Mass Analysis of Ions

Mass Analysis of Ions  [c.175]

The simplest example of this type of instmment is the triple quadmpole ms (27), in which and 2 used for mass analysis of the precursor and product ions, respectively, and 2 is a rf-only quadmpole coUision cell. The maximum possible energy uptake during coUisional activation,  [c.542]

Isotope shifts for most elements are small in comparison with the bandwidth of the pulsed lasers used in resonance ionization experiments, and thus all the isotopes of the analyte will be essentially resonant with the laser. In this case, isotopic analysis is achieved with a mass spectrometer. Time-of flight mass spectrometers are especially well-suited for isotopic analysis of ions produced by pulsed resonance ionization lasers, because all the ions are detected on each pulse.  [c.135]

The surface is bombarded with a stream of inert gas ions of energy, Eo, and the sputtered target secondary ions of energy, E, are monitored, rather than the backscattered primary beam ions. Mass analysis of the secondary ions is carried out. The intensity and the energy are also determined, Each element has a characteristic value of E/ Eq. This allows the elemental analysis of the surface.  [c.518]

When subjected to an electron bombardment whose energy level is much higher than that of hydrocarbon covalent bonds (about 10 eV), a molecule of mass A/loses an electron and forms the molecular ion, the bonds break and produce an entirely new series of ions or fragments . Taken together, the fragments relative intensities constitute a constant for the molecule and can serve to identify it this is the basis of qualitative analysis.  [c.48]

These equations indicate that the energy of the scattered ions is sensitive to the mass of the scattering atom s in the surface. By scanning the energy of the scattered ions, one obtains a kind of mass spectrometric analysis of the surface composition. Figure VIII-12 shows an example of such a spectrum. Neutral, that is, molecular, as well as ion beams may be used, although for the former a velocity selector is now needed to define ,.  [c.309]

With the exception of the scanning probe microscopies, most surface analysis teclmiques involve scattering of one type or another, as illustrated in figure A1.7.11. A particle is incident onto a surface, and its interaction with the surface either causes a change to the particles energy and/or trajectory, or the interaction induces the emission of a secondary particle(s). The particles that interact with the surface can be electrons, ions, photons or even heat. An analysis of the mass, energy and/or trajectory of the emitted particles, or the dependence of the emitted particle yield on a property of the incident particles, is used to infer infomiation about the surface. Although these probes are indirect, they do provide reliable infomiation about the surface composition and structure.  [c.304]

The first mass spectrometers to be widely used as both analytical and physical chemistry instruments were based on the deflection of a beam of ions by a magnetic field, a method first employed by J J Thomson in 1913 [8] for separating isotopes of noble gas ions. Modem magnetic sector mass spectrometers usually consist of both magnetic and electrostatic sectors, providing both momentum and kinetic energy selection. The tenn double-focusing mass spectrometer refers to such a configuration and relates to the fact that the ion beam is focused at two places between the ion source of the instmment and the detector. It is also possible to add sectors to make tlnee-, four, five- and even six-sector instmments, though the larger of these are typically used for large molecule analysis. One of the staple instmments used in physical chemistry has been the reverse-geometry tandem sector mass spectrometer ( BE configuration), which will be described below. The basic principles apply to any magnetic sector instmment configuration.  [c.1332]

Analysis of ion implanted layers and metal-silicon interactions was carried out with Rutherford backscattering at 2.0 MeV energies and with semiconductor nuclear particle detectors for several years. Rutherford backscattering became well established and was utilized in materials analysis in industrial and university laboratories across the world. The importance of hydrogen and its influence in solid state chemistry led to the development of forward scattering in which one measures the energy of the recoiling hydrogen atom. The helium ion is heavier than that of hydrogen so that by tilting the sample it is possible to measure the recoil energy of the emerging hydrogen, again with a nuclear particle detector. In other words, the modification to the Rutherford backscattering spectrometry target chamber geometry was only to tilt the target and to move the detector. These forward recoil teclmiques have of course become more sophisticated with use of heavy incident ions and detectors which measure both the energy and the mass of tlie recoiling particles (A E-Eor time of flight detector).  [c.1828]

