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Secondary Ions (secondary + ion)
Terms modified by Secondary Ions Selected AbstractsTime-of-flight studies of secondary ions produced by 400,eV He+ ion impact on Ar, Kr, and Xe thin films at 8 KRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2002Kenzo Hiraoka Secondary ions produced by 400,eV He+ ion impact on Ar, Kr, and Xe thin films deposited on a silicon substrate at 8,K were measured as a function of film thickness using a time-of-flight secondary-ion mass spectrometer. For Ar, the cluster ions Arn+ up to n,=,4 as well as the monomer ion (n,=,1) were observed and they showed characteristic film-thickness dependence with increase of the film thickness up to ,200 monolayers. This is due to the momentum transfer in the elastic collision between the incident He+ ion and the matrix Ar atoms and also to the relaxation of electronic excitations (e.g., holes and excitons) to phonons resulting in the film erosion. In contrast, neither dimer nor cluster ions were detected for solid Kr and Xe films. This is due to the less efficient momentum transfer in the elastic collision between He+ and Rg's (Rg,=,Kr and Xe) and also to the efficient electronic energy migration in solid Kr and Xe. The ions originating from the silicon substrate such as Si+, SiCH3+, SiOH+, and C+ were found to be sensitized by the deposition of Xe film in the range of 0,40 monolayers. The penetration depths of the primary ion He+ through the rare gas films increase in the order Ar,<,Kr,<,Xe. Copyright © 2002 John Wiley & Sons, Ltd. [source] Investigation of ion-pair precipitates of selected alkoxylates and complex salts of specific metal cations by liquid secondary ion mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 4 2002Abstract Liquid secondary ion (LSI) mass spectra of ion-pair precipitates obtained for Triton X-100 with strontium, lead, cadmium and mercury tetraphenylborates and for selected butoxylene,ethoxylene monoalkyl ethers with barium tetraiodobismuthate(III) are discussed. On the basis of LSI mass spectra, recorded in both positive and negative modes, the formulae of the ion-pair precipitates were determined. On the basis of B/E mass spectra, the fragmentation routes of [M , H + Ba]+ ions for butoxylene,ethoxylene monoalkyl ether complexes of barium and [M , H + Cd]+ ions for the Triton X-100 complex of cadmium are proposed. Copyright © 2002 John Wiley & Sons, Ltd. [source] A fast computation of the secondary ion production in the ionosphere of MarsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2009William P. Nicholson ABSTRACT We present an analytic method for the rapid computation of secondary ion and electron production due to electron impact as suprathermal electrons produced by primary photoproduction propagate through the neutral background Martian atmosphere. We use a one-dimensional kinetic model, Trans -Mars, that solves a stationary Boltzmann transport equation to describe the ionosphere of Mars with the neutral background atmosphere (temperatures, number densities and geopotential heights) provided by a three-dimensional global circulation model, MarTIM. Parameters are given to allow the rapid computation of secondary ion production for 11 ion species (CO+2, CO++2, CO+, C+, N+2, N++2, N+, O+2, O++2, O+, O++) as well as for the secondary electron production. We use the neutral global circulation model to show that while the efficiency (,) of ion and electron production (ratio of secondary to primary production) does vary with solar zenith angle it can be parametrized with a simple function, which is given. We also show that variations with solar cycle and solar longitude are negligible about the region of the primary and secondary production peaks. [source] In situ localisation and quantification of surfactins in a Bacillus subtilis swarming community by imaging mass spectrometryPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 18 2008Delphine Debois Abstract Surfactins are a family of heptacyclopeptides in which the C-terminal carbonyl is linked with the ,-hydroxy group of a fatty acid acylating the N-terminal function of a glutamic acid residue. The fatty acyl chain is 12,16 carbon atoms long. These compounds, which are secreted by the Gram-positive bacterium Bacillus subtilis in stationary phase in liquid cultures, play an important role in swarming communities on the surface of agar media in the formation of dendritic patterns. TOF secondary ion MS (TOF-SIMS) imaging was used to map surfactins within 16,17,h swarming patterns, with a 2,,m spatial resolution. Surfactins were mainly located in the central mother colony (the site of initial inoculation), in a ,ring' surrounding the pattern and along the edges of the dendrites. In the mother colony and the interior of the dendrites, surfactins with shorter chain lengths are present, whereas in the ring surrounding the swarm community and between dendrites, surfactins with longer fatty acyl chain lengths were found. A quantitative analysis by MALDI-TOF MS showed a concentration gradient of surfactin from the mother colony to the periphery. The concentration of surfactin was ,400,pmol/mL in the mother colony and ,10,pmol/mL at the base of the dendrites, decreasing to 2,pmol/mL at their tips. [source] Static SIMS studies of the oxides and hydroxides of aluminiumJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2007S. Verdier Abstract The degree of hydroxylation or hydration of aluminium surfaces has been examined by static secondary ion mass spectroscopy (SSIMS). The SSIMS spectra of a series of aluminium oxide, oxyhydroxide and hydroxide surfaces have been obtained using instruments in three configurations. Similarities were observed in both negative and positive secondary ions spectra. Even though a direct comparison of the relative intensities cannot be made from one instrument to the other, a similar ranking of the various aluminium hydroxylation states was observed. Several