Effects of crystallographic and geometric orientation on ion beam sputtering of gold nanorods.

Nanostructures may be exposed to irradiation during their manufacture, their engineering and whilst in-service. The consequences of such bombardment can be vastly different from those seen in the bulk. In this paper, we combine transmission electron microscopy with in situ ion irradiation with complementary computer modelling techniques to explore the physics governing the effects of 1.7 MeV Au ions on gold nanorods. Phenomena surrounding the sputtering and associated morphological changes caused by the ion irradiation have been explored. In both the experiments and the simulations, large variations in the sputter yields from individual nanorods were observed. These sputter yields have been shown to correlate with the strength of channelling directions close to the direction in which the ion beam was incident. Craters decorated by ejecta blankets were found to form due to cluster emission thus explaining the high sputter yields.

Kinetic Monte Carlo simulations of proton conductivity.

The kinetic Monte Carlo method is used to model the dynamic properties of proton diffusion in anhydrous proton conductors. The results have been discussed with reference to a two-step process called the Grotthuss mechanism. There is a widespread belief that this mechanism is responsible for fast proton mobility. We showed in detail that the relative frequency of reorientation and diffusion processes is crucial for the conductivity. Moreover, the current dependence on proton concentration has been analyzed. In order to test our microscopic model the proton transport in polymer electrolyte membranes based on benzimidazole C(7)H(6)N(2) molecules is studied.

Enhanced sputtering yields from single-ion impacts on gold nanorods.

Sputtering yields, enhanced by more than an order of magnitude, have been observed for 80 keV Xe ion irradiation of monocrystalline Au nanorods. Yields are in the range 100-1900 atoms/ion compared with values for a flat surface of ≈50. This enhancement results in part from the proximity of collision cascades and ensuing thermal spikes to the nanorod surfaces. Molecular dynamic modeling reveals that the range of incident angles occurring for irradiation of nanorods and the larger number of atoms in "explosively ejected" atomic clusters make a significant contribution to the enhanced yield.

Hybrid Monte Carlo-molecular dynamics algorithm for the study of islands and step edges on semiconductor surfaces: application to Si/Si (001).

A classical, hybrid Monte Carlo-molecular dynamic (MC-MD) algorithm is introduced for the study of phenomena like two-dimensional (2D) island stability or step-edge evolution on semiconductor surfaces. This method presents the advantages of working off lattice and utilizing bulk-fitted potentials. It is based on the introduction of collective moves, such as dimer jumps, in the MC algorithm. MD-driven local relaxations are considered as trial moves for the MC. The algorithm is applied to the analysis of 2D Si islands on Si(001). Results on early stages of island formation, island stability versus temperature and system size, and step-edge evolution are presented. In all cases good qualitative agreement with experimental results is found.

Comparison of different cell-cluster models for cell-level dosimetry.

An important factor in dose calculations for targeted radionuclide therapy is the cell-cluster model used. We developed a cell-cluster model based on optimization through mechanical hard-sphere collisions. The geometrical properties and the dosimetric effects of the new model were compared with those of two previous models, i.e. the traditional lattice model and our CellPacker model in which the cells are individually and systematically piled as a cluster. The choice of the cell-cluster model has an effect on the calculated mean absorbed doses in the cells. While CellPacker produces clusters with distinct tumour-healthy tissue interface, our new model is able to make the interface diffuse. Outside the interface the new model is capable to pack cells tighter than CellPacker enabling the description of tissues of higher cellular density. Our two cluster models make it possible to construct the cluster model according to the tissue in question.

Radiation spectra of 111In, 113mIn and 114mIn.

The radiation spectra of 111In, 113In, and 114mIn are calculated with the Monte Carlo computer program IMRDEC. The relaxation probabilities are taken from the EADL file of the Lawrence Livermore National Laboratory. Because this file does not include data for some N and O transitions, these were additionally determined by applying the Kassis rule. Two schemes are applied to calculate the transition energies: 1) a simple (Z + 1)/Z scheme, and 2) accurate calculation solving the relativistic Dirac equations. It is shown that using the extended set of relaxation probabilities leads to generation of many additional low-energy Auger and CK electrons if the (Z + 1)/Z rule is applied. On the other hand, the emissions of almost all these electrons are rejected if their energies are calculated solving the Dirac equations taking into consideration realistic electron vacancies.

Cluster models in cellular level electron dose calculations.

A program for calculating absorbed dose was developed for radioimmunotherapy (RIT) purposes. It was used to determine the difference in the therapeutic effect of (111)In electrons when using a close-packed cubic geometry and a cell cluster model developed in this project. Our cluster model piles the cells individually. The cells were modelled as spheres of diameters of 12 (tumour) and 30 (healthy) microm. Both models were used to generate clusters with spherical tumours inside healthy tissue. The program uses Monte Carlo-based dose kernels. The radiation spectra were calculated from the Auger and x-ray transition strengths and fluorescence yields of (111)In. The results show the importance of the cluster model in cellular level dose calculations. Near the tumour/healthy tissue interface in particular, the doses differ because of geometrical differences. In the case of a small cluster with tumour and total diameters of 30 and 150 microm, the ratio of the therapeutic effects is 20.

Infection markers during labor at term.

Serum levels of C-reactive protein (CRP), white blood cell count (WBC), amniotic fluid white blood cells (Gram staining) and leukocyte esterase (LE) activity were measured serially and prospectively in 30 pregnant women in labor at term. Results were retrospectively compared with amniotic fluid bacterial culture results. Leukocyte esterase activity was measured by the dipstick test (Nephurtest) and an in vitro photometric method. Amniotic fluid samples were collected through an intrauterine transvaginal pressure catheter. The serial CRP and WBC levels from admission to the delivery and CRP levels from delivery to the first post partum day increased statistically significantly. Levels of both markers correlated significantly with duration of labor. Both amniotic white blood cells and leukocyte esterase activity increased during labor. Bacterial colonization of amniotic fluid was not clearly associated with amniotic LE-activity or leukocyte count as determinated by Gram stain. The tests evaluated cannot be regarded as reliable methods in distinguishing intra-amniotic infection during labor and vaginal delivery at term.