Analysis of silicon is an almost ideal experimental situation because the masses of most implanted atoms and metal layers exceed that of silicon. In Rutherford backscattering the mass of the atom must be greater than that of the silicon target to separate the energy signals of the target atom from those of the silicon spectrum. Oxygen is an exception. It is lighter than silicon and also is ubiquitous in surface and interface layers. The analysis of oxygen, and also carbon and nitrogen, are carried out in the same experimental chamber as used in Rutherford backscattering, but tlie energy of the incident helium ions is increased to energies where there are resonances in the backscattering cross sections. These resonances increase the yield of the scattered particle by nearly two orders of magnitude and provide high sensitivity to the analysis of oxygen and carbon in silicon. The use of these high energies, 3.04 MeV for the helium-oxygen resonance, is called resonance scattering and the word Rutherford is inappropriate for a descriptor.  [c.1828]

The mix of ions, formed essentially at or near ambient temperatures, is passed through a nozzle (or skimmer) into the mass spectrometer for mass analysis. Since the ions are formed in the vapor phase without having undergone significant heating, many thermally labile and normally nonvolatile substances can be examined in this way.  [c.62]

Argon gas flows at a rate of about 1 to 2 1/min along the second of three concentric quartz tubes and is ignited to form a plasma by introducing a few sparks from a piezoelectric device. The plasma is maintained and heated by a high-frequency electromagnetic field passing through a load coil that is wound around the outside of the torch. Note the annular space between the load coil and the outermost quartz tube a water-cooled cage (discussed later) can be placed in this location. Because the very hot plasma could melt the outermost quartz tube if it impinged on it, a second flow (14 to 15 1/min) of fast-moving coolant argon gas is used to shield the walls of the tube from the plasma. Finally, there is a third flow (0.7 to 1.2 1/min) of argon through the central quartz tube this gas first passes through the sample, which is carried into the flame. The plasma is cooler at its center and hottest at its outside edge, where it is exposed to the high-frequency field. The end of the plasma flame is shown impinging onto the orifice of the sampling cone, which is part of a thick nickel-plated copper disc used to dissipate heat quickly. Electrons, ions, and neutrals pass through the sampler cone orifice and into the interface region before mass analysis. The positive ions are accelerated into the interface region by the large positive potential of about 6000 V while electrons are pulled out and neutralized at the sampling cone.  [c.88]

After the skimmer, the ions must be prepared for mass analysis, and electronic lenses in front of the analyzer are used to adjust ion velocities and flight paths. The skimmer can be considered to be the end of the interface region stretching from the end of the plasma flame. Some sort of light stop must be used to prevent emitted light from the plasma reaching the ion collector in the mass analyzer (Figure 14.2).  [c.95]

The advent of lasers and MALDI into mass spectrometry has had a major effect, especially in the analysis of large, polar biochemicals. Whereas electron ionization gives many fragment ions, which carry structural information, direct laser ionization and MALDI give mostly protonated molecular ions, so MS/MS with collision-induced dissociation becomes necessary to stimulate the fragmentation needed to obtain the same structural information. Of course, electron ionization methods are not useful for vaporizing and ionizing large biomolecules if they need to be first vaporized thermally, since this leads to their decomposition and therefore loss of molecular mass and structural data.  [c.136]

From these relationships in Equation 24.5, it can be seen that, if either the magnetic field (B) or the voltage (V) or both B and V are scanned, the whole range of masses of the ions can be brought into focus sequentially at a given point, the collector. Generally, a scanning magnetic-sector mass spectrometer carries out mass analysis by keeping V constant and varying the magnetic field (B).  [c.177]

The LDMS technique uses solid matrices (e.g., cinnamic acid derivatives) to absorb energy from a laser pulse, which volatilizes and ionizes proteins premixed within the matrix. Mass analysis is achieved by a time-of-flight (TOF) analyzer which, as the name suggests, measures precisely the time taken for the ions to travel from the source through the flight tube to the detector. The heavier the ion, the longer is the flight time. The spectrum generally contains a protonated [M -i- H+] or deprotonated [M - H] molecular ion cluster, together with doubly charged and perhaps multi-charged ions. Fragmentation, hence sequence information, is usually absent.  [c.290]

