Primary-ion-induced fragmentation in organic molecules can strongly influence the results in secondary-ion mass spectrometry (SIMS) of organic and biomolecular samples. In order to characterize this ...ion-induced fragmentation, oligopeptide samples irradiated in SIMS experiments were investigated by means of desorption/ionization induced by neutral SO2 clusters (DINeC). The latter is a nondestructive desorption method for mass spectrometry of biomolecules, which gives direct access to the fragments induced in the sample. Comparison of TOF-SIMS and DINeC mass spectra revealed qualitative differences between the fragments, which remain in the sample and the fragments sputtered during ion bombardment. The fragmentation strength and its spatial distribution were found to be quantitatively different for Bi1 +, Bi3 +, and Ar1000 + primary ions, leading to different distributions of the degree of fragmentation in the samples as directly measured by means of DINeC depth profiles.
Highly bond-specific fragmentation of oligopeptides induced by swift heavy ion (SHI) irradiation was investigated by means of mass spectrometry. In pronounced contrast to measurements of samples ...irradiated with keV ions, oligopeptides which were exposed to 946 MeV Au ions show a high abundance of specific fragments. The highly bond-specific nature of SHI-induced fragmentation is attributed to electronic stopping as the most relevant energy loss mechanism for SHI in the oligopeptide samples in combination with the subsequent coupling between the excited electronic and the atomic subsystem. Fragmentation induced by SHI is observed to be further influenced by the structure of the oligopeptides, suggesting that electronic excitation and/or the electronic-vibrational coupling depend on the details of the molecular structure.
Abstract
Hydrogen-covered Si(001) surfaces were exposed to swift heavy ions (SHI) and slow highly charged ions (HCI). Using scanning tunneling microscopy as analysis tool, the ion-induced ...modifications on the surface were resolved on the atomic scale. SHI were found occasionally to lead to changes which are restricted to one or two Si surface atoms. In comparison, HCI form pits of several nanometers in diameter, depending on the potential energy of the HCI. These observations are in contrast to many material systems for which similar effects of SHI and HCI have been observed. The results suggest a high stopping power threshold for SHI-induced modifications in crystalline silicon with major implications for the application in silicon-based nanotechnology.
Nonsequential double ionization of Ar by 45 fs laser pulses (800 nm) at (4-7)x10;{13} W/cm;{2} was explored in fully differential measurements. Well below the field-modified recollision threshold we ...enter the multiphoton regime. Strongly correlated back-to-back emission of the electrons along the polarization direction is observed to dominate in striking contrast to all previous data. No effect of Coulomb repulsion can be found, the predicted cutoff in the sum-energy spectra of two emitted electrons is confirmed, and the potential importance of multiple recollisions is discussed.
A process for production of micrometer-sized particles composed of uranium oxide using aerosol spray pyrolysis is characterized with respect to the various production parameters. The aerosol is ...generated using a vibrating orifice aerosol generator providing monodisperse droplets, which are oxidized in a subsequent heat treatment. The final particles are characterized with microanalytical methods to determine size, shape, internal morphology, and chemical and structural properties in order to assess the suitability of the produced particles as a reference material for microanalytical methods, in particular, for mass spectrometry. It is demonstrated that physicochemical processes during particle formation and the heat treatment to chemically transform particles into an oxide strongly influence the particle shape and the internal morphology. Synchrotron μ-X-ray based techniques combined with μ-Raman spectroscopy have been applied to demonstrate that the obtained microparticles consist of a triuranium octoxide phase. Our studies demonstrate that the process is capable of delivering spherical particles with determined uniform size and elemental as well as chemical composition. The particles therefore represent a suitable base material to fulfill the homogeneity and stability requirements of a reference material for microanalytical methods applied in, for example, international safeguards or nuclear forensics.
Towards the goal of covalently bound molecular wires on silicon, the adsorption of benzyne on Si(001) was studied by means of scanning tunneling microscopy (STM), X‐ray photoelectron spectroscopy ...(XPS), ultraviolet photoelectron spectroscopy (UPS), and density functional calculations (DFT). The benzyne molecule is found to adsorb preferentially via the strained triple bond on one dimer of the Si(001) surface which results in an intact π system covalently bound to the surface. With increasing coverage, the molecules primarily adsorb along the dimer rows; on stepped surfaces, these molecular wires are all oriented in the same direction.
Benzyne adsorbs preferentially via its strained triple bond on top of a single dimer. Rows of such benzene analogues in on‐top configuration show interaction along the dimer rows leading to a one‐dimensional dispersion along the dimer rows.
To support the nuclear safeguards particle analysis, a method was developed to produce micrometer-sized uranium oxide microspheres with a known uranium content and isotope ratio, which are intended ...to be characterized as certified reference material. To simplify handling of the produced particles, the collected particles have been transferred into ethanol suspensions. In addition to a demonstration of the suitability and new capabilities of such particle suspensions, such as the preparation of particle mixtures, the stability of the particles has been investigated and demonstrated with regard to dissolution and isotopic exchange.
Using a reaction microscope, three-dimensional (3D) electron (and ion) momentum (P) spectra have been recorded for carrier-envelope-phase (CEP) stabilized few-cycle ( approximately 5 fs), intense ( ...approximately 4 x 10(14) W/cm2) laser pulses (740 nm) impinging on He. Preferential emission of low-energy electrons (E(e)<15 eV) to either hemisphere is observed as a function of the CEP. Clear interference patterns emerge in P space at CEPs with maximum asymmetry, interpreted as attosecond interferences of rescattered and directly emitted electron wave packets by means of a simple model.
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