Ions Of Different Masses Research Articles

Detection and registration of ion clots in laser time-of-flight mass spectrometers

A number of factors influencing the measurement errors of analytic signals detected with secondary electron multipliers (SEMs) and registered with fast ADCs are analyzed. Such signals are generated in laser time-of-flight mass spectrometry at the stage of ion detection and recording of mass spectra. In particular, the effect of statistical factors and sources of systematic errors during both measurements of isotope ratios and elemental analysis is considered. Such errors as the statistics of formation of ion clots, the limited range of ADC records, discrimination during detection of ions of different masses, and others are considered. It is shown that, without taking into account the features of operation of SEMs and ADCs, both the statistical and systematic errors of measuring isotope ratios may reach several percent. The proposed operating modes of the detector, with allowance for its features, the design of the recording system, and use of formulas for calculating and correcting errors, allow their reduction to ∼0.10–0.01%

Development of a high resolution isobar separator for study of exotic decays

A compact isobar spectrometer and separator, based on the multi-pass-time-of-flight (MTOF) principle, is being developed by the University radioactive ion beam (UNIRIB) Consortium. It consists of two coaxial, grid-free electrostatic mirrors with auxiliary injection, focusing and extraction elements. Ions of different mass are reflected multiple times between the mirrors and separated longitudinally. Using an electron beam impact ion source and N2 as a sample gas, a mass resolving power of 110,000 (FWHM) has been achieved. In the near future, MTOF will be coupled to the on-line isotope separator UNISOR (University Isotope Separator – Oak Ridge) at Holifield radioactive ion beam facility using electrostatic beam deceleration, a radiofrequency beam cooler and a fast buncher. It will serve as a high resolution mass separator with a Bradbury–Nielsen gate, providing isotopically pure samples of exotic species in the 100Sn region and later, of neutron rich nuclei, for use in decay studies.

Three-dimensional multispecies hybrid simulation of Titan's highly variable plasma environment

Abstract. The interaction between Titan's ionosphere and the Saturnian magnetospheric plasma flow has been studied by means of a three-dimensional (3-D) hybrid simulation code. In the hybrid model, the electrons form a mass-less, charge-neutralizing fluid, whereas a completely kinetic approach is retained to describe ion dynamics. The model includes up to three ionospheric and two magnetospheric ion species. The interaction gives rise to a pronounced magnetic draping pattern and an ionospheric tail that is highly asymmetric with respect to the direction of the convective electric field. Due to the dependence of the ion gyroradii on the ion mass, ions of different masses become spatially dispersed in the tail region. Therefore, Titan's ionospheric tail may be considered a mass-spectrometer, allowing to distinguish between ion species of different masses. The kinetic nature of this effect is emphasized by comparing the simulation with the results obtained from a simple analytical test-particle model of the pick-up process. Besides, the results clearly illustrate the necessity of taking into account the multi-species nature of the magnetospheric plasma flow in the vicinity of Titan. On the one hand, heavy magnetospheric particles, such as atomic Nitrogen or Oxygen, experience only a slight modification of their flow pattern. On the other hand, light ionospheric ions, e.g. atomic Hydrogen, are clearly deflected around the obstacle, yielding a widening of the magnetic draping pattern perpendicular to the flow direction. The simulation results clearly indicate that the nature of this interaction process, especially the formation of sharply pronounced plasma boundaries in the vicinity of Titan, is extremely sensitive to both the temperature of the magnetospheric ions and the orientation of Titan's dayside ionosphere with respect to the corotating magnetospheric plasma flow.

Light and heavy ion effects on damage clustering in GaAs quantum wells

Recent experiments have shown that ion irradiation can strongly affect charge carrier dynamics in GaAs quantum wells. The irradiation conditions are such that the ions penetrate deep beyond the active layer, showing that the effect is due to damage in the lattice. Moreover, ions of different mass and energy can lead to clearly different effects even after normalization with the nuclear deposited energy. Using molecular dynamics simulation of the damage production, we show that the experimentally observed effects on charge carrier lifetime correlate well with the production of large (more than 100 disordered atoms) damage clusters. Moreover, we show that 400keV Ne and 10MeV Ni produce very similar damage in the near-surface active regions, indicating that 500kV ion implanters are sufficient to achieve the desired modification effects.

Relative information content and top-down proteomics by mass spectrometry: utility of ion/ion proton-transfer reactions in electrospray-based approaches.

