GaAs 1−x Bi x epilayers with bismuth concentrations up to x=3.1% were grown on GaAs by molecular beam epitaxy. The Bi content in the films was measured by Rutherford backscattering spectroscopy. X-ray diffraction shows that GaAsBi is pseudomorphically strained to GaAs but that some structural disorder is present in the thick films. The extrapolation of the lattice constant of GaAsBi to the hypothetical zincblende GaBi alloy gives 6.33±0.06 Å. Room-temperature photoluminescence of the GaAsBi epilayers is obtained and a significant redshift in the emission of GaAsBi of ∼84 meV per percent Bi is observed.

The melting behavior of 0.1-10-nm-thick discontinuous indium films formed by evaporation on amorphous silicon nitride is investigated by an ultrasensitive thin-film scanning calorimetry technique. The films consist of ensembles of nanostructures for which the size dependence of the melting temperature and latent heat of fusion are determined. The relationship between the nanostructure radius and the corresponding melting point and latent heat is deduced solely from experimental results ͑i.e., with no assumed model͒ by comparing the calorimetric measurements to the particle size distributions obtained by transmission electron microscopy. It is shown that the melting point of the investigated indium nanostructures decreases as much as 110 K for particles with a radius of 2 nm. The experimental results are discussed in terms of existing melting point depression models. Excellent agreement with the homogeneous melting model is observed.

We report a study of the thermodynamic properties of indium clusters on a SiN (x) surface during the early stages of thin film growth using a sensitive nanocalorimetry technique. The measurements reveal the presence of abnormal discontinuities in the heat of melting below 100 degrees C. These discontinuities, for which temperature separation corresponds to a spatial periodicity equal to the thickness of an indium monolayer, are found to be related to the atomic "magic numbers," i.e., the number of atoms necessary to form a complete shell of atoms at particle surface.

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The link between the energy surface of bulk systems and their dynamical properties is generally difficult to establish. Using the activation-relaxation technique (ART nouveau), we follow the change in the barrier distribution of a model of amorphous silicon as a function of the degree of relaxation. We find that while the barrier-height distribution, calculated from the initial minimum, is a unique function that depends only on the level of distribution, the reverse-barrier height distribution, calculated from the final state, is independent of the relaxation, following a different function. Moreover, the resulting gained or released energy distribution is a simple convolution of these two distributions indicating that the activation and relaxation parts of a the elementary relaxation mechanism are completely independent. This characterized energy landscape can be used to explain nano-calorimetry measurements. The concept of energy landscape has been used extensively in the last decade to characterize the properties of complex materials. In finite systems, such as clusters and proteins, the classification of energy minima and energy barriers has shown that it is possible to understand, using single-dimension representations such as the disconnectivity graph, the fundamental origin of cluster dynamics and protein folding [1]. For bulk systems, where the relations are more complex, the energy landscape picture has helped further our qualitative understanding of glassy dynamics and of the evolution of supercooled liquids through their inherent structures [1]. Similarly, applied to amorphous semiconductors, it has revealed an unexpected simplicity that suggests universality [2][3][4]. In spite of these contributions, many questions remain regarding the evolution of the local structure of the energy landscape itself as a function of relaxation, an evolution that determines the dynamics of disordered materials away from equilibrium [5]. For example, following measurements of heat released during the annealing of damage generated by low-energy ion implantation in amorphous silicon, it was suggested that the activation energy and the amount of heat released are uncorrelated [5,6], microscopic details were still missing, however, as well as a general picture of the phenomenon. Results presented here tie experiments and simulations and provide a clear link between the structure of the energy landscape and experimental observations, supporting the importance of this concept.More precisely, we focus on amorphous silicon, a model system studied extensively, both experimentally and theoretically, over the years [4,5,7]. Using ART nouveau [8], a saddle-point finding method, we characterize the evolution of the local energy landscape, defined by the distribution of transition states and adjacent energy minima around a local configuration, as a function of relaxation. The resulting theoretical picture can be used to understand and explain recent nano-calorimetric measurements on ion-implanted a-Si samples [5,6].Our a-Si model is...