/MS-ECE imaging system as an advanced state-of-the-art ion imaging method for wide-angle dynamic parametric studies in PFD space and other ion study applications.

25aZB-9 炭素クラスターイオン照射による2次イオン放出(放射線物理(クラスター・2次粒子放出),領域1,原子・分子,量子エレクトロニクス,放射線物理)

25aZB-9 炭素クラスターイオン照射による2次イオン放出(放射線物理(クラスター・2次粒子放出),領域1,原子・分子,量子エレクトロニクス,放射線物理)

Effect of space charge on the negative oxygen flux during reactive sputtering

Negative ions often play a distinctive role in the phase formation during reactive sputter deposition. The path of these high energetic ions is often assumed to be straight. In this paper, it is shown that in the context of reactive magnetron sputtering space charge effects are decisive for the energetic negative ion trajectories. To investigate the effect of space charge spreading, reactive magnetron sputter experiments were performed in compound mode with target materials that are expected to have a high secondary ion emission yield (MgO and CeO2). By the combination of energy flux measurements, and simulations, a quantitative value for the negative oxygen ion yield can be derived.

Cluster size and velocity dependences of sputtering and secondary ion emission under gold cluster impact

Sputtering and ion emission rates have been measured from CsI and gold targets under the impact of Au n + ( n = 1–9) clusters at energies between 30 and 350 keV/atom. The two materials have similar behaviors in regard to the variations of the sputtering and anion emission yields with energy and cluster size. The sputtering and anion emission yields increase nonlinearly with the projectile size. The maximum anion yields are found at lower energies than the maximum sputtering yields which themselves occur substantially below the maximum energy losses. The variations with energy of the atomic ion yields differ from those of the cluster ion yields. The experimental results are in agreement with an ion emission from linear collision cascades and spike collisions, the relative contribution of these two processes depending on the size of the cluster projectile and of the emitted ion. In addition they show that the ion emission yield enhancements under cluster impact result from a more effective sputtering mechanism and not from an enhanced ionization of the ejected species.

Lipid mapping in human dystrophic muscle by cluster-time-of-flight secondary ion mass spectrometry imaging

Human striated muscle samples, from male control and Duchenne muscular dystrophy-affected children, were subjected to cluster-time-of-flight secondary ion mass spectrometry (cluster-ToF-SIMS) imaging using a 25 keV Bi(3)(+) liquid metal ion gun under static SIMS conditions. Spectra and ion density maps, or secondary ion images, were acquired in both positive and negative ion mode over several areas of 500 x 500 microm(2) (image resolution, 256 x 256 pixels). Characteristic distributions of various lipids were observed. Vitamin E and phosphatidylinositols were found to concentrate within the cells, whereas intact phosphocholines accumulated over the most damaged areas of the dystrophic muscles, together with cholesterol and sphingomyelin species. Fatty acyl chain composition varied depending on the region, allowing estimation of the local damage extent.

Electron-stimulated desorption of lithium ions from lithium halide thin films

Electron-stimulated desorption of positive lithium ions from thin layers of lithium halides deposited onto Si(1 1 1) are investigated by the time-of-flight technique. The determined values of isotope effect of the lithium ( 6Li +/ 7Li +) are 1.60 ± 0.04, 1.466 ± 0.007, 1.282 ± 0.004, 1.36 ± 0.01 and 1.33 ± 0.01 for LiH, LiF, LiCl, LiBr and LiI, respectively. The observed most probable kinetic energies of 7Li + are 1.0, 1.9, 1.1, 0.9 and 0.9 eV for LiH, LiF, LiCl, LiBr and LiI, respectively, and seem to be independent of the halide component mass. The values of lithium ion emission yield, lithium kinetic energy and lithium isotope effect suggest that the lattice relaxation is only important in the lithium ion desorption process from the LiH system. In view of possible mechanisms and processes involved into lithium ion desorption the obtained results indicate that for LiH, LiCl, LiBr and LiI the ions desorb in a rather classical way. However, for LiF, ion desorption has a more quantum character and the modified wave packet squeezing model has to be taken into account.

