Size-Dependent Melting Properties of Small Tin Particles: Nanocalorimetric Measurements.
TL;DR: The latent heat of fusion for Sn particles formed by evaporation on inert substrate with radii ranging from 5 to 50 nm has been measured directly using a novel scanning nanocalorimeter and a particle-size-dependent reduction of $\ensuremath{\Delta}{H}_{m}$ has been observed.
Abstract: For the first time, the latent heat of fusion $\ensuremath{\Delta}{H}_{m}$ for Sn particles formed by evaporation on inert substrate with radii ranging from 5 to 50 nm has been measured directly using a novel scanning nanocalorimeter. A particle-size-dependent reduction of $\ensuremath{\Delta}{H}_{m}$ has been observed. An ``excluded volume'' is introduced to describe the latent heat of fusion from the enhanced surface melting of small particles. Melting point depression has also been found by our nanocalorimetric technique.
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TL;DR: The present tutorial review intends to explain the origin of this special behaviour of nanomaterials, where gold ceases to be noble, and 2-3 nm nanoparticles are excellent catalysts which also exhibit considerable magnetism.
Abstract: Gold is known as a shiny, yellow noble metal that does not tarnish, has a face centred cubic structure, is non-magnetic and melts at 1336 K. However, a small sample of the same gold is quite different, providing it is tiny enough: 10 nm particles absorb green light and thus appear red. The meltingtemperature decreases dramatically as the size goes down. Moreover, gold ceases to be noble, and 2–3 nm nanoparticles are excellent catalysts which also exhibit considerable magnetism. At this size they are still metallic, but smaller ones turn into insulators. Their equilibrium structure changes to icosahedral symmetry, or they are even hollow or planar, depending on size. The present tutorial review intends to explain the origin of this special behaviour of nanomaterials.
1,852 citations
TL;DR: It is argued that evidence for novel size-dependent properties alone, rather than particle size, should be the primary criterion in any definition of nanoparticles when making decisions about their regulation for environmental, health and safety reasons.
Abstract: The regulation of engineered nanoparticles requires a widely agreed definition of such particles. Nanoparticles are routinely defined as particles with sizes between about 1 and 100 nm that show properties that are not found in bulk samples of the same material. Here we argue that evidence for novel size-dependent properties alone, rather than particle size, should be the primary criterion in any definition of nanoparticles when making decisions about their regulation for environmental, health and safety reasons. We review the size-dependent properties of a variety of inorganic nanoparticles and find that particles larger than about 30 nm do not in general show properties that would require regulatory scrutiny beyond that required for their bulk counterparts.
1,656 citations
TL;DR: In this paper, a review of the experimental methods for the production of free nanoclusters is presented, along with theoretical and simulation issues, always discussed in close connection with the experimental results.
Abstract: The structural properties of free nanoclusters are reviewed. Special attention is paid to the interplay of energetic, thermodynamic, and kinetic factors in the explanation of cluster structures that are actually observed in experiments. The review starts with a brief summary of the experimental methods for the production of free nanoclusters and then considers theoretical and simulation issues, always discussed in close connection with the experimental results. The energetic properties are treated first, along with methods for modeling elementary constituent interactions and for global optimization on the cluster potential-energy surface. After that, a section on cluster thermodynamics follows. The discussion includes the analysis of solid-solid structural transitions and of melting, with its size dependence. The last section is devoted to the growth kinetics of free nanoclusters and treats the growth of isolated clusters and their coalescence. Several specific systems are analyzed.
1,563 citations
Cites background from "Size-Dependent Melting Properties o..."
...Lai et al. (1996) obtained an excellent fit to their experimental data on the melting of tin clusters (see Fig....
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...Electron and X-ray diffraction, and nanocalorimetry techniques have been used to study melting in deposited clusters (Efremov et al., 2000; Lai et al., 1996; Peters et al., 1998)....
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...Calorimetry experiments have been performed on deposited (for example Lai et al. (1996) considered tin clusters on a SiN substrate) and free clusters....
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TL;DR: In this article, the effects of size and confinement at the nanometre size scale on both the melting temperature and the glass transition temperature, Tm, are reviewed, and it seems that the existing theories of Tg are unable to explain the range of behaviours seen at the nano-scale.
Abstract: In this article, the effects of size and confinement at the nanometre size scale on both the melting temperature, Tm, and the glass transition temperature, Tg, are reviewed. Although there is an accepted thermodynamic model (the Gibbs–Thomson equation) for explaining the shift in the first-order transition, Tm, for confined materials, the depression of the melting point is still not fully understood and clearly requires further investigation. However, the main thrust of the work is a review of the field of confinement and size effects on the glass transition temperature. We present in detail the dynamic, thermodynamic and pseudo-thermodynamic measurements reported for the glass transition in confined geometries for both small molecules confined in nanopores and for ultrathin polymer films. We survey the observations that show that the glass transition temperature decreases, increases, remains the same or even disappears depending upon details of the experimental (or molecular simulation) conditions. Indeed, different behaviours have been observed for the same material depending on the experimental methods used. It seems that the existing theories of Tg are unable to explain the range of behaviours seen at the nanometre size scale, in part because the glass transition phenomenon itself is not fully understood. Importantly, here we conclude that the vast majority of the experiments have been carried out carefully and the results are reproducible. What is currently lacking appears to be an overall view, which accounts for the range of observations. The field seems to be experimentally and empirically driven rather than responding to major theoretical developments.
900 citations
TL;DR: The BOLS correlation mechanism has been initiated and intensively verified as discussed by the authors, which has enabled the tunability of a variety of properties of a nanosolid to be universally reconciled to the effect of bond order deficiency of atoms at sites surrounding defects or near the surface edges of the nano-material.
775 citations
Cites background from "Size-Dependent Melting Properties o..."
...Comparison of the predicted Tm ossification with those measured from Ga þ 13e17 [317,318], Sn10e19 [322], Sn19e31 [266], Ga þ 39e40 [317], Sn500 [333], and Sn nanosolid on Si3N4 substrate [289]....
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...This mechanism may explain why the latent heat of fusion of a solid has a broad range of measured values rather than appearing as a sharp peak [275,289]....
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References
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Book•
02 Dec 1996
336 citations