Softening the ultra-stiff: controlled variation of Young's modulus in single crystal diamond

TL;DR

This study demonstrates how controlled defect introduction in single-crystal diamond can precisely tune its Young's modulus without causing graphitization, combining experimental nano-indentation with multi-scale modeling.

Contribution

It presents the first combined experimental and numerical analysis of elastic property variation in defective single-crystal diamond using nano-indentation, atomistic simulations, and FEM modeling.

Findings

Defects reduce Young's modulus and density without graphitization.

Ab initio simulations confirm experimental elastic property changes.

FEM simulations verify deformation consistency and stress levels.

Abstract

A combined experimental and numerical study on the variation of the elastic properties of defective single-crystal diamond is presented for the first time, by comparing nano-indentation measurements on MeV-ion-implanted samples with multi-scale modeling consisting of both ab initio atomistic calculations and meso-scale Finite Element Method (FEM) simulations. It is found that by locally introducing defects in the 2x10^18 - 5x10^21 cm-3 density range, a significant reduction of, as well as of density, can be induced in the diamond crystal structure without incurring in the graphitization of the material. Ab initio atomistic simulations confirm the experimental findings with a good degree of confidence. FEM simulations are further employed to verify the consistency of measured deformations with a stiffness reduction, and to derive strain and stress levels in the implanted region. Combining these experimental and numerical results, we also provide insight into the mechanism responsible for the depth dependence of the graphitization threshold in diamond. This work prospects the possibility of achieving accurate tunability of the mechanical properties of single-crystal diamond through defect engineering, with significant technological applications, i.e. the fabrication and control of the resonant frequency of diamond-based micromechanical resonators.