Computer simulations of electrospray ionization (ESI) and collision-induced dissociation (CID) experiments were employed to examine the informing power associated with "top-down" proteomics implemented with some commonly used mass analyzers, i.e., the quadrupole ion trap (QIT), the Fourier transform-ion cyclotron resonance mass spectrometer (FT-ICRMS), and the time-of-flight (TOF) mass spectrometer. Using a ratio of the separated (or resolved) peaks to the total number of predicted peaks as a measure of informing power, the ESI-MS simulation of a mixture of proteins showed that the FT-ICRMS exhibited the highest informing power among the three instruments being studied, with the QIT giving the lowest informing power, which was expected from the analysis of the "component capacity" of the three approaches. Also as expected on the basis of resolving elements per component, a dramatic increase in the informing power of the approach was obtained when ion/ion proton-transfer reactions were used to reduce the number of peaks and to minimize overlap between ions of different mass and charge but similar mass-to-charge ratio. With the assumptions made in this study, the informing power of the TOF + ion/ion approach rivaled or even exceeded that of the FT-ICRMS approach, despite significantly lower mass resolution. This result stemmed from both a reduction in the number of peaks and their dispersion over a much wider range of mass-to-charge ratios. Similar results were obtained from the CID simulation, where the informing power of different approaches was evaluated on the basis of the ratio of the number of ions for which a mass could be determined unambiguously to the total number of ions in the spectra.

Optimisation of analytical method for estrogen in surface water and primary risk assessment in South Creek

A very non-polar sorbent, polystyrene-divinyl-benzene (brand: biobeads supplied by BioRad, with 30∼50 mesh) was tested for its extraction efficiency of four target compounds, estrone, estradiol, ethynylestradiol and estriol, from larger volumes (8 l) of water samples. To achieve adequate sensitivity of instrumental analysis by GC/MS, an improved estrogen derivatisation method was developed. For the simultaneous determination of the four estrogens, 50 ?l BSTFA+1% TMCS and 50 ?l pyridine was used for the derivatisation. Ions of different masses, 342 for estrone and 425 for 17α-ethynylestradiol, were formed using this protocol. The residual derivatisation reagents and pyridine were completely removed under a stream of dry nitrogen. Using the optimised extraction and derivatisation protocol, estrogen levels in the South Creek in Sydney and the Emigrant Creek in North of New South Wales were analysed. The possible contribution of the discharges from wastewater treatment plant as a source of estrogens is discussed.

Modeling of damage generation mechanisms in silicon at energies below the displacement threshold

We have used molecular dynamics simulation techniques to study the generation of damage in Si within the low-energy deposition regime. We have demonstrated that energy transfers below the displacement threshold can produce a significant amount of damage, usually neglected in traditional radiation damage calculations. The formation of amorphous pockets agrees with the thermal spike concept of local melting. However, we have found that the order-disorder transition is not instantaneous, but it requires some time to reach the appropriate kinetic-potential energy redistribution for melting. The competition between the rate of this energy redistribution and the energy diffusion to the surrounding atoms determines the amount of damage generated by a given deposited energy. Our findings explain the diverse damage morphology produced by ions of different masses.

Laser induced formation of CsI ion clusters analyzed by delayed extraction time-of-flight mass spectrometry

(CsI)nCs+ (n = 1,2) cluster ion formation from polycrystalline CsI irradiated by pulsed-UV laser (337 nm) is analyzed by delayed extraction time-of-flight mass spectrometry technique. Measurements were performed for different laser intensities and for several delayed extraction times. Experimental data show that CsI laser ablation produces the emission of (CsI),Cs+ ions (n = 0, 1, 2), whose yields decrease exponentially with n and increase exponentially with the laser pulse energy. A quasi equilibrium evolution of the clusters is proposed to extract a parameter characteristic of the cluster recombination process. The delayed extraction method of initial velocity determination was improved to take into account collisions in the high density plasma close to the target. The new parameterization helps to describe the dynamics of secondary ions of different masses for laser irradiances above the ion desorption threshold in a collision regime. The initial velocity of the secondary ions [(CsI)nCs+ (n = 0, 1, 2)] as function of the laser irradiance was determined. The distance to the target when the free expansion process starts is reported as function of the secondary ions mass and of the laser irradiance. The collision regime's influence on the secondary ion dynamics is discussed.

