Molecular dynamics simulation analysis of ion irradiation induced defects in an amorphous silicon dioxide nanowire

Nanowires made of semiconducting materials are of great relevance and significance in future nanotechnological applications. Irradiation of nanowires is a decisive method used to dope nanowires and tune their structural, mechanical and optical properties. In this study the effects of ion irradiation of an amorphus silicon-dioxide nanowire with a Si core and SiO 2 shell are studied utilizing classical molecular dynamics (MD) simulation. The groundwork is based on the analysis of structural properties and sputtering effects of nanowire or nanorod under irradiation. Here the term nanorod or nanowire refers to any cylindrical shape that has arbitrary length and the cross-sectional diameter ranging from 1 to 100 nanometers. At lengths starting from several times the diameter, it becomes possible to simulate the nanorods and their properties using MD methods. A single argon ion was used for the irradiation process and the properties of the nanowire and sputtering effects were analyzed. The argon ions used for the irradiation process range from 1 to 30 kilo-electron volts (keV). The incident argon atom is irradiated perpendicular to the nanowire surface on both edge and flat surfaces at the given energy range. MD simulation provides the circumstances to simulate and study the sputtering effects of the irradiation process with a resolution in the femtosecond range. This resolution is not possible with current experimental methods and MD simulation is one of the only methods available to study this phenomenon. We performed 200 random individual argon impacts on the nanowire and present the average over all simulation runs. The results obtained show that the highest amounts of defects are produced at the irradiation energy of 10 keV. The defects also appear to be predominantly in the shell region of the nanowire regardless of incident ion energies

Bursts of activity in collective cell migration

Dense monolayers of living cells display intriguing relaxation dynamics, reminiscent of soft and glassy materials close to the jamming transition, and migrate collectively when space is available, as in wound healing or in cancer invasion. Here we show that collective cell migration occurs in bursts that are similar to those recorded in the propagation of cracks, fluid fronts in porous media and ferromagnetic domain walls. In analogy with these systems, the distribution of activity bursts displays scaling laws that are universal in different cell types and for cells moving on different substrates. The main features of the invasion dynamics are quantitatively captured by a model of interacting active particles moving in a disordered landscape. Our results illustrate that collective motion of living cells is analogous to the corresponding dynamics in driven, but inanimate, systems