ranking methods are discussed, as well as the similarities and differences observed while using the three instruments. Similar secondary ions were detected whatever the degree of hydroxylation of the aluminium oxide. This argues in favour of the formation of fragments by the combination of individually sputtered atoms or clusters to form the more stable secondaries, rather than the kick-off of ,structure-related' clusters originating directly from the upper surface layer. Copyright © 2006 John Wiley & Sons, Ltd. [source] Reactions of gaseous ions.JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2001Editor's Note: The following paper is the first in a series that describes the gas phase reactions of positive ions derived from compounds such as methane and ethylene with other gas phase molecules to produce secondary ions. These very careful experiments formed the basis of chemical ionization, one of the ionization techniques that revolutionized mass spectrometry at that time and a technique still very much in use today. At elevated pressures in a mass spectrometer ion source reactions occur between certain ions and the neutral species present. We have studied the various secondary ions formed in methane and ethylene at elevated pressures and have determined the reactions by which they are formed and the rates of these reactions. The rates are all extremely fast. The reaction rates have been treated by classical collision theory and it has been shown that to a fair approximation the cross-sections and reaction rate constants can be predicted from a simple balance of rotational and polarization forces. [Reprinted from J. Am. Chem. Soc. 1957; 79: 2419.] Copyright © 1957 by the American Chemical Society and reprinted by permission of the copyright owner. [source] Bioimaging TOF-SIMS of tissues by gold ion bombardment of a silver-coated thin sectionMICROSCOPY RESEARCH AND TECHNIQUE, Issue 6 2004Håkan Nygren Abstract The imaging time-of-flight secondary-ion-mass-spectrometry (TOF-SIMS) method was utilized to address the problem of cholesterol localization in rat tissues. Rat kidneys were fixed, cryoprotected by sucrose, frozen, sectioned by cryoultramicrotomy, and dried at room temperature. The samples were either covered with a thin silver layer or analyzed uncovered in an imaging TOF-SIMS instrument equipped with an Au -source. The yield of desorbed secondary ions for some species was up to 600-fold higher after silver coating of the samples. Reference samples of cholesterol were silver-coated and analyzed by TOF-SIMS to define significant peaks, specific for cholesterol. Such peaks were found at m/z = 386 (C27H46O+), m/z = 493 (C27H46O107Ag+), m/z = 495 (C27H46O109Ag+), m/z = 879 (C54H92O2107Ag+), and m/z = 881 (C54H92O2109Ag+). The silver-cationized cholesterol (493 , m/z , 495) signal was localized by imaging TOF-SIMS in the kidney sections and showed a high cholesterol content in the kidney glomeruli. A more diffuse distribution of cholesterol was also found over areas representing the cytoplasm or plasma membrane of the epithelial cells in the proximal tubules of rat kidney. Microsc. Res. Tech. 65:282,286, 2004. © 2005 Wiley-Liss, Inc. [source] Cluster ion beam profiling of organics by secondary ion mass spectrometry , does sodium affect the molecular ion intensity at interfaces?RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2008Felicia M. Green The use of cluster ion beam sputtering for depth profiling organic materials is of growing technological importance and is a very active area of research. At the 44th IUVSTA Workshop on "Sputtering and Ion Emission by Cluster Ion Beams", recent results were presented of a cluster ion beam depth profile of a thin organic molecular layer on a silicon wafer substrate. Those data showed that the intensity of molecular secondary ions is observed to increase at the interface and this was explained in terms of the higher stopping power in the substrate and a consequently higher sputtering yield and even higher secondary ion molecular sputtering yield. An alternative hypothesis was postulated in the workshop discussion which may be paraphrased as: "under primary ion bombardment of an organic layer, mobile ions such as sodium may migrate to the interface with the inorganic substrate and this enhancement of the sodium concentration increases the ionisation probability, so increasing the molecular ion yield observed at the interface". It is important to understand if measurement artefacts occur at interfaces for quantification as these are of great technological relevance , for example, the concentration of drug in a drug delivery system. Here, we evaluate the above hypothesis using a sample that exhibits regions of high and low sodium concentration at both the organic surface and the interface with the silicon wafer substrate. There is no evidence to support the hypothesis that the probability of molecular secondary ion ionisation is related to the sodium concentration at these levels. © Crown copyright 2008. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd. [source] Structural analysis of secondary ions by post-source decay in time-of-flight secondary ion mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 4 2006David Touboul Tandem mass spectrometry measurements have been achieved using time-of-flight secondary ion mass spectrometry (TOF-SIMS) and a post source decay (PSD)-like method. The performance of the method has been demonstrated on model molecules with well-known fragmentation pathways. Several lipids have been fragmented including the phosphocholine ion, phosphatidylcholines, cholesterol and vitamin E. Pure samples were analyzed, and the results compared with those obtained with the same compounds on a quadrupole-TOF hybrid mass spectrometer. Then, the structures of some lipids which are currently observed in the TOF-SIMS imaging of mammalian tissue sections were verified. Copyright © 2006 John Wiley & Sons, Ltd. [source] Secondary