The separation of the rare earth elements lanthanum to lutetium provides a significant analytical challenge. Because they are difficult to separate by standard methods, ion-exchange resin systems have been developed to differentiate the elements. An initial ion-exchange separation is followed by isotopic analysis on each fraction using a ratio mass spectrometer. The separation process is time consuming. Standard mass spectrometric analyses of isotope content without any prior separation are not feasible because the rare earth elements have overlapping isotopes of equal mass (isobaric isotopes). For example, at mass 176, the Yb, Lu, and Hf isotopes are isobaric. The problem has been partly resolved by a rapid ion-exchange separation of the rare earths into just two fractions, one containing the lower rare earths (TREE La, Ce, Nd, Sm, Eu) and the other comprising the higher rare earth elements (HREE Gd, Dy, Er, Yb). The two fractions can be examined separately using an isotope ratio mass spectrometer that has a number of ion collectors, which can simultaneously collect and measure the numbers of ions in the different ion beams. With a suitable choice of which isotopes to monitor, it is possible to measure the content of all of the rare earths in a short time. Eor example, although lanthanum and cerium have isobars at 138, lanthanum has an isotope at 139, which cerium does not have, and therefore this mass can be used to estimate lanthanum. Similarly, cerium has an isotope at 140 that is not present in lanthanum  [c.351]

Evaporation of solvent from a spray of electrically charged droplets at atmospheric pressure eventually yields ions that can collide with neutral solvent molecules. The assemblage of ions formed by evaporation and collision is injected into the mass spectrometer for mass analysis.  [c.391]

Hybrid time-of-flight (TOF) mass spectrometers make use of a TOF analyzer placed at right angles to a main ion beam. Ions are deflected from this beam by a pulsed electric fleld at right angles to the ion beam direction. The deflected ions travel down the TOF tube for analysis. Hybrid TOF mass spectrometers have many advantages arising from the combination of two techniques, neither of which alone would be as useful.  [c.401]

The ions in a beam that has been dispersed in space according to their various m/z values can be collected simultaneously by a planar assembly of small electron multipliers. All ions within a specified mass range are detected at the same time, giving the array detector an advantage for analysis of very small quantities of any one substance or where ions are produced intermittently during short time intervals.  [c.409]

After the analyzer of a mass spectrometer has dispersed a beam of ions in space or in time according to their various m/z values, they can be collected by a planar assembly of small electron multipliers. There are two types of multipoint planar collectors an array is used in the case of spatial separation, and a microchannel plate is used in the case of temporal separation. With both multipoint assemblies, all ions over a specified mass range are detected at the same time, or apparently at the same time, giving these assemblies distinct advantages over the single-point collector in the analysis of very small quantities of a substance or where ions are produced intermittently during short time intervals.  [c.410]

Electrostatic analyzer. A velocity-focusing device for producing an electrostatic field perpendicular to the direction of ion travel (usually used in combination with a magnetic analyzer for mass analysis). The effect is to bring to a common focus all ions of a given kinetic energy.  [c.429]

Mass analysis. A process by which a mixture of ionic (or neutral) species is separated according to the mass-to-charge (m/z) ratios (for ions) or their aggregate atomic masses (for neutrals). The analysis can be qualitative or quantitative.  [c.429]

Total ion current (TIC), (a) After mass analysis the sum of all the separate ion currents carried by the different ions contributing to the spectrum, (b) Before mass analysis the sum of all the separate ion currents for ions of the same sign.  [c.437]

Ions can also be used as both the excitation and detection species in several surface analysis techniques. In secondary ion mass spectroscopy (sims), an incident beam of ions can sputter molecular ions from a surface providing surface elemental and molecular information. Ions can be scattered from surfaces or within interfaces in ion scattering spectroscopy (iss), Rutherford backscattering spectroscopy (rbs), and low energy ion scattering (leis) to provide elemental composition and stmctural information. Finally, an electric field can be used to stimulate ionization of an imaging gas in field ion microscopy (fim) or electron tunneling in field emission microscopy (fern) and scanning tunneling microscopy (stm) for surface imaging. A surface imaging technique which utilizes van der Waals forces as the "excitation" while monitoring what are essentially drag or frictional forces is atomic force microscopy (afm).  [c.269]