A comparison of the electron‐stimulated desorption of positive ions from NaCl‐type alkali chloride thin films

AbstractElectron‐stimulated desorption of positive ions from thin layers of alkali chlorides deposited onto Si(111) are investigated by the time‐of‐flight (TOF) technique. All the experiments have been performed under the same experimental conditions, using very low electron current densities for which the obtained data are not distorted by the charging‐up effect, which in consequence allows a direct comparison of the relative ion yields, the kinetic‐energy distributions of emitted chlorine and alkali ions, and their isotope effects. The determined isotope effect of the chlorine (35Cl+/37Cl+) desorption yield appears to be independent of the alkali component mass and its values are 1.21 ± 0.02, 1.297 ± 0.005, 1.23 ± 0.02, and 1.24 ± 0.05 for LiCl, NaCl, KCl, and RbCl, respectively. On the other hand, the chlorine ion emission yields and average kinetic energies of the ions increase with increasing mass of the alkali component, which suggests that the lattice relaxation processes influence the desorption process. The most probable kinetic energies of 35Cl+ are 0.7, 1.4, 1.7, and 2.3 eV for LiCl, NaCl, KCl, and RbCl, respectively. The observed isotope effect for alkali ions decreases somewhat with increasing ion mass. The respective values are 1.282 ± 0.004, 1.04 ± 0.02, and 1.07 ± 0.02 for 6Li+/7Li+, 39K+/41K+, and 85Rb+/87Rb+. The alkali ion emission yield tends at first to increase with mass, reaching a maximum for potassium, but then for rubidium the yield drops to the value almost the same as for lithium. The desorption yields of alkali ions appear to be correlated with their most probable kinetic energies, which are 1.4, 1.1, 1.8, and 1.5 eV for 7Li+, 23Na+, 39K+, and 85Rb+, respectively. The obtained results and the role of the different parameters are discussed in view of possible mechanisms and processes involved in chlorine ion desorption. Copyright © 2006 John Wiley & Sons, Ltd.

Lipid imaging by gold cluster time-of-flight secondary ion mass spectrometry: application to Duchenne muscular dystrophy

Imaging with time-of-flight secondary ion mass spectrometry (TOF-SIMS) has expanded very rapidly with the development of gold cluster ion sources (Au(3+)). It is now possible to acquire ion density maps (ion images) on a tissue section without any treatment and with a lateral resolution of few micrometers. In this article, we have taken advantage of this technique to study the degeneration/regeneration process in muscles of a Duchenne muscular dystrophy model mouse. Specific distribution of different lipid classes (fatty acids, triglycerides, phospholipids, tocopherol, coenzyme Q9, and cholesterol) allows us to distinguish three different regions on a mouse leg section: one is destroyed, another is degenerating (oxidative stress and deregulation of the phosphoinositol cycle), and the last one is stable. TOF-SIMS imaging shows the ability to localize directly on a tissue section a great number of lipid compounds that reflect the state of the cellular metabolism.

The Aun cluster probe in secondary ion mass spectrometry: influence of the projectile size and energy on the desorption/ionization rate from biomolecular solids

A Au-Si liquid metal ion source which produces Au(n) clusters over a large range of sizes was used to study the dependence of both the molecular ion desorption yield and the damage cross-section on the size (n = 1 to 400) and on the kinetic energy (E = 10 to 500 keV) of the clusters used to bombard bioorganic surfaces. Three pure peptides with molecular masses between 750 and 1200 Da were used without matrix. [M+H](+) and [M+cation](+) ion emission yields were enhanced by as much as three orders of magnitude when bombarding with Au(400) (4+) instead of monatomic Au(+), yet very little damage was induced in the samples. A 100-fold increase in the molecular ion yield was observed when the incident energy of Au(9) (+) was varied from 10 to 180 keV. Values of emission yields and damage cross-sections are presented as a function of cluster size and energy. The possibility to adjust both cluster size and energy, depending on the application, makes the analysis of biomolecules by secondary ion mass spectrometry an extremely powerful and flexible technique, particularly when combined with orthogonal time-of-flight mass spectrometry that then allows fast measurements using small primary ion beam currents.

