The crystallization behavior of Ge2Sb2Te5 thin films has been analyzed by atomic force microscopy and optical reflection measurements on various time scales in order to determine the crystallization kinetics including the crystallization mechanism, the corresponding activation barrier, and the Avrami coefficient. On the minute time scale, thin amorphous films were isothermally crystallized in a furnace under a protective Ar atmosphere. From these measurements the activation energy for crystallization was determined to be (2.0±0.2) eV, in close agreement with previous studies using different techniques. The isothermal measurements also revealed a temperature dependent incubation time for the formation of critical nuclei, which is compared with recent theories. On the nanosecond time scale, Ge2Sb2Te5 was locally crystallized with a focused laser. Either crystalline spots of submicron size were generated in an as deposited amorphous film or amorphous bits in an otherwise crystalline film were recrystallized. For the formation of crystalline spots in an as deposited amorphous film a minimum time of (100±10) ns was found, which is identified as the minimum incubation time for the formation of critical nuclei. In contrast, the complete crystallization of melt-quenched amorphous bits in a crystalline matrix was possible in 10 ns. This is attributed to the presence of quenched-in nuclei inside the amorphous bits. The combination of optical measurements with atomic force microscopy reveals the formation and growth of crystalline bits and shows that the crystal growth in vertical direction strongly affects the reflectivity changes.

We studied links between human malnutrition and wild meat availability within the Rainforest Biotic Zone in central Africa. We distinguished two distinct hunted mammalian diversity distributions, one in the rainforest areas (Deep Rainforest Diversity, DRD) containing taxa of lower hunting sustainability, the other in the northern rainforest-savanna mosaic, with species of greater hunting potential (Marginal Rainforest Diversity, MRD). Wild meat availability, assessed by standing crop mammalian biomass, was greater in MRD than in DRD areas. Predicted bushmeat extraction was also higher in MRD areas. Despite this, stunting of children, a measure of human malnutrition, was greater in MRD areas. Structural equation modeling identified that, in MRD areas, mammal diversity fell away from urban areas, but proximity to these positively influenced higher stunting incidence. In DRD areas, remoteness and distance from dense human settlements and infrastructures explained lower stunting levels. Moreover, stunting was higher away from protected areas. Our results suggest that in MRD areas, forest wildlife rational use for better human nutrition is possible. By contrast, the relatively low human populations in DRD areas currently offer abundant opportunities for the continued protection of more vulnerable mammals and allow dietary needs of local populations to be met.

Investigation of the optical and electronic properties of phase change material in its amorphous, cubic, and hexagonal phases

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