Crystallization of poly(ethylene-co-octene): II. Melt memory effects on first order kinetics.

Dilatometric and X-ray scattering experiments of the crystallization kinetics of a sample of poly(ethylene-co-octene) show pronounced melt memory effects, i.e., the shapes of isotherms and characteristic times vary systematically with the temperature of the melt prior to cooling to the crystallization temperature. The temperature range of the effect is limited; crystallization kinetics remains constant below a melt temperature T(m)l and above a melt temperature T(m)h and varies only in-between. Analysis shows that the melt memory effect is caused by a variation of the characteristic time of a first order crystallization process. The process can be assigned to the in-filling of crystallites into objects of a previously generated precursor structure.

Auger recombination and charge-carrier thermalization in Hg - n -cluster photoelectron studies.

Photoelectron spectra (PES) of Hg(-)(n) show strong dependence of spectral features on photon energy, i.e., peak tailing and band gap filling. This dependence suggests the existence of complex photoinduced processes in parallel with the direct photodetachment process. The "corrupted" PES, taken with intermediate photon energy, carry the signature of interband absorption followed by charge-carrier thermalization and Auger electron ejection in Hg(-)(n). These processes, so significant in the photophysics of bulk semiconductors and nanoparticles, have not yet been identified in clusters.

Caloric curve across the liquid-to-gas change for sodium clusters.

The caloric curve for Na(139)(+) has been measured from 100 K up to the temperature where the clusters are boiling hot and spontaneously emit atoms. In this limit the clusters form an evaporative ensemble, the temperature and energy of which have been determined. As the caloric curve of an atomic gas with a finite number of atoms is known, one can construct the caloric curve for this finite system below and above the boiling point. A conjecture is made on how to link the evaporative ensemble temperature of the free cluster in vacuum to the boiling temperature of a finite system at a given pressure. This allows one to determine the enthalpy of vaporization at the phase transition of the finite system.

Negative heat capacity for a cluster of 147 sodium atoms.

There exists a surprising theoretical prediction for a small system: its microcanonical heat capacity can become negative. An increase of energy can-under certain conditions-lead to a lower temperature. Here we present experimental evidence that a cluster containing exactly 147 sodium atoms does indeed have a negative microcanonical heat capacity near its solid to liquid transition.