Spontaneous Phase Fluctuations of Nanoparticles of Lead in a Silicon Oxide Matrix

Stella, A.; Migliori, A.; Cheyssac, P.; Kofman, R.

doi:10.1209/0295-5075/26/4/005

Cited by 18 publications

(7 citation statements)

References 21 publications

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“…When clusters have a low number of atoms, A / d approaches 1 and melting is not very clearly defined. Solid-liquid phase fluctuations occur 45,46 and T m is no longer a continuous function of the number of atoms. 47 As an example, a high T m material such as gold melts at 1336 K and T m ͑d͒ follows the behavior shown in Ref.…”

Section: The Size/shape Cluster-cooking Machinementioning

confidence: 99%

Vapor-liquid-solid mechanisms: Challenges for nanosized quantum cluster/dot/wire materials

Cheyssac

Sacilotti

Patriarche

2006

Journal of Applied Physics

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International audienceThe growth mechanism model of a nanoscaled material is a critical step that has to be refined for a better understanding of a nanostructure's dot/wire fabrication. To do so, the growth mechanism will be discussed in this paper and the influence of the size of the metallic nanocluster starting point, referred to later as “size effect,” will be studied. Among many of the so-called size effects, a tremendous decrease of the melting point of the metallic nanocluster changes the physical properties as well as the physical/mechanical interactions inside the growing structure composed of a metallic dot on top of a column. The thermodynamic size effect is related to the bending or curvature of chains of atoms, giving rise to the weakening of bonds between them; this size or curvature effect is described and approached to crystal nanodot/wire growth. We will describe this effect as that of a “cooking machine” when the number of atoms decreases from 1023 at./cm3 for a bulk material to a few tens of them in a 1–2 nm diameter sphere. The decrease of the number of atoms in a metallic cluster from such an enormous quantity is accompanied by a lowering of the melting temperature that extends from 200 up to 1000 K, depending on the metallic material and its size under study. In this respect, the vapor-liquid-solid VLS model, which is the most utilized growth mechanism for quantum nanowires and nanodots, is critically exposed to size or curvature effects CEs. More precisely, interactions in the vicinity of the growth regions should be reexamined. Some results illustrating the growth of micrometer-/nanometer-sized materials are presented in order to corroborate the CE/VLS models utilized by many research groups in today's nanosciences world. Examples of metallic clusters and semiconducting wires will be presented. The results and comments presented in this paper can be seen as a challenge to be overcome. From them, we expect that in a near future an improved model can be exposed to the scientific communit

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Section: The Size/shape Cluster-cooking Machinementioning

confidence: 99%

Vapor-liquid-solid mechanisms: Challenges for nanosized quantum cluster/dot/wire materials

Cheyssac

Sacilotti

Patriarche

2006

Journal of Applied Physics

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“…These models can be divided into two categories. The first one relates the restructuring of the particle to a short but complete melting period, followed by recrystallization of a new structure [6][7][8]. The second approach suggests that due to the small energy barrier between the various particle configurations, there can be random fluctuations between the different structures without melting [9].…”

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confidence: 99%

Correlated Orientations in Nanocrystal Fluctuations

et al. 1997

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The dynamical behavior of small particles has been observed by high resolution electron microscopy. Spontaneous structural fluctuations, between various orientations, were observed and quantified. Clear transitions involving appearance and vanishing of twins were detected. Measurements of the angle change between succeeding configurations of the ͗111͘ atomic plane reveal the existence of several preferred angular changes. Twin related transformations give a good fit to the observed angular correlation, which excludes complete particle melting during the transition between successive configurations. It was also found that the particles rotate by a few degrees during this transformation.[S0031-9007(97)02816-0] PACS numbers: 61.46.+w, 61.16.Bg, 61.72.Mm, 63.90.+t The structure of atomic clusters is interesting because they present a state of matter that is intermediate between single atoms and the bulk state. In ultrafine particles ͑R , 10 nm͒, new phenomena may be expected, especially due to the high ratio between surface area and volume.Previous studies performed on small particles revealed a structure which is characterized by multiple twinned domains in many fcc metals [1-3].High resolution electron microscopy (HREM) studies in ultrafine particles revealed instability in the particles structure [4] which was defined as quasimelting phenomenon. A comprehensive review on the structure and instability of small clusters has been presented by Marks [5]. Several models were proposed to explain the dynamical evolution in the cluster structure. These models can be divided into two categories. The first one relates the restructuring of the particle to a short but complete melting period, followed by recrystallization of a new structure [6][7][8]. The second approach suggests that due to the small energy barrier between the various particle configurations, there can be random fluctuations between the different structures without melting [9].Previous study of lead particles reveals a definite range of particle size in which the structure is unstable, while in the solid state [10]. In this Letter, we report the first quantitative analysis of the fluctuations which occur in lead particles. This analysis reveals a definite angular correlation between successive structures.The samples are lead particles embedded in an amorphous SiO matrix. The samples were prepared by successive evaporation of 10 nm of SiO, 5 nm of Pb, 10 nm of SiO on a copper grid covered by a thin film of carbon. The embedded case ensures better thermal coupling, which defines good thermodynamical variables and prevents oxidation, migration, and evaporation [11]. During deposition, the substrate was held at a temperature of 200 ± C, causing the particles to coalesce in the liquid state, and resulting in an equilibrium spherical shape. The specimens were observed at room temperature in a HREM (JEOL 4000-EX) at 400 kV. The structure evolution of the particles was video recorded via a low level video CCD camera with a time resolution of 25 frames͞sec. The re...

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“…After evaporation of a film of Al 2 O 3 ͑having a thickness of Ϸ50 Å͒ on sapphire, Ge was deposited on top in such a way that its vapor is condensed on alumina. Essential characteristics of the technique are the amorphous nature of Al 2 O 3 , its nonwetting or partially wetting character with respect to the deposit 14 ͑Ge in this case, or, also, metals previously grown and studied 15,16 ͒ and the absence of strong perturbations due to chemical etching or mechanical distortions. During evaporation, the temperature of the substrate is kept at such a value that nucleation of Ge takes place in the liquid phase.…”

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confidence: 99%