Crater formation by fast ions: comparison of experiment with Molecular Dynamics simulations

An incident fast ion in the electronic stopping regime produces a track of excitations which can lead to particle ejection and cratering. Molecular Dynamics simulations of the evolution of the deposited energy were used to study the resulting crater morphology as a function of the excitation density in a cylindrical track for large angle of incidence with respect to the surface normal. Surprisingly, the overall behavior is shown to be similar to that seen in the experimental data for crater formation in polymers. However, the simulations give greater insight into the cratering process. The threshold for crater formation occurs when the excitation density approaches the cohesive energy density, and a crater rim is formed at about six times that energy density. The crater length scales roughly as the square root of the electronic stopping power, and the crater width and depth seem to saturate for the largest energy densities considered here. The number of ejected particles, the sputtering yield, is shown to be much smaller than simple estimates based on crater size unless the full crater morphology is considered. Therefore, crater size can not easily be used to estimate the sputtering yield.Comment: LaTeX, 7 pages, 5 EPS figures. For related figures/movies, see: http://dirac.ms.virginia.edu/~emb3t/craters/craters.html New version uploaded 5/16/01, with minor text changes + new figure

Coulomb Explosion and Thermal Spikes

A fast ion penetrating a solid creates a track of excitations. This can produce displacements seen as an etched track, a process initially used to detect energetic particles but now used to alter materials. From the seminal papers by Fleischer et al. [Phys. Rev. 156, 353 (1967)] to the present [C. Trautmann, S. Klaumunzer and H. Trinkaus, Phys. Rev. Lett. 85, 3648 (2000)], `Coulomb explosion' and thermal spike models are treated as conflicting models for describing ion track effects. Here molecular dynamics simulations of electronic-sputtering, a surface manifestation of ion track formation, show that `Coulomb explosion' produces a `heat' spike so that these are early and late aspects of the same process. Therefore, differences in scaling are due to the use of incomplete spike models.Comment: Submitted to PRL. 4 pages, 3 figures. For related movies see: http://dirac.ms.virginia.edu/~emb3t/coulomb/coulomb.html PACS added in new versio

Pit formation on poly(methyl methacrylate) due to ablation induced by individual slow highly charged ion impact

Abstract -We report the formation of nano-sized pits on poly(methyl methacrylate) after exposure to slow highly charged ion beams. The pits are formed on the polymer surface as a direct result of individual ion impacts. Intermittent contact mode atomic-force microscopy was employed to study the size evolution of the pits in dependence of potential and kinetic energies of the incident ions. A potential energy threshold value of approximately 7 keV was found for pit formation. Above this value an increase in potential energy results in an increasing pit volume, while the pit shape can be tuned by varying the kinetic energy. Copyright c EPLA, 2012 Introduction. -Controlled and reproducible creation and manipulation of nano-sized objects in all three spatial directions are prominent goals in modern nanotechnology. Recently it has been demonstrated, that individual slow (keV) highly charged ions (HCI) are able to produce nano-sized structural modifications on various substrate surfaces by ion impact (se

Mortalidade por doenças cardiorrespiratórias em idosos no estado de Mato Grosso, 1986 a 2006

OBJETIVO: Descrever a evolução temporal da mortalidade por doenças cardiorrespiratórias em idosos. MÉTODOS: Estudo epidemiológico descritivo com delineamento ecológico de séries temporais realizado no estado do Mato Grosso, de 1986 a 2006. Foram utilizados dados sobre doenças dos aparelhos respiratório e circulatório obtidos do Sistema de Informação sobre Mortalidade do Ministério da Saúde. Modelos de regressão linear simples foram ajustados para avaliar a tendência das taxas específicas de mortalidade por grupos específicos de idade (60 a 69, 70 a 79 e 80 ou mais anos) e sexo. RESULTADOS: Houve aumento na proporção de óbitos por doenças respiratórias e diminuição por doenças cardiovasculares. Na comparação de taxas entre os sexos, as mulheres apresentaram taxas 15% menores para as causas cardiovasculares e taxas similares ao sexo masculino para as causas respiratórias. Foi observada taxa elevada de mortalidade por doenças respiratórias e cardiovasculares, com importante tendência de incremento entre os grupos mais longevos. Em idosos com idade >; 80 anos o aumento anual médio na taxa de mortalidade por doenças respiratórias foi de 1,99 óbitos e de 3,43 por doenças do aparelho circulatório. CONCLUSÕES: O estado de Mato Grosso apresenta elevada taxa de mortalidade por doenças respiratórias e cardiovasculares em idosos, com importante tendência de incremento entre os grupos mais longevos.OBJETIVO: Describir la evolución temporal de la mortalidad por enfermedades cardiorrespiratorias en ancianos. MÉTODOS: Estudio epidemiológico descriptivo con delineamiento ecológico de series temporales realizado en el Estado de Mato Grosso, Centro-Oeste de Brasil, de 1986 a 2006. Se utilizaron datos sobre enfermedades de los aparatos respiratorio y circulatorio obtenidos del Sistema de Información sobre Mortalidad del Ministerio de la Salud. Modelos de regresión lineal simple fueron ajustados para evaluar la tendencia de las tasas específicas de mortalidad por grupos específicos de edad (60 a 69, 70 a 70 y 80 o más años) y sexo. RESULTADOS: Hubo aumento en la proporción de óbitos por enfermedades respiratorias y disminución por enfermedades cardiovasculares. En la comparación de tasas entre los sexos, las mujeres presentaron tasas 15% menores para las causas cardiovasculares y tasas similares al sexo masculino para las causas respiratorias Se observó tasa elevada de mortalidad por enfermedades respiratorias y cardiovasculares, con importante tendencia de incremento entre los grupos más longevos. En ancianos con edad ³80 años o aumento anual promedio en la tasa de mortalidad por enfermedades respiratorias fue de 1,99 óbitos y de 3,43 por enfermedades del aparato circulatorio. CONCLUSIONES: El Estado de Mato Grosso presenta elevada tasa de mortalidad por enfermedades respiratorias y cardiovasculares en ancianos, con importante tendencia de incremento entre los grupos más longevos.OBJECTIVE: To describe time trends of mortality due to cardiorespiratory diseases in elderly people. METHODS: Epidemiological descriptive study with an ecological time series approach conducted in the state of Mato Grosso, Central-West Brazil, between 1986 and 2006. Data were obtained from the Brazilian Ministry of Health Mortality Database. Linear regression models were adjusted to analyze trends in mortality rates by age groups (60 to 69; 70 to 79; and 80 or more) and gender. RESULTS: There was an increase in proportion of deaths due to respiratory diseases and a decrease in proportion of deaths due to cardiovascular diseases. As for gender, cardiovascular rates were 15% lower in women than men and respiratory rates were similar in both men and women. High mortality rates for respiratory and cardiovascular diseases were observed with increasing trends among the oldest-old groups. The annual average increase for respiratory and cardiovascular diseases in those aged 80 years and older was 1.99 and 3.43 deaths, respectively. CONCLUSIONS: The state of Mato Grosso shows high mortality rates due to cardiorespiratory disease among elderly people with increasing trends among the oldest-old groups