Search results for "nucleation"

Effect of precursor concentration on size evolution of iron oxide nanoparticles

2017

Thermal decomposition is a promising route for the synthesis of magnetic nanoparticles. The simplicity of the synthesis method is counterbalanced by the complex chemistry of the system such as precursor decomposition and surfactant–reducing agent interactions. Control over nanoparticle size is achieved by adjusting the reaction parameters, namely, the precursor concentration. The results, however, are conflicting as both an increase and a decrease in nanoparticle size, as a function of increasing concentration, have been reported. Here, we address the issue of size-controlled synthesis via the precursor concentration. We synthesized iron oxide nanoparticles with sizes from 6 nm to 24 nm wit…

2020

Abstract. Residual pressure can be preserved in mineral inclusions, e.g. quartz-in-garnet, after exhumation due to differential expansion between inclusion and host crystals. Raman spectroscopy has been applied to infer the residual pressure and provides information on the entrapment temperature and pressure conditions. However, the amount of residual pressure relaxation cannot be directly measured. An underestimation or overestimation of residual pressure may lead to significant errors between calculated and actual entrapment pressure. This study focuses on three mechanisms responsible for the residual pressure modification: (1) viscous creep; (2) plastic yield; (3) proximity of inclusion …

Investigation and modeling of the anomalous yield point phenomenon in pure tantalum

2014

International audience; The monotonic and cyclic behavior of commercially pure tantalum has been investigated at room temperature, in order to capture and understand the occurrence of the anomalous yield point phenomenon. Interrupted tests have been performed, with strain reversals (tensile or compressive loading) after an aging period. The stress drop is attributed to the interactions between dislocations and solute atoms (oxygen) and its macroscopic occurrence is not systematically observed. InfraRed Thermography (IRT) measurements supported by Scanning Electron Microscopy (SEM) pictures of the polished gauge length of a specimen during an interrupted tensile test reveal the nucleation an…

A new nature of microporous architecture with hierarchical porosity and membrane template via high strain rate collision

2019

Abstract This paper presents the formation of an unusual porous structure at Al/Al interface joined by magnetic pulse welding. The porous structure consists of a hierarchical microporous architecture with pore size of less than 2 µm that represents more than 80% over the whole area, in which 38% of them are sub-micron size pores. It also exhibits ultra-thin wall, sufficiently thin enough to behave as an electron-transparent material with a wall thickness of 50 nm. The formation of this porous structure is attributed to a cavitation process of a molten material in three stages including, (1) nucleation, (2) growth and coalescence and (3) solidification. Further analysis of this cavitation pr…

Molluscan biomineralization: The proteinaceous shell constituents of Pinna nobilis L.

2005

Abstract The shell of molluscs is a remarkable example of a natural composite biomaterial, synthesized at ambient temperature. Consequently, many consider it as a model for trying to develop at little cost new biomimetic materials of superior mechanical properties. The peculiar resistance of shells to fracture lies in an organic matrix, which is closely associated with the mineral phase. This matrix regulates the crystal growth, by allowing nucleation of the crystals only where appropriate, by favoring crystal elongation in privileged directions, and by inhibiting their growth. This matrix is a mixture of glycoproteins and polysaccharides, the primary structure and function of which are poo…

Different strategies towards the deterministic coupling of a single Quantum Dot to a photonic crystal cavity mode

2011

In this work we show two different procedures of fabrication aiming towards the systematic positioning of single InAs quantum dots (QDs) coupled to a GaAs photonic crystal (PC) microcavity. The two approaches are based on the molecular beam epitaxial (MBE) growth of site-controlled QDs (SCQDs) on pre-patterned structures. The PC microcavity (PCM) is introduced previous or after the growth, on each case. We demonstrate the InAs SCQD nucleation on pre-patterned PCMs and a method to perform the QD nucleation respect to an etched ruler that is used to position the PC structure after growth. For both types of structures, we have carried out microphotoluminescence (µPL) spectroscopy experiments a…

Scaling in colloidal crystallization

1994

The process of colloidal crystallization has already been separately investigated by light scattering mearurements of the crystalline order (Bragg peaks) and of long-ranged density fluctuations (small-angle scattering). We present the firstsimultaneous small- and large-angle light scattering experiment. Our measurements have been performed on hard-sphere colloids of different particle densities. We show results for the temporal evolution of crystallization and find two distinct regimes: homogeneous nucleation and diffusion- or reaction-limited growth at early times, followed by ripening of the Lifshitz-Slyozov or Lifshitz-Allen-Cahn type. To our preliminary experience, we can already state …

Seed- and wall-induced heterogeneous nucleation in charged colloidal model systems under microgravity

2011

Understanding the process that drives an undercooled fluid to the crystal state is still a challenging issue for condensed matter physics and plays a key role in designing new materials. The crystallization kinetics and the resulting polycrystalline morphology are given by a complex interplay of crystal nucleation, growth, and ripening. A great deal of progress has been made in recent years using colloidal suspensions as model systems in the study of crystallization. Close analogies to atomic systems are observed which can be exploited to address questions not accessible in atomic solidification. Here we present systematic measurements of the crystallization kinetics of a charged colloidal …

Nucleation and growth of ZnO on PMMA by low-temperature atomic layer deposition

2015

ZnO films were grown by atomic layer deposition at 35 °C on poly(methyl methacrylate) substrates using diethylzinc and water precursors. The film growth, morphology, and crystallinity were studied using Rutherford backscattering spectrometry, time-of-flight elastic recoil detection analysis, atomic force microscopy, scanning electron microscopy, and x-ray diffraction. The uniform film growth was reached after several hundreds of deposition cycles, preceded by the precursor penetration into the porous bulk and island-type growth. After the full surface coverage, the ZnO films were stoichiometric, and consisted of large grains (diameter 30 nm) with a film surface roughness up to 6 nm (RMS). T…

The summertime Boreal forest field measurement intensive (HUMPPA-COPEC-2010): an overview of meteorological and chemical influences

2011

This paper describes the background, instrumentation, goals, and the regional influences on the HUMPPACOPEC intensive field measurement campaign, conducted at the Boreal forest research station SMEAR II (Station for Measuring Ecosystem-Atmosphere Relation) in Hyyti¨al¨a, Finland from 12 July–12 August 2010. The prevailing meteorological conditions during the campaign are examined and contrasted with those of the past six years. Back trajectory analyses show that meteorological conditions at the site in 2010 were characterized by a higher proportion of southerly flow than in the other years studied. As a result the summer of 2010 was anomalously warm and high in ozone making the campaign rel…