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Si nanocluster formation during rapid cooling from high temperature Si vapors and its subsequent interaction with substrate was simulated by molecular dynamics. It was confirmed that several nm sized clusters with a loosely bound structure form during rapid cooling and their metastable structures are retained even at temperatures below the Si melting point. Such globular clusters tend to rearrange themselves upon impingement to be a similar structure to that of the substrate, at least near the cluster/substrate interface. This is suggestive of the role of clusters formed under the mesoplasma condition as growth precursors for fast rate epitaxy. [ABSTRACT FROM AUTHOR]

The solid-state bonding of ultralow-carbon steels was conducted by hot pressing and subsequent isothermal holding at low temperatures ranging from 873 to 923 K. The evolution of the interfacial strength was found to consist of two stages; the first stage, where the increase in interfacial strength is rapid and significant, and the second stage, where the increase is gradual. The evolution of strength in the first stage primarily takes place in contact regions produced by hot pressing. In the second stage, on the contrary, the evolution seems to result from the increase in the contact regions due to the shrinkage of voids. A molecular dynamics simulation was performed to clarify the atomic behaviour at the interface during the first stage. The results revealed that the disordered atomic arrangement caused by compression was rearranged with increasing isothermal holding time, leading to improved coherency between the contact regions and increased interfacial strength. [ABSTRACT FROM AUTHOR]

Electronic devices are becoming increasingly used in chemical- and bio-sensing applications and therefore understanding the silica-electrolyte interface at the atomic scale is becoming increasingly important. For example, field-effect biosensors (BioFETs) operate by measuring perturbations in the electric field produced by the electrical double layer due to biomolecules binding on the surface. In this paper, explicit-solvent atomistic calculations of this electric field are presented and the structure and dynamics of the interface are investigated in different ionic strengths using molecular dynamics simulations. Novel results from simulation of the addition of DNA molecules and divalent ions are also presented, the latter of particular importance in both physiological solutions and biosensing experiments. The simulations demonstrated evidence of charge inversion, which is known to occur experimentally for divalent electrolyte systems. A strong interaction between ions and DNA phosphate groups was demonstrated in mixed electrolyte solutions, which are relevant to experimental observations of device sensitivity in the literature. The bound DNA resulted in local changes to the electric field at the surface; however, the spatial- and temporal-mean electric field showed no significant change. This result is explained by strong screening resulting from a combination of strongly polarised water and a compact layer of counterions around the DNA and silica surface. This work suggests that the saturation of the Stern layer is an important factor in determining BioFET response to increased salt concentration and provides novel insight into the interplay between ions and the EDL. [ABSTRACT FROM AUTHOR]

The formation dynamics of nano-sized hydrogenated Si (Si : H) clusters and their interaction with the Si(1 0 0) substrate have been investigated with molecular dynamics simulation using the Tersoff potential. Several nm-sized clusters comprising H atoms are obtained during rapid cooling of atomic Si and H vapour mixtures. Upon surface impingement, the Si : H clusters display higher degrees of deformation and atomic self-ordering than the Si clusters formed with no H atom incorporation. This is due to the movement of the high potential H atoms toward the cluster surface during deformation, not to the local heat generation by the atomic H recombination within the cluster. [ABSTRACT FROM AUTHOR]

We present putative global minimum energy structures for nanoscopic transition metal clusters, with sizes ranging from N = 3 to 100 atoms, described by the original embedded atom potential of Finnis and Sinclair (FS), using their parameter sets for molybdenum and iron, and compare selected results with predictions from semi-empirical molecular orbital (SE-MO) theory via further optimization using the AM1* and PM6 Hamiltonians. We find that, for Fe clusters, the global minima found for the FS potential consist mainly of polyicosahedral structures with magic numbers N = 13, 19, 23, 26, 29, 39, 60 and 78, whereas, for Mo clusters with sizes N > 30, they are more likely to be bcc terminated by {110} and {100}-type surface facets. We find that the global minimum energy structures obtained for the FS potential are, in general, very good starting points for further SE-MO optimization, although the relative ordering of the resulting structures by energy compared to those obtained from global minima of other potentials used to model metal clusters does not, in general, agree. [ABSTRACT FROM AUTHOR]