Thin layers of amorphous silicon (a-Si) were produced by noble gas ion implantation of (100) substrates held at 77 K. Rutherford backscattering and channeling, and differential scanning calorimetry were used to measure the heat of crystallization, ΔHac, to be 11.9±0.7 kJ/mol, substantially less than the value predicted by scaling ΔHac of a-Ge. The crystal growth velocity is found to have the form v=v0 exp(−2.24 eV/kT). We obtain a new estimate, 1420 K, for the melting temperature of a-Si.

Amorphous Si and Ge layers, produced by noble gas (Ar or Xe) implantation of single crystal substrates, have been crystallized in a differential scanning calorimeter (DSC). The MeV implantation energies resulted in amorphous layers of micron thickness whose areal densities were determined using the Rutherford backscattering and channeling of 1-MeV protons. These techniques allow determination of the amorphous-crystal interface velocity (which is proportional to the rate of heat evolution ΔḢac) and the total enthalpy of crystallization ΔHac. Amorphous Ge was found to relax continuously to an amorphous state of lower free energy, with a total enthalpy of relaxation of 6.0 kJ/mol before the onset of rapid crystallization. The interface velocity for crystallization on (100) substrates, was found to have an Arrhenius form with an activation energy of 2.17 eV. The value of ΔHac was found to be 11.6±0.7 kJ/mol, the same as for samples prepared by deposition. For Si, ΔHac was determined to be 11.9±0.7 kJ/mol without any evidence of heat release due to relaxation. The (100) interface velocity was found to have an activation energy of 2.24 eV. The effects of the implant depth profile on the regrowth velocity could also be observed directly in the DSC signal. From the value of ΔHac and Gibbs free-energy calculations, the melting temperature of amorphous Si has been determined to be Taℓ =1420 K.

Mortality for infants between 501 and 1500 gm at birth has declined over the past 5 years. There are interactions between birth weight, gestational age, gender, and survival rate. This increase in survival was not accompanied by an increase in medical morbidity.

Heat capacities of a series of mixed-alkali glasses of composition(in mol%) 24.4(Na20 + K,O) -75.6Si0, were measured in the transition region by differential scanning calorimetry. The glass heat capacities at 700 K and the equilibrium liquid heat capacities are the same for all glasses on a per-gatom basis and equal, respectively, to 5.6&0.1 and 6.8k 0.1 cal/g.atom K. The glass transition temperatures exhibited negative deviations from additivity, but the heat capacity curves in the transition region of all the glasses for identical heating rates and thermal histories could be superimposed on the same reduced plot. This behavior indicates that the shapes of the structural relaxation functions are the same for all the glasses. These results support Shelby's conclusion that there is no unique "mixed-alkali effect" on thermodynamic or structural relaxation properties and that the term should be reserved for propcrties relating to ionic transport.