Melting and superheating of crystalline solids: From bulk to nanocrystals

Most studies on melting under confinement focus only on the solid and liquid melt phases. Despite of its ubiquity, contributions from the capillary interface (liquid / vapor interface) are often neglected. In this study the melting behavior of small cylindrical aggregates in vapor attached to planar surfaces is analyzed. For the assumed boundary conditions (cylindrical solid with a non wetting top plane and a wettable side wall) solid and the liquid phases can coexist within a certain temperature range. Due to capillary instability, the liquid phase can form either an axisymmetric rouloid morphology or, above a certain threshold liquid volume fraction, a bulge coexisting with a rouloid-like section. The corresponding melting points are different. The analysis explicitly describes the behavior of a real system of small aggregates of long chain alkanes on planar substrates. It also gives qualitative insights into the melting behavior of small aggregates with anisotropic wetting behaviors in general. It reveals in particular how melting points and melting pathways depend on the energetic respectively morphological pathways leading to complete melting.

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“…In the literature this Gibbs-Thomson (GT) approach often appears in a somewhat more general version 4,[8][9][10][11][12]52 :…”

Section: Conclusion and Summarymentioning

confidence: 99%

Morphological Transitions during Melting of Small Cylindrical Aggregates

Jin

Riegler

2016

J. Phys. Chem. C

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“…Metal nanoparticles (NPs) have been shown to display anomalous electronic and thermodynamic properties, including metal to non-metal transitions, 1, 2 superheating, 3 and negative thermal expansion [4][5][6][7] . However, despite decades of intense research, the origin of these effects is still heavily debated.…”

Section: Introductionmentioning

confidence: 99%

“…11,[18][19][20][21][22][23][24][25] In addition, a correlation between T m and the NP diameter has been commonly observed, with decreasing T m with decreasing NP size. 3 Since for bulk systems T m is proportional to Θ D 2 (Lindemann's criterion 26 ), the Debye temperature is also expected to decrease in clusters relative to the bulk 27 .…”

Section: Introductionmentioning

confidence: 99%

“…According to previous studies, internal defects within the NPs or at the NP/support interface, voids, impurities, grain boundaries, as well as lowcoordinated surface atoms (for NPs not fully embedded in a support matrix) act as nucleation sites for the onset of heterogeneous melting. 3 Therefore, a global understanding of the thermodynamic properties of nanoscale materials requires in-depth insight into their geometrical structure, including its modifications in the presence of an environment (support and/or adsorbate).…”

Section: Introductionmentioning

confidence: 99%

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Thermodynamic properties of Pt nanoparticles: Size, shape, support, and adsorbate effects

et al. 2011

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“…65,66 Relying on MD simulations to observe the equilibrium melting of a solid is not optimal because, near the melting point, the melting transition is a rare event with a mean first passage time many orders of magnitude greater than characteristic lattice vibrational periods. Enhanced sampling methods, such as umbrella sampling and metadynamics, have been used to calculate free energy changes in solid-liquid transitions of ductile metals 67 and of ice/water.…”

Section: Solid-liquid Transitions Of Coppermentioning

confidence: 99%

Order-parameter-aided temperature-accelerated sampling for the exploration of crystal polymorphism and solid-liquid phase transitions

Chen

et al. 2014

The Journal of Chemical Physics

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The problem of predicting polymorphism in atomic and molecular crystals constitutes a significant challenge both experimentally and theoretically. From the theoretical viewpoint, polymorphism prediction falls into the general class of problems characterized by an underlying rough energy landscape, and consequently, free energy based enhanced sampling approaches can be brought to bear on the problem. In this paper, we build on a scheme previously introduced by two of the authors in which the lengths and angles of the supercell are targeted for enhanced sampling via temperature accelerated adiabatic free energy dynamics [T. Q. Yu and M. E. Tuckerman, Phys. Rev. Lett. 107, 015701 (2011)]. Here, that framework is expanded to include general order parameters that distinguish different crystalline arrangements as target collective variables for enhanced sampling. The resulting free energy surface, being of quite high dimension, is nontrivial to reconstruct, and we discuss one particular strategy for performing the free energy analysis. The method is applied to the study of polymorphism in xenon crystals at high pressure and temperature using the Steinhardt order parameters without and with the supercell included in the set of collective variables. The expected fcc and bcc structures are obtained, and when the supercell parameters are included as collective variables, we also find several new structures, including fcc states with hcp stacking faults. We also apply the new method to the solid-liquid phase transition in copper at 1300 K using the same Steinhardt order parameters. Our method is able to melt and refreeze the system repeatedly, and the free energy profile can be obtained with high efficiency. © 2014 AIP Publishing LLC.

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Melting and superheating of crystalline solids: From bulk to nanocrystals

Cited by 531 publications

References 232 publications

Morphological Transitions during Melting of Small Cylindrical Aggregates

Morphological Transitions during Melting of Small Cylindrical Aggregates

Thermodynamic properties of Pt nanoparticles: Size, shape, support, and adsorbate effects

Order-parameter-aided temperature-accelerated sampling for the exploration of crystal polymorphism and solid-liquid phase transitions

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