Shear melting of silicon and diamond and the disappearance of the polyamorphic transition under shear

Moras, Gianpietro; Klemenz, Andreas; Reichenbach, Thomas; Gola, Adrien; Uetsuka, Hiroshi; Moseler, Michael; Pastewka, Lars

doi:10.1103/physrevmaterials.2.083601

Cited by 31 publications

(31 citation statements)

References 39 publications

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“…Being able to capture this phenomenon at all requires system sizes beyond the nanometric length scale. We note that McMillan et al explicitly mention the presence of both polyamorphs on decompression, inferred from Raman data at the time 11 , and that Moras et al described the simulation of a gradual transition between LDA-and HDA-like a-Si under hydrostatic pressure, as well as the disappearance of this effect under shear 35 .…”

Section: Structural Transitions Under Pressurementioning

confidence: 81%

Origins of structural and electronic transitions in disordered silicon

Deringer

Bernstein

Csänyi

et al. 2021

Nature

269

226

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Structurally disordered materials continue to pose fundamental questions [1][2][3][4] , including that of how different disordered phases ("polyamorphs") can coexist and transform from one to another 5-9 . As a widely studied case, amorphous silicon (a-Si) forms a fourfold-coordinated, covalent network at ambient conditions and much higher-coordinated, metalliclike phases under pressure 10-12 . However, a detailed mechanistic understanding of the structural transitions in disordered silicon has been lacking, due to intrinsic limitations of even the most advanced experimental and computational techniques. Here, we show how atomistic machine-learning (ML) models can break through this long-standing barrier, describing liquid-amorphous and amorphous-amorphous transitions with quantum-mechanical accuracy for a system of 100,000 atoms (ten-nanometre length scale). Our simulations reveal a three-step transformation sequence for a-Si under increasing external pressure. First, polyamorphic low-and high-density amorphous (LDA and HDA) regions are found to coexist, rather than appearing sequentially. Then, we observe a structural collapse into a distinct, very-high-density amorphous (VHDA) phase. Finally, our simulations indicate the transient nature of this VHDA phase: it rapidly nucleates crystallites, ultimately leading to the formation of a poly-crystalline structure, consistent with experiments [13][14][15] but not seen in earlier simulations 11,[16][17][18] . An ML model for electronic densities of states (DOS) confirms the onset of metallicity during VHDA formation and subsequent crystallisation. These results shed new light on liquid and amorphous states of silicon, and, in a wider context, they exemplify a holistic, ML-driven approach to predictive materials mod-

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Section: Structural Transitions Under Pressurementioning

confidence: 81%

Origins of structural and electronic transitions in disordered silicon

Deringer

Bernstein

Csänyi

et al. 2021

Nature

269

226

View full text Add to dashboard Cite

show abstract

“…Reactive molecular dynamics simulations have also been applied to study the wear of silicon and silica. Simulations that employed a modified Tersoff potential with an improved angle-dependent term [68] showed that shear drives amorphization of diamond-cubic Si and diamond [69]. Further, it was suggested that shear-induced amorphous Si is denser than diamond-cubic Si, while amorphous C is less dense than diamond, so the amorphization rates of Si and C exhibit opposite pressure dependence trends.…”

Section: Reactions Between Solid Surfacesmentioning

confidence: 99%

Tribochemistry: A Review of Reactive Molecular Dynamics Simulations

2020

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Tribochemistry, the study of chemical reactions in tribological interfaces, plays a critical role in determining friction and wear behavior. One method researchers have used to explore tribochemistry is “reactive” molecular dynamics simulation based on empirical models that capture the formation and breaking of chemical bonds. This review summarizes studies that have been performed using reactive molecular dynamics simulations of chemical reactions in sliding contacts. Topics include shear-driven reactions between and within solid surfaces, between solid surfaces and lubricating fluids, and within lubricating fluids. The review concludes with a perspective on the contributions of reactive molecular dynamics simulations to the current understanding of tribochemistry, as well as opportunities for this approach going forward.

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“…This process is mechanically driven and leads to a non-equilibrium state with low shear resistance that accommodates the shear deformation. Like in other mechanically driven tribological processes 37 , 38 , this metastable material has a higher energy than the original one and sulphur penetration cannot be described thermodynamically. In contrast, on a-C:H, the ZDDP chemisorbed layer would be able to support GPa owing to steric hindrance between surface hydrogen atoms.…”

Section: Discussionmentioning

confidence: 87%

Interplay of mechanics and chemistry governs wear of diamond-like carbon coatings interacting with ZDDP-additivated lubricants

et al. 2021

Self Cite

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Friction and wear reduction by diamond-like carbon (DLC) in automotive applications can be affected by zinc-dialkyldithiophosphate (ZDDP), which is widely used in engine oils. Our experiments show that DLC’s tribological behaviour in ZDDP-additivated oils can be optimised by tailoring its stiffness, surface nano-topography and hydrogen content. An optimal combination of ultralow friction and negligible wear is achieved using hydrogen-free tetrahedral amorphous carbon (ta-C) with moderate hardness. Softer coatings exhibit similarly low wear and thin ZDDP-derived patchy tribofilms but higher friction. Conversely, harder ta-Cs undergo severe wear and sub-surface sulphur contamination. Contact-mechanics and quantum-chemical simulations reveal that shear combined with the high local contact pressure caused by the contact stiffness and average surface slope of hard ta-Cs favour ZDDP fragmentation and sulphur release. In absence of hydrogen, this is followed by local surface cold welding and sub-surface mechanical mixing of sulphur resulting in a decrease of yield stress and wear.

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Shear melting of silicon and diamond and the disappearance of the polyamorphic transition under shear

Cited by 31 publications

References 39 publications

Origins of structural and electronic transitions in disordered silicon

Origins of structural and electronic transitions in disordered silicon

Tribochemistry: A Review of Reactive Molecular Dynamics Simulations

Interplay of mechanics and chemistry governs wear of diamond-like carbon coatings interacting with ZDDP-additivated lubricants

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