arXiv subjects

Tyler P. Evans

Publications and source records attributed to Tyler P. Evans.

4 recordsLinked to original sources

arXiv2026

Morphological evolution of a semiconductor surface driven by irradiation-induced anisotropic plastic flow

While numerous models exist which explain certain aspects of irradiation-induced nanopatterning on semiconductors, a comprehensive theoretical explanation has remained elusive. However, it is increasingly apparent that such a model will require understanding the dual influence of the collision cascade initiated by ion implantation: first, as a source of material transport by sputtering and atomic displacements occurring over short time scales, and, second, as a source of defects permitting viscous flow within the thin, amorphous layer that results from sustained irradiation over longer time scales. To better understand the latter, we develop several asymptotic approximations for coupling the local ion flux experienced by the amorphous layer to the layer's evolving free interface. From these and the physical hypothesis of irradiation-induced anisotropic plastic flow, or ``ion-hammering", we derive a generalized Kuramoto-Sivashinsky-type equation for the evolving free surface. With physically plausible parameters, the present model achieves good quantitative and qualitative agreement with several aspects of experimental observations of nano-pattern formation during irradiation of silicon by argon, krypton and xenon, and with projectile energies from 500eV to 2keV. Disagreements between model and experiment are discussed, as are implications for future directions.

cond-mat.mes-hall↗

arXiv2025

Fluidity and morphological stability of an amorphous thin film with radiation-induced defect kinetics

It is common to model ion-irradiated amorphous thin films as if they were highly viscous fluids. In such models, one is frequently concerned with the ion-enhanced fluidity, a measure of the ability of the free interface to relax surface energy. Motivated by usual fluid dynamics problems, the ion-enhanced fluidity is near-universally treated as a constant throughout the amorphous layer. However, for an irradiated thin film, the fluidity is ultimately caused by radiation-induced defect kinetics within the film, leading to regions with greater or lesser fluidity, and sensitive dependence on ion energy, species, flux, irradiation angle, temperature, and other experimental parameters. Here, we develop and analyze a model of radiation-induced defect kinetics coupled to the continuum equations of a viscous thin film. Using realistic parameter values, we show that defect kinetics can meaningfully alter theoretical predictions of surface relaxation and ion-enhanced fluidity. Implications for aligning theoretical and experimental work, especially for surface nano-patterning of silicon induced by low-energy argon irradiation, are discussed.

cond-mat.soft↗

arXiv2025

Viscous flow model of ion-induced pattern formation: consistency between theory and experiment

It is known that ion-irradiation can lead surfaces to spontaneously develop patterns with characteristic length scales on the order of only a few nanometers. Pattern formation typically occurs only for irradiation angles beyond a critical angle, which varies with projectile, target, and irradiation energy. To date, there is no completely unifying physical theory. However, since predictions of the critical angle can be extracted from linear stability analysis of a given model, the ability to explain critical angle selection is a simple but important test of model validity. In this paper, we survey all existing critical angle, wavelength, and in-plane stress data for noble gas broad beam ion-irradiation of silicon and germanium by argon, krypton and xenon at energies from 250eV to 2keV. While neglecting the effects of erosion and redistribution, which are widely regarded as key contributors to ion-induced pattern formation, we find that a viscous flow model is capable of explaining these three types of experimental data simultaneously using only parameters within a physically-reasonable range, and in a manner consistent with the defect kinetics of the amorphous layer. This bolsters the case for viscous flow and stress-driven instabilities as important components of an eventual, unifying model of nanoscale pattern formation under ion bombardment.

cond-mat.mtrl-sci↗

arXiv2025

Design of resilient structures by randomization and bistability

This paper examines various ways of improving the impact resilience of protective structures. Such structures' purpose is to dissipate an impact's energy while avoiding cracking and failure. We have tested the reaction of plane elastic-brittle lattices to an impulse. Four topologies are compared: periodic triangular, square, and hexagonal topologies, and aperiodic Penrose topology. Then, structures with random variations of the links' stiffness, node positions, and random holes are compared. Combinations of these random factors are also considered, as well as the resilience of bistable elastic-brittle lattices with sacrificial links. Several parameters are introduced to measure the structural resilience of the compared designs: (i) the amount of dissipated impact energy, (ii) the size of broken clusters of links, and (iii) the spread of damage. The results suggest new routes for rationally designing protective structures using nonperiodic topology, bistability, and structural randomness. In particular, we find that some quantities of interest can be maximized by tuning the randomized design appropriately -- for example, randomly removing 8\% of links maximizes energy dissipation. We also find that randomization of bistable lattices can offer superior energy dissipation while reducing the connectivity between broken clusters of links.

physics.comp-ph↗