The implantation system shown in Figure 2 illustrates a conventional ion implantation system in widespread use within the semiconductor industry. Using different types of available ion sources, a wide variety of beams can be produced with sufficient intensity for implantation processes required for integrated circuit technology. For semiconductors, a representative ion dose is -10 ions/cm (metallurgical appHcations generally require doses from 10 -10 ions/cm ). This system produces a unidirectional beam and, in this article, is referred to as a directed beam system. A mass-separating magnet (for mass analysis) is almost mandatory for semiconductor processing in order to eliminate unwanted species that often contaminate the extracted beam. However, for metallurgical processing, mass separation is not important and, as a result, the basic instmmentation can be quite simple.  [c.390]

In its simplest form, a mass spectrometer is an instmment that measures the mass-to-charge ratios ml of ions formed when a sample is ionized by one of a number of different ionization methods (1). If some of the sample molecules are singly ionized and reach the ion detector without fragmenting, then the ml ratio of these ions gives a direct measurement of the molecular weight. The first instmment for positive ray analysis was built by Thompson (2) in 1913 to show the existence of isotopic forms of the stable elements. Later, mass spectrometers were used for precision measurements of ionic mass and abundances (3,4).  [c.539]

An important alternative to chromatographic separation (7) of a mixture is the use of tandem mass spectrometry, designated mass spectrometry/mass spectrometry (ms/ms) (8). In ms/ms, a molecular ion is mass selected by a mass spectrometer for activation in a coUision cell. Some of the excited ions have enough energy to fragment, and the resulting product ions are mass analyzed by a second mass spectrometer. In the analysis of a mixture, therefore, all the different molecular species can be individually selected and the corresponding characteristic mass spectra obtained without interference from the other components. This is only possible, however, for mixtures which do not contain isobaric components therefore, there is a practical limit to the complexity of mixtures which can be analyzed by ms /ms alone. Consequendy, ms /ms and chromatography are frequendy used together to analyze a complex sample (9).  [c.539]

Ions produced in an ion source can be separated into their m/z values by a variety of analyzers. The resultant set of m/z values, along with the numbers (abundances) of ions, forms the mass spectrum. The separation of ions into their individual m/z values has been effected by analyzers utilizing magnetic fields or RF (radio frequency) electric fields. For example, the mass analysis of ions by instruments using a magnetic field is well known, as are instruments having quadru-pole RF electric fields (quadrupole, ion trap). Ions can also be dispersed in time, so their m/z values are measured according to their flight times in a time-of-flight (TOF) instrument. These individual pieces of equipment have their own characteristics and are commonly used in mass spectrometry. In addition, combinations of sectors have given rise to hybrid instruments. The earliest of these was the double-focusing mass spectrometer having an electric. sector to focus ions according to their energies and then a magnetic sector to separate the individual m/z values. There is now a whole series of hybrid types, each with some advantage over nonhybrids. Ion collectors have seen a similar improvement in performance, and any of the above analyzers may be used with ion detectors based on single-electron multipliers or, in the case of magnetic sectors, on arrays of multipliers, or, in the case of ion cyclotron resonance (ICR), on electric-field frequencies.  [c.195]

Arnold F and Henschen G 1978 First mass analysis of stratospheric negative ions Nature 257 521-2 Eisele F L 1989 Natural and anthropogenic negative ions in the troposphere J. Geophys. Res. 94 2183-96 Oka T 1997 Water on the sun—molecules everywhere Science 277 328-9  [c.828]

