Amorphization and nanocrystallization of silicon under shock compression

Zhao, Shiteng; Hahn, Eric N.; Kad, Bimal K.; Remington, B. A.; Wehrenberg, Christopher; Bringa, Eduardo M.; Meyers, Marc A.

doi:10.1016/j.actamat.2015.09.022

Cited by 119 publications

(75 citation statements)

References 72 publications

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“…This is partially confirmed in a very recent paper by Zhao et al, 21 in which defect accumulation induced amorphization was observed locally in bulk c-Si under dynamic shock compression, resulting in a complex distribution of a-Si.…”

Section: Discussionsupporting

confidence: 72%

“…10 As such, in the absence of direct evidence, the necessity of the Si-II phase during the CAT process is uncertain, and has in fact been challenged by several research groups. 13,14,21 In an effort to directly observe the response of c-Si to indentation, Minor et al 22 carried out indentation tests inside TEM. They found no phase transformation and only dislocationmediated metal-like plastic deformation.…”

Section: Introductionmentioning

confidence: 99%

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In situ TEM study of deformation-induced crystalline-to-amorphous transition in silicon

et al. 2016

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The mechanism responsible for deformation-induced crystalline-to-amorphous transition (CAT) in silicon is still under considerable debate, owing to the absence of direct experimental evidence. Here we have devised a novel core/shell configuration to impose confinement on the sample to circumvent early cracking during uniaxial compression of submicron-sized Si pillars. This has enabled large plastic deformation and in situ monitoring of the CAT process inside a transmission electron microscope. We demonstrate that diamond cubic Si transforms into amorphous silicon through slip-mediated generation and storage of stacking faults (SFs), without involving any intermediate crystalline phases. By employing density functional theory simulations, we find that energetically unfavorable single-layer SFs create very strong antibonding interactions, which trigger the subsequent structural rearrangements. Our findings thus resolve the interrelationship between plastic deformation and amorphization in silicon, and shed light on the mechanism underlying deformation-induced CAT in general.

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Section: Discussionsupporting

confidence: 72%

Section: Introductionmentioning

confidence: 99%

In situ TEM study of deformation-induced crystalline-to-amorphous transition in silicon

et al. 2016

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“…Applying classical nucleation theory we can obtain the pressure and shear-stress dependence of the nucleation barrier, as explained previously by Zhao et al (31),…”

Section: Discussionmentioning

confidence: 99%

Generating gradient germanium nanostructures by shock-induced amorphization and crystallization

Zhao

Kad

Wehrenberg

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Gradient nanostructures are attracting considerable interest due to their potential to obtain superior structural and functional properties of materials. Applying powerful laser-driven shocks (stresses of up to one-third million atmospheres, or 33 gigapascals) to germanium, we report here a complex gradient nanostructure consisting of, near the surface, nanocrystals with high density of nanotwins. Beyond there, the structure exhibits arrays of amorphous bands which are preceded by planar defects such as stacking faults generated by partial dislocations. At a lower shock stress, the surface region of the recovered target is completely amorphous. We propose that germanium undergoes amorphization above a threshold stress and that the deformation-generated heat leads to nanocrystallization. These experiments are corroborated by molecular dynamics simulations which show that supersonic partial dislocation bursts play a role in triggering the crystalline-to-amorphous transition.amorphization | laser shock | nanocrystallization | germanium | gradient materials A morphous and gradient nanostructures are drawing intense attention due to their superior functional and mechanical properties (1, 2). Since they are thermodynamically metastable, amorphous materials can transform into nanocrystalline ones if appropriate treatments are applied (3). One of the most common methods to achieve amorphization is to quench a liquid at ultrafast cooling rates, which is extremely difficult for most pure elements (4). Alternatively, it has been shown that application of pressure leads to amorphization of materials whose melting point displays a negative Clapeyron slope (dT/dP < 0) (5-9); germanium (Ge) falls into this category (10). However, instead of pressure-induced amorphization, numerous studies, under both static (11, 12) and dynamic conditions (13-15), have shown that Ge undergoes a polymorphic transition at elevated pressures. Consequently, amorphization was not unambiguously identified in Ge until Clarke et al. (16) observed the indentation-induced crystalline-to-amorphous transition. More recently, a high-speed nanodroplet test also showed surface amorphization of Ge in an extremely localized manner (17).Despite being widely studied, the underlying microstructural mechanisms of pressure-induced amorphization remain vague. This is due to the notorious brittleness of germanium at room temperature which renders its recovery from pressurization extremely challenging. The deposition of high-power pulsed-laser energy onto a millimeter-scale target generates transient states of extreme stresses that promptly build up and decay rapidly as the pulse propagates. The short duration of the stress pulse and impedancematched encapsulation preserves the integrity of the target by suppressing the full development of cracks and enables postshock microstructure characterization. Using this methodology, we have previously reported shock-induced amorphization in silicon (18) and boron carbide (19). Before that, Jeanloz et al. (20) discovered this ...

