Critical Size for Fracture during Solid−Solid Phase Transformations

Zaziski, David; Prilliman, Stephen G.; Scher, Erik C.; Casula, Maria Francesca; Wickham, Juanita; Clark, S. M.; Alivisatos, A. Paul

doi:10.1021/nl049537r

Cited by 57 publications

(63 citation statements)

References 18 publications

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“…The thermodynamic transition pressure increases with decreasing crystal size, in agreement with the notion of different surface free-energies of the two crystal structures [73,14]. The kinetic barriers to the transition, characterized by activation energies and volumes, also show strong dependence on crystal size and pressure, indicating that transformations proceed through single nucleation events and subsequent growth [74,53,55,75]. Although it is possible to exclude certain transition routes from experimental findings [54], the time and space resolution of experiments is insufficient for an understanding of the transformation mechanism on the atomistic scale.…”

Section: The Wurtzite To Rocksalt Transformation In Cdse Nanocrystalssupporting

confidence: 81%

Transition Path Sampling Studies of Solid-Solid Transformations in Nanocrystals under Pressure

Grünwald

Dellago

2009

Challenges and Advances in Computational Chemistry and Physics

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In the past few decades, molecular dynamics simulation has grown into a very powerful tool that today is used routinely to study the dynamics of condensed matter systems consisting of up to a few million particles with atomistic resolution. Many processes occurring in nature and technology such as the folding of a protein or the transport of a dopant through a semiconductor, however, are still beyond the reach of this methodology due to widely disparate time scales that are present in the problem. Consider, for instance, the nucleation of a crystal from the undercooled liquid. For moderate undercooling, this process typically proceeds through the formation of a critical nucleus that then grows, eventually transforming the whole sample into the crystalline state. Since this process involves the creation of an interface between the crystallite and the metastable liquid, which is associated with a free energetic barrier, the formation of the critical nucleus is rare on the time scale of basic molecular motions. Indeed, it has been known for a long time that water, carefully cooled below the freezing point, can remain in this supercooled state for hours or even days. Thus, the time scale for nucleation exceeds the picosecond time scale for the formation and cleavage of hydrogen bonds by many orders of magnitude. Similar rare but important events, related to high energy barriers or entropic bottlenecks in phase space, can also dominate the dynamics of folding proteins, chemical reactions or transport on surfaces.Naturally, such a wide separation of time scales is a problem for molecular dynamics simulation. In this method, the equations of motion of the system are solved

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Section: The Wurtzite To Rocksalt Transformation In Cdse Nanocrystalssupporting

confidence: 81%

Transition Path Sampling Studies of Solid-Solid Transformations in Nanocrystals under Pressure

Grünwald

Dellago

2009

Challenges and Advances in Computational Chemistry and Physics

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“…For this reason this approach has been extensively adopted for the preparation of colloidal nanoparticles which have provided model systems for the study of crystal growth and of factors affecting phase and shape stability at the nanometer scale. [8][9][10][11][12][13] Many recent studies point out the effect of the growth conditions on the outcome of the synthesis: for example by varying the growth temperature one may achieve size and/or shape control by tuning the growth rate or phase control by making more favorable the growth of one polymorph. On the other hand, the nucleation is more difficult to control as it depends exponentially on concentration and temperature.…”

Section: Introductionmentioning

confidence: 99%

The Concept of Delayed Nucleation in Nanocrystal Growth Demonstrated for the Case of Iron Oxide Nanodisks

et al. 2006

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RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required according to the journal that you are submitting your paper to) TITLE RUNNING HEAD. Monodisperse Iron Oxide Nanodisks by Delayed Nucleation 2 ABSTRACT A comprehensive study of iron oxide nanocrystal growth through non-hydrolitic, surfactantmediated thermal reaction of iron pentacarbonyl and an oxidizer has been conducted, which includes size control, anisotropic shape evolution, and crystallographic phase transition of monodisperse iron oxide colloidal nanocrystals. The reaction was monitored by in situ UV-Vis spectroscopy taking advantage of the color change accompanying the iron oxide colloid formation allowing measurement of the induction time for nucleation. Features of the synthesis such as the size control and reproducibility are related to the occurrence of the observed delayed nucleation process. As a separate source of iron and oxygen is adopted, phase control could also be achieved by sequential injections of oxidizer.3