Mass analysis of accelerated ions is imperative for semiconductor appHcations of ion implantation because of the extreme sensitivity to impurities and is also normally used for materials modification studies using modified semiconductor equipment. Exceptions are instances, such as above, where the ion source is capable of producing relatively pure beams, ie, the MEWA source. In other cases, such as certain tribological appHcations involving nitrogen ion implantation, the presence of low levels of impurities is not regarded as a problem. However, in almost all cases when required, magnetic separation is employed for mass analysis in each of the configurations described (164).  [c.399]

Fragmentation can be spontaneous or induced, although most instmments rely heavily on induced ion dissociations. Cohisional activation is the most common approach. The system consists of an ion source, two mass analyzers separated by a fragmentation region, and an ion detector. The principles are straightforward and can be compared to conventional gc/ms. A sample mixture is introduced into the ion source where ionization takes place producing ions characteristic of the individual components. The separation of the component of interest is then achieved by the mass selection of a characteristic ion of the analyte by the first mass analyzer. This parent ion undergoes cohisionally activated dissociation through collisions with neutral gas molecules in the fragmentation region to yield daughter ions which are analogous to the fragmentation occurring in the initial gc/ms ionization step. Identification of the separated components is accompHshed by mass analysis of the daughter ions in the second mass analyzer.  [c.405]

Photoelectron spectroscopy (PES) of negative ions involves irradiation of an ion beam with laser light and energy analysis of the electrons liberated when the photon energy exceeds the binding energy of the electron. The kinetic energy of the detached electron is the difference between the photon energy and the binding energy of the electron [37, 38, 39, 40, 44, 42, 43, 44, 45, 46 and 47]. Analysis of the electron energy thus gives a direct measurement of the electron affinity of the corresponding neutral atom or molecule, a very important thennochemical quantity. Generally speaking, PES yields more infomiation about tire neutral atom or molecule than the corresponding negative ion, because the target ion is ideally in its ground state and the electron kinetic energy is then dependent on the final state of the neutral product. The energy resolution of a PES experiment is usually adequate (often 5-10 meV) to resolve vibrational structure due to the neutral molecule, certainly for low-mass systems of few atoms and likewise electronic structure, including singlet-triplet splittings and fine structure separations. In a few cases, rotational energy levels have been resolved. Features may appear in a photoelectron spectrum due to excited levels of the target negative ion and give valuable infomiation about the stmcture of the negative ion, but at the cost of complicating the spectmm.  [c.802]

The use of million electron volt (MeV) ion beams for materials analysis was instigated by the revolution in integrated circuit technology. Thm planar structures were fonned in silicon by energetic ion implantation of dopants to create electrical active regions and thin metal films were deposited to make intercoimections between the active regions. Ion implantation was a new teclmique in the early 1960s and interactions between metal films and silicon required analysis. For example, the number of ions implanted per square centimetre (ion dose) and thicknesses of metal layers required carefiil control to meet the specifications of integrated circuit teclmology. Rutherford backscattering spectrometry (RBS) and MeV ion beam analysis were developed in response to the needs of the integrated circuit teclmology. In turn integrated circuit teclmology provided the electronic sophistication used in the instrumentation in ion beam analysis. It was a synergistic development of analytical tools and the fabrication of integrated circuits.  [c.1827]

Kinetic data are available for the nitration of a series of p-alkylphenyl trimethylammonium ions over a range of acidities in sulphuric acid. - The following table shows how p-methyl and p-tert-h xty augment the reactivity of the position ortho to them. Comparison with table 9.1 shows how very much more powerfully both the methyl and the tert-butyl group assist substitution into these strongly deactivated cations than they do at the o-positions in toluene and ferf-butylbenzene. Analysis of these results, and comparison with those for chlorination and bromination, shows that even in these highly deactivated cations, as in the nitration of alkylbenzenes ( 9.1.1), the alkyl groups still release electrons in the inductive order. In view of the comparisons just  [c.185]

Depth sensitivity is an equally important consideration in the analysis of surfaces. Techniques based on the detection of electrons or ions derive their surface sensitivity from the fact that these species cannot travel long distances in soflds without undergoing interactions which cause energy loss. If electrons are used as the basis of an analysis, the depth resolution will be relatively shallow and depend on both the energy of the incident and detected electrons and on characteristics of the material. In contrast, techniques based on high energy photons such as x-rays will sample a much greater depth due  [c.269]