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“…Despite the simplicity and effective 1D treatment, this model explained many experimental results on PTs in DAC and RDAC and developed our intuition on the interaction between PTs and plasticity at the nanoscale. Due to the generic character of the model, qualitative conclusions from its application have been used by other groups to interpret their experimental findings in high pressure torsion [99,103], mechanochemistry and ball milling [108,109,110] and shock-induced amorphization in Si [111].…”

Section: Pts Under High Pressure and Compression And Shearmentioning

confidence: 99%

“…Alternative boundary conditions-free lateral surfaces-, have been applied for an exploratory study of the shearinduced PT at zero pressure in [8]. Still, results obtained in [64], again due to their generic character, were applied in [103] for the interpretation of experiments on high pressure torsion, in [112] on PTs in nanomaterials under mechanical loading, and in [111] on shock-induced amorphization in Si.…”

Section: Pts Under High Pressure and Compression And Shearmentioning

confidence: 99%

Phase field simulations of plastic strain-induced phase transformations under high pressure and large shear

Javanbakht

Levitas

2016

Phys. Rev. B

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Pressure and shear strain-induced phase transformations (PTs) in a nanograined bicrystal at the evolving dislocations pile-up have been studied utilizing phase field approach (PFA).The complete system of PFA equations for coupled martensitic PT, dislocation evolution, and mechanics at large strains is presented and solved using finite element method (FEM). The nucleation pressure for high pressure phase (HPP) under hydrostatic condition near single dislocation was determined to be 15.9 GPa. Under shear, a dislocations pile-up that appears in the left grain creates strong stress concentration near its tip and significantly increases the local thermodynamic driving force for PT, which causes nucleation of HPP even at zero pressure. At pressures of 1.59 and 5 GPa and shear, a major part of a grain transforms to HPP.When dislocations are considered in the transforming grain as well, they relax stresses and lead to a slightly smaller stationary HPP region than without dislocations. However, they strongly suppress nucleation of HPP and require larger shear. Unexpectedly, the stationary HPP morphology is governed by the simplest thermodynamic equilibrium conditions, which do not contain contributions from plasticity and surface energy. These equilibrium conditions are fulfilled either for the majority of points of phase interfaces or (approximately) in terms of stresses averaged over the HPP region or for the entire grain, despite the strong heterogeneity of stress fields. The major part of the driving force for PT in the stationary state is due to deviatoric stresses rather than pressure. While the least number of dislocations in a pile-up to nucleate HPP linearly decreases with increasing the applied pressure, the least corresponding shear strain depends on pressure nonmonotonously. Surprisingly, the ratio of kinetic coefficients for PT and dislocations affect stationary solution and nanostructure. Consequently, there are multiple stationary solutions under the same applied load and PT and deformation processes are path dependent. With an increase in the size of the sample by a factor of two, 2 no effect was found on the average pressure and shear stress and HPP nanostructure, despite the different number of dislocations in a pile-up. Obtained results represent a nanoscale basis for understanding and description of PTs under compression and shear in rotational diamond anvil cell and high pressure torsion.

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Amorphization and nanocrystallization of silicon under shock compression

Cited by 119 publications

References 72 publications

In situ TEM study of deformation-induced crystalline-to-amorphous transition in silicon

In situ TEM study of deformation-induced crystalline-to-amorphous transition in silicon

Generating gradient germanium nanostructures by shock-induced amorphization and crystallization

Phase field simulations of plastic strain-induced phase transformations under high pressure and large shear

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