共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
3.
Interest in environmental aerosol chemistry has grown over the last decade as a result of its role in both climate change and troposheric pollution. In this work, the combination of ToF-SIMS and SEM/EDX was employed to explore the surface chemistry of aerosols. The capabilities and limitations of ToF-SIMS were investigated using particles of known composition and size produced by a vibrating orifice aerosol generator (VOAG). Principal component analysis (PCA) proved to help in the distinction of particles of different types by consolidating the information generated by ToF-SIMS. 相似文献
4.
E. Vors A. Semerok J.-F. Wagner 《Applied Physics A: Materials Science & Processing》1999,69(7):S165-S166
Time of flight mass spectrometry (TOF-MS) in combination with laser ablation (LA) applied for low isotope composition measurements is limited by energy and spatial dispersion of ions, spatial charge density, and some other factors. In order to reduce these factors that make the extraction of the plasma ions difficult, we used a second laser to create ions by non-isotope-selective photoionization of neutral particles. The photoionization was carried out in uranium vapor beam by the third harmonic of a pulsed Nd:YAG laser. This work presents the results of tentative experiments to estimate the characteristics of the LA-TOF-MS method with non-selective photoionization. 相似文献
5.
S Jürschik B Agarwal T Kassebacher P Sulzer CA Mayhew TD Märk 《Journal of mass spectrometry : JMS》2012,47(9):1092-1097
In this work, we illustrate the application of proton transfer reaction mass spectrometry (PTR-MS) in the field of food and drink safety. We present proof-of-principle measurements of four different drinks (water, tea, red wine and white wine) each spiked separately with four different date rape drugs (chloral hydrate, tricholorethanol, γ-butyrolactone and butanediol). At first, the ideal PTR-MS operating conditions (reduced electric field strength and monitoring the most abundant [fragment] ion) for detection of the drugs were determined utilizing a time-of-flight-based PTR-MS instrument. We then dissolved small quantities of the drugs (below the activation threshold for effects on humans) into the various types of drinks and detected them using a quadrupole-based PTR-MS instrument via two different sampling methods: (1) dynamic headspace sampling and (2) direct liquid injection. Both methods have their advantages and drawbacks. Only with dynamic headspace sampling can rape drug contaminations be detected within a timeframe of seconds, and therefore, this method is the most promising use of PTR-MS as a fast, sensitive and selective monitor for the detection of food and drink contamination. Copyright ? 2012 John Wiley & Sons, Ltd. 相似文献
6.
The spectroscopic amplitudes, form factors, angular distributions and total cross-sections for two nucleon transfer reactions
in Zr-region in the zero range distorted wave Born approximation are calculated using consistent set of shell model wave functions.
A single normalisation factor gives a good fit to all the two neutron transfer reaction data whereas the corresponding fit
for the two-proton transfer reaction data is less satisfactory. 相似文献
7.
M. Gutowski I. Dabkowska J. Rak S. Xu J.M. Nilles D. Radisic K.H. Bowen Jr 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):431-439
The photoelectron spectra (PES) of anions of uracil-glycine and uracil-phenylalanine complexes reveal broad features with
maxima at 1.8 and 2.0 eV. The results of ab initio density functional B3LYP and second order M?ller-Plesset theory calculations indicate that the excess electron occupies a
π* orbital localized on uracil. The excess electron attachment to the complex can induce a barrier-free proton transfer (BFPT)
from the carboxylic group of glycine to the O8 atom of uracil. As a result, the four most stable structures of the anion of
uracil-glycine complex can be characterized as the neutral radical of hydrogenated uracil solvated by the anion of deprotonated
glycine. The similarity between the PES spectra for the uracil complexes with glycine and phenylalanine suggests that the
BFPT is also operative in the case of the latter anionic species. The BFPT to the O8 atom of uracil may be related to the
damage of nucleic acid bases by low energy electrons because the O8 atom is involved in a hydrogen bond with adenine in the
standard Watson-Crick pairing scheme.
Received 6 April 2002 Published online 13 September 2002 相似文献
8.
In this study, a series of random copolymers of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) were prepared as surface-initiated polymer (SIP) films on silicon substrates using atom transfer radical polymerization. Positive and negative ion static time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to characterize SIP films with different MMA/EGDMA monomer ratios in an attempt to quantify their surface composition. However, matrix effects in the positive and negative ion modes led to preferential secondary ion generation from the EGDMA monomer and suppression of secondary ions characteristic of the MMA monomer, precluding accurate quantification using standard linear quantification methods. Ion-induced degradation of these films under 5 keV SF5+ bombardment was also examined to determine the effect of cross-linking on the accumulation of ion-induced damage. Increasing incorporation of the EGDMA cross-linker in the SIP films decreased the sputter rate and increased the rate of damage accumulation under extended (>1014 ions/cm2) 5 keV SF5+ bombardment. Comparison of the ion bombardment data with thermal degradation of cross-linked PMMA suggests that the presence of the cross-linker impedes degradation by depolymerization, resulting in ion-induced damage accumulation. The increased rate of ion-induced damage accumulation with increased cross-link density also suggests that polymers that can form cross-links during ion bombardment are less amenable to depth profiling using polyatomic primary ions. 相似文献
9.
