B+ Ions (b+ + ion)

Distribution by Scientific Domains

Selected Abstracts

Reactions of BBrn+ (n = 0,2) at fluorinated and hydrocarbon self-assembled monolayer surfaces: observations of chemical selectivity in ion,surface scattering

Nathan Wade
Abstract Ion,surface reactions involving BBrn+ (n = 0,2) with a fluorinated self-assembled monolayer (F-SAM) surface were investigated using a multi-sector scattering mass spectrometer. Collisions of the B+ ion yield BF2+ at threshold energy with the simpler product ion BF+ appearing at higher collision energies and remaining of lower abundance than BF2+ at all energies examined. In addition, the reactively sputtered ion CF+ accompanies the formation of BF2+ at low collision energies. These results stand in contrast with previous data on the ion,surface reactions of atomic ions with the F-SAM surface in that the threshold and most abundant reaction products in those cases involved the abstraction of a single fluorine atom. Gas-phase enthalpy data are consistent with BF2+ being the thermodynamically favored product. The fact that the abundance of BF2+ is relatively low and relatively insensitive to changes in collision energy suggests that this reaction proceeds through an entropically demanding intermediate at the vacuum,surface interface, one which involves interaction of the B+ ion simultaneously with two fluorine atoms. By contrast with the reaction of B+, the odd-electron species BBr+ reacts with the F-SAM surface to yield an abundant single-fluorine abstraction product, BBrF+. Corresponding gas-phase ion,molecule experiments involving B+ and BBr+ with C6F14 also yield the products BF+ and BF2+, but only in extremely low abundances and with no preference for double fluorine abstraction. Ion,surface reactions were also investigated for BBrn+ (n = 0,2) with a hydrocarbon self-assembled monolayer (H-SAM) surface. Reaction of the B+ ion and dissociative reactions of BBr+ result in the formation of BH2+, while the thermodynamically less favorable product BH+ is not observed. Collisions of BBr2+ with the H-SAM surface yield the dissociative ion,surface reaction products, BBrH+ and BBrCH3+. Substitution of bromine atoms on the projectile by hydrogen or alkyl radicals suggests that Br atoms may be transferred to the surface in a Br-for-H or Br-for-CH3 transfer reaction in an analogous fashion to known transhalogenation reactions at the F-SAM surface. The results for the H-SAM surface stand in contrast to those for the F-SAM surface in that enhanced neutralization of the primary ions gives secondary ion signals one to two orders of magnitude smaller than those obtained when using the F-SAM surface, consistent with the relative ionization energies of the two materials. Copyright 2001 John Wiley & Sons, Ltd. [source]

Spectroscopic Ellipsometry as a Tool for Damage Profiling in Very Shallow Implanted Silicon

Iordan Karmakov
Abstract Summary: Ion implantation is still one of the key steps in Si integrated circuit technology. Spectroscopic Ellipsometry (SE) detects the defects created in the implanted Si. The successful application of SE for damage profiling depends on the quality of the algorithm used for evaluating the damage profile from SE data. In this work, we present retrieved SE damage depth profiles by our previously published algorithm in the as-implanted Si with very low energies Ge+ ions- from 2 keV to 20 keV and 1 keV B+ ions (1,,1015 cm,2). The comparisons of the SE retrieved damage depth profiles with experimental atomic concentration depth profiles, or simulated by the state-of-the-art computer ATHENA code of Silvaco TCAD suits were made. The functional relation was obtained by proper fitting of measured by SE a/c depths, and the depths named "ends of damage" with the experimental or simulated ions concentration depth profiles. For reasons not understood, the damage profile of 5 keV Ge+ in c-Si is smoother in shape beyond the a/c depth, with a longer tail. The damage profiles measured by SE for 5 keV Ge+ in c-Si with two different doses: curve 1 - for 6,,1013 cm,2 and curve 2 - for 1,,1015 cm,2. Curve 3 - presents the damage profile simulated by ATHENA for Ge+ ions with 5 keV; 1,,1015 cm,2. [source]

Electron capture dissociation mass spectrometry of peptide cations containing a lysine homologue: a mobile proton model for explaining the observation of b-type product ions

Sunyoung Lee
Eleven doubly protonated peptides with a residue homologous to lysine were investigated by electron capture dissociation mass spectrometry (ECD-MS). Lysine homologues provide the unique opportunity to examine the ECD fragmentation behavior by allowing us to vary the length of the lysine side chain, with minimal structural change. The lysine homologue has a primary amine side chain with a length that successively decreases by one methylene (CH2) unit from the CH2CH2CH2CH2NH2 of lysine and the accompanying decrease of its proton affinities: lysine (K), 1006.5(7.2) kJ/mol; ornithine (K*), 1001.1(6.6) kJ/mol; 2,4-diaminobutanoic acid (K**), 975.8(7.4) kJ/mol; 2,3-diaminopropanoic acid (K***), 950.2(7.2) kJ/mol. In general, the lysine-homologous peptides exhibited overall ECD fragmentation patterns similar to that of the lysine-containing peptides in terms of the locations, abundances, and ion types of products, such as yielding c+ and z+. ions as the dominant product ions. However, a close inspection of product ion mass spectra showed that ECD-MS for the alanine-rich peptides with an ornithinyl or 2,4-diaminobutanoyl residue gave rise to b ions, while the lysinyl-residue-containing peptides did not, in most cases, produce any b ions. The peptide selectivity in the generation of b+ ions could be understood from within the framework of the mobile proton model in ECD-MS, previously proposed by Cooper (Ref. 29). The exact mass analysis of the resultant b ions reveals that these b ions are not radical species but rather the cationic species with R-CO+ structure (or protonated oxozalone ion), that is, b+ ions. The absence of [M+2H]+. species in the ECD mass spectra and the selective b+ -ion formation are evidence that the peptides underwent H-atom loss upon electron capture, and then the resulting reduced species dissociated following typical MS/MS fragmentation pathways. This explanation was further supported by extensive b+ ions generated in the ECD of alanine-based peptides with extended conformations. Copyright 2006 John Wiley & Sons, Ltd. [source]