Time filter

Source Type

Safaei A.,Institute of Nano Parthava | Safaei A.,Zeus Engineering and Technical Company
Philosophical Magazine

Recently, a lattice-type-sensitive model, free of any adjustable parameter, for the size dependence of the cohesive energy of nanocrystals (nanodisks, -films, -wires and -particles) has been developed, taking into account the effects of the averaged structural and energetic properties of their surface and volume. These effects are related to the first- and second-nearest-neighbor atomic interactions. Now, considering the intimate relation between cohesive energy and other physical properties of materials, the recently obtained formula for the cohesive energy of nanocrystals has been applied to the cases of melting point (In, Bi, Si and Ag), evaporation temperature (Ag and Au), vacancy formation energy (Au), diffusion activation energy (Au), surface energy (Au, Al and Na), liquid-vapor interfacial energy (Al and Na), Curie temperature (Pb), Debye temperature (Au and Fe) and band gap energy (Si) of nanocrystals. In general, good agreement between the present model and the data has been obtained. Moreover, the surface-area-difference (SAD) model has been derived as a first-order approximation of the present model. © 2011 Taylor & Francis. Source

Safaei A.,Institute of Nano Parthava

A new simple, lattice-type-sensitive model has been developed for the size-dependency of the mass density of individual elemental and compound nanocrystals. It has also been generalized for a multi-composition nanocrystal, and can be used for metallic oxides, ionic crystals and alloys. The model has been corroborated with the experimental data for the particle size-dependent apparent density (AD) of silica nanopowder. © World Scientific Publishing Company. Source

Safaei A.,Institute of Nano Parthava | Attarian Shandiz M.,Institute of Parthava e Shargh
Physical Chemistry Chemical Physics

Considering size effect on the equations obtained from statistical mechanical theories for the entropy of crystal and liquid phases, a new model has been developed for the melting entropy of nanocrystals, including the effects of the quasi-harmonic, anharmonic and electronic components of the overall melting entropy. Then with the use of our suggested new proportionality between the melting point and the entropy temperature (0), the melting entropy of nanocrystals has been obtained in terms of their melting point. Moreover, for the first time, the size-dependency of the electronic component of the overall melting entropy, arising from the change in the electronic ground-state of the nanocrystal upon melting, has been taken into account to calculate the melting entropy of nanocrystals. Through neglecting the effect of the electronic component, the present model can corroborate the previous model for size-dependent melting entropy of crystals represented by Jiang and Shi. The present model has been validated by the available computer simulation results for Ag and V nanoparticles. Moreover, a fairly constant function has been introduced which couples the melting temperature, the entropy temperature and the atomic density of elements to each other. © 2010 the Owner Societies. Source

Safaei A.,Institute of Nano Parthava | Safaei A.,Zeus Engineering Technical Company
Journal of Nanoparticle Research

The size dependency of the cohesive energy of nanocrystals is obtained in terms of their averaged structural and energetic properties, which are in direct proportion with their cohesive energies. The significance of the effect of the geometrical shape of nanoparticles on their thermal stability has been discussed. The model has been found to have good prediction for the case of Cu and Al nanoparticles, with sizes in the ranges of 1-22 nm and 2-22 nm, respectively. Defining a new parameter, named as the surface-to-volume energy-contribution ratio, the relative thermal stabilities of different nanoclusters and their different surface-crystalline faces are discussed and compared to the molecular dynamic (MD) simulation results of copper nanoclusters. Finally, based on the size dependency of the cohesive energy, a formula for the size-dependent diffusion coefficient has been presented which includes the structural and energetic effects. Using this formula, the faster-than-expected interdiffusion/ alloying of Au(core)-Ag (shell) nanoparticles with the core-shell structure, the Au-core diameter of 20 nm and the Ag-shell thickness of 2.91 nm, has been discussed and the calculated diffusion coefficient has been found to be consistent with its corresponding experimental value. Source

Safaei A.,Institute of Nano Parthava
Journal of Physical Chemistry C

A nonlinear, lattice type-sensitive model, free of any adjustable parameter, has been developed to account for the shape and size dependency of the cohesive energy of free-standing nanocrystals (nanoparticles, -wires, and -films). In this model, the effects of the averaged structural and energetic properties of the surface and the volume of nanocrystals along with the first and second nearest-neighbor atomic interactions have been taken into consideration and gathered in a new parameter named as the surface-to-volume energy contribution ratio. This model has been compared to the experimental data of the cohesive energy of W and Mo nanoparticles, and the melting points of Au, Pb, Al, and Sn nanoparticles and Pb and In nanofilms. Moreover, the model has been corrected to account for the effect of substrate on the melting point of substrate-supported Sn nanodisks. It has been found that the present model has generally a good agreement with those experimental data measured by different techniques under different experimental conditions. ©2010 American Chemical SocietyPublished on Web 07/23/2010. Source

Discover hidden collaborations