Silicon formation in bulk silica through femtosecond laser engraving

TL;DR

This paper demonstrates that femtosecond laser pulses can induce silicon formation within bulk silica by causing ion separation and crystallization, enabling direct-write 3D silicon micro-devices in silica substrates.

Contribution

It reveals a new mechanism of silicon formation in silica via femtosecond laser irradiation, facilitating 3D silicon micro-structure fabrication without microexplosions.

Findings

Silicon micro-crystallites form in silica after femtosecond laser irradiation.

The process occurs without confined microexplosion and at moderate numerical aperture.

This enables direct-write 3D silicon structures within silica.

Abstract

Non-linear absorption phenomena induced by controlled irradiation with a femtosecond laser beam can be used to tailor materials properties within the bulk of substrates. One of the most successful applications of this technique is the ability to fabricate three-dimensional micro-devices integrating optical, mechanical or fluid handling functions in a single substrate. In this context, amorphous SiO2 is the most widely studied material. Here we show that short (50-fs) femtosecond pulses induce the separation of Si and O ions in SiO2 substrates, leading to the formation of micro-crystallites that we identify as pure crystalline phase of Si. Interestingly, this polymorphic phase transformation occurs in the absence of laser-induced confined microexplosion and with moderate numerical aperture. These findings not only unravel a key mechanism related to the transformation of the material and its subsequent properties, but also pave the road for the development of three-dimensional Si-rich structures embedded in a pure silica phase, eventually leading to novel disruptive approaches for fabricating three- dimensional micro-devices. For instance, one could imagine a silica-host substrate, in which arbitrary three-dimensional silicon-based components are direct-write using a femtosecond laser, rather than through assembly of components coming out of different substrates or using multiple processing steps.