Laser photodetachment mass spectrometry

We demonstrate that the technique of laser photodetachment spectroscopy on atomic negative ions can be used as a sensitivity enhancement tool in mass spectrometry, useful for suppressing both isotopic as well as molecular isobaric interferences. In the experiment a beam of negative ions and a laser beam are merged in a collinear geometry and the wavelength of the laser is tuned across the photodetachment threshold region. Due to the large differential Doppler shifts associated with the fast moving ions of different masses, it is possible to selectively detach ions of certain isotopes while leaving others unaffected. By choosing co-propagating laser and ion beams, the heavier isotopes of an element can be selectively detached, whereas counter propagating beams can be used to detach the lighter ones. In this paper we demonstrate the feasibility of the method in an experiment that was designed to selectively detach either 32S − or 34S − ions. The isotopic ratio of 34S/ 32S was enhanced by a factor of >50 over the natural value. This factor can be improved by using a laser that is better adapted to the measurement and by improving the vacuum conditions in order to further suppress the collisional background. The applicability of this technique to selectivity enhancement in measurements of the abundances of rare or ultra-rare isotopes is discussed.

Impact of ambient atmosphere on as-implanted amorphous insulating layers

Low energy ion implantation into SiO 2 causes a damaged near surface layer. The high number of broken bonds due to displaced Si and O atoms forms in the glassy network paths, which are open for diffusion and in which moisture from the ambient can be absorbed. Therefore chemical reactions of the implanted impurities with hydrogen and oxygen must be expected during subsequent annealing. Water absorption in heavy ion-damaged SiO 2 layers has been studied by hydrogen depth profiling using the nuclear reaction analysis. SiO 2 was implanted with ions of different mass (Si, Ge, Sn) and doses in the range 10 13–10 16 cm −2. H depth profiles were measured after storage under clean room conditions and after additional wet cleaning, as well as after annealing. At the surface and in the region of the implanted profile, the H concentration reaches 5–10 at.% after storage and increases during wet chemical cleaning up to 12 at.% for implantation doses ⩾1×10 14 cm −2.

On the mass dependence of transverse ion acceleration by broad-band extremely low frequency waves

Recent data from the Fast Auroral Snapshot Explorer (FAST) and other satellites indicate that broad-band extremely low frequency (BBELF) waves account for most of the transverse ion acceleration in the aurora. These waves tend to accelerate ions of different masses to approximately the same energy. We have shown previously that a downward parallel electric field is necessary in order to explain this result in terms of a cyclotron resonant acceleration process. In this paper we use triangular electric field distributions to investigate how strong and how extensive a field is necessary to equalize the energization of ions of different mass.

Cylindrical ion trap array with mass selection by variation in trap dimensions

A mass spectrometer array is described in which each array element is a cylindrical ion trap (CIT) within which an approximately quadrupolar, time-varying, field is established. The individual traps are of different sizes, so that when the array is operated with a fixed rf potential, ions of different masses (or mass ranges) are stored in each trap. By choosing the dimensions of each CIT element in the array, a multiple ion monitoring experiment can be performed. For example, in a two-element array with elements having internal radii of 5 and 4 mm, the smaller trap selects for m/z 91 and the larger for m/z 57, corresponding to characteristic aromatic and aliphatic hydrocarbon ions. Ion storage using both rf/dc (apex) isolation and the stored waveform inverse Fourier transform method is demonstrated.The array reduces the complexity of the electronics needed to operate the ion trap, which should make it suitable for use in a miniature mass spectrometer system.

Time-dependent angular and energy distributions of sputtered copper atoms

Time reference was introduced in the TRIM computer simulation code without changing the "event-driven" logic of the program. The code was applied to model the atomic collision cascades and sputtering of amorphous copper targets caused by bombardment of keV ions of different masses (Be, Ne, Ar, Cu, Xe, Au). Time-dependent characteristics of ion-induced processes such as mean number and energy of moving target atoms, number of collisions and vacancies (or) recoils created, sputtering yield, mean energy and angle of ejection of sputtered atoms were obtained, and their dependence on the ion/atom mass ratio is discussed. PACS No.: 79.20-m

Signal suppression in electrospray ionization Fourier transform mass spectrometry of multi-component samples

The high resolution, mass range and sensitivity of Fourier transform mass spectrometry (FTMS) suggest that it could be a valuable tool for the quantitative analysis of biomolecules. To determine the applicability of electrospray ionization combined with FTMS to the quantitation of biomolecules in multi-component samples, mixtures of varying compositions and concentrations of cytochrome c, angiotensin II, insulin and chicken egg white lysozyme were examined. The instrument used has an electrospray source with a hexapole trap to accumulate ions for injection into an ion cyclotron resonance mass analyzer. Linear responses for single component samples of angiotensin II and insulin were in the range 0.031-3 microM and those of both cytochrome c and lysozyme were between 0.031 and 1 microM. In examining various mixtures of the proteins with angiotensin II, it was found that the presence of the large molecules suppresses the signal of the smaller molecules. This is suggested to be a result of ion-ion interactions producing selective ion loss from either the hexapole trap or the ion cyclotron resonance mass analyzer trap. More massive, more highly charged ions can collisionally transfer large amounts of translational energy to smaller, less highly charged ions, ejecting the smaller ions from the trap. Mass discrimination effects resulting from the trapping voltage were also examined. It was found that relative signal intensities of ions of different masses depend on trapping voltage for externally produced ions. The effect is most significant for spectra including masses that differ by 30% or more. This suggests that for quantitation all samples and standards be run at a constant trapping potential.