Role of laser-pulse duration in the neutron yield of deuterium cluster targets

We present an experimental and computational study of the ion and fusion neutron yields from explosions of deuterium clusters irradiated with 100-TW laser pulses. We find that the cluster explosion energy and resultant fusion yield are sensitive to the laser pulse rise time as determined by the pulse duration for a fixed envelope shape. Our experimental observations are consistent with the results of particle simulations of the laser-cluster interaction which show that the explosion energies of the clusters are determined by a single parameter: the ratio of the cluster ionization time to its intrinsic expansion time. This competition of time scales sets a fundamental constraint on the ion emission and resultant neutron yield performance of these targets as a function of laser-pulse duration.

Studies of an [formula omitted] surface by low-energy ion scattering

A single-crystalline Fe 3 O 4 (1 1 1) surface has been investigated by means of a low-energy ion spectroscopy (LEIS) technique with a Ne + and Ar + ion beam in the temperature range of 85– 300 K . The LEIS results were compared to those on the (0 0 1) surface. The ion-surface collision on the triangular-shaped surface channels differs from that on the squared-shaped one by a less enhancement of the Ne +–Fe peak-intensity at 90 K , an existence of additional peak around 150 K attributed to positive-charged recoil-oxygen ions from the double Ne–O collisions, a larger enhancement of the Fe recoil signal and a specific characteristic of the azimuthal-angle distribution under Ar + ion bombardments. The large influence of the surface semi-channels on the ion emission yield was explained as due to the screening action of the neighbouring Fe ions.

Fractional ionization in plasmas produced by pulsed laser ablation

A pulsed infrared laser (Q-switched Nd:Yag) is employed to irradiate different metal targets having atomic number from Z =13 up to Z =82. The high laser fluence deposited on the metals, of the order of 100 v J/cm, produces high ablation yield and a plasma generation at the target surface. The emitted species are neutral and ionized atoms. Both components have been investigated in terms of yield emission, time-of-flight measurements and angular distribution. Results indicate that the main emission occurs mainly along the normal to the target surface, that the etching, at high fluence, is of the order of 10 v atoms/ pulse, that the atoms velocities are of the order of 10 v m/s, that the maximum ion energies are of the order of keV. During the laser irradiation, expanding and non-equilibrium plasma is produced in front of the target. The plasma has a fraction ionization depending by the metal species and generally within 10% and 80%. The plasma'temperature, at high fluence, can be theoretically calculated and reaches about 10 v K. The fractional ionization of the plasma, experimentally measured, has been investigated as a function of the laser fluence and of the energy binding of the target molecules. The ion emission yield is presented and discussed in view of the possibility to realize a laser ion source for ion accelerators.

Low energy Cs+ and Cl− ion implantation into Si — SIMS investigations

The measurements of intensity of secondary caesium, as well as chlorine ion peaks, as a function of time of irradiation were made for the Si samples using a secondary ion mass spectrometer (SIMS). The results of such measurements enable us to study the effects of variation of secondary ion emission yield during the increasing dose of irradiation of the samples. The information about saturation effects during the implantation may also be obtained. The results of measurements were compared with the computer simulation data.

