PLASTAMORPH

Complex mechanical response of silica-based amorphous materials: from the atomic to the mesoscopic scale

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 Obiettivo del progetto (Objective)

'This project focuses on the study of the mechanical behaviour of silica-based amorphous materials, which have attracted the interest of the scientific community both for their intrinsic physical properties and for the possibility to use them in technological applications, for example in micro- and nano-electronic devices, coatings and glasses. The mechanical response of amorphous materials, such as silica and silicate glasses, is still under investigation and it has not been fully understood yet because of the difficulty to visualize the microscopic rearrangements at the atomic scale. For example, the plastic response cannot be described in terms of dislocations as in crystals. Moreover, the small-scale response can be responsible for the macroscopic mechanical properties, like e.g. plastification, rupture and densification, but a clear link between the atomic-scale behaviour and the macroscopic phenomenology has not been established yet. Therefore, the aim of the project is to obtain an accurate and realistic theoretical description of the elastic and plastic response of silica-based amorphous materials by using complementary numerical techniques, trying to identify the relevant physical mechanisms of the response from the atomic to the mesoscopic length scale. We will propose a multi-scale modelling of the mechanical behaviour of these materials by performing Molecular Dynamics calculations at the nanoscale and finite-element calculations at the micrometer scale. The obtained results will be compared to experimental results found for different glasses and for several mechanical deformations. In this way we will provide a unifying description of these systems at different length scales and we will analyze the microscopic foundation of their phenomenological behaviour, thus advancing the state of knowledge in the field of amorphous materials.'

Introduzione (Teaser)

Amorphous silicon is rapidly becoming the material of choice for many electronics and optics applications. Previously lacking multi-scale models of its mechanical behaviour will provide the basis for improved product functionalities.

Descrizione progetto (Article)

Unlike the well-ordered lattice of crystalline silicon (Si), amorphous Si consists of atoms forming a continuous random network.

Intense scientific interest in the applications of amorphous silica (silicon dioxide (SiO2))-based materials has highlighted the difficulty in describing their mechanical responses at atomic scale.

EU funding of the project PLASTAMORPH supported the development of a unifying theoretical description of these materials at varying length scales.

The multi-scale modelling provided insight into the role of physical mechanisms at the atomic scale in shaping macroscopic phenomena.

An accurate description of behaviours at small length scales will help overcome problems of plasticity (deformation) and fatigue in Si-based devices.The project set four technical objectives.

Enhanced understanding of the local mechanical response of Si-based amorphous materials should be linked to their macroscopic rheological behaviour.

Researchers also sought to characterise the vibrational behaviour of the materials and to investigate effects of pressure on Si nanopillars that are gaining interest for applications in optoelectronics.Exploiting molecular dynamics simulations based on multi-body dynamics algorithms, researchers have analysed effects of shear (static conditions) and shear rate (time-varying conditions) as well as bond directionality on the small-scale mechanical response.

The simulations provided evidence of two types of plastic rearrangements: nucleation of isolated events and avalanche-like rearrangements.Studies of the vibrational properties of the amorphous Si model shed light on the unusual properties of amorphous materials.

In particular, scientists showed that the classical description in which any arbitrary vibration can be described as the superposition of elementary ones does not apply.

Finally, numerical investigations studied the mechanical properties of nanopillar as a function of size, demonstrating a decrease in inner pressure as a function of the square of the nanopillar radius.PLASTAMORPH has provided important insight into the atomic-scale behaviour of amorphous Si-based materials, filling an important knowledge gap previously inhibiting their full exploitation in optoelectronic devices.

Controlling deformation and fatigue are now within the realm of possibility.

In addition to paving the way for future development of amorphous Si-based materials, the models will be integral to the study of amorphous solids for a variety of applications.