ion formation of low molecular weight organic dyes in time-of-flight static secondary ion mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2003Jens Lenaerts Time-of-flight static secondary ion mass spectrometry (TOF-S-SIMS) was used to characterize thin layers of oxy- and thiocarbocyanine dyes on Ag and Si. Apart from adduct ions a variety of structural fragment ions were detected for which a fragmentation pattern is proposed. Peak assignments were confirmed by comparing spectra of dyes with very similar structures. All secondary ions were assigned with a mass accuracy better than 50,ppm. The intensity of molecular ions as well as fragment ions has been studied as a function of the type of organic dye, the substrate, the layer thickness and the type of primary ion. A large yield difference of two orders of magnitude was observed between the precursor ions of cationic carbocyanine dyes and the protonated molecules of the anionic dyes. Fragment ions, on the other hand, yielded similar intensities for both types of dye. As the dye layers deposited on an Ag substrate yielded higher secondary ion intensities than those deposited on a Si substrate, the Ag metal clearly acts as a promoting agent for secondary ion formation. The effect was more pronounced for precursor signals than for fragment ions. The promoting effect decreased as the deposited layer thickness of the organic dye layer was increased. Copyright © 2003 John Wiley & Sons, Ltd. [source] ,Bubble chamber model' of fast atom bombardment induced processesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 15 2003Marina V. Kosevich A hypothesis concerning FAB mechanisms, referred to as a ,bubble chamber FAB model', is proposed. This model can provide an answer to the long-standing question as to how fragile biomolecules and weakly bound clusters can survive under high-energy particle impact on liquids. The basis of this model is a simple estimation of saturated vapour pressure over the surface of liquids, which shows that all liquids ever tested by fast atom bombardment (FAB) and liquid secondary ion mass spectrometry (SIMS) were in the superheated state under the experimental conditions applied. The result of the interaction of the energetic particles with superheated liquids is known to be qualitatively different from that with equilibrium liquids. It consists of initiation of local boiling, i.e., in formation of vapour bubbles along the track of the energetic particle. This phenomenon has been extensively studied in the framework of nuclear physics and provides the basis for construction of the well-known bubble chamber detectors. The possibility of occurrence of similar processes under FAB of superheated liquids substantiates a conceptual model of emission of secondary ions suggested by Vestal in 1983, which assumes formation of bubbles beneath the liquid surface, followed by their bursting accompanied by release of microdroplets and clusters as a necessary intermediate step for the creation of molecular ions. The main distinctive feature of the bubble chamber FAB model, proposed here, is that the bubbles are formed not in the space and time-restricted impact-excited zone, but in the nearby liquid as a ,normal' boiling event, which implies that the temperature both within the bubble and in the droplets emerging on its burst is practically the same as that of the bulk liquid sample. This concept can resolve the paradox of survival of intact biomolecules under FAB, since the part of the sample participating in the liquid,gas transition via the bubble mechanism has an ambient temperature which is not destructive for biomolecules. Another important feature of the model is that the timescale of bubble growth is no longer limited by the relaxation time of the excited zone (,10,12,s), but rather resembles the timescale characteristic of common boiling, sufficient for multiple interactions of gas molecules and formation of clusters. Further, when the bubbles burst, microdroplets are released, which implies that FAB processes are similar to those in spraying techniques. Thus, two processes contribute to the ion production, namely, release of volatile solvent clusters from bubbles and of non-volatile solute from sputtered droplets. This view reconciles contradictory views on the dominance of either gas-phase or liquid-phase effects in FAB. Some other effects, such as suppression of all other ions by surface-active compounds, are consistent with the suggested model. Copyright © 2003 John Wiley & Sons, Ltd. [source] Time-of-flight studies of secondary ions produced by 400,eV He+ ion impact on Ar, Kr, and Xe thin films at 8 KRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2002Kenzo Hiraoka Secondary ions produced by 400,eV He+ ion impact on Ar, Kr, and Xe thin films deposited on a silicon substrate at 8,K were measured as a function of film thickness using a time-of-flight secondary-ion mass spectrometer. For Ar, the cluster ions Arn+ up to n,=,4 as well as the monomer ion (n,=,1) were observed and they showed characteristic film-thickness dependence with increase of the film thickness up to ,200 monolayers. This is due to the momentum transfer in the elastic collision between the incident He+ ion and the matrix Ar atoms and also to the relaxation of electronic excitations (e.g., holes and excitons) to phonons resulting in the film erosion. In contrast, neither dimer nor cluster ions were detected for solid Kr and Xe films. This is due to the less efficient momentum transfer in the elastic collision between He+ and Rg's (Rg,=,Kr and Xe) and also to the efficient electronic energy migration in solid Kr and Xe. The ions originating from the silicon substrate such as Si+, SiCH3+, SiOH+, and C+ were found to be sensitized by the deposition of Xe film in the range of 0,40 monolayers. The penetration depths of the primary ion He+ through the rare gas films increase in the order Ar,<,Kr,<,Xe. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||