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...

Semiconducting nanowires (NWs) are good candidates for new optoelectronic or photovoltaic devices due to their excellent ability to guide, scatter, or absorb light, from near ultraviolet to near infrared. The existence of morphology-dependent optical resonances opens a promising route to overcome the intrinsic limitations of the constituent material and optimize their interaction with light. We propose a thorough investigation of the optical properties of Si 1−x Ge x alloy nanowires addressing the influence of NW diameter, composition, light polarization, and angle of incidence on their scattering and absorption. Our results clearly show that the Ge composition provides an additional degree of freedom to tailor the optical response of these one-dimensional nano-objects and that resonant enhancement of both absorption and scattering can be obtained in the infrared range at relatively small diameters compared to pure Si nanowires. These results are confirmed by complementary light scattering and Raman spectroscopy experiments using confocal dark field optical microscopy on individual nanowires fabricated by Au-catalyzed vapor-liquid-solid synthesis.