Secondary charged particles emitted from non-metallic surfaces under low-energy ion impact

The secondary electron emission yields, γ −, and the secondary positive ion emission yields, γ +, from various non-metallic (perovskite type) targets induced by low-energy ion impact have been measured under ultra-high vacuum (∼10 −11 Torr) conditions. It has been found that the observed γ − from the non-metallic surfaces is proportional to the electronic stopping power over the whole impact energy range investigated. But the proportional coefficients in γ − are found to be 2–3 times larger than those for metal targets. We have observed, for the first time, that γ − strongly depends on the incident ion beam flux and becomes zero above a critical ion flux for some targets. We have also found that the observed γ + from non-metallic surfaces under Ar + ion impact is far large compared with the calculated results and, unexpectedly, is proportional to the electronic stopping power but not to the nuclear stopping power. Furthermore, it is shown that, under high incident ion fluxes, these emitted ions have large kinetic energy, almost comparable to the incident ion energy, which can be due to local charge-accumulation formed through the interactions with the incident ions on the non-metallic surfaces.

In situ characterization of ultra-thin palladium deposits on α- and γ-alumina

We have characterized ultra-thin palladium films deposited at 300 K and 600 K onto both α- and γ-alumina surfaces, by using secondary ion mass spectrometry in static mode (SSIMS). The early stages of growth were investigated by analysing the ion intensity ratios Pd + 2/Pd + and PdAlO +/AlO + typical of metal deposit and interface, respectively. On stoichiometric surfaces ( α-alumina), deposition of palladium results in a weak Pd–Al bonding with nucleation of small 3D clusters. On non-stoichiometric surfaces ( γ-alumina), monolayers or flat islands grow with the formation of Pd–Al and Pd–O bonds. The variation of ion intensities monitored during metal deposition in the adsorption, clustering and growth regimes points out the influence of morphological and electronic parameters on the ion emission yields. The variation of the local work function value during palladium deposition has been estimated for the metal and the substrate. For palladium clusters in the 0.1–0.3 nm thickness range, the work function remains at a constant value on the two alumina surfaces – it is larger on α-alumina (6.5 eV) than on γ-alumina (6.3 eV).

The effects of surface ripples on sputtering erosion rates and secondary ion emission yields

The rate of erosion by non-normal incidence ion bombardment of a sinusoidally rippled surface is calculated analytically for an arbitrary dependence of the sputtering yield on the angle of ion incidence and spatial derivatives of the surface gradient as a function of the ratio of the ripple amplitude to wavelength. It is shown that, relative to the value for a flat surface, the erosion rate first increases and then decreases as this ratio increases, but before this decrease can occur, interpeak shadowing of the incident ion flux changes the ripple habit to sawtooth form and the erosion rate reaches a steady-state value. The influence of this variation on the sputtered atom yield and, therefore, on secondary ion yield is also evaluated and shown to compare favorably with experimental studies of the behavior of this parameter.

Electron-exchange mechanisms of the secondary ion emission of metals and some incompatible experimental data

Two electron-exchange theories of secondary ion emission are known. In the first one the ionization of the ejected atom occurs as a result of electron resonant tunneling through the potential barrier separating an atom and a metal. In the second the ionization occurs by the action of strong time-dependent perturbation due to the wave function of an atom and metal overlapping. Both theories predict different dependences that can be verified by experiments. Experimental data concerning the investigation of the secondary ion emission of metals have been analyzed to show (i) the form of the dependence of the probability of secondary particle ionization on its energy — it has been shown that this agrees with the first theory but does not agree with the second one; (ii) the dependence of the secondary ion emission yield on the metal work function — it has been found that this dependence can be described as incompletely by the second theory as by the first one united with the known thermodynamic non-equilibrium theory of Saha-Langmuir-Dobretsov.

High desorption—ionization yields of large biomolecules induced by fast C 60 projectiles

C 60 molecules accelerated to MeV energies (20 MeV) have been used to induce the desorption-ionization of large biomolecules from solid samples. For a sample consisting of trypsin molecules, the secondary molecular ion emission yield is about two orders of magnitude larger than with MeV atomic ions. This is a consequence of the very high energy density deposited in solids by 20 MeV C 60 projectiles that gives rise to a large amount of matter ejected after each impact. Although time-of-flight mass spectra can be recorded within a few seconds, it is more the acquisition of knowledge on mechanistic aspects, in comparison with other particle-induced desorption methods, which is the objective of obtaining these first results with energetic fullerenes.