Mass‐dependent effects in ion conic production: The role of parallel electric fields

Previous observational studies indicate that the energies of different ion species in ion conics produced by broad‐band extremely low frequency (BBELF) waves are nearly equal. In contrast, theoretical studies predict a definite preferential acceleration for heavy ions over lighter ions. We show that this discrepancy can be resolved if a downward parallel electric field is present in the heating region: for a sufficiently strong electric field ions of different masses acquire approximately the same energy in escaping the trapping region.

Glow Discharge Source Interfacing to Mass Analyzers: Theoretical and Practical Considerations

The fundamental requirements for the optimum mechanical interface between a glow discharge ion source and a mass spectrometer are described in this paper. Specifically, the properties of a typical glow discharge ion source are compared and contrasted to those of a typical inductively coupled plasma ion source. The critical parameters and theoretical considerations of glow discharge and inductively coupled plasma ion source interfaces are reviewed, and the results of experiments using both quadrupole and time-of-flight mass spectrometers with a glow discharge source are presented. The experimental results clarify several important problems in the glow discharge ion sampling process. Our findings indicate that a shock wave structure does not occur in the supersonic expansion of the glow discharge ion source. Ions of different masses have similar initial kinetic energies in the glow discharge; thus, the angle of the skimmer cone is not a critical parameter for efficient ion beam extraction. Another consquence is that space charge effects in glow discharge ion sources repel heavy ions farther off axis than light ions. Thus, there are distinct and fundamental differences between glow discharge and inductively coupled plasma ion sources which are relevant to both ion sampling and ion extraction processes.

Quadrupole secondary ion mass spectrometer for simultaneous detection of positive and negative ions

The purpose of this study was to design a quadrupole secondary ion mass spectrometer for simultaneous detection of both positive and negative ions of different mass. An original setup based on a quadrupole electrostatic deflector configuration that allows energy and spatial separation of all types of secondary ions was proposed. The device was modeled using the SIMION 3D program before building the prototype. Trajectory and acceptance calculations were provided. Positive and negative secondary ion mass spectra for molybdenum test samples were obtained. Copyright © 1999 John Wiley & Sons Ltd.

Acceleration of ionospheric outflowing ions

The roles of various physical mechanisms in accelerating ionospheric ions upward along the magnetic field lines and their contributions to the total outflow of ionospheric ions of different masses into the magnetosphere, are summarised. The outflow during substorms and storms is discussed in some detail.

Transient Diffusion Effects of Sb and B In Si Induced by Medium- and High-Energy Implants of Si+ and As+ Ions

ABSTRACTIn this work we investigate the influence of defects injected by ions of different mass and energy on the diffusion of B and Sb markers in bulk Si. MeV (Si or As) ions induce Sb transient enhanced diffusion, whose amount increases with increasing the near-surface vacancy supersaturation generated by the knock-on recoil mechanism. The enhancement effect lasts less than 2 h at 800 °C and less than 10 min at 900 °C. At higher (1000 °C) annealing temperature it appears that the influence of extra-interstitials introduced by the implants comes into play, inducing a retardation in Sb diffusion which is larger for the higher close implant. The effect of vacancy supersaturation observed in medium-energy implanted samples is considerably weaker than the one found in high-energy implanted ones. In the case of B marker high-energy implantation induces moderate enhanced diffusion, much smaller than the one observed -after medium-energy implants.

Residual stresses and ion implantation effects in Cr thin films

The evolution of intrinsic residual stresses in sputtered Cr thin films with substrate bias and post-deposition ion irradiation is investigated. The relaxation of tensile stresses and build up of compressive stresses with increasing ion irradiation dose is studied using ions of different masses and energies such as 110 keV Ar, 33 keV C and 330 keV Xe. The stress evolution is related to the corresponding microstructural changes in the films. The changes in the residual stress during ion irradiation are explained by considering the manner in which the interatomic distances and forces change during irradiation, and the generation of defects during irradiation.