Robyn E. Goacher 《Applied Surface Science》2010,256(7):2044-908
Time of flight secondary ion mass spectrometry (ToF-SIMS) depth profiles of several inorganic layered samples using Cs+ and C60+ primary sputtering ions of different energies are compared to evaluate sputter yield and depth resolution. A gold/silicon model system is employed to study interfaces between metals and semiconductors, and multilayers of AlGaAs, Al, and InAs in GaAs are analyzed to explore the ability of C60+ to analyze semiconductor interfaces in GaAs. Roughness measurements are reported to differentiate between different factors affecting depth resolution. The best depth resolution from all samples analyzed is achieved using 1 keV Cs+. However, C60+ sputtering has advantages for analyzing conductor/insulator interfaces because of its high sputter yield, and for analyzing deeper heterolayers in GaAs due to lower sputter-induced roughness. 相似文献
10.
11.
Protein glycosylation has a major influence on functions of proteins. Studies have shown that aberrations in glycosylation are indicative of disease conditions. This has prompted major research activities for comparative studies of glycoproteins in biological samples. Multiple reaction monitoring (MRM) is a highly sensitive technique which has been recently explored for quantitative proteomics. In this work, MRM was adopted for quantification of glycopeptides derived from both model glycoproteins and depleted human blood serum using glycan oxonium ions as transitions. The utilization of oxonium ions aids in identifying the different types of glycans bound to peptide backbones. MRM experiments were optimized by evaluating different parameters that have a major influence on quantification of glycopeptides, which include MRM time segments, number of transitions, and normalized collision energies. The results indicate that oxonium ions could be adopted for the characterization and quantification of glycopeptides in general, eliminating the need to select specific transitions for individual precursor ions. Also, the specificity increased with the number of transitions and a more sensitive analysis can be obtained by providing specific time segments. This approach can be applied to comparative and quantitative studies of glycopeptides in biological samples as illustrated for the case of depleted blood serum sample. Copyright ? 2012 John Wiley & Sons, Ltd. 相似文献
12.
S. M. Ibrahim F. Mabood K. Suneetha G. Lorenzini 《Journal of Engineering Thermophysics》2017,26(2):234-255
The elevated temperature electromagnetic materials production system in chemical engineering requires increasingly more refined theoretical and computational models for describing multiple, simultaneous thermophysical effects. Motivated by this application, the present paper addresses heat and mass transfer in a chemically reacting laminar mixed convection flow from a vertical sheet with inducedmagnetic field. The governing equations of the flow are solved analytically using a perturbation technique. The influences of various established parameters on the flow, induced magnetic field, and heat and mass transfer are studied graphically in the present analysis. Finally, we also obtained expressions for shear stress, current density and Nusselt number, and discussed the results through tables. 相似文献
13.
14.
15.
16.
Molecular ion yield enhancement induced by gold deposition in static secondary ion mass spectrometry
Static ToF-SIMS was used to evaluate the effect of gold condensation as a sample treatment prior to analysis. The experiments were carried out with a model molecular layer (Triacontane M = 422.4 Da), upon atomic (In+) and polyatomic (Bi3+) projectile bombardment. The results indicate that the effect of molecular ion yield improvement using gold metallization exists only under atomic projectile impact. While the quasi-molecular ion (M+Au)+ signal can become two orders of magnitude larger than that of the deprotonated molecular ion from the pristine sample under In+ bombardment, it barely reaches the initial intensity of (M−H)+ when Bi3+ projectiles are used. The differences observed for mono- and polyatomic primary ion bombardment might be explained by differences in near-surface energy deposition, which influences the sputtering and ionization processes. 相似文献
17.
18.
G. E. Belovitsky V. P. Zavarzina E. S. Konobeevski S. V. Zuyev N. G. Polukhina A. S. Rusetsky N. I. Starkov S. M. Lukyanov Yu. G. Sobolev 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(3):311-314
To estimate the probability of two-neutron configuration in halo nuclei, an experimental method for studying neutron-neutron correlations at the periphery of such nuclei by measuring the two-neutron transfer reaction is proposed. Experimental investigation of the 6He + A → 4He + B reaction was performed using a 60-MeV 6He radioactive beam at the Flerov Laboratory of Nuclear Reactions (Joint Institute for Nuclear Research, Dubna); the technique of nuclear photoemulsions was applied. Search for events of the two-nucleon transfer reaction was performed at the PAVIKOM setup (Lebedev Physical Institute, Russian Academy of Sciences). 相似文献
19.
Gnaser H. Fleischhauer J. Hofer W. O. 《Applied Physics A: Materials Science & Processing》1985,37(4):211-220
A mass spectrometer is described, which allows the analysis of sputtered neutral and charged particles as well as of residual gas composition. This combined SIMS, SNMS, and RGA instrument consists of a scanning primary ion beam column, an electron impact ionizer, an electrostatic energy filter and an rf quadrupole mass analyzer.Various examples of surface and bulk analysis are presented which demonstrate the beneficial complementary features of these techniques. These are, in particular: a substantial reduction of the matrix effect and fewer complications with samples of low electrical conductivity in SNMS, and the possibility of measuring the depth distribution of gases included in small cavities in the solid in the SNMS/RGA mode. SIMS, on the other hand, allows in many cases higher detection sensitivities.EURATOM Association 相似文献