180 research outputs found
Segregation and precipitation of Er in Ge
Although Er-doped Genanomaterials are attractive for photonic applications, very little is known about the basic properties of Er in Ge. Here, the authors study the annealing behavior of Geimplanted with keV Er ions to doses resulting in â˛1at.% of Er. Large redistribution of Er, with segregation at the amorphous/crystalline interface, starts at âł500°C, while lower temperatures are required for material recrystallization. However, even at 400°C, Er forms precipitates. The concentration of Er trapped in the bulk after recrystallization decreases with increasing temperature but is independent of the initial bulk Er concentration for the range of ion doses studied here.Work at the ANU was supported
by the ARC
Deformation behavior of ion-irradiated polyimide
We study nanoindentationhardness, Youngâs modulus, and tensile strength of polyimide (Kapton H) films bombarded with MeV light ions in the predominantly electronic stopping power regime. Results show that, for all the ion irradiation conditions studied, bombardment increases the hardness and Youngâs modulus and decreases the tensile strength. These changes depend close to linearly on ion fluence and superlinearly (with a power-law exponent factor of âź1.5) on electronic energy loss. Physical mechanisms of radiation-induced changes to mechanical properties of polyimide are discussed.This work was performed under the auspices of the U. S.
Department of Energy by the University of California, LLNL
under Contract No. W-7405-ENG-48. The project (03-FS-
027) was funded by the Laboratory Directed Research and
Development Program at LLNL
Effects of carbon on ion-implantation-induced disorder in GaN
Wurtzite GaN films bombarded with 40keV C ions to high doses (5Ă10š⡠and 1Ă10šâ¸cmâťÂ˛) are studied by a combination of Rutherford backscattering/channeling spectrometry, transmission electron microscopy, and soft x-ray absorption spectroscopy. Results show that, contrary to other ion species, implanted C forms nitrilelike carbon-nitride bonds (âCâĄN) and suppresses ion-beam-induced material decomposition involving the formation and agglomeration of âł5-nm-large Nâ gas bubbles.Work at the ANU was supported by the ARC. The ALS is supported
by the Director, Office of Science, Office of BES,
Materials Sciences Division, of the U.S. DOE under Contract
No. DE-AC03-76SF00098 at LBNL
Cell boundary confinement sets the size and position of the E. coli chromosome
Although the spatiotemporal structure of the genome is crucial to its biological function, many basic questions remain unanswered on the morphology and segregation of chromosomes. Here, we experimentally show in Escherichia coli that spatial confinement plays a dominant role in determining both the chromosome size and position. In non-dividing cells with lengths increased to 10 times normal, single chromosomes are observed to expand > 4-fold in size. Chromosomes show pronounced internal dynamics but exhibit a robust positioning where single nucleoids reside robustly at mid-cell, whereas two nucleoids self-organize at 1/4 and 3/4 positions. The cell-size-dependent expansion of the nucleoid is only modestly influenced by deletions of nucleoid-associated proteins, whereas osmotic manipulation experiments reveal a prominent role of molecular crowding. Molecular dynamics simulations with model chromosomes and crowders recapitulate the observed phenomena and highlight the role of entropic effects caused by confinement and molecular crowding in the spatial organization of the chromosome
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Recipes for high resolution time-of-flight detectors
The authors discuss the dynamics, construction, implementation and benefits of a time-of-flight (TOF) detector with count rates an order of magnitude higher and resolution three to four times better than that obtainable with a surface barrier detector. The propose use of design criteria for a time-of-flight detector is outlined, and the determination of a TOF detector`s total relative timing error and how this value determines the mass resolution are illustrated using a graphical analysis. They present simulation and experimental examples employing light ions and discuss advantages and pitfalls of medium-energy heavy ion TOF spectrometry
Oxidation of uranium nanoparticles produced via pulsed laser ablation
An experimental apparatus designed for the synthesis, via pulsed laser deposition, and analysis of metallic nanoparticles and thin films of plutonium and other actinides was tested on depleted uranium samples. Five nanosecond pulses from a Nd:YAG laser produced films of {approx}1600 {angstrom} thickness that were deposited showing an angular distribution typical thermal ablation. The films remained contiguous for many months in vacuum but blistered due to induced tensile stresses several days after exposure to air. The films were allowed to oxidize from the residual water vapor within the chamber (2 x 10{sup -10} Torr base pressure). The oxidation was monitored by in-situ analysis techniques including x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and scanning tunneling microscopy (STM) and followed Langmuir kinetics
Hydrogen adsorption on Pd(133) surface
In this study used is an approach based on measurements of the total energy
distribution (TED) of field emitted electrons in order to examine the
properties of Pd (133) from the aspect of both hydrogen adsorption and surface
hydrides formation. The most favourable sites offered to a hydrogen atom to be
adsorbed have been indicated and an attempt to describe the peaks of the
enhancement factor R spectrum to the specific adsorption sites has also been
made.Comment: to be submitted to the Centr. Eur. J. Phy
Workshop report on the evaluation of the updated and expanded carcinogen database to support derivation of threshold of toxicological concern values for DNA reactive carcinogens
Threshold of toxicological concern (TTC) values are frequently used for compounds occurring at low concentrations in feed and food or as impurities in drugs. This workshop report addresses the emerging alternatives for deriving TTC values for DNA reactive carcinogens and evaluating the acceptability of the Cramer Class TTC values to be adequately protective for non-DNA reactive carcinogens
Adsorption energies and ordered structures of hydrogen on Pd(111) from density functional periodic calculations
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