Coherent X-ray measurements of ion-implantation-induced lattice strains in nano-crystals

TL;DR

This study uses Bragg Coherent X-ray Diffraction Imaging to measure and analyze the lattice strains and structural damage caused by focused ion beam milling in nano-crystals, revealing significant distortions and defect formations.

Contribution

It provides the first detailed 3D measurements of FIB-induced lattice strains at the nanoscale, linking ion doses to structural damage and instabilities.

Findings

Low gallium doses cause substantial lattice distortions.

Higher doses lead to defect structures and stresses exceeding the bulk yield limit.

Structural damage and inhomogeneous morphologies are driven by FIB-induced strains.

Abstract

Focussed Ion Beam (FIB) milling is a mainstay of nano-scale machining. By manipulating a tightly focussed beam of energetic ions, often gallium (Ga+), FIB can sculpt nanostructures via localised sputtering. This ability to cut solid matter on the nano-scale has revolutionised sample preparation across the life-, earth- and materials sciences. For example FIB is central to microchip prototyping, 3D material analysis, targeted electron microscopy sample extraction and the nanotechnology behind size-dependent material properties. Despite its widespread usage, detailed understanding of the functional consequences of FIB-induced structural damage, intrinsic to the technique, remains elusive. Here, we present nano-scale measurements of three-dimensional, FIB-induced lattice strains, probed using Bragg Coherent X-ray Diffraction Imaging (BCDI). We observe that even low gallium ion doses, typical of FIB imaging, cause substantial lattice distortions. At higher doses, extended self-organised defect structures appear, giving rise to stresses far in excess of the bulk yield limit. Combined with detailed numerical calculations, these observations provide fundamental insight into the nature of the damage created and the structural instabilities that lead to a surprisingly inhomogeneous morphology.