Ion Beam Techniques. Secondary-ion mass spectroscopy (sims) uses ion beams having high enough energies to penetrate the surface and break surface bonds, ejecting neutral and ionic species from the surface in a process called sputtering. The primary beam is typically 0" 2- The ejected secondary ions are analyzed and identified according to mass. The sensitivities of ejection, or the ratio of ejected ions to atoms present in the substrate varies greatly according to the particular element, the substrate chemistry, or the substrate stmcture. The principal advantage of sims analysis is in its very low detection limits, which are appHed to the analysis of doping profiles and the detection and identification of surface contaminants. Time-of-flight secondary mass spectrometry (tof-sims) is a new surface-sensitive technique that analyzes both organic and inorganic contaminants in the top monolayer of a surface at ppm detection limits (49). Sims is a destmctive analytical process, and requires a large surface area for analysis (5x5 mm) (51) (see Mass spectrol try).  [c.356]

One ion implantation system which does not use mass analysis and is capable of extremely high ion currents is the broad beam system. Broad beam ion sources (Fig. 3) typically employ grids at the front end of the source to obtain electrostatic acceleration of ions. These sources originated in research programs in the early 1960s as a technology for space propulsion. Since that early work, broad beam systems have been successfully used in the areas of ion implantation, ion beam deposition, and ion beam-assisted deposition where the ions employed are in the low energy range of a few tens of electron-volts (eV) to several thousand eV. Like conventional ion implantation systems, broad beam systems are also referred to as directed beams.  [c.391]

The performance and reflabiUty of an implanter s ion source largely determines the system s commercial viabiUty. As such, the majority of commercial (semiconductor) ion implantation ion sources have been based on isotope separator source design. More recent sources are based on filamentless designs promising longer lifetimes and higher currents (156). These include radio frequency (RF) and electron cyclotron resonance (ECR) type ion sources. In any case, the objective is to obtain a low maintenance ion source that is (relatively) long Hved, stable, and deflvers an intense beam of positive ions of the desired species with a minimum of unwanted species. Most plasma-based heavy-ion sources produce ions utilizing a gaseous discharge at low pressure containing the elemental species of interest (157). The positive ions are extracted from the plasma by means of an electric field (between the extraction electrode and source) and are subsequently focused and directed through a mass analysis magnet to obtain adequate ion purity that is cmcial to semiconductor processing but generally less so for materials processing. The advantages and limitations of the predominant sources used for commercial directed beam systems are outlined in Table 1.  [c.399]

The term mass range refers to the range of masses of singly charged ions which can be analy2ed by the mass spectrometer. Because the mass scale is actually a scale of mass-to-charge ratio, the detection of multiply charged ions makes it possible to determine the mass of a molecule outside of the mass range of the mass spectrometer. Sensitivity is generally defined in one of two ways, either as a single-to-noise ratio for a specific compound under defined analysis conditions, or as a signal strength, eg, C/p.g.  [c.540]

There is a wide range of mass analy2ers available and numerous hybrid ms / ms instmments have been produced. The most common are those having a sector ms for msl and a dual quadmpole system for the collision chamber and ms2, ie, EBqQ or BEq. High energy collision spectra are obtained as in a two-sector mass spectrometer, eg, when B/E is a constant (37), all products of a given precursor ion are detected. Low energy collisions can also be performed, by using the first rf-only quadmpole, q, for coUisional activation and the second quadmpole, for mass analysis. Ions are decelerated to kinetic energies between 0 and 500 eV before entering the collision quadmpole by floating both quadmpoles at a voltage close to the ion source voltage. The precursor ion can be selected at high resolution by the first two sectors, as shown by the data in Figure 8, and the analytical quadmpole gives unit—mass resolution for product ions up to around 1000 mass units.  [c.544]

See pages that mention the term Mass Analysis of Ions : [c.139]    [c.812]    [c.1828]    [c.135]    [c.282]    [c.289]    [c.393]   
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Mass Spectrometry Basics  -> Mass Analysis of Ions