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“…10A). However, fracture was observed at lower pressure in large-scale two-dimensional CdSe and ZnS nanocrystals without surface-ligand bonding (32)(33)(34). Similarities in structure and properties of several related semiconductors allow one to correlate CdS and CdTe, and to estimate the elastic strengths of CdSe (35,36).…”

mentioning

confidence: 99%

Reconstructing a solid-solid phase transformation pathway in CdSe nanosheets with associated soft ligands

Wang

Wen

Hoffmann

et al. 2010

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

129

110

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Integrated single-crystal-like small and wide-angle X-ray diffraction images of a CdSe nanosheet under pressure provide direct experimental evidence for the detailed pathway of transformation of the CdSe from a wurtzite to a rock-salt structure. Two consecutive planar atomic slips [(001) h110i in parallel and (102) h101i with a distortion angle of ∼40°] convert the wurtzite-based nanosheet into a saw-like rock-salt nanolayer. The transformation pressure is three times that in the bulk CdSe crystal. Theoretical calculations are in accord with the mechanism and the change in transformation pressure, and point to the critical role of the coordinated amines. Soft ligands not only increase the stability of the wurtzite structure, but also improve its elastic strength and fracture toughness. A ligand extension of 2.3 nm appears to be the critical dimension for a turning point in stress distribution, leading to the formation of wurtzite (001)/zinc-blende (111) stacking faults before rock-salt nucleation.phase transition | semiconductor | dimensionality R ational synthesis of materials with defined structure and properties requires a reasonably complete understanding of the associated kinetic transformations and microscopic mechanisms (1). We need to know these in order to understand how associated soft-bonded organics may tune structural stability, elastic strength, and fracture toughness (1-3). The study of solid-solid phase transformations of materials, and their structural stabilization upon incorporation of soft materials at different scales, can be very helpful in this regard. For instance, application of pressure and temperature converts graphite to a hard diamond phase that persists at ambient conditions, allowing for a wide range of known applications (4). Upon addition of soft materials such as silicon and metals (5, 6), the sintered diamond-dominant nanocomposites show improved yield strength and fracture toughness (by several orders of magnitude) without significant diminution of hardness.Many fascinating natural substances, such as human bone and other biological materials, also contain exceptionally strong building blocks (2, 3) essential to their function. The subtle interplay between soft organics and embedded brittle materials is responsible not only for enhancement of the structural stability of embedded brittle materials, but also for improvement of the yield strength and fracture toughness of assembled hierarchical organizations (2, 3).Microscopic mechanisms of transformation are difficult to determine. In bulk solids, as metastable higher energy and higher density phases nucleate in multiple domains, structural features (such as defects, microstructure, and impurities) may modify significantly the kinetics and mechanism of a phase transformation. In principle, calculations could provide the energy difference between structural polymorphs at a given pressure or temperature. But putting aside problems in computing activation barriers, there is often a large discrepancy between theory and experiment. F...

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Critical Size for Fracture during Solid−Solid Phase Transformations

Cited by 57 publications

References 18 publications

Transition Path Sampling Studies of Solid-Solid Transformations in Nanocrystals under Pressure

Transition Path Sampling Studies of Solid-Solid Transformations in Nanocrystals under Pressure

The Concept of Delayed Nucleation in Nanocrystal Growth Demonstrated for the Case of Iron Oxide Nanodisks

Reconstructing a solid-solid phase transformation pathway in CdSe nanosheets with associated soft ligands

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