On the size dependence of the melting temperature of nanoparticles

The size dependence of the melting temperature of nanocrystals has been investigated within the thermodynamic approach. A formula is obtained, which, in contrast to the classical Thomson formula, takes into account the metastable character of equilibrium between the crystal core and melt shell. Comparative investigation of the size dependence of the melting temperature, disregarding and taking into account the size dependences of the surface tension of the solid and liquid phases and the interface tension, has been performed by the example of aluminum, tin, and copper nanoparticles.     

On the size dependence of the heats of melting of metal nanoclusters

The size dependence of the heats of melting of transition metal nanoclusters (Ni, Au, Cu and Ag) is investigated using two alternative methods of computer simulation (isothermal molecular dynamics and Monte Carlo). Au and Cu nanoclusters are subjected to more detailed study over a wide range of their sizes. The heats of melting are shown to fall along with nanocluster size and to tend in some approximation to a linear dependence on inverse particle radii.     

On the melting point of amorphous silicon

The entropy and melting point of amorphous silicon cannot be measured in a thermodynamic sense.     

Modeling size dependence of melting temperature of metallic nanoparticles

A model has been developed to account for the dependence of melting temperature of nanoparticles on their size, shape and lattice type. This model is consistent with reported experimental data and shows better consistency than the liquid drop and bond energy model. A general equation is proposed which correlates with the bond energy model formula and has high potential for application in research and development. The model also leads to an equation showing the limiting size for nanoparticles.     

Thermodynamic approach to the size dependence of the melting temperatures of films

The size dependence of melting temperature T _m of metallic films (tin and copper) on different substrates, including amorphous carbon and another refractory metal (i.e., the dependence of T _m on film thickness h) is investigated. It is found that the effect of the interfacial boundary can result in the growth of T _m for thin metallic films on carbon substrates with a reduction in film thickness h. For a system with a metallic film on a metallic substrate, the size dependence of T _m is less pronounced and T _m falls with a reduction in h.     

Stress dependence of electron-hole liquid parameters in silicon

The electron-hole liquid recombination luminescence in silicon is studied as a function of stress up to corresponding valence band splittings of 30 meV for <100>- and <111>-stress directions. EHL densities and exchange-correlation energies as obtained from lineshape fits are in general agreement with recent theoretical data. Systematic deviations in detail, however, indicate that - contrary to simplifying theoretical assumptions - a band structure dependence of the exchange and correlation energy E_xc has to be taken into account.     

On the size dependence of surface tension in the temperature range from melting point to critical point

The problem of size dependence of surface tension was investigated in view of a more general problem of the applicability of Gibbs’ thermodynamics to nanosized objects. For the first time, the effective surface tension (coinciding with the specific excess free energy for an equimolecular dividing surface) was calculated within a wide temperature range, from the melting temperature to the critical point, using the thermodynamic perturbation theory. Calculations were carried out for Lennard-Jones and metallic nanosized droplets. It was found that the effective surface tension decreases both, with temperature and particle size.     

On the size dependence of the surface tension

The general form of a differential equation that deduces a size dependence of the surface tension is derived. The well-known Gibbs-Tolman-Koenig-Buff equation for the spherical surface is a particular case of the newly derived one. Analytical solutions to this equation for the spherical, cylindrical, parabolic, and conical surfaces are found.     

Volume dependence of the melting temperature for aluminium

We present a simple and straightforward relationship for evaluating the volume dependence of melting temperature based on the Lindemann’s melting equation (F.A. Lindemann, Z. Phys. 11 (1910) 609) and the Al’tshular et al. model for the volume dependence of the Gruneisen parameter (L.V. Al’tshuler, S.E. Brusnikin, E.A. Kuz’ menkov, J. Appl. Mech. Tech. Phys. 28 (1987) 129). The formula for the volume dependence of melting temperature obtained in the present study has been used to determine the results for aluminium up to a pressure range of 77 GPa. The results obtained for the melting temperature present a good agreement with the available experimental data.     

Anomalous size dependence in the melting temperatures of free sodium clusters: an explanation for the calorimetry experiments

The meltinglike transition in unsupported Na(N) clusters (N = 55, 92, 147, 181, 189, 215, 249, 271, 281 and 299) is studied by first-principles isokinetic molecular dynamics simulations. The irregular size dependence of the melting temperatures Tm observed in the calorimetry experiments of Schmidt et al. [Nature (London) 393, 238 (1998)] is quantitatively reproduced. We demonstrate that structural effects alone can explain all broad features of experimental observations. Specifically, maxima in Tm(N) correlate with high surface stability and with structural features such as a high compactness degree.     

