# Void Swelling Induced Surface Modifications: Exploring the Relation between the Crystallographic Orientation and Surface Facets

## TL;DR

This paper explores how surface patterns form in nanocrystalline nickel during ion irradiation, linking the patterns to crystal orientation and void swelling.

## Contribution

A novel mechanism is proposed for nanopattern formation in nanocrystalline nickel under high-temperature ion irradiation.

## Key findings

- Surface nanopatterns in nanocrystalline nickel form due to void swelling during irradiation.
- Facet morphology is strongly influenced by crystallographic orientation, with <100> and <111> grains showing smooth or wavy patterns.
- Low stress and surface energies favor wavy facets, while higher values lead to complex shapes.

## Abstract

The phenomenon of surface facet formation during ion implantation has captured considerable scientific and technological interest. Surface facets—including wavy, pyramidal, and terraced morphologies—are typically formed during off‐normal keV and MeV ion beam implantation, and due to injected gas effects. In certain circumstances, these features may also emerge during irradiation at normal incidence: when differential sputtering occurs in biphasic regions, when contaminants are inadvertently added as dopants, or when the experimental arrangement permits the coimplantation of metals. The formation of surface nanopatterns in nanocrystalline nickel under high‐temperature ion irradiation at normal incidence has been observed—a phenomenon that conventional mechanisms fail to explain. A novel mechanism driving nanopattern formation under these conditions is presented. These findings offer compelling evidence that facets result from voids forming on the surface and in its vicinity. A strong correlation between the crystallographic orientation and the facet type has also been identified. Specifically, grains oriented in the <100> and <111> directions display smooth and wavy morphologies, while grains with orientations in between exhibit more complex shapes. The research indicates that grains with low stress and surface energies tend to exhibit wavy facets, while higher values lead to the formation of more complex shapes.

A novel mechanism for nanopattern formation in nanocrystalline nickel under high‐temperature ion irradiation is unveiled. Facets evolve from surface and subsurface voids, with their morphology dictated by crystallographic orientation. The <100> and <111> grains develop smooth or wavy facets, while others exhibit intricate designs. Low stress and surface energies favor wavy facets, whereas higher values result in more complex shapes.© 2026 WILEY‐VCH GmbH