On the linear dependence of 13C spin polarization parameters

The Jahn-Teller (J-T) effect in systems of four-fold symmetry is well known to differ from that in all other point groups with respect to the nature of the J-T active normal modes of vibration. The present report addresses some previously unnoticed features which are of intrinsic importance in recognizing and understanding the unique manifestations of quadrate symmetry in both the static and dynamic Jahn-Teller effects. We first consider the nature of the static J-T potential surfaces when coupling to and strains in two modes, b ₁ and b ₂, are included in the hamiltonian.

The second part of this paper is devoted to an examination of the dynamic J-T effect in four-fold systems. Utilizing both perturbation theory and numerical solution to the Schrödinger equation, we examine the spin-hamiltonian parameters for a metalloporphyrin ³ E_u triplet state and discuss some dynamical processes, including reorientation of the system between minima, spin-lattice relaxation, and the dependences of these phenomena on the nature and magnitude of the off-diagonal terms in the hamiltonian. There emerge from this analysis several signal differences between the Jahn-Teller effect for a doubly degenerate state in four-fold systems and in the more usual cubic or tetrahedral situation.     

On the quark mass dependence of the parameters of quantum chromodynamics

The running coupling constant and quark masses in QCD are calculated in the one-loop approximation using the 3-gluon vertex to define the coupling constant. Our results differ for finite quark masses from those reported previously in the literature. We discuss the origin of this apparent discrepancy. We also make some comments on the gauge dependence of the QCD parameters.     

Defect-molecule parameters for the divacancy in silicon

The hamiltonian eigenvalue problem is solved for a diva cancy in silicon within the framework of the defect-molecule model. A direct connection between the solution of this problem and a self-consistent multiple-scattering cluster calculation is established in order to determine the parameters of the model. The obtained results provide a quantitative confirmation of the currently accepted microscopic picture of the divacancy.     

On the size dependences of the crystal-liquid phase transition parameters

A comparatively simple method is proposed for calculating the size dependences of the latent heat, volume jumps, and the interfacial surface energy for the crystal-liquid phase transition proceeding from the results of experiments (real or computer) on determining size dependences of the melting point and the crystallization temperature. The method is tested on the basis of computer simulation data for copper, gold, aluminum, and nickel nanoparticles and experimental data for tin.     

Relationship between solid state parameters and melting parameters for alkali halides

In the present communication we report some interesting relationships found between solid state parameters and melting parameters for alkali halides. Values of the melting temperatures and relative changes in volume after melting are found to exhibit systematic trend of variation with the Phillips ionicity parameter defining the amount of fractional ionic character. An empirical analysis is presented for determining the nearest-neighbour distances in alkali halide melts. The predictions made in the present work are shown to be consistent with available X-ray diffraction measurements.     

Effect of electron-hole pairs on the melting of silicon

We compute the variation of the melting temperature T_m of silicon, with the density np of electron-hole pairs created by laser illumination: T_m0(1?αnp)2, where α^?11 = 8 × 10²¹ cm^?3. A similar formula is given for amorphous silicon and the application to laser annealing of damaged silicon is discussed.     

Pressure dependence of photoconductivity for hydrogenated amorphous silicon

Abstract

Measurements of steady-state photoconductivity for hydrogenated amorphous silicon (a-Si:H) have been carried out at pressures up to 14 GPa and at room temperature. The ratio of photoconductivity to darkconductivity [sgrave]p/[sgrave]D decreases with increasing pressure. The activation energy for photoconductivity Ep, which is 0.25 eV at ambient pressure, decreases with increasing pressure at the rate -7 meV/GPa. These resultls are discussed with change in density of states.     

Pressure dependence of the melting temperature of rare-gas solids

According to Lindemann's law and the Debye model and with the assumption that the volume derivative [Formula: see text] of the Grüineisen parameter [Formula: see text] is a constant depending on the material, we present a new expression for the analysis of the experimental data for the melting temperature of solids under a high pressure. The test on rare-gas solids (Ne, Ar, Kr and Xe) shows that the calculated results are in good agreement with the corresponding experimental data.     

Estimation of melting critical point parameters

Melting is considered using a model of the equation of state proposed for the nonrelativistic range. A critical point in the melting curve calculated for copper is found. Based on an approximate expression for the shear modulus, the pressure at the critical point is estimated for most elements. It is shown that this pressure falls into the range 1 Mbar-1 Gbar, being much lower for readily compressible elements, helium, and alkaline metals (for them, P ∼ 1 Mbar). The possibility of existence and finding of the critical point is discussed.